Sir Rudolph Peierls: Selected Private and Scientific Correspondence

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Sir Rudilf Peierls Selected Private and Scientific Correspondence Vol.2

Sabine Lee University of Birmingham, UK

World Scientific NEW JERSEY . LONDON. SINGAPORE . BEIJING . SHANGHAI . HONG KONG . TAIPEI . CHENNAI

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Published by World Scientific Publishing Co. Pte. Ltd. 5 Toh Tuck Link, Singapore 596224 USA office: 27 Warren Street, Suite 401-402, Hackensack, NJ 07601 UK office: 57 Shelton Street, Covent Garden, London WC2H 9HE

British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library.

SIR RUDOLF PEIERLS Selected Private and Scientific Correspondence Volume 2 Copyright © 2009 by World Scientific Publishing Co. Pte. Ltd. All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the Publisher.

For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy is not required from the publisher.

ISBN-13 978-981-279-706-3 ISBN-10 981-279-706-8

Printed in Singapore.

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Contents

Acknowledgements

vii

Editorial Comments

xi

6. Resettling at Birmingham: Postwar Physics in the UK

1

7. Birmingham: A ‘Most Stimulating Theoretical Group’

284

8. 1954–1963: Spreading the Seeds of the Birmingham Group

437

9. 1963–1974: Oxford

679

10. 1974–1986: Retirement — Two Birds of Passage

754

11. 1986–1995: The Tree Needs to Grow New Rings

922

Bibliography

1064

Archival Sources

1065

List of Correspondence

1067

Name Index

1089

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Acknowledgements

In October 2004 the Institute of Theoretical Physics at Oxford was formally named the Rudolf Peierls Centre for Theoretical Physics. The occasion was memorable for the impressive line-up of guests who had come from all over the world for the ceremony. It was also memorable for the personal account of Rudolf Peierls’ youngest daughter, Jo Hookway, who gave an insight into life in the Peierls household and beyond. In talking about her father, she said: I feel an overwhelming sense of pride and responsibility in being here today and this is for a number of reasons. Firstly a pride in my father and all he achieved and stood for. Secondly there is the pride, coupled with responsibility, of being here representing the Peierls family. This task is also a huge one because of the size of the family — obviously I am here as part of the Peierls nuclear family. But the Peierls family is so much larger than this — its membership is worldwide and is probably of indeﬁnable boundaries as it contains not only everyone who ever was a member of my father’s department, but also all their partners, children, grandchildren and so on. As Jo continued to explain, she may not have understood, what being a theoretical physicist meant, or what the squiggles produced by her father on backs of envelopes and on blackboards signiﬁed; but what she did know and understand was that her father, with the considerable support of his wife, was building a community of people in his department: the extended Peierls family. Volume II of the Peierls Correspondence bears witness to this very special extended family. Correspondence of work-related and personal matters intermingle, and the strong sense of camaraderie among the

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members of Peierls’ department and their families is clearly visible throughout. Most of the letters reproduced in this second volume of the Selected Correspondence of Rudolf Peierls were part of the collection that Rudolf Peierls passed on to the Contemporary Scientiﬁc Archives Centre in two instalments in the mid 1970s and mid 1990s. They were catalogued and duly deposited at the Department of Western Manuscripts of the Bodleian Library, Oxford where they are now held. I am grateful to Colin Harris and his colleagues in the Western Manuscript Department for all their support and advice, which greatly facilitated the completion of the project. Some of the letters exchanged between Rudolf Peierls and his family remain in family possession, as do many of the photos. These are reproduced here with kind permission of the Peierls family. Other material was collected from the Library of Congress (Papers of J. Robert Oppenheimer), the Pauli Archive at CERN, the Division of Rare and Manuscript Collections, Cornell University Library (Bethe Papers), the Churchill Archives Centre, Cambridge (Chadwick Papers, Dirac Papers), the National Archives, Public Record Oﬃce, London, and the Niels Bohr Library of the AIP Center for History of Physics. In all these archives and many other libraries I have received valuable assistance in assembling this collection and researching the historical background of the material and the work described therein. Material authored by Rudolf and Genia Peierls is reproduced by permission of the Peierls family; letters written by James Chadwick are reproduced by kind permission of the Master and Fellows of Churchill College; letters authored by Wolfgang Pauli are reproduced with permission of the Pauli Archive, CERN; letters written by Niels Bohr are reproduced with permission of the Niels Bohr Archive, Copenhagen. Some of the letters reproduced in this volume have previously been published. This applies to some of the letters exchanged with Wolfgang Pauli,a and Niels Bohr.b a Karl von Meyenn (ed.), Wolfgang Pauli, Wissenschaftlicher Briefwechsel mit Bohr, Einstein, Heisenberg u.a, Vol. 3: 1940–1949, Vol. 4: 1950–1956, Berlin/ Heidelberg/New York: Springer, 1993ﬀ. b Peierls, R. E. (ed.), Niels Bohr Collected Works, Vol. 9: Nuclear Physics (1929– 1952), North-Holland: Amsterdam, 1985.

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Acknowledgements

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Among other copyright holders who have kindly granted permission to reproduce letters in this collection are: Mrs. Rose Bethe; Prof. Jochen H. Heisenberg; Dr. I. Landau; Dr. Olga Cherneva; Frau Monika Baier; Mrs. A.F. Crampin; Prof. Gustav Born; Christian Suter; F. Anthony Placzek; the Fowler family; Mrs. Jane Gatrell; Dr. Susan K. Martin; Mrs. K.D. Baxandall; A. and J.L.J. Rosenfeld; Ida Nicolaisen and Josh Pais; Jae Riebe; Gerald E. Brown; Ursula Frisch; Ed Salpeter, Prof. Emeritus, Cornell University; the British Pugwash Group, Ilse Thorner; the family of Robert S. Aitken, Denys Wilkinson, Roger H. Stuewer, Prof. Brian Pippard. Research for this project, in particular archival work in Russia and the United States, has been supported by the British Academy and the Royal Society. The work was facilitated by a term’s research leave from the University of Birmingham and an AHRB grant which permitted the extension of this leave by a further term. My thanks go to the entire Peierls family, and in particular to Jo Hookway who has supported this project with enthusiasm, insider knowledge and much common sense. She greatly facilitated access to material which had not been archived and is still in family possession, she read and commented on parts of the book, and gave useful insights into many aspects of the Peierls family life which would have been diﬃcult, if not impossible, to gain in any other way. Other family members oﬀered helpful insights and constructive criticism and they provided most of the photos reproduced in this volume. When I embarked on this two-volume edition of a selection of Rudolf Peierls’ Correspondence, I had little idea about the magnitude of the enterprise. I have been living with this exciting project for over a decade. So has my family. My husband, a theoretical physicist himself, knows that he only has himself to blame for introducing me to the work of Rudolf Peierls when we were both ﬁnal-year Ph.D. students at Cambridge. Our children, however, who had little choice in the matter, have been living with the project tolerantly. Without my family’s encouragement, understanding and patience, this edition would not have come to fruition. Thanks! Birmingham, 2008

Sabine Lee

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Editorial Comments

The introduction to volume 1a explains the background, provenance of and selection criteria for the material reproduced in the Selected Correspondence. For easy reference, below the main editorial principles followed in this volume, have been relisted. 1. The letters are listed chronologically, and, unless stated otherwise, reproduced in toto. 2. The transcription is limited to the text content, not to layout or graphic details. 3. Typos and misplaced letter sequences are corrected.b 4. The letters reproduced in this collection are held in the Bodleian Library,c the Library of Congress (Papers of J. Robert Oppenheimer), the Pauli Archive at CERN (Pauli Letters), the Division of Rare and Manuscript Collections, Cornell University Library (Bethe Papers), the Churchill Archives Centre, Cambridge (Chadwick Papers, Dirac Papers), and the National Archives, Public Record Oﬃce, London. Often Rudolf Peierls and his colleagues kept carbon copies of typed letters, and therefore both original letter and carbon copy survive. Unless otherwise stated, the letters reproduced here are the originals; however, to clarify, a list in a

S. Lee, Sir Rudolf Peierls. Selected and Private Correspondence, Vol. 1, Singapore: World Scientiﬁc, 2007, pp. 1–11. b This applies in particular for correspondence in the late 1980s and 1990s. As a result of failing eyesight in later life, many of Rudolf Peierls’ word-processed letters written in those years contain a large number of typographical errors which have been corrected. c Sir Rudolf Peierls, Papers and Correspondence, 1898–1996; CSAS catalogue no 52/6/77 and NCUSACS supplementary catalogue 57/6/96.

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the appendix speciﬁes whether the text used in the edition is an original or a carbon copy. 5. Handwritten additions, where included, are identiﬁed as such. 6. Editorial additions are made in square brackets. 7. Text which was deleted in the manuscript is not transcribed. 8. The reproduced material makes no distinction between single and multiple underlining. 9. Gaps arising from punching or ﬁling are ﬁlled and only noted in square brackets, if there are doubts. Abbreviations are only completed where necessary. 10. Illegible words are noted as [??], with [?] for one word, [??] for two words and [???] for three or more words. 11. Handwritten additions missing from the typed text of a carbon copies are noted as [...] and are identiﬁed as missing text in an editorial note. 12. Footnotes in the text are marked with asterisk and added at the end of the page on which they occur. Editorial notes appear at the bottom of the page. 13. Repeated words at the page break are transcribed as one word.

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6.

Resettling at Birmingham: Postwar Physics in the UK

“My God, what have we done?” Reportedly, these were the words of Robert Lewis, the co-pilot of Enola Grey, the B-29 that dropped the ﬁrst atomic bomb on Hiroshima on 6th August 1945. The scientists who had spent the previous years developing the atomic bomb, knew about its fatal eﬀects. Those who had witnessed the Trinity Tests, the explosion of the ﬁrst atomic bomb in the New Mexican desert had been in awe. Robert Oppenheimer, the scientiﬁc head of the mission, not only remarked that scientists knew that the world would no longer be the same, he also famously commented the event with a passage from the Bhagavad Gita: “· · · now I am become Death, the destroyer of worlds · · · ”. Despite the destructiveness of the weapon which had been built, despite the horror caused by its use on Hiroshima and Nagasaki, and despite the deep concern over the destructive power among the scientists who had created the bomb, their scientiﬁc and technological achievements are without question. General Groves, who would later be at pains to minimise the contributions of the British contingent at Los Alamos was one of the ﬁrst to congratulate James Chadwick, the head of the British Mission, on the success of the joint project.1 Most members of this British contingent at Los Alamos, who had been instrumental in the Manhattan Project at the level of research and development, returned to the UK at the end of the hostilities in the Paciﬁc. For them the subsequent years were dominated by the key issues of resettling into peacetime academia and of dealing with the consequences of their war-time research. Most chose to return to Higher Education and help 1

Letter [380].

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build or rebuild the academic landscape in the UK. While this was true to a greater or lesser extent for virtually all academics who had been involved in the war eﬀort away from their home institutions, for those nuclear scientists who returned from the Manhattan Project, this task had qualities which diﬀered signiﬁcantly from that of their colleagues. The production eﬀort of nuclear weapons had moved forward nuclear physics and chemistry in a way that would have been impossible without this wartime enterprise, and this in itself altered the scientists’ outlook.2 But the success of the Project also had momentous repercussions of political and psychological nature. The Manhattan Project, epitomised by the joint leadership of the military (General Leslie Groves) and the scientist (Robert Oppenheimer) had brought together politics/warfare and science in a way that had been unknown before. From now on, spheres of inﬂuence had to be determined, territory defended and scientists had to face the huge political, military and humanitarian consequences that their scientiﬁc discoveries had had and would continue to have at much closer range than ever before. It is not surprising, therefore, that after 1945 many of those leading scientists became involved in eﬀorts to control nuclear weapons. They set up their own national scientists’ organisations such as the American Federation of Scientists in the US3 or the Committee of Atomic Scientists, later called the British Association of Atomic Scientists in the UK.4 Beyond the non-governmental realm of these organisations, scientists also became increasingly involved in consulting governments on nuclear issues, both on questions of weapons development and nuclear energy and on issues of the control of these weapons. In the UK, a further issue arose largely out of the changing nature of the Anglo-American relationship, namely how to develop one’s own nuclear programme in response to American attempts to monopolise the production of nuclear power. At Los Alamos, (and at the other research centres of the Manhattan Project) science had been truly international — within the conﬁnes of a wartime enterprise under the 2

See letters [381], [384], [386], [390–391], [394]. Letter [390]. 4 Letters [395], [413–414], [418–19]. 3

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military command of General Leslie Groves. Hence, it is not possible to quantify precisely the achievements of what became known as the British mission to Los Alamos. Their number never exceeded more than about twenty-ﬁve (even counting the ‘consultants’) which was negligible in comparison with thousands of workers at Los Alamos at the peak of activities. During the war, General Groves commented that British research was ‘substantial’ and that the British scientists made an ‘invaluable’ contribution to the American project. Yet, after the war, he claimed that while the quality of the work of the British team was high, their number was far too small to have had a signiﬁcant impact, a reasoning which was adopted by American policy makers who were soon to engage in a more restrictive policy of nuclear sharing. Others disagreed and argued that the British contribution to the project went far beyond what a mere head count would suggest and was out of all proportion to the team’s size. American accounts of the Los Alamos years dominated the early historiography of developments on the Hill, just as American economic and military power dominated international relations after the end of the war. Throughout the war, nuclear co-operation and/or lack of it had followed a very similar pattern to the general development of AngloAmerican relations more generally, with strategic, psychological, economic and political considerations and suspicions playing a crucial part in the formulation of policies. The British government clearly expected wartime nuclear collaboration to be continued after the end of the war. Prime Minister Attlee, in a letter to President Truman in early August 1945, proposed a ‘joint declaration of our intentions to utilise the existence of this great power not for our own ends, but as trustees for humanity in the interest of all peoples in order to promote peace and justice in the world.’5 But the Americans had rather diﬀerent ideas. Some, especially in the military, intended to build on what they perceived to be a ﬁve-year technological lead by accelerating nuclear research in national (and secret) projects, while at the same time controlling uranium supplies. This would allow the Americans to accumulate a stockpile of 5

Attlee to Truman, 8.8.1945, Foreign Relations of the United States, 1945, pp. 36–7.

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weapons and to extend their strategic advantage.6 Others envisaged closer co-operation with the Soviet Union (at the expense of the United Kingdom) in order to avoid a nuclear arms race.7 Others were contemplating some form of co-operation with the British (and Canadians) while expressing doubts about collaboration with the Soviet Union. The terms of the Quebec Agreements of August 1943, the AngloAmerican Declaration of Trust of June 1944 and the Hyde Park aidememoir of September 1944, had led the British to expect a continuation of nuclear collaboration ‘after the defeat of Japan unless terminated by joint agreement’.8 This was not forthcoming. Within less than a year, the approach of substantial technology and scientiﬁc transfer had been replaced by a more restrictive American policy of the Atomic Energy Act, the so-called McMahon Act, of August 1946 which prevented the transfer of information about technical processes and ‘restricted data’, such as the production of ﬁssionable material to other nations. The correspondence between Rudolf Peierls and James Chadwick, who continued to act as technical adviser and head of the British Mission until his return to the UK in late 1946, give some indication of the underlying tension.9 Moreover, they touched on the implications of the McMahon Act for the future of British nuclear ambitions. On an immediate practical level the McMahon Act meant that the British scientists, some of whom had remained at Los Alamos beyond August 1945, were no longer allowed access to documentation and reports which they had been able to utilise without restrictions before. More signiﬁcantly in the medium and long term it meant that the British were forced to (or felt forced to) develop nuclear weapons independently, because they were no longer allowed to beneﬁt from the scientiﬁc collaboration within 6 Timothy J. Botti, The Long Wait. The Forging of the Anglo-American Nuclear Alliance, 1945–1958, New York: Greenwood Press, 1987, p. 9 7 Henry Stimson to Harry S. Truman, accompanied by a memorandum, September 11, 1945, Washington, 11.9.1945, Foreign Relations of the United States, 1945, pp. 41ﬀ. 8 Anglo-American Declaration of Trust, 13.6.1944, www.nuclearﬁles.org/ redocuments/1944/440613-anglo-amer-decl.html; Hyde Park Agreement, Foreign Relations of the United States, 1944, Vol. 2, Washington D.C., 1967, pp. 1026–28. 9 Letters [395], [402], [414], [416].

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the gigantic American enterprise. And indeed, a decision as taken by a handful of people without full Cabinet consultation in January 1947 to develop nuclear weapons. It was a sensitive area of public policy, and the programme was not oﬃcially communicated to the public until ﬁve years later, when the then Prime Minister Winston Churchill, in February 1952, announced plans for testing the ﬁrst British-built nuclear weapons. The exchange of letters between Rudolf Peierls and G.P.Thomson indicates that fundamental and applied research in nuclear physics was continuing at British universities, and that Rudolf Peierls’ expertise was sought on these issues.10 But Peierls was also concerned about progress of the new Atomic Energy Research Establishment(AERE) at Harwell, where the Ministry of Supply had taken over an RAF airﬁeld for the purpose of providing the infrastructure for the research and development of civil nuclear power. To direct the British eﬀort, Air Marshal Viscount Portal of Hungerford was made Controller of Production, Atomic Energy; John Cockroft became director of the Atomic Energy Research Establishment, and Christopher Hinton, a senior ICI engineer, became the leader of the ﬁssile material production programme.11 At that stage, no decision on nuclear weapons development had been made, but in January 1946, already, William Penney had been put in charge of Armament Research, an appointment which suggested that the British Government was seriously considering the option of an independent development of a nuclear arsenal. In June 1947 Penney was chosen to lead Britain’s nuclear weapons program, although this decision was not made public until much later. Secrecy surrounded the early stages of the project, with the press being discouraged to visit Harwell, and with public and political debates about atomic energy suppressed. As one MP put it during a parliamentary debate: ‘When an Hon. Member asks the Prime Minister about the atomic bomb, he looks at him as if he had been asked something indecent.’12 And even when one of the senior members of the AERE, the head of the Theoretical Physics Division 10

Letters [393–394], [397], [400]. See letters [402], [427]. 12 Hansard, House of Commons Debates 1948, Col. 574 (4 March 1948). 11

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at Harwell, Klaus Fuchs, was arrested in early February 1950, charged with violation of the Oﬃcial Secrets Act, little oﬃcial comments were passed on the work carried out at Harwell. The arrest of Klaus Fuchs was a severe blow to the British scientiﬁc community as a whole, and it was a particular blow to Rudolf Peierls and his family personally.13 Klaus Fuchs, who had worked on Tube Alloys, the British atomic bomb research project, had been transferred alongside Peierls to New York and later to Los Alamos to work on the Manhattan Project. During his work on the British and AngloAmerican atomic weapons projects he supplied the Soviet Union with valuable information about those, and he continued to do so after his return to England in 1946 when he joined the AERE at Harwell. In the late 1940s, as a result of the successful deciphering of the Venona transcripts, incepted messages that had been sent between several Soviet intelligence agencies, a leak of atomic secrets to the Soviets was identiﬁed as leading to the British Mission at Los Alamos, and eventually Klaus Fuchs was isolated as the key suspect. Under interrogation from MI5, he confessed, in January 1950, to having broken the Oﬃcial Secrets Act by passing on classiﬁed information to the Soviets. On the basis of this confession, he was convicted to 14 years in prison in March 1950.14 Klaus Fuchs had been a close friend of Rudolf and Genia Peierls’, he had lodged with them when he ﬁrst came to Birmingham, and he had collaborated closely with Rudolf Peierls who had not only hired him into his department at Birmingham but had also been instrumental in securing his appointment at Los Alamos. Much of the correspondence in early 1950 reﬂects this. The letters exchanged with friends an colleagues are part of the attempt to come to terms with the personal disappointment as well as an endeavour to limit the damage done to the scientiﬁc communities in the UK and the US.15 13

Letter [493]. Fuchs was released early after serving a little more than nine years of his sentence. After his release he returned to his native East Germany where he continued his scientiﬁc career, being elected to the Academy of Science and the Communist Party central committee. Eventually he became deputy director of the Institute for Nuclear Research in Rosendorf, from where he retired in 1979. 15 Letters [495–497], item [500]. 14

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The Fuchs trial was interesting in what it revealed as much as in what it concealed. Many aspects of the case were kept from the public in order to cover important political secrets. A number of people in the highest echelons of British secret intelligence had a distinct interest in ensuring that the Fuchs case would not lead to further disclosures. They and the British Government did not want details of Fuchs’ work at Harwell publicised, as he was involved in the then still secret British atomic weapons programme. In Britain, the case vanished from the public view within days of the verdict without Fuchs’ spy contacts in Britain ever being apprehended fully. British anger over Fuchs dissipated very quickly. The initial public outrage and the discussion in the press about the wisdom of accepting political and religious refugees and employing them in sensitive ﬁelds soon subsided. It never escalated into the Mccarthyism of the US, which was shaken by espionage cases in the aftermath of Fuchs’ exposure, when the Rosenbergs, Harry Gold, and the Greenglasses were exposed. One of the victims of the widespread anti-communism, often culminating in political hysteria, was Robert Oppenheimer.16 Rudolf Peierls never shied away from expressing his views in public. He did so regardless of the eﬀect this would have on is own position. He would later support Oppenheimer openly as well as privately,17 just as he defended civil liberties in the aftermath of the Fuchs aﬀair in his memorandum ‘Lesson of the Fuchs Case’.18 He was never secretive about his friendships with people from communist countries and of communist persuasion, he argued for the re-establishment of scientiﬁc exchange with the Soviet Union and its satellites. He rejected the idea of oppressing the voices of dissenters by arguing that this totalitarian measure would bring security at the expense of values that any democracy had to ﬁght to retain. In the aftermath of the Fuchs arrest, Peierls’ overt expression of these views led some to question his reliability, especially in view of the fact that he had access to sensitive and secret information in connection with the UK nuclear programme.19 16

See below, pp. 442–43. See e.g. letters [597], [601]. 18 Item [500]. 19 Letter [525]. 17

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However, at that time, as on many other occasions during the subsequent decades, it was recognised by people in authority that the views may have been uncomfortable at times, but at no point did they undermine the security and values of democracy in the UK, and at all times did Peierls prove loyal to the UK national interest.20 Another issue on which Rudolf Peierls expressed his views clearly and encouraged others to do likewise was the question of how to deal with defeated Germany and the German scientists in particular. The questions engaged the thoughts of many British scientists, and even more so many German-born British scientist many of whom, due to their Jewish origin, had been forced to leave Germany under National Socialism. In early 1948 Peierls circulated a memorandum,21 which was widely discussed as a string of conferences in the UK required the scientists to clarify their position with regard to the invitation of German colleagues,22 the organisation of social, non-scientiﬁc contacts, and decisions on foreign membership of learned societies, such as the Royal Society which conferred membership to distinguished foreign scientists.23 Beyond the attempts of dealing with the legacy of the weapons development, many scientists, especially in the early post-war years, were also concerned with rebuilding the international science community. The totalitarian regimes in Europe had led to a massive displacement of scientists, as had the war itself. Many who had been forced to leave their home countries in the 1930s and early 1940s, had no desire to return and were looking positions in their adopted homes, mostly in the UK and the US.24 Given the shortage of highly trained scientiﬁc staﬀ in UK academia, many such positions could be found. Conversely, ﬁlling Chairs even at prestigious British universities often proved diﬃcult.25 Rudolf Peierls, throughout the post-war era, received numerous oﬀers to take up such positions, including Chairs at Oxford, Manchester and 20

See below chapter 10, pp. 756–57. Item [440]. 22 Letters [404–406]. 23 Letters [442–443], [445], [447], [458–461]. 24 See e.g. communications with G. Wick, letters [382], [385], [387]. 25 See letters [388], [390], [415]. 21

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London. He considered few of these seriously, but the oﬀer to take up the Plummer Chair at Cambridge was an oﬀer which he thought about very thoroughly, and about which he consulted several close colleagues.26 The correspondence in this context indicates some important aspects which help to explain his loyalty to Birmingham, but also his clear ideas of what he regarded as important for a prosperous theoretical physics community in the UK:27 a balanced ﬂexible system that provides good training and high standards without prejudicing against students outside Oxbridge. Beyond the question of securing academic leadership within the UK, there was also the issue of retaining Britain’s standing as a recognised centre of research excellence. Rudolf Peierls had come to Birmingham in 1937 as the ﬁrst professor of Mathematical Physics and had set himself the task of establishing a school devoted to both ﬁrst-class research and ﬁrst-class teaching. The war had put the eﬀort on hold, but as soon as Peierls returned to Birmingham, he re-engaged in the process and, virtually from scratch, he developed a school of mathematical physics, or theoretical physics as it would be called later, which was arguably the best in the country and which could compete with any in Europe and with most others globally. His correspondence during the ﬁrst post-war decade gives some clues as to why he succeeded where many others failed. • Peierls regarded teaching as his main responsibility.28 While he enjoyed his research and recognised its importance as a contribution to a discipline which was undergoing exciting developments, increasingly this research was being done in collaboration with research students and younger research staﬀ and thereby became virtually indistinguishable from teaching. • His enthusiasm for teaching and building up a viable team found expression in time and energy devoted to securing funding for young scholars and ﬁnding the best possible people to carry out the 26

Letters [383–384]. See in particular letter [384]. 28 R.E. Peierls, Bird of Passage. Recollections of a Physicist, Princeton: Princeton University Press, 1985 (cited hereinafter as Peierls, Bird of Passage), pp. 249 ﬀ. 27

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increasingly complex research.29 Within a few years, he had built a reputation for his institute, of being an ideal training ground — a reputation which helped achieving both the above aims; but it also enabled Peierls to work within a group of a critical mass which would always be certain of being supplied with the best of talent from within Britain and from abroad. • Peierls’ commitment to his students and research fellows did not end with the completion of their period at Birmingham. Much thought and letter writing went into the task of securing future positions and exchange opportunities. In this, the prospects of the individual scientist was as important as the future of his own institute at Birmingham. • Collaboration with the US throughout the war and close contact with many friends and colleagues across the Atlantic, had sharpened Rudolf Peierls’ awareness of the role reversal which had occured with regard to academic physics. As early as September 1945, he expressed, in a letter to Raymond Priestley, the Vice Chancellor of Birmingham University, that ‘American universities [had] matured a great deal and contact with this country [was] now less important to them, and more important to us’.30 The consequence of this, in Peierls’ view, had to be regular academic exchanges which would allow the UK to beneﬁt from scientiﬁc achievements of colleagues in the US. And his attempts to put Birmingham ﬁrmly on the academic map in theoretical physics meant that he was keen to secure a sizeable fraction of the exchange for this institution. • A supplementary ingredient which could not be found in any other institute was what some would later term the ‘Genia-factor’. Genia Peierls was an enthusiastic supporter of her husband’s endeavours to attract the best young scientists to Birmingham, a place which — with post-war rationing, shortage of housing and 29 30

Letters [389], [403]. Letter [381].

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generally meagre facilities was not the most appealing location. Her hands-on eﬀorts which ranged from provision of short-and long-term accommodation to general advice, from organising social gatherings to job-advice for spouse and general counselling, had a signiﬁcant impact on the cohesion of the growing ‘Peierls school’.31 • Peierls himself had studied in an environment which had encouraged travel and intense exchange of research ideas through students moving from research centre to research centre and of course, through scientiﬁc meetings and conferences. Convinced about the stimulation brought about by this exchange of knowledge, he organised two international conferences at Cambridge, in 1948 and 1953. These and the regular seminar programmes organinsed in the department attracted some of the leading ﬁgures of the national and international physics communities, including Bohr, Heisenberg, Pauli, Mott, Born, Lise Meitner, Frisch, Oppenheimer, Bethe, and many others.32 That a professor would take his teaching and administrative duties seriously was not in itself something that set Rudolf Peierls apart from many of his contemporaries. But he was quite prepared to make personal sacriﬁces and put departmental interest before his own. One such example was his reaction to Robert Oppenheimer’s invitation to spend the academic year 1951/2 at Princeton. The oﬀer was very appealing, not only because of Peierls’ friendship with Oppenheimer and the prospect of a year’s research largely uninterrupted by administrative chores and teaching commitments. Princeton, at the time, was buzzing with activity in the wake of recent developments in ﬁeld theory in which Peierls himself was very interested. Nevertheless, he informed Oppenheimer that he could only spend one term at the Institute, because he felt responsible for a large number of new research students and considered it necessary to take his share of administrative responsibility 31

See Genia Peierls. Reminiscences collected on the occasion of Genia Peierls’ 70th birthday, July 1978., copy in Peierls Papers, Supp. A.119. 32 See e.g. letters [445], [447], [451], [456], [474–476].

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at Birmingham for the ﬁrst half of the academic year in question.33 The war had interrupted some of Peierls’ research, most notably the famous Bohr-Placzek Peierls paper.34 The three scientists picked up the threads in 1945 and communicated extensively about the manuscript.35 The paper remained unpublished at the time, although the results were written up in a manuscript which several decades later was published in Bohr’s Collected Works.36 Peierls’ closest friend from his student days in Munich, Hans Bethe, had moved to Cornell in 1935. At Los Alamos, the two scientists again had the opportunity to work together closely with Hans Bethe as the Head of the Theoretical Physics Division and Rudolf Peierls in charge of the hydrodynamics group. After the end of the war, the two friends, again, parted to take up their roles as leading theoretical physicists in their respective adopted home countries, the US and the UK. Over the subsequent decades, they remained in close contact through correspondence, academic and social exchanges and, equally signiﬁcantly, through establishing a network of research collaboration of their students and junior colleagues.37 Most inﬂuential among these was the recommendation of Hans Bethe to Freeman Dyson, in early 1949, to spend some time at Peierls’ institute.38 The fellowship arranged between Rudolf Peierls and Robert Oppenheimer, at the time director of the Institute of Advanced Studies at Princeton, where Dyson, the rising star of theoretical physics was based, demonstrates two points very clearly. Firstly, Peierls was excellent at spotting talent, and secondly he was ﬂexible enough to make Birmingham an attractive option for your scholars to choose his institute despite stiﬀ competition from 33

Letter [524]. S. Lee (ed.), Sir Rudolf Peierls. Selected Private and Scientiﬁc Correspondence, Vol. 1, Singapore: World Scientiﬁc, 2007 (cited hereinafter as Lee, Selected Correspondence, Vol. 1), Chapter 4, pp. 522–524. 35 Letters [392], [417], [421], [435], [444], [485–486], [490]. 36 R.E. Peierls (ed.), Niels Bohr. Collected Works, Vol. 9 Nuclear Physics (1929– 1952), Amsterdam: North Holland, 1986, pp. 505–519. 37 Letters [396], [401], [412], [424], [426], [428–430], [432], [434], [436], [438], [448], [453–455], [457], [465]. 38 Letters [468–470], [473]. 34

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Cambridge, Oxford, Liverpool, Manchester, Bristol and other universities.39 Dyson was based at Birmingham, but it was agreed that he was at liberty to spend time at Princeton regularly, as long as it ﬁtted in with departmental requirements at Birmingham.40 This resulted in Birmingham being in direct contact with the development of quantum ﬁeld theory, which at the time was worked on by Schwinger, Tomonaga, Feynman and Dyson.41 Others similarly made the journey across the Atlantic, and the exchange went both ways with, among others, Byers, Lieb, Langer, Brown, Dalitz, Salpeter, Claude Bloch and Stanley Mandelstam moving between the US and Birmingham. Another example of Peierls spotting talent and being slightly unconventional in securing it for Birmingham was Gerry Brown. A native of South Dakota, Brown had studied at Wisconsin and Yale, where he obtained an M.S. and a Ph.D. His short-lived membership of the Communist Party, from which he was eventually expelled, put his academic career in the US at risk despite his outstanding doctoral work with Gregory Breit. Various enquiries to universities in England led to the by now famous three-penny folded airmail return from Rudi Peierls saying: ‘Come ahead.’42 In February 1950 Gerry Brown arrived as a political refugee from pre-McCarthy anti-communist America; in 1960 he left to take up his appointment as full professor of Theoretical Physics at Niels Bohr’s Nordic Institute for Theoretical Physics (NORDITA). While not many of Peierls’ students arrived as refugees in the same way as Gerry Brown did, many left into distinguished positions, and a signiﬁcant number eventually ended up ﬁlling the Chairs of the most prestigious European, American, Asian and Australian Universities. Peierls’ correspondence throughout the 1950s demonstrates the paths of some of these talented young men and women.

39

See also letter [484]. Letters [477], [479]. 41 Letters [507–508], [510], [513–514], [518]. 42 G.E. Brown, ‘Flying with Eagles’, Annu. Rev. Part. Sci. 51, 1–22 (2002), here, p. 6. 40

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[380] L.R. Groves to James Chadwick Washington, 10.8.1945 Dear Sir James, I have received your nice letter of August 9 and I wish to convey through you to all members of the T.A. Directorate my sincere and heartfelt appreciation of their congratulatory message and for their own great contributions to the success of our project. Sincerely yours, L.R. Groves

[381] Rudolf Peierls to Raymond Priestley [location unspeciﬁed], 13.9.1945 (carbon copy) Dear Vice-Chancellor, As I mentioned to you the other day, I believe that the universities in this country can gain a great deal by an arrangement that will make it possible for visitors from abroad, in particular from the United States, to spend short periods ranging from one month to one year according to circumstances, at British universities. Such men could have a very welcome stimulating inﬂuence particularly in subjects in which at the moment, owing to better equipment and greater manpower, the United States are leading. In addition to the actual beneﬁt derived from such visits, there would be the possibility that some of these men might like the life here, and might make themselves popular with their colleagues here so that they could be induced to accept permanent jobs, and thus help to alleviate the great manpower shortage that now exists among scientists of high standing. After the last war this type of exchange was largely helped by Fellowships awarded by the Rockefeller Foundation, the Guggenheim Foundation, and similar bodies, most of whom I think have ceased to award such Fellowships, or have restricted them to special subjects (Rockefeller

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Fellowships are now only available to men working in medical science and allied subjects). I do not believe we can expect the Americans to provide new funds for this purpose, largely because American universities have matured a great deal and contact with this country is now less important to them, and more important to us, than in the past. I believe, therefore, that this country could try to provide funds for this purpose. This might either be done by individual universities, or by a national organisation for all universities, and the latter would probably make administration somewhat easier. In many cases such visitors could be given existing jobs, in particular Research Fellowships would appear very suitable; at a time when our own training of young scientists has been held up to a degree which will make it impossible to ﬁll all these Fellowships immediately. In that case the Fund I am suggesting would merely have to provide travel expenses; which I believe should be on a generous scale, and shall allow senior people to come for extended periods and to bring their families; and it should also provide some subsistence allowance to take care of the fact that these people cannot bring their own furniture, and are not familiar with conditions in this country, so that they will not be able to live as economically as people who are at home here. In the long run it may be undesirable to take up existing Research Fellowships in this way, and it would then be preferable to have the central fund responsible for both travelling expenses and living costs. I believe most of my colleagues will agree that such a scheme would be of greatest importance to British universities, and I am sure that, in my own subject in particular, it would make an enormous diﬀerence. I know that there are many Americans in my subjects. However, this scheme should not start immediately but, say, in a year’s time, when we have overcome the immediate administrative diﬃculties which will result from converting the universities to a peace-time basis. [R.E. Peierls]

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[382] Gian Carlo Wick43 to Rudolf Peierls Rome, 14.9.1945 Dear Peierls, It is a long time now that I gave a friend who was coming to London your address, begging him to enquire about you. But without result. Now I venture to write to you directly, hoping to ﬁnd you still in your old place. There is not much use now writing about the past years; perhaps we shall talk about our experiences one day. I sincerely hope that you and your family have gone through these hard times unhurt. I, for my part, have been in Rome most of the time. Fortunately I was not called up — except for twenty days in the summer 1943 — and I was not asked to do any war work. If I had, I hope I would have had the courage to refuse, but it would not have been pleasant! Now I am rather anxious to get back to work, after a month of rest in a small village on the hills. We have received, only now, the Physical Review.∗ Although scientiﬁc production has been slowed down by the war, still four years of Phys. Rev. make a lot of reading! It will take much work to get up to date again. You would help me a lot with a hint or two. 1) I have received from Schr¨ odinger several reprints on a new unitary theory which seems to explain a lot of things.44 I am ∗ But

not the Proceedings R.S., not the P. Cambr., nor Nature. These will be very hard to get, we are told! 43

Gian Carlo Wick (1909–1992) a native Italian studied at Turin and later worked at Leipzig and G¨ ottingen before returning to Italy, eventually working under Fermi, before becoming professor at Palermo and then Padova. 44 Throughout the war, Erwin Schr¨ odinger published a large number of papers, primarily in the Proceedings of the Royal Irish Academy on a variety of subjects. Most notably, in 1943 he published E. Schr¨ odinger, ‘The General Unitary Theory of the Physical Fields’, Proc. Roy. Ir. Ac. 49A, 43–58 (1943) and in the following year E. Schr¨ odinger, ‘The Point Charge in the Unitary Field Theory’, Proc. Roy. Ir. Ac. 49A, 225–35 (1944); E. Schr¨ odinger, ‘Unitary Field Theory: Conservation Identities and Relation to Weyl and Eddington’, Proc. Roy. Ir. Ac. 49A, 237–44 (1944) and E. Schr¨ odinger, ‘The Union of the Three Fundamental Fields (Gravitation, Meson, Electromagnetism)’, Proc. Roy. Ir. Ac. 49A, 275–87 (1943).

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very intrigued and I would study this theory carefully if I were not engaged in a number of complicated papers on nuclear forces, strong interactions and so on. I have never bothered very much about unitary theories. What is the general opinion about this particular one? 2) Has non-linear electrodynamics made any important advance? 3) Has the theory of nuclear reactions made any important advance? I am specially interested in this, as I am writing a book with Amaldi;45 I have left aside until now the chapter on the theory of resonance phenomena and so on; I expected that the paper by you, Bohr and Placzek would oblige me to change much of what I might have written. Has the paper ever appeared? Will it ever appear? Which subjects would be especially aﬀected by it? I should be very indebted to you, if you were so kind to answer, even very brieﬂy, to these questions. Have you heard of Amaldi’s experiments on neutron scattering? They seem quite interesting. With kindest regards, also to Mrs. Peierls, Yours truly Gian Carlo Wick

[383] Rudolf Peierls to John Cockroft Washington, 13.12.1945 (carbon copy) Dear Cockroft, I have just received an oﬀer of the vacant chair in Cambridge. I ﬁnd it extremely diﬃcult to make up my mind. I am tempted by the better supply of students in Cambridge, but doubtful about the chances of having contact with a strong experimental nuclear physics team in Cambridge. This depends on a number of factors, in particular on who is likely to be your successor in the Jacksonian Chair.46 45

The book does not appear to have materialised. John Cockroft had held the Jacksonian Chair since 1939 but was leaving Cambridge to become the ﬁrst director of the Atomic Energy Research Establishment at Harwell in 1946. In 1947 Otto Frisch accepted the Jacksonian Chair. See letters [415] and [428]. 46

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If you have any information about what is likely to happen there, or know anything more generally about the future of fundamental physics in Cambridge, I would be very grateful for your advice. I am planning to go to Washington to see Chadwick and shall probably be there on December 19 and 20. If you plan to be in Washington at the same time, do not bother to reply. Otherwise, would you be good enough to send a copy of your reply to Washington for me. Yours sincerely, [Rudolf Peierls]

[384] Rudolf Peierls to Raymond Priestley [location unspeciﬁed], 13.12.1945 (carbon copy) Dear Priestley: After having successfully disposed of an invitation from Oxford and one from Manchester, I have now received an oﬀer of the Plummer Chair in Cambridge. As you can imagine, I ﬁnd it somewhat harder to make up my mind on this. My personal preference is strongly on remaining in Birmingham. I have enjoyed the work in the University. I am looking forward to the collaboration with Oliphant on his new plans, and I like the Administrative machinery of a modern university which in Birmingham seems to run particularly eﬃciently and smoothly. I feel I should not decide on personal preference alone, but the overriding consideration ought to be the chances of success in starting a school of theoretical physics and training up a new generation which is very badly needed, and I feel my decision should be based entirely on where there are the best prospects of success in this. On this question, too, there are arguments on both sides. I believe research in theoretical physics can be successful only in close contact with experimental work and I believe I shall ﬁnd much more fruitful collaboration with Oliphant’s department on the kind of fundamental problems that I would be particularly interested in than I could expect in Cambridge. I also know that in any changes of policy, both as regards

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the teaching and organisation of research, I should ﬁnd more support in Birmingham than the somewhat cumbersome machinery in Cambridge would make possible. The important factor on the other side of the balance is, of course, the availability of good students and the present examination and scholarship system which, particularly in mathematical subjects, canalizes the supply of ﬁrst-class students to Cambridge. If this situation remains unchanged my choice, therefore lies between ﬁrst-rate students in Cambridge and between a ﬁrst-rate set-up with a restricted supply of students or a plentiful supply of students with a somewhat diﬃcult set-up. This is true unless it is possible at this moment to break the vicious circle which attracts all good students to Cambridge and Oxford because of their high reputation and maintains a high reputation because they get the best students. For several reasons it might be the best psychological moment to change this now in a limited number of subjects, and it might be possible to attract to Birmingham a research team of graduate students, including some who had their undergraduate training in Cambridge. I have put down my view on this question in so much detail because I think it is only fair that you should know the position fully, and also because you may have more deﬁnite views on the chances of putting the provincial universities, and in particular Birmingham, in a better place compared to Cambridge than was possible in the past. In that case, I would greatly appreciate your advice. I would also like to make it clear that, in writing this letter, my object is not to obtain any further promises or concessions from the university. You probably know that in the case of the oﬀer from Manchester, I wrote to Haworth in order to clear up beyond doubt a point on which I was almost satisﬁed, but on which a brief statement in Faculty minutes had raised some slight doubt. The reply from Haworth was very enthusiastic and gratifying and I am now satisﬁed that I can expect from the Faculty and from the other University authorities all the support and assistance I can reasonably expect. The one attraction of Cambridge which makes me hesitate now, the supply of ﬁrst-class students, is clearly not a point for bargaining.

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In replying to Cambridge, I shall try and postpone a decision until my return to England, which I expect to be approximately February 1, and I shall say that, whatever the decision, I shall not consider moving before the summer since I think the least I owe to the University of Birmingham is to return and get things running again after they have patiently put up with my absence for so long. With kind regards, Yours sincerely, [R.E. Peierls]

[385] Rudolf Peierls to G.C. Wick [location unspeciﬁed], 14.12.1945 (carbon copy) Dear Wick: I have just sent you a cable asking you whether you would be prepared to consider a research job in Birmingham. By the time this letter reaches you, you may already have replied one way or another but, in any case, I am writing to give you a little more explanation than is possible in a cable. I intend to be back in Birmingham around February 1 and I shall then have a separate department of mathematical physics with a rather small staﬀ. There is, at the moment, only one man besides me, who is interested in research,47 but I have now managed to get funds from which to create new research fellowships, and we will be able to get more good people, provided we can ﬁnd them. If you would ﬁnd it possible to come, I think the least we could oﬀer you is a research fellowship at £800 p.a. which would carry no teaching duties except that you would 47 Hugh McManus had already been a research student in 1938/9. After the war, his results could not be reconstructed and he had to restart his career as a research student with work on inﬁnite self energy. Peierls, Bird of Passage, pp. 137, 227. McManus eventually moved to Chalk River, the Canadian Atomic Energy Laboratory and later became professor of physics at Michigan State University.

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probably like to give a small number of lectures, say three or four a week, to senior students. The post is not a permanent one, but it is not limited to any deﬁnite period, and can be held for a number of years. The shortage of competent theoretical physicists in England is now so great that I do not have any doubt that you would ﬁnd an equivalent or better job before very long. My department is in close contact with Oliphant’s department, which is expanding greatly and which I hope will be one of the centres of fundamental research. Oliphant has plans of constructing a machine for accelerating particles to energies of the order of 109 volts. He has quite a good staﬀ including Moon. There is no speciﬁc date at which we would want you to take up your duties except, of course, that the sooner you can come the better. I have no knowledge of what diﬃculties we shall meet in greeting the necessary papers and permits, but I shall try to do my utmost to get this through in as short a time as possible. I should express that technically, the appointment to such a fellowship has to be made by the university authorities, but I do not anticipate any objections from them. I have heard rumours to the eﬀect that you have been oﬀered a job in this country and it is not for me to give you advice one way or other, but personally I would very much hope that you still can and will choose England, since I would be looking forward to collaborating with you with great pleasure. It might be useful to bear in mind that there is an extreme shortage of good people in England, and for this reason advancement to senior and individual positions is comparatively easy (there are at least three professorships vacant now). I personally ﬁnd life in England particularly attractive, even with the postwar diﬃculties in housing, food and clothing that are likely to continue for some time, but this clearly is a personal matter. With best wishes, [R.E. Peierls]

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[386] Rudolf Peierls to James Chadwick Washington, 14.12.1945 (carbon copy) Dear Chadwick, I was trying to arrange to come to Washington to see you after your return to this country, but I ﬁnd transportation conditions at the moment so diﬃcult that it would probably mean a great loss of time. I therefore decided to abandon the idea for the present, but I could always arrange to come if you think there are important matters to be discussed. I shall, in any case, try to speak to you on the phone early next week. In any case, I am planning to leave here ﬁnally on January 10 and expect to be in the East from January 14 until my ship sails, which will probably be around January 25. I intend to spend some days in Washington during that period. Placzek will be able to tell you most of the news. I believe the most conspicuous fact since your departure is the amazing deterioration of morale in this place. There is very little work going on beyond writing up the “encyclopedia”48 and many people whose original intention had been to stay on for the summer have decided to get out. Bradbury49 is trying to rally his remaining forces and things are a little better now because, in most places, the new men have been appointed who will act as division and group leaders during the interim period. They have taken over the work in most places, and naturally pursue it more intensely than the people who are about to leave anyway. As regards the British team, Bretscher and with him French50 have still 48

After the development of the ﬁrst operational nuclear weapons, the scientists of the Manhattan project wrote up the scientiﬁc developments in what became commonly known as the ‘Encyclopedia’. 49 Noris Bradbury (1909–97) replaced Robert Oppenheimer as director of the Los Alamos Scientiﬁc Laboratory in 1945 and led it for 25 years until 1970. 50 Egon Bretscher (1901–1973) and Anthony P. French (1920–) both returned to England in 1946, the former to take up a post at Harwell, the latter to work at the Cavendish in Cambridge. French emigrated to the US in 1955 to join the Physics Department at the University of Carolina. In 1962 he moved to MIT.

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plenty of work to do and I believe are quite satisﬁed with their facilities. Bretscher still is quite happy to stay on until summer, except that he is somewhat worried about his relation to Cambridge since all letters from there seem to imply that he is expected there immediately. I hope you have brought some information with you that might clarify his position. Tuck has been given a free hand in doing experiments of fundamental interest and seems quite satisﬁed that these would keep him supplied with interesting work until June.51 Similarly, Titterton52 has plenty of work to do; the proposal to make him group leader did not materialise after all, because it turned out that Hans was prepared to stay on. He is somewhat senior to Titterton and, in addition, is likely to stay not only during the interim period but also after June and it is therefore, better for continuity for him to be in charge of the group. In this connection, I found that the letter that Hans wrote to you on the subject of Titterton’s salary was a spontaneous action of Hans on taking over the group and should, I think, be taken as a conﬁrmation of the high value he places on Titterton’s work. Fuchs feels that when he has completed his writing he would be of more value in the development of the new Establishment53 than he could be here and is, accordingly, planning to leave some time in February. Skyrme54 has been asked to remain until June and will do so unless pressure is brought to make him return to England. 51 James L. Tuck stayed on at Los Alamos and worked with Teller on the development of thermonuclear weapons. 52 Ernest W. Titterton (1916–1990) continued work at Los Alamos until 1947, when he returned to England to become group leader in charge of nuclear emulsion and cloud chamber research at Harwell. 53 Klaus Fuchs returned to England in 1946 to become head of the Theory Division at Harwell. 54 Tony H.R. Skyrme (1922–1987) returned to a research fellowship at Birmingham after the war before moving on to M.I.T., Princeton and eventually also to Harwell as head of the nuclear physics group in 1950. In 1963 he succeeded Rudolf Peierls as Professor of Theoretical Physics at Birmingham.

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Frisch55 is completing his work and plans to leave approximately in February. Hughes56 seems quite happy to work in Frisch’s group and might even stay on after Frisch has left. Marshall, however, is still anxious to get back home at the earliest opportunity; I hope you have brought some information on the possibility of his returning to university work. Placzek57 will no doubt tell you himself about his plans. You will have heard about the interviews with the various prospective staﬀ members for the Establishment. In discussing who was or was not interested in the interview, it turned out that Bretscher was quite interested in the possibility of a job in the Establishment. I encouraged him to go to the interview with the others, but he evidently decided not to go. I have not seen him since then, since I was on vacation and he went on vacation just before I returned, but I believe what was in his mind was that he was anxious to talk the situation over with you before discussing any new job more seriously. He is still away, but expected back here on December 22, and I imagine will be anxious to see you as soon as possible after that. While you were away I had oﬀers of jobs from Oxford and Manchester, which I turned down after some reﬂection. I now had an oﬀer from Cambridge and on this I ﬁnd it very hard to make up my mind. I have one or two questions in that connection that I would like to ask you and I shall try to do that on the phone. You may be interested to know that the censorship here has now been lifted and, in general, security has been relaxed a great deal. For 55

Otto Frisch (1904–1979) returned to England after the war to become head of the nuclear physics group at Harwell before taking up the Jacksonian Chair at Cambridge in 1947. 56 Donald J. Hughes (1914–1960) had worked at the Metallurgical Laboratory. He was a member of the committee charged with studying the social and political implications of nuclear weapons which produced the so-called Franck Report. Hughes later became Head of the Neutron Physics Measurement Group at Brookhaven. 57 George Placzek (1905–1955) had moved from the Canadian Nuclear Research Laboratory at Chalk River, where he had been head of the theoretical physics division, to Los Alamos in 1945. A year later he transferred to General Electric Co., before joining the Institute of Advanced Studies at Princeton in 1948.

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example, in many cases friends or relatives have been allowed to come to the site as visitors. Are you planning to come out here again in the near future? There are plenty of people who would be very happy to see you here, although I am afraid I cannot promise much in the way of startling new developments. Yours sincerely, [R. Peierls]

[387] Rudolf Peierls to G.C. Wick [location unspeciﬁed], 18.12.1945 (carbon copy) Dear Wick: Thank you very much for your prompt reply to my cable. I was rather afraid that it might be too late, and if the reason against your being able to consider an oﬀer is that you have already accepted the job at Notre Dame, I feel very foolish not to have thought of asking you in time. Since I wrote to you there has been a further development since I have been oﬀered Fowler’s professorship in Cambridge. At the moment, I am very undecided as to what I should do. The oﬀer is quite attractive, yet there are many reasons for staying in Birmingham. My point that aﬀects my decision is what will happen to Birmingham if I leave. They will ﬁnd it diﬃcult to replace me because of the well-known shortage of theoretical physicists in England, and I feel under a strong obligation to them. If I decide to go to Cambridge, I do not think they could do better than oﬀer the job to you. Naturally, this is a matter for the Faculty at Birmingham to decide and I can only advice them, but I believe that my advice would carry some weight. I imagine that your answer to my previous enquiry would equally apply to such an oﬀer if made at this time. However, if you think that the oﬀer of a full professorship might put you in a better position to try and get released from commitments

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already entered into, please let me know. In any case, I would probably not leave Birmingham until next autumn and you might still be prepared to consider coming then or a little later. Please tell me frankly what your feelings in this matter are. It is, of course, quite possible that having once gone to this country, you would want to remain here, particularly since you are liable to be oﬀered better jobs fairly soon. All this must, of course, at the moment be regarded as unoﬃcial and conﬁdential, but having an informal reply from you will help me greatly, both in making my own decision and in advising the Faculty at Birmingham. Quite apart from all this, there is the question whether, on your way to America, you might ﬁnd it possible to visit England for a short period. Clearly, if you catch a boat from England this would be very easy. If you were proposing to get a boat directly from Italy or elsewhere, it might raise some complications with transportation and papers. However, if it can be done at all, I would be very happy to see you again and have some discussions. I am sure that we could arrange to have your expenses met. My movements are as follows: I shall leave here on January 10; can be reached after than until about January 24 through: c/o J.F.Jackson, P.O. Box 680, Benjamin Franklin Station, Washington 4, D.C. I hope to be back in England around February 1 and my address is then The University, Birmingham 15. Yours sincerely, [R.E. Peierls]

[388] Rudolf Peierls to James Chadwick Washington, 4.1.1946 Dear Chadwick, I have disobeyed your instructions to some extent and I have had a brief and very informal conversation with Bob Wilson about Cambridge. In doing so I have, of course, made it perfectly clear that this was at this

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stage merely a vague idea — that as far as I knew the idea had never even yet been discussed by people concerned in Cambridge, and that I was talking to him purely on my own initiative to ﬁnd out what the chances were of getting him into such a scheme. I did not, of course, expect on this very vague basis to get any deﬁnite reply, but this reaction was suﬃciently favourable to make me think that there is a fair chance of his accepting and it would certainly be worthwhile, in my opinion, to pursue this proposition with all possible energy. What I discussed with him was the idea of his going to Cambridge for a limited period of a few years, and as was to be expected, this idea would appeal to him more than a permanent job, provided, of course, he would not have to spend the greater fraction of his time in just preparing future developments and designing equipment that would not materialize during his period there. At present his plans are, as you know, to go to Harvard, but he proposes ﬁrst to go to Berkeley in order to design there a new cyclotron for Harvard. Clearly, if he was not going to go to Harvard for the time being, he would not be particularly interested in spending his summer on developing equipment and, for that reason, I believe that the chances of getting him would rather depend on how soon a deﬁnite approach could be made. This, of course, does not mean I am certain he would accept — one of the questions being whether he can arrange for leave of absence from Harvard or otherwise ensure that he will not spoil his position here and ﬁnd himself stranded on his return. Yours sincerely, R. Peierls

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[389] Rudolf Peierls to Niels Bohr Birmingham, 21.2.1946 (carbon copy) Dear Uncle Nick,58 (If you will permit me to retain this form of address which is now obsolete, but which we all got to like very much). As you will see from the heading I have now returned to Birmingham, and am trying to get back to a somewhat more normal mode of life. Before leaving America, I had received a message asking whether I would go to Cambridge to take Fowler’s chair. As you can imagine, I found it hard to make up my mind on this, since Cambridge is so very attractive in many ways, and in particular because of the number and quality of students available there. After long deliberations, however, I ﬁnally decided to stay in Birmingham. My chief reason is that I like the spirit of that place, and that I think, it is most important, for any theoretical team to be in close contact with a life experimental group, and I have much more assurance of ﬁnding that here, with Oliphant and Moon close at hand. In addition, I think it would be healthier for the whole country, of the modern universities were to be strengthened and if there were subjects which are well represented in some of them, Birmingham seems a good place for this, and the present a very suitable time. This means I am now trying to build up a good research team here. I have already one or two people for a start, and there are visitors whose presence will certainly help to create the right atmosphere. One of them is Jensen, a pupil of Møller’s, who is here primarily to learn experimental physics, but who does show considerable interest also in theoretical problems. I am naturally most anxious to hear about any other promising men whom we could induce to come here, and if you hear of any such people whose plans are unsettled and who are, or might be, considering to come 58

At Los Alamos, Niels Bohr’s code name was Uncle Nick, an address which Peierls continued to use after the war.

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to England, I would be very grateful, if you could bear Birmingham in mind. I think it will be reasonably easy to get ﬁnancial support for them, if necessary. I hope you and your family are well, and are at last being given a chance to be all together. With best wishes, Yours sincerely, [Rudolf Peierls] [390] Rudolf Peierls to James Chadwick [Birmingham], 26.2.1946 Dear Chadwick, I hope you will forgive me for not writing to you until now, but you probably understood that, in addition to the ﬁrst rush of business, I had the problem of deciding where to go and also where to put my family. As rumours travel, you have probably already heard that we have decided to remain in Birmingham, and I think the chief argument that ﬁnally tipped the balance was the rather attractive prospects of experimental physics in Birmingham as compared with the uncertain situation in Cambridge and the need, in general, to build up the modern universities to get a fairer share of the good students, not to the detriment of Cambridge, but to reestablish fair proportions. I also felt that the spirit of Birmingham University as a whole and the greater ﬂexibility of the modern university will make a lot of diﬀerence. I realise, of course, that this makes things rather diﬃcult for Cambridge, but I do not think the problem is insoluble. I have suggested to Bragg that they should consider Casimir,59 and Mott is backing me on that. An alternative would be L.H.Thomas,60 whom one might have a chance of persuading to return. 59

In 1942 Hendrik Casimir (1909–1945) had joined the Philips Research Laboratories in Eindhoven, where he remained until his retirement in 1972. 60 Llewellyn Hilleth Thomas (1903–1992) had studied at Cambridge before taking up a professorship at Ohio State University in 1929.

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You may have seen that I wrote a short and rather superﬁcial article for the Sunday Dispatch,61 at their request.∗ It is not a paper of which I approve, but the practice seems to be for everybody to write for papers indiscriminately as long as they are left free to say what they want. I was somewhat hesitant over the procedure that should be followed, since clearly there would not be time to send such an article to you for approval. I did, however, attempt to write it in such a way that I was certain it contained no unpublished information other than obvious deductions from such information and that it was not likely to upset anyone on the other side. I also had it cleared by Akers,62 who submitted it to the appropriate authorities in the Ministry of Supply. Frightened by other people’s experiences with papers, I made it a condition that they should not make any alterations without my approval. This condition was accepted and, surprisingly enough, observed. There exists now a somewhat complicated situation with the Committee of Atomic Scientists. I believe you had a letter from the organisers of the committee, which at present is sponsored by the Association of Scientiﬁc Workers.63 It consists of about twenty people whose names happened to be known to the sponsors, and at a meeting we had a few days ago, we all pressed strongly for a change in the set-up, in which the committee, in order to be able to speak for anybody, should contain at least representatives elected by the groups still existing in places where project work was being carried out. In addition it was felt widely that it would be better for such a committee to be independent of the Association of Scientiﬁc Workers, since such a connection would only antagonise ∗ Copy 61

enclosed.

Sunday Dispatch, 17.2.1946. Wallace Alan Akers (1888–1954) had been co-director of Tube Alloys during the Second World War and returned to ICI after the war as research director. 63 The National Union of Scientiﬁc Workers was founded in 1918. In 1927 it changed its name to the Association of Scientiﬁc Workers; in 1968 it amalgamated with the Association of Supervisory Staﬀs, Executives and Technicians to form the Association of Scientiﬁc, Technical and Managerial Staﬀs. 62

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certain people. It is, however, not yet clear, how an independent committee could be ﬁnanced, unless, like the new American Federations of Scientists, it collects members from all branches of science outside the project. On the advisability of this step on other grounds there is much controversy. I personally feel that the two activities at present attempted by the Association of Scientiﬁc Workers, namely to act as a trade union for scientists, and to express the general view of scientists as unbiased experts, do not mix and should be carried out by separate bodies. Everybody is asking now, how soon you will be back and I hope it will not be so very long now. Yours sincerely, R. Peierls

[391] James Chadwick to Rudolf Peierls [location unspeciﬁed] 6.3.1946 (carbon copy) Dear Peierls, I have just received your letter of February 26.64 I am very glad to hear that you have settled down already but cannot help but feel sorry that you have decided not to go to Cambridge. I appreciate your reasons and sympathise with them, and even share some of them, but I still regret the loss to Cambridge. I hope Bragg will consider the suggestion of Casimir seriously for this would be quite a reasonable solution of the diﬃculty. I had not heard about your article in the Sunday Dispatch, and I am glad to have a copy of it. I think it is very good and you have avoided most adroitly a number of pitfalls while still appearing to give some information. There has been quite a lot of publicity on this side and a good deal of sheer nonsense. The chief topic we have to avoid in 64

Letter [390].

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discussion of the Navy Test is any mention of British participation.65 The point is that they do not want to have to refuse requests from other countries, which might ask to send representatives, if it were known that we were sending observers as well as taking part in the work. A second topic is the animal experiments. Here they fear pressure from the antivivisectionists, who are very active just now. A little has leaked out but the arguments have been played down by saying that the animals are nearly all rats. The preparations for the tests are most hectic. My own opinion is that there has been too much display and that it would have been better to carry out the operation quietly; also that they are attempting far too much in the way of measurements and observations. I think that much of the work is not necessary for the real purpose of the test. Some of the scientists are more active than ever in public aﬀairs. The young Federation is doing quite well, although I do not agree with a good deal of what they say publicly. I think they have gone too far and that they have lost support by being too emphatic, but they have not yet fallen into discredit. Urey66 continues to be very vocal and I am afraid he is now losing ground. If Groves seizes his chances, he will be able to re-establish himself, after having almost lost the game. It is a very odd situation at the moment. Yours sincerely, J. Chadwick 65

The immediate post-war years were characterised by tensions in Anglo-American nuclear, defence and other relations. British hopes for ‘full and eﬀective co-operation’, as postulated in the Quebec Agreement between the US and Great Britain in 1943, were not fulﬁlled in essential nuclear development matters. Technology transfer was limited to basic scientiﬁc research only. It did not apply to development, design, construction, and operation of plants per se and was in fact limited to mutually advantageous ad hoc arrangements. At that time great care was taken by the US not to raise awareness of continued British presence at Los Alamos or indeed at other venues of nuclear work. This was most evident during ‘Operation Crossroads’, a series of nuclear tests carried out on the Paciﬁc island of Bikini in July 1946. See S.Lee, ‘Birmingham — London — Los Alamos — Hiroshima: Britain and the Atomic Bomb’, Midland History 27, 146–64 (2002). 66 Harold Clayton Urey (1883–1981), had been Director of War Research, Atomic Bomb Project, Columbia University, between 1940 and 1945; after the war he moved to the Institute of Nuclear Studies at Chicago.

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[392] Niels Bohr to Rudolf Peierls Copenhagen, 7.3.1946 Dear Peierls, Thank you very much for your kind letter67 which recalled so many pleasant remembrances of the time we all spent together at Los Alamos where you and your wife looked after Aage and me with so great kindness. It was a great pleasure to learn from your letter that you are now back in Birmingham and, after your great contribution to the war work, are able again to concentrate on general scientiﬁc problems and to cooperate with Oliphant and Moon. I shall certainly bear in mind your oﬀer for a time to take up in your group a promising young physicist for whom a stay with you will be such a proﬁtable experience. We are also here trying to reorganize our experimental as well as our theoretical work and I am myself endeavouring to complete the various investigations which I had to leave unﬁnished on my escape from Denmark. Among these I have an especially bad conscience about our common work with Placzek and I wonder whether there might soon be an opportunity where we could meet again to look properly into it.68 I need not say how great a pleasure it would be to us all here if you would soon be able to visit us. My own plans are somewhat unsettled, but there is the possibility that I might come to England some time in May, and as soon as I can survey my obligations I shall, of course, write to you again. With kindest regards from us all to your wife and the children, and also to common friends in Birmingham, Yours, Niels Bohr 67

Letter [389]. Georg Placzek, Niels Bohr and Rudolf Peierls had been working on a joint paper on resonance processes since the late 1930s. They published a short note in Nature with the intention of publishing a fuller exposition of the argument in a separate paper. Lee, Selected Correspondence, Vol. 1, Chapter 4. Their work had been interrupted by the war. At the conference in Copenhagen in September 1947, it was agreed that Peierls would complete and update the earlier draft of 1939–40. 68

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[393] G.P. Thompson to Rudolf Peierls London, 8.3.1946 Dear Peierls, I send you herewith a M.S. in the hope that you will look through it. It contains an idea on the generation of nuclear energy from deuterons. I have discussed it with Blackman69 who has helped in some of the calculations, and consulted Akers. He agrees with me that it is of suﬃcient importance to ask you to give an opinion, and I sincerely hope you will be able to do so. Some of the quantities concerned are uncertain, notably the crosssections. Perhaps you may know better ﬁgures than I have been able to ﬁnd. The working conditions chosen are rather arbitrary, and I think it would be necessary to put up the quantities I have called X and H in order to retain a suﬃcient share of the products of the reaction to make the reaction self sustaining as regards temperature. What I am most concerned about, however, is not whether the reaction would or would not be self sustaining, but whether the general scheme is sound. If it is, and the balance is not too far on the wrong side, somebody will probably be able to make it work even if some of the heat produced has to be fed back as electrical energy to keep the thing going. Besides that it would be a formidable source of plutonium using very little uranium and making comparatively little demands on cooling. It would probably be cheaper than a pile and would have at least political importance. For these reasons, if the scheme is sound, Akers wants to take out some kind of patent in my name. Please let me know if you are likely to be in town any time so we can arrange a lunch, or if necessary I could come to Birmingham. Yours sincerely, G.P. Thompson 69

Moses Blackman (1908–1983), lecturer at Imperial College, London, was working with G.P. Thompson on a gas discharge apparatus for a nuclear reactor. For details see M.G. Haines, ‘Fifty Years of controlled fusion research’, Plasma Phys. Control. Fusion 38, 643–56 (1996).

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[394] Rudolf Peierls to G.P. Thomson [Birmingham], 12.3.1946 (carbon copy) Dear Thomson, Thank you for your interesting letter and manuscript.70 I ﬁnd myself in a very peculiar situation when I try to comment on this problem. The reason is that I am in possession of a great deal of information obtained on our topics by work at Los Alamos. This work concerns a part of the project which is regarded as particularly secret, and I am sure it would be felt very strongly that I ought not to pass on any information except to a very limited number of people. I had previously obtained from Sir John Anderson permission to mention similar matters to members of the Technical Committee,71 provided that they were warned to keep this information to themselves. This clearly means that I should also be able to talk freely to you about this, but if I do so it might handicap you in working along such lines with the help of further collaborators, and, for that reason, it seems to me possible that you might prefer not to receive this information from me. If you wish to carry on work utilising the information I have brought on this subject from Los Alamos and to disclose it to other members of your staﬀ, my feeling is that it would be advisable to report this to Chadwick and get his comments as to likely reactions in America. I would like, however, now to make at least one remark, which I think I can make without drawing on this special knowledge, and that is that the beginning of your manuscript refers to heating the substance to temperatures of the order of 100,000 electron volts. It seems to me that this is the crux of the matter and that this will be extremely diﬃcult, because, while it is true that a magnetic ﬁeld will diminish the heat conductivity, it will not completely prevent the transmission of 70

Letter [393]. In the Tube Alloys project not all the information was distributed to all members of the project but rather kept within subcommittees. 71

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heat unless the magnetic ﬁeld were inﬁnitely large and, for that reason, the amount of energy that will have to be fed into the system to reach or maintain this high temperature may well prove prohibitive. I ﬁnd in your manuscript no estimate of the required energy input. I may have overlooked this and you may have considered this point, but it seems to me the chief diﬃculty. For the rest, any comments I could make are of a more detailed kind and could not be made without using this special kind of information I possess, and I do not want to do so before knowing whether this is your wish. I shall not spend much time in London during the next two weeks or so, since I am tied up with lectures very heavily, owing to the illness of a member of staﬀ here. I shall be glad to meet you in London early in April if you think that further discussion of the matter can wait until then. If you were able to come to Birmingham I should be very glad to see you here almost any time. Yours sincerely, R.E. Peierls P.S. Please also regard as conﬁdential information the fact that I know aspects of the problem that are specially secret, since it is not too hard to guess what these aspects might be.

[395] Rudolf Peierls to James Chadwick Birmingham, 12.3.1946 Dear Chadwick, Thank you for your letter of March 6th.72 I have since seen Bragg again and he has approached Bohr on the question of Casimir and got a very favourable answer. My impression was that Bragg was in favour of this plan and felt he would be able to carry the other electors. It is not certain, however, whether Casimir would accept, although I think the chances are fairly good.73 72 73

Letter [391]. Casimir remained at Philips Research Laboratories. See letter [390].

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The fact that the British observers are participating in the naval tests seems fairly widely known in this country, and in an introduction to my article the Sunday Dispatch, in fact, stated this. They said that British observers were on their way to the Paciﬁc now. They did not get this information from me, and I did not think I could or should prevent them from printing this. In other newspapers I have seen lengthy accounts of the numbers and types of animals that are being used in the tests; I do not know, of course, whether this information is correct. My own feeling on the tests is that the ﬁrst two are not likely to give much information that could not be derived from blast measurements at Trinity and observations at Hiroshima, together with some commonsense and some model experiments on the formation of tidal waves. Their main eﬀect would seem to me to be to delay the third experiment, which, of course, is the really interesting one. You may be interested to know that an attempt is now being made to set up an Association of Atomic Scientists,74 in some way similar to the ﬁrst federation formed in America.75 This started as a committee called together by the Association of Scientiﬁc Workers, whose papers, I believe, you have seen, but it has now been agreed, and I think very wisely, that it would be best to have such an organisation independent of the Association of Scientiﬁc Workers. A provisional committee has been formed of which I am a member, and it is expected that within a week or so things will have reached the stage where one can enroll members. In the meantime, the committee is taking over all the work started by the committee of the Association of Scientiﬁc Workers. We are trying to avoid some of the mistakes made by the Americans, by insisting from the outset that a proper division should be made between statements of the scientiﬁc facts and opinions held by scientists, and that on the latter type of question the association should not express 74

The Atomic Scientists’ Association was set up in 1946 primarily to educate British public opinion about nuclear matters and to make a case for international control of atomic energy 75 The Federation of American Scientists had been formed in 1945 by atomic scientists from the Manhattan Project to address a broad spectrum of national security issues of the nuclear age and to promote the humanitarian uses of science and technology.

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any deﬁnite views or advocate any deﬁnite policies. Their job should primarily be to promote discussions which will help to make clear the implications of such views or policies and to make available statements of such views drawn up by individuals either inside the association or outside on their own behalf. They should, as an association, advocate views on such questions only if, after submitting proposals to all the members, they are found to be shared by all, or essentially all, the scientists in the association. We have considered the question of widening this, as the Americans have done, into an organisation including all scientists in this country, but it was felt that this would be invading territory which at present other associations such as the A.Sc.W. and the British Association regard as their own, and that it would be wiser to wait until means of working through existing organisations had been explored, without, in doing so, getting deﬁnitely labelled in any political direction, as would be the case under A.Sc.W. As soon as the necessary steps have been taken, we will, of course, send you all the literature about the new association, and even if in your present position76 you would consider it unwise to become a member of it, we will, of course, always be grateful for any advice or opinion that you care to express. I am very disappointed at the rate at which things are moving in the project in this country and at morale throughout the project. I have been trying to think out what are the main factors responsible for all this, and, while this letter is getting too long to get into details, I hope to write to you soon to explain my views on this. With best wishes, Yours sincerely, R. Peierls

76

Chadwick was still Head of the British Mission to the Manhattan Project.

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[396] Rudolf Peierls to Hans Bethe [Birmingham], 14.3.1946 (carbon copy) Dear Hans, Thank you very much for your article, which I think is admirable.77 I believe it will ﬁt into the series without altering a single word. This completes the series, except for the article from Phil Morrison from whom I have not heard yet. As what you sent me was a carbon copy, I assume that you have sent the original to Groves’ oﬃce. They have in the past been quite good about clearing things quickly, in particular when reminded from time to time, and Mr. MacMillan in Chadwick’s oﬃce is looking after that. If, by any chance, you should not have sent your article to Groves’ oﬃce, McMillan will get in touch with you directly. I am in your debt in many ways, owing you (a) a letter, and (b) a nickel. On the latter, will you please begin to charge interest.78 In other words, I have decided to stay here, largely because the spirit of the place is more attractive than it appears to be now in Cambridge, and it is hard to predict how Cambridge will change in the near future. It is, of course, possible that a good man will succeed Cockroft, but even then the whole administrative machinery is very cumbersome and conservative. Birmingham is rather fun and I have the ambition to put Birmingham on the map and get a good team of research workers started here, which would, I think, be a healthier thing from a wider point of view than to begin concentrating everything at Cambridge. People in Cambridge were naturally disappointed and they are now trying to ﬁnd an alternative solution. There are, I think, one of two possibilities which would work quite well; if they are reasonable about it, but I know that amongst others, your name is on their list and I am trying to tell them that to attempt to oﬀer this job to you would be a waste of time and of a postage stamp. 77

Peierls helped put together a series of articles on atomic weapons as part of the Penguin News Series. Science News 6, London: Penguin, 1948. 78 Bethe and Peierls had had a bet over Peierls’ future career.

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Even in Birmingham, with all the help from the University, it takes, of course, time to build up. So far I have 1 (one) research student,79 with two more expected in the near future and one apparently good undergraduate ﬁnishing in the summer who might stay on. There is practically any amount of money for fellowships, so that I could get more people if I could ﬁnd them. In particular I am trying to induce Skyrme to leave Los Alamos, but have not heard from him as yet. The process of settling down and getting rid of excess papers etc. is a very painful one, as no doubt you have found yourself, and it is not made easier by the fact that a week or so after my return one of our lecturers fell ill and I had to take over most of his work, which, for a month or so, involves me in about thirteen lectures a week, mostly to large classes of engineers. I do not regret this, because I always meant to try these engineer courses in order to see whether they cannot be given in a more reasonable way and it is rather fun. Anyway, there are only two more weeks of this and, on the principle of the old story with the pig and the goat, etc., I shall then ﬁnd that never before in my life did I have so much free time. My one research student is now tidying up the question of the integral theory of the electro-magnetic ﬁeld. As you know I was going to try this out. So far it appears that the classic side of this is perfectly straightforward and contains no snags. We are trying to apply this to some speciﬁc problem, such as the emission of radiation by an electron, to see how it works, but the real question is, of course, that of quantization and I have no conﬁdence that this can be done.80 You will by now have received an invitation to the conference in Cambridge in July.81 It is, I think, unfortunate that the organisers are not able to pay people’s fares but only their stay in Cambridge. Even so, I very much hope that you will be able to come. It goes without saying that once you are here, and if you are not too hard pressed for time, we would count on seeing you in Birmingham. 79

Hugh McManus. See letters [385], [412]. R.E. Peierls and H. McManus, ‘Classical electrodynamics without singularities’ Proc. Roy. Soc. A 195, 323–36 (1948). 81 Between 22 and 27 July 1946, a Physical Society Conference on fundamental particles and low temperatures took place in Cambridge. 80

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We are still living in a boarding house, but we have bought the tail end of the lease of quite a nice house and hope to move in on April 15th. With very best wishes to all of you, Yours sincerely, [Rudi]

[397] Rudolf Peierls to G.P. Thomson [Birmingham], 26.3.1946 (carbon copy) Dear Thomson, Thank you for your letter82 which has made the position much clearer. I see that your scheme is based essentially on the assumption that the nuclei will not contribute to heat conduction at all. Granting this assumption, I believe your conclusions are correct, although I am not quite satisﬁed that it is altogether in order to count only collisions which give deﬂections of 90◦ . In this kind of problem, collisions with small deﬂections are very much more frequent, and I believe it would be more correct to take an average cross-section, weighing each collision with the factor 1 − cos. This is likely to result in a somewhat similar free mean path which, in your conditions, means a somewhat greater conductivity. However, since you have a considerable factor in hand, I do not believe this will essentially aﬀect the argument. The essential point is, then, that of the contribution to the nuclei. If I understand your argument rightly, it is that you are essentially in the Knudsen case and that only a negligible fraction of the nuclei will make a collision with other nuclei before hitting the wall after once they have acquired their high temperature, and you have further assumed that any nucleus that has hit the wall will get stuck there. This will continue until the potential diﬀerential between the gas and the wall will have risen to a point where the potential energy becomes 82

Letter could not be located.

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greater than kT and, from then on, no further nuclei can reach the walls. The number of nuclei needed to produce this charge is small and the energy carried away by them is, therefore, negligible. I am a little worried about this argument, for three reasons. In the ﬁrst place, once you are dealing with deuterons striking a wall at high speed, it seems to me unavoidable that one should get some phenomena of secondary emission. Secondary emission of electrons, of course, is of no importance, since these will not leave the wall, but with the energies concerned I rather think it will be possible to knock oﬀ positive ions, which, of course, would break down the charge contribution, and this seems likely if the wall contains near its surface a lot of deuterons which had got stuck there previously. It might, however, be possible to make the wall of such a material that it would be very hard to dislodge any atom from its surface and that, at the same time, the deuterons would penetrate too deeply to ﬁnd their way out again. Possibly some experiments could be devised to throw light on this question. The second point is the following. Supposing that the surface itself acts as a perfect trap for deuterons, then there will be a strong electric ﬁeld normal to the surface and this will give to any electrons circling there in the magnetic ﬁeld an average velocity component at right angles to both ﬁelds. I ﬁnd, for the kind of ﬁgures that you have quoted, an average electron velocity component in the direction of 2 · 5.108 cm./sec. which means a current density of 3000 amps./cm.2 This will cause a gradient of the ﬁeld of the magnitude of 4000 gauss/cm. As a result, the magnetic ﬁeld gets neutralised in the centre of the tube and, therefore, also the electric ﬁeld will disappear from there. This will increase the electric intensity in the outer part and hence the current density, and in this way progressively the ﬁeld will be forced into a narrower shell near the wall. In the end it will mean that your temperature diﬀerence, as well as your potential diﬀerence, would have to be maintained over a very small gap comparable to the radius of the electron orbits, and this is clearly impossible. Thirdly, there is a fact that, owing to electron collisions, this gas will have a ﬁnite electric conductivity, and this is another reason why, together with the electric ﬁeld, there will be a transport of electrons to the wall, since the migration of every electron to the wall requires a

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deuteron to go as well to restore the potential, it seems to me that this process would continue until all the gas has been cleared up. I ﬁnd it hard to say how one can escape all three of these diﬃculties together. But I would be very glad to have your comments on this. Yours sincerely, [R.E. Peierls]

[398] Rudolf Peierls to William G. Penney [Birmingham], 29.3.1946 (carbon copy) Dear Bill, I have only just heard that you are back in this country. I hope there will be an opportunity of meeting you before you disappear again, as there are a number of questions, both about the project and otherwise, that it would be nice to talk over. I have not seen you since you got your new job and, while I am sure you will make a success of this work and will enjoy it, I cannot help regretting that this means one more defection from the ranks of theoretical physicists in this country, of which, in any case, there are too few.83 I was glad to see your name on the new list of the Royal Society. I am sure that is well deserved. I do not know whether you know that I helped put together a series of articles on the atomic bomb to make up a number of the new Penguin Science News. This number will deal entirely with atomic energy.84 I have the articles all completed except for an article by Philip Morrison on “the atomic bomb as a weapon” This was promised for mid-January, 83 William Penney (1909–1991), who had been part of the British delegation at Los Alamos, had taken up the position of Chief Superintendent of Armament Research (CSAR) which put him in charge of the Armament Research Department in January 1946. 84 See letter [396], note 77.

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but it is not complete yet and cannot be sent for another month. I have reported this to the publishers to ﬁnd out whether they are prepared to wait so long for the article, but while I am waiting for a reply I would be glad to know whether, by any chance, you might be prepared to write such an article in a hurry. This is intended to be on a rather popular level. The other articles are about seven thousand words each on the average, but this is not a very precise limitation either way. There are other articles dealing with the chain reaction in general, with the separation of isotopes and the production of plutonium, with the properties of the atoms, electrons and neutrons, so that for this article is remains to explain in some detail the processes involved in the actual explosion, in particular the competition between the rate of reaction and the increase in volume due to the expansion and the eﬀects. All this, of course, within the limits laid down by present security rules. I would, of course, let you have the existing articles as a basis, Penguin pay, I believe three guineas for a thousand words, but they intend to publish the series also in other languages like Spanish and Portuguese, and they may well decide to publish it in America as well and there would be additional royalties from these. I do not know whether you have heard that we are trying to get an atomic scientists’ organisation along somewhat similar lines to the American organisations, though on a smaller scale, and suited to the conditions in this country. I hope you will agree to support this. Does your business ever bring you to the Midlands? If so, I would certainly be glad to see you here, and otherwise, maybe we could meet in London. How easy is it for you to get to the centre of town? With kindest regards, Yours sincerely, [R.E. Peierls]

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[399] William G. Penney to Rudolf Peierls Fort Halstead, Sevenoaks, 1.4.1946 Dear Rudy, I was glad to hear from you.85 If there had not been a delay I should have returned to the States on the 23 March; my present plans are to leave about the 15th April. I should also, very much like to talk with you on several matters but unless you are coming to London in the next fortnight and have a few hours to spare when you come, it is not likely that we shall meet before my return. It would not be diﬃcult for me to get up to London at any time, if you came. Your suggestion about an article for the Penguin Science is one which I am afraid I must refuse. To me, it is not at all clear what should be said in such an article. I am not so much worried about Security but rather about the eﬀect that an ill-considered article might have. You may be interested to hear that it is likely that a Government White Paper will be issued on the atomic bomb damage in Hiroshima and Nagasaki. This paper will be written by the team from the Ministry of Home Security which went to Japan with the Strategic Bomb Survey Group. I have seen the report which these people have prepared and it seems to me that they can usefully prepare a White Paper; they report only things which were obvious to everybody who went into the cities; in fact, they missed a great deal. I hope that you and your wife and children are all well and not ﬁnding austerity too severe. Yours sincerely, Bill

85

Letter [398].

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[400] G.P. Thomson to Rudolf Peierls London, 2.4.1946 Dear Peierls, Many thanks for your letter and criticisms.86 The second point you make is a very serious one and invalidates the scheme as originally proposed except for very low densities. I think, however, that there is a way out as follows. In order to get the energy in for heating purposes we had already proposed to use the toroid as a sort of wave guide and drive the electrons forward by what is virtually the pressure of radiation. They would then transfer energy to the nuclei by collisions. Now this process will create a current round the toroid which will cause a circumferential magnetic ﬁeld (circumferential round the circumference of the circular section of the toroid). This magnetic ﬁeld will serve to anchor the electrons instead of the solenoid ﬁeld originally proposed. The velocity of the electrons corresponding to the combination of this ﬁeld and the radical electric ﬁeld is now in the direction of the current and in the same sense. Another way of looking at it is to say that the diﬀerent current elements attract and so balance the outward radial force on the electrons. The electrons once anchored, all is as before. This case is harder to work out than the former but as far as Blackman and I can see it should work out. As regards your other objection: There is no evidence to my knowledge that ﬁelds of the order considered ∼ 10, 000 volts/cm will produce any secondary emission of positrons from metals. There might be some spluttering of neutrals due to bombardment of the walls, but this can be made very small by lining with aluminium and perhaps in other ways. I envisage holes in the walls through which deuterium would be admitted and the products of the decomposition withdrawn. The amount of gas in use will be controlled by shooting electrons into the centre to make up for those driven to the walls by collision. Some nuclei of H3 .H .H3l will reach the walls, some but 86

Letter [397].

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fewer H2 since these will not have the energy of disintegration to help them overcome the ﬁeld. At ﬁrst they may penetrate a short distance into the walls but this thin skin will soon become saturated and the nuclei will collect on the surface picking up electrons from the secondaries formed. (If there is any diﬃculty about this the solid walls could be shielded from the electron ﬁeld by a lining of gauze say 1cm away, but I don’t believe this will be necessary.) This thin layer of gas will mix with the deuterium supply and be drawn oﬀ at some of the holes in the wall while deuterium is wasted in this way, but it could be recovered with the valuable tritium. Some of the deuterium gets ionised by collision and is drawn in to the body of the gas to an extent determined by the loss of disintegration nuclei and the balance of electrons shot in over those lost. The controls are two; — rate of shooting of electrons, supply of deuterium. I should very much like to discuss all this as it is so diﬃcult to explain by letter. I am going to Ireland on Friday for a holiday, returning on the 24th. If you are likely to be in London before the end of April, could you let me know? If not, I think I should come to Birmingham. What day would suit you? It is most kind of you to help as you are doing. Yours very sincerely, G.P. Thomson

[401] Hans Bethe to Rudolf Peierls Ithaca, 8.4.1946 Dear Rudi: Thanks a lot for your letter of 3rd April.87 It is unfortunately true that I had not sent my manuscript to Washington, but I am doing this today. It had weighed on my conscience for about a week past, but I was away all the week. I am very happy to have won the nickel. I think in the long run you are going to be happier at Birmingham than at Cambridge. Still, it is a 87

Bethe almost certainly refers to letter [396] dated 14 March 1946.

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pity that Cambridge has gone so much to the dogs as you indicated by your refusal. Bretscher is apparently so disgusted that he will not come back to Cambridge. I am just having a visit with Wentzel for two days. He mentioned that there were several young theorists in Zurich who took their degrees in the last two years. He wanted to send one over to Cornell with a Fellowship, which we like very much. But I thought also of your problems and thought you might be interested in getting one or two to England. Wentzel is going back to Zurich at the end of this week. You might like to write to him there as to what kind of people you would be interested in. I got the oﬃcial invitation from Cambridge. It is very tempting to go, but I had promised myself to take a really long vacation this summer. So it is probably “no”, but this is certainly the most diﬃcult invitation to refuse. I got settled here quite nicely and ﬁnd some time to study mesons and nuclear forces and to do a little bit of work myself. Physics is, after all, a fascinating subject. You may have seen the report of the State Department on international control of atomic energy of which Oppie is one of the authors.88 I think it is very good. Greetings from Rose who is enjoying the comforts of civilisation and from myself to you and the family. Yours sincerely, Hans [402] Rudolf Peierls to James Chadwick [location unspeciﬁed], 3.5.1946 (carbon copy) Dear Chadwick, For some time I have intended to write to you my impression of the situation here as regards the project and what is wrong with it. In the 88

United States Department of State Committee on Atomic Energy, ‘Report on the International Control of Atomic Energy’, (Washington, 28.3.1946).

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meantime things have changed considerably through Portal89 taking oﬃce and through his establishing a new Technical Committee under his Chairmanship. This has removed at least some of the diﬃculties, in that there is now at least a body in which the scientists meet from time to time and through which they can be kept informed of what is going on. But I still feel far from satisﬁed that things are going as well as they ought to. Probably the great snag is the incredible ineﬃciency and red tape in the Ministry of Supply. You will have heard stories about this from other sources. Here are some examples, by way of illustration. The general experience is that it takes three months to get any payment of outstanding balance to people returning from North America. I have not been able, in spite of intense pressure, to get these matters straightened out, but in my case this is less serious than in the case of younger people like Marshall, who has not had his payment yet, or Morris, for whom it took an incredible time, although it is ﬁnally settled now. As you know, most of us had to be appointed honorary consultants in order to legalize our position in retaining reports. The writing of even the formal letters necessary for this purpose took ages, and probably would never have been done if Akers had not written such letters oﬀ his own bat, against instruction. I had, in fact, a letter from Summer telling me that it was a violation of the Oﬃcial Secrets Act, if I retained any reports beyond 11th March. The letter reached me about 13th March. It was, of course, of no consequence, but similar things happen to people who are less familiar with the project and it does not actually make them keen to continue to help. The worst of all these things is, as no doubt you know, the situation at Harwell. Oliphant and I visited Harwell this week and there is practically nothing going on there. No construction work has progressed, or even started. Skinner has an uphill job ﬁghting petty oﬃcials over petty regulations. The greatest diﬃculty was the arrangements for making appointments, but I understand that this is now being handled in a somewhat diﬀerent way, giving Skinner more direct responsibility, and maybe things will work a little more eﬀectively. 89

Air Marshal Viscount Portal of Hungerford (1893–1971), had been Commanderin-Chief of RAF Bomber Command and then Chief of the Air Staﬀ and Marshal of the RAF. After the war he became Controller of Production, Atomic Energy (CPAE).

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Another example is that one hangar is ﬁlled with equipment from Valley. While we were there we had a visit from the former Foreman at Valley to explain the nature of some of the equipment. It turned out that a catalogue of this equipment had been sent to the Ministry of Supply but had never reached Skinner. It would evidently be desirable to dismantle some of the equipment and to take out parts that would be of value to Harwell, but they have at the moment not even a crew of people who could get hold of some screwdrivers to get to work on this. They have of course not the screwdrivers and spanners either. In addition to all this, every little job connected with living conditions there, such as the distribution of mail, leaking taps, transportation and so on, becomes a problem that needs to be fought out and takes time. I am not suggesting that any of these items is, in itself, serious. Probably by the time this letter reaches you, most of the diﬃculties will have been overcome somehow, and they will be ﬁghting about something else. But all this wears out the personnel, in particular Skinner, completely and keeps their attention away from more important questions, and it illustrates the complete lack of comprehension in the oﬃcial mind of what the project is about and how it ought to be tackled. Asking for reasons for this, it seems to me that the chief reason is the position of the project in the Ministry of Supply, in which it is just one of many activities and in which at every level, not only at the top, it requires the action of people who are concerned with it for only a very small fraction of their time. For every little wall that has to be built at Harwell, the Ministry of Works has to be brought in and contact with the Ministry of Works is made by the Ministry of Supply oﬃcials who have no idea about atomic energy. I understood some time ago from Longmir that in anything he does he reports to civil servants in the Ministry who are busy men and not particularly interested in atomic energy, and his recommendations reach people at a higher level merely in the form in which these civil servants choose to summarise or forward them. I believe there is hope that all these things will improve as the activities of the project grow, since it will then be possible to allocate more full-time staﬀ to the project speciﬁcally, but it will involve a ﬁght at each step.

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What I am particularly concerned about is that before the decision was taken to place this project under the Ministry of Supply it was our general impression that things would not be allowed to get to this state, but that, if the project were to come under an existing ministry it would have a special organisation set up for it which would make use of the priority and ﬁnancing arrangements of the ministry and would link up also with it at a high level but within that framework would have a completely independent organisation. All the scientists concerned with the project felt strongly about this and were prepared to ﬁght. They are in an unassailable position because without them the project cannot be carried on, and most public opinion and Parliament would react very strongly if this project had to be abandoned because the scientists felt that they were not given the working conditions that would enable them to carry on eﬃciently. What is needed now for this is concerted action by all scientists. The new organisation under the Ministry of Supply was, I believe, accepted by Cockroft and yourself before anyone else knew what was proposed. Since Cockroft and you are the people who primarily have to ﬁght out all these diﬃculties, very clearly no-one can raise a major protest against such arrangements as long as you two feel that you can make a satisfactory job of the proposed arrangements. It was certainly no-one’s desire to make life more diﬃcult for you than it is. What has gone wrong, I think, is that there is insuﬃcient contact and cooperation between all the people who essentially are in agreement on the objects, and, in broad outline, what is needed to implement them, and I think that minor diﬀerences of opinion in technical or administrative matters have now been allowed to prevent concerted action in major matters. I feel sure that for the past years all the members of the Technical Committee, as well as Akers and Perrin, were in essential agreement on what had to be done, yet in talking to any of them (and I do not except myself) one would hear more criticism of the others, of their technical views, of how they handled a particular question of organisation or policy, than of essential agreement and concerted action. The result is that the enormous prestige and power which the scientists possess is, in fact, lost. The only way in which we can bring pressure to bear is by making clear that there are certain limits beyond which we are not prepared to go, and that if the government depart-

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ments want our collaboration they have to adhere to these limits or else they will not have us. It should not be necessary to carry things far enough to threaten resignation, or actually resign, but if things are handled in such a way that it is perfectly clear that certain steps will not be tolerated by the scientists it will have the same eﬀect. This, of course, is a weapon that must be used very cautiously and to use it lightheartedly over minor matters would weaken our position more than not to use it at all. But I cannot help feeling, on looking at the present state of the project in this country, that things have been allowed to go too far and that if we had been in a position to get together and review the situation from time to time we would have found the point at which to dig our feet in. Things were, of course, made diﬃcult by the dispersion of the team across the Atlantic and the unavoidable break-up of the old Technical Committee. When, in due course, you and Cockroft get back and when we can again get together around a table, these things will be easier, but it does not look as if this can be achieved very soon, meanwhile the organisation may have drifted a long way in a direction from which it is hard to retrieve it and in any case time will have been lost which, from every point of view, is most vital. I cannot oﬀer any very constructive suggestion as to what should be done about it, except generally to stress the importance of trying to spread amongst this group, as far as possible, information on what action will be or has been taken and the reasons for which it may or may not be wise to accept such action and on people’s attitude in general. I believe it is our job now, being on the spot and in close touch with the set-up here, to keep you and Cockroft informed of what is going wrong, and it is for you and Cockroft, as the people with the best knowledge of policy and the contacts at a higher level, to give us a lead in saying how far one must compromise and at what point one should stop. A relatively minor point compared with all this, is the following. I believe there is some kind of vicious circle as regards Harwell, in that many people who will eventually go to Harwell are still in Canada because there is little for them to do here and there is a tendency for construction work at Harwell to be delayed because the urgency is not appreciated as long as the people who want to get to work are not on

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the spot. I believe that if all the people who are not essentially needed in Canada, but who are merely remaining there to learn what they can while they cannot be used in Harwell, were to come back so that the place would be ﬁlled with people who were pressing for accommodation, which is about to be completed, for equipment, which theoretically was promised but has not arrived, then if there was someone waiting for each of the instruments which are on order, the job would in fact be accelerated and the result would be a saving of time, although it might appear to be an uneconomical use of the men. At the same time, as people collect there, the structure of the various teams, their plans and responsibilities, would begin to crystallize out and one would realise more clearly what is needed in the way of additional staﬀ. It is essential that this should be done while men can still be found. I would therefore suggest that many of the people who can be spared from Canada should be brought back as soon as possible. This does not apply to all of them, since for the temperament of some people this situation I have described would have very unsatisfactory results and they might get dissatisﬁed with the project forever. One particular case I have in mind is Fuchs. In understand he is committed to stay in Los Alamos until June, and he is probably very useful there. I would feel strongly, however, that his commitments there should not be allowed to drag on and that, in the circumstances, he should not go to Canada after leaving Los Alamos, but should come back immediately to help settle the staﬀ problems for his team, to discuss in broad outline the research programme and to choose the arrangements as regards machines, computers, etc. that will be required for this programme. If, when this is done, there is still nothing for him to do (this seems to me to be quite unlikely), he could still visit Canada afterwards and get some experience there. I believe, however, that from Montreal reports and from discussions with Buneman, Guggenheim, Pryce and others, he could, in fact, learn as much from a visit in Chalk River. Another case which occurred to me was Arms. I do not know what he is doing and it may be of vital importance, but if it is not, I believe that he would help accelerate matters a good deal by chasing around after equipment and helping in the layout of laboratories, workshops, etc. and that he would do this quite readily if the situation were explained

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to him, even though it would mean that for a few months he would not do any scientiﬁc work. It is a relief to get all of this oﬀ my chest, and I would be very glad to hear whether you think I am misunderstanding the situation or whether you agree with my attitude. Yours sincerely, R.E. Peierls

[403] Ed Salpeter to Rudolf Peierls Santa Fe, 19.5.1946 Dear Rudy, I thank you very much for your several letters concerning the Research Fellowships at Birmingham. I have waited to obtain the opinion and advice of others before reaching my decision, which is that I should like my name to be considered as that of a candidate for a junior fellowship. I have come to this conclusion after weighing the disadvantages of (or rather my antipathy towards) living in your city against the following points — ﬁrst the opportunity to participate in a more general ﬁeld of fundamental research, second the probability of making contact with a wider circle of people, and third, which is perhaps the most decisive, my feeling that this would leave most open the ultimate direction of my career. These last points are chieﬂy in comparison with going to Harwell, as regards other possibilities I have thought it desirable not to leave things until I should return to England. I am sending a formal application to the Secretary of the Faculty of Science. Please give my best wishes to Genia and the children, and I shall look forward to seeing you all in the summer. Yours sincerely, Ed Salpeter

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[404] Rudolf Peierls to Max Born [Birmingham], 12.6.1946 (carbon copy) Dear Born, Thank you for your information about Miss Walker.90 I had also encouraging reports from other people and we shall ask her for interview as soon as that can be arranged. I saw Dirac the other day and he mentioned to me the remark in your letter about Heisenberg. I do not think the matter will arise because I do not believe that Planck is being invited and I understand, in fact, that the committee organising the Conference have ruled against inviting any Germans.91 I feel one must be careful about pressing for admission of people like Heisenberg, since I believe that for the resumption of international contacts it is essential that people should be made to understand the distinction between the behaviour of people like Laue and Hahn, of whom one hears from all sides that they have kept aloof from all government activities and have resisted any temptation to ingratiate themselves with the Nazis either by collaborating or making public statements, and the others of whom this seems much less clear. For example, the chief reason for excluding Germans from the coming conference seems to have been the argument that it would cause resentment among the people from the occupied countries. I believe, in fact, that amongst the latter, in particular the Dutch, Belgian and French people, the part played by Laue and Hahn is well known and that they would not have resented their coming, whereas they would have resented it if Heisenberg or Becker or others had been asked. They would, in fact, have appreciated it if their opinion had been obtained about people who could be trusted. The whole problem is very diﬃcult and one has, of course, to remember that Heisenberg is by far the best scientist of all the ones mentioned and in any question depending solely on scientiﬁc merit all other arguments should not count; but, in fact, in a conference of the kind 90 91

Letter could not be located. See also item [440].

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planned in Cambridge, scientiﬁc discussions will be inseparable from social gatherings and I, for one, while I would welcome an opportunity to hear Heisenberg’s ideas on scientiﬁc matters and discuss them, would feel very reluctant to have any social contact with him until we are able to take a more detached view of the past than we can do just yet. These problems are most complicated and I would be glad to know what you think. Fuchs is still in Los Alamos but is due to leave there in few days and I expect he will be back in this country early in July. I imagine he will get in touch with you as soon as he gets back. No doubt you have heard that he has accepted a job at the new Atomic Energy Research Establishment at Harwell. If you want to get hold of him urgently, a letter addressed to him c/o J.F.Jackson, P.O.Box 680, Benjamin Franklin Station, Washington, 4, D.C. will reach him until he leaves North America. I hope to see you at the Cambridge meeting in July. Will you be staying in the south between 11th and 22nd, and if so is there any chance that you could spend a day or so in Birmingham? I expect to have Rosenfeld here at that time and he would, of course, love a chance of seeing you. Yours sincerely, [R.E. Peierls]

[405] Max Born to Rudolf Peierls [Edinburgh] 13.6.1946 Dear Peierls, Thank you for your letter and the interesting remarks about the German physicists.92 About 2 years ago, when I was a member of the Sectional Committee for Math[ematics] of the R[oyal] S[ociety], Dirac asked me to join him in proposing Heisenberg for election as a Foreign Fellow of the R.S. After some consideration I refused and kept to this decision in 92

See letter [404].

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spite of Dirac’s persuasion who rightly said that Heisenberg’s discovery will be remembered when Hitler is completely forgotten. I said I would reconsider the matter after the war when we had the opportunity of knowing exactly how far H[eisenberg] has collaborated with the Nazis. Meanwhile I have heard contradictory reports. He was certainly not behaving like Laue and Hahn. But it is said he tried to obstruct the development of nuclear explosives. I do not know whether this is true. My feeling is now that these fellows have got their punishment. They are not only having a hard life and little to eat, but their conceit is badly shaken. In my letter to Dirac I wanted to show that I was prepared to reconsider the question. But if you object, and if the people of the occupied countries object I shall not move any further. Heisenberg’s new papers on relativistic quantum mechanics (Z. f. Phys. 120, pp. 53, 675, 1943)93 have impressed me rather much. They contain no solution of the diﬃculties, but they clear away some rubbish. I hoped that Peng’s work had removed some of the inﬁnities,94 but I got a letter from him telling me that there is a mistake in it and just these results are wrong. My own ideas look to me quite promising but I am too old and tired to work them out alone, and I have no collaborator suited for this kind of work. I hope Fuchs may spend some holiday weeks in helping me, when he returns. I shall write to him. I shall be in the south between July 11th and 22nd, and I intend to visit my daughters, Irene in Cambridge and Gritly in Oxford. I should like [to] spend a day or two in Birmingham, if it would ﬁt in. I shall let you know. With kind regards, Yours, M. Born

93

W. Heisenberg, ‘Die beobachtbaren Gr¨ ossen in der Theorie der Elementarteilchen. I’, Z. Phys. 120, 513–38 (1943); and W. Heisenberg, ‘Die beobachtbaren Gr¨ ossen in der Theorie der Elementarteilchen. II’, Z. Phys. 120, 673–702 (1943). 94 Huan-Wu Peng, educated at Tshingua University, was working with Heitler at the Institute of Advanced Study in Dublin. In 1944 he had published some papers jointly with Max Born. Proc. Roy. Soc. Edinburgh 62, 40, 92, 127 (1944).

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[406] Rudolf Peierls to Max Born [Birmingham], 14.6.1946 (carbon copy) Dear Born, Thank you for your letter.95 I am glad to know your views on this question and if you will be in the south next month I hope we shall have to opportunity to talk about this. If you were in Oxford, you might like also to discuss the question with Simon, who, I believe, has strong feelings in the matter. I have just seen Peng’s paper in the P.R.S.96 and, while it is very interesting, it seems to me that he has not given enough information to say really how the calculation should be carried out. It does justify, however, the hope that something can be done along those lines and I hope his new calculations, which you mention, will not dispose of this completely. I am not at all impressed with Heisenberg’s new scheme or Møller’s work on the same subject.97 It seems to me quite an empty scheme which is completely indeﬁnite until one formulates the laws to which his matrix S is subjected. One might, of course, hope ultimately that the matrix S itself will be found to obey some very simple laws, but since these must contain ordinary quantum theory as a limiting case and since in the ordinary case of a collision with non-Coulomb forces the expressions for S become extremely complicated, I do not see much hope in that direction. I did hear from Dirac about your idea of linking this up with “reciprocity” and that is very interesting, but I always had grave doubts as to what would happen to the reciprocity in a many bodied problem. 95

Letter [405]. H.-W.Peng, ‘On the divergence diﬃculty of quantized ﬁeld theories and the rigorous treatment of radiation reaction’, Proc. Roy. Soc. A186, 119–147. 97 See letter [405], note 93. 96

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I would be extremely happy to see you here in July. So far I have no deﬁnite engagements during the time you mention, but no doubt there will be all sorts of meetings. As Rosenfeld will probably be staying with us, we may not be able to oﬀer you a room, but I am sure something can be ﬁxed up, if it would be convenient for you to stay overnight. With kindest regards, Yours sincerely, [R.E. Peierls] [407] Rudolf Peierls to Y.I. Frenkel [Birmingham], 20.6.1946 (carbon copy) Dear Frenkel, I have now for some months been back at my normal job at Birmingham and I am trying hard to settle down again to some more normal work. I imagine you will be in a very similar position. I do not know whether you are back in Leningrad yet, but I hope this letter will reach you anyway. Has your institute suﬀered very much, and have you been able to resume work there? I have seen the many papers you have published during the last years and been very interested in many of them. I expect that I myself shall try to work chieﬂy on ﬁeld theory, meson theory and the theory of nuclei. On the latter we still have to ﬁnish some work started in Copenhagen before the war. I am at present trying to revive the idea of introducing a ﬁnite length into the theory of the electron, in order to remove the inﬁnities, and I have found a way of doing this in classical theory without destroying Lorentz invariants, but at the expense of obtaining the ﬁeld equations and the equations of motion in the form of integral equations in time. Classically, it all looks straightforward, but we have not yet succeeded in quantising the theory. I am not at all convinced that this is the right approach, but I am also not very impressed with the view of Dirac, since I do not like his reinterpretation of the negative possibilities, nor do I believe the recent theories of strong coupling. The recent attempts by Peng to prove that

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all the inﬁnities are merely due to the perturbation and that the ﬁeld equations have ﬁnite solutions is very intriguing, but I do not see how this particular method of solution can be right.98 Many of these problems will, of course, be discussed at the International Conference in Cambridge in July and I very much hope that you will be able to accept the invitation to the Conference. It would be very nice to have a really good discussion of physical problems again after so many years and I believe that just now the resumption of normal contacts between scientists is of enormous importance. I am trying to build up a bigger team here, of whom some, of course, will be rather junior. With this, and through the collaboration with Oliphant’s department, who are completing the installation of a cyclotron now and are working on a machine for very much higher energies, I am looking forward to a very interesting time. My family are back in Birmingham, too. With the great housing shortage it was quite a problem to ﬁnd a place to live, but in the end we were lucky and got settled quite comfortably. The children are at school again and life is now more or less back to normal. I very much hope to see you at Cambridge in July, but if you will not be there I should greatly enjoy hearing from you again about your family and friends. With very best wishes, Yours sincerely, [R.E. Peierls]

[408] Y.I. Frenkel to Rudolf Peierls Leningrad, 21.6.[1946] Dear Peierls, Thank you very much for your kind invitation to the conference. I shall be very glad to attend it, if that proves possible. Among other things I would like to discuss the question of relativistic quantum theory of 98

See letters [405–406], notes 94 and 96.

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complex particles, which I have considered rather loosely a couple of years ago. I have transferred your letter to the Academy of Sciences and shall telegraph, if I get a positive answer to my application. I hope you are all well. Please give my kindest regards to Jenney and to our common friends. Yours sincerely, J. Frenkel

[409] Y.I. Frenkel to Rudolf Peierls Leningrad, 21.7.1946 My dear Peierls, Although I wrote you a few lines through a young physicist [??] who was expected to go to England, I am writing you again in reply to your letter of June 20th99 which I received on the next day after sending you a telegram informing that I had just seen Jenney’s parents in good health at Moscow (you probably interpreted this telegram as a preliminary reply to your letter.) After 3 1/2 dreary years spent with my family in Kazan (where I lost my mother in 1944) we came back to Leningrad, rather amazed at the possibility of returning to our pre-war relatively comfortable existence. I changed my old ﬂat for a better one, further away from the street and was lucky to ﬁnd most of our furniture and other belongings, including the books, more or less intact. At the beginning of the war it seemed unthinkable that we should ever come back to the pre-war conditions. In some respects this maybe true, (particularly in America); but in regard to our living conditions — especially those of the scientiﬁc workers in large cities — we have practically reached to pre-war status owing to a number of facilities put at our disposal by the government. This may be illustrated by the fact that a great many scientists — of all professions 99

Letter [407].

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myself including are buying cars for our own private use. As a result of adverse living conditions and various troubles during the war period, I have developed a hypertonia, (i.e. abnormally high blood pressure or arterial tension), which I have to take care at present. Last year, when it was discovered, I succeeded to get rid of it after one month’s rest at a sanatorium near Moscow. I am afraid that this will take longer this time. Outside my childhood I have never [been] sick in my life, and it worried me terribly to have to follow the prescription of the physicians. With respect to r´egime etc. in fact I have not begun to follow them yet, but shall try to be a “good boy” in a sanatorium near Riga where I am going in a few days with all my family for 4 weeks. My wife is always “so-so”, since 1943 owing to an abdominal haemorage; but as a whole her health has improved since 1936 when she suﬀered from acute haemorages due to her trombopenia. The children are prosperous; The elder (23 years) studies physics at the polytechnical institute but is more interested in poetry (he has written and translated a number of excellent verses) and in chess; the younger will graduate his high school next year, but has not chosen any profession yet.100 I have been pretty active scientiﬁcally both at Kazan, and after my return therefrom to Leningrad. Unfortunately my activity has recently been arrested by my hypertonia and the associated headaches. As soon as I return to good health I shall set to work again. As usual I am interested in a large variety of diﬀerent problems, which prevents me from digging deeply enough in a single place. I am of course very much interested in the problem of fundamental particles and ﬁeld theory. I think, however, that the present dualistic treatment, in which the particles and the ﬁeld are dealt with as two independent components of the whole is fundamentally wrong and that the particles must be considered as secondary entities, produced by the quantization of the ﬁeld

100

Viktor Zakovlevich Frenkel (1930–1997), became a physicist and historian of science in his own right. From 1948 he studied physics and mechanics at the Leningrad Polytechnic Institute. After work for the Svetlana Works on the design and construction of electrovacuum devices he joined the theoretical department of the Ioﬀe Institute of Engineering Physics in 1959, to which he remained attached until his death in 1997.

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which is the bearer of all mechanical properties (energy, momentum, etc., there being no such thing as the kinetic energy of the particles or their mutual energy with the ﬁeld). The actual realization of this monistic programme which has been initiated by Lorentz’ theory of electron is of course very diﬃcult; a modiﬁcation of Lorentz’ theory by introducing a certain length into the ﬁeld equation may help to solve it. What do you think of my approach to the problem of the relativistic quantum theory of complex particles (I think I have sent you reprint thereof.),101 which I propose to treat as elementary particles with internal degrees of freedom. I have recently written another paper which may interest you on the asymmetrical splitting of heavy nuclei.102 I shall send you a reprint as soon as it will be available. One of my luckiest achievements during the recent two years is probably a theory of atmospheric electricity which I have succeeded to greatly improve quite recently. I also shall have a team of about 10 young people working with me during the next term. Most of them have been recently demobilized and require a certain induction period for beginning research work. All our common friends in Moscow (Tamm, Landau, etc.) are in good health and probably will write to you themselves. I am visiting Moscow regularly once a month, owing to my association with two research institutions there (one in geophysics, the other in molecular physics). It is a great pity that the present state of international aﬀairs does not enable us to establish a direct contact with our colleagues and friends abroad. Let us hope that the situation will change for the better soon and that we shall be able to discuss scientiﬁc and other matters soon in a less cumbersome way than letter-writing.

101

J. Frenkel, ‘On the theory of relaxation losses, connected with magnetic resonance in solid bodies’, J. Phys. (U.S.S.R.) 9, 299–304 (1945). 102 J. Frenkel, ‘Some features of the process of ﬁssion of heavy nuclei’, J. Phys. (U.S.S.R.) 10, 533–539 (1946) Frenkel had been working on the splitting of heavy nuclei for several years. See also Frenkel, J., ‘On the Splitting of Heavy Nuclei by Slow Neutrons’, Phys. Rev. 55, 987 (1939).

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Give my best regards to Jenny — also from my wife — and from us both to yourself. Cordially yours, J. Frenkel Will you kindly subscribe me to the “Vogue”. The expense will be covered by the Oxford Press which are just going to produce a new book of mine.103 If you get across some really interesting book (ﬁction) please also send us a copy (stating the price). My wife will be very grateful to you for such things.

[410] Tony Skyrme to Rudolf Peierls Santa Fe, 29.7.1946 Dear Rudy, I had better acquaint you with the arrangements that I have made for the transmission to England of the document that I have decided to submit as a dissertation at Trinity College, Cambridge. At the moment this is in the General’s Oﬃce in Washington for clearance; in the rather unlikely event that it should be completely declassiﬁed I have arranged that it shall be sent directly to Trinity. I anticipate that it will remain more or less classiﬁed; and in this case I have asked the Washington Oﬃce to transmit it to you, as a responsible person who can keep custody of it. I have informed Trinity College of this arrangement and have asked them to tell you to which authorised person(s) they would wish the document to be transmitted for examination. With regard to my leaving this country, I have applied for a passage home early in September; however, no sailing dates are yet known and I shall ﬁt my plans to this date when I learn it. I shall leave Los Alamos at the end of this week and go to the West Coast and then up to Vancouver; 103

J. Frenkel, Kinetic Theory of Liquids, Oxford: Clarendon Press, 1946.

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I shall arrange that any mail reaching here during August is forwarded to me. Mrs Daily has asked me to be remembered to you; with best wishes to your family, Yours sincerely, Tony Skyrme

[411] Rudolf Peierls to Robert Oppenheimer Birmingham, 26.8.1946 Dear Oppy, I am writing to let you know that one of our Members of Parliament, Captain Raymond Blackburn, is expecting to be in the United States from about September 3rd to September 27th and is most anxious to see you. His contacts are arranged largely through the Atomic Scientists of Chicago. He hopes to spend the ﬁrst week of his stay on the west coast and if you are in California he would, if possible, like to see you during that ﬁrst week. I think you will ﬁnd it worth your while talking to him. He is a young Labour M.P. who has made atomic energy his special interest and he has repeatedly pressed in Parliament for a constructive discussion and for a statement supporting the Lilienthal Report.104 He is, of course, not a scientist and his knowledge and judgement have not always been perfect, but I think it is most important that we should keep reasonable people like him as well informed as we are permitted to do. I heard from Oliphant that you were critical of the statement by the British Atomic Scientists on international control on the grounds that it recommended U.N.O. continued making bombs. This was I believe, based on press reports and in the meantime you will have seen the full text of our statement which was reprinted in the Chicago Bulletin and 104

‘A Report on the International Control of Atomic Energy’, prepared for the Secretary of State’s Committee on Atomic Energy, Washington D.C., Dept. of State Publication 2498, 16.3.1946.

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you will have seen that we have tried to keep an open mind on this question. I would be very interested to know if you still disapprove. Here quite a stir has been caused by press extracts from an article by Urey in “Air Aﬀairs” in which he is supposed to have said the United States might be forced to declare war itself “with the frank purpose of conquering the world and ruling it as desired and preventing any other sovereign nation from developing mass weapons of war.”105 This has produced a rather unfortunate eﬀect, although I feel sure that the words must have appeared in the context that gave them a diﬀerent meaning from that which they convey by themselves.∗ We have regretted very much that you could not come to Cambridge. It was quite a successful and stimulating meeting, but it would have been better if we had had your views as well. With best wishes, Yours sincerely, R. Peierls ∗ We

have now seen the full text and conﬁrmed this. Though I still think his wording was unfortunate.

[412] Rudolf Peierls to Hans Bethe Birmingham, 24.1.1947 Dear Hans, There are many things to write about after such a long time but for the moment I shall leave the domestic matters and write only about shop. My department has got going and we have started on quite a number of problems, although we have not as yet produced much in the way of results. I would like, in this letter, however, to tell you what we are doing, for two reasons: ﬁrstly I would be glad of your comments on any 105

See Harold C. Urey’s papers, University of San Diego, Series 1, Box 135, folder 5.

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of these points and, secondly, many of the problems are of such a type that I rather expect someone in America is also thinking about them. In that case it is quite likely that you may know and, while it may be quite worth while to go ahead tackling such problems in several independent ways, it would in any case be a comfort to us to know. I think I can best describe our work by listing the people who are here and what they are doing. Jahn106 is a man whose name I am sure you know. He has been here since August and in connection with his knowledge of group theory he was particularly interested in Wigner’s theory of symmetries in nuclei. His ultimate aim is to see which of Wigner’s results, in particular about the most reasonable coupling to assume, have to be modiﬁed in the light of the existence of non-central forces. No doubt this problem is also being thought about by other people, but we want to know the answers and want to learn the techniques. For the moment he is trying to alter the presentation of the Wigner theory by bringing in the explicit representation of the permutation group to see why the results appear only to depend on whether the nucleus is of the type 4, 4r + 1 etc., although for the derivation one has to use explicitly the permutation groups of a higher order. What he is trying to do is analogous to Slater’s method in the case of the atom. This, I think, would be a very useful step.107 Preston,108 a pupil of Infeld’s from Toronto, came here with an almost completed paper on the theory of alpha-decay.109 This carried the one-body-problem to a logical conclusion, ﬁtting the 106

Hermann Arthur Jahn (1907–1979) studied under Heisenberg and van der Waerden in Leipzig, joined Peierls’ department in 1946 and later became professor of applied mathematics in Southampton. 107 See among others H.A. Jahn, and J. Hope, ‘Symmetry Properties of the Wigner 9j Symbol’, Phys. Rev. 93, 318–21 (1954). 108 Melvin A. Preston, studied at Toronto before joining Peierls’ research team in Birmingham where he completed his Ph.D.. In 1953 he returned to McMaster, where, apart from a few years at Saskatchewan, he spent the rest of his career. 109 M.A. Preston, ‘The Theory of Alpha-Radioactivity’, Phys. Rev. 71, 865–77 (1947).

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phases of the wave function inside the nucleus and using an exact analytical solution, even for the case l = 0. It is doubtful whether it makes sense to carry the one-body model that far but in the course of his calculations two interesting points have come out: (1) the formula given by Gamov from the transparency barrier in the case l = 0 is completely wrong110 and based on an inaccurate evaluation of the integral, which, of course, with some trouble can be done in closed form. Apparently this wrong formula has been used ever since, e.g. by you. (2) In the one-body model, the transparency of the barrier as a function of l ﬁrst increases and then decreases. This surprising result is due to the fact that if you always assume a rectangular potential barrier, but ﬁt its eigenvalue correctly, higher l forces you, for the same total energy, to assume a deeper well (because of the eﬀect of the centrifugal term) and therefore both the density and velocity near the edge of the nucleus increases. It is, of course, very questionable whether this feature of the one-body problem has a real meaning, but it might have and there seems some evidence that the assumption of the decay constant behaving in that way allows a somewhat better ﬁt for the experimental data. Preston is also working on an explanation of Chang’s peculiar results on alpha ﬁne structure assuming that the nucleus is excited by long-range Coulomb forces after passing the potential barrier.111 A simple calculation regarding the alpha-particle as a classical point charge gives a perfectly reasonable estimate for the probability. We felt, however, that this should be done more decently and we struck some snags in that calculation which have dissolved themselves now, leaving him only with somewhat nasty integrals to evaluate. We have seen now a reference to work by

110

G.A. Gamow, Constitution of Atomic Nuclei and Radioactivity, Oxford: Clarendon Press, 1931, pp. 91 and 103; G.A. Gamow, ‘Zur Quantentheorie des Atomkernes’, Z. Phys. 51, 204–212 (1928). 111 W.Y. Chang, ‘A Study of Alpha-Particles from Po with a Cyclotron-Magnet Alpha-Ray Spectrograph’, Phys. Rev. 69, 60–77 (1946); W.Y. Chang, ‘Low-Energy Alpha-Particles from Radium’, Phys. Rev. 70, 632–39 (1946).

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Dancoﬀ112 on the same idea but, as from this it is quite impossible to understand how Dancoﬀ has done the calculation or what the answer is, we propose to continue. In any case, it is a fascinating problem.113 When this is ﬁnished he will tackle the question of the eﬀect of non-central forces on proton-proton scattering. This, of course, appears only at higher l and therefore at higher energies than the p − n scattering, but it is likely that such energies will be, or in fact have been, reached. In this connection we computed for the experimentalists some curves for the angular distribution of the p − p scattering at about 13 MeV and the curves are very entertaining. They mean, in particular, that in order to sort out the contributions of s, p, etc. waves, one has to measure the scattering with quite a ﬁne angular deﬁnition. Experiments along these lines are planned here now, but as the cyclotron is not working yet they will have to wait. Skyrme is studying the problem arising from the dispersion formula (Bethe-Placzek,114 Kapur-Peierls etc.)115 with a view to seeing what one can get out about potential scattering and the like. We have just received Wigner’s latest papers on this subject116 but do not appreciate yet to what extent they dispose of the problem. Skyrme has also given a tidier proof of the completeness of the complex eigenfunctions used in my paper with Kapur. 112

S.M. Dancoﬀ, Metallurgical Project Report, Short Range Alphas in Natural Radioactivity. 113 Preston published his results two years later in M.A.Preston,‘The Electrostatic Interaction and Low Energy Particles in Alpha-Radioactivity’, Phys. Rev. 75, 90–99 (1949). 114 H.A. Bethe and G. Placzek, ‘Resonance Eﬀects in Nuclear Processes’, Phys. Rev. 51, 450–89 (1937). 115 P.L. Kapur and R. Peierls, ‘The dispersion formula for nuclear reactions’, Proc. Roy. Soc. A166, (1938), 277–95. 116 Eugene P. Wigner, ‘Resonance Reactions’, Phys. Rev. 70, 606–18 (1946).

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Salpeter,117 an Austro-American, is tackling the problem of self-energy and has succeeded in proving that (contrary to the idea of Peng’s paper118 ) the inﬁnities are not due to using perturbation theory, at least in the following sense: if the integrals are cut oﬀ at a certain maximum wave factor k0 and the wave equation are then solved rigorously for any k0 : then in the limit k0 = ∞ the energy tends to inﬁnity. This proof is now complete for all one particle problems. In the relativistic one-electron problem it leads to a divergence as dk rather than k, as in Waller’s case. This, however, we have convinced ourselves, justiﬁes no hope of a similar improvement in the Weisskopf case. The next step would be, of course, to try and generalise such a proof to Weisskopf’s case of pair theory.119 In attempting this, however, we discovered that Weisskopf’s method is wrong, since the subtraction of the inﬁnite charge density due to the electrons in negative states is done by reference to the states in zero ﬁeld comparing the two inﬁnite sums, term by term, for the same momentum. Since, however, momentum is not gauge invariant, the whole procedure is not gauge invariant, as I have shown years ago in the Royal Society Proceedings. This makes the whole theory inconsistent, since in the ordinary quantum electro-dynamics used by Weisskopf the relation divE = 4πρ can hold at all times only if all interactions are gauge invariant. We are trying to put this right, but cannot say yet whether this will aﬀect Weisskopf’s result.

117

Edwin E. Salpeter (1924–), a graduate from the University of Sydney, completed his Ph.D. under R. Peierls in 1948. He then moved on to Cornell, where he became professor of physics in 1957. 118 H.W. Peng, ‘On the representation of the wave function of a quantized ﬁeld by means of a generating function’, Proc. Roy. Ir. Acad. 51, 113-22 (1947). 119 Weisskopf had published several papers on self-energy. See e.g. V. Weisskopf, ‘On Self Energy and the Electromagnetic Field of the Electron’, Phys. Rev. 56, 72–85 (1939). See also R.E. Marshak and V.F. Weisskopf, ‘On the Scattering of Mesons of Spin 1/2 by Atomic Nuclei’, Phys. Rev. 59, 130–35 (1941). For a survey of developments in electron theory see V.Weisskopf, ‘Recent Developments in the Theory of the Electron’, Rev. Mod. Phys. 21, 305–15 (1949).

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McManus120 is still working on the ﬁeld theory for ﬁnite size electron, of which you know the general idea. There were many snags in the mathematics but as far as the classical theory is concerned everything straightened itself out, with one exception: we have obtained the equation of motion of an electron without external ﬁeld which, in this case is an integral equation. We can easily prove that this has a trivial solution corresponding to motion at constant velocity and also that if you add external ﬁelds you get the usual radiation terms up to the normal radiation damping, with corrections only of higher order in the frequency than the Lorentz damping. It seems very plausible that these should be the only solutions of the type of Dirac’s runaway solutions. We are still struggling, however, with a reasonable proof for this. As to the quantisation of such theory we need a brainwave but we have not yet given it up. An attempt to do this is also being made by Bleuler,121 one of Wentzel’s pupils whom I managed to get largely through your good oﬃces and who also is tackling one or two more formal problems in the theory of quantised ﬁelds. A young research student is just starting work on an attempt to calculate internal pair creation in the case of a gamma-ray of arbitrary multipole character.122 I do not believe this has ever been done but in the case of gamma-rays of energies well above 1MeV internal pair creation should be quite well observable and experiments on the sharing of energy between electron and positron or on their relative angular distribution ought to give a convenient way of determining the order of the multipole. This, of course, can also be done with internal conservation, but as for high gammaray energy and low atomic number in the distinction between K, 120

Hugh McManus who had been a research fellow at Birmingham before the war, returned to Birmingham from his war-time assignment at Chalk River, where he had been working at the Canadian atomic energy laboratory. He continued his work as a research fellow at Birmingham until 1951 and eventually became professor of physics at Michigan University. 121 Konrad Bleuler, (1912–1992), completed his Ph.D. under Wentzel’s supervision in Zurich. 122 The student was R.A. Fatehally.

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L, etc. electrons may not be easy, this alternative method seems of interest. This, in particular is a problem which one would hardly like to duplicate, so if you know of anyone else doing this I would be glad to know. Krook,123 a South African who formerly worked on astrophysics, is trying to calculate the continuous gamma-ray spectrum emitted in a proton-neutron collision when the neutron is not captured. For low energies, this will, of course, be quite a small eﬀect although it should be observable. For high energies, it will be more likely than capture and may there help to get information about forces. What is planned at present is to calculate it for some simple type of force so as to have this available for comparison when we get experimental date. Another research student is looking into Landau’s theory of liquid helium.124 We are rather dissatisﬁed with that theory because, while it makes out an excellent case for the existence of what Landau calls “rotons”, he assumes that there is a lower limit to the roton spectrum from dimensional arguments, leaving out of account that there is a dimensionless number, namely the number of helium atoms, which may enter into this result. We think it should, in fact, be possible to prove that this is the case and that for a reasonable amount of helium the lowest roton level is practically zero. This, however, is not quite an easy problem. It is mathematically connected with the old problem of the rotation of nuclei, on which I am dissatisﬁed with the paper by Teller and Wheeler.125 Probably if one can decently solve one of the two problems one can also get the solution to the other. 123 Max Krook, had studied astrophysics at Cambridge before becoming research fellow at Birmingham. Eventually, he returned to astrophysics, becoming professor at Harvard. 124 After the discovery of superﬂuidity and liquid helium in 1938, Lev Landau constructed a theory of ‘quantum liquids’ at very low temperatures. His papers between 1941 and 1947 are concerned with the quantum liquids of the ‘Bose type’ such as the superﬂuid liquid helium (4 He). 125 E. Teller and J.A. Wheeler, ‘On the Rotation of Atomic Nucleus’, Phys. Rev. 53, 778–89 (1938).

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Another research student is learning all about luminescence in solids in order to assist Garlick126 (whom I believe you met at a recent meeting at Cornell) in the analysis of the rather interesting experiments he is doing here. Kynch,127 who is rather busy with teaching, is working on the non-central forces in the nucleus. There seems, in particular, a peculiar discrepancy between your result and a similar result of Schwinger and Rarita on the one hand128 and the result of Rosenfeld and Møller on the other.129 You ﬁnd that in order to account for the observed quadrupole moment of deuteron one has to assume a very strong tensor force, comparable in order of magnitude to the central force. Møller and Rosenfeld start with a tensor force which, coming only from the non-static terms, is about ten times smaller, treat it with perturbation theory and get the right quadrupole moment. One would say, at ﬁrst sight that this simply means the perturbation theory is not justiﬁed, but it is the same kind of perturbation theory that one uses for calculating the ﬁne structure in the atom and there we are reasonably conﬁdent that it works. It might, in fact, be that because of the peculiar nature of the problem the perturbation theory is more trustworthy than the rigorous solution. In this connection Kynch is also exploring 126 G.F.J. Garlick was experimenting with phosphors and phosphorescence. See G.F.J. Garlick, ‘Phosphors and Phosphorescence’, Rep. Prog. Phys 12, 34–55 (1948). He later published a joint paper with Fatehally: G.F.J. Garlick and R.A. Fatehally, ‘Measurement of Particle Energies with Scintillation Counters’, Phys. Rev. 75, 1446 (1949). 127 J.G. Kynch (1915–2003) had studied theoretical physics at Imperial College, London, he joined the Birmingham department initially to take over Rudolf Peierls’ teaching, while the latter was engaged in work for the M.A.U.D. committee. His temporary appointment was extended several times and he stayed until 1952 when he accepted the Chair of Applied Mathematics at University College of Aberystwyth. In 1957 he became professor of mathematics at UMIST. 128 W. Rarita and J. Schwinger, ‘On Neutron-Proton Interaction’, Phys. Rev. 59, 436–52 (1941); W. Rarita and J. Schwinger, ‘On the Exchange Properties of NeutronProton Interaction’, Phys. Rev. 59, 556–64 (1941). 129 C. Møller and L. Rosenfeld, Kgl. Danske Vid. Math.-Fys. Med. 17, No. 8 (1940); C. Møller and L. Rosenfeld, Kgl. Danske Vid. Math.-Fys. Med. 23, No 13 (1945).

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the use of the Svartholm method, which treats the Schr¨ odinger equation as an integral equation in momentum space and uses iteration. It appears that this works also for tensor forces and is, in fact, quite convenient. This, I think, completed the list, except that I have not said what I am doing, but that is easy — I sit on committees and write letters. I shall be writing about other things soon. Yours sincerely, Rudi

[413] G. Placzek to Rudolf Peierls Schenectady, 7.3.1947 Dear Peierls, Many thanks for your detailed letter130 and the statement of the Council of the British Atomic Scientists, which I have read with great interest. It tends to show that, if even scientists of one nation cannot agree in the fundamentals of the matter we need not be surprised to see the politicians landed in the present hopeless mess. You are probably aware that the statement has been extensively misquoted by Mr. Gromyko in yesterday’s session of the Security Council.131 This is of course not your fault since even if it had been possible to write it from a more uniﬁed point of view, this would not have afforded protection against distortions. I hope you can get a verbatim copy of the speech, it was rather long and the papers left out the most interesting passages. I happened to listen to it on the radio and it was rather characteristic to hear Gromyko state in terms which were clearly sincere conviction that the idea of an inspector who could freely travel 130

Letter could not be located. On 5 March 1947 Soviet foreign minister Gromyko gave a speech in the U.N. Security Council denouncing American nuclear policy. See New York Times, 5.3.1947, p. 16. 131

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in a “foreign” country and even ﬂy over it, could not have been meant seriously. The Russians, of course, have by no means a monopoly on such a mentality; the recent statement by Senator Taft, warning against the danger that communists might “inﬁltrate” into an international control agency, is on a very similar level. Enclosed a pictorial record of yesterday’s meeting, taken from today’s New York Times. You will probably enjoy the subscript. I am afraid I cannot entirely share the Olympian detachment of your American military friend who hopes that chances of an agreement might be better once stories of successful Russian bomb manufacture begin to circulate. I am rather inclined to believe the opposite. But, unfortunately, we shall see. Clayton132 (from Chalk River) asked me for a copy of the table of the exponential integral for complex argument, so that he could forward it to you. Unfortunately I have no copy here. I believe I left one at Montreal, but whether or not this is so, they cannot ﬁnd it. The rest of the copies is in Carlson’s hands133 at Los Alamos and to extricate one from there, under present circumstances, might take longer than to have the whole tables recalculated. I therefore recommended to Clayton to get in touch with Lowan, (Math. Tables Project) who might have a spare copy or could perhaps get one reproduced. I hope you will keep me informed on the result of your and Skyrme’s investigations re Wigner Dispersion formula, and gauge invariance of Weisskopf’s logarithmic divergence. Newspaper reports here inspired, in some credulous souls, the hope that Schroedinger might have discovered the laws of the universe. Mr. W.L. Lawrence was speeded into action. Jumping at the opportunity to act as a great patron saint of science, he got hold of Schroedinger’s 132

Henry H. Clayton (1906–89), English-born physicists who had studied at the University of British Columbia. In 1945 he joined the Montreal Laboratory and moved to Chalk River in 1946. In 1950 he became head of the theoretical physics branch, a position held until his retirement in 1969. 133 Bengt Carlson (1915–), Swedish-born physicist who had studied at Stockholm and Yale. He worked in Placzek’s group at Montreal from April 1943.

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manuscript, had it photostated at the Times expense, and distributed far and wide throughout the country. Of course, it turned out to be bunk. A lesson for the above mentioned souls showing that the more traditional channels of scientiﬁc information still seem to be fully adequate. With best regards to you and Genia, yours sincerely, G. Placzek

[414] Rudolf Peierls to James Chadwick [location unspeciﬁed], 10.3.1947 Dear Chadwick, A few days ago the “Times” had an item about the last statement by Gromyko (I believe the date of the statement was 5th March) and in reporting this the American correspondent of the “Times” added that most of Gromyko’s ammunition seems to have been supplied by the memorandum from the British Atomic Scientists’ Association.134 In view of this we are naturally anxious, ﬁrst of all, to get the verbatim text of Gromyko’s speech in order to see how he quoted us and whether the quotation was a fair one. I wonder whether you could be good enough to arrange for a transcript of this speech to be sent over by air mail? The “Times” statement rather implies that the quotation has made an unfavourable impression in America, although I conclude this merely from the use “ammunition.” Any comment you could make about this would, of course, be very welcome. We had, some time ago, a letter from the Executive Oﬃcer of the American Delegation, in reply to our memorandum, in which his main criticisms were that some of the points we were pressing had already been taken care of in some of Baruch’s 134

See letter [413].

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statements.135 This is, therefore, a useful conﬁrmation that there seems to have been nothing in our memorandum that came as a violent shock to the American Delegation. Yours sincerely, R. Peierls I enclose copies of both our memoranda, in case they are of use in this connection.

[415] Otto Frisch to Rudolf Peierls [location unspeciﬁed], 10.3.1947 Dear Peierls, Cockroft asked me today whether I was interested in becoming his successor in Cambridge (that is the Jacksonian Chair, isn’t it?). I was not quite unprepared for this question since Dee had been here a few weeks ago and had told me that he felt he could not accept the oﬀer and that he thought I would get asked next. Now this is a diﬃcult decision to take. I feel a certain amount of loyalty towards Harwell, and I also think that in a year or two it might be quite a well-equipped place. On the other hand, the emphasis will always — and perhaps increasingly — be on the engineering side and though we shall be able to [d]o some pure research we shall probably do it with a bad conscience, feeling that we are not going all out to develop atomic energy. In Cambridge this should not be so, and I should be able to put my whole heart in the job. And of course Cambridge is a much nicer place. On the other hand, again, my administrative responsibilities will be even greater than here, I suppose, and my inexperience in University teaching will be a handicap. 135

Bernard Mannes Baruch (1870–1965) was the American delegate to the United Nations Atomic Energy Commission. On 14 June 1946 he had proposed the international control of atomic energy, the so-called Baruch-Plan.

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I should very much like to hear what you think about it. You know the setup in Cambridge well (so well that you declined a job there!) and you might help me to understand why that chair is so hard to ﬁll. Also, you know me fairly well. I was very glad to hear from Fuchs that Genia is home again and that everything went well. I am going to Denmark and Sweden on Tuesday, returning immediately after Easter. (Unless I decide to cancel my berth in view of the Cambridge matter). I should be very thankful for a reply before I leave, please address it c/o Meitner, Flat 2, 85 West Hill, London, S.W.15. I shall be there on Friday night and again on Monday night, and I may go to Cambridge over the weekend or part of it. Yours, O.R.F.

[416] James Chadwick to Rudolf Peierls New York, 13.3.1947 (carbon copy) Dear Peierls, I sent yesterday to Philip Moon the verbatim record of the meeting of the Security Council on March 5th. This is the only complete record which I have and it is my own ﬁle copy, so that I shall want it back. Gromyko’s use of your memorandum was just a typical example of Russian methods. You will be able to judge for yourself whether it was fair or not. The Security Council and the audience were certainly rather surprised to ﬁnd Gromyko supporting the Russian views by means of quotations from a memorandum by the British Atomic Scientists’ Association. Very few of them would, at any time, realise how dishonestly Gromyko was quoting, for very few read the memorandum. It was, as you know, published in the February issue of the Chicago Bulletin, but not many people outside the American, the Russian and our Delegation read this. Some of the journalists were naturally very interested to hear Gromyko claiming support for his thesis from English sources. They

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pursued that matter, and two days later both the New York Times and the Herald Tribune carried articles which I enclose. I should like to have these back. Yours sincerely, [J. Chadwick]

[417] Rudolf Peierls to George Placzek [Birmingham], 24.4.1947 (carbon copy) Dear Placzek, Thank you for your letter of 7th March and the highly amusing picture of Uncle James.136 Meanwhile we have had the full text of Gromyko’s speech and, as you say, it is a very depressing document even if it has its amusing points. If, however, one looks at the earlier statements made at one time or another by Gromyko and Molotov and the many contradictions in them. It is clear that the fact of their saying decidedly “no” today rules out as little the possibility of their saying “yes” tomorrow as vice versa. As far as the British Atomic Scientists’ Association is concerned, we feel we ought to appoint Gromyko honorary publicity manager or something for the way he has put us on the map. With one exception his quotations are quite correct, although, of course, torn from the context they give the wrong impression. I saw the articles in the New York papers that followed Gromyko’s speech by a few days in which other passages from our memorandum were quoted, in this case, of course, carefully picking those parts in which we agree with the American point of view. I do not quite share your view that the document was quite futile; it is, of course, a question whether the present situation can be remedied at all by a rational discussion in the Atomic Energy Commission of the Security Council and it is likely that if any progress is made it may depend on discussions behind the scenes and on factors that have 136

Letter [413].

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nothing to do with the problem in hand, but to the extent that it was worthwhile to keep rational discussion going I do believe that we have raised points where obstacles to the acceptance of the details could be removed. Even more amusing, perhaps, are the Senate hearings about Lilienthal.137 I enjoyed particularly the picture of Groves releasing the Smyth report against his better judgement because of the bullying of scientists. On the question of tables of the complex potential integral, it will be interesting to see what ultimately comes out of the revolutions in the wheels of the machine. In practice, as you may remember, there was a blueprint of the original typescript of those tables here and that is still accessible to us. We can therefore await further developments with patience, unless in the meantime, Lowan has carried out further subtabulation. On the general dispersion formula we have not yet made much progress beyond one small point: In the Kapur-Peierls method one expands the whole wave function inside the nucleus in a series of complex eigenfunctions. As a result, one gets a potential scattering term representing the scattering from a hard sphere and alongside with it a dispersion sum which seems to converge rather slowly. Skyrme has pointed out that one could equally use an alternative procedure, namely to expand not the whole of the function but its diﬀerence from the incident plane wave. In that case the potential scattering term represents the Born approximation and, in particular, the artiﬁcially chosen nuclear radius no longer appears explicitly. For high energies of the incident neutron it seems fairly clear that in this formula the contribution from the distant terms of the dispersion sum are smaller than in the alternative case. This will certainly be proved when the energies are so high that the Born approximation becomes a useful approximation and is likely to be true even for somewhat lower energies. Once one has recognised that there is this amount of freedom in the method, a third alternative immediately suggests itself and that is to 137

On 4 February 1947 David E. Lilienthal had issued a controversial statement ‘This I Deeply Believe’, also known as the ‘Credo’. See David E. Lilienthal Papers, Volume 1, 1900–1949, Box 118–119. Princeton University Library.

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start by solving a one-body problem with a complex potential representing, in other words, the nucleus as a black rather than a reﬂecting sphere, and after subtracting the wave functions ascertained from the whole wave function expand the residue in a series as before. This means using the theory of a black nucleus as developed by Bethe as a starting point. Evidently this will lead to a formula in which the potential scattering appears explicitly as that due to a black sphere and added to it there will be again a dispersion sum. On physical grounds I suspect that this description would be the most convenient one, i.e. it would make the dispersion sum converge more rapidly than the alternatives. Of the three possibilities this third one certainly is the most complicated one mathematically and there seems no obvious way either to prove that it is a good approximation or to decide the value of the absorption coeﬃcient which ought to be used. I would much appreciate your comments on this situation. We have not been able to get much thrill out of the recent papers by Wigner or by Weisskopf on this subject.138 I agree with your comments on the wisdom or otherwise of letting newspapers distribute scientiﬁc manuscripts, but not that the traditional channels are very adequate at the moment. Printing is deplorably slow, particularly in this country, and one has to rely largely on casual gossip and, while this is apt to make more sense than the eﬀorts of Mr. W.L.Lawrence, it is hardly more eﬃcient. With best wishes, [R.E. Peierls] P.S. I am working on a plan to have a small theoretical conference at Birmingham this summer, to deal with the fundamental diﬃculties and with elementary particles. The likely dates are July 23rd to 26th, and I hope to get some of the theoreticians in this country and a fair number 138

E.P. Wigner, ‘Resonance Reactions and Anomalous Scattering’, Phys. Rev. 70, 15–33 (1946); E.P. Wigner, ‘Resonance Reactions’, Phys. Rev. 70, 606–18 (1946); E.P. Wigner and L. Eisenbud, ‘High Angular Momenta and Long Range Interaction in Resonance Reactions’, Phys. Rev. 72, 29–41 (1947); H. Feshbach, D.C. Peaslee and V.F. Weisskopf, ‘On the Scattering and Absorption of Particles by Atomic Nuclei’, Phys. Rev. 71, 145–58 (1947).

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from the Continent to take part. Our funds do not make it possible to pay transatlantic fares but if, by any chance, you were intending to be on this side this summer, we would look after your board and lodgings, probably in the University hostel here, during the conference. You will get a more oﬃcial notice in due course but I thought I would let you know at once that this is likely to happen. I need not say that we should be delighted to see you here.

[418] Rudolf Peierls to Robert Oppenheimer Birmingham, May 1947 Dear Oppie, I enclose particulars of an informal conference that we are hoping to hold at Birmingham this summer. If you or any of your colleagues are planning to be on this side of the Atlantic at the time (or are just waiting for a reason to make such a trip) we would be delighted to see you here. I would also be grateful to have the names of others to whom you suggest such an invitation should be sent. Yours sincerely, R. Peierls Congratulations on the new job! Hardly more restful?139

[419] Niels Bohr to Rudolf Peierls Copenhagen, 2.6.1947 Dear Peierls, I want to tell you that my plans have been somewhat changed since I wrote last. Circumstances are that under the pressure of various obligations I have recently been somewhat overstrained, and I have therefore 139

Robert Oppenheimer had resigned from his post at Berkeley to take up the directorship of the Institute of Advanced Studies in Princeton.

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felt it necessary to give up my journey to England and Ireland this summer and try to get some real recreation in July, such as I have not had for several years. I am sorry that I shall thus not be able to see you as I hoped, but on the other hand I am sure that the change in the plans will give us better possibilities in the near future to complete our work which had been so long postponed. I was very glad to learn that it will be possible to you to come here for a time in August or September. In the Institute we plan a little conference in the later part of September, and it would be very nice if before that time we could have some thorough discussions about the general problems. Perhaps it would be the best of you could come here in the middle of September and stay over the conference or as long as you can. With kindest regards, Yours, Uncle Nick

[420] Rudolf Peierls to Niels Bohr [Birmingham], 5.6.1947 (carbon copy) Dear Uncle Nick, Thank you very much for your letter. I am very sorry to hear that you have not been well, although it is hardly surprising that you should feel tired in view of the very many diﬀerent things that must be making demands on your time now. I had just heard from Møller about the proposed conference and I had written to him that things are a little diﬃcult because of the two fairly oﬃcial lectures that I had promised to give on the 20th and 25th September. I probably could get out of either or both commitments, but I would have to make the necessary arrangements very soon. Alternatively, if the conference were to start before the 20th I might be able to stay for at least part of the conference and get back in time to deliver the lecture on the 20th; but then I should start fairly soon booking my passage, as I believe pressure on space in the ships and planes is going

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to be very heavy. I realise of course that the precise arrangements for the conference must depend on many factors and they cannot be settled at once, but I would be very grateful to know the dates as soon as they are ﬁxed. From what you say, it would at the moment sound best if I tried to arrive, say, about 10th September and to leave either in time to be back in London on the 19th or a little later, if the conference is later and if I can still cancel my lecture on the 20th. I need hardly say that I am looking forward intensely to this visit. Yours sincerely, [R.E. Peierls]

[421] Niels Bohr to Rudolf Peierls Copenhagen, 26.6.1947 Dear Peierls, I am sorry not before to have answered your kind letter of June 5th,140 but I have been somewhat doubtful what to propose as regards the best time for your visit here. Circumstances are that due to wishes of some of our American friends who could not come before, the conference here has so far been planned for the last week in September. Furthermore, Sir John Anderson is coming on an oﬃcial visit to Denmark from September 11th to 18th and will be staying with us for some of the time. I hope very much that the schedule of the conference can be made to ﬁt in with your own plans but, on account of the other commitments in September, it might perhaps be best if, instead of coming before the conference, you could manage to stay on a little longer to give us the opportunity to talk about how it stands with a possible completion of our work with Placzek.141 I take the occasion to tell you that Jacobsen is going to England for the last part of July and intends to come to Birmingham to learn 140

Letter Rudolf Peierls to Niels Bohr, 5.6.1947, Peierls Papers, Ms.Eng.misc.b203, C.32. 141 See Lee, Selected Correspondence, Vol. 1, Chapter 4.

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about the developments in Oliphant’s laboratory. It will also be a great pleasure for him to attend your conference, at any rate such a part of it which is not too speciﬁc mathematical. Further, one of the younger of the experimental collaborators in the Institute, Børge Madsen, who has done some beautiful work on recoil particles is going to England in July to visit various laboratories. Also Madsen intends to come to Birmingham towards the end of the months and hopes to be allowed to attend such parts of the conference as are not too far from his line. Please inform Oliphant about these visits. I need not say that it would be a great pleasure for us if he could attend your conference himself. With kindest regards from us all, Yours, Uncle Nick, P.S. Mr Madsen will arrive in London at July 2nd, where his address will be at the Society for Visiting Scientists, 5, Old Burlington Street, W.1.

[422] Rudolf Peierls to Niels Bohr [Birmingham], 1.7.1947 (carbon copy) Dear Uncle Nick, Thank you for your letter of 26th June.142 I would, of course, not have wanted you to alter the date of your conference to ﬁt my particular plans and I think it will be possible for me to be present at least for part of the time. It would be somewhat diﬃcult to cancel my lecture to the Institute of Physics on September 25th since it is a rather formal aﬀair and since I have already given them notes on what I propose to say, which have been used by the other speakers to plan their papers, and I think I 142

Letter [421].

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could not ﬁnd anyone else who could take my place and say just what I would have said. I would try, however, to come across by ‘plane on the afternoon of the 25th or, if that is impossible on the morning of the 26th and so could at least take part in some of the discussions. It would then be possible also for me to stay for part of the following week since our term does not start until 7th October. I would, however, want to be back here a few days before the beginning of term. I am very glad to hear that Jacobsen and Madsen are likely to visit Birmingham and if they should ﬁnd it convenient to be here at the time of our conference they will, of course, be welcome to take part in any discussions that they do not ﬁnd too mathematical. Oliphant and Moon similarly are very glad to hear about these visits. It would be a help to know fairly soon when Jacobsen expects to be in Birmingham so that we can ensure that accommodation will be ready for him. I can get in touch with Madsen directly when he gets to London and ﬁnd out more about his plans. With kindest regards, Yours sincerely, [Rudolf Peierls]

[423] Rudolf Peierls to Niels Bohr [Birmingham], 18.7.1947 (carbon copy) Dear Uncle Nick, In connection with your conference in September, I wondered whether you would allow Ferretti, who as you may know, is spending a year with me, to take part in it?143 You probably know some of Ferretti’s work; 143 Bruno Ferretti who been the remaining theoretical physicist in Rome after Giancarlo Wick had emigrated to America, spent a year at Birmingham. He was working on methods for solving scattering and eigenvalue problems. See B. Ferretti and M. Krook, ‘On the Solution of Scattering and Related Problems’, Proc. Phys. 60, 481–90 (1948).

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I have formed an extremely high opinion of his ability and judgement from what I have seen of him and in particular he is now working on a calculation of the energy loss of mesons in their orbits inside atoms and it is conceivable that he might produce some deﬁnite result one way or another in time for the conference.144 I think we could probably arrange to get a grant for the expenses of his journey but before exploring this I wanted ﬁrst to ask whether it would be all right for him to come. Several others of my collaborators would, of course, also be very interested in the discussions of the conference but I imagine that, as on previous occasions, you want to keep the conference limited to a fairly small group, and then of all the people here Ferretti would seem the most likely one to make an important contribution to the discussion. As for my own plans, I ﬁnd there is unfortunately no ‘plane in the evening so that I could only travel in the morning of Friday 26th September. I shall make sure of a reservation on that ‘plane which would get me to Copenhagen by lunch time and I try to get a reservation to return towards the end of the following week. If you think these dates would not be suitable, would you let me know? With best wishes, Yours sincerely, R.E. Peierls

144

Peierls and Ferretti had collaborated on radiation damping theory and had produced a joint paper. R.E. Peierls and B. Ferretti, ‘Radiation damping theory and the propagation of light’, Nature 160, 531–34 (1947).

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[424] Rudolf Peierls to Hans Bethe [Birmingham], 28.7.1947 (carbon copy) Dear Hans, Thank you for your letter. Our conference has just ﬁnished145 and it was a lot of fun, though no doubt it would have been more fun if you had managed to get here. We discussed a number of problems, including the one related to your note146 . My personal impression is that physically you are almost certain to be right, i.e. that the observed shift is due to self energy, but that this will not come out of the present theory and that, in particular if one applies present theory to this problem the reduction in the order of magnitude due to pair theory and that due to taking the diﬀerence between two states will not be cumulative, so that one will get at least still a logarithmic inﬁnity in this result. One may not even get a deﬁnite result at all because, as far as I know, no formulation of pair theory exists which is consistent and Lorentz invariant beyond the ﬁrst approximation. I do believe, however, that in a future theory in which one has eliminated the inﬁnities the result for the level shift will look very much like yours. We have discussed further the paper by you and Oppenheimer147 on the Heitler theory and Ferretti has traced the trouble to the result that in the damping theory light signals do not propagate with light velocity.148 This, of course, is the eﬀect of the reinterpretation of the theory in which one gives up the ordinary space-time description. We have all come to the conclusion that this is a fundamental feature of all 145

Peierls had organised a small theoretical conference at Birmingham which dealt with the fundamental diﬃculties and with elementary particles. This took place between July 23rd and 26th. See letter [417]. 146 Bethe had just submitted a note on the electromagnetic shift of energy levels which was to be published later that year. H.A. Bethe, ‘The Electromagnetic Shift of Energy Levels’, Phys, Rev. 72, 339–41 (1947). 147 Hans A. Bethe and J.R. Oppenheimer, ‘Reaction of Radiation on Electron Scattering and Heitler’s Theory of Radiation Damping’, Phys. Rev. 70, 451–58 (1946). 148 Ferretti’s results were the basis of a paper published in Nature. See letter [423], note 144.

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those theories in which one tries to throw out all self-energy terms and therefore one should now consider only theories involving a fundamental constant of the dimensions of a length in which only the contributions from very short waves are neglected but the others, which, as you point out, are needed, are retained. Your letter, of course, tends to strengthen this view. How about plans for next year? I think it should not be diﬃcult, if you can get leave of absence, to ﬁnd a suitable position for you for a few months. Needless to say that it would appeal to me most if that position could be found in Birmingham, but it depends somewhat on what you want. There are a number of places which, at the moment, have no decent theoretician — for instance, Dee in Glasgow has only some rather junior men and a new Chair has just been created at Liverpool which I imagine it will be hard to ﬁll. In one or the other of these places, you would therefore be carrying out a valuable job of putting the experimentalists on the right lines. On the other hand, I take it your point in taking sabbatical leave is to get away for a time from administration and teaching duties and to sit in a place with the right atmosphere in which you could do your own research and where there would be enough younger people to pick up any spare problems you happen to scatter. From my point of view Birmingham might be the best place, though this would, of course, not exclude your meeting the people from other universities. Another alternative would be a kind of general job, sponsored, perhaps, by the Royal Society, in which you would spend periods at all the places that want to see you, but if you want to sit down and get some work done this is hardly to be recommended. Please let me know what your ideas are on this subject so that we can set the wheels turning. Another question is about the ﬁnancial side of the arrangements. The new scheme of sabbatical leave that we are going to institute here provides that the full university salary continues and may be supplemented by a grant to cover travel expenses and higher cost of living. In trying to organise something here, one would have to know whether your regulations are similar, because if one of us went on study leave and got a grant by the university he was visiting, this would merely serve to reduce the cost to this home university, and naturally nobody

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here would be anxious to make a grant merely to save expenses to Cornell. On the other hand, we would, of course, be anxious to make sure that you are not out of pocket as a result of the transaction. Would you want to bring your family and, if so, would they be with you or perhaps in Belfast.149 There is no doubt whatever that we can arrange for you to get the necessary status and facilities and very little doubt that we can arrange an adequate grant. Yours sincerely, [Rudi]

[425] Rudolf Peierls to Robert Oppenheimer Birmingham, 6.8.1947 Dear Oppie, I enclose for your information a copy of letter we have sent to Nature150 which I think strengthens the argument of your paper with Hans.151 It seems to us that this objection is not conﬁned to the speciﬁc formalism of Heitler’s, but applies equally to any theory not involving a constant of the dimension of a length which would allow a quantitative distinction between the terms which are wanted and those which are not. Yours sincerely, R. Peierls

149

Paul Ewald, Hans Bethe’s father-in-law, had settled in Belfast. See letter [423], note 144. 151 See letter [424], note 147. 150

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[426] Rudolf Peierls to Hans Bethe Birmingham, 14.8.1947 (carbon copy) Dear Hans, Thank you for sending me a draft of your paper on the two-meson hypothesis.152 This is all very interesting as Uncle Nick would say, but I do not believe that the second kind of meson which you postulate can have anything to do at all with the Bristol photographs.153 The chief reason for this is that in the Bristol technique for any heavy meson stopping in the plate, the probability of the track of the light meson, if any, also lying within the plate is very small. In other words, for any track which they have found in which a light meson is visible there must be many others which also exist, but do not appear. This means that the heavy mesons do not represent, as you say, something like 6% of all mesons stopping in the plate, but from the latest Bristol ﬁgures something like 50%. In the light of this, the discussion on your page two is somewhat misleading. Incidentally, the photographs were not taken at 30,000 feet as you say on page two, but on top of a mountain and your guesses on page ﬁve about the dimension of the plane do not make much sense, instead there was a lot of snow around. Similarly, your footnote seventeen is hardly justiﬁed since it is very likely that there was in that case a secondary meson present but that it went out of the plane of the emulsion. Equally, of course, this may have been a light meson. 152

Hans A. Bethe and R.E. Marshak, ‘On the two-meson hypothesis’, Phys. Rev. 72, 506–509 (1947). 153 At Bristol, photographs had shown the development of light mesons from heavy heavy ones. C.M.G. Lattes, H. Muirhead, G.P.S. Occhialini and C.F. Powell, ‘Processes involving charged mesons’, Nature 159, 694–97 (1947). The results were reported, among others, at a conference at Harwell, where Powell explained the experiments in detail. See also C.M.G. Lattes, G.P.S. Occhialini and C.F. Powell, ‘Observations on the tracks of slow mesons in photographic emulsions’, Nature 160, 453–56 and 486–92 (1948). Further developments are described in S. Schweber, ‘Shelter Island, Pocono, Oldstone. The emergence of American quantum electrodynamics after the war’ Osiris 2, 265–302 (1986).

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I cannot help feeling that all the facts we have at present, if they are right, cannot even be understood with the help of two kinds of mesons. I enclose a re-draft of our note to Nature which I hope is more intelligible than the ﬁrst.154 Yours sincerely, [Rudi]

[427] Rudolf Peierls to Klaus Fuchs [Birmingham], 27.8.1947 (carbon copy) Dear Klaus, Thank you for your note about the plant design. My chief comment is that its wording, perhaps, is too aggressive for instance in the ﬁrst sentence it is a bit condescending, it might be better to say “I have only minor comments on the L.S.D. plant. While I have not checked the detailed ﬁgures, I would like to mention the following points.” This is almost what you have said, but I am trying to make it sound a little more polite. In the addition to your item three, I think most of the members of the committee will understand what is meant here by diﬀerential ﬂow, why not say “consequently the two sections will temporarily be isolated from each other.” Incidentally, I am no longer satisﬁed that it is really such a vital point, we tend to think too much in terms of stationary conditions, but if the diﬀerential ﬂow ceases for a time between the two sections, will it not simply mean that the amount of light product increases at the top of the lower section so that when exchange is resumed not much has been lost? This hardly aﬀects your note because it is likely that the alternative place for the drum is better anyway and one ought not to accept it in the present position without checking its [e]ﬀect on performance. 154

See letter [423], note 144.

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H.S.D. item two. I do not know whether an increase of compression ratio would really be feasible, one might get too near to the un-stable region of the compressor. Would it be worthwhile to end on a more optimistic note, pointing our that it is very likely that all these problems can be solved in the time available before the H.D.S. design is to be frozen. As your note stands it sounds as if there was serious doubt whether it is possible to build such a plant at all. Yours sincerely, [R.E. Peierls]

[428] Hans Bethe to Rudolf Peierls Ithaca, 3.9.1947 Dear Rudi: Thanks very much for your many letters, scientiﬁc and otherwise. I liked your paper about Heitler’s Theory very much.155 It is certainly the most striking argument against the theory that it does not give the correct velocity of light. It ought to be possible to show this not only by indirect argument but also by direct calculation. You are probably doing this right now. I did a little more on the electro-magnetic line shift. I have done it relativistically and it is indeed ﬁnite. I do not have the numerical result because there are too many terms, each of which has to be evaluated. But the result is essentially the same as in the unrelativistic ca[l]culation. There are some interesting points in it, concerning the subtraction of the electron-magnetic mass, and also concerning the cut-oﬀ procedure for the self energy. But the main point is that it is ﬁnite and depends essentially on ψ 2 (0). Thanks for your criticism of our note on the heavy meson. I am afraid the note was written in a great hurry, and what is worse, it will 155

See letters [423], note 144.

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be printed in the “Phys. Rev.” without our getting any proof.156 So the large density of mistakes will stay in. I am particularly unhappy about the mess I made concerning the altitude in which the measurements were made; as they were made on a mountain, our statement is not correct that most of the mesons are produced in the neighborhood of the measuring apparatus. You are also at least qualitatively right that there must be many heavy mesons which do not appear as such because they escape from the plate. However, I believe that quantitatively this is not quite as important as you say, because the emulsion is rather thick and amounts to about 40 ∗ percent of the range. I think some change in ionization density should be noticed in that distance. The famous Footnote 17 is of course unintelligible, but the meson in question originates in a nuclear disintegration in the plate itself, and should therefore be a heavy meson according to our theory. Since this statement was omitted in the footnote, your objection that it might be a light meson will occur to most readers, but really it cannot be. Now about the plans for the future. It was awfully nice of you to write immediately about the possibility for my possible visit. I have not yet got my leave approved but I am working on it and I hope it will be deﬁnite in about a month or so. The ﬁnancial arrangements are that the University pays my regular salary but no expenses. I am losing a considerable amount in consultation fees from the General Electric Company which of course I cannot visit while I am in England. None of the money which I might get from an English University will go to Cornell. So it would be nice if I could get some sort of position; in this case I will probably come out just about even, that is I will be able to pay the travelling expenses and replace the loss of GE fees. I should like to go to a place where I am really useful and should like to give some regular lectures, as long as there is not too much of this (let us say no more than six a week). I think at the present time, with physicists so scarce, I should not completely retire to the luxury of pure research. Concerning places I want to try — ﬁrst of all to make a ∗I

did not have time to look up the numbers, so this may be wrong.

156

See letter [424], note 147.

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deal with Mott.157 Our department here has invited Mott previously to come for a semester and would still be very anxious to have him. There is a lot of work in the solid state going on here, and I am too much out of this to give any advise. So the present plan is to ask Mott to change places with me for one semester. Please keep this to yourself for the time being, because I have not yet approached Mott, since my leave has not deﬁnitely been approved. If this does not work out, I think Liverpool would be a very attractive place. Also, now with Frisch there,158 Cambridge would be interesting. But I think I should let fate take its course and not put too many boundary conditions on this problem. Any University where there is an attractive program in experimental physics and where a theoretical physicist is needed, will be ﬁne. I should like to stay at one place and not travel around too much. Of course I would want to see you frequently, but distances generally are not very great. The plan is to take the whole family and this might make a diﬃculty from the standpoint of housing. We would visit Rose’s parents during the summer and would expect to leave the children there while Rose and I go to the Continent for a few weeks. But when term begins, it would be nice to have the family happily reunited. The time would be approximately from July to the end of January. I do not know how this ﬁts in with your terms; as I remember the fall term ends at Christmas. If the job I am going to get is just for the fall term, it might be very nice if I could spend a month with you in Birmingham. This is just to give you a vague idea, I hope it won’t make too much trouble for you to look for a suitable place. But both Rose and I are dreaming very much of this visit. We had a very nice time together in southwestern Colorado. At present, Rose’s mother is visiting us and it is really very nice. She has hardly changed at all in the nineteen years since I know her. Best regards to the family. Yours sincerely, Hans 157

Nevill Mott (1905–1996) held the Chair of Theoretical Physics at Bristol at the time. 158 Otto Frisch had accepted the Jacksonian Chair in Cambridge in 1947.

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[429] Hans Bethe to Rudolf Peierls Ithaca, 23.9.1947 Dear Rudy: One of my students, Edwin Lennox,159 is very much interested in spending a year or two in Europe. He will probably get his Ph.D. next June and would like to come over after that. He would like best to come to you if you would like to have him, and if you could give him some research position. You may remember Lennox from Los Alamos while he was in Vicky’s group. In the meantime, he has developed very well and had learned a lot of physics. When he was at Los Alamos, he had had only a very small amount of physics courses. I think he is very good; at least he shows great interest in all problems and tries to get a real understanding of everything in physics. I remember that you had some research position available when you went back to Birmingham. Would any of these be available to Lennox for next year? What would be the salary that he could get? He just encumbered himself by marrying a widow with three children; however, they get some pension from the U.S. Government and possibly some ﬁnancial support from the grandfather of the children. So the situation is not as desperate as it sounds and you may consider him simply as married without any children, as far as ﬁnancial needs are concerned. If it is possible for you to take Lennox, he would of course also be interested in the problems of life, especially whether there is any chance to ﬁnd a place for him to live. If this looks very black, he may be better advised not to come. He would also be interested in knowing for how long your research appointments would run. Physics continues to be very exciting especially the electromagnetic shift of the energy levels and the mesons. At a conference the other day, 159

Edwin Lennox completed his Ph.D. with Hans Bethe and later took up a post at Ann Arbor before moving to the Department of Chemistry at the University of Illinois, Urbana.

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we admired the latest pictures from Bristol, especially the one in which a meson is produced in a star and then produces another star.160 I hope to hear from Vicky and Placzek very soon on what happened in Copenhagen. I assume you were there.161 Best regards to the family. Yours sincerely, Hans

[430] Rudolf Peierls to Hans Bethe [Birmingham], 27.9.1947 (carbon copy) Dear Hans, Thank you for your letter. I still do not agree with your interpretation of Powell’s experiment.162 The point is not that if the track goes at an angle to the plate it cannot be recognized as that of a meson, but that it is not detected at all. The plate is always horizontal under the microscope and if the track has a strong “dip” the focal plane will only contain one or a few grains at a time and, therefore, no recognizable track will appear. No doubt a more elaborate inspection technique would disclose such tracks, but there would be no point in trying this since all the information can be obtained by observing only the tracks which are nearly in the plane of the emulsion. In any case, the others have not been looked for, and all the dozen or so cases found at Bristol are cases in which both primary and secondary 160

Prior to the advent of large-scale accelerators in the mid 1950s, Cecil Powell and his collaborators at Bristol (Occhialini, Lattes, Camerini, Muirhead, and many others) made a number of important discoveries in the study of cosmic radiation, so much so that Louis LePrince-Ringuet referred to Bristol as ‘the big sun surrounded by little satellites’. 161 Rudolf Peierls attended the latter part of the conference organised by Niels Bohr in late September 1947. 162 Cecil Frank Powell (1903–1969), studied natural sciences at Cambridge where he gained his Ph.D. working under Wilson and Rutherford. He moved to Bristol where he eventually (1948) became Melville Wills Professor of Physics.

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mesons lie in the plane of observation. Powell is going to publish his conclusions about the statistics.163 Now about your plans, I am not taking any action at present since the question of Bristol is best explored by your approaching Mott directly. Here are, however, a few points for your information; the winter term lasts in all universities from early October until Christmas. The term is, however, not an important unit for teaching; all courses are planned on the basis of a whole session and as far as I can see it would make no diﬀerence if your visit did not cover an integer number of terms. (A whole session, October to June would be diﬀerent but I take it that is too long for you.) In Bristol, the teaching of Applied Mathematics is in the hands of the Mathematics Department. The theoretical physicists do not do the teaching. I do not think that Mott himself gives as many as six lectures a week. At Birmingham (and in some other places) people with our background do lecture on mechanics, hydrodynamics, electricity etc. to undergraduates including engineers, and we have now a staﬀ of three besides myself, for this purpose. It would be hard to justify a temporary appointment for this kind of work, particularly if it is only for part of the session, so that someone else would have to ﬁnish the courses which you start. Here, at any rate, it would be much easier to build a case on the stimulating eﬀect your presence would have on the research in both experimental and theoretical physics. I cannot speak for Bristol, but I imagine things would be rather similar. If you just swap places with Mott, your main function would be to replace him in the administration of the department and in the supervision of research. Housing is, as you know, not easy. One does, however, see from time to time furnished houses or ﬂats at not unreasonable rents, and there are also boarding houses that might take you with the family. (Best of all close to somebody’s house where Rose could go for washing or similar activities not tolerated in a boarding house.) 163

C.M.G. Lattes, G.P.S. Occhialini and C.F. Powell, ‘Observations on the tracks of slow mesons in photographic emulsions’, Nature 160, 453–56 and 486–92 (1948).

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Liverpool are trying to ﬁll a new chair in theoretical physics.164 This is likely to be ﬁlled before your visit. If they are unsuccessful and the chair is still vacant in 48–49 they would, of course, jump at the chance of having you for a short period and it would there be particularly easy to organize funds since the job exists. Failing this, I think Cambridge should also not be diﬃcult. Next come some plans of mine. I ﬁnd I shall have to attend a meeting in Washington on 14th and 15th November, though there is some talk of it being a week earlier. It comes at an awkward time from the point of view of my duties here and I do not want to stay away longer than necessary. But I might get in an extra day or two and in that case would, of course, very much like to come and see you. As we are very limited on dollars now, this would only work, if my fare from Washington to New York could be covered somehow. What are the chances of this? I could, of course, give a lecture on any subject. I shall let you know more about dates as soon as possible. Greetings to everybody. Yours sincerely, [Rudi]

[431] Y.I. Frenkel to Rudolf Peierls Leningrad, 7.10.1947 My dear Peierls, I am very sorry to have missed your attractive conference. I hope there will be another opportunity of meeting you either here or in England in the near future. The negative theory of the results of an inspection of the present quantum theory and the mathematical intrications to which the attempts to remove its diﬃculties lead, seem to indicate that these 164

The Chair was ﬁlled in 1948 by Herbert Fr¨ ohlich who remained at Liverpool until 1973.

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attempts are not radical enough and that one must discard certain notions which seem inherent in the present theories and are considered as fundamental. One of these notions is the association of the particle concept to the ﬁeld one. In the case of radiation this association leads to the idea of “longitudinal photons” which are assumed to the particle correlate of the electrostatic ﬁeld. In the case of meson theory a similar rˆ ole is played by neutral mesons. I believe that both of these particles are non-existent while the ﬁeld with which they are associated is a reality. Further, matter is unusually described in a dualistic way, as a system consisting of ﬁeld and particles interacting with each other, the interaction between the particles being transmitted by the ﬁeld. I think that this dualistic conception of matter must be replaced by a monistic ﬁeld conception, the particles appearing as quantum eﬀects due to the ﬁeld. This programme has been outlined by Lorentz classical theory, when its development was, however, chivied by the intricacies of the problem of electron structure. Now, from the point of view of quantum theory, this problem must be considered as ﬁcticious — just as the problem (which seems never to have been discussed) of the structure of a photon. I do not think it necessary to introduce in the fundamental equation a quantity corresponding to the classical radius of the electron. I rather believe that one must introduce a quantity corresponding to the energy of formation of an electron pair. As a matter of fact this quantity appears in Dirac’s equation as a mass of an electron. But Dirac’s equation is an equation of motion, while the fundamental equation must be an equation of the electromagnetic ﬁeld, the behaviour (“motion”) of electrons and positrons following (as in Lorentz’ theory) from the laws of the conservation of electromagnetic energy-tensor. This is the programme which I think has to be realized. In the case of nucleus we have a similar situation with the additional complications, corresponding to the interaction between the two ﬁelds (nuclear and electromagnetic). The main thing is to remove the particles from the ﬁeld equations, introducing them eventually as quantum eﬀects.

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The publication of Soviet work in foreign languages has recently been wholly discontinued. I am afraid that this may lead to a complete loss of contact between ourselves and our foreign colleagues, unless the latter take some pains to study the elements of Russian language, which will enable them to read our papers in Russian. It is hoped that we shall be allowed to publish a yearly report on our scientiﬁc work in English. I shall be glad to help you, meanwhile, in getting our Russian journals for the libraries of the British universities, in particular the “Journal of Physical Chemistry, the Journal of Colloid Sciences, the Drolady (C.K. of the A of Sc.) All is well with us both here and in Moscow. Give my love to Genia. Natasha is sending her greetings to both of you. With kindest regards. Yours sincerely, J. Frenkel

[432] Rudolf Peierls to Hans Bethe [Birmingham], 8.10.1947 (carbon copy) Dear Hans, Thank you for your letter about Lennox.165 I am naturally very interested in the possibility of having him here. He must, however, realise that things are not going to be easy at all from his own point of view. Our research fellow-ships vary in seniority and salaries range from £450 a year to £700. This is subject to the usual 5% deduction for superannuation with the University adding 10%. The superannuation is optional and would not apply to anyone who was not intending remaining in academic life in this country. In addition there is a family allowance of £50 p.a. for each child of school age or below. I would, of course, have to know more about his 165

Letter [429].

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progress and ability before expressing an opinion where his salary would lie within the range I have quoted, but unless he has developed in quite a spectacular way, it is hardly likely that he would ﬁnd himself at the top of the grade. My present guess would, therefore, be that he might well expect £500 to £550 and more if we can make out a case. I cannot also at this moment give an assurance that there will be a vacancy for him, we are likely to have a vacancy next session for which there may also be competition, but more vacancies may arise. The terms of these fellow-ships are yearly appointments up to a total tenure of ﬁve years. This last limit is not likely to be serious since, if he wants to settle down in this country, it is quite likely that he will ﬁnd a teaching job that would attract him either in Birmingham or elsewhere. He would, however, have to pay his own passage as well as that of his family, since we have no grant that could be used for this purpose. I do not know whether it would be possible to ﬁnd some outside grant to help him, but I am sure that at most his own passage could be covered in this way. As regards living conditions here, the salaries I have quoted are adequate though not generous for young married men. To support three children on them would be very tough. Housing is still very short here and it is virtually impossible to rent a house or ﬂat unless he is exceedingly lucky or unless he is allocated one of the very few houses under the control of the University for which, however, there is very strong competition. One can occasionally rent furnished accommodation, but that would be rather expensive and it may not be easy to ﬁnd anything satisfactory for the size of his family. It is possible to buy houses, a small modern house is likely to cost about £1,500, of which two thirds, or with luck a little more, could be covered by a mortgage. This would have to be furnished unless he can bring furniture from America, this again is diﬃcult and expensive. It should also be born[e] in mind that the style of dress, especially for the children, is rather diﬀerent here from what it is in America, and he would, therefore, probably have to get almost completely new outﬁts before he came over. It looks, therefore, as if the whole project was extremely diﬃcult unless he was able to supplement his income at least for the initial ex-

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penses and during the ﬁrst year quite substantially from private means. If he feels, provided things turn out the right way, he might settle in Europe for good, it may be worth going through all this trouble; if what he has in mind is a year or two on this side, it would seem too big a sacriﬁce. Perhaps you would discuss these facts with him and if you would let us know a little more both about his progress in research and about his other plans, I may be able to give more deﬁnite advice. The meeting to which I have to go in Washington has now deﬁnitely been ﬁxed for 14th–16th November. I intend to leave here about the 10th and to start back on the 19th. If during that time there could be a chance of seeing you, that would, of course, be very nice. Yours sincerely, [Rudi]

[433] Rudolf Peierls to John Cockroft [Birmingham], 26.10.1947 (carbon copy) Dear Cockroft, I have thought further about the recent diﬃculties over the release of photographs and other information. I feel strongly that this places us really in an impossible position for discussing declassiﬁcation with the Americans. This may not merely involve technicalities, but we may have to support our advice by discussing reasons for our attitude. How can we do this if there is a likelihood of a government which instructs us acting on completely diﬀerent ideas? I feel so strongly on this point that I have seriously considered to withdraw from the delegation unless this point can be cleared up before our departure.166 I have decided against this, since such a step by one 166

Rudolf Peierls was planning on attending a declassiﬁcation conference in Washington in November 1947. See letter [430].

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member of the delegation would tend to give the impression that the scientists are divided in their attitude; this might do more harm than good. Any pressure that is brought could only come from you either personally or speaking on behalf of all of us. There will, I hope, be a possibility of talking these things over at Malvern, but I thought it might help if you knew my views beforehand. Yours sincerely, [Rudolf Peierls]

[434] Rudolf Peierls to Robert Oppenheimer Birmingham, 1.11.1947 Dear Oppie, I have to attend meetings in Washington on 14th – 16th November, and my only available transportation will get me to New York with any luck on the 6th of November. I would like to use the extra time for a few visits and I am trying to arrange to call at Princeton about November 12th. I am hoping to call at Chicago between 7th and 9th, at M.I.T. on the 19th and perhaps 11th, although I do not know whether these dates will be suitable in those two places. I shall telephone your oﬃce on arrival in New York, but if this letter reaches you in time, it would help if you would leave a message for me at La Guardia Airport where I am due to arrive by B.A.O.C. Flight 15–16a on the 6th, saying what your movements are likely to be during that week. I do not know whether you will also happen to be in Washington at the time of our meetings,167 and if so you may prefer to have a chat 167

Since the passing of the Atomic Energy Act of 1946 (McMahon Act), the declassiﬁcation of atomic energy information, both basic scientiﬁc and related technical information, was regulated by this legislation. Under the terms of the McMahon Act, the so-called ‘restricted data’ (RD) which concerned the manufacture and utilization of atomic weapons, as well as the production of ﬁssionable material, was no longer to be shared with other countries. UK scientists, however, were consulted in declassiﬁcation meetings, such as the one in Washington in November 1947.

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there rather than in Princeton where you may be busy, but in that case I would still try to visit Princeton to see Wigner and others. Yours sincerely, R.E. Peierls

[435] Rudolf Peierls to Niels Bohr Birmingham, 2.11.1947 (carbon copy) Dear Uncle Nick, Here is, at last, the promised redraft of the paper.168 I was very disappointed that it took me so long to get it ready, but I struck a number of minor formal diﬃculties in the presentation. It also has increased somewhat in length, but I think it would be hard to say the same things in a substantially shorter paper. I am particularly sorry about the delay since, owing to diﬃculties with transportation, I have to leave for the United States already on 5th November, so that there is no hope of getting your comments before I leave. Your comments would reach me, if they were sent c/o British Supply Oﬃce, P.O. Box 680, Benjamin Franklin Station, Washington D.C. to get there by 15th November, or c/o Bethe at Cornell, by the 18th. This applies in particular if there are any questions you would like me to discuss with Placzek.169 Otherwise, it would, of course, be quite all right for you to make any changes you wish and send the paper oﬀ. I hope to be back here on the 21st November. 168

Here Peierls refers to the second draft of the manuscript entitled ‘On the Mechanism of Transmutations of Atomic Nuclei. II. Processes in the Continuous Energy Region of the Compound State’, reproduced in R.E. Peierls (ed.), Niels Bohr. Collected Works, Vol. 9, Amsterdam: North Holland, 1986 (cited hereinafter as Bohr. Collected Works), pp. 487–502. It was produced after agreement had been reached by Bohr, Placzek and Peierls that the latter should update the pre-war drafts of their joint paper in order to publish it. 169 Georg Placzek had moved from Los Alamos to a job with General Electric, until he secured a position at Princeton, working at the Institute for Advanced Studies with Oppenheimer.

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It may help if I add a few notes on my reasons for changes which I have made. (“Old draft” here refers to the typescript dated 9.10.47, which you sent me.170 ) Section 1: This is meant to be a rough sketch, and you may like to change the wording of this. Section 2: This is substantially the old section 1, but with the discussion of the Breit-Wigner formula omitted,171 as we agreed. I have left the discussion of the phenomena at very high energies, which, I believe, helps to complete the picture. You were doubtful whether this should not be omitted. If that still is your view, it can easily be taken out without breaking the continuity of the rest. I have added on p. 3, the point that the “potential scattering” need not be exclusively elastic. Section 3: This is the new section which gives an elementary derivation of the Breit-Wigner formula. I gave a misleading picture of this in Copenhagen by stating that four principles are involved. Actually, the conservation theorem is not necessary for this purpose. Section 4: It seems more logical to discuss detailed balancing before the conservation theorem, and this required some slight changes in this section, which otherwise is just the old section 3. I have shortened somewhat the discussion of the precautions necessary in applying detailed balancing to quantum problems. It seems a satisfactory point of view that, in all cases in which the states of the 170 This refers to a typescript produced from pre-war manuscripts which were typed up to form the basis of Peierls’ attempt to redraft the paper. See R. Peierls, ‘Introduction’, Bohr. Collected Works, Vol. 9, p. 50. 171 Breit and Wigner had derived the general theory of resonance processes for a single resonance level (G. Breit and E. Wigner, ‘Capture of Slow Neutrons’, Phys. Rev. 49, 519–31 (1936).) When applied to the case where the width of the resonance level is greater than their spacing, the Breit-Wigner method gives a result that does not conform to the derivation of the cross section for the formation of the compound nucleus by the capture of a particle from the general theorem of detailed balancing. Contrary to Kalckar, Oppenheimer and Serber, who believed the Breit-Wigner formula to give the correct answer (F. Kalckar, J.R. Oppenheimer and R. Serber, ‘Note on Resonances in Transmutation of Light Nuclei’, Phys. Rev. 52, 279–82 (1937)), Bohr, Peierls and Placzek argued that, in fact, the answer from the detailed balancing argument was the right one.

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compound nucleus can be described as deﬁnite states in the sense of the quantum mechanics formalism, the formalism automatically implies the law of detailed balancing, and it is therefore not necessary to construct an actual circular process which would violate the Second Law of thermodynamics, if detailed balancing did not hold. (It must of course always be possible to construct such a process.) Section 5: This is based on the old section 2. I have altered the mathematics slightly by retaining the complex scattering amplitude Si rather than splitting it at once into modules and phases. This seems to make it a little easier to see how the potential scattering term enters in (32). On the potential scattering term itself, it seems to me unnecessary to regard the application of (32) to the potential scattering alone as approximate (old p. 14 bottom) since the potential scattering by itself should be deﬁned as the solution of a deﬁnite wave equation. The interference between potential and “true” scattering by itself would present no diﬃculty at all if the potential scattering were purely elastic. This was true in the very ﬁrst draft of this part in which the potential scattering was deﬁned in a formal way based on the Peierls-Kapur equations. In the view now taken, which I regard more satisfactory from a physical point of view, this is no longer true, but this leaves a certain amount of conjecture as regards the interference between the inelastic potential and “true” scattering. A more precise answer could, however, come only from a much more quantitative study, including a deﬁnite model for the potential scattering, and I feel we ought not to attempt this at the present stage. I have also put back the generalization to particles with spin to a later point so as to avoid introducing the quantity that is called δAJ . The reason is that in the case of spin one must consider, instead of one incident wave, a number of diﬀerent waves with diﬀerent spin directions, which are incoherent, and which, in general will have diﬀerent phases. The cross section is then obtained by averaging. I believe therefore that an equation like (26) of the old draft could not be justiﬁed in the case of particles with spin, though, of course the inequality (35) with J in place of l will still hold. I have omitted the analogy with the scattering of light by a system of oscillators in a box. It seems to me that most readers would not be suﬃciently familiar with the theory of this model to accept the state-

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ments about its properties as obvious, and one would hardly want to present an extensive mathematical study of the model. I have also omitted the statement at the bottom of p. 12 of the old draft that in the continuous level region the phase is always that corresponding to full resonance. It seems hard to justify this in a convincing manner. In the pre-war draft of the statement, this was justiﬁed from the Peierls-Kapur formalism,172 but it depended again on a very formal, and probably inconvenient, deﬁnition of the potential scattering. Since the statement is not needed for the conclusion, it seemed wiser to omit it. Section 6: is very short, and you may prefer to treat it as part of section 5. This can be done by just omitting the heading. With best wishes. Yours sincerely, [R. Peierls] Apologies for the typing, which is my own.

[436] Rudolf Peierls to Hans Bethe Birmingham, 24.11.1947 (carbon copy) Dear Hans, On my return here, I found a list of people who have been invited to write reports for the Solvay Conference,173 and I am glad to see your name. I had already promised to write a report on self-energy problems, not knowing, of course, the rapid progress that is now taking place in the United States in this ﬁeld. Deﬁnitely we should try and avoid too 172

This formalism was developed in P.L. Kapur and R. Peierls, ‘The dispersion formula for nuclear reactions’, Proc. Roy. Soc. A166, 277–95 (1938). 173 The 8th Solvay Conference, the ﬁrst post-war conference, took place in September 1948 in Brussels.

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much overlap and we ought to agree what is the best division of labour, if any. Could you let me know as soon as possible whether you are proposing to come to the conference, whether you are agreeing to write a report and what your views are about the best division. For example, I might try to summarise the account of the diﬃculties of the old theories including a criticism of the attempts by Dirac, Gustafson, Heitler etc., and deal with the position of theories not including perturbation. This would include your own proof that the divergence does not depend on perturbation theory. It would also include the classical theory of McManus and the general method of Feynman to the extent to which I have understood it, or shall understand it. It would leave you all those theories in which ﬁnite results can be obtained by an intelligent application of perturbation theory without modiﬁcation, including your own work, the recent Princeton results, Schwinger etc. This, however, is only a tentative suggestions and any division would be all right with me provided it does not involve my writing about the Princeton results I have only heard in conversation, and Schwinger’s calculations174 which I do not know at all. With best wishes, Yours sincerely, [Rudi]

174

After Bethe had completed non-relativistic calculations about the Lamb shift and magnetic anomalies of the electron momentum, Weisskopf and Schwinger had done some relativistic calculations. See S. Schwinger, ‘On quantum electrodynamics and the magnetic moment of the electron’, Phys. Rev. 73, 416–17 (1948).

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[437] Rudolf Peierls to Abram Pais [Birmingham], 27.11.1947 (carbon copy) Dear Pais, Thank you for your letter and typescript175 which arrived here yesterday. I am writing at once to let you have my immediate reactions. If within the next few days I have any second thoughts or suggestions from my collaborators here, I shall send them oﬀ on the oﬀ chance that you may still be able to use them. I have not so far found any further reference to be added to your survey or any further papers to reproduce. I am also not aware of any errors in my paper. Your survey seems to me an admirable and most helpful piece of work. Of a number of comments, perhaps the most serious one refers to the discussion of the Lorentz and Abraham electrons starting on page six, and the corresponding quantum theories. To my mind the discussion involving self-stress has always appeared as a most unnecessary piece of learned complication, although I realise the part it has played in the historical development. Surely all that one must realise is (a) that a formula based on an electron with rigid charge distribution not subject to Lorentz contraction violated relativity in the most elementary way; (b) that a charge distribution which is subject to Lorentz contraction can be formulated in an invariant way as long as only motion with uniform velocity is considered, but that such a motion becomes impossible if acceleration is allowed because of the well-known fact that relativity does not permit the existence of a rigid structure capable of being accelerated. This, of course, can be traced to the fact that a charge distribution which depends uniquely on the location of its centre, involves 175

Letter could not be located. Abraham Pais had attended the Shelter Island Conference ‘on the foundations of quantum mechanics’ between 1st and 3rd June 1947. On the suggestion of Oppenheimer and Wheeler, he edited a collection of earlier papers to be published in 1948. The book itself was never published, but the preface written by Pais was published as A. Pais, Developments in the Theory of the Electron, Princeton: Princeton University Press, 1948.

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of necessity a transmission of impulses with inﬁnite velocity (since a change of velocity at the centre must cause instantaneously corresponding change in velocity of the distant parts of the distribution). From this statement it is clear that neither the Abraham nor the Lorentz picture can be compatible with relativity dynamics. Historically this discussion was important at a time when not only the electron problem, but also the problem of relativity dynamics were in question. Now that the principles of relativity are no longer in doubt, I see no advantage in discussing in detail the feature of schemes evidently not compatible with these principles. My own feeling would, therefore, be that the fewer equations written for these schemes, the clearer the story will become to the reader and one can, of course, refer for the mathematical details to the references you are quoting. Similarly, I do not see much advantage in classifying, as you do on page nine, the non-invariant theories according to just where they go wrong. Similarly, (unless I have misunderstood an important point) you place some weight on the fact that there is a procedure in quantum theory leading to your equations (7a’) and (7b’) which are equivalent to the classical theory which is of historical importance but which is inadmissible owing to its contradiction to relativity. Other smaller points, page ten, line ﬁfteen, it is misleading to say that the Dirac theory leads to that of Lorentz. The Lorentz equation was meant only as an approximate one, neglecting higher terms which would be important if the frequencies of the motion became compatible to c/... In this connection it would, I think, be useful to mention the remark, due, as far as I know, to McManus here, that the Dirac theory here is equivalent to putting into the Lorentz theory a negative mechanical mass so as to make the total mass equal to the observed value and then letting the electron radius tend to zero. I found this helpful in understanding the signiﬁcance of the runaway solutions. Page fourteen, footnote — “The Kramers theory mentioned previously”, I did not see the reference to which this applies. I suspect it might apply to your reference (27) which is only mentioned on the following page and which in any case is merely a private communication. If this is correct, would it be possible to give a little more detail? Otherwise, could you make it clearer which application by Kramers you had in mind? Page fourteen,

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line nine, “It should be recalled” this is one of Bohr’s favourite expressions, but I think one should be a little more explicit. Page 24a, your account of the diﬃculties conveys the impression that the source of the trouble is the fact that the new terms contain higher powers of the ﬁeld intensities. If this were the only diﬃculty, one might, of course, question, as Bohr has done, the validity of the derivation of such equations from correspondents. Nevertheless, it might still be possible to derive the non-linear ﬁeld equations resulting from such a scheme by means of a new Hamiltonian and then apply the standard procedure of quantization. I have always thought that the real trouble was the occurrence in the equations of motion of quantities containing time derivatives of higher order or even the values of the ﬁeld equations at diﬀerent times. This means that the equations are no longer of Hamiltonian form and that, therefore, the standard procedure of quantization can no longer be applied. This is important because if this were the main point, it would mean that there might be a chance of getting over the diﬃculty by means of the Feynman method which starts from the action function directly without the use of a Hamiltonian. Evidently the equations in question could be derived from an action principle. I am not yet satisﬁed, however, that the Feynman method wold be applicable to such a situation. Also, of course, it does not follow that the results would be physically reasonable. Page 28, footnote, you mention a quantity λcrit of which I could not ﬁnd a deﬁnition. This may be due to my hurried reading, but it would also help, if a clear statement were given somewhere what you mean by λcrit . Page 30, line 5 from bottom you refer to page 20a which is not included in my copy. As page 20 refers to my old paper, II am naturally interested to know whether I have missed there an important addition. Also, in the list of references, items 104 and 105 are omitted in my copy and I would be glad to know what these are. Reference 87 strikes me as odd, only a minority of your readers will have been present at the conference and the purpose of the reference to such a discussion is usually to show the channel through which you have learned of somebody else’s views. In quoting yourself in this way the impression is given that you merely want to ensure the priority of having made an unspeciﬁed statement at a certain time, and I am sure that is not you intention.

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I do not know whether it is worthwhile to include amongst the list of classical theories, say on page twelve, a reference to the integral ﬁeld equations by McManus which I reported to you the other day. I still believe that from a classical point of view these are free from all objections one can raise against the proposals which you list. I have just sent to Feynman a typescript containing mathematical details to which, no doubt, you could refer if you wish. On the other hand, I appreciate that it is hopeless to attempt to be completely up-to-date if you ever want to go to press, and it may well be too late to include a reference to this theory. One last remark, if it is possible in the available time, it would, I think, be worthwhile to check the language of your survey. Some of the sentences do not read very well and I had to read some of the passages several times, before I could make out their sense. Yours sincerely R.E. Peierls

[438] Hans Bethe to Rudolf Peierls Ithaca, 4.12.1947 Dear Rudi, Thanks for your letter of 24th November.176 It tells me, among other things, that you arrived safely back in England which is ﬁne. In the meantime, we also saw Fuchs whose visit was very nice. For the Solvay Conference, I would have proposed exactly the same division of labor as you. I wrote Bragg that I would talk about level shift and related problems. By this I mean the Princeton results, Schwinger’s results and any other results we might obtain in subtraction physics. I would leave everything about the free electron and the relation to classical theory to you. So in short, I agree. I[t] was very ﬁne to have you here and we all got a lot of ideas from your visit. Unfortunately, Feynman has not yet quantized your theory 176

Letter [436].

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but got sidetracked into some invariance problems. He and Lennox have shown tentatively that Pais’ method for getting a ﬁnite self-energy does not give an invariant result.177 The last two days Vicki was here, so we got still more ideas and still less work done. I will let you know if anything new develops. Greetings to everybody, especially to Genia. Yours sincerely, Hans

[439] Rudolf Peierls to Nevill Mott [Birmingham], 17.12.1947 (carbon copy) Dear Mott, In connection with the conference in Bristol that you mentioned to me, I have the impression that this would not overlap seriously with conference we might hold here on somewhat similar lines to the one last year. Ours would concentrate on fundamental theory, steering clear, as far as possible, of cosmic rays, but concentrating on the problem of self energy, pair theory and the like. We might also include nuclear reactions and in that case widen the conference to one that would include experiments as well as theory and make it a joint aﬀair with Oliphant’s department. This will, I think, not overlap much with your plans unless the latter included some sessions devoted speciﬁcally to Powell’s work on n-p scattering, or on the D-O reactions etc. As you said your conference would start on the 20th of September, I am planning to have ours start on the 13th, but perhaps ﬁnish it well before the end of the week so as to give some time for foreign visitors who want to visit other places in between. I would 177

Hans Bethe reported the results at the Solvay Conference. H.A. Bethe, Report to the Solvay Conference, September 1948. See also R.P. Feynman, ‘Relativistic Cut-Oﬀ for Quantum Electrodynamics’, Phys. Rev. 74, 1430—1438 (1948).

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be glad to hear your comments on these suggestions and also whether I can assume that the date of your conference is ﬁxed. I would also like to write to Bohr in order to make sure our plans would not interfere with anything he has in mind and in that connection would like to mention your conference. Is that in order or are your plans still conﬁdential? R.E. Peierls

[440] Our Relations with German Scientists [date unspeciﬁed, probably early 1948] Since the war there have been few occasions for contact between British and German scientists. Gradually scientiﬁc life in Germany seems to get organised again, and with the resumption of scientiﬁc publications there are bound to be more exchanges of scientiﬁc views and, sooner or later, more opportunities for personal contacts. How will we receive our German colleagues? I have put oﬀ writing anything on the subject in the hope that what I am going to say might be said by others. I regard myself as poorly qualiﬁed to write, for two reasons: Firstly, I have not visited Germany since the war, and my knowledge of scientiﬁc life there is based on reading and on other people’s reports. Secondly, as a former German, I may be suspected of prejudice. However, the matter is important and if others will not speak I cannot remain silent. The problem of the scientists is, of course, not an isolated one, but it is linked up with the position of all the German people after the war. I shall concentrate on the scientist because that is the aspect of the problem of which I have detailed knowledge, and also because it is a particularly acute one in view of the particularly close personal relations that usually exist between scientists of all countries. Amongst scientists, as amongst other people, one ﬁnds in this country a widespread readiness to forget the past, to blame the war and the pre-war events on a few political leaders who have been (or in some

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cases will be) tried before the courts and to reestablish with all our German colleagues the relations we had when we broke oﬀ. This is an attitude which deserves the greatest admiration. It is amazing that after a war which caused so much suﬀering in this country and which brought Britain so near to ruin, there should be so little ill feeling against the former enemies. It is almost incredible that, with food here severely rationed, pressure of public opinion should have forced the authorities to grant permission for food parcels to be sent to Germany, and that even now, the correspondence columns of the papers reﬂect more concern with the plight of the Germans than the opposite. All this reﬂects a mature and enlightened understanding of the fact that there is no sense in collective retribution, that personal hardship on individual Germans will bring no comfort to people here who suﬀered as a result of the war. It is good to be generous, but there is danger in indiscriminate generosity. It must be remembered that in the interest of the Germans themselves, and in the interest of the future peace of the world, the rebuilding of a sane public life in Germany is of the utmost importance. We must, therefore, consider what eﬀect our attitude is having on German public life, and scientiﬁc life in particular. During (and before) the rise of the Nazi party to power, there were some German scholars who were active supporters of the party and who were taken in by the catch phrases and the ‘theories’ of Nazism. They were few in number. The ideas of the party were so crude that extreme passion, ignorance or stupidity were necessary to be taken in by them, and the few who fall in that category were not as a rule scholars of rank. They can safely be ignored. But there were vastly greater numbers of people who had perfectly suﬃcient intelligence not to be taken in. When in 1933 the Nazi “reforms” hit the German universities there were certainly a large majority of their staﬀ who would not have themselves advanced such changes, and who, if you had asked them, would have declared themselves in favour of academic freedom. They did not like the idea of colleagues being dismissed for no other reason than that they were Liberals, Socialists or Jews. Yet, when the changes came, nearly all of them acquiesced and if they were not personally aﬀected, continued to serve under the new system. This involved in many cases adopting the new language of

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the Nazi system, taking part in ceremonies glorifying this regime and professing admiration for it. A few people would not play. Some left quickly and accepted jobs abroad, some went underground and tried to ﬁght the regime. They soon ended up in a concentration camp or realised the hopelessness of their struggle and left the country. The number included many young people with no established reputation, or with professions in which the work cannot easily be transplanted and these often had to struggle hard to ﬁnd work abroad in spite of the very generous reception many refugees found in other countries. Some stayed in their jobs with barely concealed disgust, but kept away from administrative responsibility so as to avoid becoming tools of the vicious system. They did not usually go as far as to oppose the regime outright and thus to court certain disaster, but they tried to keep their hands clean. But the majority of university teachers made their peace with the system. Certainly they regretted the excesses, though reading only German newspapers it was easy to forget such uncomfortable facts as concentration camps. They did not like to see useful members of their staﬀ discharged for non-professional reasons and if by pleading it was possible to retain such a person they did their best. But on the whole they accepted the instructions of the authorities loyally just as, being good citizens, they had followed the laws of the previous regime. In fact, as it was considerably more dangerous to be found disloyal to the new regime, the new laws were observed more scrupulously than the old ones. Many of these men must at some time have considered the question of resigning, but as a rule they persuaded themselves that it was their duty to stay in their jobs (or to advance into the jobs vacated by the dismissals) so as to exercise a restraining inﬂuence and perhaps to protect some of their junior staﬀ (in practice such protection was never eﬀective for long) or at the most to save their families from hardship. There is, of course, a vast diﬀerence here, between junior people for whom resignation might have meant starvation for themselves and their dependents. Much as one admires the few who would not bend no matter what the consequences, one cannot expect everyone to be a hero. But no heroism was involved for the front-rank men, many of whom could have found

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jobs abroad at once, or who (during earlier years) could have left the country with part of their savings and would never have been destitute, though resignation would have entailed serious sacriﬁce for them too. Few would admit that they stayed for the sake of their own comfort. This did not always mean that the money mattered; many were too keen to keep their positions because of the prestige (and sometimes because of the research facilities) attached to them. These front-rank men could have given a lead that might have been followed by many of juniors (though the risk was greater for the juniors). We have heard of the refusal of the personnel of a Dutch University to sign a loyalty declaration during the occupation. This resulted in wholesale arrests and deportations. But even the Nazi regime would have hesitated to carry on without the majority of German University teachers. Resignation of a majority might have won the universities respect and a measure of freedom. All of us who were lucky enough not to be faced with a decision of this kind will wonder how sure we are of our own courage in such a situation, and none of us can be quite sure before we have faced it in reality. Yet I refuse to believe that any authority whose justiﬁcation rests on the shoddy formulations as the Nazi ideology could manage to dismiss a number of University teachers in this country with the remainder staying loyally at their jobs. The general inertia amongst the senior people set the pattern for the younger ones. The more declarations of loyalty were signed by leading people, the greater was the risk for any other man who wanted to keep out. Accordingly the courageous few who risked serious suﬀering felt almost greater resentment against the “good citizens” who compromised for the sake of peace and comfort, than against the few fools who were taken in, or the scoundrels who joined the party for personal gain. Now they are nearly all back in academic life. The good citizen, who is good at signing papers and getting along with the authorities, is back in the leading job and gets on excellently with the representatives of Military Government. He has now found the courage to disassociate himself from the Nazi creed. He is beginning to discover that it is much less dangerous to contradict the Military Government than to contradict the Nazis, and he is now found to hold an opinion of his own. Of the

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active collaborators, some are back, too, since they have a chance of counting as “victims of Nazi persecution” if they had a row with a party oﬃcial or got into a concentration camp for embezzling party funds. The decent people, who managed to keep their hands clean are back. They are much more awkward people to deal with; they think about principles and they get worried if they think the Military Government is making mistakes. They are not too easy to get along with. The real victims are back too — if they have survived. They are rarely in leading positions; they have been out of the business for too long to have administrative experience or to be up-to-date in their professional work. So they work under the good citizen whom it makes very uncomfortable to look at them or in some cases under the old party member who proved his integrity by having a row with Nazi oﬃcials. On paper they have some privileges, they do not amount to very much. In this atmosphere the education continues. Many of them are still inﬂuenced by their earlier education under the Nazi system. They are, to a varying degree, ready to accept new ideas and there is no doubt that the spirit of their teachers and professional leaders exercises a profound inﬂuence on their attitude, and thus may determine the attitude of the future professional men and administrators. Here is the place where it would be vitally important to encourage the democratic ideals, unprejudiced thought about the past as well as the future, personal integrity, and independence of opinion. On several occasions I have met Germans who throughout the war have managed both to retain their self-respect in spite of temptation and their lives in spite of persecution, and they deeply regretted that the Universities were reopened too soon. They argued that compromises were justiﬁed in the case of key administrators or technicians in industry without them the economy of the country would have deteriorated even more. If reliable people could not be found for these jobs, one had to make do with more doubtful ones. But in the Universities, the position is diﬀerent. The aims they serve are long-range ones, and one has to balance the immediate eﬀects of a shortage of professional men against the danger of allowing again the growth of a professional class whose spirit may repeat to a dangerous

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extent the pattern that was a vital element in the growth of Nazism. Much better for Germany, those Germans argue, to build up a few centres staﬀed with people whose records are known, and who would attract in the course of time, others of similar attitude. One or two such centres do, I believe, exist, but they are overshadowed by the majority of other universities. This is the background against which we should consider our attitude to German colleagues. We much remember the prestige attached, in German eyes, to an invitation to go abroad, at a time when foreign travel is virtually impossible, the eﬀect on morale of close personal relations with people in other countries, and above all the eﬀect on the feelings of those few decent people who do not get the same reception. I do not, of course, for a moment wish to suggest that we should interrupt, or fail to resume, the exchange of scientiﬁc information. If a scientist, whatever his personal record, has ideas or results to contribute, it would be foolish and contrary to the principles of scholarship to take no notice of them. Equally we would wish him to be acquainted with our own results and ideas which we publish in scientiﬁc literature so as to make them openly available to all. Most of us are so accustomed to carry on technical discussion with our good friends that it seems almost impossible to distinguish one’s personal relations from the professional ones. And evidently it is much pleasanter, and more convenient, if we are able to receive our colleagues as friends. But it is certainly not impossible to draw a distinction. Those of us who had the experience between 1933 and 1939 of meeting German scientists whom they knew to be party members and in active support of the regime, will remember that it was painful but quite possible to discuss technical matters without letting one’s memory of the other person’s record be blunted. We might get some advice on this from scientists in countries occupied during the war for whom it was a common experience to meet men whom they respected professionally, but from whom they wanted to keep aloof personally and socially. It is not, of course, easy to discriminate, quite often we do not know enough about each of these men to deﬁne our attitude. It would be much more comfortable for us if this work were done by the authorities, or by the denaziﬁcation tribunals. But their decisions rest on a diﬀerent basis.

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They are concerned with questions of expediency as well as principle and (much as we may deplore the large part expedience plays in German university plans) they do not decide the problem which I have tried to formulate. The problem of deciding is not unsurmountable. About the senior men, who held positions of responsibility under the old regime, much is widely known, and more can be learned from colleagues in Holland, Belgium, Scandinavia and other countries who mostly had ﬁrst-hand knowledge of this problem at a time when it was far less academic than it is now. Much less is known about the younger ones, but about them we can far better aﬀord to be generous in case of doubt.

[441] Nevill Mott to Rudolf Peierls Bristol, [date unspeciﬁed]178 Dear Peierls, I promised Kurti to write something on Skinner’s proposals, and this led me into putting down my opinion now ab[out] control of A[tomic] E[nergy]. I hope you can read my scrawl. Would you like to have it circulated to the A.S.A.Council as a basis for discussion? Actually, I don’t think that we shall any more get agreed statements — unless we shed our left wing — if then! Also if people want to meet and discuss our policy on this, I think we should urge them to put down their views in writing ﬁrst, or else say how they agree or disagree with a statement like this — purposely rather than controversial. P[lease] return for typing. N.F. Mott

178

The letter was received on 6.1.1948.

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[442] Nevill Mott to Rudolf Peierls Bristol, 2.2.1948 Dear Peierls, Thank you for sending me your MS.179 As you know, though I agree with your diagnosis, I do not agree with your conclusions. I do, of course, agree with what you say about the wet behaviour of German University Professors during the war. Also that I can’t imagine British Universities behaving in the same way. The question is, what to do about it? I believe your solution impossible. One cannot dig up the political past of each man whom one might invite to come here. I tried over Justi,180 to whom Simon had strong objections. I could not ﬁnd anyone else in Holland or England who knew Justi (I don’t mean I wrote more than a dozen letters). What I did get was a lot of opinions, favourable as unfavourable, on Simon’s judgements in such matters. The whole thing made me rather sick. I shall not do it again. Have you read last week’s leading article in the Economist? I very much agree with it. We ought now to give the Germans full authority again over their own economic and cultural aﬀairs. To attempt to reeducate them through Military Government will probably have the opposite eﬀect to what we intend. Then, as regards to our scientiﬁc contacts, I think they should be based on scientiﬁc achievement, and be coupled with normal friendliness. What you ask, (though your case looks strong in this instance) is that the scientiﬁc invitations should be aﬀected by political judgements. It seems to me simply untrue that we as a body, can choose “decent” Germans (or decent Americans, those who have stood up to the Committee of Unamerican activities???) because noone will agree on who is “decent”. Your proposal opens the door to such questions as “is he anti-nazi?’; “Is he anti-Soviet?”; “Is he pro or anti-Marshall · · · ?”, and I would not like to see this enter our scientiﬁc relations. 179

Item [440]. Eduard Justi (1904–1986), German electrochemist who had been working on fuel cells at the University of Braunschweig. He later became professor of low-temperature physics at Braunschweig (1946–74). 180

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Well, like the question of whether or not we should make atomic bombs, these are emotional and ethical judgements. I don’t expect to convince you; your experience is diﬀerent from mine and, of course, you’ll have diﬀerent ideas on what is of ﬁrst importance. Yours ever, N.F.M

[443] Rudolf Peierls to Nevill Mott [Birmingham], 6.2.1948 (carbon copy) Dear Mott, As you say,181 the problem of German scientists is one on which we shall have to agree to diﬀer, but I would like to comment on one or two points in your letter. I quite agree, of course, and I have experienced myself, the diﬃculty of ﬁnding out something about the lesser known people, but the point is the importance of the cases of the prominent people whose record is known to everybody in Germany, since what matters i[s] the eﬀect on German people. I also agree that there will never be unanimity on the merits of one particular person, but what I am asking is not that we should agree, but that each of us should form judgement, not of course about anybody’s political views but on his personal integrity which is a rather diﬀerent story. If any scientists in this country had been convicted of robbing a bank or fraudulent bankruptcy, we would still listen to his lectures or read his papers, but if an occasion arose to ask him to dinner or shake his hand on a social occasion, we should want to know what we personally felt about his record. To quote a relevant example, if we will have an occasion again to meet Nunn-May, no doubt, people’s reactions will diﬀer to what their 181

Peierls refers to letter [442].

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personal relations to him should be, some will decide that their behaviour will not be inﬂuenced by his actions, others will have nothing to do with him, but this is quite apart from what we think about his political views. All of us will wish to do what we can to see that he is enabled to carry on scientiﬁc work in the most favourable circumstances. All I am asking for is the things that people in Germany did or failed to do, be considered as important as robbing a bank or violating the Oﬃcial Secrets Act. There is a lot in what you say in letting Germans run their own aﬀairs, but this would have been a lot more convincing if it had been done from the beginning. This would have led to a good deal of unpleasantness, possibly even a good deal of bloodshed, but after having intervened to restore order and to back the “respectable” people, the occupation authorities have accepted the responsibility which they cannot suddenly drop. If my article gets published, I hope this will start some correspondence including letters from people holding views like yours and the result of that will be to help people appreciate the issues and make up their minds one way or another. Yours sincerely, R.E. Peierls

[444] Rudolf Peierls to Niels Bohr Birmingham, 6.2.1948 (carbon copy) Dear Uncle Nick, I should probably have written before to say that I had a brief opportunity while I was in America182 to discuss the draft of our paper 182 Rudolf Peierls had been to the US for a conference, and on that occasion met George Placzek with whom he discussed the Bohr-Peierls-Placzek paper. Peierls appears to have left a copy of the draft with Placzek who commented on it and passed the revised manuscript on to Bohr, when the latter came to Princeton in May 1948. See R. Peierls, ‘Introduction’, Bohr: Collected Works, Vol. 9, p. 51.

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with Placzek. Placzek raised a number of small points that might want amending, but it seemed to us that all these could be taken care of by alterations of a few words, they could well wait until we knew your reaction to the main outline. It has occurred to me that one of these points might be causing you diﬃculty and that it might save you trouble to draw your attention to it. It concerns the derivation of the Breit-Wigner formula. The derivation which I have sketched is valid only for the part of the resonance curve for which the kinetic energy of the emerging neutron (or other particle) diﬀers only by a small fraction from its value at resonance. It does not cover either cases in which the width of the resonance level is comparable to the kinetic energy of the neutron at resonance or the cross section for thermal neutrons (1/ν law). We tried to see whether it was easy to generalise the derivation so as to cover these cases as well, but we felt that this was not possible without spoiling the transparency of the argument, but that it was preferable, therefore, to leave the derivation as it stands and merely to make clear to which category of problem it is applicable. Since the purpose of the paper is mainly to deal with high energies, it would be quite reasonable to use an argument which is not appropriate for very low velocities. I am afraid that local arrangements made it necessary to make a decision on our plans for the summer about which I wrote to you before, and we have decided to go ahead with a conference here in the week starting 20th September.183 This will be a joint aﬀair of the Physics and Mathematical Physics Departments. I very much hope that in doing so, we are not clashing too badly with any plans you have in mind. With very best wishes to all friends in Copenhagen, Yours sincerely, R.E. Peierls

183

While Rudolf Peierls was at Birmingham, he co-organised two major international conferences, one in 1948 and one in 1953. See Peierls, Bird of Passage, pp. 261–2.

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[445] Rudolf Peierls to Werner Heisenberg [Birmingham], 11.2.1948 (carbon copy) Dear Professor Heisenberg, I hear that you are spending some time in this country and I would be very glad if it were possible to visit Birmingham and talk to our Seminar. I have a group of about 15 people, most of whom are working on ﬁeld theory and other fundamental problems and of whom all have heard a good deal of fundamental theory so that they will appreciate a talk on a rather advanced level. They would also be interested to hear about superconductivity, though they are much less familiar with the background there and one could not assume too much to be known. Our seminar normally meets on Thursday afternoons, but if necessary it would be easy to arrange a meeting on another day. In any case, you would have to spend at least one night in Birmingham and if you can manage it, it would be even better if you could stay for several days so that there would be more opportunity for full discussion of any problems you care to tell us about and also of the work we are trying to do here. I have lately thought a good deal about the problems arising from the relations of scientists here and in other countries with those in Germany, and you may be interested to see what my views are from the enclosed copy of an article that I hope to get published.184 I feel that while these problems are not easy to discuss, it is important that they be faced frankly and I hope that during your visit there would be an opportunity to have a frank talk about these things. It may well be that you will not agree with me on these matters, but that is no reason why we should not, in any case, get together over physics. Please let me know whether it would be possible for you to come and what would be a good time. The coming week would not be convenient for us, but from 24th February almost any day would be possible. If 184

Item [440].

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you will let me know how long you are able to stay, I can make sure accommodation is arranged for you. Yours sincerely, R.E. Peierls

[446] Hans Bethe to Rudolf Peierls [Ithaca], 12.2.1948 Dear Rudy: Thanks for your letter of February 5.185 There seems to be quite a mess about paying the fares for the Solvay Conference.186 I saw Blackett for a few minutes and he told me he would talk to the U.S. Navy. At that time he did not seem to want any help, but if he does I shall of course stand by. Bragg wrote me recently that “he was sure they could arrange to pay for my fare.” I am not sure how much that means, but I shall wait for developments. I am sorry I will be very much in a rush around the Solvay Conference because it is in the midst of our term. Moreover, I am still planning to come over for a more leisurely visit this summer. So I would rather not visit you in connection with the Solvay Conference, unless it just happens that my return plane is delayed. It seems that our summer trip will also be made by plane so that we shall arrive quite early in June. My plans are to spend the time from then until July 15 visiting various places in England, except for about two weeks that I want to spend with my parents-in-law. That can easily be arranged at my convenience. When will it be best to come to 185 Letter Rudolf Peierls to Hans Bethe, 5.2.1948, Peierls Papers, Ms.Eng.misc.b2102, C.16. 186 The 8th Solvay Conference was to take place in October 1948. From the ofﬁcial photograph it appears that Bethe did not take part in the conference after all.

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you and to go to other places in England? Will you have a conference during this time? This might be a great advantage to me because it would probably facilitate getting my trip paid. Skyrme187 is of course most welcome. The only boundary condition is that I will be in Columbia the ﬁrst semester next year and at Cornell the second. I do not think that the Commonwealth people and Skyrme will mind this. Yours sincerely, Hans [447] Werner Heisenberg to Rudolf Peierls Cambridge, 17.2.1948 Lieber Peierls! Haben Sie vielen Dank f¨ ur Ihren Brief. Ich komme gerne nach Birmingham, und ich kann ja vor Ihrem Seminar u ¨ber das wenige sprechen, was ich von der Theorie der Elementarteilchen zu wissen glaube. Ich danke Ihnen auch sehr daf¨ ur, dass Sie mir oﬀen Ihre Meinung u ¨ber ein schwieriges politisches Problem geschrieben haben.188 Es ist so, wie Sie vermuten: ich bin nicht mir Ihnen einverstanden. Aber die Tatsache, dass Sie mir so oﬀen geschrieben haben, gibt mir Hoﬀnung, dass wir in einem Gespr¨ ach wenn auch nicht zu einer Angleichung der Standpunkte so doch zu einem Verst¨ andnis des anderen Standpunktes kommen k¨onnen. Zur Frage des Zeitpunktes: Vom 10.–12. M¨ arz bin ich bei Blackett; ich k¨ onnte am 12. nach B[irmingham] kommen und bis zum Abend des 13. bleiben. Eventuell auch 8. und 9. M¨ arz, wenn aus dem geplanten Besuch in Oxford nichts wird. W¨ urde Ihnen das passen? Also auf gutes Wiedersehen, Ihr Werner Heisenberg 187

Tony Skyrme, at the time university research fellow at Birmingham, spent the academic years 1948–50 in the United States, as research associate at M.I.T. and as a member of the Institute of Advanced Study at Princeton. 188 Peierls had sent Heisenberg a copy of his memorandum [440].

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[448] Rudolf Peierls to Hans Bethe [Birmingham], 3.3.1948 (carbon copy) Dear Hans, Thank you for your letter of 13th February.189 I have now at last my Solvay report ﬁnished and, while you will receive a copy through oﬃcial channels, I thought I had better let you have one as soon as possible for your information. In most English universities term ﬁnishes about 1st July, in Birmingham in particular is ﬁnishes with the Degree Ceremony on the 3rd. Between the 24th and 29th of June are our examiners’ meetings when there is one or sometimes two meetings almost every day. I am hoping to go on a holiday about the middle of July, so that the best time to see you here would be either before 22nd June or between 30th June and about 12th July. I shall be away for three weeks and then again here from early August, though naturally, of course, during August other members of my department may be away at various times. Lastly, we shall have a conference here from the 14th to 18th September. I hope this is not too late for you. It will this time be a bigger aﬀair covering experimental as well as theoretical problems, but we hope nevertheless to preserve the informal character of our last conference, at any rate in the theoretical meetings. You will receive an oﬃcial invitation to that conference in a day or two. Yours sincerely, [Rudi]

189

Refers to letter [446].

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[449] Robert Serber to Rudolf Peierls Berkeley, 4.3.1948 Dear Rudolph: The experimental facts about the np scattering are about as follows: Good measurements have been made, under Segre’s direction, using triple coincidence counters to detect the protons. These have been carried from 5◦ to 50◦ (perhaps 55◦ ) in the lab system. The average neutron energy is 90 Mev. The cross section in the center of mass system looks like

There is evidence from the counter work that the curve rises again on the left. However, the conclusion about the symmetry comes principally from the work of Powell, who scatters the neutrons in a hydrogen ﬁlled cloud chamber. While the statistics of the cloud chamber results are not very good yet, they are in good agreement with the counter data for cos θ > 1, and are symmetric. I didn’t quite say that this is support for strong coupling (in fact Dancoﬀ and I are on record in the Physical Review as saying that strong coupling theories can’t account for nuclear forces).190 What I said was that the easiest way of describing what symmetrical scattering means is to say that after the collision, the neutron forgets whether it started as a neutron or as a proton. This would be natural with strong coupling; and, although weak coupling theories may be ﬁxed up to give the same result, it would involve apparently arbitrary and accidental choices of coupling parameters. 190

R. Serber and S.M. Dancoﬀ, ‘Strong Coupling Mesotron Theory of Nuclear Forces’, Phys. Rev. 63, 143–61 (1943).

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I doubt if a symmetric theory will turn out to ﬁt the facts. At 90 Mev the Born approximation is not very bad, and although the double scattering eﬀects are then all right, and quite visible to the naked eye, they are not big enough to do much symmetricising. This isn’t by any means conclusive — the errors in the cloud chamber work are still too big to say that the symmetry of the scattering is really established.191 I would be interested in hearing of your new method of calculating. We have fooled around with variation methods, but ﬁnally decided the easiest and quickest way was to use a partial wave analysis, and determine phase shifts by WKB approximation. The WKB method gives remarkably good wave functions, and, if better accuracy is wanted, a single iteration of the WKB solutions in the integral equation for the wave function gives a better result than we ever need. Also, it is just as easy to get the WKB solutions including tensor forces. Assuming that the scattering is symmetric, we can get a pretty good description of the facts by taking a simple Yukawa potential with a range of 1.2 × 10−13 as determined by Breit from the p − p scattering. This gives σ(0◦ )/σ(90◦ ) = 3, in agreement with experiment, and a total cross section of 0.087 barns, compared to McMillan’s 0.084 ± .003. However, if tensor forces are included, it is a real strain to get a big enough quadripole moment with such a short range force. Perhaps it is not possible at all, but we quickly found out that the tensor force would have to be so large that the calculated ratio σ(0◦ )/σ(90◦ ) = 3 would be reduced greatly. So we are now engaged in seeing if with a larger range we can ﬁt the data. The n − p scattering has been crowded into the background at the moment. Perhaps you have already heard that Lattes and Gardner192 have found mesons made in the cyclotron. The experimental arrange191

Serber had recently published on the subject R. Serber, ‘Nuclear Reactions at High Energies’, Phys. Rev. 72, 1114–1115 (1947). Another important contribution was his paper, together with Fernbach and Taylor published in the following year; S. Fernbach, R. Serber and T.B. Taylor, ‘The Scattering of High Energy Neutrons by Nuclei’, Phys. Rev. 75, 1352–55 (1949). 192 J. Burfening, Eugene Gardner and C.M.G. Lattes, ‘Positive Mesons Produced by the 184-Inch Berkeley Cyclotron’, Phys. Rev. 75, 382–87 (1949).

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ment is like this:

This all takes place inside the vacuum chamber of the cyclotron, and the magnetic ﬁeld focuses negative mesons on the plates. This density on the plates is about 108 what one can get in cosmic rays. Most of them are seen to end in stars, and probably all do. Their mass, determined by Hρ and range measurements on 50 tracks, is 313 ± 16. This is all the information we have at the moment, but we look forward to a busy future. Needless to say, I would be delighted to hear any ideas you may have concerning either scattering or the mesons. With best regards, Robert Serber [450] Werner Heisenberg to Rudolf Peierls Cambridge, 4.3.1948 Lieber Peierls! Leider haben sich meine Pl¨ane wieder etwas ¨andern m¨ ussen, da ich aller Wahrscheinlichkeit am Freitag, d[em] 12. abends in London sein muss. K¨ onnten Sie eventuell, wenn ich nicht nach B[irmingham] kommen kann, — etwa f¨ ur Donnerstag — nach Manchester kommen? Ich w¨ urde Sie wirklich gerne wieder sprechen. Vielleicht k¨ onnte ich auch Samstag fr¨ uh noch nach B[irmingham] fahren. Jedenfalls will ich versuchen, Sie am Mittwoch abend oder Donnerstag fr¨ uh in B[irmingham] anzurufen. Bis dahin weiss ich genau, was meine Verpﬂichtungen sind. Hoﬀentlich auf gutes Wiedersehen! Ihr W. Heisenberg

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[451] Hans Bethe to Rudolf Peierls Ithaca, 18.3.1948 Dear Rudy: I suppose the enclosed letter to Bragg is self-explanatory.193 I should really like very much to be back in time. This of course also applies to your conference. In view of the new date for the Solvay Conference, I wonder whether your Theoretical Conference would not be more convenient in June or early July. I do not know whether that is possible. If not, could it be early in September? Otherwise the program outlined in your letter suits me very well. I intended to be in Switzerland and possibly Germany from the middle of July to the end of August which overlaps with the time you intend to be absent from Birmingham. I shall probably come to see you in the beginning of July but maybe I shall stop for a day or two in early June. Yours sincerely, Hans Thanks a lot for your Solvay report!

[452] Rudolf Peierls to Hans Bethe [Birmingham], 23.3.1948 (carbon copy) Dear Hans, Thank you for your letter.194 I am very sorry that the date of our meeting is too late for you. Unfortunately, it is impossible to change it 193

Letter Hans Bethe to W.L. Bragg, 18.3.1948 asking Bragg to take into account the American academic calendar when rescheduling the Solvay Conference. Carbon copy in Peierls Papers, Mc.Eng.misc.b202, C.16. 194 Letter [451].

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now since the invitations have gone out, the accommodation has been booked (this is very short as you may imagine) and particularly as there are a number of other events in September. It begins with a[n] International Conference on Applied Mathematics and Mechanics from 6th–11th September which will overlap to a slight degree in membership with ours. There are also likely to be some business meetings involving a number of our people as well as possible foreign visitors during the later half of that same week. In the week following our conference is the Cosmic Ray Conference at Bristol which was the ﬁrst one to get ﬁxed and, in fact, our date was partly chosen to enable the overseas visitors to attend both conferences. Following that, of course, is the Solvay. I am surprised at what you say about the starting date of the American universities since last year the majority of visitors seemed to remain in Europe until the end of the Copenhagen Conference in the very last days of September. I very much hope you will be able to delay your return to take in our conference at least, if not Bristol and the Solvay. I understand the meeting sponsored by the American Emergency Committee of Atomic Scientists will now not be held in Jamaica, but in the United States. I have said that I accept in principle, but if the date remains in June I shall probably not get away in time. I would be grateful to have your views as to whether this meeting is likely to serve a useful purpose and whether it would be worth the eﬀort to go there, particularly if it means missing important University meetings. With kindest regards, Yours sincerely [Rudi] [453] Hans Bethe to Rudolf Peierls Ithaca, 7.4.1948 Dear Rudy: Thanks for your letter of March 23.195 I am rather sad that the conference cannot be moved. The starting of American Universities has 195

Letter [452].

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always been around September 20. The trouble was only that Uncle Nick has always disregarded university schedules and chosen the dates for his Copenhagen Conference at random. Some visitors, like Vicky, were too anxious to go to the grand reopening of the Copenhagen meetings196 last year and therefore did not return in spite of the semester. (I appreciate that the Bristol meeting was the ﬁrst to get ﬁxed and I protested immediately to Powell about his date, but without success.) I have pretty much decided to go to your conference but none of the later ones. I hope that I will hear everything in Birmingham then and earlier in the summer. The meeting sponsored by the American Emergency Committee197 is not likely to serve a useful purpose. It was Szilard’s idea to have such a meeting to bring together scientists from all countries east and west of the iron curtain. Those from the east of the curtain have already refused to attend, as was to be expected. In the present situation, it is my opinion, that nothing useful can be done from the side of atomic energy or of scientists in general and that any stress on atomic energy can only deepen the international conﬂict. I was very much against holding this conference and this opinion is shared by other people such as Oppenheimer and Weisskopf. By the way, I resigned from the Emergency Committee, not because of the conference but because of my conviction of the futility of these endeavors at the present time. I have also heard some rumors that the Federation of American Scientists is giving up the idea of the International Conference. This seems sensible to me, but of course the Emer196

The conference had attracted a large number of physicists who spent some time in Copenhagen during the last two weeks of September 1947. Among them were Kramers, Weisskopf, Pais, Rosenfeld, Peierls, Blackett, Placzek, Wheeler, Rossi, Ferretti, Klein. See letter Wolfgang Pauli to Otto Stern, 19.8.1947, K.V. Meyenn (ed.), Wolfgang Pauli. Wissenschaftlicher Briefwechsel mit Bohr, Einstein, Heisenberg u.a., Vol. 3: 1940–1949, Heidelberg: Springer, 1993 (hereinafter cited as Pauli, Wissenschaftlicher Briefwechsel, with volume number), p. 471. 197 See letter [452].

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gency Committee is an independent agency. Anyway, I would much rather talk physics with you than have you go to that conference. Thanks very much for the parliamentary debates of the House of Lords.198 I am of course very proud. Yours sincerely Hans

[454] Robert Oppenheimer to Rudolf Peierls and Mark Oliphant [Princeton], 8.4.1948 Dear Peierls and Oliphant: Thank you both for your good notes of invitation to the Birmingham Conference. I am sending in an acceptance which I only hope will correspond to reality when the time comes. I want very much to visit with you and talk over the many wonderful developments in physics, as well as other problems with which we have had a common concern in the past. You ask for other suggestions for invitees to the conference. There are two who have carried out essentially parallel and very beautiful developments in quantum electrodynamics, Julian Schwinger at Harvard and Sin-itiro Tomonaga in Japan. It would surely be a great addition to the conference if they could both come. I hope that there is nothing improper in my accepting an invitation in which it is inevitable that there be a little uncertainty as to my plans. With all warmest greetings, Robert Oppenheimer

198

Almost certainly this refers to the parliamentary debate on the perils of atomic warfare launched by the Archbishop of York, 18 February 1948, Hansard, HoL, Vol. 153, cols 1178–1213.

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[455] Rudolf Peierls to Robert Oppenheimer Birmingham, 15.4.1948 Dear Oppie, Thank you for your letter.199 We are delighted that there is at least a chance of seeing you here, and it is, of course, quite in order to accept provisionally: we only hope you will be able to keep to it. We had already invited Schwinger. As regards Sin-itiro Tomonaga, we do not know anything about him directly, but would be very glad to have him on your recommendation, if the administrative side of it could be managed. Presumably he could not be brought here without some help from the U.S. authorities in Japan, and I imagine you know better than we do whether, and how, they can be approached. I accordingly enclose an invitation for this purpose and we would be very grateful to you if you could have it passed along the right channel, or alternatively suggest to us the right “ansatz”. With best wishes, Yours sincerely, R.E. Peierls

[456] Rudolf Peierls to Robert Serber [Birmingham], 17.4.1948 (carbon copy) Dear Bob, Thank you very much for your letter of 4th March.200 I quite agree with you that the new discoveries about artiﬁcial mesons are much more exciting than n–p scattering, still, it seems worth continuing the discussion on n–p scattering. I enclose a curve giving the results of 199 200

Letter [454]. Letter [449].

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calculations by Barker201 here and a copy of a note to Nature202 explaining the calculations. The method of Ferretti and Krook which he used and which is being published in the May number of the Proceedings of the Physical Society203 goes as follows: We need to determine the logarithmic derivative at some point r = a beyond the range of the forces. Supposing we start with the right value of [. . . ]204 we will get a solution which is regular at the origin, otherwise the solution is singular at the origin. Consider the Taylor series for [. . . ]205 at a. For the general solution which is singular at the origin the radius of convergence of this Taylor series can at most be a and usually is just a. For the regular solution it is larger. If I consider, therefore, the ratio between two successive Taylor coeﬃcients, it should converge to a much lower value if the parameter [. . . ]206 is chosen in the right way. The approximation now consists in applying this criterion not to the limit, but to a Taylor coeﬃcient of ﬁnite order. It is found in practice that for a sensible choice of a, something like the 10th coeﬃcient will give a very good accuracy and the determination of these coeﬃcients is very rapid, provided the potential function is such that the required successive diﬀerentiations do not give too much trouble. The method is also applicable to tensor forces and Barker is now engaged in a discussion of this problem using something like the Schwinger theory. I am a little puzzled by your statement that at 90 Mev the Born Approximation would give only backward scattering, whereas the more likely case B of Barker’s, the forward and backward intensities for exchange forces diﬀer only by a factor three. Qualitatively Barker’s curves are very similar to those published by Bethe, but we were reluctant to 201

See also F.C. Barker and R.E. Peierls, ‘On the Deﬁnition of the “Eﬀective Range” of Nuclear Forces’, Phys. Rev. 75, 312–13 (1949). 202 F.C. Barker and D.G. Ravenhall, ‘Scattering of like particles at 100 MeV’, Nature 163, 20 (1949). 203 B. Ferretti and M. Krook, ‘On the Solution of Scattering and Related Problems’, Proc. Phys. Soc. 60, 481–90 (1949). 204 Missing in carbon copy. Details of the calculation found in the above paper, note 203. 205 Missing in carbon copy. 206 Missing in carbon copy.

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use the square well, since at short wave lengths the sharp boundaries are liable to give spurious eﬀects. However, we need not have worried apparently, since it looks as if the wave length is not as yet very short. As far as I can see from your account of the experiments, the statement that the curve is symmetrical rests entirely on the cloud chamber data, and it would seem a little premature to draw conclusions until one knows with what accuracy symmetry is really established. With kindest regards, Yours sincerely, R.E. Peierls

[457] Rudolf Peierls to Hans Bethe [Birmingham], 6.5.1948 (carbon copy) Dear Hans, You may be interested in the enclosed note which we have sent to Nature. The results bear out qualitatively what you have found independently with a square well. We were afraid of a square well, since at very short wavelength the sharp edges of the well are liable to give serious interference eﬀects. We started, of course, like most people with the idea that 100 MeV is a high energy. The results show that it isn’t, and so probably the square well is as good as anything else. It is, however, desirable that at these energies the results are insensitive to the nature of the forces, no doubt this would change at still higher energies, but even if these could be attained, they will be very much harder to interpret because of relativistic eﬀects and the like. What is more pleasing is the rapidity with which it is possible to calculate phases by a method of Ferretti and Krook.207

207

See letter [456], note 203.

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The trick is as follows: You choose a point r = 2 beyond the range of the forces and you imagine that you integrate the equations inwards from this point. In general, i.e. choosing the wrong slope, the answer will be singular at the origin and its Taylor series about a will have a radius of convergence at most equal to a. For the correct slope the radius of convergence will be larger and may even be inﬁnite. Accordingly you can get the correct slope by imposing the condition that the Taylor series should converge as well as possible. As an approximation you make the nth term in these series as small as possible, i.e. equal to zero, and for quite reasonable n this gives a good approximation of the slope and hence to the phase. Since in this operation only successive diﬀerentiations are required, it is quite easy to go to, say n = 10 without much trouble if your potential is of a reasonably simple analytical form. The method works amazingly well and can be generalised to tensor forces. We are getting rather excited about the self-energy problem. You remember Salpeter here having a proof for the one-body problem that the self-energy is calculated exactly and without perturbation theory and was really inﬁnite.208 In trying to generalise this to the case of hole theory, he struck some snags, however, and there seems now the possibility that the statement is not in fact true in hole theory, but that the logarithmic inﬁnity disappears if one calculates exactly. We are very far from having proved this, but the mere possibility is, of course, very important. Another point that agitates me is the self-energy of the photon. In the ordinary way this, of course, is again inﬁnite and one would expect with the usual tricks or, for example, with the kind of modiﬁcation that McManus or Feynman are playing with,209 to make it ﬁnite. However, the rest mass of the photon is not merely ﬁnite, it must be very exactly zero, and the only way to get this in any of these theories is to assume a ﬁnite mechanical rest mass for the photon which would then exactly 208 Ed Salpeter (1924–) was completing his Ph.D. at Birmingham in 1948. After a brief period he went to Cornell to work with Hans Bethe where, apart from brief research spells elsewhere he stayed for the remainder of his career. 209 R.P.Feynman, ‘Relativistic Cut-Oﬀ for Quantum Electrodynamics’, Phys. Rev. 74, 1430–38 (1948).

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cancel the ﬁnite (negative) dynamic mass. This is rather interesting formally and it means, amongst other things, that perturbation theory applied to this must always give utter nonsense since you can never get a ﬁnite rest mass to rest mass zero by a small perturbation. See you in June. Yours sincerely, [Rudi]

[458] Max Born to Rudolf Peierls Edinburgh, 22.5.1948 Dear Peierls, There are two things I would like to have your opinion about. The ﬁrst is this: I got to-day an information from the R[oyal] S[ociety] about the recommendations of names for election of Foreign Members. Apart from Cripps, and two names unknown to me, there are Browser and Pauling. But not Schr¨ odinger. Dirac and I have tried for years to bring him into the R[oyal] S[ociety] The main obstacle is the letter he wrote in Graz, in which he expressed his agreement with the Nazis (or something like that; part of it was, I think, published in “Nature”).210 On account of this silly document a group of people have prohibited his election. The formal diﬃculty is that he is not British; hence he cannot be an ordinary Fellow. And as he lives in Eire which is regarded as part of the British Empire, he cannot be a Foreign Member. Now the latter obstacle has been removed, as far as I know, by a special decision of the Council. When I heard that Heitler was to be elected I wrote some strong letters to members of the Sectional Committee, saying that it would be an aﬀront to Schr[¨ odinger], if H[eitler] would be in the Society and he not. Actually I have a very high opinion of H[eitler], but still I think Schr[¨ odinger] is of a higher order of magnitude. There is hardly any paper in theoretical physics in the world where not 210

See Letter [273], note 1029 in Lee, Selected Correspondence, Vol. 1, Chapter 5.

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the Schr[¨ odinger] equation is used. He has actually revolutionised our science. That he was not very lucky in recent years seems to me of less importance. Planck has also not done any fundamental work after 1900. Therefore I feel rather strongly in this matter. I should like to know what you think. It is a great pity that Dirac is not here; I think I could agree with him on some drastic action. But now I do not know what to do. I am quite aware of Schr[¨ odinger]’s shortcomings and of the enmity he has accumulated through his own behaviour. But I think that all this ought not to matter in the question of election to a purely scientiﬁc society. The other point is Palestine. I am not a Zionist, not even a Jew by religion. I tried always to be as impartial as possible, on account of my ignorance of the facts. It appeared to me from the newspapers that Britain played a nasty game, arming and training the Arabs and then retiring, to leave the dirty work to the sons of the desert. But I had not proof that this is really so. To-day Manchester Guardian has a leader conﬁrming my worst fears. I think nobody can doubt any more that this is really Bevin’s politics. I think it is almost worse than Hitler, sit still and watch quietly this second mass murder arranged by our own Government? I am a member of the Labour Party — can one stay in it? Should we — you, Polany, Goldstein, I and as many others, as we can get — not publish some protest? I shall write to Einstein for advice. But let me know what you think, or better feel, and also your wife’s opinion. From the Department I could tell you some interesting things, but I am not in the mood for it. With kind regards, Yours ever, M. Born

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[459] Rudolf Peierls to Max Born [Birmingham], 24.5.1948211 (carbon copy) Dear Born, odinger, there is no doubt Thank you for your letter.212 As regards Schr¨ whatever about his merits as a scientist and surely no member of the Royal Society can have any doubt that he is much better than practically all Fellows and Foreign Members recently elected. This issue is, however, whether scientiﬁc distinction is the only factor taken into account in the election. As regards election of Fellows that is perhaps the case. The rule is, however, that he is not eligible to be a Fellow and for the election for a foreign member it is probably true that the personal record has also to be weighed. Election of a foreign member has some of the characteristics of conferring an Honorary Degree when personal factors undoubtedly play a legitimate part. I have understood the decision of the Council to mean that they take this view. On grounds of personal record I think there is a very strong case against Schr¨ odinger. The famous Graz letter is only one example, but it is bad enough. To describe it just as ,,silly” is minimising this too much. Our distress at events in Germany was so bitter just because there were so many people who failed to understand the importance of personal integrity and the disastrous eﬀect of men with a worldwide reputation saying what they knew to be wrong for the sake of expediency. It is true that most of us would say or sign such things under strong pressure or in acute danger. We would, however, expect to pay for it and we would disassociate ourselves from such statements as soon as the danger was passed. Schr¨ odinger has never troubled to do so. About other facts my opinion is only based on hearsay, but it adds up to a consistent 211

Two drafts of letters dated 24.5.1948 exist and a further draft dated 29.5.1948, which is the one likely to have been sent. The second draft dated 24.5.1948 is reproduced here to demonstrate the development of Peierls’ thinking on the two issues about which Born had enquired. 212 Letter [458].

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impression of irresponsible behaviour. At a time when scientists are in the public eye and when their word counts, there is a particularly strong duty to apply severe standards. The only case you could make out is to claim that the election of a foreign member should be based on scientiﬁc merit alone, but if this is done, it must be done consistently. Would you take the same view if Heisenberg’s name were proposed? Or in the hypothetical case that Weizs¨ acker had done work of comparable importance, would you take the same line in his case? On the other matter I agree with you in being distressed over the recent events. I also agree that it is foolish for this country not to recognize the new state. This, however, is only foolish and short-sighted. I do not believe it is particularly immoral. The moral question has been confused ever since, in a spirit of wishful thinking, promises were made to both Arabs and Jews which at least in the interpretation given to the words by each side were outright contradictory. I think it is a tragedy that this whole Palestine adventure was ever started. The numbers that can be accommodated there are pitifully small to make any diﬀerence to the wider problem and the trouble arising from it will only make more diﬃcult the problem of settling homeless Jews elsewhere and of creating a tolerable situation for others in the places where they are now living. I believe that nationalism is always bad and Jewish nationalism is no exception. This does not diminish the distress one feels about the violence which is abundant there now and which, as always, must hit harmless people. I do not think, however, one has any right to protest in public, unless one also protested at the violence from Jewish terrorists when this was hitting harmless civilians on the other side. What one can argue about is expediency in the long run. I do not believe that your opinion or mine on this point will be particularly welcome, but I believe that political pressure from America which is undoubtedly being exerted is much more likely to change the position. If you hear from Einstein it would, of course, be interesting to know his views, but one should not follow his example which is to give his

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name to any cause for which it is requested regardless of whether or not he has any knowledge of the case and thereby achieving a position where nobody takes any notice of his signature under any appeal. Yours sincerely, R.E. Peierls

[460] Rudolf Peierls to Max Born [Birmingham], 29.5.1948 (carbon copy) Dear Born, Thank you for your letter.213 I am sorry it has taken me so long to reply, but I have been away from Birmingham for several days. As regards Schr¨ odinger, there is, of course, no doubt whatever about his merits as a scientist, and surely no member of the R[oyal] S[ociety] Council can have any doubt that he is much more eminent than practically any Fellow or Foreign Member recently elected. The issue is, however, whether scientiﬁc distinction is the only factor to be taken into account in the election. As regards Fellows that is perhaps the case. Schr¨odinger, however, does not appear to be eligible as a Fellow and election of a Foreign Member is a rather diﬀerent story. It is in many ways analogous to conferring an honorary degree, where the personal record is most certainly taken into account. I have understood the decision of the Royal Society to mean that this is their interpretation. On grounds of personal record I think there is a very strong case against Schr¨ odinger. The famous Graz letter is only one example, but it is bad enough. I would not pass it over by just describing it as ,,silly”. Our distress at events in Germany surely was so bitter just because there were so many people who failed to understand the seriousness of the issues, and the importance of personal integrity. If a man with a worldwide reputation says what he knows not to be true for reasons of 213

Letter [458].

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expediency, it is not merely silly. Admittedly most of us would say or sign such things under strong pressure or in acute danger. But we would expect to pay for it, and in any event would presumably disassociate ourselves from what we said as soon as it was safe to do so. To my knowledge, Schr¨ odinger has never troubled to explain this letter was written under pressure. (As far as I know it was not very severe pressure at that). About other similar things I only know from hearsay, such as his retaining his name on the books of the German Legation in Dublin practically as long as such Legation existed. It all adds up to a consistent impression of irresponsibility. At a time when scientists are so much in the public eye and when their words count more than ever, standards of behaviour must be particularly severe. The only case you could make would be to claim that the election of Foreign Members should be based exclusively on scientiﬁc standing. But this would have to be applied consistently. Would you take the same view if Heisenberg’s name were proposed? Or in the hypothetical case that Weizs¨acker had done work of comparable importance, would you take the same line in his case? On the question of Palestine, I agree with you in feeling acute distress. Of course, Britain ought to recognize the new state. Their not doing so is short-sighted and foolish, but not particularly wicked. The moral question is incredibly confused and has been confused ever since promises were made both to the Zionists and to the Arabs which, at least in the sense in which each side understood them, were outright contradictory. I have no particular liking for the Arabs, but one must admit that there is considerable justiﬁcation in their claims. True the Arabs are backward. In the view of the Americans, England is a backward country, too, but noone would admit that this entitles the Americans to take over the country and run it. True also the Arab population is not dense enough to work the land eﬃciently (at least I imagine it is true) but their refusal to allow others to come in is as justiﬁed as the refusal of the British agricultural labourers to allow foreigners to work on the land, even with the present shortage of labour. True, Palestine was a Jewish country in Biblical times; but you cannot reverse history, and hand over America to the Red Indians, or the French, or England to the Celts (if you can ﬁnd enough).

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With all this I do not mean to say that the Arabs are right and the Zionists wrong, but merely that the question is confused and that we have here one of those situations in which each side genuinely had the conviction of being in the right, and where nobody can prove them wrong. This could, of course, have been the perfect situation for UNO to prove its worth. I believe, however, that the utter failure of UNO (which may ﬁnish it in the same sense in which Manchuria ﬁnished the League of Nations) cannot be blamed on the British Government, it is due to quite irresponsible behaviour on the part of America. I believe it is a pity that this Palestine adventure was ever started. The numbers that can be settled there are pitifully small compared to the number of displaced Jews. The trouble arising over Palestine is bound to make more diﬃcult the problem of ﬁnding acceptance for the Jews in countries capable of taking large numbers, or creating tolerable conditions for them in the countries in which they live now. Nationalism is bad anywhere, and Jewish nationalism is no exception. All this, of course, is not the fault of the unfortunate victims who are suﬀering now in Palestine. Unfortunately, things have gone so far that there is bound to be suﬀering and violence in Palestine whatever is done. If the British Army moved in again to take over the country and restore order, the violence from terrorists on both sides would not be less severe than the present war. We tend to overestimate the scale of this war, for example a recent statement that a hundred Jews were killed in Jerusalem since the beginning of the ﬁghting shows that the matter is serious but has hardly reached the scale of warfarer. I am sure the government are genuinely anxious to ﬁnd a solution that would avoid further violence. They probably believe that to recognize the new state, and to withdraw support from the Arab state would cause perhaps fewer victims amongst the Jews but more among the Arabs. Much as our sympathy may be on the side of the Jews, can we really insist that it makes any diﬀerence whether men, women and children are killed who speak one language or another? It might make quite the wrong impression if we made public our indignation at attacks on Jewish civilians by the Arab armies, unless we have previously protested against attacks on Arab civilians by Jewish terrorists.

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In the end the problem boils down to expediency, and of what would actually happen if British help to the Arab states was withdrawn. I do not believe that on this question your opinion or mine would carry much weight — or, for that matter, whether it would be based on a particularly sound knowledge of the facts. It is very sad to have to watch these things happening without taking any action, and I can understand your impatience, but I believe that in this particular situation action would not make particularly good sense, nor would it be likely to assist in getting a satisfactory solution of the problem. Yours sincerely, R.E. Peierls

[461] Leon Rosenfeld to Rudolf Peierls Manchester, 4.6.1948 Dear Peierls, I enclose the proof of the last chapters of my book containing among others a short account of Ramsay’s argument concerning Schwinger’s theory.214 I need not say that I shall be grateful for your criticism. Blackett showed me your article on the German scientists.215 As you would expect I agree entirely with your views and I think that it would be extremely useful if it could be published. I would like, however, if I were to write such an article myself, to lay perhaps more emphasis than you do on the detrimental inﬂuence of the present situation on the youth and I would speciﬁcally stress the fact that most German intellectuals are now taking an entirely passive attitude, and instead of contributing their share to the material and moral reconstruction of their country, they pin their hopes on the advantages to be gained from the conﬂict between the two occupying powers. I would also allude to the regrettable fact that after the liberation there hardly was any spontaneous manifestation from the part of the 214 215

Leon Rosenfeld, Nuclear Forces, Amsterdam: North-Holland Pub. Co., 1948–9. Item [440].

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Germans of any regret for the past and desire to do better in the future. I feel also that you should perhaps try to formulate more ﬁrmly and more concretely the conclusions of your essay, since as it is now it gives the impression that the problem is hopeless and that there is hardly anything to do about it. Perhaps after all this is true, but still we are confronted with the urgent practical problems such as whether to invite the Germans and so on, on which we have to make up our minds. There is one small point needing correction: the situation in Holland to which you allude on page 3 was a bit more complicated. The so called loyalty declaration was in itself a harmless document that could be signed and was actually signed by all state functionaries, including University teachers. But the conﬂict arose when the Germans tried to enlist the students for work in Germany. They tried to make the authorization to continue the study dependent on signing similar loyalty declarations. The refusal of most students to do so had nothing to do with the declaration itself, but was a clear protest against the attempts to force them to work for the beneﬁt of the Germans. This protest led to wholesale arrests and deportations of students and also to the persecution of a small number of professors who had been prominent in supporting the students’ action. From this you may see how to modify your text at that particular place in order to avoid inaccurate statements. The cautious way in which the nazis manoeuvred with us in Holland, seems to support your opinion that “even the nazi regime would have hesitated to carry on without the majority of German University teachers”.— With best wishes, Yours sincerely, L. Rosenfeld I enclose the report on the examination for your signature.

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[462] Robert Oppenheimer to Rudolf Peierls Princeton, 16.8.1948 (carbon copy) Dear Peierls: Your good note of August 5th has just reached me. I shall be glad to give the introductory Thursday afternoon talk on the ﬁeld theory although I have no doubt that a number of people on your list could do a better job.216 We shall probably come up to Birmingham on Monday, September 13th. Kitty will be with me, and we both look forward very much to seeing you both. Am I right in assuming that there will be some place where both she and I can stay? We plan to be with Bohr in Copenhagen the ﬁrst ten days in September and if you have messages you can best reach us there. Sincerely, [Robert]

[463] Rudolf Peierls to Robert Serber Birmingham, 8.10.1948 (carbon copy) Dear Bob, In trying to remember what I had learned at the Solvay, I came across the following point: I believe you said that the curve for the n − p scattering at 90 MeV looked so symmetrical as between 0◦ –180◦ that you were led to the assumption that there is no scattering at all in the states of odd angular momentum and that you had obtained a good ﬁt with a cental force of such a description. Now, Mr. Preston here points out, in my view correctly, that such a force would not be compatible with the saturation of nuclear forces, since for saturation you must not 216

This refers to the Birmingham Conference to take place in September 1948.

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have more “ordinary” force than is contained in the symmetric mixture of Kemmer.217 Of course, all this depends on there being approximate charge independent and negligible many-body forces, but it would be very important to have evidence which forces us to abandon one or the other of these assumptions. The tensor force in itself cannot save the saturation, though, of course, it may alter the nature of the central force that one derives from the Berkeley data. These points have probably occurred to you, but I would be glad to know your reaction and also in view of this it is particularly important to examine how well the symmetry of the pattern is proved from the available data. From what I remember of your slide the points at angles below 90◦ seemed to show more scatter than those above and one could, perhaps, tolerate some deviation from this symmetric pattern. No doubt, you are now examining your suggestion of a non-exchange tensor force and if this works, which I ﬁnd hard to believe, it may also have some eﬀect on the nature of the central force that you have to assume.218 Yours sincerely, [R.E. Peierls]

217 N. Kemmer, ‘The charge-dependence of nuclear forces’, Proc. Cam. Phil. Soc, 34, 354–64 (1938); N. Kemmer, ‘Quantum Theory of Einstein-Bose particles and nuclear interaction’, Proc. Roy. Soc A166, 127–153 (1938). 218 This point is addressed in S. Fernbach, R. Serber and T.B. Taylor, ‘The Scattering of High Energy Neutrons by Nuclei’, Phys. Rev. 75, 1352–55 (1949).

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[464] Robert Serber to Rudolf Peierls Berkeley, 4.11.1948 Dear Rudolph: I am enclosing prints of the slides I showed at the Solvay Conference.219 −Kr 1 The curve labelled II is for the potential 12 (1+Px ) e r , K = 1.2×10−13 . Curve I is for 40 Mev. For charge symmetric forces with this Yukawa potential the cross section at 180◦ would be about 40 × 10−27 , so to get a more reasonable looking curve, the results for charge symmetry with a square well of range 1.8 × 10−13 were plotted as curve IV. (With a square well one can get considerably smaller cross sections than with a smooth potential.) III was intended to be the curve for the Yukawa potential with tensor forces included. However, III is not right, according to our latest results. The trouble was that in plotting III the phase shifts for the 3 D3 +3 G3 states were taken from a Born approximation (a fact I wasn’t aware of when I last saw you). Although the phase shifts are small, the weight factors are big, and using the correct phase shifts makes a quite appreciable diﬀerence in the diﬀerential cross section. We now think that the proper curve, including tensor forces, is still quite close to II, though some checking of this conclusion is necessary. If true, the diﬃculties concerning tensor forces have disappeared. As to the symmetry of the scattering: the counter data indicates some asymmetry, though a rather small one, while the cloud chamber data seems to show quite appreciable asymmetry developing at small angles (if the last point can be believed). However, the curve still appears not as asymmetric as one would predict from, say, the “charge symmetric theory”. A small repulsive force in states of odd angular momentum could be invoked to account for the asymmetry, i.e. slightly more exchange than ordinary force. The argument for keeping the forces in the odd states as small as possible in that zero force gives the minimum total cross section from the calculations. 219

See also letter [463].

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To explain saturation, one would certainly have to give up charge independence — repulsive forces would have to appear in the like particle interactions. I don’t believe the work which has been done on p − p scattering is much help here; the limit on the amount of repulsive p wave force compatible with the observation is so sensitive to range, and, as far as I know, calculations with short-range forces haven’t been made. There are no results to report yet from our 32 Mev p − p scattering experiments. The latest result on the meson mass ratio is 1.32 ± .0 − 2, so zero mass for the third particle seems pretty certain. The geometry of the apparatus for measuring the π lifetime has been checked by running −8 (half α particles through it. The present ﬁgure is τ 1 = 0.9 +.25 −.15 × 10 2 life). With best regards, Robert Serber

[465] Hans Bethe to Rudolf Peierls New York, 10.12.1948 Dear Rudy: Thanks for your several letters. I shall be very happy to have Salpeter220 and I have just written to Wilson about giving him an appointment. I am reasonably sure that we can give him a position as a Research Associate at a salary of $3500 to $3800. This, I think, should be adequate and will correspond approximately to his current salary plus traveling expenses to this country and back. We cannot make any separate arrangement for travel expenses. I hope Dyson will actually decide to come to you.221 He gets better every day. However, he has so many oﬀers that he has not yet made 220

Ed Salpeter moved to Cornell after completing his Ph.D. at Birmingham. Freeman Dyson (1923– ), had studied at Cambridge between 1941 and 1943. After war service in the research division of the R.A.F., Bomber Command, he undertook research at Cambridge (1946–47) and Cornell (1947–1948) before becoming research fellow at Birmingham. 221

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up his mind where to go in England. He has some excessive loyalty to Cambridge; I told him he would waste his time if he went there. I have sent your Letter to the Editor to The Physical Review.222 I knew this derivation or a rather similar one; in fact, I am planning to write a paper in which a still more general and exact relation is derived and used.223 Blatt224 has used still another derivation, but for practical purposes has used essentially your relation. Everything about the scattering of neutrons and protons by protons is getting to be exceedingly simple. Especially the complicated calculations by Breit225 are now quite unnecessary. I have also taken care of your application for membership in The Physical Society. I am enjoying my stay at Columbia.226 I ﬁnd that I have much more time than usual to do some work. There is quite a lot of progress in quantum electrodynamics and the people most concerned, namely Schwinger, Feynman and Dyson, have been busy writing up their knowledge. At the moment, Rose is visiting me but without the children. Regards to all of you. Yours sincerely, Hans

222

F.C. Barker and R.E. Peierls, ‘On the Deﬁnition of the “Eﬀective Range” of Nuclear Forces’, Phys. Rev. 75, 312–12 (1949). 223 H.A. Bethe, ‘Theory of the Eﬀective Range on Nuclear Scattering’, Phys. Rev. 76, 38–50 (1949). 224 John M. Blatt and J. David Jackson, ‘On the Interpretation of Neutron-Proton Scattering Data by the Schwinger Variational Method’, Phys. Rev. 76, 18–37 (1949). 225 G. Breit, H.M. Thaxton and L. Eisenbud, ‘Analysis of Experiments on the Scattering of Protons by Protons’, Phys. Rev. 55, 1018–64 (1939); L.E. Hoisington, S.S. Share and G. Breit, ‘Eﬀects of Shape of Potential Energy Wells Detectable by Experiments on Proton-Proton Scattering’, Phys. Rev. 56, 884–890 (1939), and G. Breit, L.E. Hoisington, S.S. Share and H.M. Thaxton, ‘The Approximate Equality of the Proton-Proton and Proton-Neutron Interactions for the Meson Potential’, Phys. Rev. 55, 1103 (1939). 226 Hans Bethe was visiting professor at Columbia University in the autumn of 1948.

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[466] Rudolf Peierls to J.R. Oppenheimer [Birmingham], 16.12.1948 (carbon copy) Dear Oppie, I am writing to ask about two problems which were mentioned in discussions here at the Solvay. The ﬁrst is that you drew attention to the results by Finkelstein, according to which the lifetime of τ -mesons for the decay into [. . .]227 with the emission of one or two photons was sure to be much shorter than observed. The published paper by Finkelstein covers only some special cases.228 We have looked into this problem more generally. It is easier, of course, to survey the case of the emission of one photon. In this case it seems possible to choose the spin and parity of the two mesons and type the coupling in such a way that this process is forbidden. We are proposing also to study what happens in three cases to the emission of the two photons and to see whether there are cases in which this also can be reduced. I imagine that you may have similar calculations going and, while a certain amount of overlap does no harm, the job of listing all the possible combinations and compiling the results of such a high-order process is one that is scarcely worth duplicating. If, therefore, you think that this problem has been completely explored, or if this is being done, could you let me know? The second point also concerns work by Finkelstein; in this case the question of non-linear theories. You explained that the classical wave equation for two scalar ﬁelds, one with, the other without mass, and with a coupling term proportional to the square of the ﬁrst and the ﬁrst power of the second wave function has a non-singular stationary solution. We have played a bit with these equations and we have found it very hard to decide whether they have only one solution or an enumerable set. Here again the explanation involves a good deal of hard work and if 227

Missing in carbon copy. R. Finkelstein, ‘The gamma Instability of Mesons’, Phys. Rev. 72, 415–22 (1947); Oppenheimer and Finkelstein had collaborated on this work. E.g. S.T. Epstein, R.J. Finkelstein and J.R. Oppenheimer, ‘Note on Stimulated Decay of Negative Mesons’, Phys. Rev. 73, 1140–41 (1948). 228

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Finkelstein knows the answer to this question we would not want to do it again. According to our notes of the meeting you said that there was “at least one” non-singular solution, but our notes may not be accurate. Another point is that you mentioned the question of ﬁnding an operator representing the coordinate of the centre of this structure in the quantized equations. I have not yet succeeded in seeing the purpose of this; surely if there exists in quantum theory something corresponding to a structure of ﬁnite extent in this equation, its position can be deﬁned in an obvious way to an accuracy given by its size and to that accuracy it must also satisfy the commutation laws with a momentum, since the momentum operator corresponds to an inﬁnitesimal displacement of all ﬁelds together. I see no reason, however, why one should expect to have an exact coordinate operator which is deﬁned to a better accuracy than the size. One would be in a position rather similar to that of the ordinary Dirac equation without coupling in which the existence of precise coordinate operator is rather a mathematical luxury and goes by the board as soon as one used pair theory. The direction in which it would be nice to explore such a theory is to ﬁnd what one can about the existence, or otherwise, of stationary states of ﬁnite energy in the quantum equations, but this, of course, is not easy. We greatly enjoyed reading all about you in Time229 and I thought that, with some allowance for the habits of journalists, the article was excellent, except for the remarks about Einstein to which you objected. We were rather amused by the somewhat backhanded compliment to the state of European physics, though, of course, it is easy to reconstruct the remark that you presumably made which got translated in this fashion. Yours sincerely, R.E. Peierls

229

On November 1948, TIME magazine published ‘The Eternal Apprentice’, a cover story on Robert Oppenheimer.

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[467] J.R. Oppenheimer to Rudolf Peierls Princeton, 30.12.1948 Dear Rudi: Thank you for your ﬁne letter.230 It was good to hear from you and made me homesick for a long talk. Let me try to answer your questions. To the best of my knowledge, no systematic search for selection rules to lengthen the lifetime of τ -mesons has been made. Of course examples of selection rules can be found in Finkelstein’s paper;231 and Furry’s theorem gives one other examples. I must say that this last strikes me as somewhat unpromising. Surely in pursuing it one must also investigate stability with regard to electron-positron pairs. I gather that we are looking for a factor which is something like 10−9 , since certainly the characteristic decay process is not a gamma instability or an electro-positron instability. Of course, I do not have anything against pursuing this, but am only trying to explain why we have not ourselves done it. There is just one point: If one does not wish to question the materialization processes for nucleons, one may believe, as far as today’s evidence goes, that the production of the τ meson is always accompanied by the production of another particle of equal or greater mass. This does not seem too likely either; but I do not believe that there is any real evidence against it. I meant really only that we should keep open-minded about the materialization process and this might be one of the ways that we might learn about them in the not too remote future. As far as the non-linear theories, I profoundly agree with every word you write. The business of deﬁning center of mass coordinates is a rather trivial, rather formal and quite sterile one, and in any case has been pretty well looked into both by Pryce and by Møller. Finkelstein says that there is more than one non-singular stationary solution, but whether there is an inﬁnite number and how they are related, I do not know, and I doubt whether he does. It seems to me that the 230 231

Letter [466]. See letter [466], note 228.

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essential questions, and this is being worried about a little locally, is to understand the relation between the classically coupled ﬁelds and the quantum theory; to understand this, that is, when one cannot use the principle of super-position and the theory of normal modes. I will promise to keep you informed if we get anywhere with this, and I would hope that you would let us know as things become clearer to you. One reason which may not be too good a one for my own interest in this problem is the following: One can integrate the Tomonaga equation formally as follows: ∞ mtµ ν Tν (x)η ηµ d4 x Ψ(−∞) Ψ(σ) = “eψp”i/l −∞

The essential point in all electrodynamic treatments so far is that in order to deﬁne the “exponential” one must approximate to it by a power series so that one can order the non-commuting factors properly; i.e., with the latest point to the left, etc. These diﬃculties of the order do not occur in a classical ﬁeld theory; and if one should solve the classical problem, one would have a starting point for a perturbation theory based on the smallness of h and not of e. To date this is a program only; and I suspect that there are some deep reasons why it will not work, because a number of us have been trying without success. One piece of news which you need to know is how very very good Dyson is. He wants to return, and in fact must return, to England for the next years, but we have made a ﬂexible arrangement with him to come back here for as many semesters as he can spare. I think he likes the arrangement and we are all delighted by it. He has gone a long way towards answering the questions about the ﬁniteness and uniqueness of electrodynamics and has established strong presumption that in going to more complicated processes and higher order corrections nothing worse than the Lamb shift will turn up.232 The Lamb shift itself, after agonizing ﬂuctuations, appears to be settling 232

F.J. Dyson, ‘The Electromagnetic Shift of Energy Levels’, Phys. Rev. 73, 617– 26 (1948); F.J. Dyson, ‘The Interactions of Nucleons with Meson Fields’, Phys. Rev. 73, 929–30 (1948).

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down to 1052 meg, a result which was not obtained by the highbrow Feynman-Schwinger-Tomonaga methods, but by much more pedestrian ones.233 There is still a real question as to the complete uniqueness of procedures; but as for the moment — things have been changing rapidly — it does not appear that this has contributed to the uncertainty of the result; and it does not appear that only rather arbitrary and odd methods of following the integrations, which have not, in fact, been used, can give a diﬀerent answer. You are most kind about “Time”. I think it stank, and suﬀered very much for a couple of weeks until I could forget it. It would be very good to have a talk with you about many things in physics and some in politics and the atom. I hope that business will bring you to this country soon and that you will stay with us for a while. We both send you both our warmest, friendliest wishes for the New Year, Oppie

[468] Freeman Dyson to Rudolf Peierls Princeton, 16.1.1949 Dear Professor Peierls, I am sorry to be so slow in answering your very nice letter of November 30th.234 During this interval I have been trying to get my own mind ﬁrmly made up about what I want to do and I have now ﬁnally decided that Birmingham is the place, and I will take up your oﬀer of a Research Fellowship. The salary will not be of crucial importance to me, to start with at any rate, and so I leave it to you to get what you can for me. More important will be the question of ﬁnding somewhere pleasant to 233

F.J. Dyson, ‘The Radiation Theories of Tomonaga, Schwinger and Feynman’, Phys. Rev. 75, 486–502 (1949). 234 Peierls had invited Freeman Dyson to join his department as a research fellow. Letter could not be located.

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live, and I should be very grateful for any help or advice you can give about this; I shall be arriving in England about July 15th, and so I shall have two months to make arrangements before actually moving in. The “usual particulars” about me are: Age, 25 Degree, Cambridge B.A. (1st class) in mathematics, 1945 British subject by birth, Academic history; Research Fellow of Trinity College, 1946–49; Member of the Institute for Advanced Study, Princeton, 1948. If they want to know further details concerning the colour of my hair, membership of the Communist Party, etc. I will be glad to supply them. For your own information (this is a little conﬁdential), Oppenheimer has very generously arranged for me a 5-year membership of the Institute, on the understanding that I make use of it for no more then 1 12 years between now and 1954. This means that I shall be able to come here at intervals and keep abreast with what the U.S. is doing, and it is an arrangement which would combine well with a Fellowship at Birmingham carrying no departmental responsibilities. Of course I should stay at Birmingham for the whole of the ﬁrst year at least. I think it is extraordinarily thoughtful of Oppenheimer to have so anticipated my needs. I was interested in the remarks you made in your letter about physics (probably by now you have completely forgotten what you said). The problem of dealing with the hydrogen atom rigorously as a two-body system rather than as an electron in a given ﬁeld has been thought about a great deal, and nobody has yet proposed a simple way of doing it; however I am convinced that it is not a fundamentally diﬃcult matter or a gap in Schwinger’s theory. One can see quite well that the secondorder radiative corrections arise from the same kind of processes as in the Lamb-shift, only you have processes in which the proton takes part in addition to those involving the electron. The diﬃculty in carrying out a complete calculation seems to be due mainly to the fact that people have not yet found a decent method of treating the hydrogen atom as

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a two-body problem, even without radiative corrections. This is said, with all due apologies to Breit.235 Concerning the more general questions of the validity of electrodynamics `a la Schwinger and Feynman, I hope soon to be able to send to you a long paper of mine in which these things are discussed. The paper is ﬁnished and is at the moment in the process of being mimeographed; with luck it will be published some time in the summer (the ﬁrst paper appears in the Feb. 1 Physical Review).236 In the paper I have dealt with scattering problems exclusively, and shown that for them at least the theory always gives ﬁnite and sensible results. Also, we know now (Schwinger found it out) that there is no real discrepancy in the Lamb-shift calculations; everybody now agrees on 1052 as the right value, and the mistake in the old “highbrow” calculation was not a question of principle but was just a wrong neglect of terms at the lowenergy end. It seems to me now not at all likely that the bound-state problems will give worse troubles than the scattering problems, though of course the calculations will always be tougher. You will see from my paper that I do not believe in a program of making inﬁnite self-energies ﬁnite. The reasons for this are too long to be talked about here. I agree with you in not taking seriously Feynman’s cut-oﬀ methods; he himself does not take them very seriously either. His big paper on electrodynamics will unfortunately not be appearing for some time. With many thanks for your letter, Freeman J. Dyson 235

Gregory Breit at Yale was working on related problems. In the late 1940s he published several important papers about the ﬁne and hyperﬁne structure of hydrogen. G. Breit and G.E. Brown, ‘Eﬀect of Nuclear Motion on the Fine Structure of Hydrogen’, Phys. Rev, 74, 1278–84 (1948); G. Breit and G.E. Brown, ‘The Eﬀect of Nuclear Motion on the Hyperﬁne Structure of Hydrogen’, Phys. Rev, 76, 1299–1304 (1948). But Breit’s relativistic two-body interaction had limitations in that it could only be used as an expectation value. Gerry Brown, Breit’s collaborator at Yale, later tackled these limitation when he was working as a research assistant at Peierls’ institute at Birmingham. 236 F.J. Dyson, ‘The Radiation Theories of Tomonaga, Schwinger, and Feynman’, Phys. Rev. 75, 486–502 (1949).

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[469] Rudolf Peierls to Freeman Dyson Birmingham, 21.1.1949 (carbon copy) Dear Dyson, I am very glad that you are coming here and I shall now set the machinery in motion to oﬀer you an appointment. From what preliminary enquiries I have made I am now doubtful whether this will be at the top of the salary range I mentioned before, but from what you say you would not make that a condition. As I have vacancies now which I do not expect before the end of the session your appointment could run from any date you choose and if, for example, you would like to start immediately on arrival or, for example, on the 1st of September, will you let me know? It will make no diﬃculty if you want to visit Princeton from time to time, on the contrary, this will obviously increase your value to us. I would, of course, expect that the dates of such visits be discussed and that you would meet me if I was anxious to have you here at some speciﬁc time because I want to be away or for other reasons. Equally obviously, your salary would not continue during your absence, if during that period you are getting a full salary from another source (subject to anything special we might be able to arrange about travelling expenses). The information in your letter is quite adequate, luckily we have not reached the stage in this country where a university would consider it reasonable to ask questions about the political views of their staﬀ. To avoid delaying this letter I shall not comment on your remarks about physics which were most interesting beyond saying that we are looking forward to seeing your paper237 from which we hope to learn a lot of things that we have not yet managed to understand. Yours sincerely, R.E. Peierls

237

Letter [468], note 236.

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[470] Rudolf Peierls to Hans Bethe [Birmingham], 25.1.1949 (carbon copy) Dear Hans, I am writing again, this time about a number of assorted points, instead of sending you three of four letters in succession. The ﬁrst point is that Dyson has now decided to come to Birmingham next session, which, of course, cheers me very much. It remains now to get the authorities here to ﬁx his salary and I am trying to get for him a reasonably high salary which may be a little diﬃcult in view of his age. Would you be good enough to write me a letter with a frank statement of your opinion of him; this should cover not merely his ability and promise but also his actual achievement to date, since the point at issue is the extent to which he can be regarded as of fairly senior standing. For example, it would help, if you could state what sort of job he could expect to have in an American university if he was an American, or if you were able to compare him to the general run of people holding senior jobs in this country (if this can be done without being rude). The next point is a question of physics. I don’t remember whether I have mentioned to you before some work which Swiatecki238 here has done recently trying to get to the bottom of the magic numbers, 20, 50 and 82, in nuclear structure. The occurrence of these numbers smells of the existence of “shells”, i.e. single particle states to some approximation, but there are two factors against this. (1.) that on a shell model you would have to explain why you get only the breaks at these numbers and none at the intermediate numbers which should correspond to closed shells. (2.) you cannot get a complete shell at 50 unless you omit the 2s level, whereas you cannot complete 20 unless you include it. Both these diﬃculties can be met in principle by observing that with increasing weight the shape of any potential well would have to change both on 238

Wladek J. Swiatecki (1918–), completed his Ph.D. under Peierls in 1949 working on nuclear structure. He later went to Copenhagen, Uppsala, and Berkeley where he spent the rest of his career.

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account of the predominance of the surface eﬀects for light nuclei and because of the increase in the Coulomb forces which tends to decrease the density near the centre as compared to the edge. In particular, the latter eﬀect will make the sequence 2s, 3p · · · go up with increasing weight relative to 1s, 2p · · · It is, therefore, not impossible that when Y or N (= A − 2) is about 20 the 2s level should still be fairly low, whereas near Z or N = 50 it might have moved up above 3d. At the same time, this would explain why intermediate shells do not appear to be marked when two levels are just about passing each other one would not get any clear break. On this view one would be dealing with a situation analogous to the rare earths in atomic structure. The question whether the reduction in the density near the centre is big enough to do this depends on what one assumes for the compressibility of nuclear matter. There exists on this only a paper by Feenberg239 in which one of the two required parameters ﬁxed from the observed mass defect curve, whereas the other is ﬁxed from ﬁshy theoretical treatment. We have been unable to rule out the possibility that the compressibility might be somewhat larger than is usually assumed and it might even be possible that heavy nuclei are almost hollow. We have thought of means of deciding this question approximately; in principle it might be done by observing nuclear radii, but this is very insensitive. One interesting possibility is to use the diﬀraction of electrons by nuclei using energies of 30MeV or more. Now the diﬀraction patterns to be observed have been calculated by Rose using the Born approximation and if one does this both for a solid and a hollow nucleus the diﬀerence is small but not altogether negligible. Now Born approximation is, of course, very poor, particularly for heavy nuclei and, while it can hardly be expected to give a long order of magnitude, it would be nice to have a better theory. I believe this is in principle contained in the work of Smith240 which you mentioned when you were here and the main object in telling you this long story (apart from getting your general comments) is to see whether Smith’s work, when complete, will cover the answer to this question, or 239

E. Feenberg, ‘Nuclear Shell Structure and Isomerism’, Phys. Rev. 75, 320–22 (1949). 240 Presumably Jack H. Smith at Cornell.

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if not whether his method can be used for the purpose. If you do not intend to have this done we would very much welcome a chance to see Smith’s work in advance so that we could adapt it for this purpose. My third problem arises from the planning of the 1950 volume of the Physical Society Progress Reports which you know, as you wrote an article for it in the past.241 We were wondering whether we could have an article on nuclear forces; would you be interested in writing this? The date of publication is not ﬁxed yet, but probably the MS. would have to be received during the late summer for publication early next year. You will remember that these articles are not generously paid but serve a very useful purpose. Compared to the Review of Modern Physics they are rather less specialised and less high-brow. If you cannot do this, can you suggest someone else? Equally, of course, other suggestions about articles in the series would be welcome. Lastly, we understand that the Fulbright Scheme is coming into eﬀect next session and that, as you probably know this will allow research students and more senior people to come and work here. We have been asked to say whether we would accept research students, which, of course, we would, if they are suitable, and what kind of more senior people we would like. This information was required at such short notice that it was impossible to ﬁnd out who would be interested. I have mentioned a few names at random including Feynman and Placzek, though these are long shorts, but if you hear of anybody who might like to spend a year or so in Europe, will you let them know or get directly into touch with the Fulbright people. I have also mentioned to them that I would quite like to have someone who works on solids and/or metals to arouse some interest in this here, though of course he could not learn very much on this subject from us. Under this heading I have not mentioned any names at all, but would be grateful for suggestions. Yours sincerely, [Rudi]

241

H.A. Bethe and R.E. Marshak, ‘The physics of stellar interiors and stellar evolution’, Reports on Progress in Physics 6, 1–15 (1939).

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[471] N. Kemmer to Rudolf Peierls Cambridge, 31.1.1949 Dear Peierls, There are two things I should like to consult you about. The ﬁrst concerns the Schwinger, Tomonaga etc. stuﬀ. I have 2 1/2 men here studying these things and now that Schwinger has published Pt 1242 there is hope that we shall eventually learn publicly all that has been done. In the meantime, however, we have played with the obvious generalisations to meson theory and though (using later work by Tomonaga) the general lines of a consistent extension to these cases are clear, we are still by no means clear about the details. I myself have unfortunately only very little time to devote to thinking about these things. So I wanted to ask you whether you have had any more recent news of progress on this front. We possess the things duplicated at Birmingham, and Vol. III 1& 2 of the Japanese Journal (Prog. Th. P.243 ) also of course the Pocorvo notes. I should be most grateful to learn of any other information. So far we cannot report any results, though the lads have done masses of exploratory paperwork. The second matter is of a diﬀerent nature. Do you know Felix Adler244 who at various times was in Switzerland, Paris, Montreal and now Wisconsin? If you do, you will remember that he is an almost pathologically shy person, but has improved in recent years. At Wisconsin he has, I understand, been quite a success as a lecturer, but he doesn’t like life in the States and, partly under the inﬂuence of relatives, I believe, he wants to get over here. He realises that he doesn’t stand much of a chance to be oﬀered an attractive post and that, although 242

Julian Schwinger, ‘Quantum Electrodynamics, I. A Covariant Formulation’, Phys. Rev. 74, 1439–61 (1948). 243 Progress in Theoretical Physics, monthly journal founded in 1946 by Hideki Yukawa and now published for the Yukawa Institute for Theoretical Physics and the Physical Society of Japan. 244 Felix T. Adler (1911–1979), theoretical nuclear physics who later moved to Illinois, where he was instrumental in establishing the university as a national centre for reactor science and engineering.

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there are quite a few poorly paid posts at small universities going one hardly would import a foreigner from Wisconsin for one of those. So his only chance would be to come here for a year or so on some grant and then look around. I was wondering what your attitude would be to having him around for a year, if possible with some ﬁnancial assistance provided by some source you can tap. I think he is quite a good man when in the right atmosphere and his yield of scientiﬁc work has been small. Apart from early work under Wentzel, which wasn’t very independent there have been some things on neutron diﬀusion and now, I hear, on theoretical chemical lines. But he does know quite a lot. I am asking you about this mainly because Mrs Burkill to whom he is related, turned to me for advice. Don’t hesitate for a moment if you feel you must give a deﬁnite and not encouraging reply. I have just thought of another thing I wanted to mention, and that is that I expect to have a really good young man in search of a post by October so that I should be glad to hear from you if you know of anything going. Sorry to bother you. Best regards. Yours sincerely, N. Kemmer

[472] Rudolf Peierls to N. Kemmer [Birmingham], 2.2.1949 (carbon copy) Dear Kemmer, On the question of information about Schwinger theories, Schwinger has completed Part II of his paper which is being published in the Physical Review.245 He sent me a duplicated copy of this which is at 245

Julian Schwinger, ‘Quantum Electrodynamics, II. Vacuum Polarization and Self Energy’, Phys. Rev. 75, 651–79 (1949).

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present in enormous demand here. You might try to see whether he can spare you another copy of this. It is much more readable than the earlier Part II which you have. Another paper on the same subject has just been completed by Dyson in which the equivalence of Schwinger and Feynman’s method is proved and in which is also shown how to generalize the method beyond the second approximation.246 I have just received a duplicate copy of this and besides Dyson, Weisskopf has also had copies made. You might be able to get a copy from either (Dyson is now at Princeton). As regards the Japanese journal, I have had correspondence with the American Scientiﬁc Advisor in Tokyo and also directly with Tomonaga as a result of which we are just putting into eﬀect an exchange scheme. The American Oﬃce has informed me that besides Tomonaga also Dr. Kobayasi is interested in such an exchange; I am not clear whether this is an alternative to the arrangement with Tomonaga or in addition. I expect to hear shortly from Kobayasi and I also expect to hear which British journal Tomonaga wants from us. Perhaps the best thing would be to wait until I have both these replies and I shall let you know. We are, of course, also studying the Schwinger papers intensely and perhaps in a little while it would be a good idea if one or two of the people in your team who are interested could come across for a day or so to compare notes. We would, of course, be delighted if you could join in this. I think, however, it would be best to wait another month or two when everybody will have digested things somewhat further and when we can get more out of such discussions. As regards Adler, it would, no doubt, be nice to have him around, but competition for the Research Fellowships I have available here is likely to be keen and my impression both from what I know and from what you say is that he would not be a very strong candidate. The only other type of grant I can think of is under the Fulbright Scheme which does make it possible to pay for American scientists to spend a year or so in this country. I do not know very much as yet how one goes about getting such a grant in practice and I would not commit myself at this 246

See letter [468], note 236.

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stage to asking Adler unless I knew whether this would spoil the chances of getting someone more senior. Meanwhile it may be possible for him or the head of his department to apply directly from the American end. Jobs at smaller universities are not always badly paid and ﬁnding a more attractive grant he could do worse than accepting a teaching or research job at a smaller university which will certainly pay a living salary, provided this is geographically within reach of bigger centres so that he can make contacts and get himself known. In this connection I heard recently that ter Haar also is interested in a job in this country.247 He is, of course, much more senior and he would give up a full professorship at Purdue to come here so that he would obviously not consider a very junior job. If you hear of any vacancy you might like to bear this in mind. As regards your other bright young man, could you tell me more about him, particularly whether he would be suitable for a D.S.I.R. Maintenance Award or a Senior Research Award or, of course, a University Research Fellowship. It is a bit early yet to consider the ﬁnal staﬃng for next session, but I would like to consider him as a possibility. Yours sincerely, R.E. Peierls

[473] Hans Bethe to Rudolf Peierls Ithaca, 2.2.1949 Dear Rudy: I think the enclosed letter on Dyson is strong enough but the strange thing is that it is all true and sincere. He is really incredibly good. Concerning your calculations on nuclear structure, I just have on my desk 2 papers, one by Nordheim248 and the other by Feenberg,249 about 247

Dirk ter Haar eventually took up a post as Reader at Oxford University in 1956. L.W.Nordheim, ‘On Spins, Moments, and Shells in Nuclei’, Phys. Rev. 75, 1894–1901 (1949). 249 Eug`ene Feenberg had published a paper on nuclear shell structure in early 1949 248

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the same subject. Feenberg especially uses a model similar to yours in which he takes into account that the nucleus may be something like a hollow shell. Having just returned to Cornell I have not had time yet to ﬁnd out about the recent calculations of Jack Smith. I think he has calculated the eﬀect of the distribution of protons on the nucleus and came to the conclusion that the eﬀect is hardly observable if the distribution is that assumed by Feenberg in previous papers. However, if the nucleus were actually a hollow shell, this should be observable in electron diﬀraction. Nobody as yet has experimented on this but this will probably soon be done. The Berkeley synchrotron is going and ours is beginning to go, and electron diﬀraction is one of the points on our program. I will write more about this when I have checked with Smith. Concerning the Physical Society progress reports, I should like to think it over a little more. At the moment I would rather say no, because I still have a good deal of writing to do for the books of Segre250 and Schein251 on nuclear physics and cosmic rays respectively. I will ask Phil Morrison if he wants to do it; he would do it very well. Weisskopf may be another possibility. Concerning exchange students, I had a very good boy at Columbia by the name of Slotnick252 who would like to go to Europe next year. His ﬁrst choice is Pauli, but he is also very much interested in coming to you. Possibly he will want to divide his time between Birmingham and Zurich. He will write you directly. I am writing to Eyges253 about possible jobs for next year for him. (see letter [470], note 239.) and had submitted another paper on nuclear shell structure to be published later in 1949. E. Feenberg and K.C. Hammack, ‘Nuclear Shell Structure’, Phys. Rev. 75, 1877–93 (1949). A few weeks after Bethe’s letter to Peierls, Feenberg, Hammack and Nordheim submitted a joint note on the same theme. E. Feenberg, K.C. Hammack and L.W. Nordheim, ‘Note on Proposed Schemes for Nuclear Shell Models’, Phys. Rev. 75, 1968–69 (1949). 250 Emilio Segr`e (ed.), Experimental Nuclear Physics, New York: Wiley, 1953. 251 D.J.X. Montgomery (ed.), Cosmic Ray Physics: based on lectures given by Marcel Schein at Princeton University, Princeton: Princeton University Press, 1949. 252 Murray Slotnick, in fact went to Princeton in 1950, before moving to the University of Michigan, Ann Arbor. 253 Leonard Eyles went to Berkeley, M.I.T. before joining the Air Force Cambridge Research Laboratory in Massachusetts.

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I had a rather fruitful semester at Columbia and will soon send you a paper on the eﬀective range of nuclear forces.254 I am also sending you a copy of the ﬁrst paper by Dyson which will soon appear in print.255 With best regards to you and the family, Yours sincerely, Hans

[474] Wolfgang Pauli to Rudolf Peierls Z¨ urich, 14.2.1949 Lieber Herr Peierls! Ich habe mich soeben entschlossen, eine freundliche Einladung des “Faculty Board of Mathematics” in Cambridge anzunehmen und dort die sogenannte “Rouse Ball lecture” zu halten.256 Da der Term dort am 11. M¨ arz schließt, habe ich vorgeschlagen, die letzte Woche dieses Terms als Zeit der Vorlesung zu w¨ahlen. (Meine Korrespondenz l¨ auft mit dem Sekret¨ ar der Faculty Board Dr.A.J.Ward, Emmanuel College, Cambridge). Das Thema der Vorlesung ist “Physical and mathematical aspects of recent developments in quantum electrodynamics”. Vor etwa 2 Wochen habe ich einen langen Brief an Schwinger geschickt.257 Leider habe ich nur eine begrenzte Zahl von Kopien zur Verf¨ ugung, hatte aber Ma258 (zur Zeit in Dublin) gebeten, Ihnen eine Kopie zukommen zu lassen. Wenn Sie sie noch nicht erhalten haben, wird sie sicher bald zu Ihnen gelangen. 254 H.A. Bethe, ‘Theory of the Eﬀective Range in Nuclear Scattering’, Phys. Rev., 76, 38–50 (1949). 255 See letter [468], note 236. 256 These were lectures about new developments in quantum ﬁeld theory, which took place between 8 and 19 March 1949. 257 Letter W. Pauli to Julian Schwinger, 24.1.1949, Pauli, Wissenschaftlicher Briefwechsel, III, pp 609–19. 258 Shih-Tsun Ma, Chinese physicist who was working with Walter Heitler at the Dublin Institute for Advanced Studies.

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Es handelt sich mir darum, versteckte Annahmen, die in Schwingers “Beweisen” implizit enthalten sind, an’s Tageslicht zu bringen. Das gilt nicht nur f¨ ur die Fragen der Polarisation des Vakuums, sondern auch f¨ ur das interessantere Problem der Korrektur des magnetischen Momentes des Elektrons. Die in meinem Brief an Schwinger zum Schluß erw¨ahnte Rechnungen von Villars259 sind inzwischen im wesentlichen alfte von Schwingers “Part fertig geworden,260 auch haben wir die erste H¨ 261 ∗ uhrten Rechnungen u ¨ber das III” inzwischen erhalten. Die dort angef¨ magnetische Moment des Elektrons sind formal richtig, ich betrachte sie aber als deﬁnierende Regel, wie die betreﬀenden bedingt konvergenten Integrale auszuwerten seien und nicht als hypothesenfreie Beweise. Dies kann ich auf Grund von Villars Rechnungen n¨ aher begr¨ unden. Ich bin jetzt an einem Punkt angelangt, wo ich gerne mit anderen u ¨ber diese Fragen diskutieren m¨ ochte. Denn ich verstehe zwar die Mathematik, bin aber von der Physik darin nicht befriedigt. Die ,,Regulatoren” k¨ onnen dem Wesen der Sache nach nur eine provisorische Formulierung sein. Ist Herr Salpeter noch bei Ihnen? Was haben Sie sonst f¨ ur Leute in Ihrer Gruppe? Ich w¨ urde eigentlich gerne noch einige Tage l¨ anger in England bleiben und auch andere Orte als Cambridge sehen. Da ich an die Konferenzen in Birmingham so oft abgesagt habe, k¨ onnte ich diesmal kommen. Es liegt mir aber nichts an popul¨ aren Vorlesungen, sondern mehr an “technical talks” in Seminaren u ¨ber theoretische Physik. Ist Rosenfeld an solchen Fragen interessiert?262 ∗ Dagegen

habe ich von ihm noch keine Antwort auf meinen Brief. It seems that he thinks it over. 259 Felix Villars (1921–2002), studied physics and mathematics at the ETH where he completed his Ph.D. in 1946, before working as Pauli’s assistant between 1946–49. He became research associate and later lecturer and professor at the MIT where he stayed until his retirement. 260 W. Pauli and F. Villars, ‘On the invariant regularization in relativistic quantum theory’, Rev. Mod. Phys. 21, 434–44 (1949); F. Villars, ‘On the energy-momentum tensor of the electron’, Phys. Rev. 72, 122–28, (1950). 261 This refers to the draft of J. Schwinger, ‘Quantum Electrodynamics III. The electromagnetic properties of the electron-radiative corrections to scattering’, Phys. Rev. 76, 790–817 (1949). 262 Rosenfeld spent the academic year 1949/50 at Peierls’ institute in Birmingham.

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Vielleicht k¨ onnen Sie die Nachricht meines Kommens nach England auch sonst dort verbreiten und sich u ¨ber Daten mit Dr. Ward in Cambridge verst¨ andigen. (Vor dem 7. oder 8. M¨ arz kann ich nicht nach England kommen, habe aber Zeit hinterher.) Viele Gr¨ uße Ihr W. Pauli

[475] Rudolf Peierls to Wolfgang Pauli [Birmingham], 17.2.1949 (carbon copy) Dear Pauli, Thank you for your letter. If after your visit to Cambridge you could manage to spend a week or so in Birmingham this would suit us both very well indeed. We would not expect you to give any lectures to a big audience but we would get most out of your visit if you could give us one talk (or more) in our Seminar and for the rest just discuss things informally. Besides myself, Salpeter is very interested in the Schwinger theory and has studied it extensively, also a Pole, Rzewuski,263 (a friend of Rayski) who is working now on the coupling between nucleons and the meson ﬁeld a` la Schwinger. McManus is also very interested in ﬁeld theory,264 though he has as yet spent less time with the Schwinger technique and there are three or four others who know enough about the problems to ask intelligent questions. The period from 11th–19th March is quite free as far as I know, except that we are arranging for Dirac to come over on the 17th to give a talk in our Seminar. However, it would add to the attraction to have both you and Dirac here at the same time and there is no reason why our Seminar should not meet several times during the same 263

Jan Rzewuski had come to Birmingham on a fellowship of the Polish government and returned to Gdansk where he continued to teach physics. 264 See letter [396], note 80.

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week. Our term does not end until the 19th and I, therefore, shall have to give a few lectures but not enough to interfere seriously with our discussions. If your time is limited and you want to spend only a few days in Birmingham, I think it would be better if you came during the early part of the week, since Dirac’s talk will be about monopoles and presumably this is not what you want to discuss in the ﬁrst place.265 We can take care of your fare from Cambridge and back to Cambridge or London and we can pay your hotel expenses while you are in Birmingham, but apart from this I am afraid we cannot oﬀer you a fee for your lectures. I am writing to Ward in Cambridge so that he can keep us informed about the dates of your visit there. A copy of your letter to Schwinger has arrived here a few days ago from Heitler; we have not yet, of course, digested it completely, but I tend to agree with you that this represents a considerable advance in our understanding of the mathematical structure of the theory, but leaves it physically in an unsatisfactory state. One interesting question would be to see the relation between your method and Dyson’s treatment of the higher approximations.266 In particular, one would like to know whether in the treatment of higher order treatments each order has again to be treated by using appropriate “regulators” or whether the same trick will do for all orders. I suppose you have seen Dyson’s paper, if not we could probably lend you a copy. I think it would be very important to let Dyson see your note if that has not yet been done. As you know he is now at Princeton. Yours sincerely, R.E. Peierls

265

Pauli had initially been very doubtful about magnetic monopoles (P.A.M. Dirac, ‘The theory of magnetic monopoles’, Phys. Rev. 74, 817–30 (1948)), but after discussing the idea in detail with Dirac at the Solvay Congress in 1948, he revised his views. See letter Wolfgang Pauli to Arnold Sommerfeld, 1.2.1949, Pauli, Wissenschaftlicher Briefwechsel, III, p. 624. 266 F.J. Dyson, ‘The radiation theories of Tomonaga, Schwinger and Feynman’, Phys. Rev. 75, 486–502 (1949).

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[476] Wolfgang Pauli to Rudolf Peierls Zurich, 23.2.1949 Lieber Herr Peierls, ur Vielen Dank f¨ ur Ihren Brief vom 17.267 Zeit und Bedingungen f¨ meinen Besuch in Birmingham passen mir ausgezeichnet so wie Sie es vorschlagen. (Inzwischen habe ich von Kramers auch eine Einladung nach Holland erhalten. Ich soll ab 21. M¨ arz dort sein, werde also von Birmingham nach Leiden fahren.) Die Vorlesung in Cambridge ist am 10. M¨ arz, ich rechne also damit, etwa vom 14. bis 19. M¨ arz in Birmingham zu sein. Daß ich auf diese Weise einen Vortrag von Dirac u ¨ber die Monopole h¨ oren werde, ist mir auch ganz recht. Diese Theorie von Dirac hat eine gewisse Sch¨ onheit in sich und es ist m¨ oglich, daß die Monopole tats¨ achlich in der Natur existieren. Wenn man sie aber ernst nimmt, ¨ber sie wissen als was in Diracs Arbeit steht. m¨ ußte man viel mehr u 1) Was ist ihre Masse? 2) Wie beeinﬂußen sie die Kernkr¨afte? Diracs Theorie kann richtig sein, aber sie ist zu arm an Aussagen. Da alle Theorien u ¨ber die magnetischen Momente von Photon und Neutron falsche Resultate geben, k¨ onnte man wohl auf den Gedanken verfallen, die Neutronen als aus zwei Diracschen Monopolen zusammengesetzt zu denken. Ich m¨ochte gerne von Ihnen wissen, ob in Birmingham Kopien von Schwingers “Part II” und der ersten H¨ alfte von “Part III” available onnte ich n¨ amlich meine Exemplare Herrn Villars sind.268 (Wenn ja, k¨ hier lassen, der sie gut brauchen kann.) I have a copy of Dyson’s paper269 here and also a letter of his in which he announced a second paper, which, however, has not yet arrived. I also made an arrangement that a copy of my letter to Schwinger should 267

See letter [475]. J. Schwinger, ‘Quantum Electrodynamics II. Vacuum polarization and selfenergy’, Phys. Rev. 75, 651–79 (1949) and J. Schwinger, ‘Quantum Electrodynamics III. The electromagnetic properties of the electron-radiative corrections to scattering’, Phys. Rev. 76, 790–817 (1949). 269 See letter [475], note 266. 268

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be sent to Princeton. Dyson seems to be a good man, his letter was in some respect enlightening for me. We shall talk more about it. Schwinger’s deep silence is continuing. Meanwhile my best regards. Yours sincerely, W. Pauli

[477] Rudolf Peierls to J.R. Oppenheimer Birmingham, 7.3.1949 Dear Oppie, I wrote to you before that we were looking a little more quantitatively into the lifetime of the τ -meson following the process discussed by Finkelstein. This has not been completed and as you predicted the result is quite independent of the type of particle and the type of interaction. What we had been looking for was not so much a selection rule which, as you say, would not alter things as it would be broken in the next approximation, but rather a factor depending in a diﬀerent way on the various dimensionless mass rations which occur. I enclose a copy of a paper on this subject which is still in the draft stage and may still need some editing. Since the whole problem goes back to a suggestion you made here, I would be glad to know if you had any objections to being quoted on this and also whether you have, in the meantime, made this point in any other publication to which reference should be made. Yours sincerely, R.E.P I am just getting Dyson’s appointment here conﬁrmed. There will of course be no diﬃculty in the way of his coming to Princeton whenever it suits him and you and I am very glad of this further link with the Institute.

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[478] Robert Oppenheimer to Rudolf Peierls [Princeton], 16.3.1949 Dear Rudi, Thank you for your good letter and for sending Van Wyk’s paper,270 which I was glad to get, and with the results of which I have no quarrel. There is not yet in published form a discussion of this question on my part, but in the records of the Solvay Congress, there is to be, I think, a brief summary of my views on the alternatives, in which the connection of this diﬃculty with the materialisation process is raised, and the possibility of other coupling schemes brieﬂy indicated. I do not know whether it is worth referring to this document, which is not yet out and which may never be widely available. In the meantime, our thoughts have not matured much. Powell’s wonderful picture, of course, raises the possibility of τ → 3ω, where the lifetime, barring some mystical selection rule, should be even shorter than for gamma rays. If one assumes that τ → 2ω+µ is made impossible by the conservation laws, then it appears that the lifetime of τ → ω + 2µ may well be of the [r]ight order of magnitude to ﬁt observation. This point is in fact being explored by Sheila Power.271 We will let you know when and if we have anything that looks as though it had any connection with the real world. We sent you Dyson’s second paper272 and also, I believe, some long works of Case273 on the nucleon-meson problem. It is turning out to be a very tough thing to digest these developments of the last two years and maintain any sort of perspective, the more so because at the moment one can neither get any sensible results with the mesons, nor devise 270

Presumably C.B. van Wyk, ‘On the Decay of the τ -Mesons’, Proc. Phys. Soc. A62, 697–709 (1949). 271 S. Power, ‘Decay of a Heavy tau-Meson into Three Lighter Mesons’, Phys. Rev. 76, 865–66 (1949). 272 F.J. Dyson, ‘The Interaction of Nucleons with Meson Fields’, Phys. Rev. 73, 929–30 (1948). 273 K.M. Case, ‘On Nucleon Moments and the Neutron-Electron Interaction’, Phys. Rev. 76, 1–13 (1949).

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methods suﬃciently powerful to justify expecting them. It would be good to have a chance to talk again, and I hope that one or another pretext will bring us together in one or another country before very long. I have high hopes that on the matter of our more eﬀective collaboration the situation will begin to clear long. Kitty joins me in sending the warmest greetings to you and Genia. We think of you often with great gratitude for the wonderful time in Birmingham. Robert Oppenheimer

[479] Freeman Dyson to Rudolf Peierls Princeton, 31.3.1949 Dear Professor Peierls, Thank you very much for your last letter.274 The salary you are mentioning is really astonishingly generous, as also is your anxiety not to tie me down to Birmingham. I enclose herewith the particulars you wanted for the Royal Society; I am very much obliged to you for undertaking yourself to handle the details of applying for the Royal Society grant. The Institute has not made me a speciﬁc travelling allowance for my expenses on future visits here, but the funds it provides are so ample as to cover all such expenses very comfortably. So you need not bother about that. I will now brieﬂy reply to the physical half of your letter. Incidentally, I have spent the last month, and shall spend the next, travelling around from place to place and giving talks and consuming excessive quantities of food and liquor. While this sort of life is good for acquiring general knowledge about what is going on in physics, it is certainly not conducive to serious thinking. For this reason my thoughts have not progressed substantially beyond the stage at which they were when 274

Letter could not be located.

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I wrote the S-matrix paper.275 I believe I am not likely to be smitten with any new ideas until I have taken a long and complete holiday, which will not be until the midsummer at the earliest. I am glad you have had a talk with Pauli, who seems to be the one member of the “old gang” who takes the trouble to thoroughly understand the new methods. We are all very pleased with his regulators;276 especially the programme of using regulators harmonizes very well with the programme of systematic segregation of renormalisations outlined in my S-matrix paper. The regulators just make it clearer why the rules of procedure I have proposed are sensible, and vice versa. To demonstrate the equivalence of my rules with Pauli’s it is only necessary to show that all the convergent operators, which appear in my method as the physically real eﬀects after separation from the renormalisation, actually tend to zero with increasing electron rest-mass. That this is so seems to follow just from dimensional arguments; since the real eﬀects always begin by being proportional to the particle momenta to some positive power, they must also have some positive power of the electron mass in the denominator. However, I have not yet tried to make a rigorous argument out of this. You will see, if you read the last section of the S-matrix paper, where the physical meaning of the theory is discussed, that I diﬀer very much from your view of these matters. Of course, one is here arguing about things which are matters more of taste than of judgement, and either or both of us may turn out to be completely wrong. However, I will here summarise my point of view for your consideration. I regard the method of regulators as a method of making predictions of electrodynamics mathematically precise. As such it introduces into the theory a few additional physical hypotheses which were left vague in the old electrodynamics but these new hypotheses do not assert any physical signiﬁcance for the method of regulators itself. In other words, 275 F.J. Dyson, ‘The S-Matrix in Quantum Electrodynamics’, Phys. Rev. 75, 1736– 55 (1949). The paper was published in June 1949 but had been submitted in February 1949. 276 See W. Pauli and F.Villars, ‘On the Invariant Regularization on Relativistic Quantum Mechanics’, Rev. Mod. Phys. 21, 434–44 (1949).

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the physics of the method is to be found in the formulae which are obtained after going to the limit and letting all additional masses tend to inﬁnity, and not at any earlier stage. The hope which is expressed in the last section of the S-matrix paper and which I believe is a promising hope, is that electrodynamics can now be put into a consistent and divergence-free shape by a purely mathematical reformulation, without any additions to its physical content. The method of regulators is a rather modest step in this direction. I certainly envisage the necessity later on of making alterations in electrodynamics of a more fundamental and physical kind. But I think the nature of such alterations cannot be guessed at, for example, by proposing to take seriously the formulae which arise in the method of regulators before passing to the limit of inﬁnite auxiliary masses, you are making such a guess. I am less ambitious and conﬁne myself to squeezing all I can out of the existing theory. Again with many thanks, Freeman Dyson

[480] Rudolf Peierls to Robert Oppenheimer [Birmingham], 13.4.1949 (carbon copy) Dear Oppie, Things have changed a little as regards the calculation of van Wyk,277 about which I wrote to you before. We had not noticed before that the list of cases he had covered in his paper did not contain the case in which both mesons have zero spin. In this case the emission of one photon is forbidden by conservation of angular momentum. The next process one would think of is then the emission of a positron-electron pair which might give an intensity only 137 times smaller. We have not studied this process but this is also forbidden if the two mesons have opposite parity, i.e. if one is scalar and the other pseudoscalar. In that 277

See letter [478], note 270.

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case the most likely allowed process is the emission of two photons. This has now also been calculated by von Wyk taking only the “g” coupling terms, i.e. coupling terms without derivatives. The result is: [. . . ]278 which would not seem to contradict any known evidence. I suspect that taking f type coupling instead, the result would only diﬀer by a small numerical factor, but this must be conﬁrmed. Admittedly this is a somewhat artiﬁcial explanation because it would give a [. . . ]279 -meson the same status as an isomeric nucleus, but it might exist in nature for some reason that isomeric nuclei are found. It might well be true that in principle mesons are possible with all sorts of diﬀerent masses and spins and that they all have very short lifetimes and are, therefore, never seen except the [. . . ]280 which is metastable and therefore just visible. Until we have evidence about the spin and parity of these mesons we should therefore bear in mind this rather simple possibility which does not require a drastic breakdown of current theory. Von Wyk’s paper has not been sent oﬀ for publication as yet, and he has amended his calculations accordingly. I would be interested in your reaction to this development. Yours sincerely, R.E. Peierls

[481] Rudolf Peierls to Freeman Dyson [Birmingham], 22.4.1949 (carbon copy) Dear Dyson, Thank you very much for your letter.281 In the meantime I had a chance to digest your second paper282 a little more and I think I now 278

Missing in carbon copy. Missing in carbon copy. 280 Missing in carbon copy. 281 Letter [479]. 282 Ibid., note 275. 279

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understand its ideas, though, of course, I have not yet mastered every detail of technique. I think, as Bohr would say, “we agree much more than we think”. You have shown in your paper that as long as the expansion in powers of the coupling constant is justiﬁed, one can ﬁnd the prescription which will make the coeﬃcient of any power unambiguous and ﬁnite. The new point which I had not appreciated when I last wrote was that only two or three divergent intervals recur and that everything is unique once one has made up one’s mind what value to attribute to them. Up to this point, of course, there can be no possible controversy. However, the penalty for using an arbitrary prescription imposed after constructing the fundamental equations is that the procedure is not convincing as regards consistency with a diﬀerent approach. If one could calculate the whole thing from a theory which would give only ﬁnite answers either by introducing a fundamental length or by using auxiliary masses of the Pauli type, one would at each stage get a deﬁnite answer and could then go to the limit of the point charge or of inﬁnite auxiliary masses. I have little doubt that by proceeding in this limit your prescription for identifying and discarding self-energy terms would justify itself and that the questionable divergent integrals would in all orders take the values that you require. However, what is doubtful is the part played by the series expansion in this procedure. One may, I think, learn a little from the analogy with the classical case. The nonsense one gets in the Dirac equation with runaway solutions is directly due to the fact that this theory assumes the inﬁnite positive self-energy to be oﬀset by an inﬁnite negative mechanical rest mass. At high acceleration the ﬁeld lags behind and hence the negative mechanical energy provides an unlimited store for further acceleration. If the use of a cut-oﬀ in the Weisskopf theory of the self energy is any guide, it is likely that in a ﬁnite theory the self-energy will again be positive, though, of course, only varying as a logarithm of the cut-oﬀ energy. If you then proceed to the limit of zero radius you will reach a point at which the mechanical mass changes sign. Now in the classical theory the mischief brough[t] by this is not apparent if you only look at solutions which are power series in the electric charge and trouble arises from the appearance of new solutions which cannot be so expanded. In the quantum theory it

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is likely that the corresponding trouble, if it arises will take the form that no solution corresponds to a convergent series. Whether or not this diﬃculty arises in your cases is not easy to say and there are two separate questions: (a) whether the series obtained with your existing method converges. This would seem rather likely. (b) the other question is whether a theory in which a self-energy is made ﬁnite would converge for all values of the self-energy so that one could go to the limits. If (a) is all right but (b) is not, in other words if the elimination of the self energy and the limit of zero radius are not interchangeable, one could begin to have doubts whether your theory would be logically consistent with a treatment of the case where one deals with the case of discrete levels. It is perhaps not quite fair to attack you on this point because you admit yourself that you have not covered the case of stationary states, but my point is that if one can succeed in rendering your prescription as plausible from a physical point of view, one would gain increased conﬁdence that it must hang together with a reasonable treatment of stationary states. If it is regarded merely as a mathematical procedure justiﬁed by its consistency and by its results, one is, of course, left with the job of proving the consistency fully for all conceivable combination of cases. I was also rather interested in your discussion of observability and I very much like the tendency to say that because one cannot detach particles from their ﬁelds, the range of possible observations is rather more limited. This ﬁts on to what Landau and I tried to do many years ago283 but did not do right. However, I think this must be studied very much more deeply because from the way you put it one does not get a clear distribution what the limits of observation are and what physical factors in them are responsible for the limitation. You will have an amusing controversy on your hands as soon as Bohr reads that section of your paper because Bohr is very sensitive to anything being said on this subject that he does not fully approve. The controversy, however, will be both entertaining and instructive. 283

R.E. Peierls and L. Landau, ‘Erweiterung des Unbestimmtheitsprinzips f¨ ur die relativistische Quantentheorie’, Z. Phys. 69, 56–69 (1930).

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I always feel that there is something inconsistent in the whole present approach because we take as a starting point the wave equation, i.e. the relation between energy momentum and spin, for free particles which is about the only thing we must be sure of. However, when one proceeds with the theory it turns out that the wave equations we have written are not really the equations for real particles, but they are the equations for ﬁcticious particles uncoupled from the surrounding ﬁeld about which we ought not to postulate anything. One could, of course, start diﬀerently by postulating in the ﬁrst place that the wave equations for one real electron or one real photon should be simple and in that way would make the variables used by Schwinger after the ﬁrst transformation the real basis of the theory. However, in these variables the equations, of course, are not linear but contain coupling terms of any arbitrary order giving direct matrix elements for processes in which an arbitrary number of particles are created, provided you have at least two to start with. Obviously it is hopeless to expect that each of these treatments of arbitrary order should be derived from the new physical principles, but it might be possible that there exists some common functional form for all these terms taken together which could be justiﬁed by reference to general principles. If this could be done one would have a basic formulation in which the “bare” particle never enters and in which accordingly the question of self-energy never arises. This would, I think, be very close to the spirit of your treatment but would diﬀer from it by the fact that the self-energy is not ever written down and then eliminated. But whether such a treatment is possible I have no idea. Yours sincerely, R.E. Peierls

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[482] Rudolf Peierls to Wolfgang Pauli [Birmingham], 10.6.1949 (carbon copy) Dear Pauli, Following our discussions here284 we have thought more about some of the problems arising from regularization and some more quantitative work has been done by Rzewuski. I think you might be interested to know the position we have reached at present, particularly since Rzewuski is going back to Poland now and for some time our own further progress here will not be rapid. The ﬁrst things that Rzewuski tried was to see whether in place of using particles of integer spin one could obtain your regularization also if the auxiliary particles were Fermi particles of higher spin. It seems somehow more satisfactory to couple electrons with other Fermi particles, though, of course, in regularizing such things as the electron self-energy one has to use “auxiliary photons” and one would like those to be Bose particles. Rzewuski has limited himself to auxiliary electrons of three-halves and he has looked at the problem of vacuum polarisation.285 In this case, it turns out, however, that the terms which give the same singularity as that for spin one-half, also have the same sign and therefore cancellation is impossible. Moreover, one obtains singularities of higher order because of the occurrence of higher derivatives in the commutation laws and these cannot be cancelled unless perhaps one introduces particles of still higher spin, but at this point we give up. The situation, however, is still worse in which it is a condition on the Schwinger formalism that the local interaction Hamiltonian should 284

Wolfgang Pauli had visited Birmingham in March 1949. See letters Peierls to Pauli, 17.2.1949, Pauli to Peierls, 23.2.1949 in Pauli, Wissenschaftlicher Briefwechsel, III, pp. 631–2 and 638–39. 285 J. Rzewuski, ‘Some cut-oﬀ methods for the electron self-energy’, Proc. Roy. Soc. A62, 386–91 (1949). He later took up this work in a joint paper with Rayski. J. Rayski and J. Rzewuski, ‘On a system of ﬁelds free of divergences of the mass renormalization type’, Acta Physica Polonica 10, 159–72 (1951).

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have the property that its value at two points on the same space-like surface should commute. Schwinger discusses this condition for his case and he claims that it is all right, but as far as we can see the proof involves the same kind of doubtful treatment of products of singular functions which you have criticised. This diﬃculty does not arise in Schwinger’s case, if the electro-magnetic potentials are not quantized. In the case of spin three-halves this further goes wrong, already for a given external ﬁeld and therefore one cannot really draw any conclusion at all, but this diﬃculty in itself seems to me to oﬀer a ray of hope. It has been shown by Tomonaga that a similar diﬃculty arises in the case of meson ﬁelds or in other cases where the interaction Hamiltonian contains derivatives of the ﬁeld variables and Tomonaga has succeeded in adding a term to the interaction which restores the Lorentz invariance as well as the commutability. One might try to do the same for the general Schwinger case and the extra terms would then have to be as ambiguous as the term Schwinger uses, but in such a way that the total expression becomes unambiguous and therefore for its evaluation one can use any reasonable representation of the D-function. We have not yet seen, however, how to start looking for the right kind of term. In case of spin one-half one can write the commutator between different local Hamiltonians including ﬁeld quantization and if one takes only the vacuum expectation value, which certainly ought to vanish, it actually becomes somewhat identical with your K[· · · ]286 , but with the function [· · · ]287 x − x replaced by D[· · · ]288 (x − x ). One other point that we notice and which shows how sloppy the Schwinger mathematics can be arises from the zero-point energy. In equation 1.46 of Schwinger’s second paper289 he claims, for example, that the vacuum expectation value of the energy density of the electromagnetic ﬁeld is zero. This, however, is also equal to the expectation value of E 2 + H 2 and it is rather a tall order to be asked to believe that this can be zero. Of course, the zero-point energy can always be 286

Missing in carbon copy. Missing in carbon copy. 288 Missing in carbon copy. 289 Letter [476], note 268. 287

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subtracted in an invariant way and will not give trouble, but to claim that a calculation of this quantity can give zero shows how dangerous the Schwinger methods are. This makes us feel that a decent solution of the diﬃculties which you have pointed out in connection with vacuum polarization is really essential even at the very beginning and even the basic equations of the theory hang in the air until this problem has been faced. I would be very interested in your reactions to these various points. Yours sincerely, R.E. Peierls [483] Wolfgang Pauli to Rudolf Peierls Z¨ urich, 10.7.1949 Lieber Herr Peierls! Ich beantworte erst heute Ihren Brief vom 10. Juni,290 da ich hierzu noch einige Resultate abwarten wollte. Zu den von Ihnen aufgeworfenen Fragen wollte ich folgendes sagen: 1. Ich weiß jetzt, daß alle Zweideutigkeiten betreﬀend Kommutatoren von physikalischen Gr¨oßen (Viererstrom, Dichte der Wechselwirkungsenergie) in Punkten mit raumartiger Verbindungslinie fortfallen in einer Mixtur aus “wirklichen” geladenen Elektronen und geladenen Spin 0-Bosonen, wenn die Bedingunen erf¨ ullt sind 2 Ci Mi = 0 Ci = 0, (Dies ist demnach gen¨ ugend f¨ ur Eichinvarianz der Resultate.) mit ur alle Spin 1/2-, Ci = −1/2 f¨ ur den speziellen Werten Ci = 1 f¨ ∗ alle Spin 0-Teilchen. ∗ Dieses

Resultat stammt (f¨ ur die erste N¨ aherung in e2 /c unabh¨ angig von Rayski und Jost [Jost und Rayski (1949)], von Uhlenbeck und Pais [Pais und Uhlenbeck (1949)] und von Umezawam Yukawa und Yamada [(1948)](nach brieﬂicher Mitteilung von Tomonaga). 290

Letter [482].

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Dieser “realistische” Standpunkt d¨ urfte auch gen¨ ugend sein, um die Nullpunktsenergie zu kompensieren, da diese ja negativ ist f¨ ur Elektron-Positronpaare.∗∗ (Man soll Kompensation der Nullpunktsenergie-dichte in allen Raum-Zeitpunkten verlangen. ∂ 2 ∆(1) Es handelt sich um Ausdr¨ ucke der Form i Ci ( ∂xµ ∂xν )x<0 mit verschiedenen Massen.) Ich weiß allerdings nicht auswendig, ob auch hier die Zahlenwerte Ci = 1 f¨ ur Spin 1/2, Ci = −1/2 f¨ ur Spin 0 die richtigen sind, aber ich vermute das. Dieser “realistische” Standpunkt versagt f¨ ur die 2. Aber: Selbstladung. Diese (logarithmisch unendliche) Konstante hat dasselbe Vorzeichen f¨ ur Spin 1/2 und Spin 0-Teilchen (aus physikalischen Gr¨ unden vermute ich dasselbe f¨ ur alle Teilchen) und eine Kompensation ist unm¨ oglich. Dieser Sachverhalt macht mir die gr¨ oßte Sorge (siehe jedoch unten sub 5). (Jost nennt die Selbstladung den ‘top-nonsense’ der jetzigen Theorie.) 3. Was Teilchen mit h¨ oherem Spin betriﬀt, so habe ich bisher immer vermutet, daß f¨ ur geladene Teilchen mit h¨ oherem Spin im a¨ußeren (nicht quantisierten) elektromagnetischen Feld die Komponenten des Viererstromes in Punkten mit raum-artiger Verbindungslinie wirklich nicht kommutieren werden (und nicht nur zweideutig sind). (Wissen Sie etwas bestimmtes dar¨ uber?) Ich war deshalb geneigt, geladene Teilchen mit Spin > 1 auszuschließen (seit etwa 1940). Einer meiner Sch¨ uler hat mich darauf aufmerksam gemacht, daß dieser Schluß nicht zwingend sei, da eine Mischung geladener Teilchen mit h¨ oheren ganz- und halbzahligen Spins existieren k¨ onnte, f¨ ur welche der Vakuums-Erwartungswert des Kommutators der Totalstromkomponenten in Punkten mit raumartiger Verbindungslinie wirklich Null ist. Vielleicht werden wir das hier noch weiter untersuchen. ∗∗ Das

ist eine alte Idee von Pais und Bohr (1946).

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4. Ein Schwede in Lund namens K¨ all´en, der jetzt in Z¨ urich ist, hat das von Ihnen bei meinem Besuch in Birmingham angeregte Problem der h¨ oheren N¨ aherungen (d.h. nicht linear im ¨außeren Feld) der Vakuumpolarisation mit großem Erfolg behandelt. (Dabei wurde zun¨ achst das elektromagnetische Feld nicht quantisiert.) F¨ ur Elektronen kam dabei heraus, daß die Divergenzen in den sukzessiven N¨aherungen imachsth¨ oheren N¨ aherung ist mer schw¨acher werden. In der n¨ dann nur noch eine (die Eichinvarianzst¨ orende) logarithmische Divergenz vorhanden, die mit Ci = 0 formal weggeht und alle folgenden N¨ aherungen (von e6 angefangen) konvergieren von selbst. Nun rechnet K¨all´en dasselbe auch noch f¨ ur Bosonen (Spin 0). Ich vermute, daß die oben beschriebene Mixtur — bis auf die unendliche Selbstladung! — in allen N¨ aherungen konvergiert.291 5. Dabei blieb, wie gesagt, das elektromagnetische Feld unquantisiert. Das andere Problem, wo man sich umgekehrt auf ur aber die die im a¨ußeren Feld lineare N¨aherung beschr¨ankt, daf¨ von der Quantisierung des elektromagnetischen Strahlungsfeldes herr¨ uhrenden Korrekturen in h¨ oherer N¨ aherung berechnet, wird hier von den beiden Polen Rayski und Weyssenhof behandelt.292 (Rayski ist eben nach Hause gefahren, aber Weyssenhof — der bessere Physiker von den beiden, der auch sehr eifrig ist — bleibt noch bis Herbst hier.) Bei diesem Problem gibt es nat¨ urlich etliche Korrekturen zur Selbstladung. Ich bin sehr neugierig, welches Vorzeichen diese Korrekturen in n¨ achst h¨ oherer N¨aherung haben werden und hoﬀe, daß es negativ sein wird. Es schwebt mir n¨ amlich — als letzter Ausweg beim Selbstladungsproblem — etwas vage eine Art Bestimmung von e2 /c aus der Bedingung des Verschwindens der Selbstladung vor. Nat¨aurlich ist es dann sehr unsch¨ on, daß man nach Potenzen 291

G. K¨ all´en, ‘Higher approximations in the external ﬁeld for the problem of vacuum polarization’, Helv. Phys. Acta 22, 637–654 (1949). 292 See J. Rayski, ‘Polarization of the vacuum’, Phys. Rev. 75, 1961 (1949).

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von e2 /c entwickelt, {Das denke ich mir aber nur als Ersatz f¨ ur 2 die Behandlung einer strengen Gleichung f (e /c, m1 , m2 , · · · ) = 0 wobei man eben f (.) nach der Variablen e2 /c entwickelt.} Zun¨ achst muß man nat¨ urlich sehen, ob auch die Terme n¨ achster ur die Selbstladung bei Elektronen und bei N¨aherung in e2 /c f¨ geladenen Bosonen kompatibel sein sollen. (Nat¨ urlich werden auch die zur Kompensation bei der Selbstenergie der geladenen Teilchen ben¨ otigten neutralen skalaren Hilfsfelder mit m = 0 in dieser N¨aherung Beitr¨ age zur Selbstladung geben.) Es w¨ urde mich interessieren, nun Ihre Kritik zu meinem momentanen Standpunkt zu h¨ oren. Es ist merkw¨ urdig, daß ich aus Ihrer Kritik immer sehr viel mehr lernen kann als aus Ihren eigenen Arbeiten (oder Arbeiten Ihrer Sch¨ uler). Meine allgemeine Idee ist die, daß die in beliebig kleinen Raum-Zeitgebieten deﬁnierbaren physikalischen Gr¨ oßen (TotalEnergie-Impulsdichte, Total-Vierer-Strom) keine Speziﬁzierung der Massen und Spins der beteiligten Teilchen erlauben d¨ urfen (siehe oben sub 1 des u ¨ber die Nullpunktsenergie Gesagte). Mit vielen Gr¨ ußen and Sie selbst und Ihre Familie (how is the baby?) Stets Ihr W. Pauli P.S. 1) Der Inder Vachaspati muß sich erst an die europ¨ aische Umgebung gew¨ohnen und hat vorl¨ auﬁg noch nichts geleistet. Er soll, ﬁnde ich, vorl¨ auﬁg ruhig hier bleiben und so weit deutsch lernen, daß er Vorlesungen h¨ oren kann, statt schon wieder den Ort zu wechseln. Sollte er bis Herbst noch immer nichts verstanden haben, so m¨ ußte man ihn dann heimschicken, aber ich habe die Hoﬀnung f¨ ur ihn noch nicht aufgegeben. 2) Ein Sch¨ uler von Schwinger hat mir einen langen, aber keineswegs inhaltsreichen Brief betreﬀend meiner Kontroverse mit seinem verehrten Lehrer geschrieben. Die Diplomatie dabei besteht darin, daß Schwinger ihm zwar gestattet hat, mir zu schreiben, sich aber geweigert hat, den

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Brief seines Sch¨ ulers selbst zu lesen!— Inhaltlich konnte ich nichts anderes aus der langen Rede entnehmen als daß Schwinger eine Art Oﬀenbarung (auf irgendeinem Berg Sinai) gehabt hat: Und der Herr sprach: (1) ur x − 0, tue aber nicht so f¨ ur ∂x∂ ν ∂ (4) (x) ,,Setze immer ∂∆ ∂xν = 0 f¨ trotz gleicher Symmetrieeigenschaften.”— Was Schwinger bei der Nullpunktsenergie macht (im Gegensatz zu meinem Kompensationsversuch) ist nat¨ urlich ganz a¨hnlich. [484] Rudolf Peierls to Hans Bethe [Birmingham], 27.7.1949 (carbon copy) Dear Hans, It looks almost as if I have not written to you since your letter of 7th February.293 Meanwhile your letter about Dyson has done just what I wanted it to do, namely not merely persuaded the university to oﬀer him a good job, but also got the Royal Society to appoint him to a Warren Fellowship which has advantages. He has been here already for two days and it will make all the diﬀerence to the department to have him here next year. I assume that you have not done any more about the Physical Society Progress Reports and that is just as well, because with all the experiments going on now it is likely that a report written now would be obsolete before it appeared (the volume now in preparation will not come out before July 1950). Things may have settled down a little more in a year’s time. The closing date for manuscripts for the following volume is going to be about September 1950 and it is much too early to talk about an article for that volume. However, I need hardly say that if you actually have started to write an article and if you are prepared to let us have it by September, everybody will be delighted to see it go in to the forthcoming volume. 293

Letter Hans Bethe Ms.Eng.misc.b.202, C16.

to

Rudolf

Peierls,

7.2.1949,

Peierls

Papers,

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On the question of nuclear structure it seems indeed that Feenberg and Swiatecki here have been thinking along very similar lines, but for some time, Swiatecki has been working on a decent derivation of the surface tensions of a nucleus which is essential for the question under discussion and he had discovered that nothing said on this subject in the literature is any good. He has now developed a generalization of the Thomas-Fermi method which is suitable to treat potential gradients and, while the numerical work is not complete as yet, he seems to be able to derive a fairly good value for the surface term in the semiempirical formula and one can then have some conﬁdence in applying the methods to internal density gradients. I have not heard anything from Slotnick,294 but I had some correspondence with Gerald Brown of Yale 295 who makes a very good impression and who is coming here probably with a Fulbright Grant. He was coming in October, but he has to ﬁnish some job for Breit and will not be free before January. The last session has not been very productive, largely, though not entirely, because we were always trying to catch up with the work on ﬁeld theory by Schwinger, Feynman and Dyson etc. We are now preparing for a determined attack on discussing meson theory by the new techniques without the use of perturbation theory; most of what has been said in the literature seems just to be perturbation theory run riot. Dyson told us the sad story of your car; I hope it is making a good recovery and that in spite of it you are by now all reunited. Yours sincerely, [Rudi]

294

Murray Slotnick, at the time at Columbia University then moved on to Princeton postdoctoral fellow. 295 Gerry Brown had worked with Gregory Breit at Yale. He joined the Birmingham group in 1950.

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[485] Niels Bohr to Rudolf Peierls Copenhagen, 22.8.1949 Dear Peierls, It has been a pleasure to me that it has now been arranged that Lindhard296 will be with you next year. I am sure that it will be a great experience to him and I also hope that it will mean a still closer cooperation between our groups. As a small beginning I reckon that Lindhard’s stay with you will be helpful in completing our old work with Placzek. In the last weeks I have gone through the old manuscripts with Lindhard and discussed with him the latest progress as regards nuclear constitution and in particular the success of the method of considering the binding energy of the nucleons separately in the nuclear ﬁeld. I realize that one sometimes has taken the drop model too literally, and to clear my thoughts, I have written down a few tentative comments297 of which I shall be very glad to hear your opinion. They do not contain much new, but I feel that the development gives a simple basis for the treatment of the problems of nuclear reactions and removes doubts as regards the conclusions to be drawn from dispersion theory and detailed balancing. As soon as I get time, I will try to incorporate such views in our old manuscript and will, if not before, give it to Lindhard when he leaves. This summer I have been busy with the preparation of a series of lectures on general topics, which I shall deliver at Edinburgh in the autumn 298 and have also worked with Rosenfeld on the completion of our work on the measurability of ﬁeld and charge quantities.299 It has come out that the situation is just as required by Schwinger’s formalism, and that it is simpler than assumed by Heisenberg in that respect that charge ﬂuctuations are well deﬁned in sharply limited space-time 296

Jens Lindhard (1922–), student of Niels Bohr’s, later professor of theoretical physics University of Aarhus. 297 Manuscript ‘Tentative Comments on Atomic and Nuclear Constitution’, (1949), reproduced in Bohr. Collected Works, Vol. 9, pp. 523–55. 298 See letters [486], [490]. 299 N. Bohr and L. Rosenfeld, ‘Field and Charge Measurements in Quantum Electrodynamics’, Phys. Rev. 78, 794–98, (1950).

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extensions, just like ﬁeld ﬂuctuations. Also, this work I hope to complete in the autumn months. As you may understand it will be quite a busy time for me and, if it is not too inconvenient to you, I should be glad if Lindhard could stay here and leave for Edinburgh in the middle of October or in any case till the end of September. With kindest regards and best wishes to your family and yourself from us all, Uncle Nick

[486] Rudolf Peierls to Niels Bohr Birmingham, 26.8.1949 (carbon copy) Dear Uncle Nick, Thanks you for your letter.300 It will be all right for Lindhard to come here in the middle of October. I gather from Born that your lectures in Edinburgh will have longish intervals between them and this makes me wonder whether there might be a chance of you spending a little while in Birmingham while you are in this country. It would, of course, give us the greatest pleasure, if that were possible and we would be able to look after your expenses arising from such a visit. However, you need not decide this now.301 I have read your note with great interest,302 but I am afraid I do not agree with some of the points. If I understand correctly the argument on the second page, you deduce from the large indeterminacy of position that it is possible to describe the motion of each particle as if it were moving in a smooth ﬁeld of force. I do not believe that this conclusion is correct. At least if one assumes the forces between the nucleons to be of the type usually assumed (i.e. two-body forces, partly of exchange character, and compatible with the properties of light nuclei) 300

Letter [485]. Bohr did go to Birmingham and Peierls also met him in Edinburgh during the summer. See letter [490]. 302 See letter [485], note 299. 301

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then the attempt to ﬁnd the best potential to represent the motion has been carried out by Euler303 for a nuclear force obeying a Gaussian law and by Huby304 for the “meson potential”. Both have calculated the higher approximations which take into account the correlations between individual nucleons and ﬁnd that these higher terms are by no means small and severely alter the magnitude of the total binding energy. This tends to prove that, while the potential energy of the particle does not depend much on its position relative to the centre of the whole nucleus, it does depend decisively on the position relative to the neighbouring nucleons. It is in the nature of exchange forces that this kind of correlation becomes particularly strong since each nucleon tends to be coupled strongly with only three others. Now in the last few months we have seen evidence that properties of nuclei could be described very well by means of a “shell model” which would seem to contradict the conclusion about the importance of correlations. Supposing that this evidence is really conclusive, it would mean either that the nuclear forces are not of the kind which are now generally accepted, or that there exists some other way of describing the motion in which correlations are not neglected and in which nevertheless, the energy values can be put in correspondence with the shell model. I think it is important to face this diﬃculty and to recognize that with at least the usual assumptions about nuclear forces the uncertainty in the position is not suﬃcient to make the shell model a good approximation. For the same reason I am not very happy about the view you take at the end of the second page, in which the capture of a particle into the nucleus proceeds ﬁrst by way of a stationary state in a smooth potential. In a formal way one can, of course, always consider such states with limited life-time due to the possibility of exchange of energy between the nucleons. I should expect, however, that in the energy region corresponding to the capture of a neutron of few MeV, the life303

¨ H. Euler, ‘Uber die Art der Wechselwirkung in den schweren Atomkernen’, Z. Phys. 105 (1937), 553–75. 304 R. Huby, ‘Investigations on the Binding Energy of Heavy Nuclei’, Proc. Roy. Soc. London A62, 62–71 (1949).

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time of such a state would be so short that it would not be very helpful in describing nuclear processes. However, at much higher excitations energies it may well be that such states would help to understand the maxima and minima in the excitation curves found, for example by Pollard and his collaborators at Yale.305 Kindest regards, from all of us and also to Mrs. Bohr, Yours sincerely, R.E. Peierls

[487] Rudolf Peierls to Robert Oppenheimer Birmingham, 16.10.1949 Dear Oppie, I am afraid I vanished from Princeton without trace, and without saying again how much I enjoyed the day; I was very conscious of having come at a time when you could have used a day’s quiet much better than any visitor, and if I had known before that I could aﬀord a few days in U.S. after the conference, I would have suggested coming later. The Chalk River Conference turned out to be much more fruitful than I expected, and we had an opportunity of saying what ought to be done next and why.306 Whether this will get us anywhere, I do not know, of course, but the discussion was at least interesting. I have been very much intrigued by your idea that the nuclear forces (apart from tensor interactions) might, in fact be contact forces, and that the “eﬀective range” might, in fact, be due to damping. There is in this, a mathematical problem, whether damping eﬀect of the kind we know now can result in a ﬁnite range, while not, at the same time, also contributing to the p−, d−, · · · scattering about as much as a “real” 305

E.C. Pollard (1906–1996), had studied at Cambridge under Chadwick. In 1933 he joined the Yale faculty and later became the ﬁrst professor of biophysics there. In the late 1940s he worked on exchange forces and he carried out experiments involving the deuteron bombardment of various elements. 306 Peierls had attended a declassiﬁcation conference at Chalk River. While on the other side of the Atlantic, he had spent a day at Princeton.

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potential of the same eﬀective range. No doubt you will be pursuing this further; I am trying to look into this for my own satisfaction, but I would be very glad to know if you reach a deﬁnite conclusion. I would have written before, but on my return we discovered that our last baby has achondroplasia, which means she is one of those dwarfs with normal bodies and very short arms and legs. We were naturally in great distress, but it makes it a little easier to know that she is likely to reach 4 or 4 12 ft. and that people of this type are usually very happy and well-adjusted. We are now trying to ﬁnd some adult people with this condition, so as to learn better the sort of life for which to educate her; but the condition is quite rare. Dyson has been here for a week or so; he makes a great diﬀerence to the place. With many thanks again and greetings to Kitty. Yours sincerely, R.E. Peierls

[488] Rudolf Peierls to Raymond Priestley [Birmingham], 9.11.1949 (carbon copy) Dear Vice-Chancellor, I believe that the next meeting of the Senate Executive Committee will have before it again the proposal concerning the method of deciding promotions at the eﬃciency bar. As no doubt you know, this was discussed by the Faculty of Science Executive in a long and heated debate ending in a close vote in favour of the proposal that the discussion be limited to Professors. I do not wish to be disloyal to my colleagues in raising again a question on which I voted with the minority, but I have very strong doubts whether the decision was constitutionally possible. The presently accepted constitution of the Faculty of Science provides clearly that questions of salary are to be decided by Faculty Executive which includes the Chairman of Faculty Boards. I do not believe this constitution can

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be altered by one of the bodies of which Faculty consists, though, of course, Senate can over-rule it. The responsibility, therefore, rests with Senate and is not settled by the decision of Faculty Executive. Turning now from the legal form to the substance of the programme, it seems to me a retrograde step to exclude non-professorial members of staﬀ from such discussions. For some years we have had in the Faculty of Science the Chairmen of two Boards present and I have never seen any signs of embarrassment resulting from their presence or any contribution from them which was not as constructive or as responsible as from Professors. I believe we have a lot to gain from the presence of men who, while they cannot repeat outside the meeting the arguments that were used, will be able to assure their colleagues that each problem was discussed fairly and on the basis of available facts and without personal prejudice. One hears stories of cases in the past where members of nonprofessorial staﬀ behaved irresponsibly. I think we must recognise that whatever may have been the quality of our staﬀ twenty years ago we would have failed badly in our duty if this was possible now and in any event if such people were appointed Chairmen of Faculty Boards or in other ways members of Faculty. In the particular case of the Faculty of Science the proposed constitutional change would make a very illogical position since it would leave promotion to Grade I, the withholding in exceptional cases of routine increments, the temporary re-appointment of members of staﬀ beyond retiring age and similar matters involving delicate personal matters, in the hands of the full Faculty Executive with the sole exception of the increase at the eﬃciency bar. The only logical step to take if this is passed would be to exclude the Chairman of the Boards also from the discussion of all thee matters, leaving them in practice merely to present the report of their Boards and depart. This would completely wreck the spirit of the present experiment in the Faculty and give oﬀence to the non-professorial staﬀ. I hope Senate Executive will bear these points in mind when making their decision. Yours sincerely, R.E. Peierls

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[489] Ed Salpeter to Rudolf Peierls Ithaca, 4.12.1949 Dear Peierls, A. Physics (i) “Rochester Star”. You’ve probably heard of Brodt and Peter’s famous star by now, but just in case you haven’t, here it is: In a star with 18 heavy-fragment prongs (Ag or Br nucleus), 23 minimumionisn. particles were emitted in a cone making ∼ 2.5◦ (total projected angular spread) with forward direction and 33 at larger angles. In 1/4 ” radiation length of glass & emulsion 15 to 20 more charged p[articles] were produced in this forward cone. (These are presumably e+ − e0 pairs created by the γ-rays given oﬀ by the decay of the neutral mesons. ∴ most probable number of neutral mesons ∼ 20). Av[erage] energy of these neutral mesons estimated (from spread of the pairs, I think?!) to be 10BeV each. The conclusion is (a) Must be multiple production in a single act (at least the forward cone), (b) evidence for neutral mesons and either (c) Meson production in C.G. systems is isotropic, but only fraction of energy converted into mesons or (d) Most of energy converted, but mesons produced in cone (∼ π/10) around the direction of each of the nucleons. (ii) Electron Sprays: Exp[erimen]ts of Oppenheimer & Ney307 (Phys. Rev. 76, 1418 (1949)) have been separated and conﬁrmed: Up to 50 particles of mass < 10me and kinetic energies not much greater than their rest mass (since almost all absorbed in one radiation length of Pb without starting showers) have been observed. According to one report these sprays have been so frequent, that every second primary at 100.000ft must create one!! Noone here has an explanation as yet (if the exp[eriments] are really correct). 307

F. Oppenheimer and E.P. Ney, ‘Wide Angle Sprays of Minimum Ionization Particles’, Phys. Rev. 76 1418–1419 (1949).

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(iii) I don’t know of any spectacular results I can report on but here are some topics on which people are working: (a) Multiple meson production (Princeton Inst. Rochester). Attempts to modernise the 1949 paper of Lewis, Oppenheimer and Wouthuysen308 and rescue what can be secured of it. Interest (mainly scepticism) in Heisenberg’s view (Z.P. 126, 569, (1949)309 that mesonic interaction at high energies is so strong that methods like L.O. & W’s (which assume “statistical independence” of meson emission) are entirely unjustiﬁed. (b) Investigations for all types of meson interactions which nucleon-mesonic ﬁeld interactions, give ﬁnite results with massand charge renormalisation alone — which can be rescued by a ﬁnite number of additional renormalisations (i.e. adding inﬁnite quadruple moment coupling terms in original Hamiltonian etc. ) (Princeton Inst., Cornell, etc.) (c) Diﬃculties of ﬁnite cut-oﬀs (Pais & Uhlenbeck, Feynman310 ): With ﬁnite order diﬀ[erential] equations on P[ais] & U[hlenbeck]]s theory (equiv[alent] to discrete values of masses of auxiliary “photons” on F[eynman’s] theory) the theories seem to be mathematically self-consistent but lead to predictions which are physical nonsense (emission of negative-energy auxiliary particles, etc.) On F[eynman’s] theory of continuous distribution of auxiliary masses it seems possible to make prob[abilities] of emission of these negative energy p[artic]les zero. (F[eynman]’s dodge is to calculate the excitation of a far-away atom, say, by means of these auxiliary p[artic]les — instead of calculating their emission pr[obability] in the orthodox way — so that he adds amplitudes and not pr[obabilities] and the contributions of the diﬀerent masses cancel.) But in this case the theory is self-inconsistent, e.g. the

308 H. W. Lewis, J. R. Oppenheimer, and S. A. Wouthuysen, ‘The Multiple Production of Mesons’, Phys. Rev. 73, 127–140 (1948). 309 ¨ W. Heisenberg, ‘Uber die Entstehung von Mesonen in Vielfachprozessen’, Z. Phys. 126, 569–82 (1949). 310 See A. Pais and G.E, Uhlenbeck ‘On Field Theories with Non-Localized Action’, Phys. Rev. 79, 145–65 (1950).

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life-time of an excited atomic state (imaginary part of Lampshift) does not tally with emission pr[obability] of real photons (as calculated by the eﬀect of a far-away atom). On P[ais] and U[hlenbeck]’s theory with inﬁnite number of orders the positrons is more obscure, but seems to be similar. B: Gossip: Believe it or not, I have tracked Tony Skyrme down to earth! In fact I spent Thanksgiving with the Skyrmes. They live in one of the Institute Housing Project apartments, own a car (ancient, but sturdy); still have their English accents without any trace of contamination and generally maintain a little oasis of England. Tony seems to prefer the Institute to MIT and is working on some rather abstract topics of ﬁeld theory. The Princeton Institute seems to have more Theoreticians this year than ever before — the only ones who haven’t arrived yet are Jost & Pauli (and they’re probably here now). There have been a few changes at Cornell — the only other addition to the Theor. Dept. is Fritz Rohrlich311 , an Austro-Israelien (ex-Jerusalem, ex-Harvard, exPrinceton). I haven’t seen very much of the Bethes or Wilsons yet, so I can’t report any news there, but they seem to be ﬁne and send their regards. I am sharing an apartment with Darcy Walker at the moment (and have managed to ﬁll it with junk). I have little to report about myself except that I, quite inexplicably, have lost my giant appetite on arrival in this country and eat no more than an average American (in my present form I just can’t touch Bethe). With best regards to you, the Peierls household and the Dept. Ed Salpeter P.S. I am enclosing a cheque for phone calls, etc. which I owe the Dept.

311

Fritz Rohrlich (1921–) who had previously been at Harvard, joined the Institute of Advanced Studies in 1949; he later went to the University of Iowa (1953–1963) and Syracuse University (1963–1991).

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[490] Rudolf Peierls to Niels Bohr Birmingham, 7.12.1949 (carbon copy) Dear Uncle Nick, I have made provisional arrangements to ﬂy to Copenhagen on the morning of 2nd January (there is no suitable plane on the 1st) and if this arrangement is still convenient to you I shall arrive at Copenhagen about 3.30 p.m. I shall be needed again in Birmingham on the 9th January and will probably have to leave on the 8th. It may help if I put down a few points that I did not have time to explain adequately either here or at Edinburgh.312 It seems to me that the contents of the paper as at present drafted are largely, if not entirely, independent of the model one makes of the nucleus, though the values one would tend to guess for the various constants occuring in the equations do, of course, depend very much on the model. In the past there has been a tendency to confuse these matters, i.e. to identify the model that you ﬁrst proposed of the nucleus, with the mathematical formalism developed to investigate this model, which, however, is far more general. For this reason I entirely agree that it would be desirable in the introduction to explain this and to say also that one should now have an open mind about the model and that the experimental facts about “magic numbers” and the success of the theory of Jensen313 and Goeppert-Meyer314 are vital pieces of evidence. However, the question of what exactly one must conclude from these things is, to my mind, essentially unsolved. In earlier correspondence I insisted that it was not correct to regard each particle as moving in the average ﬁeld of the others, if our present view about these forces were anything like correct. This, however, does not prove that one cannot 312

Bohr had given a series of lectures at Edinburgh, and on this occasion, he had met Peierls and visited him in Birmingham. See letter [486]. 313 O. Haxel, J.H.D. Jensen and H.E. Suess, ‘On the Magic Numbers in Nuclear Structure’, Phys. Rev. 75, 1766 (1949). 314 Maria G. Mayer, ‘On Closed Shells in Nuclei. II’, Phys. Rev. 75, 1969-70, (1949).

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get a shell structure out of the present forces. It might be possible, at least in the case of a single nucleon outside a closed shell, to ﬁnd a picture describing it as a particle moving in a suitable ﬁeld of force which would, however, not be the average potential of the others. The situation is reminiscent of that in ﬁeld theory, where one gets large errors (and indeed inﬁnities) if one regards the disturbance caused by the electron in the ﬁeld as small. We are now learning how to take into account the disturbance which inevitably accompanies an electron and in some sense this is the meaning of “renormalization”. One might hope in the nucleus equally to think of the momentum of a nucleon in an otherwise saturated nuclear ﬂuid, taking into account the disturbance it will locally cause in it, and this might lead to a reasonable one-body picture. I am, therefore, not sure that there is enough evidence on which you say we must abandon our present picture of the forces, but equally it is not certain that we can retain this picture and, while I am most anxious to discuss these problems with you and see what progress one can make, I feel that for the present paper it would be wiser to admit the existence of unsolved problems than to attempt a complete answer in this context. Yours very sincerely, R.E. Peierls We greatly enjoyed your brief visit. I am looking forward to the days in Copenhagen, but please say quite frankly, whether this is still convenient. If you would rather leave it until you pass through this country, this would be very nice for me, too.

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[491] Rudolf Peierls to James Chadwick [Birmingham], 8.12.1949 (carbon copy) Dear Chadwick, I believe I have not yet written to thank you for your second letter on the problem of Oliphant’s successor.315 For various complicated reasons our Committee did not, in fact, meet until this week and I was glad to be able to put your views before them. We have not made very much progress yet beyond ruling out a number of names on the grounds either that they were no[t] suitable or that it was known that they would not accept. We have, in particular, ascertained that Dee could not be persuaded to change his mind. We are now left with the following names as possibilities: (1) Moon; I have explained the position as regards him already. (2) Devons316 ; this was one of the names you mentioned and it was also mentioned by Cockroft. The Committee felt that before ruling out Devons as a candidate for the Poynting Chair, they would want to be quite clear about his merits. They might face the possibility of oﬀering him the appointment in preference of Moon if there was a really strong case for doing so. This means judging his merits as a physicists as regards past performance and future promise and his suitability from the point of view of administration and teaching. I gather that his reputation is of being somewhat intolerant with people and of expecting too much from students, but I do not know how seriously one ought to take this. I would expect, personally, that to appoint Devons would mean loosing Moon and apart from my personal regret at such a step one would want 315

Mark Oliphant was planning to take up an appointment as ﬁrst director of the Australian National University Research School of Physical Sciences in Canberra in 1950. 316 Samuel Devons (1914–), had studied at Cambridge where, after war work as senior scientiﬁc oﬃcer for the Air Ministry, he became a lecturer after the war. He later became Professor of Physics at Imperial College (1950–1955), before taking up an appointment as Langworthy Professor of Physics at Manchester. He later became Professor of Physics at Columbia University (1966–1984).

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to be sure that in the end we are gaining by the transaction. (3) Powell; this name has not previously been mentioned, partly because we always took it for granted that the appointment should bear some relation to the operation of the big machines. However, it may be possible to delegate the day-to-day supervision of the machines to some of the ﬁrst-rate people who are now with Oliphant on this job, subject, of course, to a supervision on policy and overall responsibility in the hands of one or both of the Professors. On the experiments done on the machines as opposed to their operation, one would feel that the proton synchroton should, in fact, come into very close contact with Powell’s work. I believe it may be that Powell would, in fact, prefer, if he accepted at all, to hold the second chair, but it might still be the correct course to oﬀer him the more senior job and let him choose. I am sorry to trouble you again over this, but you will appreciate that this is a most diﬃcult problem for us and it would be most helpful if you could let us have your comments on these three possibilities. We have not yet considered the problem seriously of who would be appointed to the Second Chair, if Moon were to be Poynting Professor, but (unless Powell would be interested in that position) an interesting suggestion would be Pontecorvo, but this is by no means clear and need not be settled at this stage. Yours sincerely, R.E. Peierls [492] Rudolf Peierls to Ed Salpeter [Birmingham], 26.1.1950 (carbon copy) Dear Salpeter, Thank you very much for your long and most welcome letter and the various bits of information in it. I have no particular comments on them, except that I have now understood why the results of Pais317 seem to 317

Abram Pais was working on ﬁeld theories with non-localised action. See letters Peierls-Pais, Peierls Papers, Ms.Eng.misc.b212, C.230.

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be rather diﬀerent from ours, in particular, Irving’s.318 The answer is that the work of Pais is based on the theory by Bopp319 which leads to equations for a free electron in which the integral goes over the past but not the future motion. Such theories are not equivalent to McManus’s form of the equation.320 They arise only if the ﬁeld allows a photon of ﬁnite mass as well as zero mass and I believe it follows from Pais’s arguments that to get the self energy ﬁnite, one must then assume negative energy densities for these auxiliary masses. McManus’s theory leads to integrals going over past and future and can always been arranged so as to give a ﬁnite energy but Irving has demonstrated the danger of runaway solutions. We have not yet found a form function which avoids this and it may well not exist. Whether an oscillatory runaway solution in the classical theory is necessarily fatal is, of course, another question. We have made no progress about quantisation. Rumour has it that Feynman can quantize equations having only a Lagrangian and not a Hamiltonian. I wonder whether this rumour is correct, or whether he can do this perhaps only for the Wheeler-Feynman formalism which is special in the sense that one has started from a diﬀerential theory of two ﬁelds and then eliminated one of the ﬁelds. Other current work: we are having a beautiful course of lectures from Dyson which, amongst other things, help to show how little ﬁeld theory we knew before, but a few people are now beginning to learn how to use it. Of these Dalitz has completed his calculation on the corrections to angular distribution of pairs ejected by a 0-0 nuclear transition as in oxygen. The correction is several percent but it varies rather slowly with angle and it is not easy to observe experimentally. It is of the wrong sign as well as too small for explaining results which Devons appeared to ﬁnd, which, however, in any case, were still uncertain. Ravenhall found the problem about complex eigenvalues in Feynman theory too vague and in view of what your letter says in this context I see 318

J. Irving, ‘Applications of the Peierls-McManus Classical Finite Electron’, Proc. Phys. Soc. London A62, 780–790 (1949). 319 F. Bopp, ‘Eine lineare Theorie des Elektrons’, Ann. Phys. 38, 345–84 (1940). 320 See letter [396], note 80.

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now that the problem is much deeper than I had thought. He has just completed a calculation of the production of pairs by electrons which had never been done decently and which is of interest in connection with the Bristol experiments.321 He is now going on to look at the problem of bound states in ﬁeld theory. Gunther got here ﬁnally after waiting two months for his British visa and is still living mostly on air and he is now waiting for his money from Poland. He is making rather heavy weather of the derivation of the Breit terms from ﬁeld theory (so far only the order e2 , nothing to do with Lamb shift etc.). He is tying to do it by means of a 4n dimensional conﬁguration space. I thought at ﬁrst that this would lead to unsurmountable trouble. He has convinced me that it can be done but not yet that there is an advantage in doing it. Moorhouse has shelved ﬁeld theory for the time being and has worked out the theory of scattering neutrons by ferromagnetism. It appears that one can give a very direct and instructive interpretation to such experiments which will not teach us much about neutrons, but may throw light on models of ferromagnetism. Barker has sent his paper on the Schwinger model oﬀ for publication322 and is now worrying about nuclear models, investigating, in particular, a two-particle problem which may give a lead to estimating the extent to which the existence of shells may be compatible with the general Bohr picture. Wroe has turned over to cosmology and the origin of the elements. It now looks as if the general idea of Teller and Meyer323 can be rescued assuming that the universe was at one time so small that it was completely ﬁlled with matter and nuclear density and low temperature and then expanded. This leads to condensation more or less as in the cloud chamber and the rest proceeds as in Teller’s picture. There are, 321

R.H. Dalitz, and D.G. Ravenhall, ‘On the Tomonaga method for intermediate coupling in meson ﬁeld theory’, Phil. Mag. 42, 7 (1951). 322 F.C. Barker, ‘Schwinger Potential in Nuclear Forces’, Proc. Phys. Soc. A63, 898–909 (1950). 323 Maria G. Mayer and E. Teller, ‘On the Origins of the Elements’, Phys. Rev. 76, 1226–31 (1949).

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of course, very many complications to be allowed for and one cannot yet be sure of the answer.324 Butler extended Wroe’s work on the three-body problem and set out a programme of carrying out the necessary integrations numerically. This is not prohibitive but too long for Butler to do himself and we have shelved this until we can ﬁnd a suitable computer. Lindhard, whom you don’t know, has settled down very well in the department. He is interested in the degree of ionization of nuclear fragments and in nuclear models. I am also working with him and van Wieringen on an old problem in the theory of metals in which, after ﬁfteen years, we have now made one step forward, but seem to be unable to take the remaining step necessary to get an answer. The synchrotron is getting along well but, of course, it is much too early to make any predictions. The cyclotron is now behaving well at a D voltage, somewhat below the design ﬁgure and hence giving a beam that does not quite get to the edge. It has now been decided to reduce the magnetic ﬁeld a little and thus to get certainty of a particle beam at a slightly lower voltage rather than hopes of a hypothetical beam at the design energy. You are not the only ex-member of the department who writes letters. Several people heard from Skyrme and we had a letter from Rzewuski saying that he got married recently. Gardner is settling down at Harwell but largely is continuing the kind of problem he was working on here. I forgot to mention Swiatecki. He is still engaged in mopping up operations resulting from his work on nuclear surface tension.325 We are at last getting round to issuing a list of papers of which reprints are available. I do not know whether your reprints will be sent out from Cornell, but if you like us to put your papers on the list could you let me know more or less by return as I would like to get the list out within the next week or two. In that event you should either mail 324

The results were later published as R.E. Peierls, K.S. Singwi and D. Wroe, ‘The Polyneutron Theory of the Origin of the Elements’, Phys. Rev. 87, 46–50 (1952). 325 See W.J. Swiatecki, ‘Density distribution inside nuclei and nuclear shell structure’, Proc. Phys. Soc. A63, 1208–18 (1950); and W.J. Swiatecki, ‘Nuclear Compressibility and Fission’, Phys. Rev. 83, 178–9 (1951).

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us a supply of reprints or else we should send you from time to time a list of names of people who have asked for your papers. If I do not hear from you I shall assume that you wish to stand on your own feet in this matter. Yours sincerely, R.E. Peierls [493] Genia Peierls to Klaus Fuchs Birmingham, [date unspeciﬁed]326 (carbon copy) Dear Klaus, Rudi just came home from London, and I am writing to you in front of our sitting room ﬁre, where we so often talked about so many things. This is a hard letter to write, perhaps even a harder one to read, but you know me well enough not to expect me to mince my words. I am taking it all much easier than everybody else, because my Russian childhood and youth taught me not to trust anybody and to expect anyone and everyone to be a communist agent. Twenty years of freedom in England softened me somewhat, and I learned to like and trust people, or at any rate some of them. But early attitudes are deeper and after the ﬁrst half hour I feel I can take it. I certainly did trust you. Even more, I considered you the most decent man I knew. I do that even now. This is the reason why I am writing to you. I understand that you have now changed you views and want the best of our civilisation to go on. The best is trust in human beings, friendship, this bit of freedom and fresh air which is still lingering here and there in the world and makes life worth living, and bringing up children a joy. Your actions have tremendously endangered just these things. And this in two ways: one is directly and as was your intention, and one cannot do much about that now. But one can and one must do something about the other. 326

The letter was probably written on the 4th of February 1950, the day that Rudolf Peierls visited Klaus Fuchs in prison.

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Do you realize what will be the eﬀect of your trial on scientists here and in America? Specially in America where many of them are in diﬃculty already? Do you realize that they will be suspected not only by oﬃcials but by their own friends, because if you could why not they? For your “cause” you did not have to be on such warm personal relations with them, to play with their children and laugh and drink and talk. You are such a quiet man that you could have kept yourself much more aloof. You were enjoying the best of the world you were trying to destroy. It was not honest. In a way I am glad that you failed in this, because [???] you the value of humanity, of warmth of freedom, what did you do to them, Klaus? Not only that their faith in decency and humanity is shaken, but for years to come they will be suspected to be involved in this with you. Perhaps you did not think about it at the time, but you must think now. [???] to say who were your real connections. It is awfully hard, perhaps the hardest thing of all to do. But you went all the way in one direction, don’t stop half way now. You are not soft, and not one for an easy way out. You are a mathematician. This problem has no rigorous solution. Try to ﬁnd the best approximation. Rudi told me that you don’t want to give the impression that you want to ease your own position. Klaus, don’t be a child. This is the schoolboy code of honour. Impressions don’t matter. You personally do not matter. The issues are too important for that, and you know it, otherwise you would have taken the only easy way out for you personally — to take your life. Thank you for not doing that. You could not leave all this terrible mess for others to sort out. This is your job, Klaus. And you know you never shirked. No even the washing up!! Oh Klaus, my tears are washing away the ink. I was so very fond of you, and I so much wanted you to be happy, and now you never will be. I still think that you are an honest man, it means that you do what you think right, whatever the cost. Do the right thing. Try and save as much as you can of this decent and warm and tolerant, this free community of international science which gave you so much these last ten years.

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This letter is just a sea of ink, I am asking Rudi to copy it. Would you like me to come to see you? You are now going through the hardest time a man can go through, you have burned your god. God help you! [Genia]

[494] G.I. Taylor327 to Rudolf Peierls Cambridge, 5.2.1950 Dear Peierls, Like everyone I have come across who knows Fuchs I was shocked and astounded when I heard what has happened. I cannot imagine that our police would have acted unless they had overwhelming evidence because they must have understood how terribly bad their action would be for Anglo-American co-operation and even then I cannot understand why they did not get Fuchs to resign quietly. Then the thing is quite outside anything I could imagine. It is just impossible to imagine anyone person acting as the police allege Fuchs did. But Frisch suggested to me the only possibility that I have heard that has any chance of being conceivable. He tells me that Fuchs came over from Nazi Germany early as a refugee and that he was interned at the beginning of the war and was in a group that was so badly treated that there was in fact an enquiry into the matter. Frisch suggested Fuchs might have an insane resentment and has for years been stiring up a punishment which has now been let loose. If this is indeed the case, it is indeed an extraordinary case for resentment against bad individuals has been turned into a desire to punish all people who have since treated him extremely kindly. People like Cockroft & you and me for instance, as well as the whole body of the scientiﬁc workers. Of course one looks 327

Geoﬀrey Ingram Taylor, (1986–1975), studied mathematics and physics at Trinity College, Cambridge, where he became a fellow, lecturer and later professor of physics. Member of the British mission at Los Alamos.

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against all reason that a mistake has been made, but I feel that’s the least probable of the possibilities. I write to you because you know F[uchs] better than I do + you may have some light to shed on the psychological aspects of the question. Don’t answer if you feel you can’t. I wrote because I feel I am one of a small group who have been dealt a shattering blow and that some comfort may come from a feeling of solidarity with other members of that group. Yours sincerely, G.I. Taylor

[495] Klaus Fuchs to Genia Peierls London, 6.2.[1950] Dear Genia, It was wonderful of Rudi to visit me on Saturday, although I could not do anything to cheer him up. On the contrary. It is up to you. Do you mind if I talk of other things? Sometime I shall try and describe to you what went on in my mind. But you will have to be very patient. I have been sitting here for an hour, trying to think what to write next, when your letter arrived. I have told myself almost every word you say, but it is good that you should say it again. I know what I have done to them and this is why I am here. You ask: Perhaps you did not think about it at the time. Genia, I didn’t, and this is the greatest horror I had to face when I looked at myself. You don’t know what I had done to my own mind; and I thought I knew what I was doing. And there was this simple thing, obvious to the simplest decent creature, and I didn’t think of it. I had used my god to make myself into this, and that was the point where it ﬁnally crashed down. Controlled schizophrenia is the nearest description I can give to it; but I didn’t control the control; it controlled me. I know that it is my job to try and clear up the mess I made. I am afraid I did shirk it at ﬁrst, and that made the mess even worse. They gave me a much easier way out. I could have left Harwell to go to a

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university a free man, free from everything, free from friends, with no faith left to start a new life. I could even have stayed at Harwell if I had admitted just one little thing and had stayed quiet about everything else. I bungled the “take your life” stage; yes I went through that too, before the arrest. The elaborate precautions taken after my arrest, I am glad to say, were quite unnecessary, though a triﬂe inconvenient. I was only afraid they would discover the safety pins which held my pants together. In that case my appearance in court the following morning might have been somewhat undigniﬁed. I suppose you would almost enjoy the kind of things I am learning about here. All these people [are] in their way kind and decent. Even the chap who apparently made prison his home by occasional excursions to pick up a few hundred pounds and have a few riotous weeks on them. He grew quite sympathetic when I admitted that I hadn’t made any money out of it. Nothing could shake him from the belief that I had been double-crossed. Many many thanks for your letter. Funny that women see such thin[g]s so much clearer than men. And that they are so much kinder by saying hard words straight out. Klaus Sorry I have not got anybody to type this out for me. I hope you can read it. And don’t worry if you can’t see the tears, I have learned to cry again. And to love again. K[laus]

[496] Rudolf Peierls to G.I. Taylor Birmingham, 7.2.1950 (carbon copy) Dear Taylor, Your letter reached me only now, as it went to an old address, owing to an error in the Royal Society Year Book.

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I very much appreciate your writing to me at once, and I entirely agree with all you say about the consequences this is likely to have. You can imagine that this came as an even greater shock to us than to anybody else, after ten years of the closest personal and scientiﬁc association with Fuchs. At the present moment I cannot say very much for reasons that you will appreciate, but I can say that I do not think the picture Frisch has given you is at all likely to be accurate. One must still keep an open mind, as long as the facts are not clear, and they are certainly not clear to me. But assuming the facts to be as alleged, the only explanation is that for him his political views took, as these particular views do so often, the form of almost religious convictions and psychologically the situation would be rather like that of a Jesuit, who may feel free to act against the ordinary standards of morality in a higher cause. I also have reason to think that, always the facts are as alleged — which I do not yet accept — he must have gone through a process of development in which he abandoned these views but after the date of what is said to have happened. I felt I should tell you this at once because, while it would not for a moment excuse the action, it would at least raise it to a somewhat higher level than the kind of personal grudge that you speak of. However, I have put all this in such a conditional form for a deﬁnite reason, and I can yet see a possibility of an explanation which would be less distressing. This may be wishful thinking, and I cannot know until I have more of the evidence than I can obtain at the present. If this should be true, it would become clear quite soon, and meanwhile one has to be patient. Your sincerely, R.E. Peierls On re-reading the last paragraph, I ﬁnd it sounds more deﬁnitive than I intended. It is a very long shot.

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[497] Rudolf Peierls to Niels Bohr [Birmingham], 14.2.1950 (carbon copy) Dear Uncle Nick, I feel I should write to you about Fuchs, though I have really very little to say that you do not know already. This has come as a distressing blow to very many people and I am sure that it must also have caused you terrible distress. I do not know whether from the American papers it was possible to sort out fact from imagination, but you will have seen a report of the Police Court Proceedings last week in which statements by Fuchs himself were described. If one takes these statements as genuine, and it is very hard to believe anything else, he has lived all these years hiding his real allegiance, yet at the same time acquiring a genuine and almost passionate interest for his job and building up personal relationships and friendships which were kept quite separate from his secret contacts. One can believe that a man should hold political views of such strong, almost religious, conviction that he should let them override all other considerations, but it is incredible that, at the same time, a man who had never thought for himself and who was always ready to go to enormous lengths in the interest of others, should allow himself to become so attached to the people and to allow other people to become so attached to him without seeing what he was doing to them. According to the statements quoted in court, this was really what broke him in the end, and because it was the trust and conﬁdence shown him by his friends which convinced him in the end that there was something wrong with the cause, but it was, of course, then too late to undo the damage. The whole picture is so unbelievable that we continue to ask ourselves whether he has really done all the things to which he is reported to have confessed, or whether some, or all of them, are perhaps hallucinations created by a very great mental strain. It is impossible for us to judge this because the answer depends, of course, on what other evidence exists besides his own statements and quite properly the authorities will not tell us whether such evidence exists and how strong

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it is, but until then I know I shall continue to regard this at least as a possibility. There is no doubt that this whole case will have disastrous eﬀects, quite apart from personal relations on the political atmosphere and the positions of scientists both here and particularly in America. It is, of course, quite illogical if all security clearance and investigations have missed such a case to seek a remedy in submitting people to further checks and clearances. Nevertheless this will, of course, be done. We are beginning to wonder whether the real lesson is not that it is impossible to maintain secrecy in a project involving so many people without creating the atmosphere of a totalitarian country in which everybody is ready to suspect his best friend of being an informer. Russia has found how to stop leakages very eﬀectively. If this is the only eﬀective solution do we want to go that way ourselves or should we not say that at that price security is not worth having. With kindest regards, Yours sincerely, R.E. Peierls

[498] Rudolf Peierls to E.C. Bullard328 [Birmingham], 15.4.1950 (carbon copy) Dear Bullard, As you may know, I had some correspondence with Womersley329 about the possibility of employing a ﬁrst-rate man who is graduating this summer and there is a point of principle arising from this which I would like to put before you. 328 Edward Crisp Bullard (1907–1980), studied physics at Cambridge under Blackett, and later turned to geophysics. In 1949 he became director of the National Physical Laboratory, Teddington Middx. 329 John R. Womersley (1907–1958), Superintendent of the Mathematics Division of the National Physical Laboratory.

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It emerges that the only thing this man could do would be to apply to the Civil Service Commission for the general entry to the Scientiﬁc Civil Service though he could state a preference for the N[ational] P[hysical] L[aboratory] but I gather from Womersley that it is not possible to conduct direct negotiations about the type of work he might be taken in for. I have often felt from previous experience that the centralised method of recruiting for scientiﬁc work was bad. It is, of course, modelled on the procedure invented for the administrative class where presumably a man decides in the ﬁrst place that he wants to become a Civil Servant and does not mind very much, even though he may have some preference, whether he collects taxes or issues building permits. In the case of scientists I ﬁnd the best people are usually those who have some concrete ideas as to what they would like to do although they may later change their ideas, and I have never come across a case which makes it as obvious as the present one to what extent the present system discourages applications from such people. In writing to you I do not want in the least to press the particular case since the man was somewhat doubtful about it anyway. I had oﬀered him a place as a research student and he is quite keen to stay on except that his age gives him some reason not to prolong his training excessively. I was making enquiries about possible jobs mainly to help him make up his mind whether he wants to stay on here and it is likely that he may stay on anyway. I thought, however, that the particulars of this case might interest you and in case your views about the Civil Service recruiting are similar to mine it might provide useful ammunition. Yours sincerely, R.E. Peierls

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[499] Egon Orowan to Rudolf Peierls Cambridge, Mass., 20.4.1950 Dear Peierlses, You would not believe how often, in certain situations, the question occurs to me: How would you expect me to behave in this (mess, quandary, tight spot, problem, and the rest of Roget’s). I am afraid, however, just at the moment, there is no real problem on the table for you; so this is just a sign that I am thinking of you not only when strictly utilitarian reasons demand it. Also, I should like to thank you for sending me to Weisskopf; he was very useful indeed. He said: 1) he would not go from MIT to Princeton if he were oﬀered an equivalent job; 2) Cambridge Mass. is far better than Princeton; 3) apart from Bethe and Wigner, he could not tell the name of another physicist whose salary exceeds 10,000. This is his own salary, too. With the MIT, the main problem is merely to discover the snags and the ﬂies in the ointment. So far, the whole place appears so improbably nice that it seems to me the less good spots are reserved for later discovery. As a university and research place, it seems Paradise after Cambridge – Eng. The people are incredibly nice; partly it is the attitude of the couple before the marriage ceremony which cools down when they leave the church. The surroundings are pretty, one can recognise it even now when the trees hardly begin to bud. As you see, therefore, there is a deﬁnite recession with Canberra and Princeton. However, I have not arrived at the zero line yet, and I have duly sent to Hugh S. Taylor a project he asked from me about the new group for applied physics of solids (or materials engineering) that they want to set up at Princeton. Having penetrated into the skin of American life, it seems to me far more attractive than it appeared from the distance. Of course, this place is a bit highbrow and too full of intelligentsia as far as I am concerned, but I can easily learn a few words like repression, existentialism etc. to ﬁt into the picture. I hope you are well; since you are very busy, I do not suggest that perhaps once one of you might take pity of a poor exile to the extent of a few lines.

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Between this line and the previous one I had a visitor belonging to the wire-pulling class who broached pointedly the question of the Harvard metallurgy department which they want to re-open when they ﬁnd somebody to put in. At the same time, he was so positive that you cannot live in the U.S. a life better than a dog’s with less than 20,2000 or 30,000 p.a., that I am beginning to think Canberra is better. With the kindest regards to you all, Yours ever, E. Orowan

[500] Memorandum Rudolf Peierls The Lesson of the Fuchs Case [Birmingham, around March 1950] To all those who were associated with Dr. Fuchs during his work on the atomic energy project the disclosures at his trial have caused great distress. One could wish nothing less than to go on talking about this, particularly in public. However, the case will do such serious harm and there seems to be so much contradiction and confusion about it that I feel it necessary to write up the picture as I see it. The main point will be the conclusions to draw (or not to draw) and I shall describe the past events only as far as they have a bearing on this. For me the story starts in 1941 when a small team was then working on atomic energy in this country. I was mainly responsible for theoretical physics and more help was needed on this side. Most people of suitable ability were then already on high priority work but when I heard that Fuchs was available I knew he was a man of the right scientiﬁc qualiﬁcations. I knew he had left Germany because of his opposition to the Nazis and I respected him for this. I knew of his connection with left-wing student organisations in Germany since at that time the communist controlled organisations were the only ones putting up any active opposition. It was natural for a young man who wanted to ﬁght the Nazis to work with any available allies, as indeed this country did later during the war.

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Approval for his appointment had, of course, to be given by the authorities. I do not know what their methods of investigations were, and what was disclosed, but I assumed that they had to weigh the value of his help (at a time of great shortage of scientiﬁc manpower) against any risk of his having retained from his early contacts in Germany (8 years earlier) a loyalty to a party that owed allegiance to a foreign power. During all these years we saw much of him. Shy and retiring at ﬁrst he made many friends and in many conversations politics was, of course, a frequent topic. His views seemed perhaps a little to the left of ours, but he seemed to share the attitude to Communism — and to any kind of dictatorship — of most of his friends. I remember an occasion when he talked to a young man who was in sympathy with communism and in the argument Fuchs was very scornful of the other’s dogmatic views. When I heard of his arrest I regarded it as quite incredible that anyone should have hidden his real beliefs so well. Looking back it seems that at ﬁrst he shared in the life of his colleagues and pretended to share their views and attitude only in order to hide his own convictions. But gradually he must have come to believe what was at ﬁrst only pretence. There must have been a time when he shared one attitude with his colleagues and friends and another with the agents to whom he then still transmitted information, and when he was himself in doubt which of the two was conviction and which was pretence. I do not want to enter into speculations about the state of his mind during all this time. Some have described it as an abnormal case of a split personality, others tend to regard it as a superb piece of acting, but either way it is certainly quite exceptional. In the past his close friends were mostly amongst people who shared his extreme views. Of course, the case for the democratic way of life must have been made to him also by many people who felt a genuine conviction for it, but apparently this had not converted him. The years spent here and in America on the project brought him more and closer association with new friends, and it is one of the most unusual features of his case that a man who was not selﬁsh should, in spite of his position, allow these close associations to form on false pretences. But as a result there was something new that grew on him. Nobody ever argued the case because nobody knew that he needed convincing, but he discovered

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that implicitly all shared principles which gave him a strength that his ideals were losing. From his point of view this is perhaps the most tragic: that he does not now even have the satisfaction of suﬀering for a cause in which he believes. But it contains a slight piece of comfort: the story has shown up a weakness in the defence of democratic countries beca[u]se the atmosphere of mutual conﬁdence that is so essential a part of our life, makes this kind of betrayal harder to guard against. Yet, it also shows the strength of our system which in time won over such a strong supporter of a diﬀerent ideology, though, in his case, only too late. Our problem must be how to reduce the risk of further cases of this kind, while yet preserving those features that make us so sure (and that ultimately convinced Fuchs) that we are right. How, then, can we avoid further leakages: As an ordinary mortal I do not presume to know the methods of the security services but broadly speaking they can work in three ways; by “counter-espionage”, i.e. by inﬁltrating into the espionage organisation which they are trying to frustrate, by “clearance”, i.e. by investigating the background of people employed or to be employed on secret work and by “supervision” of the conduct of the men on the job. The ﬁrst is obviously a good method if practicable, but one would not imagine it to be a complete safeguard in itself. “Clearance” investigations are, of course, employed in connection with secret work. In the case of Fuchs, they would have had to probe very deeply to disclose his continued adherence to the communist cause and that would have required a depth of human insight that is very hard to achieve. Anything that could be done to raise the level of knowledge in this way would, of course, be most valuable. But, in any case, such investigations would presumably have shown that he had been a member of a left-wing organisation in his youth. Should we now exclude others of whom this is found? Fuchs was German born; should one now all be suspicious of foreign born people? Fuchs was a scientist; should one mistrust all scientists? Should one mistrust all men with the initial F? The Fuchs case came as such a shock to the public that I would not blame anyone for advocating all these measures, except perhaps the last one. But we must not be under the illusion that they would bring

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safety. They would not even have prevented the case of Nunn May.330 But they would have lost the country a great deal of ability. I believe that it is fair to say that if from the atomic energy teams in England and in America one would have excluded all foreign born scientists as well as those who in their youth had held extreme political views of one kind or another, the leakage of atomic energy would have been prevented by the fact that there would have been no atomic secrets. The work could not have continued eﬀectively under such restrictions. This may sound an immodest statement for me, as a foreign born scientists, to make. But a glance at the names in the Smyth Report331 which summarises atomic energy work in America will make my point obvious. I am not saying that one should take no notice of the background of the people to whom one entrusts secrets. As long as there are any secrets (and all this story increases our longing for a state of the world in which they would not be necessary) it is important to judge who can be trusted with them, but one cannot insist that the precautions should be such that they would necessarily detect a second Fuchs. We are not likely to ﬁnd a second person who can for years maintain the impression of being a politically inactive but generally liberal and reasonable person. But if there should be further cases of the same kind of psychology (or of equally perfect acting) they may well be people who had never openly professed communism. Should one then rely more on supervision? The diﬃculty in the large number of scientists and others on secret work. To “shadow” a person day and night takes more than one investigator. Where would one ﬁnd the necessary number of intelligent investigators and how does one check their reliability? Probably this method had its best chance in the atomic bomb work in Los Alamos, New Mexico, which was located at the remote spot largely just in order to reduce the risk of leakage. While

330

Alan Nunn May (1911–2003) had worked at the Chalk River Plant of the Manhattan Project. In 1946 he was sentenced to 10 years; hard labour for spying for passing information on the Manhattan Project in to the Soviet Union. 331 Henry De Wolf Smyth, The Oﬃcial Report on the Development of the Atomic Bomb Under the Auspices of the United States Government, Princeton: Princeton University Press, 1945.

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the gates of this “atom city” were not actually locked, travelling by its members was discouraged and few ever travelled beyond the immediate neighbourhood. We always assumed that on our rare trips we would be watched by the eﬃcient army security services and that this applied particularly to those employed by the British rather than the American authorities. Yet one of the charges against Fuchs relates to February 1945, a time when he was working at Los Alamos and presumably just absent to attend some meeting or collect some technical information elsewhere. If his secret rendez-vous could pass unnoticed in these circumstances the prospects of generally keeping all people under supervision does not look promising. If one considers these problems objectively, one sees that as long as there are large projects employing thousands of people we cannot have absolute assurance against leakage except in one way. The governments of totalitarian countries presumably ﬁnd it easy to keep their secrets, and by adopting their methods we might succeed, too. If we build up an iron curtain preventing travel across the border, except in rare cases, if we suspect people who are talking to a foreigner, if we give the police the right to act on suspicion and, above all, if we build up a state of aﬀairs in which everyone suspects his best friends of being police informers (and half of them probably are) then our military secrets might be safe, but at what price? If this were really necessary, we would lose most of the assets of democracy including even the pleasure of convincing a man like Fuchs in the end that we are right and he was wrong — because there would not be much diﬀerence. Nobody has yet proposed such drastic measures, but the insistence that one now hears frequently on security measures without specifying them exactly and the very understandable desire for certainty that there will be no further such cases, may logically lead us in that direction. Must we then choose between helplessly tolerating all foreign agents and becoming a police state? Fortunately things are not as black as that. Of course the authorities will continue to ﬁnd out what they can about the people entrusted with important secrets and they will make the job of any future Fuchs or Nunn May as diﬃcult as they can; they

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will not pretend that they are infallible. A good general knows he is bound to lose a battle occasionally. The details of all military equipment such as tanks and aeroplanes have always been considered as important secrets. Nevertheless, no country ever succeeds to hide their main features indeﬁnitely, but this does not even out the assets. The country with the better technical skill, the greater ability for research and design and the greater industrial potential will still be better oﬀ because no leakage can replace the value of the right skill and knowledge of the man actually on the job. The question of the importance of atomic weapons for the future safety of this country and of the United States is a controversial one which I do not want to raise here but accepting their importance more can be gained by assuming a positive need through eﬃcient development work and good planning than by a frustrating attempt to seal up hermetically all possible channels by which others may get to know things which, after all, they might discover for themselves. One fallacy that would be particularly dangerous in this context is to extend the principle of clearance to cover not merely the employment of men to be entrusted with secret work but to a wide variety of cases which it is argued that people with extreme political views might abuse their position for seditious propaganda. This is dangerous because it would lead to political discrimination and to a restriction of the freedom of expression. It is clear that in certain circumstances the spreading of extreme political opinions might be a danger, but the diﬀerence is that propaganda is something that cannot be pursued in secret. If people misuse their position to advocate their own views, this can easily be known and they can be dealt with on the basis of their actions. There is no need to suspect them in advance. In the cases where the job is concerned with non-political matters, in particular, technical information, anybody engaged in political propaganda would, in fact, not be carrying out his duties properly and could be dealt with on that basis. In jobs concerned with the discussion of such problems as international relations of political theory or practice, it is most desirable that all views should be heard and that people should be in a position to make up their minds on a full knowledge of all arguments. This means that it is, in fact, undesirable that people should be prevented from expressing

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any views however extreme or unpopular, provided one takes care to balance their views by having others available who would speak for the other side. This has always been the tradition of this country and it is important that the danger of disloyal acts which, as the Fuchs case has reminded us, is serious and should not be confused with the danger of extremist propaganda which at the present time is negligible and, in any case, must be fought by argument and not by prohibition.

[501] D.H. Wilkinson to Rudolf Peierls Cambridge, 12.5.1950 Dear Professor, I hoped to see you at the A.S.A. Council Meeting last Saturday, but I hope you will not mind being written to instead. I have been doing a series of measurements on the photo-disintegration of the deuteron at various gamma-ray energies between 6 and 18 MeV, and there is one point which I would be pleased if you would clear up. It is whether or not the state of polarisation of the gamma-rays, linear, elliptical, or anything else, has any inﬂuence on the photo-disintegration or whether it depends solely on the gamma ray energy when the deuterons are randomly oriented. I pass the gamma-rays which are derived from nuclear reactions and may be very strongly polarized, through an ionisation chamber containing ordinary deuterium gas and observe the total number of disintegrations they produce and also, eﬀectively, the angular distribution of the photo-protons I(Θ) in the Θ co-ordinate only. Now does the number of disintegrations or I(Θ) depend on the state of polarisation? It seems instinctively obvious to me that it should not, but I do not know how to write it out properly. People who do calculations never mention this problem, so it is probably pretty trivial, but on the other hand, nobody is prepared to give me a whole-hearted yes or no answer. As you did the early calculations on this problem you can probably tell me straight away, and I would be very grateful, if you would. I measure the gamma-rays through matter and measuring the amount

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of ionization they produce, and I presume that here again there is no inﬂuence of the state of polarisation? I would also be pleased if you would let me know your views on the reliability of recent calculations such as those of Bethe and Longmire.332 What I am most concerned about is the validity of the fundamental formula derived from perturbation theory. Is this eﬀectively exact or are unknown approximations involved? If this formula is exact then the rest follows automatically, and one may use the formula of Bethe and Longmire for determining the eﬀective triplet range. But are there any troubles back in the fundamentals which people never remark on nowadays? If one uses my values of the photo-disintegration cross section one derives a value for the triplet eﬀective range almost the same as the “new” value of 1.71 derived from the liquid mirror slow neutron scattering, though the photodisintegration results are not so accurate as the others. The results so far are: E(MeV) 6.11 8.45 12.4 17.6

σ(1028 ) cm2 21.5 18.6 10.0 8.5

± ± ± ±

1.2 1.5 1.2 1.2

I hope you do not mind these questions, but I would like to be sure about the straight forwardness of the interpretation of the experiments, and that I need not worry about complications of multipolarity and so on. Yours sincerely, D.H. Wilkinson

332

H.A. Bethe, ‘Theory of the Eﬀective Range in Nuclear Scattering’, Phys. Rev. 76, 38–50 (1949); H.A. Bethe and Conrad Longmire, ‘The Eﬀective Range of Nuclear Forces II. Photo-Disintegration of the Deuteron’, Phys. Rev. 77, 647–54 (1950).

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[502] Rudolf Peierls to John Cockroft [Birmingham], 15.5.1950 (carbon copy) Dear Cockroft, If Pryce does go to Princeton next year I shall certainly do my best to help with the running of the theoretical division at Harwell.333 My main diﬃculty in this, as you will realise, is going to be one of time and I would suggest that a little later it would be good to plan out in what way this would least interfere with running my department here. I assume that I can count on assistance with such matters as petrol supply where the use of a car makes it possible to ﬁt in visits to the Establishment with less dislocation. As regards the question of fees, I can not really pretend that this extra work would be carried on without loss of eﬃciency in the performance of my duties to the university and it may well be a reasonable suggestion that part or the whole of any further fee should be passed on to the university. The whole arrangement is, of course, subject to approval by the university but before consulting them it would be better to know precisely how we are going to arrange my visits. Yours sincerely, R.E. Peierls

333

Maurice Pryce had helped run the theoretical division at Harwell after the arrest of Klaus Fuchs.

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[503] Rudolf Peierls to D.H. Wilkinson [Birmingham], 18.5.1950 (carbon copy) Dear Wilkinson, Thank you for your letter.334 The question of the polarization of the gamma rays will depend on the symmetry of the source from which they are obtained in relation to the direction of observation. For instance, if your gamma rays go in the forward direction as seen by the bombarding beam then the problem has complete axial symmetry and therefore gamma rays will be unpolarised. Of course, each individual photon will have a polarization correlated with the direction of the fragments and your disintegration but since the direction of these fragments is statistically symmetrical about the direction of the beam, this will make no diﬀerence. One must remember in this connection that there is no physical diﬀerence in the gamma ray beam according to whether you produce an unpolarized beam by superimposing waves of linear polarization in diﬀerent directions or waves of opposite circular polarization or intermediate elliptic cases, as long only as one averages over all possible orientations. Therefore, in this case of forward emission of the gamma rays it follows rigorously that polarization is unimportant. Now, in general, you will be working at diﬀerent angles and then there may be a greater likelihood of gamma rays being polarized in a direction at right angles to the plane formed by your bombarding beam and the line of travel of the gamma ray then in that plane and vice versa. Even in that case, however, your method of observation would not be sensitive to polarization since you only measure the angle between the proton and the gamma ray and any eﬀect of polarization must disappear if you imagine your chamber rotated about the line of the gamma ray and the results averaged. This clearly would not make any change to your set-up. 334

Letter [501].

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It is an interesting question whether one could conduct the experiment in such a way as to distinguish protons forming the same angle with the gamma ray but orientated diﬀerently with respect to the plane of symmetry set up by bombarding beam and gamma ray. If the gamma ray were polarized, one would then expect a strong correlation of the protons with that direction. At low energies this correlation would be something like a cos2 distribution for the electric dipole eﬀect. At the energies you mention the magnetic eﬀect will be quite negligible but there may be contributions from higher multipoles and things are then a little more complicated, but this will only make the correlation stronger. All this, of course, depends on how strongly the gamma rays are polarized and this depends on the reaction in which they are emitted. To take an example, if the reaction is such that bombarding a nucleus with no spin the proton comes in with angular moment 1 and the ﬁnal state of the nucleus is again without spin, then the angular momentum has to be taken over by the emitted gamma ray which for observation at right angles would give complete polarization. This is an extreme case and unlikely to be realised in practice. Another simple case about which a simple statement is possible is that in which the protons arrive with angular momentum zero. This is usually the most important case at low bombarding energies unless it is forbidden by selection rules. In that case, the proton entering the nucleus has no memory of the direction from which it came and as a result the gamma rays are rigorously unpolarized. If you can tell us a little more about the reactions you are using I could probably say in what cases there is a chance of observing polarization and in some cases such observations might, in fact, throw a new light on the mechanism of the reaction. The principle of the argument is very similar to the coincidence measurements made, for example, by Martin Deutsch at M.I.T.335 or discussed in the recent paper by Gard-

335

Martin Deutsch and his collaborators at MIT had published various papers on disintegration schemes of radioactive substances throughout the 1940s and into the 1950s, using coincidence methods.

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ner in the Physical Society (LXII, 763, 1949).336 The diﬀerence is only that here one takes as one datum the direction of the bombarding particle rather than that of another particle emitted in the interaction. Yours sincerely, R.E. Peierls

[504] Niels Bohr to Rudolf Peierls Copenhagen, 25.5.1950 Dear Peierls, I thank you for your kind letter of May 16th337 and hasten to answer that Mr. Barker shall be most welcome indeed to work with our group for the next academic year. I was very interested in what you wrote about his abilities and about his work. We are also here just now occupied with the problems of nuclear reactions on such lines and expect in a few weeks a visit of Dr. Hill from U.S.A. who has worked with Wheeler and me on ﬁssion problems, and I hope with him soon to complete a paper just on the relationship between the drop model and an individual particle model in such respects.338 In Paris you probably have heard that considerable progress has recently been made in the relationship between nuclear shape and nucleon binding. This gives not only a far-reaching quantitative account of the quadrupole moments of nuclei, but implies also a coupling between the excitation of individual nucleons and the oscillations of the whole nucleus which oﬀers a general understanding of the properties of the formation of the compound state on nuclear reactions. Our old work with Placzek has also been much on my mind, but both Placzek and I were so pre-occupied in Princeton with other work 336

J.W. Gardner, ‘Directional Correlation between Successive Internal-Conversion Electrons’, Proc. Phys. Soc. A62, 763–79 (1949). 337 Rudolf Peierls to Niels Bohr, 16.5.1950, Peierls Papers, Ms.Eng.misc.b203, C.33 338 The results were published by Hill and Wheeler in D.L. Hill and J.A. Wheeler, ‘Nuclear Constitution and Interpretation of the Fission Phenomena’, Phys. Rev. 89, 1102–1121 (1953).

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and interests that we only had a few discussions about this paper, which I hope we all can complete as soon as I have got the work with Wheeler and Hill oﬀ my hands. It has been a great pleasure to learn that Lindhard has had such a good time in Manchester, and I look forward to see him soon again and to go to work in the charge of ﬁssion fragments, about which Lassen’s experiments339 have given such interesting results. Would you kindly greet Lindhard from me and say that I shall be glad to learn about his plans. I have not written myself to him because I found so much to do in the ﬁrst weeks after my return from Princeton. I cannot close this letter without remembering the very noble and moving letter you sent to me to Princeton about the tragic case which has brought some much anxiety into wide circles.340 We are certainly not living in a pleasant world, but in spite of all I keep up the hope that we shall see better times before it is too late. With the kindest regards from my wife and me to the whole family and your self. Yours ever, Uncle Nick

[505] Rudolf Peierls to Raymond Priestley [Birmingham], 13.6.1950 (carbon copy) Dear Vice-Chancellor, Sir John Cockroft, the Director of the Atomic Energy Research Establishment of the Ministry of Supply, has asked me to give them some help 339 N.O. Lassen was working on the ionisation of ﬁssion fragments, and he had recently completed some experiments which were published in N.O. Lassen, ‘Total Charges of Fission Fragments in Gaseous and Solid Media’, Phys. Rev. 79, 1016–17 (1950). 340 Letter [497].

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during the next academic year with the supervision of their Theoretical Physics Division.341 The position is that they have so far been unable to ﬁnd a successor to Dr. Fuchs, and there is no prospect of a suitable man being man being found in the near future. At present Professor Pryce of Oxford is directing the work of the division in a part-time capacity but he has arranged to spend the next academic year at Princeton and Cockroft is asking me to take his place. I am not looking forward to this further commitment with much pleasure since it will be extremely hard to do this and at the same time do justice to my own research team, but I do not see how in such circumstances such a request can be refused. I am, therefore, writing to ask you to bring the matter before the Council for their approval. I understand that Pryce was spending half-a-day a week at Harwell for this purpose. I expect that I shall probably go there for one day from time to time on the average probably twice in three weeks. This depends a little on how much of the business can be done by Harwell people coming to see me here. I expect also to spend a little more time there during the vacations. In the correspondence the question of a fee has also been raised; you may remember that I am now a Consultant for the Ministry of Supply. Until recently this meant that I was receiving a fee of £ 300 p.a. but recently when I completed my term of oﬃce on their Technical Committee, this was reduced to £ 200. Cockroft now says that if I take on the extra work they should pay an increased fee and, while the exact amount has not been ﬁxed, a ﬁgure of £ 500 p.a. has been mentioned. My own feeling in this matter is that I could not really accept such a large payment for spare time work since I cannot fairly claim that this is a commitment I can carry in addition to my full university duties. I feel, therefore, that, while the Ministry of Supply ought of course to pay for what they get, I should return at least part of the increased fee to the university. If we can see any way to minimise the harmful eﬀect to my department of the extra weight I have to carry, for example, by 341

See letter [502].

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temporary staﬀ to relieve some of my other duties, this might well be regarded as ﬁrst charge on the money obtained in this way, though I do not see clearly at the moment any arrangement that would really help to give me more free time. Yours sincerely, R.E. Peierls [506] Rudolf Peierls to Manchester Guardian Birmingham], 17.6.1950 (carbon copy) LETTERS TO THE EDITOR Professor Bohr’s letter Sir. — Your leading article today about Professor Niels Bohr’s letter to the United Nations makes disappointing reading for those who respect your paper highly for its liberal tradition.342 By all means let us, as you suggest, keep our feet on the ground, but also let us try to keep our head out of the sand. Professor Bohr tried to show us some hope in an imaginative approach towards restoring openness in the ﬁeld of international relations, particularly in scientiﬁc matters. He was trying to show the value in itself of even a small step in that direction. If I read his letter right he did not say speciﬁcally how far such a ﬁrst step should go, and he certainly did not imply that the United States should forthwith publish complete blueprints of their atomic energy installations, but he talks of an “oﬀer · · · of immediate measures towards openness on a mutual basis.” No progress in international relations is possible which does not involve mutual concessions, but Bohr was stressing the advantage to be gained by reversing the present trend of increasing the height of barriers on all sides. Maybe, as you suggest, such an oﬀer would not meet with any response, but then nothing would be lost, and a great deal gained, by the fact that the oﬀer had been made. 342

On 9th June 1950, Niels Bohr had sent an open letter to the United Nations, arguing for rational peaceful atomic policies. See www.galilean-library/bohr.html.

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You describe the United States’ “atomic mysteries” as her trump card. If this were correct, the security of the Western Nations would look very sad indeed. The Fuchs case gave proof again, if proof was needed, that in democratic countries it is impossible to keep large projects secret for long. We must guard against the danger, which is becoming evident today, of drifting more and more away from that personal freedom and freedom of knowledge which is so important a part of our way of life. We all know that an eﬃcient way of keeping secrets is to curtail freedom of expression, freedom of movement, and the free ﬂow of information, but this leads us surely towards the loss of what we value most in our democratic institutions as we understand them. The real trump card of the United States lies in her resources, her industrial potential, and her scientiﬁc and technical staﬀ of high quality and enterprise. They are of little value in the end, as the example of German scientiﬁc eﬀort has shown, unless they will, if need be, pull their weight inspired by the enthusiasm for their system of government and by conﬁdence in their method of government. From this point of view a genuine eﬀort in this direction suggested by Bohr would add to the moral strength of the countries that value personal freedom. The danger of losing any part of the moral strength by related or not fully consistent attempts to protect secret information is likely to be far greater than the danger of the possible loss of some secrets that, for all we know, may already be compromised. R.E. Peierls [507] Rudolf Peierls to Freeman Dyson [Birmingham], 19.6.1950 (carbon copy) Dear Dyson, Here is some assorted information; There has been some delay in writing up Ravenhall’s note about pair creation343 but this is now practically 343

G.E. Brown and D.G. Ravenhall, ‘On the Interaction of Two Electrons’, Proc. Roy. Soc. A208, 552–59 (1951).

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ready. I have asked Kolsrud344 to look into the eﬀect of screening on the partition of energy between positron and electron in gamma ray pair creation (King’s anomaly); Brown is looking after that and they are also keeping in touch with Ravenhall so this should be all right. Dalitz has found that in his calculation on O16 he has omitted a term which does not inﬂuence the answer greatly but might in principle be observable since it leads to a relatively large anomaly at small angles. The reason for the error was that in the double integration of the Feynman type he had not noticed that a pole crosses the real axis in the course of the integration so that caution is needed. He is now anxious to make sure that there are no other similar troubles and this will delay the completion of his paper a little. He has, however, solved the other diﬃculty in the discussion of the ordinary Born approximation to Coulomb scattering and this is now perfectly reasonable and intelligible as far as it has been carried and it is not worth going further. My own paper is still held up while I search for a more satisfactory derivation which is not messed up by the presence of non-commuting factors. One can always carry out the proof for Lagrangians of the usual type but the result is so obviously of more general validity that it seems a pity to prove it in such a restrictive way. Brown has helped a good deal with sorting this out but in the last week or two examinations have been a major nuisance; thank God these are over. Gunther is leaving in a few days and neither of his papers is ready for publication.345 His derivation of the Breit terms seems now all right in principle but it has to be explained better and it really has not made much progress in the last few months. He also gave us a Seminar about his use of conﬁguration space. Without pair theory this now looks all right but there are still some proofs missing for statements which are probably correct. He comes periodically to say that everything is wrong 344

Marius Kolsrud, later Institute for Theoretical Physics, Oslo. Marian G¨ unther later published a paper in two parts. M. G¨ unther, ‘The Relativistic Conﬁguration Space Formulation of the Multi-Electron Problem’, Phys. Rev. 88, 1411–21 (1952); and M. G¨ unther, ‘The Relativistic Conﬁguration Space Formulation of the Multi-Electron Problem. II’, Phys. Rev. 94, 1347–57 (1954). 345

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because, for example, an integral which ought to vanish does not do so and in this particular case it turned out that he had merely shown that the integrand did not vanish identically as he had thought. As regards the use of this method, with pair theory everything is in a complete mess because he had carefully assumed that the S+ function (summing over positive energy states only) vanishes outside the light cone, which, of course, is not true. This means one needs a new idea and whether it can be done at all is now doubtful. Schonland has now evaluated the Scott and Snyder formula346 for the case in hand instead of improving the 7% discrepancy it increases it to about 20%. This may be due to some misunderstanding about density and composition of the emulsion and we are checking up on this now, because I cannot believe that the Williams formula which the Bristol people have used, can diﬀer that much more from the correct result. But if it is conﬁrmed, I would begin to suspect the method of Snyder and Scott.347 You will now have seen the letter by Bohr which I was not allowed to talk about before. As I expected it has not made a strong impression because it was not easy for the newspapers, with the best intentions, to sum it up clearly in the space they have. In particular the Manchester Guardian had a leader which was very unreasonable and I have just sent them a furious letter on the subject.348 Cockroft, whom I saw the other day, seemed quite shaken by your decision to go to Cornell. He seemed worried for one thing that your reply might be taken to indicate that you would have given a diﬀerent answer if you had, in fact, been oﬀered a job which involved the full responsibility of running the division, whereas he had made the sug346 H.S. Snyder and W.T. Scott, ‘Multiple Scattering of Fast Charged Particles’, Phys. Rev. 76, 220–25 (1949); H.S. Snyder and W.T. Scott, ‘On Scattering Induced Curvature for Fast Charged Particles’, Phys. Rev. 78, 223–30 (1950). 347 In his paper D.S. Schonland, ‘On the Utilization of Multiple Scattering Measurements’, Proc. Phys. Soc. A65, 640–56 (1952), Schonland used the method of Scott and Snyder after Corson had conﬁrmed that it was in agreement with experiment. Dale R. Corson, ‘Multiple Scattering of Fast Electrons on Nuclear Emulsions’, Phys. Rev. 80, 303–304 (1950). 348 Letter [506].

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gestion of being free to do your own work mainly to make the thing more attractive to you. I told him that it was not my impression that you would have taken the job either way but I feel you ought to know about this. He asked me whether, in general, we could improve our p[ro]spects of keeping young theoreticians in the country if there were more research Professorships. My reply to that was that I thought in your case this would not help because even if the job with the status of the Cornell job was created somewhere in this country you were likely still to prefer Cornell and that otherwise I did not know of people who have yet reached the stage where they would expect to get a Research Fellowship, though this may well arise in a few years time. If I have misrepresented your position on this I would be interested to know even if it is now too late to do anything about it. With kindest regards, Yours sincerely, R.E. Peierls

[508] Freeman Dyson to Rudolf Peierls Princeton, 24.6.1950 Dear Professor Peierls, Tomorrow I am leaving Princeton for Ann Arbor, and so I think I may send you a report on what I have learned here. I was lucky in arriving here just before a large number of people left. Tomonaga says he has spent a proﬁtable year here, not working very hard but enjoying his leisure and the relief from running a department and ﬁnding problems for numerous graduate students. The ﬁrst months he spent in an attempt to combine his variational method of describing radiation ﬁelds (as he uses it in his papers on meson theory where the nucleons are treated as non-relativistic ﬁnite sources) with the covariant formulation of electrodynamics. He found this did not work out, he got into great complications of detail and could not see his way through, and so he never wrote the work up and ﬁnally abandoned it. Since then he has worked on the problem of describing the behaviour of a

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degenerate gas of Fermi particles with strong interactions. (It seems that everybody has to have a rest from ﬁeld theory occasionally!) He has found a method like that of Bloch spin-waves which describes the state of the gas as a superposition of sound-waves which behave like simple harmonic oscillators on Bose particles. The method is however worked out for the one-dimensional case. Also it is restricted to longrange interactions and may not be at all applicable to nuclear material. He says the relation of the particles to the sound waves is very similar to that of neutrinos to photons in the neutrino theory of light. For this reason the three-dimensional case is not to be handled by any simple extension of the one-dimensional case. He has written a paper on the one-dimensional model349 which is now being mimeographed and you shall receive a copy of it. Jost and Luttinger, also exhausted with ﬁeld theory, have been amusing themselves about the Ising lattice problem.350 They have only succeeded in convincing themselves that the 3-dimensional case is too diﬃcult for them. Jost now intends to go back and work some more on ﬁeld theory, and he has some ideas which are good though nebulous. Case has written with Pais a very good paper on the analysis of the P − P and N − P scattering experiments in terms of the spin-orbit coupling potential.351 He seems to think the evidence for some such a coupling is now really convincing. I am sending you also copies of this paper. It seems that now Harwell can make a valuable contribution by doing some accurate measurements of the scattering, especially the P − P scattering at 150 MEV. I hope you can bring this to their notice. In particular the Case-Pais potential predicts a P − P scattering at 90◦ which is roughly constant from 150 MEV to 350 MEV at 4 millibarns per steradian. 349

S. Tomonaga, ‘Remarks on Bloch’s Method of Sound Waves applied to ManyFermion Problems’, Prog. Theor. Phys. 5, 544–69 (1950). 350 They had just submitted, together with M. Slotnick, a paper on pair production by photons. R. Jost, J.M. Luttinger and M. Slotnick, ‘Distribution of Recoil Nucleus in Pair Production by Photons’, Phys. Rev. 80, 189–96 (1950). 351 K.M. Case and A. Pais, ‘On Spin-Orbit Interactions and Nucleon-Nucleon Scattering’, Phys. Rev. 80, 203–11 (1950).

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Yang has been continuing to play with the calculation of the SMatrix in the Heisenberg representation. Nothing very useful has come out of this. Placzek said the reports of his death had been partly exaggerated. He is, in fact, walking around and working, and seems in as a good a state as last year. They are staying here through the summer and living quietly because they are afraid his kidney may give more trouble, but at present it is behaving well. Placzek has been working all this year with a young Dutchman called Nijboer352 on the details of the interference phenomena in neutron scattering, even a lot of numerical work has been done. He and Else send you and the family all their best wishes. Skyrme you shall soon see and he will tell you what he has been doing. Karplus and Neumann carried through the calculation of the scattering of light by light and found it much more unpleasant than they had believed possible. It seems the results are of no possible value except as a warning to others who may want to calculate such things.353 Karplus gave me a report on the doings of Schwinger. He was working until 4 months ago on an attempt to formulate the whole of electrodynamics and carry through the renormalizations without expressions in α. Then Kroll found a simple mistake at the beginning of the whole work and so he gave it up in disgust. Since then he has become interested in making a rigorous formulation of the Feynman description of ﬁeld theories using “sum over histories”. He has apparently translated the Feynman ideas into his own language and made them work both for Bose and Fermi ﬁelds. I have not seen the details of this. But I gather it departs rather radically from the Feynman method as Feynman uses it. Schwinger uses a method in which the ﬁelds are already quantized 352

The result of their work was published as G. Placzek, B.R.A. Nijboar and L.V. Hove, ‘Eﬀect of Short Wavelength Interference on Neutron Scattering by Dense Systems of Heavy Nuclei’, Phys. Rev. 82, 392–403 (1951). 353 Karplus and Neumann had just submitted their result which was published as Robert Karplus and Maurice Neumann, ‘Non-Linear Interactions between Electromagnetic Fields’, Phys. Rev. 80, 380–385 (1950).

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before the sum over histories is written down, and I do not know what use he then can make of the sum over histories.354 Schwinger will lecture on this work during the summer at Brookhaven. So I will hear about it ﬁrst hand from Karplus later on. I think this is all I have to report on physics. You will be not surprised to learn that this year the Princeton group has been suﬀering from a feeling of frustration, just as some of us have at Birmingham. Indeed, there has been very little serious work done, and none of outstanding importance. Driving force has been entirely lacking. Oh, I forgot. I also talked with Van Hove.355 He has been thinking about the connection between classical and quantum mechanics and the foundations of quantum theory. He has clariﬁed these questions quite a lot. But of course it is an abstract mathematical piece of work, and I do not know if it will have any practical consequences. Roughly he says in the classical theory deﬁne the Hilbert Space H of all squareintegrable functions of the position and momentum variables. The scalar product F G is just F Gdpdq. Now since by Liouville’s theorem dpdq is invariant under contact transformations, every contact transformation under pq is associated with a linear unitary transformation of H. Also, to every classical function K(p, q) corresponds an inﬁnitesimal classical contact transformation in H, i.e. a Hermitian operator K in H. The correspondence classical function K ↔ Hermitian operator K is 1–1. Now the process of quantization is a projection of H on to a Hilbert 354

Schwinger’s work led to a sequence of publications throughout the early 1950s. J. Schwinger, ‘The Theory of Quantized Fields. I’, Phys. Rev. 82, 914–27 (1951), J. Schwinger, ‘The Theory of Quantized Fields. II’, Phys. Rev. 91, 713–28 (1953), J. Schwinger, ‘The Theory of Quantized Fields. III’, Phys. Rev. 91, 728–40 (1953), J. Schwinger, ‘The Theory of Quantized Fields. IV’, Phys. Rev. 92, 1283–99 (1953), J. Schwinger, ‘The Theory of Quantized Fields. V’, Phys. Rev. 93, 615–28 (1954) and J. Schwinger, ‘The Theory of Quantized Fields. VI’, Phys. Rev. 94, 1362–84 (1954). 355 L´eon van Hove (1924–1990), studied mathematics and physics at Brussels and received his Ph.D. in 1946. After three years of research at Brussels he went to Princeton and Brookhaven before becoming professor of theoretical physics at Utrecht in 1954. He later worked as leader of the theory division at CERN and at the MaxPlanck Institute for Physics and Astrophysics, before becoming Research Director General at Cern in 1976 (1976-80).

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space of functions of fewer variables (e.g. q or lg instead of p and q), i.e. onto a linear subspace of H. Van Hove is about so show: (i) that this process of projection is connected in a direct way with the “averaging over histories” of the Feynman method. And so he thinks he can make the Feynman method mathematically watertight. (ii) that the full space H divides in a natural way into a kind of direct product of two subspaces, either of which can be chosen as the subspace onto which to project. And in each subspace there is a set of coordinates and momenta. I do not understand all the details of this. But I thought you might like to know about it. I hope he will write is up before long. My best wishes to all the students of Birmingham. For the attention of Dalitz and/or Salam. Nobody here seems to have seriously tackled the question of whether a consistent renormalization theory can be made with a λφ4 term. They all thought Matthews had proved it could be done, and so they left it at that. Now for my personal news: I have now understood why it is that in the Lamb shift calculation one has to use a contact transformation of the form t ∞ −2 n 1 t − P (H(x1 ), · · · , H(xn ))dx1 · · · dxn S(t) = c n! −∞ −∞ n=o with the order of integration as written, in order to get an operator which really is unitary when you throw away all the ﬁnite oscillating terms at −∞. The proof of this is not diﬃcult. At the same time this clears up completely the appearance of the Z 1/2 factors in the Smatrix, by a straight-forward physical argument. So the Karplus-Kroll argument to which you objected is now unnecessary. That is all I have done since leaving Birmingham. I will write it down and send you a copy some time.

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I look forward to hearing your news and seeing your quantization paper.356 But of course I do not expect you write at this length! This is intended to be a news-letter and you have full permission to circulate it if you think it is worth it. Yours Freeman Dyson

[509] Rudolf Peierls to Robert Oppenheimer Birmingham, 27.7.1950 Dear Oppie, You may remember that we chatted last Autumn about our problem here of ﬁnding another Professor of Physics. In the course of this conversation you mentioned the name of Panofski357 as a man who might possibly be interested in such a position, and who would be very suitable. As you have probably heard, since then Oliphant has in fact departed and Philip Moon has been appointed to succeed him as Head of Department. We must now appoint a professor to succeed Moon. Moon himself is interested more in nuclear physics proper than in building machines, and it would therefore be useful to have another man who could play a strong part in the supervision of the cyclotron, which is now operating satisfactorily, and in helping to complete the synchrotron. However, at the same time we are trying to appoint another man of the senior staﬀ whose speciﬁc duty would be the supervision of the machines, and there are prospects of ﬁnding a suitable man in this way. It is therefore not a necessary condition that the new professor should be machine-minded, but we have to consider the two appointments as part of the same problem. 356

See letter [507]. W.K.H. Panofsky (1919–), studied at Princeton and obtained his Ph.D. from CalTech in 1942; after wartime nuclear work, he moved to Berkeley before taking up a professorship at Stanford in 1951 where he remained for the rest of his academic career. 357

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I am now writing to see whether it still looks to you as if Panofski might still be a candidate for our job, and if so, whether you would be kind enough to let me have a few words about him which I could pass on to our committee, or if you prefer, would give me one or two names of people who could give well-informed opinion about Panofski. To put this matter into proper perspective I ought to say that we are still at the stage where we are making enquiries fairly widely, and it is therefore too early to say with whom Panofski would be competing if he were interested in the job. I have an idea that a letter which I wrote to you last October never reached its destination.358 If it didn’t you must have thought me very discourteous for fading out without saying a word about the enjoyable time I spent with you at a time when you probably had many more things on your mind. I also wrote in that letter the story about our smallest child which we had just discovered. We have now had almost a year to get used to the idea and, like so many other things, once one ﬁnds out enough about the trouble it is not as bad as it seemed at ﬁrst sight. Higginbotham has told me about your views and advice as regards the proposed conference between American and British scientists. Your remarks will be most useful, and their spirit is very close to what we had hoped would be the line taken by the meeting. I have no illusions about many concrete results to be expected from such a meeting, but I still think it would be worthwhile, and Uncle Nick’s open letter359 would provide some useful material. I only wish it could have been written in such a way that more than the select few could understand it. But then, of course, it would not be Bohr! Yours sincerely, R.E.P.

358 359

Letter [487]. See letter [507], note 348.

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[510] Freeman Dyson to Rudolf Peierls Ann Arbor, 3.8.1950 Dear Professor Peierls, In answer to your letter of 19 June.360 (i) If the Williams approximation and the Snyder-Scott method diﬀer by 20% I would certainly trust the latter rather than the former. But probably this trouble has been cleared up by now. I wish we had put more eﬀort into these calculations while I was in Birmingham; looking back on the past year this seems to be my main mistake, I was always dividing my time between ﬁve or six problems and never sat down and concentrated upon one thing long enough to ﬁnish it. I hope you and Schoenland will now be able to do something with it. (ii) We had a colloquium talk the other day from Chandrasekhar361 on the multiple scattering of light in the atmosphere. Everyone agreed that this was a work of art, a masterpiece. He has solved exactly the integral equation for scattering in a plane atmosphere, including the direction and degree of polarization. And everything comes out in precise agreement with observation. I felt after this that if we had attacked our multiple scattering problem with the same determination we should long ago have reached an exact solution. Certainly our problem is not nearly so formidable. (iii) My course of lectures is now over and the notes will be mimeographed in a few days. They contain my new ideas so far as they have yet developed, which is not far. (iv) About my letter to Cockroft. I said “It is clear that I am too young to be given a position of real responsibility and working primarily on pure science, it is best that I go to Cornell where I 360

Letter [507]. Subrahmanyan Chandrasekhar (1910–1995), nephew of C.V. Raman, studied in Lahore and Cambridge before joining the faculty of the University of Chicago where he stayed for the remainder of his academic career. 361

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can work best.” He seems to have interpreted this to mean that I was sorry he had not oﬀered me a job as Head of Division. Actually, I meant two things. (a) I had already told him when I was at Harwell before the Cornell job had arisen, that if I came to Harwell I would come to work on atomic energy and not to do pure science. Therefore I naturally expected that he would have taken this into account in making me this oﬀer. (b) It was my own estimate of the situation that I was too young for a position of real responsibility. I still think this is true. Now he has written to me again, as you know, with the oﬀer of the position of Head of Division. I wrote back saying that I would like to talk with Bethe before making a ﬁnal decision but that the answer would almost certainly be No. I am becoming more and more convinced that I am right in not accepting the job. But if you have any criticisms to make, or advice to oﬀer, I shall naturally be glad to listen to you. Concerning the question of keeping young men in England, I have nothing to say. Certainly the only thing that would keep me in England would be either (a) a clear and urgent call of patriotic duty, or (b) if Cornell should get involved in political squabbles of the kind they are enjoying this year in Berkeley. I do not think that more Research Professorships would really help in this respect. I agree with what you have said about this in your letter. (v) I am not yet married but am rapidly approaching that condition. So if all goes well I will be needing an apartment for 3 in Birmingham next January.362 It is, however, still uncertain whether Verena’s College can ﬁnd a replacement for next academic year. If they can’t get one, she will be rather obliged to go on teaching there. Yours sincerely, Freeman Dyson 362

Freeman Dyson married Verena Esther Huber in 1950. daughter.

She already had a

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[511] Robert Oppenheimer to Rudolf Peierls [Princeton], 6.9.1950 (carbon copy) Dear Rudi, It has been many weeks since your good letter has been here.363 I have been away on New Mexico and I hope that my delay in writing will have caused you no trouble. Let me turn ﬁrst to your departmental question. I still think that Panofski would be a magniﬁcent choice. I am somewhat less conﬁdent that he could be lured away from Berkeley. I believe, though it may be a breach of conﬁdence to write this, that he has been oﬀered positions both at Harvard and at Columbia and has turned them down. I think he is quite attached to life in California. However, at the present moment, due to a variety of serious diﬃculties which have turned up at the University, this may be an auspicious time and I would encourage you to move quickly, if this is the direction in which you want to move. You ask who would write recommendations for Panofski. I should think that Macmillan and Rabi would both do very well on that. If you want a detailed appreciation from a theoretical side, probably Serber knows his work in greatest detail. I don’t know of anyone in this country who combines better than he does the appreciation of the problems of highenergy accelerators with a real understanding of the physics that can be done with them. I hope very much that the conferences to take place this month will be successful, both the conference at Harwell364 and your own undertaking.365 You know how much I would have wished to be there, but it did not seem like the proper moment for me to leave my modest duties here. I cannot, of course, hold very high hopes for the outcome of even the most earnest collective eﬀort with regard to the problems of peace and atomic control; but I hope very much that I shall learn if possible 363

Letter [509]. In September 1950, a nuclear physics conference was taking place at Harwell. 365 Peierls was organising a second international conference at Birmingham in September 1950. 364

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from you as well as from Placzek and Higginbotham what the views were. It would be good if Bohr came himself. You must be sad that Dyson has deserted you.366 He will have one year here, I guess, and then go to Cornell. Matthews367 has just arrived and I have not yet had a chance to talk with him. There has been nothing in physics which seems to me to constitute a real theoretical advance, as far as the work that has been going on in this country. It would be good to be able to talk of problems in physics with you. Both Kitty and I were deeply touched by your few words about your youngest child. We send Genia and you our love and our warmest good wishes. [Robert]

[512] Rudolf Peierls to Philip Moon [Birmingham], 19.9.1950 (carbon copy) Dear Philip, I hope that, in spite of the winterly weather, you are managing to get a good holiday and in particular you are getting a little bit of the rest you must badly need. I am now writing ﬁrst of all to say that I have now a reply from Oppie which I enclose.368 You have probably heard about the trouble at Berkeley369 and perhaps it is not inconceivable then even a ﬁrstrate man might get fed up and might want to leave in the present 366 In 1951, Freeman Dyson accepted a professorship at Cornell, before, in 1953, rejoining the Institute of Advanced Study at Princeton as professor of physics. 367 P.T. Matthews was lecturer of theoretical physics at Birmingham between 1952 and 1957. He then joined Abdus Salam at Imperial College London and later became Vice Chancellor of Bath University. 368 Letter [511]. 369 The University of Berkeley operated what was known as the ‘speaker ban’, which allowed the university authorities of censor public speaking on campus. The censorship was largely, though not exclusively, directed against communists.

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circumstances. The way in which Panofski’s work was referred to at the Oxford Conference does make one feel that if you could get him it would be a marvellous acquisition, both from the point of view of machines and of nuclear physics. On the other hand, of course, this would be bound to cause further delay. Since we talked at Oxford I have heard further rumours repeating the suggestion that Blackett made to you and indicating that Cockroft also seems to be thinking in that direction. I do not really believe seriously that this idea will be pressed and if it comes before the Nuclear Physics Committee of which, no doubt, you will be made a member, I think we shall have an ally in Chadwick. It does mean, however, that one should think out the problems and the future programme rather carefully so that we have the right answers available at the right time, but all this we can discuss when you are back. With kindest regards, Yours sincerely, [R.E. Peierls]

[513] Freeman Dyson to Rudolf Peierls Princeton, 23.9.1950 Dear Professor Peierls, I am now installed at the Institute, having acquired a house on the Institute Housing estate. With luck I shall soon start again to do some work. I am sending you by ordinary mail a copy of some notes made by Goldberger for a lecture course on the latest Schwinger theory. These notes are very confused and diﬃcult to read, but I believe they contain a lot of good ideas and one ought to take trouble to understand them. I think now, after 3 readings I understand them at any rate better than Goldberger does. In this new theory Schwinger does three things which I consider of ﬁrst-class importance.

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(i) He translates the Feynman Lagrangian formalism with “integration over histories” into a rigorous and conventional language. And he makes it work also for Fermi-style ﬁelds. Thus the full strength of the Feynman method is now available in a more practical and convenient form. (ii) He has a simple and convincing explanation of the connection between spin and statistics, quite diﬀerent from either Pauli’s or Feynman’s more complicated arguments. (iii) He has a way of treating electrodynamics which does not treat the four potentials as dynamical variables, and thus avoids all trouble with supplementary conditions. You have to search carefully to ﬁnd how (i) is hidden in the notes. Of course, the name of Feynman is never mentioned. Only I happen to know from other sources (as is also obvious when you see what Schwinger’s method actually is) that Schwinger started the whole thing from the idea of making Feynman’s method intelligible to himself. As a consequence of (i), Schwinger is able to derive from the classical Lagrangian function simultaneously the equations of motion and the commutation-relations of a quantum ﬁeld theory. I believe also your form of the commutation-relations will come out of this method in a natural way. Probably Schwinger will not avoid the diﬃculties you have found when the Lagrangian is not quadratic in the ﬁelds. I hope you will look into this.370 With the Schwinger notes is a paper by Placzek which may interest somebody at Birmingham. My own work has not progressed any further since we left Ann Arbor. I am held up by some mathematical diﬃculties which may not be easy to overcome. I do not think the whole method is so very valuable and important that it is worth while to present it to the world in a unﬁnished state. So I am letting it sleep for a few weeks while I think about other things. 370

Peierls was working on the commutation laws of relativistic ﬁeld theory.

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We have had some stimulating talks with Prof. Laurent Schwartz371 from Nancy. Probably you have heard of his ideas. He is a mathematician with a new kind of function-theory which is much better adapted to physical applications than the old kind. For example it deals with ∆-functions. So he has in fact made mathematically honest a lot of doubtful manipulations of ﬁeld theory. He has not, of course, thrown any light on the main problems, real divergences and such. But he is a man with a good understanding and a lot of interest in these problems, and so he says he will look carefully and try to understand the mathematical situation lying underneath the “renormalization” theories. I hope he may do something worth while. In any case we shall continue to correspond with him. The Institute is just now waking up from its summer slumbers. There is no further news of general interest to report. My family is in very good state. Oppy was very pleased when I told him about your new commutation method. We just heard that my wife Verena is free from her job in Baltimore. They were able at the last moment to ﬁnd a replacement. This is very good news. Now we shall deﬁnitely be able to come to England together about Dec. 23. We shall spend some days with my family in London and then move into something in Birmingham (I hope) in time for the start of term in January. Now of course I ought to be getting busy ﬁnding a home before the very last moment. Perhaps you would be kind enough to let me know what you think I ought to do about this. E.g. is it sensible to write at once to the University housing oﬃce? Or to put advertisements in the paper? I do not want in any way to saddle you with the responsibility of getting us housed. Verena is also interested in getting some part-time or occasional work in connection with the university. I do not know at all what possibilities 371

Laurent Schwartz (1915–2002), studied at Paris and Strasbourg where he obtained his Ph.D. in 1943. In 1945 he became professor at Nancy, before moving to Paris in 1953 where he taught in diﬀerent institutions until his retirement in 1983.

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exist in this direction. She thinks she is in danger of getting very lazy, if she only has a house and a husband and a child to look after, and no regular job. Another question that arises is that of Katrin’s school. Here she goes to the township school, which is a good school and free, but of course she does not learn much. She is now 5 1/2, will be 6 next April. What school do you recommend us to go to in Birmingham? And should we start negotiating early to be sure of a place? All these questions of course need not be answered, if you think it is all right to wait until Christmas before dealing with them. In that case we shall be glad to deal with them ourselves in person. All best wishes to your family too. Thanking you very much for your letters, and for any information you may be able to give us. Yours sincerely, Freeman Dyson

[514] Rudolf Peierls to Freeman Dyson [Birmingham], 25.9.1950 (carbon copy) Dear Dyson, I have a very bad conscience for leaving your two long and interesting letters372 unanswered and even more for failing to send you my personal best wishes to your marriage. On the latter point I have at least the consolation that you will have taken the long letter from Genia as speaking on all our behalf and there was really nothing I could add to what she had already said. We are now all looking forward to meeting your wife and her daughter when you get them over. We hope it will not be too bad a shock to be transferred suddenly into the middle of an English winter. If you will let us know approximately when to expect you we shall look around for a ﬂat which will at least mitigate the worst hardships. 372

Letters [510], [513].

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About the correspondence with Cockroft, it was not my intention to persuade you to change your mind but merely to report to you what had been said to make sure I was not creating further confusion.373 I have now come to the conclusion that the best I can do to counteract the drift of young theoreticians away from this country is to try and create a visiting Professorship somewhere, I would hope Birmingham, which one could use to invite here for one year at a time the people who on the whole want to remain in America. I think there are good prospects of achieving this. If you have any ideas about people who might be interested in such an oﬀer a little later on I would be glad to know. Now about physics. My progress in completing the proof of my method of quantization has been very slow and this, in fact, is the main reason why I have delayed writing to you. I always hoped I could send you the complete answer. At present the position is as follows: the method is consistent only if one can prove the inversion theorem. I have got a very transparent proof of this in the classical case, but on trying to extend this to non-commuting factors I have discovered that it is not, in fact, true as generally as I thought. That is to say keeping the order of the factors unaltered the retarded and advanced solutions which should be equal diﬀer in fact by a commutator. This commutator vanishes by virtue of the commutation laws themselves, but this means one can only prove the consistency of the whole scheme and one cannot ﬁrst establish the identity and then base the commutation laws on it. In this situation it would look more reasonable to think of a proof of the kind you have given, but I am reluctant to rely on this for two reasons. (a) because one then needs the Hamiltonian formalism to prove the consistency of my scheme and one then loses its main attraction, namely that one does not have to formulate a Hamiltonian to start with. (b) it is then necessary to prove the equality of the extra term in the Lagrange function and in the Hamiltonian to ﬁrst order, even when this term contains derivatives or momenta. This follows, of course, if one uses your trick regarding the inﬁnitesimal factor as a new dynamical variable, but I ﬁnd it very

373

See letter [507].

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hard to see how this procedure can be justiﬁed. I have got some ideas of how to get around this diﬃculty but they are still very nebulous. Here many things are going well. Ravenhall’s work is ﬁnished, probably just in time to get this thesis in and the result is that the Breit terms are not correct to the order to which they claim to be correct when applied to the ground states of the helium atom. We are not yet sure of the exact magnitude of the diﬀerence but it seems certainly large enough to explain the observed discrepancy. Brown has shown how to do the same thing in conﬁguration space and everybody now agrees about the result. Just now Brown has discovered an even more exciting use to be made of this new correction term but I dare not write about this yet since it is only two days old and needs conﬁrmation.374 Butler’s work has come out very well too and he has now shown how one can use the result of the d − p reaction to identify the spins and parities of nuclear levels.375 In particular in the case of [. . . ]376 this leads to a result diﬀerent from what everybody had assumed. No doubt Pais will have told you about all this. We also had some interesting talks with Ferretti. He has a new way of deriving the wave function renormalization terms that arise in your expansion of the S-Matrix. This is probably identical in content with what you have done recently, but it is put in a way which, to my mind, makes it[s] signiﬁcance particularly clear. He has also got some nice results about how exactly the expansion in powers of the coupling constant breaks down when there are discrete states and he has derived an equation which formally at least contains the answer to this, so it remains to be seen whether it can be turned into a practical method. Schonland is still working on the scattering problem. On the point I mentioned to you last, it turned out as one could expect that there is no substantial agreement between the older theory of Williams and the

374 See G.E. Brown and D.G. Ravenhall, ‘On the interaction of two electrons’, Proc. Roy. Soc. A208, 252–59 (1951). 375 S.T. Butler, ‘On Angular Distributions from (d, p) and (d, n) Nuclear Reactions’, Phys. Rev. 80, 1095–96 (1950). 376 Missing in carbon copy.

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formula by Snyder and Scott.377 The confusion has arisen because the Bristol people had evaluated the Williams theory in a manner which we still do not understand, but there is now still a disagreement in the constant of the scattering formula, not only between experiment and theory but also between the diﬀerent experiments. Moreover, according to the Bristol experiments, the constant for protons seems to vary with proton energy. We are now looking to see whether there is any chance that the method used for evaluation, including the cut-oﬀ, could be reasonable for this. Dalitz has written up his work on [. . . ]378 for his theses and is now preparing it for publication.379 He also has some interesting results on Born-approximation (I don’t quite remember whether you knew already about these when you left; if so, I must apologise for the repetition). First of all in the formula for the scattering of electrons by nuclei he discovered that all results published as power series in Z were wrong except the paper by McKinlay and Feshbach380 which came to our notice only recently. Dalitz has found a mistake in each of the previous papers and obtained the correct formula which agrees with McKinlay and Feshbach and with Mott’s exact formula if correctly expanded.381 The point where most people went wrong arises from the presence of both virtual and real intermediate states in second order Born approximation and he ﬁnds that all this business can be made much more transparent if one uses Feynman notation. He has also looked at the ordinary non-relativistic Coulomb scattering where it is usually believed that although ﬁrst order terms give the correct answer, the second order terms do not vanish but, in fact, diverge. To this a lot of philosophi377

See letter [507], note 346. Missing in carbon copy. 379 R.H. Dalitz, ‘On higher Born approximation in potential scattering’, Proc. Roy. Soc. A206, 509–520 (1951); R.H. Dalitz, ‘On radiative corrections to the angular correlation in internal pair creation’, Proc. Roy. Soc. A206, 521–538 (1951). 380 William A. McKinley, Jr. and Herman Feshbach, ‘The Coulomb Scattering of Relativistic Electrons by Nuclei’, Phys. Rev. 74, 1759–63 (1948). 381 N. Mott, ‘The scattering of fast electrons by atomic nuclei’, Proc. Roy. Soc. A124, 425–43 (1929); N. Mott, ‘The polarisation of electrons by double scattering’, Proc. Roy. Soc. A135, 429–58 (1932). 378

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cal discussion has been attached, but Dalitz ﬁnds that the statement is quite wrong, again because the role of real and virtual states was not properly understood. He will get rid of both these papers soon and then hopes to start on the problem you suggested, though he realises that by now someone else may already be well on the way. Field has nearly ﬁnished his problem and the answer seems to be identical with your result obtained by low-brow methods but he is at present checking this before making a ﬁnal statement. Kolsrud is looking into the discrepancies in pair production. You remember that the Bristol people found disagreement as regards the energy distribution between positrons and electrons and there are other experiments reporting disagreements as regards the angular distribution. We are now satisﬁed that screening cannot be responsible for either of these and we propose to look at the eﬀect of Born approximation but this is, of course, a long job. I think this is most of the progress as far as will interest you. With kindest regards, Yours sincerely, R.E. Peierls

[515] Rudolf Peierls to John Cockroft [Birmingham], 16.10.1950 (carbon copy) Dear Cockroft, Thank you for your letter about Luﬀman.382 I shall make a point on my next visit to talk to Luﬀman about this. Your question, however, prompts me to tell you the position of solid state work at Harwell. It seems to me that it is almost impossible to get any useful work done by having members of the present staﬀ learn about solid state theory however good they may be. The trouble is that solid state theory is not 382

Letter could not be located.

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a very rigorous discipline but a complicated mess of diﬀerent methods which work in some cases and do not in others and to say that anything sensible one must not only know the literature, but also have a sound judgement as to what statements in the published literature one should or should not believe. It takes many years for even the best men to reach that stage. I am all in favour of allowing some suitable people to read about the subject because they will then be suitable to work under the direction of a more experienced man if and when you ﬁnd one, but they will not be very much use as long as they are on their own even with such help they can get from part-time consultants such as Mott and myself. I spent some time talking to T.M. Fry and my conclusion was that it would be well worthwhile to make every eﬀort to get such a more senior man on the theoretical side, even though he probably will not do everything that Fry hopes can be done. Fry seems to be somewhat optimistic about the reliability of calculations from ﬁrst principles and of giving absolute interpretations to miscellaneous measurements. Solid state theory will always remain a semi-empirical science and the best that can be done is to discuss the experiments intelligently in the light of responsible theoretical speculations. This may mean that once an expert in that ﬁeld has acquainted himself fully with the position there may be enough work to occupy all his time, but the answer to that should be to give him some freedom to branch out in more academic problems. The main thing is to have someone who is there all the time and who would have to give ﬁrst priority to whatever can be done on the problems of relevance to the work in hand. When I last talked to you on this subject I mentioned the name of H.R.Paneth.383 He is now here on my staﬀ and, while I am very glad to have him and expect him to be very useful here, I do not think I should recommend him for a job at Harwell where, for several reasons, I feel he would not ﬁt in too well. This, of course, may change but for the present I am pretty sure he should be counted out. There are two men at present at Cambridge who deserve serious consideration: they are Dingle and 383

Heinz Rudolph Paneth (1926–2004), later known as Henry Post, son of pioneering radiochemist Friedrich A. Paneth, had worked at Montreal in Halban’s group.

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Sondheimer. Of the two Dingle384 is probably in the long run th[e] better man and more used to contact with experimental work. At the present he is still a little wild in the sense that he might quite happily investigate an eﬀect which is 104 times too small to matter for the problem until someone else points that out to him. It is very doubtful, in any case, whether he could be persuaded to leave Cambridge. Sondheimer’s strength is perhaps more on the side of the more formal mathematical theory, but he is very good, and he has a varied experience. You probably know that he has just returned to a fellowship at Trinity after spending a year at M.I.T.385 Before that he also spent a year with Mott at Bristol who also speaks very highly of him. He is of German origin and I know that his appointment might therefore cause some shaking of heads, but he has just got married and that usually means that he might be more liable to succumb to temptations of a job at Harwell. I have not, of course, asked him and I may be wrong about this. I do not know him well, and you should not accept my opinion about him without support from other people, in particular, Mott and perhaps Sch¨ onberg. It is suggested that after Mott’s return from America he should meet me at Harwell to discuss the solid state problems and probably a decision would be left until after that, but it might be useful to think about the possibilities in the meantime. Otherwise, as far as I can see now, the main need of the theoretical division would seem to be to explore what theoretical work is required for the general programme of a long-range point of view. As regards pile and reactor programme, this would seem to be well in hand, though, of course, I would like to discuss the work in detail with Davison, Rennie, etc.. More exploration is needed in connection with fundamental nuclear physics and the cyclotron work and there Skyrme is making a good start. 384

R.B. Dingle had come from Bristol to Cambridge and worked, among others, with D. Shoenberg. He moved on to the University of Western Australia, before becoming professor of physics at St. Andrews University. 385 While working with Nevill Mott at Bristol and at M.I.T. Sondheimer had been working questions of conductivity in metals. His most recent publication dealt with this issue. E.H.Sondheimer, ‘The Inﬂuence of a Transverse Magnetic Field on the Conductivity in Thin Metallic Films’, Phys. Rev. 80, 401–406 (1950).

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The question must be answered whether the division should do something in parallel with Risley on the isotope plant and I believe some people should also think about the programme on which G.P. Thomson and Thoneman are working.386 I hope to see you next week in London or later, but I though[t] it might save time to put some of these points on paper. Yours sincerely, [R.E. Peierls] [516] Claude Bloch387 to Rudolf Peierls Copenhagen, 26.10.1950 Dear Professor Peierls, Please ﬁnd enclosed a reprint of a paper on a variation principle in nonlocal ﬁeld theory. It is, of course, all unquantized, except for the free ﬁelds, where the quantization is rather trivial. As regards the quantization when the interactions are taken into account, I think that a method similar to that recently developed by Yang and Feldmann,388 and by K¨ allen,389 can be used. I would be extremely interested in learning your opinion about this procedure. The equations of non-local ﬁeld theory can be written by means of local ﬁeld functions only, if one introduces a smearing function. Thus, the interaction term in the Lagrangian reads g dx dx dx F (x , x , x )ψ t (x )u(x )ψ(x ), 386

For details on the work of the diﬀerent divisions working on nuclear energy see R. Carruthers, ‘The Beginning of Fusion at Harwell’, Plasma Physics and Controlled Fusion 30, 1993–2001 (1988). 387 Claude Bloch (1923–1971), studied at Paris and received his doctorate in 1946. He continued to do research at Copenhagen (1948–51) and CalTech (1952–53), before joining the Commissariat ` a l’´energie atomique where he eventually became director of the physics division. 388 C.N. Yang and D. Feldman, ‘The S-Matrix in the Heisenberg Representation’, Phys. Rev. 79, 972–78 (1950). 389 G. K¨ allen, ‘Formal integration of the equations of quantum theory in the Heisenberg representation’, Arkiv Fysik 2, 371–410 (1950).

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in the case of a charged spinor ﬁeld interacting with a neutral scalar ﬁeld. The ﬁeld equations deduced from the variation principle are  ∂  + M ψ(x) = g dx dx F (x , x , x )u(x )ψ(x ),  γ  ∂x (1)   2 t ( − m )u(x) = y dx dx F (x , x , x )ψ (x )u(x ).  Assume now for a moment that the right hand side of the equations (1) are known functions, the solution of the linear diﬀerential equations thus obtained is the sum of the free ﬁeld and of a particular solution of the non-homogeneous equations. The latter can be expressed by means of a Green function. This gives  ψ(x) = ψ m˙ (x)+g dx dx dx S+ (x−x )F (x , x , x )u(x )ψ)x ),   (2)  m ˙ +  u(x) = u (x)+g dx dx dx D+ (x−x )F (x , x , x )ψ (x )u(x ). Here, S+ and D+ are the usual retarded Green functions, ψ m˙ and um˙ are the incoming ﬁelds, which are equal to ψ and u for x4 → −∞. (The latter statement is true only under suitable restrictions). The equations (2) are integral equations equivalent to the system (1). A similar system (2’) can be obtained by means of the advanced Green functions. It will contain the outgoing ﬁelds ψ out and uout . Clearly, (2) and (2’) deﬁne the outgoing ﬁelds as functions of the incoming ﬁelds (which may be arbitrary), or conversely. Quantization can be introduced by postulating for the incoming ﬁelds (or the outgoing ﬁelds) the normal commutation relations of the ﬁelds. Clearly, this is consistent with the ﬁeld equations, which can be used to deduce the commutation relations of the other ﬁeld functions. It can be shown that the outgoing ﬁelds satisfy also the normal free ﬁeld commutation relations. Hence, there is a unitary matrix such that ψ out (x) = S −1 ψ m˙ (x)S,

uout (x) = S −1 um˙ (x)S,

which can be taken as the S-matrix of the system.

(3)

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Assuming that expansions in powers of g can be used, it is possible to obtain a formal extension for the n-th term in the expansion of the outgoing ﬁelds as functions of the incoming ﬁelds. In the conventional case, in which F (x , x , x ) = δ(x − x )δ(x − x ), it is possible, of course to go one step further, and to obtain Dyson’s expression for the n-th term of the expansion of S. In the more general case, however, I have not been able to deduce an explicit expression of S, and this makes the calculations of transition probabilities more diﬃcult than in the normal theory. In fact I do not yet know whether convergent and reasonable results can be obtained for a proper choice of the smearing function F . At any rate, the general scheme seems to be very suitable for theories containing smearing functions, still, due to the lack of causality in the strict sense, the Hamiltonian formalism or the Schr¨odinger equation do not seem to be very natural approaches. I would be very grateful, if you could spare some time and let me know your opinion on the subject. Yours very sincerely, C. Bloch P.S. After the 30th of this month, my address will be: Claude Bloch, 10 Boulevard Barb`es, Paris (18e ).

[517] Rudolf Peierls to Claude Bloch [Birmingham], 1.11.1950 (carbon copy) Dear Dr. Bloch, Thank you very much for your letter390 and the reprint of your paper. Since I saw you in Paris we have made an eﬀort to understand the physical meaning of the non-localised theory of Yukawa, but, while we see the consistency of the mathematics, I am afraid we have been quite 390

Letter [516].

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unable to see what it all means and, in fact, my feeling was [that] there is not even a theory but just some equations. We shall read your paper and hope this will help us to understand this a little better. In your letter you write equations which seem to me to be very similar to those of McManus, except that you have a smearing function depending on three points in space instead of two. This is an important point, because one would like to have such a function in order to make certain self-energy terms ﬁnite. However, we always believed that one would get into trouble with gauge invariance if in a product such as [. . . ]391 one took the two functions at diﬀerent points in space. We are, in fact, playing with equations for a quantized theory which are identical with the ones you set out except for the diﬀerence in the smearing function, and we believe now even that we can justify them from some general principle that leads to quantized equations directly from an action principle without formulating a Hamiltonian. There are still, however, some mathematical diﬃculties which are holding us up. These diﬃculties concern the general principle and not the results. We are fairly clear now what the results will be and they will be just that not all the inﬁnities are removed by this method, but as I said this has very much to do with the question of whether you have a smearing function depending on two or three coordinates. I hope soon to have the answer to the problem about the general principle and if I get that written up, I will send you a copy of it. Yours sincerely, R.E. Peierls

391

Missing in carbon copy.

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[518] Freeman Dyson to Rudolf Peierls Princeton, 8.11.1950 Dear Professor Peierls, I am sending you a copy of some work of Schwinger, and I enclose a copy of a letter to Bethe with some remarks392 which you might ﬁnd helpful, among a lot of irrelevant material. Thank you very much for your letter to Verena which she is answering separately. Also I was glad to get news from Dalitz and Ravenhall. Please will you thank them. It will amuse you to see that once again Schwinger has been directly anticipated by Nambdu393 in a paper in Prog. Theoret. Phys. Vol. 5, part 1 published 6 months ago. But of course Schwinger has done a much better job than Nambu with the new method. Yours Freeman Dyson

[519] Verena Dyson to Rudolf Peierls Princeton, 8.11.1950 Dear Professor Peierls, Thank you very much indeed for your kind letter discussing the possibilities of jobs for me. I am very sorry we are bothering you with such questions. But since we are so far away and since I should like to start working as soon as possible after arriving in Birmingham we are bound to do this. First of all you might like to know something about my education: Elementary and high school in Athens, Greece, where 392

Letter Freeman Dyson to Hans Bethe, 8.11.1950, Peierls Papers, MS.Eng.misc.b202, C.17. 393 Y. Nambu, ‘The use of proper time in quantum electrodynamics’, Progr. Theor. Phys. 5, 83–94 (1950).

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I graduated with the “reichsdeutsche Abitur” in 1940. From 1940 to 1947 regular studies at the University of Zurich. My main subject was mathematics, the ﬁrst minor subject as usual physics, the second minor subject chemistry. I went through some chemistry and physics labs, and also through examinations in these ﬁelds as well as theoretical physics. I also heard some lectures in Astronomy and some of more general contents, my hobby at the time was logistics. In 1947 I made the PH.D. in mathematics with a thesis on group theory “supervised” by Speiser. Ever since then I was interested in research in abstract group theory, but I have never succeeded in doing anything worth publishing. In 1949–50 I was an instructor of mathematics at Goucher College in Baltimore. There I taught trigonometry, analytic geometry, calculus and advanced calculus. I am looking forward to having a job again, mainly because I ﬁnd it healthy and satisfactory to do some honest, solid and deﬁnite more or less useful work. Furthermore I should like to be able to contribute to the ﬁnancial support of our household, especially since we shall try to get a maid. From all the possibilities you mention the most appealing seems to me applied research. I think I would be adaptable enough for such a job. Surely I would not spare any eﬀorts to do it well. I am not afraid of the dull part of it. I would like to learn something about the back ground and the meaning of such a work and this would make it interesting. As to teaching: I rather liked Goucher. But I understand that I would not be likely to ﬁnd a place with the same advantages: small department, easy schedule, College level, and so forth. However, I still consider this as a possibility if nothing else could be found. As to languages, I know quite a few, but none of them really thoroughly: English, German, French, some Greek, Italian, little Spanish. On the whole I am looking forward to doing some work I have never done. Of course I wish to ﬁnd a work which I start on the basis of what I have learnt, and through which I can learn some more about physics or mathematics. I am very much looking forward to our trip to England, and to meeting you and your family.

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Again very many thanks and best regards also to Mrs Peierls. Sincerely yours, Verena Dyson P.S. In view of the short time left to us I shall be glad if you will accept deﬁnitely in my name any job which you think suitable, giving priority to applied research, second choice school teaching. If possible, a fulltime job would be ﬁne.

[520] Rudolf Peierls to J. Rzewuski [Birmingham], 8.12.1950 (carbon copy) Dear Rzewuski, I have an extremely bad conscience because I know that I never wrote a reply to your long letter some time ago, both to send you our best wishes on your marriage which by now must be quite a well-established institution and to thank you for the very interesting paper by yourself and Rayski.394 In fact, in a way this paper was the reason for the delay because I thought I would write when I have had a chance to read this paper and make some intelligent comments, but life was particularly hectic at that time and I never got down to it properly. Meanwhile I have received your very interesting paper about the result of the McManus theory. We had, in fact, intended to do just the same thing and you have beaten us to it. As soon as we saw that this was a possibility of carrying the work out we also guessed what the answer would be and, in particular, that it would not remove all the inﬁnities. I would have said that even the self energy of an electron would not come out ﬁnite, and as far as I have been able to understand your calculations that is also your result. The diﬀerence lies merely in 394

See letter [482], note 285.

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the question of terminology what exactly what one means by the self energy and what names one gives to other similarities. One reason why we were slow over this was that we always wanted to see whether the theory applied in this manner could be part of a consistent formalism and I had just succeeded in seeing a way how one could formulate the commutation laws in a way which was derived directly from the Lagrangian and did not need the deﬁnition of a Hamiltonian. If this method is applied to the McManus theory or for that matter to any other theory in which one can expand in powers of the coupling constant, then the results must lead to just what you have done, but by my more general method it should be possible to see whether the commutation laws which one obtains in this way are consistent and satisfactory and therefore whether the operators deﬁned by this series really exist or whether one gets into contradictions. I have struck some trouble with developing this method further and, in particular, with proving what conditions must be satisﬁed for consistency, but I hope it will not take long to straighten this out and I shall then send you an account of the whole thing. The department continues to ﬂourish: we now have a fair number of people interested in ﬁeld theory who have learnt the modern techniques from Dyson when he was here last year and we are just expecting Dyson here for the remainder of the present session. He seems to have developed a new theory by means of which one can also treat bound states and therefore make a decent approach to the problem of nuclear forces. We have made one slight step towards the treatment of bound states by applying ﬁeld theory to the problem of interaction of two electrons, for example in the helium atom. This has been done so far only to the accuracy of the Breit terms: already the next step beyond that looks very complicated, but it is very interesting to ﬁnd that already in this order there is a correction to the Breit terms which vanishes for free electrons (i.e. for the Møller problem) but which is important in helium and which, in fact, seems to remove the discrepancy between the present theoretical values and the experiment. This is mainly Ravenhall’s work and he is now trying to generalise the method and apply it to other problems.

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I also enclose a circular which I have sent to all former members of the department. If by any chance you have a picture which you could let us have for the purpose if would be very much appreciated. I hope to hear from you again about your further progress. All the old members of the department send their best wishes. Yours sincerely, [R.E. Peierls]

[521] Robert Oppenheimer to Rudolf Peierls Princeton, 12.2.1951 Dear Rudi: Of all the many things of which we might write, it has come my time to write of the pleasantest. That is to ask whether in fact you wish to come to the Institute next year. I earnestly hope that your answer will be aﬃrmative. We would be glad to have you for the whole academic year or for either of your terms. The formal terms will run from the ﬁrst of October until just before Christmas, and from mid-January to about the ﬁrst of April. We always hope that our members stay beyond the formal terms. You will know so much about what sort of place this is from your many friends here that I need not burden this letter with anything more than an assurance of our hope that you will come and a cordial welcome if you do. It would be helpful for us to know when your plans are clear, whether Genia will come with you and whether you will be able to bring your family, and what sort of a grant we might make to make your visit possible. None of this is urgent; but when the time comes, you must let us try to make your visit as agreeable and fruitful as possible. With every warm good wish to you both, Robert Kitty sends you both her love. R.

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[522] Hans Bethe to Rudolf Peierls Ithaca, 19.2.1951 (carbon copy) Dear Rudy: Thanks for your letter recommending Noyes. I would like to hear more about your trip to India395 if you have more time to collect your thoughts. Of course I constantly feel that I owe you a long letter about science but there always seems to be too much else in the way. This letter is to announce the visit of our family to Europe this summer, Uncle Joe permitting. If you are there and are willing to have us, we would like to visit you. As usual in our family we follow Napoleon’s principles and travel separately. Rose and the children are planning to go by boat and to get to England about June 1. They would like to come to you some time in early June, and they would like to stay for about a week, if you can accomodate them. I could imagine with the increased family, that space is limited even in your house. I am planning to come by plane about the middle of June and to spend about two weeks in England. One of these I would like to travel around and spend the other week with you. Again if this ﬁts in with your plans. After that I was planning to go to Uncle Nick’s conference396 which I believe is about July 4 to 10. After that I would like to join the family in Germany. Please write me what your plans are and how you are ﬁxed up for accomodation. We would all like to see you and to replace by a personal visit what is lacking in correspondence. With best regards, [Hans] 395

Between 14 and 22 December 1950, an international theoretical physics conference on elementary particles had been held at the newly-opened Tata Institute of Fundamental Research. Rudolf Peierls attended the conference and spent some time afterwards visiting, among others, Raman’s institute at Bangalore. 396 The conference took place between 6 and 10 July 1951, see Pauli, Wissenschaftlicher Briefwechsel, IV/1, p. 339.

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[523] Rudolf Peierls Hans Bethe Birmingham, 28.2.1951 (carbon copy) Dear Hans, I am delighted to hear of your impending visit. It will be great fun to have Rose and the children with us and I am sure we can manage to squeeze them into the house somehow. In fact, Genia is planning to take the children to the seaside for a week or two during June and if should so happen that Rose’s visit should fall in that period she might like to join Genia and the small children at a seaside holiday and the best, of course, would be if this were either at the beginning or at the end of that period so that Rose could also have at least a few days at Birmingham. As regards your own visit, you will, of course, also be most welcome at any time. I am also due to go to the conference in Copenhagen, and our plan is to take the car across via Ostend and to drive up to Copenhagen. I understand that the conference was to start on the 6th. We would probably be able to leave only on the morning of the 1st and cross on the 2nd. It looks possible that we should reach Copenhagen on the evening of the 5th. What would you think about joining us in the trip? I would, of course, hope that this would not curtail the length of your stay in Birmingham since all the other people here, including Dyson, would certainly like to talk to you. However, all these plans are subject to conﬁrmation; it may still be that Genia might prefer to take her holiday elsewhere and I would in that case, go directly to Copenhagen by boat or by plane. Scientiﬁcally the most important result of the Bombay conference for me was that the Bristol people produced convincing evidence in favour of multiple as opposed to plural production of mesons.397 The point is that for plural production you would expect that for a greater number of mesons there should either be also a larger number of reasonably 397

See Report of the international conference on elementary particles, Bombay: Commercial Print Press, 1951.

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fast protons (“grey tracks”) or else if the energy should be completely dissipated a greater energy in the star formed by low energy tracks. They have looked for correlation of either kind and they are completely absent. On the average, for example, the energy in the star increases only by 55 MeV per meson produced and this is clearly not enough. I also learnt there for the ﬁrst time about Fermi’s theory of meson production which is very attractive and simple as everything else that Fermi does. Whether it is right is another matter and I think particularly that his explanation of the angular distribution is rather ﬁshy. Of course there was much more to India than physics, but to do justice to the many impressions there would take a pretty long letter and I shall leave it until we meet, I hope in June. Yours sincerely, [Rudi]

[524] Rudolf Peierls to Robert Oppenheimer Birmingham, 10.3.1951 (carbon copy) Dear Oppie, I owe you a reply to your very kind invitation to visit Princeton next Session. I did not write at once because I wanted ﬁrst to explore the possibilities. May I say ﬁrst of all how much I appreciate the invitation. I have considered my arrangements for next year and have come to the conclusion that I could not possibly get away for the ﬁrst term. There are many reasons for this, one is that there will again be a fair number of new research students joining our group and while I have some promising young men on the staﬀ I do not think I have yet reached the stage, where I can leave them to decide on the programme of the new men. Another reason is that our Professor of Pure Mathematics G.N.Watson, is retiring and there will be a new Professor of Mathematics starting next Session. Since the two departments are jointly concerned with the teaching of Mathematics students, I feel I should

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be here to take my share of the responsibility at the beginning of the Session. However, it seems feasible for me to come for your second term which practically coincides with our Spring term, by that time the new men should have settled down and there is not much administrative work in the undergraduate teaching at that time. If, therefore, the international situation has not deteriorated in a drastic way it looks to me as if I shall be able to accept your invitation for the second term with delight. As regards the ﬁnancial side it is almost certain that the University will grant me leave of absence with pay except that they might deduct any fees that have to be paid to lecturers that have to do my teaching while I am away, and as far as I can foresee other sources of income would continue also, with the possible exception of some fees for consulting work. I would not expect to bring my family to Princeton, but possibly Genia might join me for a few weeks, during my stay. You generously asked me what payment would be necessary to make the visit possible and this puts me into a diﬃculty; broadly speaking my commitments here, would probably use up my normal income so that what would be required would be the cost of my stay in the United States. I shall of course apply to the Fulbright Scheme for a grant to cover my passage and I assume that this will be granted, however, I have no knowledge of the present cost of living in the United States in general and in Princeton in particular, and I feel that you can probably judge this better than I can and I would therefore be grateful if you could ﬁx whatever sum seems to you appropriate. I am looking forward with great pleasure to the opportunity of spending a term at the Institute and to a chance of refreshing my very inadequate knowledge of modern ideas. Yours sincerely, R.E. Peierls

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[525] Rudolf Peierls to Viscount Portal of Hungerford [Birmingham], 9.4.1951 (carbon copy) Dear Lord Portal, On thinking over our recent conversation I feel I would like to send you my comments in writing, both because this will allow me to add one or two remarks that did not occur to me on the spot, and because this will make it possible for you, if you see ﬁt, to pass the letter on to the people who raised the matter in the ﬁrst place.398 There are several diﬀerent ideas that may have been in the minds of the security people when they drew attention to the position, and I shall comment on some of them though they may not all be relevant. The most obvious question is whether the reported accusations throw any doubt on my reliability. On this I cannot comment usefully, but I was very gratiﬁed to know, both from your direct assurance, and from the fact that you raised the matter with me, that you regard the answer to this question as satisfactory. There may have been doubt whether I was aware of the possible aﬃliations of the two men, and if I was not, whether I might inadvertently disclose to them any conﬁdential information. If such a warning was intended, I am grateful for it, but would like to say that I did know of Prof. P. that he held extreme and rather dogmatic, political views; while I did not have the same impression of Dr. B. I would have hesitated to rely on his disgression anyway. But the main point is that whatever I thought of these people, I know enough about my obligations, and about the importance of the information I have access to, I would not dream of passing conﬁdential information to these people any 398

As a result of Klaus Fuchs’ arrest, many British scientists were facing criticism over their links with Eastern European colleagues. In Peierls’ case, the allegations were particularly frequent, because of his personal contacts to Russia and his close links with Klaus Fuchs. In this case, Peierls was accused of having close contacts to two Birmingham colleagues, referred to here as Prof. P and Dr. B, both of whom were said to have communist aﬃliations.

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more than to my many other friends who may be safe, but who are not connected to the project. Or perhaps there may have been concern that the political thoughts of these acquaintances might sow dangerous seeds in my mind. If a warning against this danger was intended, I am grateful for it, but I am not afraid of this danger. I have lived in many countries and discussed politics and principles with many diﬀerent types of people. As a result I have developed my own views and principles, and I hold these with conviction. They are not easily shaken by propaganda. In fact, I believe it to be one of the greatest advantages of the democratic way of life, and a great source of strength, that we hold our beliefs from free choice, and after mature consideration of the alternatives, and not because dangerous ideas have been kept from us. There might also have been a suggestion (though I would like to stress that nothing in your very fair and reasonable explanation would support this inference) that my contacts with the two men in question was liable to be misconstrued, and that it would be better to disassociate myself from them. If there was any such suggestion, I would like to make it clear that I see no cause whatever to alter my personal relations with people. Almost anything one does can, in suitable circumstances, be open to misinterpretation; this is a risk one cannot escape. To these remarks I would like to add a comment of a diﬀerent kind. The points you raised worry me because, on the face of it, the implication seems to be that of a very low standard of eﬃciency in the security services. It is quite correct that Professor P. is an old friend of mine, though I have not, in fact, seen him for at least eight months (outside university senate meetings, &c). But my association with Dr. B. is much more tenuous than that. He stayed at our house when he ﬁrst came here in 1939 as a very poor refugee. About 18 months ago when their child was born, my wife tried to help and advise them on their domestic diﬃculties. As a result of diﬀerences in outlook which became apparent then, the two ladies have not seen each other since then. My own contacts with B. do not go beyond exchanging, on rare occasions, a few words about some topical news item. I mention these thoroughly unimportant facts only because they tend to show that the information available to the security services is

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somewhat obsolete and not terribly signiﬁcant. I would have thought there were a great many facts about me that could be made to look much worse. I would naturally assume that these were known, and regarded as innocuous, but I am now beginning to wonder whether perhaps they have not yet been reported? Is it known, for example, that, when we were in Cambridge, we were on friendly terms with D.P. Wooster,399 and spent a summer holiday with him and his family in 1937? Or that my wife is on very friendly terms with Mrs Betty Waddington at Cambridge, whom she has known well since about 1934, and whose views since then have shifted so far to the left that I believe she is now a member of the communist party? My wife still visits her every time she is in Cambridge, and when we go to Cambridge together I usually do as well. Is it known that I am acquainted with Prof. P.Y. Chau of Peking, from the days when we were both research student[s], and that, when he recently visited Birmingham as a member of the oﬃcial “goodwill” mission on behalf of the Chinese government, he spent an evening at our house? Is it known that, when in 1949 we arranged an exchange visit which brought a Belgian girl to our house for a few weeks, and my son later to her house in Brussels, she turned out to be the daughter of the General Secretary (or similar high oﬃcial) of the Belgian Communist Party? Is it known that I am well-acquainted with Dr. Gremlin in the Physics Department here, whose name appeared on the letterhead of the committee organising the Sheﬃeld “Peace” congress? It is true that my social contacts with the Gremlins are not very frequent, but rather more so than with Dr. B. Is it known that I was greatly disappointed when the proposal to get Professor C.F. Powell of Bristol for our physics chair fell through, in spite of his reputation as a left-winger? Is it known that I had recently in my department two Polish scientists who came with scholarships awarded by the Polish government,400 399

Peter Wooster, a Cambridge crystallographer, and his wife Nora held pronounced left-wing views. 400 Jerzy Rayski and Jan Rzewuski.

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and that we were on friendly terms with both of them, one even staying in our house for a few nights? I suppose it is known that my brother, like myself, has a Russianborn wife (this is pure coincidence); but is it known that, before she married him in about 1930, she was a secretary in the Russian Trade Delegation in Berlin? On the other hand, is it known that my wife is the cousin of Kannegiesser, a counter-revolutionary who assassinated Uritzky, who was then the head of the Russian secret police? With the same, very rare surname, she was never allowed to forget this connection. Is it known that her family was banished from Leningrad in 1935, partly because of this old connection, and partly no doubt because of her marriage to a foreigner. They have not dared communicate with her for several years, and we do not know whether they are still alive. I hope you will appreciate that this letter is not written in a spirit of complaint. I appreciate the great importance of security checks, and I have great sympathy for the diﬃculty in the way of such investigations, in particular in the case of intellectuals who rarely present a case without complications. But with so many facts in my case that could be open to unfavourable interpretation, if the attention of the experts is caught by just the two men in question, one naturally wonders whether they have missed many of the other facts, or whether they have a rather curious sense of proportion. Thank you once again for the frankness and courtesy with which you talked to me about all this. Yours sincerely, [R. Peierls]

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[526] Rudolf Peierls to Herbert Fr¨ ohlich401 [Birmingham], 26.4.1951 (carbon copy) Dear Fr¨ ohlich, Thank you for your letter.402 May I say ﬁrst of all how pleased I was that your election to the Royal Society has come through at last.403 About the other problem, I was meaning to write to you as soon as I knew you were back.404 The point is the following: in your treatment of the interaction of electrons with the lattice you are in fact writing down a one body problem, but because of the Pauli principle this results in terms which are essentially two-electron terms when you [. . . ]405 a statistical problem. We have set ourselves the problem, ﬁrst of all of ﬁnding out what those terms look like if one writes down the equation for two electrons and also to see whether there are any other two-electron terms. We have already found the following facts: ﬁrstly if one transforms your terms into coordinate space they have the peculiar property that they do not seem to depend on the distance between the two electrons. In other words if your two electrons are represented by wave brackets, which are known to be 10 cm apart, the interaction term would be equally strong, as if they were close together; secondly there are terms which come only in the two electron problem and the most important of these can be described as one electron emitting a phonon and the other absorbing it. These, however, are not diagonal terms and if one restricts oneself exactly to ﬁrst-order perturbation theory they are of no importance, however, one should not be pedantic about ﬁrst-order 401

Herbert Fr¨ ohlich (1905–1991), studied in Munich where he obtained his Ph.D. under Sommerfeld in 1930. He left Germany in 1933, initially working in Leningrad with Joﬀe, before emigrating to England to work with Mott in Bristol. In 1948 he accepted a Chair at Liverpool where he remained until his retirement in 1973. 402 Letter could not be located. 403 Herbert Fr¨ ohlich was elected fellow of the Royal Society on 15 March 1951. 404 Herbert Fr¨ ohlich had been on leave at Purdue University, Indiana. 405 Word missing in text.

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theory since one is dealing practically with a continuous spectrum, so that one has to consider cases in which the electron[s] have exchanged quite small amounts of energy. I believe now that if one takes such terms into account they should remove the apparent discrepancy and in that respect it is satisfactory that the discrepancy is important particularly for large volumes of metal when of course it is also particularly important not to regard the energy levels as far apart. At present we do not claim that the result w[ould] necessarily make any diﬀerence to the application of the theory, but I am fairly certain that an exploration of these problems will help one to understand what goes on. I am fairly conﬁdent that by our methods it will be possible to solve the two-electron problem with some simpliﬁcations but without assuming perturbation theory, but it remains to be seen whether this will throw suﬃcient light on the many body problem so as to be independent of perturbation theory for the physically important case. Yours sincerely, R.E. Peierls

[527] H. Fr¨ ohlich to Rudolf Peierls Liverpool, 1.5.1951 Dear Peierls, Many thanks for your letter and congratulations.406 I was very interested to see that you have ideas which might lead to an interaction which also depends on the coordinates in ordinary space. I felt that in a better approximation than I have used this should be expected. My reasons were as follows: Consider classically the interaction of two sources of a ﬁeld. When the sources are at rest then the interaction no doubt depends on their distances only. When they move, velocity dependent terms have to be introduced which become increasingly important when the velocity of the sources approach the critical velocity of the ﬁeld (velocity of sound 406

Letter [526].

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or light). In my case the velocity of the particles is large compared with the velocity of sound. The velocity dependent terms would therefore be expected to be very important. But nevertheless there should be some dependence on the distance in the approximation in which one does not neglect s/v entirely. I realise, of course, that this is merely an intuitive argument and not at all compelling. I am very glad to see therefore that you have better reasons to expect such a term. You may be interested, in this connection, that I have seen Wentzel and he appears to feel satisﬁed now that the main ideas of the theory are correct. I agree with him, of course, that one ought to ﬁnd improved methods. The great diﬃculty in this case is that metal theory is essentially based on the hypothesis of free electrons (modiﬁed by periodic potentials only). The question then arises at what point exactly should one make this hypothesis. One might, for instance, make it for a Fermi distribution at absolute zero with any number of free vibrations excited. In this case, one would be concerned with the difference of the properties of other distributions from the f0 distribution only. I should like to have your opinion, if possible, on a further point concerning Bardeen’s interpretation of the magnetic properties. His argument is essentially based on his belief that in the case of very small eﬀective mass the Landau-Peierls formula breaks down in such a way that homogeneous ﬁelds are not possible. I think however that his argument is wrong. The L-P formula can be derived from a calculation of the change in the energy of an electron gas due to the presence of a vector potential A; and the result can be written as 1/2|χ0 |(curl A)2 . Here, strictly speaking, A is a self=consistent vector potential and very nearly curl A = b and = H, for otherwise one would obtain the wrong Lorentz forces. In general the above energy is still to be corrected because it contains, twice, the terms due to the magnetic interaction. This interaction does, of course, depend on the macroscopic shape of the specimen. The simplest way of dealing with it is to consider the

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case of a slab between poles of a permanent magnet, in which case the interaction is negligible. One then ﬁnds, immediately, that χ0 is not the susceptibility χ but rather χ = µχ0 or |χ| = |χ0 |/(1+4π|χ0 |) < 1/4π so that the contradiction which Bardeen believes to derive (negative µ) never arises. Yours sincerely, H. Fr¨ ohlich

[528] Rudolf Peierls to Raymond Priestley [Birmingham], 22.5.1951 (carbon copy) Dear Vice-Chancellor, I have discussed with Prof. Garner407 the question of an appointment in my department which raises a point of principle on which your opinion would be very welcome. The vacancy arises with the resignation of Mr. H.McManus, who was a lecturer in Grade II, his present salary being £650. His appointment was only a temporary one, the reason being that I knew he wanted a change and was going to leave as soon as he could ﬁnd a satisfactory job elsewhere, but the job is deﬁnitely part of my establishment. I would now like to recommend for appointment Dr. R.H.Dalitz, who is at present a research fellow, his salary being £550 p.a. I have no doubt that Dr. Dalitz is a most suitable person for the job, but the question is what his salary should be. Dalitz is now 26. He graduated with 1st Class Honours in Mathematics at Melbourne in 1944, and with 1st Class Honours in Physics in 1945. He spent a short time doing research there, which led to two C.S.I.R. Reports on hydro-dynamic problems, and was then awarded a research scholarship that took him to Cambridge. He spent the two 407

Frederic Horace Garner (1893–1964), Professor of Chemical Engineering at Birmingham University, 1942–1960.

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years 1946–48 in Cambridge and the following session in Bristol, and came here as a research fellow in 1949. He completed last summer a thesis which got him the Cambridge Ph.D., and this work led to two papers which have been accepted by the Royal Society and will appear shortly. He is one of the best research men in my department, very mature for his age and is at the moment completely responsible for one graduate student and takes a great share in helping and advising others. In addition, under our customary arrangement by which research fellows also help in undergraduate teaching, he has for the last two years been giving all the lectures that we normally give as part of Honours Physics Course IV. These are the hardest courses in my department, because a lot of information has to be conveyed in a very short period of lectures to people not familiar with mathematical techniques, and Dalitz has acquitted himself very well; in fact, I understand from the physicists that of the ﬁve lecturers who have given these courses recently, Dalitz is the only one who has made a real success of this job. Dalitz himself is somewhat reluctant to take on a teaching job instead of continuing in his present research fellowship, and I can see that from his point of view to take on the extra teaching duties would be a sacriﬁce. I still hope to be able to persuade him to accept this if we can make it worth his while. It would not be reasonable, in any case, to ask him to take on extra duties without an increase in salary, and I feel therefore, we could in any case not oﬀer him less than £600 p.a. I would very much like, however, to be able to oﬀer him £650. This is still saving, since McManus, if he had stayed, would presumably have been entitled to £700 next year. In this connection it is relevant that a year ago I replaced a lecturer Grade II who was then leaving by an appointment in Grade III, so that the balance of seniority on my staﬀ would not be unreasonable. The question of principle that arises is therefore solely concerned with Dr. Dalitz’s age. Incidentally, Dr. Dalitz is married and has two children. He is, of course, entitled to family allowance both as a research fellow and as a lecturer. I have discussed this problem also with Professor Moon, who knows Dalitz and knows in particular of the teaching work he has done. He is prepared to support the recommendation for £650 as an exceptional case.

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I believe Garner is going to talk to you about this case at the next opportunity, but the purpose of this letter is to put all the facts before you to save time. Yours sincerely, R.E. Peierls

[529] Robert Oppenheimer to Rudolf Peierls Princeton, 27.8.1951 (carbon copy) Dear Rudi: I was very glad to get your letter of August 24th. Just three days ago I was in the oﬃce of the Science Advisor of the State Department listening to the many tales about visas in general and in particular, and I am concerned that nothing should interfere with your planned stay at the Institute.408 Your status here is that of a Member, analogous to a fellow supported by a foundation. The formal purpose of your coming is to enable you to pursue your own studies; the Institute makes and can make no formal demands whatsoever on your time. You are thus fully eligible to come on a Visitor’s visa, and I am attaching a formal statement indicating that we have been designated by the Department of State as a sponsor of the Exchange Visitor Program. The grant that we make to you is not a salary; and whatever great tangible or intangible beneﬁts we derive from your being here, our grant and your coming are in no way conditioned by their realization. Quite recently, I have been told that you are coming next month with an oﬃcial passport; and it has not been clear to me that it would be wise or even possible for you to use this for the extended visit next Spring. The Department of State 408 Rudolf Peierls, during the McCarthy era, on several occasions, had problems with obtaining the necessary visa for the United States. After problems in obtaining a visa for attending the nuclear physics conference in Chicago in October 1951, again his attempts to get the travel documents necessary to embark on his visit to Princeton in 1952 met with delays, but were approved eventually.

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is aware of our great interest in having you and our desire that nothing delay or interfere with your visit, and you must let us know if there are any ways in which we can help in bringing this about. My present plans are to attend the Chicago conference. But since I have kept almost no plans in the last months, I do not know with assurance that I will actually be there. I do very much hope to see you, both in connection with the basic problems which will be taken up in Chicago and in connection with the always important question of eﬀective collaboration between our two countries. I hope you will arrange, in connection with this visit, to spend a little time in Princeton and to stay with us if at all possible. Allison has asked that I tell you of my willingness to join the discussion on meson theories at which you will be a chairman. You know, I expect, that I have no great clarifying light to shed; but you know me well enough to know that I am always willing to join in a discussion. With every warm good wishes from both of us to both of you, [Oppie] [530] Rudolf Peierls to Claude Bloch [Birmingham], 13.12.1951 (carbon copy) Dear Bloch, In Copenhagen you mentioned to me the very nice idea that an oper¯ 1 )ψ(x2 ) could be made gauge-invariant if one ator like F (x1 − x2 )ψ(x expressed ψ(x2 ) by the Taylor series and replaced in it the derivative by the gauge invariant operator, so that formally the expression becomes ∂

ie

¯ 1 )ex1 −x2 )( ∂xµ − e Aµ ) ψ(x1 ) F (x1 , −x2 )ψ(x

(1)

We have taken to the study of such theories again and I would therefore be glad to know whether you have published your suggestion and whether you would allow me to refer to is in a talk I have promised to give to the American Physical Society in New York in February. The following results may interest you. (perhaps you have already obtained them yourself):

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1. The above expression can be evaluated explicitly and is essentially identical with ie

¯ 1 )e F (x1 , X2 )ψ(x

x

2 x1

Aµ dxµ

ψ(x2 )

where the integral in the exponent is to be taken over the straight line joining the (four-dimensional) points x1 and x2 . 2. It is nevertheless not possible to assume a Lagrangian of the form x ¯ 1 )γµ eie x12 Aν dxν ψ(x2 ) dx41 dx42 dx43 F (x1 x2 x3 )Aµ (x3 )ψ(x Le+Lf + (2) where Le and Lf are the usual free-electron and free ﬁeld functions, since this leads to gauge invariant functions only if ∂jµ =0 ∂xµ

(3)

where jµ (x3 ) is the factor of Aµ (x3 ) in the action principle (2). 3. One does, however, obtain a consistent scheme for the action principle: x ¯ 1 )G(x1 , x2 )eie x12 A˜µ dxµ ψ(x2 )d4 x1 d4 x2 ψ(x (4) Lf +

where G(x1 x2 ) =

∂ γµ − im F (x1 − x2 ) ∂xµ

(5)

and F is an invariant form factor of the usual kind. A˜µ is a “smeared” potential ˜ (6) Aµ (x1 ) = Ø(x1 − x2 )Aµ (x2 )d4 x2 This second “smearing” process may not in fact, be necessary. It is easy to see that (4) reduces to the usual theory if F and Ø are taken as δ functions.

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We are rather attracted by the equation (4) and are proposing to investigate it further. I shall be in Princeton for the Spring Term, leaving this country on 4 January, so unless you reply before Christmas could you write to the Institute for Advanced Studies at Princeton? With kindest regards, Yours sincerely, R.E. Peierls

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7.

Birmingham:

A ‘Most Stimulating Theoretical Group’

The 1950s were the most vibrant period in the history of Birmingham’s theoretical physics department. When Gerry Brown commented on his forced exit from the American academic circuit in 1950, he commented that with the beneﬁt of hindsight his seeming ill fortune turned out to be great luck as he was ‘settled in the most stimulating theoretical group in the world.’409 That ‘Prof’, as Peierls was known and addressed as affectionately by many of his junior colleagues, was the core around which this active research community congregated, is evident in the extensive correspondence between him and other members of the department between January and April 1952, when he spent a term at the Institute of Advanced Study at Princeton. With Freeman Dyson’s arrival at Birmingham in the autumn of 1949, quantum electrodynamics arrived at Peierls’ institute, as Dyson at ﬁrst lectured about the Feynman/Schwinger/Dyson results and later about new formulations of the old theory. Princeton was one of the nerve centres of the new developments. At the time, apart from its director Robert Oppenheimer, the other permanent staﬀ members at Princeton were C.N. Yang, Abraham Pais, and Peierls’ old friend George Placzek. And in addition the departments of physics and mathematics with Eugene Wigner, Arthur Wightman, Menahem Max Schiﬀer and David Feller, and many transients at the Institute410 helped to create a stimulating research environment. As Sam Schweber recalls, during his time at Princeton, between 1949 and 1952, most of the presentations 409

G.E. Brown, ‘Fly with Eagles’, Ann. Rev. Nucl. & Part. Sci. 51, 1–22 (2001), here p. 7. 410 At the time among those transients were Francis Low, Murray Gell-Mann, L´eon Van Hove, Frank Yang, Bryce de Witt and Robert Karplus.

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at the Institute were at the frontiers of quantum ﬁeld theory and in particular quantum electrodynamics (QED).411 QED, the theory of interactions of charged particles with the electromagnetic ﬁelds, describes mathematically interactions of light with matter, and also interactions of charged particles with one another. Following on from the Dirac Equations which represented motion and spin of electrons in a way that incorporated both the quantum theory and the theory of special relativity, Feynman, Schwinger, Tomonaga and Dyson further reﬁned the idea and developed it more fully. Their theories rest on the idea that charged particles such as electrons or positrons interact by absorbing and emitting photons, particles of light that transmit electromagnetic forces. These photons are virtual, as their existence violates the conservation of energy and momentum. The interaction of two charged particles occurs in a series of processes of increasing complexity. In the early 1950s, the new developments in quantum mechanics had not been applied to two-electron interactions or to higher-order interactions between electron and proton in hydrogen. In 1951, Hans Bethe and Ed Salpeter at Cornell had developed an equation for these bound-state problems, and Gerry Brown also worked on a formulation of a perturbation theory for these problems.412 The letters exchanged between Gerry Brown and Rudolf Peierls, mostly dealt with the comparison of the work which Salpeter and Bethe had just published and Gerry Brown’s own progress.413 Schwinger, Feynman and Dyson had demonstrated how to eliminate inﬁnities in the theory, and the kind of perturbation calculations, especially in the two-body systems of hydrogen and positronium which Salpeter and Brown were engaged in, also occupied many other physicists, including Robert Karplus, Norman Kroll and Francis Low. They were technically complex, but conceptually less exciting.414 411

Interview of Arne Hessenbruch with Sam Schweber, 27.8.2001. http:// hrst.mit.edu/hrs/materials/public/schweber interview.htm. 412 G.E. Brown, ‘Bound-State Perturbation Theory in Four-Dimensional Momentum Representations’, Proc. Roy. Soc. A215, 371–85 (1952). 413 See letters [532], [535–536], [538], [540], [543], [545–47], [549–50], [553–54], [557–58]. 414 See letters [535], [538], [540], [550], [554–55], [557].

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More conceptually signiﬁcant were some other theoretical considerations tackled at Birmingham (and elsewhere), after the techniques and formalisms of the new QED approach had been mastered. Some of the letters sent between Birmingham and various American universities, pointed to the new avenues which were being explored in the wake of these ﬁeld theoretical developments. Among those were problems arising from Rayleigh Scattering, and the calculation of the Lamb-Shift in heavy atoms. Philip Moon, at the time professor of experimental physics at Birmingham, had been scattering γ-rays coherently oﬀ complex nuclei, both intermediate and heavy. John Woodward, assistant lecturer at Peierls’ department, and Gerry Brown developed a theory which was to explain some the phenomena encountered by Moon. Woodward had been using Thomas-Fermi-approximations for the purpose, but it became clear that rather than treating the electrons closest to the nucleus as a Fermi gas, their replacement by their relativistic Dirac wave functions, might be more promising. Brown had used such relativistic electrons in his doctoral work with Gregory Breit.415 Their work, which received a lot of input from ‘Prof’, is discussed extensively in the correspondence.416 W. Franz in the 1930s had worked out the form factor for Rayleigh scattering, the cross section to lowest order in an expansion in Zα.417 Brown, however, worked out that the next term of higher order in Zα was larger than Franz’s calculations suggested for higher γ-ray energies, which went against scientists’ preconceptions that with an increase in the incident energy the expansion in Zα should converge more rapidly.

415

Brown had published four papers while working on his Ph.D. with Breit at Yale. G. Breit and G.E. Brown, ‘Eﬀect on Nuclear Motion on the Fine Structure of Hydrogen’, Phys. Rev.74, 1278–84 (1948); G. Breit, G.E. Brown and G.B. Arfken, ‘The Eﬀect on Nuclear Motion on the Hyperﬁne Structure of Hydrogen’, Phys. Rev. 76, 1299–1304 (1949); G.E. Brown and G.B. Arfken, ‘Eﬀects of the Proton Radius on Nuclear Motion Correction for the Hyperﬁne Structure of Hydrogen’, Phys. Rev. 76, 1305–1306 (1949); and G. Breit and G.E. Brown, ‘Perturbation Methods for Dirac Radial Equations’, Phys. Rev. 76, 1307–1310 (1949). 416 See letters [532], [536], [538], [546], [554]. 417 W. Franz, ‘Rayleighsche Streuung harter Strahlung an schweren Atomen’, Z. Phys. 98, 314–20 (1935). See letter [540].

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Peierls later commented that this was ‘almost a classical case of a theoretical surprise’, when he described the problem in his Surprises in Theoretical Physics, a collection of physical problems where plausible expectations are not borne out by careful analysis.418 In fact, this ‘surprise’ presented Peierls with a good opportunity to reinforce collaboration with his close friend Hans Bethe. Having brieﬂy met him at the Rochester Conference early in January 1952, he visited him at Cornell later in the month, among others to discuss the Brown/Woodward work.419 Bethe had calculated the Rayleigh scattering in impulse approximations in order to explain experimental results which Bob Wilson at Cornell had obtained.420 The discussions with him and also with Joseph Levinger who had an interest in the problem, were fruitful and encouraged by regular feedback from ‘Prof’, Brown and Woodward drafted a paper which explained why the main contributions to Rayleigh Scattering came from closer to the nucleus as (∆x)2 became larger.421 Another quantum ﬁeld theoretical problem tackled by Peierls concerned the development of a non-localised theory, a theory spaced out in time as well as in space. Translating the equations, which worked satisfactorily in the classical framework, into quantum theory required the introduction of quantum rules which did not exclude ‘non-local theories’. Peierls and his Swiss post-doc Max Chr´etien investigated the problem and discussed it in detail with Claude Bloch, Wolfgang Pauli and J. Valatin.422 As the correspondence indicates, their progress led to the publication of two joint papers on these non-local theories.423 418

R.E. Peierls, Surprises in Theoretical Physics, Princeton: Princeton University Press, 1970. 419 Letter [538]. 420 R.R. Wilson, ‘Scattering of 1.33 MeV Gamma Rays by an Electric Field’, Phys. Rev. 90, 720–21 (1953). 421 G.E. Brown and J.B. Woodward, ‘Coherent Scattering of Gamma Rays by Bound Electrons’, Proc. Phys. Soc. A65, 977–80 (1952). 422 See letters [533–34], [537], [542], [548, 551, 556, 561, 563–64, 566–70, 573, 584–89, 591–92]. 423 M. Chr´etien and R.E. Peierls, ‘Properties of Form Factors in Non-Local Theories’, Nuovo Cimento 10, 668–76 (1953); M. Chr´etien and R.E. Peierls, ‘A study of gaugeinvariant non-local interactions’, Proc. Roy. Soc. A223, 468–81 (1954).

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If Peierls had been concerned about the eﬀect of his temporary absence on the well-being of the department, his worries would have been dispelled by the comment of Gerry Brown about two months into the former’s absence: ‘I’m not anxious for you to get back from the States’, he writes, ‘because the information you’ve been passing on has been a tremendous spur in getting a lot of things cleared up’.424 Most other letters which Peierls exchanged with colleagues at Birmingham and elsewhere concerned these and other questions of quantum ﬁeld theory. But the Princeton-Birmingham correspondence also reﬂects the second leg on which Peierls’ department stood, namely the training of undergraduate and graduate students. His younger colleagues had stood in for lectures, and while Peierls left them the freedom to design and alter the lectures freely, he was approached for and happily gave advice on methodology and examinations.425 More importantly he continued to oversee the progress of more advanced students (Sheila Brenner, John Radcliﬀe, P.G. Harper,) by communicating with them directly and through their temporary advisers, Gerry Brown, Dick Dalitz, or George Kynch to ensure that they would not be disadvantaged by his decision to pursue more actively his own research at Princeton. Peierls’ communications with Dick Dalitz demonstrate that ‘Prof’ was keen for his junior colleagues to participate actively on the international research scene, as he advised and encouraged Dalitz to consider spending some time in the US,426 while balancing the needs of the individual staﬀ member with the smooth running of the department. For Peierls, his stay at Princeton did not only allow him to participate in stimulating exchange at the cutting edge of his discipline; it also provided him with uninterrupted time to think and calculate, which was exactly what was needed to complete the project which he was working on himself. He was looking for a new expression of some of the basic rules of quantum mechanics, namely the formulation of commutation laws of relativistic ﬁeld theory. Heisenberg and Pauli had formulated a consistent formulism for quantum ﬁeld theory more than twenty years 424

Letter [554]. See particularly letters exchanged with Gerry Brown. 426 Letters [539], [541]. 425

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earlier.427 However, they had used the Hamiltonian form of the ﬁeld equations to construct pairs of canonically conjugate variables, and as the Hamiltonian form of the equation was linked to a choice of the time axis, the Lorentz-invariance of the formulation was not evident. Alternative approaches based on ‘interaction representation’, such as those formulated by Tomonaga428 , Schwinger429 and De Wet430 had similar limitations, and Peierls attempted to formulate a general rule for obtaining commutators for any two points in space and time. In March 1952, Peierls reported about his progress to Dirac with whom he had written a paper on Lorentz invariance in quantum theory a decade earlier.431 The previous two months of concentrated work had led to the construction of Poisson Brackets, related to the action principle but not requiring the introduction of canonical variables.432 This permitted the laws for forming the commutators of canonical theory as well as the anticommutators of Fermi-Dirac particles to be stated in a covariant way.433 However, while the commutation laws could be applied to theories in which there was no Hamiltonian, there was not guarantee that it was anti-commutative, i.e. that the identity [a,b] = −[b,a] was satisﬁed. When the paper was published later in 1952, Wolfgang Pauli queried a number of important details, which led to a lengthy exchange of views. Pauli had become interested in non-local ﬁeld theories during discussions at Copenhagen in June 1952, and after his return from a trip to

427

W. Heisenberg and W. Pauli, ‘Zur Quantenmechanik der Wellenfelder’, Z. Phys. 56, 1–61 (1929); W. Heisenberg and W. Pauli, ‘Zur Quantenmechanik der Wellenfelder II’, Z. Phys. 59, 168–90 (1930). 428 S. Tomonaga, ‘On a relativistically Invariant Formulation of the Quantum Theory of Wave Fields’, Progr. Theor. Phys. 1, 27ﬀ. (1946). 429 J. Schwinger, ‘Quantum Electrodynamics. I. A Covariant Formulation’, Phys. Rev. 74, 1439–61. 430 J.S. de Wet, ‘The interaction representation in the quantum theory of ﬁelds’, Proc. Roy. Soc. A201, 284–96 (1950). 431 R.E. Peierls, P.A.M. Dirac and M.H.L. Pryce, ‘On Lorentz invariance in the quantum theory’, Proc. Cambr. Phil. Soc. 38, 193–200 (1942). 432 Letters [552], [555]. 433 R.E. Peierls, ‘The commutation laws of relativistic ﬁeld theory’, Proc. Roy. Soc. A214, 143–57 (1952).

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India434 he took up the problem more energetically, which is evident in his correspondence with Peierls as well as with Møller and Bloch.435 By January 1953, Peierls could send a proof of the Jacobi Identity, which Pauli has been urging him to provide, 436 but Pauli remained sceptical. In March 1953, in a presentation at the Turin Conference on non-local theories,437 he was very pessimistic about the theory, and on his return from Turin he wrote to Peierls. ‘For me it looks like a cemetery for the lorentzinvariant formfactor theory in its present form.’438

434

Letters [584–589]. See Pauli, Wissenschaftlicher Briefwechsel, IV/1. 436 Letter [584]. 437 W. Pauli, ‘On the Hamiltonian structure of Non-Local Field Theories’, Nouvo Cimento 10, 648 (1953). 438 Letter [591]. 435

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[531] Rudolf Peierls to R.H. Dalitz [Princeton], 14.1.1952 (carbon copy) Dear Dalitz, I saw Dyson at the Rochester conference last week.439 To my great surprise he seems to have lost interest in his programme for treating divergence, and partly he seems to feel that all that can be done with his technique could be done more simply with the Bethe-Salpeter equation. I tried to question him a little about his reaction to Salam-Matthews440 but he just did not know anything about their calculation. He did, however, agree that to do a one-particle problem properly in his scheme, one would have to solve ﬁrst the vacuum problem and then the vacuum plus one particle, and where necessary, subtract the two. Of all this, I think the most important is the remark that a solution to the same problem is contained in the Bethe-Salpeter equation. If that is true it would probably not be wise to invest much further eﬀort in the Dyson (or ex-Dyson) programme. However, I think we would need a better understanding of the B.S. equation before we could be sure. I hope to ﬁnd out more about this and shall, of course, let you know. There was a lot of interest at Rochester. The conference notes are supposed to be written up within a week (authors Noyes and Messiah441 ) and a copy will be sent to Birmingham, so I need not go into detail, but I shall try to bring out a few important points. I shall include where relevant what I learnt at Bristol, since I never had a chance to tell you properly about that. Firstly about π and π o mesons. The most interesting results are by Anderson (Chicago) and Steinberger (Columbia) about scattering by 439

Second Annual Rochester Conference on Meson Physics 11.–12.1.1952. Abdus Salam and P.T. Matthews had published a paper which discussed the extension of Dyson’s proof of ﬁniteness after renormalization of matrix elements for scattering processes to certain meson interactions. See P.T. Matthews and Abdus Salam, ‘The Renormalization of Meson Theories’, Rev. Mod. Phys. 23, 311–14 (1951). 441 A.M.L. Messiah and H.P. Noyes, ‘Proceedings of the Rochester Conference on Meson Physics, January 11–12, 1952’, Rochester University Technical Report, (1952). 440

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hydrogen. It is conﬁrmed that the cross section rises with energy, the total cross section going from about 21 millibarns at 89 MeV to 60 mb at 217 MeV for negative mesons, and from 20 mb at 56 MeV (50 at 82) to 152 at 135 Mev for π + . The puzzling feature is that the scattering of positives is larger and rises more steeply with energy.442 In the case of π − gamma rays were found, which indicate a (π−, π 0 ) reaction. By measuring at 90◦ the cross section for pure scattering at 112 MeV was estimated to be σ(π − , π − ) ∼ 13mb, while σ(π − , π 0 )25mb. In the same circumstances the (π − , π + ) cross section is near 100. Fermi points out that these three cross sections are not far from the ratio 1:2:9, which could be interpreted according to the following picture. Assume the forces to be charge symmetric. Then the total isotopic spin is a good quantum number in this reaction. A nucleon having isotopic spin 1 1 2 , and a meson 1, we are then dealing with states of total T = 2 or 3/2. In the collision of a positive meson with a proton we have in fact a pure state 3/2, in the other case a mixture. Now suppose that the interaction is strong only for T = 3/2 and negligible for 12 . Then one would have to resolve the state of H + π − into states of given T , and the state of T = 3/2 then should have a cross section as large as in the positive case. The scattered wave is then again resolved into positive and neutral mesons. The answer to this is, of course, unique and gives just 1:2:9. Next one asks why the interaction is so strongly dependent on isotopic spin and a suggestion is that there might exist isobaric states, as in the strong-coupling theory, except that, if the coupling is not strong, they would be rather wide. The phenomenon would therefore be a kind of broad resonance with a T = 3/2 virtual level of the system. The experiments show, in fact, that the negative cross section ﬂattens oﬀ near 200 MeV, and with enough imagination one can in fact see it going 442

H.L. Anderson, E. Fermi, E.A. Long, R. Martin and D.E. Nagle, ‘Total Cross Section of Negative Pions in Hydrogen’, Phys. Rev. 85, 934–35 (1952), H.L. Anderson, E. Fermi, A. Lundby, D.E. Nagle and G.B. Yodh, ‘Ordinary and Exchange Scattering of Negative Pions by Hydrogen’, Phys. Rev. 85, 935–36 (1952), H.L. Anderson, E. Fermi, E.A. Long, R. Martin and D.E. Nagle, ‘Total Cross Section of Positive Pions in Hydrogen’, Phys. Rev. 85, 936 (1952), C. Chedster, P. Isaacs, A. Sachs and J. Steinberger, ‘Total Cross Sections of pi-Mesons and Several Other Nuclei’, Phys. Rev. 82, 958–59 (1952).

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down again. This maximum is not, however, a very direct indication of a resonance level, since one assumes anyway that the interaction is mainly in p states (in order to get the rapid rise with energy) and if one had no other waves contributing, a p state gives, of course, ﬁrst a rise and then a fall because of the 12πχ2 limit. Brueckner reported some calculation ﬁtting the resonance formula of the Breit-Wigner type, and obtained an energy and a width from it (resonance energy 137 MeV in centre of mass system) but I do not believe it means much. Because these facts support the concept of an isobaric state, Wentzel dug out the old strong-coupling theories again and he is trying to apply them, but I do not think one could do that. Now about heavier animals. It is clear there exists neutral V which decays into a proton and a negative particle which probably is a π − . It is now fairly probable, but not yet certain, that there is no other particle and that the energy release is in the neighbourhood of 75 MeV. The actual number 75 comes from Leighton443 at Cal Tech who has a very good set-up for getting lots of particles and measuring them accurately. However, according to the Manchester group, there exists in addition a second type of V particle, called V20 in Manchester, and v at the Rochester Conference, which is supposed to decay into two charged mesons. Leighton disagrees with this now strongly, but claims instead a second group of particles, which also gives a homogeneous value for the energy release if interpreted as decaying into a proton and a π − . Leighton would probably interpret the cases where the positive was seen to be light, as involving a negative proton. This second group has a reaction charge of 34 MeV, and in this group it is only the negatives (i.e. mesons) which are ever seen to be slow, which is very hard to understand. There is therefore doubt whether the lighter V (or v) exists. On the other hand, the Bristol people now ﬁnd plenty of Kρ . In very energetic showers which are mainly two-nucleon collisions (seen in the plate as having few or no low-energy nucleons) they seem to be generated as frequently as πρ . 443

R.B. Leighton, S.Dean Wanlass and William L. Alford, ‘On the Decay of Neutral V -Particles’, Phys. Rev. 83, 843–85 (1951).

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Also the existence of τ has become more certain. There are now six cases known in photographic plates, and Cal Tech have two cloud chamber pictures of a triple decay into similar particles in ﬂight. Oppenheimer stressed the diﬃculty of explaining the comparatively long life of all three particles together with their copious production and Pais has an approach to systematise this. He supposes that particles in families, one family being the nucleon, which he calls N0 , the heavier V -particle which he calls N1 , and there might be more. This evidently goes with the picture of isobaric states, except that N1 must be at a much higher energy, and live much longer, than the level mentioned before. The second family is ﬁrstly the π, which for this purpose he calls π0 (regardless of charge) and the controversial v, which becomes π1 . Again there are presumably other members of this family. Now Pais postulates that all strong interactions, which must in general be of the form (Ni , Nj , Nk ) are limited by the requirement that i + j + k be even. This includes for the case (0,0,0) the ordinary Yukawa interaction, the case (0,1,1) which leads to the simultaneous production of V and v in the same collision, and (1,1,0) which produces a virtual transition of a neutral [..] into two V ’s and hence leads to the usual [..] decay.444 If only such interactions are permitted, then V and v are stable. One can now add a much weaker coupling which comes in the case when i+j+k is odd. For this the g2 /hc would have to be about 10−11 .445 The attractive feature of this scheme is that no complicated calculation is needed to show that the lifetimes can really be made long enough to any order of approximation, since the restriction on the matrix ele[m]ents that has been imposed has a group property and higher orders cannot bring any surprises. Still, of course, it is building a very large structure of ideas on a few uncertain facts! With kindest regards, Yours [R.E. Peierls]

444 445

Missing in carbon copy. A. Pais, ‘Some Remarks on V -Particles’, Phys. Rev. 86, 663–72 (1952).

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[532] Rudolf Peierls to Gerry Brown [Princeton], 14.1.1952 (carbon copy) Dear Jerry, I have just arrived here at the Institute, and so my holiday is really beginning. I have obviously not yet been able to do anything about your various errands. I also have not yet ﬁnished reading your paper,446 but I gather that Salpeter is interested in rather similar problems.447 I am therefore sending your MS to him, which I hope is o.k. with you, but I shall tell him to be ready to send it back to you at short notice if you want it back. Otherwise it will come back to me and I shall then send it on with any comments I have about editing &c. I also hope to send the hydrodynamics paper.448 On the boat I played a little more with the non-local equations, particularly from the point of view of deﬁning anything without the series expansion. This main point is that I now think one should ﬁrst look at the case of electrons in an external ﬁeld, without bringing in the quantized ﬁeld. In such a case one cannot, of course, talk about self-energy, but one can discuss vacuum polarization (and hence photon self-energy) and it is not a trivial case. In this case, the wave equation is still linear in the ψ ’s and the nature of the general solution of the inhomogeneous equations that we need for the commutators is quite straightforward. In particular, the commutators themselves will not depend on the wave function, and the usual interpretation of ψ, ψ as emission and absorption 446

G.E. Brown, ‘Bound-State Perturbation Theory in Four-Dimensional Momentum Representation’, Proc. Roy. Soc. A215, 371–85 (1952). 447 After the progress of Schwinger, Feynman, Tomonaga and Dyson on quantum electrodynamics, one of the research foci was that of two-electron interactions or higher-order interactions between electron and proton in hydrogen. Ed Salpeter and Hans Bethe had applied Feynman’s S-matrix formalism to the bound-state problem for two interacting Fermi-Dirac particles. See E.E. Salpeter and H.A. Bethe, ‘A Relativistic Equation for Bound-State Problems’, Phys. Rev. 84, 1232–42 (1951). 448 Gerry Brown was lecturing the hydrodynamics course for which the examination paper had to be prepared.

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operators is still correct. The problem of ﬁnding a basic set of operators which are simultaneously measurable now reduces to an ordinary, non-unitary transformation, whose properties I have not yet completely sorted out. It seems to me that one should not tackle the case of a quantized ﬁeld before this similar problem is clear, and perhaps too optimistically, that if we have solved the simpler problem we ought to see a way to get at the bigger one. I saw Bethe at Rochester, and shall probably be at Cornell on Jan. 30. He was interested in the present state of Woodward’s work449 and your argument that the ﬁrst-order terms should be larger than the zeroorder ones for hard gamma-rays. He pointed out that, apart from the factors brought in by the matrix elements, the ﬁrst-order terms contain an energy denominator, which goes through zero. The singularity arising from this is, of course, not serious, but since this means the term will be sometimes positive and sometimes negative, the result may still come out fairly small. I have looked at it again, and it does not look very plausible. But one cannot be sure until the integration has been done. They have not done much more about this problem, except to notice that the imaginary term in the scattered amplitude (which arises from the possibility of photoeﬀect, and, in the forward direction [· · · ]450 is important. If you and Chr´etien451 know anymore about non-local equations before Jan 31., or Woodward about scattering before Jan. 30. let me know.452 449

John Woodward, studied mathematical physics at Birmingham and obtained his Ph.D. under Peierls. He became assistant lecturer, and was working on the theory of scattering γ-rays. 450 Line cut oﬀ in carbon copy of the letter. 451 Max Chr´etien, postdoctoral research visitor at Birmingham who eventually moved from physics into computer sciences. He was associate professor for computer science at Brandeis University. 452 Brown and Woodward later published the results as G.E. Brown and J.B. Woodward, ‘Coherent Scattering of Gamma Rays by Bound Electrons’, Proc. Phys. Soc. A65, 977–80 (1952).

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I enclose a letter, mainly for Dalitz, which however will interest you, too. I shall write to Sheila Brenner453 in a day or so, I would like to take another look at the programme for the summer school before replying. Keep you powder dry and the hydrodynamics wet. Yours, [R. Peierls]

[533] Claude Bloch to Rudolf Peierls Pasadena, 18.1.1952 Dear Professor Peierls, I thank you very much for your interesting letter.454 I am very sorry that it was delayed a long time in Paris, so that my answer comes very late. About the formula involving ie

e

x

2 x1

Aµ dxµ

,

(1)

I should perhaps mention to you that a similar expression has already been given by Sachs (Phys. Rev. 74, 433)455 in connection with the phenomenological theory of exchange currents in nuclei, which is indeed a very similar problem. An obvious remark, is that this expression is not unique. In fact, a gauge invariant expression is obtained if the integral is taken along any arbitrary path going from x1 to x2 . More generally, one could take the average of (1) over a set of paths chosen in such a way that the whole expression has the required invariance properties. A great similarity with Feynman’s integrals over the paths appears then, specially as the integral in the exponent of (1) is the action integral of a charge e going from x1 to x2 along the considered path. 453 Sheila Brenner (1930–2002), studied at Birmingham and obtained her Ph.D. under Peierls. She later taught at Swansea, Royal Holloway and Liverpool. 454 Letter [530]. 455 R.G. Sachs, ‘Phenomenological Theory of Exchange Currents in Nuclei’, Phys. Rev. 74, 433-441 (1948).

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This, of course, is nothing more than playing with the equation and there is no doubt that the interaction you are considering is the most natural of this type. It seems very attractive, and I would be very interested in knowing about the development of the theory. I quite agree that form functions of three points cannot be introduced in electrodynamics. When I mentioned to you such a possibility, I was thinking of a meson-nucleon interaction such as (2) g dx1 dx2 dx3 F (x1 x2 x3 )ψ + (x1 )u(x2 )ψ(x3 ). This type of interaction is the only one I have studied so far. I have not published anything as yet on non-localized interactions, but I have just ﬁnished a manuscript about this problem. I hope to be able to send you a copy of the manuscript in a week or two. It is concerned with the general formulation of the problem taking as particular example the interaction (2). An investigation of the convergence of the self energies to all orders is made. It turns out that whereas convergence at the second-order is easily secured, divergences reappear at higher order unless it is speciﬁed, in particular, that the Fourier transform of the form function should have only time-like components. As this requirement does not seem to be in contradiction with any other requirement, everything is all right. Besides I made a detailed investigation of the conditions under which the non-localizability remains limited to small domains. It is very simple, but I think it was useful to do it. I also show by a general argument that the commutation rules are consistent with the ﬁeld equations. A further check of this fundamental requirement is given by the actual calculation to all orders of the commutation relations of the outgoing ﬁelds in functions of the incoming ﬁelds. Altogether, I think it is proven that the theory rests on sound basis. I have not yet made any calculation of cross section, correction to the magnetic moment of the nucleons due to the exchange current coming from (1), etc... I have heard rumours that during your stay in this country you would spend some time at Cal. Tech. I hope it is true. With many thanks for your interest in my work. Yours, very sincerely, Claude Bloch

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P.S. Please do not mention my suggestion of replacing a non-localized interaction by a Taylor series; a) it is a very old trick, which can be traced back to Wheeler’s velocity dependent potentials b) it is an extremely bad idea since the factor (1) can be found very simply as follows: Consider a gauge transformation Aµ = Aµ (x) +

∂∆ , ∂xµ

ψ(x) = ψ(x)e−ie∆ ,

ψ + (x) = ψ + (x)eie∆ , (3)

where a bar has been put below the transformed quantities. The transformation law of the expression we are interested in is ψ + (x1 )ψ(x2 ) = ψ + (x1 )ψ(x2 )eie(∆(x1 )−∆(x2 )) . We have

∆(x1 ) − ∆(x2 ) = − C

∂∆ = ∂xµ

(4)

C

(Aµ − Aµ )dxµ ,

(5)

where C is any path going from x1 to x2 . Substitution of (5) into (4) gives ψ + (x1 )eie C Aµ dxµ ψ(x2 ), which is the gauge invariance equation we want.

[534] Rudolf Peierls to Claude Bloch [Princeton], 21.1.1952 (carbon copy) Dear Bloch, Thank you very much for your letter.456 I found also that the expression involving the line integral of the vector potential had been used by Sachs.457 This is, however, a rather diﬀerent matter from its particular use in a non-local theory. I also think that your derivation from the 456 457

Letter [533]. Letter [533], note 455.

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Taylor series is useful in showing that the expression is a natural one. The identity of ∂ e(x2 −x1 )( ∂x −ieA) ψ(x1 ) with ee

2 1

Adx

ψ(x2 )

can, of course, be demonstrated without using a series expansion, merely ∂ − ei A). by ﬁnding the eigenfunctions of the operator ( ∂x I have studied further the equations one gets from using in electromagnetic theory the action principle I gave in my last letter, and have not so far found any objections to it. Dr. Chr´etien in Birmingham is now working out the solutions of these equations by expanding in powers of the coupling constant. The results, which I do not have as yet, should be very similar to yours for the meson case, except that the occurrence of the line integrals causes some slight mathematical complications. I am surprised to hear that you ﬁnd still some divergence with a general form function. I was always afraid of using a form function which has a diﬀerent behaviour inside and outside the light cone since I did not feel sure that this would preserve the causal character of the theory, but from what you say you seem to have covered this point. In fact, just as your letter arrived, I was engaged in looking again at the requirement for (large-scale) causality so I shall expect your manuscript with gre[a]t interest. My main interest at the moment is to formulate the theory in such a manner that the deﬁnitions are independent of the expansion in powers of the coupling constant. I had derived, some time ago, commutation laws which were derived directly from the Lagrangian and could be used in a non-Hamiltonian theory, only it is not easy to prove that they are consistent, i.e. that they have solutions. I can now do this for a very special case, namely the equations for quantized electrons in an external (i.e. unquantized) ﬁeld. This is a very easy case, but not quite trivial, since one can discuss such problems as vacuum polarization. In this case one can understand the general behaviour of the equations quite well. I can also get explicit solutions for the case of a uniform (but not necessarily weak) magnetic ﬁeld, provided I use for my form factor a function whose Fourier transform is a simple exponential. This

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function is probably not admissible because it rises instead of falling for time-like momentum vectors, but for the particular problem in hand it gives no trouble, and its behaviour should be fairly typical. About your remark that the integral in the exponent need not be taken over a straight path: If one is to specify a particular path, the only deﬁnition that is Lorentz invariant is the straight line. One could mix terms with diﬀerent paths, and even integrate over all paths in the Feynman way, as you suggest, but I feel this would be useful only if one could use it to see some new connections between diﬀerent parts of the theory. Within the framework of the kind of equations I am using it would just seem an unnecessary complication. How long are you staying at Pasadena? Are you likely to be in the East at all? If you should be in this neighbourhood before the middle of April, I very much hope we can arrange to meet. I do not think I shall be able to get to California during this visit. What are your plans for the next year? Yours sincerely, R.E. Peierls

[535] Rudolf Peierls to Gerry Brown [Princeton], 23.1.1952 (carbon copy) Dear Gerry, I have not yet sent oﬀ your paper to Salpeter, as I said I was going to do, because I wanted some more time to read it myself, and in particular to discuss it with Low,458 which proved most interesting. I am sending it oﬀ now and this is to report to you about a number of point[s]. The most interesting point is that Low has a suggestion to understand why your terms cancel approximately in the end. He says that while for the purpose in hand one has to allow for the motion of the 458

See letter [532].

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proton, the proton velocity will be small in all the important terms. The most rational way of proceeding would therefore be to go over to the second-order equation for the proton (I mean second order in the momentum) which can be approximated by the non-relativist Schr¨ odinger wave function for the proton. In this form one can see that the A2 term will be important. This term evidently is not a spin term and will have no low-order eﬀect on hyperﬁne structure. Now if one proceeds as you do from the linear equation, there are terms involving the exchange of a transverse photon, which will contribute, when i[n]terated, to the A2 term mentioned above, and it is plausible that those will be in the leading correction terms for the hyperﬁne structure is not surprising. Other points on your paper: I think it is important that you should state quite clearly what kind of calculation you assume preceded the formulation of your correction terms. In other words what is the wave equation from which you obtained the function deﬁning your matrix element. One can visualize two diﬀerent alternatives: (a) you solve exactly the two-body equation in which the interaction is the even (++) part of the Coulomb interaction which, for example, is used in your paper which Ravenhall.459 Then this should be supplemented by terms representing the creation of virtual pairs, and you have to satisfy not only yourself, but also the reader, that the contributions such terms make to the hyperstructure, for example through their commutators with transverse interactions, are of a higher order than you need. (b) You solve exactly the two-body equation in which the odd parts of the potential have been retained. This is possible since the equation in this case does not blow up. Starting from an electron and a proton in a bound state, conservation of energy and momentum prevents either of them going oﬀ into a state of negative energy. You must then carry out the usual re-interpretation of positron theory. Based on the solutions of the two-body equation this has never been done, and it may not be easy. In any case, this reinterpretation as it stands does not contain such eﬀects as the action on the electron of the vacuum polarization produced by the proton. I do not think it is likely that these terms 459

G.E. Brown and D.G. Ravenhall, ‘On the interaction of two electrons’, Proc. Roy. Soc. A208, 252–59 (1951).

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will have a large eﬀect on what you calculate but the worry is that in this procedure (b) it is not clear how one should formulate such eﬀects, and therefore it is not clear that this procedure can be reduced to the same basic equation as the usual approach to ﬁeld theory where one re-interprets the negative-energy states ﬁrst and then proceeds to solve the equations. This remark also applies to the problem of a single electron in a Coulomb ﬁeld of high Z, where in your other paper460 you propose doing the re-interpretation after solving the Dirac equation with ﬁeld, and the point may therefore have some bearing on what Sheila Brenner is doing. On p. 3 of your MS you refer to the approximation as taking intermediate states as free, and state that the error caused by this will be of higher order in [· · · ]461 . Later on you explain that the reason for this is that the relevant intermediate states have momenta of the order mc. This is probably right, but I would have to do a considerable amount of thinking before I could satisfy myself that this was so, and you should be a little more explicit. A trivial remark: on p. 5a you refer to transient eﬀects arising from the switching of the interaction and say that they are “neglected anyway in the usual theory.” This is a poor way of stating a good case. Is not the point that the switching is only a mathematical trick, and that one should imagine going to the limit of switching so slowly that there are no transients. If there were any terms due to the transient included in your answer, they would, in fact, be wrong. This is no doubt what you mean, but it should also be what you say. Equally trivially: Also on p. 5a you write the matrix element for graph IIIc II ) (−i∆E2II T )2 + (−i∆E4c If I have succeeded in understanding what you are talking about, there should be a factor T on the second bracket. I mention this only in case there is something very deep which I have missed. 460

G.E. Brown, ‘Electron-Electron Interaction in Heavy Atoms’, Phil. Mag. 43, 467–71 (1952). 461 Missing in carbon copy.

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On p. 3a you refer to the mesonic part of the proton moment, which of course you do not treat, and express the hope that to ﬁrst order it would still act as a point-dipole. This is reasonable or otherwise according to what you mean by ﬁrst order. One can visualize this term as representing a current density spread over a distance h/µc, and the correction will come in for any electron wave components corresponding to momenta of order c. This is quite apart from terms involving a spin reversal of the proton, in which of course virtual mesons may play a much more direct part (your remark sounds as if you had eﬀects of this second kind in mind). Lastly, on p. 5c, in connection with the discussion of your equation (7), you explain that wherever there is a γi γi1 this should really be understood to be the transverse part, but that the eﬀect [· · · ]462 a factor 2/3. Now here you do not give an argument, but ask the reader to take your word for it, since you have worked it out, but Low points out that this is rather surprising, since you are dealing with a product of four matrices. These refer to two diﬀerent photons, and one can see that it might be plausible to average over the direction of the two photons independently (Though neither Low nor I have looked into this.) But if so, surely each of the averages would contribute a factor of 2/3, and one would expect the overall 4/9. Alternatively, if the photon cannot be treated as independent, one would be most surprised if the result were as simple as just a factor 2/3. So on this point some little explanation might be useful. As regards the general technique of applying Feynman methods to stationary states, I hear that Kroll463 gave a talk here last term, in which he explained this, and the idea is no doubt equivalent to yours, though I have not heard any detail. I do not know whether this is being published (I hope to ﬁnd out) but in any case this is not an argument against publishing your version. Now about non-local theory. I have played mainly with the case of a non-quantized electromagnetic ﬁeld. Then the wave equation for the 462

Line missing in carbon copy. Norman M. Kroll, at the time fellow at the Institute of Advanced Studies, later became professor of physics at the University of California, San Diego. 463

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electron is still linear, and one should evidently expand the quantized electron wave function in terms of the unquantized non-local wave equation in the ﬁeld. I have tried to obtain these solutions, and the only case I can do exactly is that of a homogeneous magnetic ﬁeld which need not be weak. I can solve it only if I assume that Fourier transform of 2 2 the form factor to be a simple exponential, i.e. eλ(E −p ) . This has the mathematical advantage that it factorises between energy and momentum, and in that case the integral equation can be transformed into a diﬀerential equation. This form factor has, of course, the disadvantage that it increases with energy, and is therefore probably inadmissible, but in the special problem this does not seem to give any trouble. The solutions come out to be oscillator functions as in the diﬀerential theory, but the scale factors contain the constants in diﬀerent combinations. The equation blows up when the ﬁeld gets stronger than 2λc/e. I have not yet understood the physical reason for this. In the course of construction (sic) the commutators for this case, I have seen that one can do a bit of general theory for the case of an external ﬁeld. The argument goes as follows. The wave equation is /)f (x1 − x2 )]α(x1 x2 )ψ(r2 ) = 0 d4 x2 [(m + k where f is the invariant form function, k is understood to be a differentiating operator acting on f only, and α(x1 x2 ) is an abbreviation for 2 e−ie/c 1 Adx Now I consider all solutions of this equation, with any value of the mass (real or imaginary). Then is it clear from the usual arguments that d4 x1 d4 x2 u ¯jt (x1 )[k /f (x1 − x2 )]a(x1 x2 )uis (x2 ) = 0 (mi − mj ) where i, j speciﬁes t[w]o masses, and s, t, each a state (stationary or otherwise) for masses i or j. Hence in the sense of this four-dimensional integral operation, the states of diﬀerent mass are orthogonal. It would therefore be nice to specify the states of any given mass in such a manner as to make them also orthogonal and normalized in the same senses, i.e.

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to have d4 x1 d4 x2 u ¯jt (x1 )[k /f (x1 − x2 )]α(x1 , x2 )uis (x2 ) = δ(mi − mj )δst If this is done, one can express the D functions which appear in the commutators explicitly: ψ(x )

2 = Dψ(x ¯ )

1

i,s

1 u ¯is (x1 )uis (x2 ) m − mi

Here the summation over i is in eﬀect an integration over the mass, the fact that we require the retarded solution means that in this integration one should go above or below the pole according to whether the state s has a positive or negative energy (how one formulates this for a time-dependent energy ﬁeld in which there are no stationary states is at the moment not clear). Now in the commutator one wants the diﬀerence between the retarded and advanced solution, and since these diﬀer merely by how one passes the singularity, this leaves just the residue. The result is therefore (factors not guaranteed) ¯ 1 )ψ(x2 )]+ = [ψ(x

¯ us (x1 )us (x2 )

s

where the summation is now taken for a constant mass (the correct mass) and where, with the above normalization, the factor is +1 or −1, according to whether s refers to positive or negative energy. I have now looked at this in the particular case of no ﬁeld, where one can compare this normalization with the usual one. It turns out that the normalization condition, if the wave functions are u = a · eipr−iEt amounts to a ¯·a=

m |E|

Since for a free-particle state a ¯a = ma∗ a/E, the requirement is that a∗ a = , where has the same meaning as before. Therefore, for posi-

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tive energy, the prescription reduces to the conventional normalization. For negative energies it becomes impossible, since a∗ a cannot be negative. Hence one must alter the normalization condition by the inclusion of [..]464 on the right, which then means that [..]465 goes out of the commutation rule. The need for this factor in the normalization is deplorable since it complicates life. I am now trying to see what happens when one carries out the re-interpretation leading to positron theory, and whether this will not give a reasonable scheme without [..]466 in it. But I have not got far with this. I shall now send oﬀ your paper to Salpeter, and ask him to send it back to you as soon as possible. Low also asks whether you have, or can easily get, the ﬁne structure of positronium, apart from any annihilation terms, to order compared to the magnitude of the ﬁne structure. The reason is that he and Ward467 are trying to ﬁnd a method of taking into account annihilation terms to the same order, and in order to state the results as observable predictions one needs the order terms as well. Nobody here believes in the Dyson progamme as a realistic scheme. Low thinks, in fact, that the Bethe-Salpeter equation is equivalent in that one can use [it] for everything that the Dyson scheme would do, and in particular that the elimination of the inﬁnities is easy. He claims that in writing the paper with Gell Mann468 he saw quite clearly what one should do about the inﬁnities, but that it was too obvious to write it down. He thinks, however, that the Bethe-Salpeter equation also is terrible to handle and is looking for better methods.

464

Missing in carbon copy. Missing in carbon copy. 466 Missing in carbon copy. 467 John Clive Ward (1924–2000), studied at Oxford and completed his Ph.D. under Maurice Pryce. He researched at Princeton, Bell Labs, Adelaide, Aldermaston, University of Maryland, University of Miami, Carnegie Institute of Technology, John Hopkins University and Victoria University, Wellington, before settling as professor of physics at Macquarie University in Sydney. 468 Murray Gell-Mann and Francis Low, ‘Bound States in Quantum Field Theory’, Phys. Rev. 84, 350-354 (1951). 465

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I have a preprint from Salpeter in which he also treats the corrections to hyperﬁne structure. I have not studied it yet, but I shall ask him to send you a copy if he has not already done so.469 I had a reply from Claude Bloch to my letter about non-local theories.470 He is working on very similar lines, but he is interested in the meson ﬁeld and therefore not troubled by gauge invariance, and he always uses the series expansion (philosophy of Yang-Feldman)471 and therefore is not troubled about generalized commutation laws. He claims that to second order one gets ﬁnite results, but that in higher order there still appear inﬁnities, unless one makes a special choice of the form factor, one possible choice being that in which the Fourier transform of f vanishes for all time-like momentum vectors. This surprises me, but I have seen no details. He has promised to send a manuscript in a week or two. It would be interesting to see if this corresponds to anything Chr´etien has found. Bloch also writes that he has written out clearly the condition in which such a non-local theory is compatible with macroscopic causality, i.e. does not contain actions transmitted into the past over measurable times. He does not say what these conditions are, but he does not sound as if they were stringent. Greetings to everybody, Yours sincerely, [R.E. Peierls] [536] Gerry Brown to Rudolf Peierls [Birmingham], 25.1.195[2] Dear Prof, First of all, I might say, there is nothing of importance for me to report which will aﬀect either your Cornell discussions or your smeared out talk. I’m enclosing this just to let you know how things are coming. 469 E.E. Salpeter and W.A. Newcomb, ‘Mass Corrections to Hyperﬁne Structure’, Phys. Rev. 87, 150 (1952). 470 Letter [533]. 471 C.N. Yang and D. Feldman, ‘The S-Matrix in the Heisenberg Representation’, Phys. Rev. 79, 972–978 (1950)

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First of all I’d like to ask you to expedite the sending of Salpeter’s MS on this ﬁne and HFS of hydrogen472 in case it has not been sent. This note of mine on electron-electron interaction in heavy atoms has been accepted by Phil. Mag. and I’m sending you a carbon copy today of the MS.473 The calculation of this latter business — the electron-electron interaction in heavy atoms — is proceeding well. Sheila has it calculated for the k shell and there it raises the energy of the two K electrons by .906Zα2 mc2 I’m checking thru the calculation rather carefully and the numerical factor may be wrong, but I am quite sure that the whole business can be done analytically and that her method is more or less all right. As soon as I have it checked, I’ll have her send it on to you. Woodward’s scattering of γ-rays has not made any important progress that I am aware of, but he has been properly exhorted to write to you in case it has. The hydrodynamics lectures are going quite easily now. They are fairly enjoyable, but are taking up a good bit of time. My own research is not particularly glowing, mainly because I have been putting in some time trying to organise Sheila, who is working pretty hard, but quite inaccurately, albeit cleverly with respect to methods, etc. I think that she’ll get over the inaccuracies if she learns to write things down properly. I have managed to keep up with vacuo-polarisation things well enough to talk to Chr´etien intelligently, perhaps. All in all, things are percolating quite well about the department. Edmond’s lectures have improved no end, although he still needs a little wind taken out of his sails; Dalitz nuclear theory lectures are superb as far as organisation etc. go and are attended by what looks to be 30 or 40 people. Sincerely, Gerry 472

Salpeter, E.E., ‘Mass Corrections to the Fine Structure of Hydrogen-Like Atoms’, Phys. Rev. 87, 328-43 (1952) 473 G.E. Brown, ‘Electron-electron Interaction in Heavy Atoms’, Phil. Mag. 43, 467–71 (1952).

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[537] Rudolf Peierls to Chr´ etien [Princeton, date unspeciﬁed]474 (carbon copy) Dear Chr´etien Thank you very much for your long screed. I have not ﬁnished digesting it but it does not overlap at all with anything I have been doing, so I am not in a position to check it. It is depressing that the results look so complicated, but that was to be expected. The most urgent job now seems to me to ﬁnd methods to discover whether they are ﬁnite or not. In view of the results claimed by Bloch, one might even have to go to higher order, but I would feel that this should not be attempted before we have thoroughly understood the results as they are now. In the meantime we shall get a copy of Bloch’s calculations, and can examine his claim that the higher orders may diverge. If you try to discuss the magnitude of the quantities occurring in your formulae, it will be important to be clear about the properties in the form function, and I have recently learnt a little more about this. I shall summarise the position here both because it may be of help to you, and also in the hope that you will check it. Consider the function F in coordinate space. It was proved by McManus that if one takes its Fourier transform to be an even function of k2 (four-dimensional) then F is an odd function of R2 .475 It therefore follows that the following moments vanish: 2 F dR , R4 F dR2 , · · · where R2 , of course, always goes from [−∞] to [+∞].476 Now consider the case where a ﬁeld is disturbed by a small source restricted to a small region near the origin. One then wants to make sure that the eﬀect of this at a distant point on the light cone is small, both in order 474

February 1952. See letter [396], note 80. 476 Missing ∞ in carbon copy. 475

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to avoid trouble with macroscopic causality, and in order to ensure that the theory goes to the correct limit when r0 tends to zero. Then the integral F (R2 )f (x )d4 x where f represents the source can, for a point x near the light cone, but not close to the source, be approximated as 1 R2 1 3 2 F (R2 ) d r dR f r , t − r − r + 2 t 2t Actually this expression is correct only to order R2 , but this does not aﬀect the argument. Now we expand f in a Taylor series with respect to time, and integrate over R2 . The result obviously give a number of successive derivatives of f , multiplied by the moment of F . The ﬁrst non-vanishing term of F is odd, is R2 F dR2 . Now this is dimensionally a pure number, and therefore independent of r. If it does not vanish it will therefore remain ﬁnite in the limit and give corrections to the usual local theory. We must therefore require that it vanishes. Then the next non-vanishing term contains the 6th exponent. R6 F dR2 which is dimensionally r 4 . The integral multiplying this will be proportional to t−4 , where t, of course, is the time diﬀerence between the action of the source and its direct eﬀect on the ﬁeld. This presumably falls oﬀ suﬃciently rapidly to avoid observable troubles and it certainly behaves all right as r0 [→] 0.477 One may still ask whether it is always legitimate to use the Taylor series for the source function. Obviously, if the source function behaves irregularly, there will be trouble. However, in our theory, one will not expect any physical quantity to vary steeply within a distance small compared to r0 because of the smoothing eﬀects built into the theory. Since the Taylor series is used only over a distance of r02 /t where t by deﬁnition is large compared to r0 this would seem to be all right. The next question is whether the vanishing of the second moment is compatible with the requirements that the Fourier transform of F should 477

Missing → in carbon copy.

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be positive for all values of k2 . This had me rather worried, because the day before my New York talk I suddenly felt doubts about this compatibility. At ﬁrst I thought it was all right, because the paper by McManus478 contains some functions for which g is obviously positive, and some for which the second Moment of F obviously vanishes. But then I saw that he had given the one only in momentum state, the other only in coordinate space, so the compatibility was not proved. I now think it is all right, but it should be checked. For this one needs an explicit formula for conversion, and the easiest procedure seems as follows. We wait to ﬁnd F as a space-like argument. Since, for even g we already know that F is odd, this is suﬃcient. We then put t = 0 without loss of generality. Writing next the Fourier transform explicitly, and integrating ﬁrst over the direction of the space part of k, and then over the magnitude of the space-part, keeping the resultant constant (which has to be done separately for time-like and space-like k) one obtains: (common factors not guaranteed)

∞ 4π 2 ∂ 2 2 Re sdsg(e )K0 (sr) + (ds)d(is)g(−s )K0 (isr) F = r ∂r 0 C where Re means real part of, and K0 is essentially a Hankel function: (2)

K0 (x) = 0iH0 (−ix) I believe this result is essentially given in the McManus thesis, but not in the published paper. It is now clear that the expression can be written as a contour integral

4π ∂ 2 Re zdzg(z )K0 (zr) r ∂r Cx where the contour C goes from a real inﬁnite z down to the positive real axis to the origin and up the positive imaginary axis to +i. This encloses exactly the quadrant in which K tends to zero for inﬁnite argument, except just along the imaginary axis where it oscillates. This oscillatory behaviour is of course of the kind that occurs always in a 478

See letter [396], note 80.

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Fourier transform and can be dealt with in the usual way. It is evident that this is equivalent to shifting the contour oﬀ the imaginary axis by a small angle, and therefore we are allowed to move the whole contour oﬀ to inﬁnity, provided g is an analytic function. The result can therefore be expressed simply in terms of the [. . . ]479 poles of g in the ﬁrst quadrant, and the corresponding residues 4. 1 For example the function g = const. k4 +a 4 which is quoted by McManus has only one pole in the relevant quadrant, and its Fourier transform can immediately be written down in terms of a derivative of K0 . Now consider the integral r 2 F dr 2 . Since the integrand is even it is suﬃcient to integrate over positive values of r 2 . After some algebra and using the diﬀerential equations for K, this can be written as 36π 2 Re i

pj j

zj

I have also used the fact that for x = 0, xK0 (x) has the value 2/π. Hence, the integrand vanishes if pj /zj is real. This is correct if one arranges that g should be an even function and should be real for both real and imaginary values of z. For example, McManus’ function const/(z 4 + a4 ) can be seen to satisfy this condition. Since I started writing this letter, I have found another argument, which is much simpler. Consider a source f as before, and the result of folding it with F , say f . Then from the expression given on the ﬁrst page of this letter it is clear that, if the integral in question did not vanish, f would near the light cone have regions in which it is as large as const/r 2 . The distance from the light cone where the values occur is independent of r, since the function will clearly decrease only if I get away from any light cone crossing the region where f is appreciable. Hence, if I consider the integral

479

Missing in carbon copy.

|f |2 r 2 d3 rdt

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over all space and time, it ought to diverge. I have inserted the modular sign in order not to discuss reality conditions, in fact [. . . ]480 will usually be real. Now, if the Fourier transform if f is [. . . ]481 then the Fourier transform of [. . . ]482 f is [. . . ]483 g. With this, the above integral can be written as 3 ∂ 2 3 2 484 485 2 )|2 d d k ∂kn |g(k /[. . .] n=1

Now g is always less than 1, so the above integral is less than its value with the factor g omitted, which is however, just the corresponding integral ﬁr the function f instead of f [. . . ]486 which therefore is ﬁnite of the source function vanishes suﬃciently rapidly outside a limited region. This argument pleases me from the point of view of ensuring that there will be no trouble with causality, but I am not sure whether it really proves that the integral of R2 F vanishes, since for suitable form function the argument could be extended to arbitrarily high powers and it is obvious that not all the moments of F are going to vanish. While I am writing this, I have had a look, and it seems to me that all the moments will vanish, so the eﬀect along the light cone will in fact fall oﬀ exponentially, if the source function does. This is merely due to the fact that all the integrals diﬀer from each other by containing a higher moment of the K0 for real argument, which is always ﬁnite and real, and multiplied by a power of zj4 [. . . ]487 which is a real factor if the poles lie on the diagonal, as in McManus case. If they do not lie there the[y] must lie symmetrically to the diagonal with conjugate residues, in order to make g real, and the same will happen again. I better close this letter before I make any more discoveries. However, you may ﬁnd some of these arguments useful in trying to see what 480

Missing Missing 482 Missing 483 Missing 484 Missing 485 Missing 486 Missing 487 Missing 481

in in in in in in in in

carbon carbon carbon carbon carbon carbon carbon carbon

copy. copy. copy. copy. copy. copy. copy. copy.

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is ﬁnite and what is not, and I suggest you make try the McManus function as an illustration, of the behaviour of k−4 is not strong enough to make your integral converge, you can take the diﬀerence between two such functions with diﬀerent parameters, which can be made to be[h]ave as k−8 which should surely be enough. I am very glad to know that you will be in Birmingham next year. I don’t know anything further yet about the chances of a University Fellowship. With kindest regards, Yours sincerely, [Rudolf Peierls] [538] Rudolf Peierls to Gerry Brown [Princeton], 3.2.1952 (carbon copy) Dear Gerry, Your letter to Cornell488 was beautifully timed, it was handed to me as I entered Bethe’s oﬃce, and I believe it had just arrived. I had some talks with Salpeter about your calculation. He has posted it back to you, and he has also sent oﬀ a pre-print of his paper.489 The following points arise from a comparison of results: (a) The main term in the ﬁne structure correction is almost the same, but there is a discrepancy of a factor 2. This may be a slip [in] the algebra in either paper, it may have some connection with the question of allowing for the transversality by a factor 2/3 (see my previous letter490 ) and it might even be that he has included terms which you have left out, though this does not seem likely at this point. (b) Your result gives only the log term, but not the numbers added to the log. These come from a careful integration over non-relativistic momenta, and he assumes that you realize that they should be there but have not bothered to work 488

Letter [536]. See letters [534–35]. 490 Letter [535]. 489

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them out. (c) He gets non-negligible contributions from other diagrams, involving a cross-over of a longitudinal and a transverse photon. This again is related to a query I raised in my last letter. Deutsch491 has now measured the ﬁne structure of positronium to a better accuracy than available theories, and it is therefore interesting to improve the calculation. A lot of people are trying this. I believe you know of the thesis by Ferrel (not sure this spelling is right) who worked at Princeton University with Wightman and is now at G¨ ottingen.492 He claims to have done the whole thing, but I heard a third-hand rumour that his calculation is not right. Low here is also starting a calculation together with Ward and Stern (an ex-Schwingerite here). Ravenhall was originally reluctant to start on positronium because he believed Radcliﬀe was doing it, and by now feels there are altogether too many people doing it. I am afraid I cannot remember who are the others, but there are several. The next item will interest you and Woodward. I talked at Cornell with Bethe and Levinger on the gamma-ray scattering.493 Bethe now believes that your argument is correct, though of course one cannot be sure until the factors have been estimated. Levinger was rather perturbed by this, since he had put a lot of eﬀort into the calculation of the zero-order term. (See his abstract at the NY meeting, which should have arrived by now.) However, he was mainly concerned with the case where the change of momentum of the photon is less than mc. He then ﬁnds that the correction to the usual form factor is of the order q/mc where q is the momentum transfer. Now it looks as if the correction that Woodward is calculating does not give a useful answer in itself, but it is not wasted since it should merely be supplemented by the ﬁrst order term. He asked whether we would have any objections to his calculating 491

Martin Deutsch (1917–2002), studied at M.I.T and received his Ph.D. in 1941, and later joined the Manhattan Project. After the war he returned to M.I.T. where he spent the remainder of his career. In 1951, he measured and conﬁrmed the existence of positronium. 492 Richard Ferrell summarized the ﬁndings of the doctoral thesis in a letter in Phys. Rev.. Richard.A.Ferrell, ‘The Positronium Fine Structure’, Phys. Rev. 84, 858–59 (1951). 493 See letter [531].

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the ﬁrst-order term for that case, and I told him that this would not really overlap with what Woodward is doing, since this is at the moment mainly concerned with the case of large q, but that he should keep us informed about his progress. I also promised we would let him know about any results we get. He is now at Louisiana State. I feel incapable of listing all the odd bits of information which I came across though I am writing to the appropriate people about some of them. I also cannot list the many people who were asking about you and send you their best wishes, but I remember amongst them Blair, Arfken and Pollard. Breit was in an amazingly tolerant mood and after Salpeter’s talk merely asked what was the diﬀerence between Ed’s equation and his earlier one. Salpeter suppressed the desire to say that the diﬀerence was that his formula was right, and merely explained which kind of graphs gave additional terms in his calculation. So everything was very peaceful. Possible new members for the Birmingham department for next year include Jack Davidson494 from Washington University, St. Louis, Segall495 from Illinois, a man called Stuart, who accosted me in New York and who is from somewhere in the East, and a man from Manitoba. Also Brueckner has expressed a desire to spend a year in England and this is to be encouraged, but it will probably not work out for next year. We counted together 12 ex-members of the department now on this continent (without Singwi) of these 9 were present at the New York meeting. I am sorry the hydrodynamics course takes so much of your time, but you have been warned. Still, as long as you enjoy it, it will soon be over. I do not understand what you say about Sheila Brenner’s result. Unless there is a typing error, the result you quote is a number times ZRydberg which is the order of the ordinary non-relativistic Coulomb 494

John P. Davidson, at the time at Washington University, later moved to Rio de Janeiro, New York, and eventually to the University of Kansas, where he remained for the rest of his career. 495 Benjamin Segall, at the time at the University of Illinois, later moved to the Radiation Laboratory at Berkeley, to the General Electric Research Laboratory, Schenectady, New York and eventually to the Department of Physics at Case Western Reserve University Cleveland, Ohio.

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interaction between the two electrons, which surely must have been calculated before. The next term presumably is two orders higher in (Z) and would correspond to the usual Breit correction. Only a term in (Z) would be new. This would be very small unless Z was very large, and then, presumably, one should not use a series at all. Or did you mean that the calculation has been done for a particular Z which makes the analytical expression you quote somewhat misleading. In that case, what was the Z? I enclose some notes on things concerning mainly other people though you will also want to see them and vice versa. Yours sincerely, [R.E. Peierls] Krook496 got your radio all right, but he claims it does not work.

[539] Rudolf Peierls to R.H. Dalitz [Princeton], 4.2.1952 (carbon copy) Dear Dalitz, I would like to add a few more comments to the points I made in my last letter to you.497 First, I have had some more talks with Low here, who asserts that it is completely obvious that the renormalization of the Bethe-Salpeter equation is no more complicated than the renormalization of S-Matrix theory, in fact he says he knew this when he wrote the paper with Gell-Mann,498 but the point was so obvious that it was not worth writing down. I have not yet had the chance of having this out with him in detail, but from the amount of work he has done with the equation and his general soundness I would bet that he is right. I there496

Max Krook, South African born research fellow at Birmingham who later became professor at Harvard. 497 Letter [531]. 498 Letter [535], note 468.

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fore suggest that you and Radcliﬀe drop the work on the Dyson-method and turn to the BS equation instead. Furthermore it seems to me that the arguments about isobaric states of both isotopic and ordinary spin 1/2 playing a part in meson scattering tend to remove the evidence against pseudoscalar coupling. Whatever the coupling, such a state contributes only to p scattering, and the strong rise of the cross section with energy is therefore an immediate consequence. There should, of course, also be contributions from the s wave, which do not have resonance character, but which will matter at low energy, but the experiments are not accurate enough to exclude these. When Dyson was here recently, he pointed out that the existence of an isobaric state did not necessarily mean that the coupling was very strong (though it does mean, of course, that one must not use Born approximation). He points out that the parameter which has to be large to justify the usual “strong coupling” approximation contains both the coupling constant and the radius of the source which has to be introduced in such a theory. If the source radius is the nuclear Compton wave length, then one can have “strong coupling” with a reasonably small coupling constant, for which for example the expansion of the kernel in the Bethe-Salpeter equation might still be reasonable. I do not claim to have understood this quite clearly, but quote it as it will interest you in a general way. On the question of the scattering of neutrons or protons by a deuteron, I had not previously realized that the objection by Kohn499 is valid only for the doublet S state, but neither for the quartet S state nor for any states of higher angular momentum of the whole system, since for these the triton presumably has no bound states. It would therefore seem perfectly possible to use the iteration method for those other states. This is not without interest because (a) Christian tells me that one can make a phase shift analysis, which determines the separate 499

W. Kohn (1923–) had completed his Ph.D. at Harvard in 1948 working with Schwinger and Van Vleck; between 1950 and 1969 he worked at Carnegie Mellon University before taking up a post at the University of California at San Diego. In 1979 he became Founding Director of the Institute of Theoretical Physics at Santa Barbara.

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phases from the experiments except for an ambiguity, by which either a small doublet S and a large quartet S phase or vice versa will do. (b) there is hope that Skyrme will get an answer by this method, but this will be easiest for the doublet S state, and a method to do the other would therefore combine well with his. Lastly I think you will be interested that Brueckner,500 who is now at Illinois has expressed an interest in coming to Birmingham, and mentioned the idea of an exchange. It is probably too late to organise anything for ne[x]t session, but the session after might be a possibility. It is not clear whether it would not be more useful if he came on a Fulbright or some such grant, but the idea of an exchange would not be without interest. By all accounts Illinois seems to be a very lively place. However, this is all still very vague. Yours sincerely, [R.E. Peierls]

[540] Rudolf Peierls to Gerry Brown [Princeton], 6.2.1952 (carbon copy) Dear Gerry, About your calculation. I do always keep carbon copies of any typed letters. I hope you do the same, because I shall refer to points in your last letter. But I do not have a copy of your screed, which is on its way back (to you[)], so if you have occasion to write about it you better refresh my memory. About the Salpeter-Low letter the phrase taking into account the proton recoil meant just the obvious thing, namely keeping the kinetic energy of the proton in the energy denominators, and is obvious in calculating any eﬀect proportional to l/M . However, he had in that paper a curious canonical transformation which appeared to simplify 500

Keith A. Brueckner, at the time at Indiana University, Bloomington, later went to Pennsylvania, before taking up an appointment at the University of California, San Diego in 1959.

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the problem which Low now believes actually obscures some points. In particular, there is a term of which he believed it did nothing but change the mass to the reduced mass. This is true for the ground state but for the excited states which come into second order calculations it does other things. His reasons for thinking that this is important is that in the paper he gets a logarithmic term which he thinks is not real, since it has no analogue in the corresponding calculation for positronium which he is doing now by a simpler method. All this is not very clear to me but it may help to explain why you were in diﬃculty. The argument about cancelation before integration is nice and would have saved you a lot of work, if one had seen it earlier. I have now understood what kind of zero-order function you assume is used, but I still think a little more explanation is needed for publication than is given in your note. I do not mean you should say how one actually obtains them, but what equation (in abstract terms) they are supposed to be the solution of and to what approximation. The omitted terms are therefore commutators between longitudinal and transverse eﬀects involving also states of negative energy, and that agrees with Low’s comments (and presumably also with Salpeter’s). However, Low is convinced that those terms are not small, and in your last para. but one on p. 3 of your letter you seem to admit that this is possible. As to method “b”, I used the argument about conservation of energy and momentum only to satisfy myself that a ﬁnite solution to the two-body problem omitting radiative corrections does exist. The possible ﬁnal states into which it might disintegrate are, of course, asy[m]ptotically free-particle states of positive or negative energy, and hence the use of conservation laws does not imply that one is using any approximation for the bound state itself. The trouble seems to be that the excited states of this system always will lead to a coupling of positive and negative-energy states, and since one needs a complete set of solutions for carrying our the re-interpretation of pair theory this may get one into diﬃculties. About the factor 2/3, I ﬁnd your argument still hard to follow. However, Low had another way of looking at this, and we checked the factors together. We came to the conclusion that the factor 2/3 is all right for the ﬁne structure, but not the h.f.s. Since you have not

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calculated the latter, except for the cancellation, which is not aﬀected by the numerical factor, this is not serious, but it is interesting merely from a formal point of view. About the mesonic part of the proton moment I know exactly what you meant, but it would be better not to use the expression “ﬁrst order”, since everybody will understand this to mean something else. Salpeter’s paper was sent to you by ﬁrst-class surface mail well over a week ago, so it should arrive before long. Your screed went oﬀ ditto on 30th Jan. About Sheila Brenner’s work. This is very nice, and it is nice to see that all the nasty integrations can be carried out. I think it would be good to publish a short note about this (not too short but shorter than what she sent me). I do not think that the photoeﬀect is necessarily the best way of getting an experimental check. In principle, the X-ray line corresponding to the transition of the electron from the L to the K shell is very accurately known. The question here is whether all other corrections like screening can be estimated with suﬃcient accuracy for the L shell. What about the K-absorption edge? I tried to explain this business to Low and suddenly could not remember your argument for saying that for the purpose one should take the l-[??] term instead of [. . . ]. This is in your note that is being published.501 If you could spare a copy or proof of this, it would help. On a point of mathematical technique, I ﬁrmly believe that it is always easier, even in bound state problems not to specify the special representation of the Dirac matrices. That one can solve the hydrogen problem conveniently without has been shown in a German paper by Franz.502 He always treats his wave functions as square 4 × 4 matrices, so that in eﬀect he obtains the solutions for at least two states together (and even then his matrix has to degenerate so that two rows vanish.) This seems to be an unnecessary complication. Should I return Miss Brenner’s note? I am just about to give a seminar about the non-local theory. I have several new quite wild ideas, but I shall write about them later. 501

Letter [536], note 473. W. Franz, ‘Rayleighsche Streuung harter Strahlung an schweren Atomen’, Z. Phys. 98, 314–20 (1935). 502

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There is quite a race on about positronium. It seems that the results of Ferrel are not right, and now Low and Ward here are trying to beat Karplus & Co. to it.503 Yours sincerely, [Rudolf Peierls] [541] Rudolf Peierls to R.H. Dalitz [Princeton], 7.2.1952 (carbon copy) Dear Dalitz, Thank you for your letter, which crossed with my last one to you. I do not believe one should ﬁnd observable anomalies of scattering of π mesons by protons due to the actual or virtual formation of V particles. Even if we assume that the (V) decay is just onto a proton and a π one can get the cross section of the inverse reaction by detailed balancing from the life time. The lifetime is, in natural units so long that the cross section will come out extremely small. This means also that any resonance scattering will give a very narrow peak (the width is of the order of 10−5 ev) which not only would not show up in the existing experiments but is probably quite unobservable in practice. I did not mention that the people working with Schein in Chicago504 reported at Rochester an attempt to ﬁnd the production of V particles by the passage of π mesons from the cyclotron through matter. Amongst hundreds of tracks in their photographic plates they had a few which could possibly be interpreted in that way, but the evidence is extremely messy, and they do not claim to have established anything. If this eﬀect were conﬁrmed it would, of course, prove that the V s are not produced together with another particle as Pais suggests.505 I also asked Dyson what use the BS equation would be for a one body problem and he replied that such things as the magnetic moment of the 503

See above letter [537]. Marcel Schein (1902–1960), studied in Zurich where he obtained his Ph.D. and habilitation. He later emigrated to the US and became professor at Chicago. 505 See A. Pais, ‘Some Remarks on the V -Particles’, Phys. Rev. 86, 663–72 (1952). 504

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nucleon could probably be done by a slightly modiﬁed form of S-Matrix theory, which would still represent an expansion of g2 only. (After all this is how Schwinger did the anomalous moment of the electron). This expansion may not be good, of course, but such expansions are used anyway in the case of the Dyson programme, and in the BS equation. Dyson therefore believes that the speciﬁc need for this theory arises only in bound-state problems, and that for those the BS equation is better. About positronium see my remarks in the enclosed letter to Brown.506 I was under the impression that Radcliﬀe had got tired of it and was dropping it. If he continues he faces heavy competition, though he may have a head start. I suggest he might write me a brief note about what exactly he is trying to do and how far he has got, so that I could then ﬁnd out how this progress compares with that of the people here. If he is not ahead of them, but is using a diﬀerent method it might well be worth continuing, since one is bound to learn something from it. I am not surprised by your remark that you have not got much research work done, you are certainly carrying an extremely heavy load this term. I certainly think it would pay to write a short note on your re[s]ults about the polarization eﬀects in a cascade. I am not clear whether this question arose as a result of questions of experimentalists (Harwell? Halban?) who are planning to do some measurements on it. In that case, of course, it would be courteous to consult them before you decide to publish your comments. The other question about p + P = D + π should, I think, not be covered in the same note, particularly since you have already discussed the general principles common to both in a separate note. There may be a case for waiting with this second one until one can quote some rough numbers, but this depends on whether there is a prospect of someone being available to do the calculation in a reasonable time. In this connection, I should perhaps mention that I have left Harper in a rather unsatisfactory stage of his work.507 I have made a number of suggestions, and perhaps he has enough to do. But if he is stranded, he might prefer to do a simple calculation on a 506

Letter [540]. P.G. Harper, graduate student working on conduction electrons in uniform magnetic ﬁelds. After completion of his studies in Birmingham he joined the Commonwealth Scientiﬁc and Industrial Research Organization in Sydney. 507

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scattering problem rather than do nothing, even though it is quite far from his main ﬁeld of interest, which is the electron theory of metals. I do not know of any conference for 1952, except a summer meeting of the Physical [Society] and the Institute of Physics at Glasgow. This is not planned as an International Conference, and will probably be only a two-or three-day aﬀair. Moon is likely to know the latest position about this. I am glad to know your reaction about spending a period abroad. You will have seen my reference to Brueckner in my last letter. I am now wondering whether it is too late to do anything for next session, but the diﬃculties are (a) all present proposals are still so vague that it will be some time before anything can be decided, and, for example if one thinks of a direct exchange, the co-operation of a number of authorities would be required. (b) You would not apply for a visa before the scheme was decided and conﬁrmed at least in outline and this will make it rather late. It would not be very pleasant to be in a situation where you will not know until the last minute whether the visa will come through in time or not. (c) It would add one more change in the department, and things might be a bit chaotic next session. However, none of these arguments is absolutely decisive and if, for example you would have very strong feelings that next session would be much better than the year after we could have a shot at it. I think Redmond would be a valuable addition to the team. I have written to him to say so and have also sent a recommendation to the Fulbright people in London. Yours sincerely, [R.E. Peierls] [542] Rudolf Peierls to M. Chr´ etien [Princeton], 7.2.1952 (carbon copy) Dear Chr´etien, I have now had time to look through your notes more carefully. I have not checked the numerical factors and signs, but I ﬁnd general expressions of much the same form.

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Two important points, however: Why do you call const/const - p2 the McManus transform. This function is not given in the paper by McManus, perhaps it occurs in his thesis. I would think it highly undesirable to choose a function with poles in it. This is likely to make the result ambiguous, and, for the reasons given in my last letter, one ought to have a function whose derivatives are bounded. The function which McManus discusses a good deal is a4 /(a4 + p4 ) and this is entirely satisfactory. The Fourier transform is found in my last letter. not yet understood whether the occurrence of integrals like iqI2 have 4 e d q arises from the speciﬁc form function you have chosen, but I am surprised that anything so unpleasant should come in. If it recurs with a better form factor, I would try to alter the order of integration, and see if one cannot get rid of the ambiguity that way. I gave a seminar on these things yesterday, but did not ﬁnish and will continue next week. In the meantime I shall see whether I ﬁnd a simple reason for believing that answers should be ﬁnite or not. Also, at the seminar Wigner raised the question whether our Lagrangian was Hermitian (or rather, in the ﬁrst place, whether it is real treating wave functions and potentials as c-numbers). I could not answer this oﬀhand, but I do not expect any trouble from this, in the worst case we may have to deﬁne the Lagrangian as the real part of what we wrote before. I hope also to get clear about this point by next week. Yours sincerely, [Rudolf Peierls] [543] Gerry Brown to Rudolf Peierls [Birmingham], [date unspeciﬁed]508 Dear Prof, I’m sending immediately a few notes concerning your comments, in the same order as the l[e]tter, so that if you have a carbon copy handy, it will be easy to follow this. On second thought, I’ll make this more or less complete in itself since I’m sure that you have not kept a CC. 508

The letter was written in early February 1952.

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It seems to me that Low’s comment on the A2 term and the reason for no spin-spin term occurring is very reasonable. I’ve been thinking about this ever since I read his letter to the Phys. Rev. with Salpeter,509 and I understand it better from your comments. (Incidentally, Low and Salpeter take into account proton-recoil in corrections to the hfs arising from the exchange of one transverse photon. Could you please discover what he means by this statement what proton recoil means here? I’m very anxious to ﬁnd him out what he calculated. I tried to ﬁnd out through writing him, but I confess that I’m still mystiﬁed, although he gave a clear exposition of everything else.) One can make a similar mathematical argument within the formalism of the MS. In the two terms describing balancing. That means to say, one can see immediately, that the coeﬃcients of the spinor terms are equal for any given photon momentum k, and consequently that the equality of the two terms and hence the lack of spin-spin interaction is assured even before integration over k. One has the dominant terms (i)

/γ j ) (γ i 2k (p + k)2 + m2

γ1i 2k /γ1j (p1 − k)2 + m21

from

/γ i ) (γ j 2k (p + k)2 + m2

γ i 2k /γ j (pl1 + k)2 + m21

from

and (ii)

the numerators in (i) are things like ip / + ik− m, ip /1 − 2k− m; and in l / − m parts go three γi (ii) things like ip / + 2k− m, ip /1 + ik− m but the ip etc. to operate on the wf and are negligible aside from common factors 1/k2 , 509

1 & etc. (k − ∆P )2

F. E. Low and E. E. Salpeter, ‘On the Hyperﬁne Structure of Hydrogen and Deuterium’, Phys. Rev. 83, 478 (1951).

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which he will then integrate over k. Now, choosing p to be the electron momentum, one sees that the denominator involving proton momenta p1 , p1 give factors which are equal and opposite in sign in the two cases. Since photon energies of order mc2 (to be discussed later) are involved, one can call the proton momentum sensibly equal to the fourth component and this iM , where M is the rest mass. Further, all k’s are to be disregarded in this particular denominator unless they combine somehow with M . Hence, the denominator (p1 − k)2 + M12 becomes equal approximately to −|k0 |M1 and it is clear that the second denominator is equal to just the negative of this. Hence one has for the sum of the[ir] two terms: +

1 1 {(γ i 2k /γ j + γ j 2k /γ i }(γ i k /γ j ) 2 2 (p + k) + m |k /0 |M1

(1)

As explained in the MS, only the 4th component of k in the numerator will bring in velocity-independent spinor terms, since otherwise one has the product of three velocity-dependent spinors. Hence, one has sensibly: −

1 1 [γ4 (γ i γ j + γ j γ i )][γ4 (γ i γ j )] (p + k)2 + m2 M1

(1)

However, the argument is rather messy. It seems to amount to the same thing as Low’s argument. In fact, in considering things from the point of view of a time-ordered theory, one has split a non-spin-dependent term into two spin-dependent terms. You are, of course, quite right that I should state a bit more explicitly what kind of a calculation I assume to precede the formulation of these correction terms. I think that within the framework of this MS one should point out only, however, that it is possible to separate the exchange of two transverse photons from other eﬀects, and to formulate the whole problem possibly in another note in which one could concentrate on the main points involved. The approach used here is that of

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Brown and Ravenhall.510 Only (++) parts of the wave functions are allowed. (For convenience, ++ is taken in terms of free electron and free proton functions, although I should think it would be possible to choose hydrogen-like functions). The interference of the “unlike parts” of the Coulomb potential with the transverse interaction do indeed contribute m Ry to both ﬁne and HFS, or order α of the main eﬀect, in order α3 M but the coeﬃcient is so small as to make the correction to the hfs about 10% that of the recent Karplus-et-all-, Schwinger-et-all correction511 The important terms are — in the non-covariant perturbation theory which I used — such things as

a) Electron-positron pair with electron in state I is formed with the emission of a transverse quantum b) Through the “unlike” part of the e2 /r interaction, the pair annihilates and the proton is scattered. c) The proton absorbs the transverse quantum returning to initial state. 510

See letter [535], note 459. Robert Karplus, Abraham Klein, and Julian Schwinger, ‘Electrodynamic Displacement of Atomic Energy Levels’, Phys. Rev. 84, 597–98 (1951); Robert Karplus and Abraham Klein, ‘Electrodynamic Displacement of Atomic Energy Levels. I. Hyperﬁne Structure’, Phys. Rev. 85, 972–84 (1952); Karplus and Schwinger were doing further work which was published in subsequent months. Robert Karplus, Abraham Klein, and Julian Schwinger, ‘Electrodynamic Displacement of Atomic Energy Levels. II. Lamb Shift’, Phys. Rev. 86, 288–301 (1952); Robert Karplus and Abraham Klein, ‘Electrodynamic Corrections to the Fine Structure of Positronium’, Phys. Rev. 86, 257 (1952); Robert Karplus and Abraham Klein, ‘Electrodynamic Displacement of Atomic Energy Levels. III. The Hyperﬁne Structure of Positronium’, Phys. Rev. 87, 848–58 (1952). 511

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This possibility is forbidden to the vacuum plus proton because of the presence of the electron in state I. Hence it represents an interference with the vacuum self-energy of the proton in the negative energy electron ﬁeld. The energy correction looks like (being careful to use pair theory):

∆E =

= = .! (forbidden)

2

αi ∗ ψ e ψ I ψ )(ψ ∗ √ C(ψp∗ √αωi ψp )(ψpos p r12 el p el ω ψpos )

(Ep − Ep − ω)(−Eel − Epos − ω)

ψpos creates a positron in an arbitrary state. ∗ creates an electron in state I. ψel The mathematics involved in calculating these terms is easy but tedious and I’ve been trying to think out a way of doing it a bit more schmelegantly. These corrections should, of course, appear automatically in any sort of treatment using the Bethe-Salpeter equation, which presumably handles pairs correctly. To summarize the above: One does the e2 interaction as Ravenhall and I did it, then corrects the terms involving the exchange of one photon for the eﬀects described in the paragraph above; this I have not done in the MS because these latter eﬀects come from one transverse photon; then calculates the eﬀects of the exchange of two transverse photons as I did in the MS. In this latter calculation, the cancellation of the spin-spin interaction terms is insensitive to the choice of zeroorder wave function, but the spinorless operator for the ﬁne structure — calculated in the momentum representation in the MS should be inserted between the correct wave functions containing only positive energy components. (The actual value of the ﬁne structure correction will be determined by the value of the hydrogen wave function at a distance of order h/mc from the origin, if relativistic corrections are brought in. The cutting out of the negative energy components of the wave function will change this value slightly, and I should really make a decent calculation of this rather than rough estimates, so I’ll get after it). I think, however, that it is clear that one can separate the various eﬀects unambiguously and evaluate only the exchange of two traverse photons as an eﬀect-in-itself. (Wirkung-in-sich-selbst)

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One of my main worries these days is a procedure like (b) that you mention for handling a two-body problem. I should prefer, however, to think the problem out, beginning from bound state solutions rather than falling back on the fact that energy and momentum of electron and proton cannot be conserved in this special case. Of course, one should demonstrate that for the case of weak coupling, perturbation theory gives the same answer as the above. However, I’d rather save these worries for later. In heavy atoms, even, I don’t see yet how to take vacuum polarization correctly into account, and this is still the problem of one particle in an external potential! That binding in intermediate states is of order higher than the main eﬀect is best seen by considering graphs like

where one inserts a Coulomb scattering - - - - - - -. I don’t claim to have evaluated this eﬀect, but I’ve gotten the coeﬃcients of the leading terms, I don’t know of any convincing way of showing that the important intermediate states are of energy order mc2 except by breaking up the large number of terms represented by each graph and evaluating them co-variantly. I’ve looked at lots of terms this way. Also, all order of magnitude estimates, when compared with the ﬁnal answer, turn out to be consistent with this assumption. I’ll look at this from the A2 point of view. Thanks for the comment about switching on the potential as a mathematical device. Also, I did drop a T. With respect to the mesonic part of the proton moment, I meant only that I didn’t treat it. By ﬁrst order treatment of it, I meant the usual treatment of Fermi, Breit etc. where they multiply the e2 contribution to the hfs calculated using the Dirac part of the moment by a factor 2.6? to take account of the mesonic part of the moment.

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The factor 2/3 coming from employing γ i γ1i −

γ · k γ1 · k 2

k

instead of γ i γ1j

is easy to explain. First, a few comments: The two photons are horribly unindependent in the sense that they must have, to within order α, opposite momenta. Let’s assume that the “A2 argument” is right and that I understand it. Then one has, as far as the numerators of the matrix elements are concerned, something like / + ik / − m)γi ]el [Aj Ai δij ]P [γj (ip The polarizations of the two photons appear to be the same. If the polarization of the ﬁrst photon is limited to the plane ⊥ to the propagation axis, then the polarization of the second photon will automatically be also ⊥ to its propagation axis. Now, in [ ]el the dominant term is [γj iγ4 K4 γi ]el and hence all directions are equally favourable here. Consequently have two thirds of what we had before. Within the framework of the MS, one can put the argument: Because of the detailed equality of the coeﬃcients of the spinor terms, explained on page 1, for the crossed and uncrossed exchange of the two photons, one can combine these two terms before integrating over k. The sum of the expressions on p.2. goes over into: |K| 1 γ4 γ41 {(γi γj )(γi γj )(1) + (γj γi )(γi γj )(1) 2 2 (p + k) + m M1 1 − 2 [(γi γ · k )(γi γ · k )1 + ( γ · k γi )((γi γ · k )1 k

+( γ · k γj )( γ · k γj )(1) + (γj γ · k )( γ · k γj )(1) ] 2 + 4 ( γ · k )( γ · k )(1) ( γ · k )( γ · k )(1) }; k and { } = 4

using the commutation properties of the γ’s. At the time I wrote the draft of the MS, I had a more formal business in mind, but the above is perhaps more convincing, because it is simpler. Now, to pass on to other matters. I’m looking forward most expectantly to the pre-print from Salpeter. With reference to Low’s question,

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the ﬁne structure of positronium can be gotten to order α of the main eﬀect along the lines in the MS if one makes the corrections coming from the “unlike” parts of e1/r12 mentioned above. The arguments of the MS would need a bit of tidying up since at one point I use the fact that m/M is a small quantity. This doesn’t seem to be necessary, but it gave a bit more convincing proof at this point. Thanks to Low for the reprints which I received today. I’ve been reading your comments on smearing with great interest. I like the idea of throwing the job of forming on orthogonal set on to the mass mi . It seems to me that using positron theory, your troubles with [. . . ]512 are eliminated. But I’d rather wait to write more on this until the weekend since I have my Wed. lectures to prepare. Probably you’re already way ahead of me on this anyway. I haven’t looked through the hydro exam yet, but will get around to it over the weekend.513 Thanks a lot for taking so much trouble with my MS. Sincerely, Gerry

[544] Rudolf Peierls to M. Chr´ etien [Princeton], 14.2.1952 (carbon copy) Dear Chr´etien I have sweated the last week or so over the question whether the vacuum polarization to order e2 is ﬁnite. By a procedure similar to yours I obtain the following expression: jν (k) = Bµν aµ (k) 512 513

Missing in carbon copy. See letter [538].

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with 2

Bµν = −4e

0

1

4s

dσ

2pµ pν + δµν (k · p − kν pµ ) 1 δµν d p g(p) p 2 + m2 4

· g(p − sk)g(p − σk) − (1 − s)pµ gν (p − sk)g(p − σk) − (1 − σ)(pν u − kν )g(p − sk)gµ (p − σk)

− (1 − s)(1 − σ)(p(k) − k)gν (p − sk)gµ (p − σk)

1 · δ((p − k)2 + m2 ) − [pµ gν (p + (s · σ)k) 2 + pν gµ (p + (s − σ)k)]δ(p2 + m2 )

I have taken real coordinates, with the summation convention in the form aµµ = a11 + a22 + a33 − a44 ,

δµν = 1,

µ = ν = 1, 2, 3,

δ44 = −1

which is similar to Feynman’s except for a sign, g is the Fourier transform of the form function (your [..]514 except for a factor) in such units that in the point theory g = 1. gν stands for δg/∂pν . a(k) is of course a Fourier component of the external ﬁeld, and the condition k.a = 0 has been used, which accounts in part for the unsymmetric appearance of the result. Now at ﬁrst I did not dare put k = 0 directly in the above, since then the pole of the 1(p2 m2 ) comes on top of the singularity of the delta function. I have, however, now seen that, since the pole is to be taken as principal value, this is not serious. Then if one puts k = 0, one can perform a partial integration which ﬁnally leaves the expression in a form in which it all depends on g (−m2 ) where g is the derivative with respect to p2 . Now the argument −m2 is, of course, just the value which matters in the limit of long wavelength, and it would appear reasonable to choose the function in such a way that it is symmetric about this point (instead of about 0 as we usually assumed). Then the term independent 514

Missing in carbon copy.

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of k2 seems to disappear fairly unambiguously. (the reasoning would not apply in the local limit, since the integration by parts then leaves an indeﬁnite residue at inﬁnity.) I am not yet very happy about the whole argument, because the evaluation still looks a little arbitrary, so that one might still get diﬀerent answers by working in a diﬀerent way. It is certainly disappointing that the theory is not yet convergent in an absolute sense. The reason is, of course, that divergence in the nongauge invariant term which I have discussed, comes from an integration over the immediate neighbourhood of the hyperbolic surface p2 +m2 = 0 and in this neighbourhood the g factors do not help convergence. It may be that things would be much clearer and less ambiguous if written in coordinate space, but they are then just too damn complicated. However, the next step is to get the term proportional to k [..]515 which represents charge renormalization. Of this we must expect that it be unambiguous and ﬁnite, otherwise the theory is no use. I shall have a look at this now, and hope you will do the same, and at the same time I shall continue thinking about the general problem of quantising such a theory without using a series expansion. So far I have not made much sense of this, beyond the remark that it can be done in principle for an unquantized ﬁeld. Yours sincerely, [Rudolf Peierls]

[545] Gerry Brown to Rudolf Peierls [Birmingham], 18.2.1952516 Dear Prof, I’m just getting oﬀ a short note to tell you that I found — actually before the arrival of Salpeter’s MS — the place where the calculations diﬀered. Remember the factor 2 I found wrong in Feynman’s work? It 515 516

Missing in carbon copy. Misdated 1951.

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is a very dangerous thing to do and Dalitz checked it for me and showed me where it came right. I had previously had Radcliﬀe and Field check it, but they made the same mistake as I. This part of the problem is in almost complete agreement, then. Salpeter seems to have integrated the resultant expression a bit more carefully, but this could be done equally easily here. One thing that I like in his work is that one can see whether things come from negative energy states or positive. On the whole, for two-body problems, his method is undoubtedly far more powerful than mine. However, I think that I understand his work far better for having gone through the calculation and also in electrons interacting with external ﬁelds etc. there is some advantage in seeing how Feynman theory can be applied for calculating bound state corrections. In the interference of Coulomb terms and transverse photons, I haven’t yet collected up my coeﬃcients for the ﬁne structure, but they are much like Salpeter’s result for this. My graphs, however, give an α correction to the HFS and Salpeter claims that the ﬁrst correction to come in is of order αm/M . I’ve not thought thru the business properly yet, so I may very well be in error. But this I will look at. I now understand how one handles low energy eﬀects where binding has to be taken into account — one doesn’t in this formalism. I’ve been worrying about how to evaluate them, but it seems to me that one just has to go back to the NR treatment and do things like the NR part of the Lamb Shift. At any rate, I have enough to do to keep busy until you get back. I think that there is no use in worrying about publication of the MS until I understand better the interference of Coulomb and transverse parts, and all in all it would be best to wait till you got back. I wonder, however, if you would have any objection to having Miss Sparkes type a tentative copy, which I can form from your comments and Salpeter’s, in the case that she has time, since several people (Ferrell, Breit, etc.) have asked me for copies of the MS and they have been very decent in keeping me informed of what they are doing and thinking about similar things. If anything is ﬁnally published from this work, it will take a long time until it gets to the proper stage. I wonder how Breit’s bearing up under it. The Salpeter business is really schmelegant. A number of problems come to mind.

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Incidentally, Salpeter says that Kroll et all, Karplus et all, Baranger are all writing things to publish.517 Yours, Gerry

[546] Rudolf Peierls to Gerry Brown [Princeton], 19.2.1952 (carbon copy) Dear Gerry, Thank you for your letter of 15th Feb.518 I have no useful comments on your points (a) or (b). As regards (c) I do not object to using transformations involving free propagators as intermediate states. Only one has to be careful, because one can get caught out. It is always all right if you can satisfy yourself that in a space-time representation the propagators only act for short enough time (or alternatively that the main weight comes from states of very high energy). But the higher the order of the terms, the harder it will be to see through this. Even then, of course, one can get caught out, as Woodward’s problem shows, but this, I think, is a very special situation because one is calculating a very small eﬀect, and one really has a position where both the zero-order and the ﬁrst-order terms are extremely small, only as it happens the zero-order one is even smaller than the other. In this connection we had a nice talk from Wick about the “impulse approximation” used in treating the collision of mesons with deuterons &c, where the usual procedure is to take the n − p interaction into account exactly in the ground state wave function but neglects it in all the propagators. This can be shown to be the ﬁrst step of a rigorous expansion (though its convergence is not proved) and the reason for 517

See N.M. Kroll and F. Pollock, ‘Relative Corrections to the Hyperﬁne Structure and the Fine Structure Constant’, Phys. Rev. 84, 876–88 (1952); M. Baranger, ‘Relativistic Corrections to the Lamb Shift’, Phys. Rev. 85, 1064 (1952). 518 Gerry Brown to Rudolf Peierls, 15.2.1952, Peierls Papers, Supp., C.51.

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expecting it to work is just again that the propagators are required only over short time intervals. A paper by Wick and Chew on the subject is being published.519 As for positronium, Low’s calculation seems to be quite under control, and his answer agrees with what Karplus gets by a diﬀerent method. Karplus is coming here next week, and it will presumably all get sorted out then. I’m rather disturbed by what you report about Radcliﬀe’s progress. I’m writing to him separately, and I hope this will endorse what you are telling him. I agree with you about Woodward’s problem that the non-relativistic approach to the ﬁrst-order terms should give very nearly the right answer, but it is still desirable to discuss the more accurate expression and show that the rest is indeed negligible. I think it would be a good idea if he, or you and he jointly, were to publish the remark that one cannot neglect ﬁrst-order terms, and also give the result by the simple method, leaving for a later paper the more pedantic treatment. This is desirable because the point is likely to be quoted by Levinger (and was referred to in his New York talk) so it is important to have it on record in a tidy manner. Would you discuss this with Woodward?520 I did not mean to suggest that there was anything fundamental in not using speciﬁc representations of the Dirac matrices. Certainly where a calculation has been done, and is not too laborious there is no sense in going back and doing it another way. My remark was intended merely to point out that the other approach often simpliﬁes life and should be borne in mind as a possibility, either for making a calculation more convenient, or for making it easier to write up. I do not quite understand why you think it is important to treat the 2s state. For the K-absorption edge one wants to have the energy diﬀerence between the atom with and without the K electron, and in the K − L emission line one presumably is concerned with the transition 1s − 2p. But in either case it is, of course, important to discuss what 519

Geoﬀrey F. Chew and Gian Carlo Wick, ‘The Impulse Approximation’, Phys. Rev. 85, 636–642 (1952). 520 See letter [532], note 452.

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happens to the rest of the electrons, if the K-electron is removed, or transferred to the L-shell. With the question of the comparison between your term and the Breit term I meant primarily the point that, if one uses product wave functions they are identical. This follows in a straightforward manner by an integration by parts. Probably this fact is know, but it would be useful to have a reference. Even though you have already returned the proofs it may not be too late to add a footnote, or a note at the end, containing a brief reference to this point (even the bare statement about the equivalence without derivation, would be helpful) and if you like a reference to Breit. It is worth asking the editor whether this would be possible without inconvenience. It may well be that the type has not yet been broken into pages, or if it has, that there is room at the end for a note, I feel pretty sure that it would not have gone to press yet. Another point made by Low is that in the logarithmic terms of the ﬁnite structure which you derive in your calculation the leading terms come entirely from transitions in which two pairs are created. To that order the same result should therefore be obtainable from the A2 terms in the non-relativistic equation for both particles. These presumably give a logarithmic divergence at the upper end, and this should be cut oﬀ at mc. This should give your logarithm in a simple manner. If after you see the students’ work you think there is a reasonable chance of some of them doing your question, go ahead with it.521 There is no great harm done even if one question is too hard, it just limits their choice a little. We have actually one question fewer than last year, so if you can think of another nice question that is ﬁne, but otherwise let it go. Yours sincerely, [Rudolf Peierls]

521

This refers to an examination paper drafted by Gerry Brown for his hydrodynamics course.

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[547] Rudolf Peierls to Gerry Brown [Princeton], 23.2.1952 (carbon copy) Dear Gerry, I see no reason why you should not have a report of your calculations typed out, even it they are not ready yet for publication.522 If there is any clash between this and other typing jobs, this is for Kynch to settle.523 If it can be done, you should consider whether it would not be worthwhile duplicating it. One always needs more copies than one thinks, and also it is much easier to get the formulae in and correct typing errors. But it does mean somewhat more work and expense. I had also a letter from Breit in which he pointed out that he had previously published a formula equivalent to yours. I replied politely that it was not quite the same thing, since in his case it came from an equation (6) which has no solutions, and which should be understood to be applied in some sense to the positive parts only. In general one expects corrections from the negative or pair production parts which are left out, and in your other paper it is evident that indeed there are such corrections. So it is a new result that in this particular problem there aren’t (except for vacuum polarization terms, which ought to exist, already in the case of a a single electron near a heavy nucleus. Have you considered how important these should be in relation to the corrections Sheila Brenner is working on?) I agreed with Breit, however, that you ought to quote him, and told him I had suggested you should try and get the reference inserted. If that failed, we would have to consider what we could do about it (presumably nothing). I spent some time trying to understand the proof about my general commutation laws which you gave me just when I left. I have come to the conclusion that it does not wash. The point is that you assume that 522

See Gerry Brown’s request in letter [545]. George Kynch, who had been lecturer of mathematical physics since 1941, had taken over administrative duties for the department while Rudolf Peierls was on leave in Princeton. 523

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both the original and the modiﬁed problem have a Lagrangian and a Hamiltonian which are linked by the usual relation H = pq˙ − L However, this is correct only apart from the order of factors, since in the general case p will not commute with q. ˙ On the other hand you make use of the Taylor expansion ˙ + ∂L δ + · · · L(φ, φ˙ + δ) = L(φ, φ) ∂ φ˙ This again in general gets the factors in the wrong order, since with noncommuting variables one has to form the Taylor series by inserting the [. . . ]524 in every product in the place where a factor has been removed by diﬀerentiation. As your equations stand they are therefore wrong by two commutators, and the job is to prove that these two errors just cancel. Disregarding the order of factors I have known for a long time how to get the result. One can try to restrict the theorem to such cases (limiting both the nature of the original Lagrangian and the operator A whose commutator is desired) that the diﬃculty does not arise. But this means discussing an awful lot of speciﬁc cases in order to make sure one does not rule out any case of practical interest. I am just making another attempt to write up this stuﬀ, and I am still stuck at the same point. I have invented a few more tricks, but they are all not strong enough. I have here a set of lecture notes by Dyson on ﬁeld theory (given at Cornell). These were on sale, and after seeing them I wanted to get a second copy for the department, but I was too late. Actually, most people here missed the bus. So you will have to wait for these until I get back. I expect to ﬁnd a queue all lined up for them! Yours sincerely, [Rudolf Peierls] 524

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[548] M. Chr´ etien to Rudolf Peierls Birmingham, 24.2.1952 Dear Professor Peierls, Many thanks for your many letters. I progressed very much along the same lines, although with less success. 2 First to your question, why call a2a+p2 a Macmanus-form function. I’m afraid I have no other excuse for this than temporal mental blackout. I used it only for two days or so, unfortunately just at the time when I sent my letter. 4 I had already calculated the Fourier transform of a4a+p4 when I got √ 4π K1 (ia2 t2 − r 2 ), your letter. The result was f (r, t) = −2i(2π)−3 √ta2 −r 2 which I think is identical with yours. Now to the vacuum current. After evaluating the traces I get (In the formula I quoted last time the sign of Lµν was wrong): (2π)3 Bµν (p) 1 2 [g(ps−q)g(pσ−q)δµν ds dσ d4 q = −4e g(q) +g(ps−q)(1−σ)gν (pσ−q)+(1−s)gµ ·(1−σ)gν ]δ((q−p)2 +m2 )   g(ps−q)g(pσ−q) [pµ q ν −2q µ q ν −δµν (pq)]    q µ (p2 −2(pq)) δ(ps−q)(1−σ)gν (pσ−q) 1    +   µ ν 2 g(p)  q (p −2(pq)) g(ps−q)(1−σ)g (pσ−q)  (p2 −2(pq)) (1−s)gµ (ps−q)(1−σ)gν (pσ−q) 1 δ((q−p)2 +m2 ) 2 −4e ds dσ d4 q · [q µ gν (q+(σ−s)p) · 2 2 q +m 2 +q ν gµ (q+(σ−s)p)+(s−σ)gµν (q+(σ−s)p)]δ(q 2 +m2 ) If I use ((q − p)2 + m2 )δ((q − p)2 + m2 ) = D I get your result, apart from the sign of the last bracket and the absence of its last term,∗ which you ∗ The

one with gµν =

∂ ∂ ∂qµ ∂qν g(q

+ (σ − s)p).

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may have omitted by mistake or some other reasons. Now you see (i.e. I believe you see) that putting p = 0 gives Bµν (0) = 0. Unfortunately, I have no believe in the validity of my formula for p = 0. I have to confess the following sins, which you will have noticed already: In the calculation of ψ1 (k) I used the wave equation to reduce /−k /s) + m)ψ0 (r − k) to ik! / (l − s)ψ0 (r − k) in the current one ψ1 ∼ · · · (i(r 1 ψ1 (k) Taking vacuum expectation values gives a gets terms like ir!/ +m /+ factor δ(p − k) and putting p equal to 0 gives ir!/ 1+m ψ1 (0) = ir!/ 1+m (ir! m)ψ1 (0) = ψ1 (0) If one uses the wave equation ﬁrst and puts then p equal to 0 one gets 0 instead. Thus I recalculated jµ (0) from the beginning and got the result 3

(2π) Bµν (0) =

g(q)δµν

2g2 1− 2 q + m2

1 ν µ µ ν − (g (q) · q + g (q)q ) 2

× δ(q 2 + m2 ) This is diﬀerent from the result I obtain by putting p to zero in your formula by the factor 12 in front of the second term, but it does not seem to give a vanishing Bµν (0) neither. Finally, I couldn’t understand, why or how you get the above Bµν to be proportional to g(−m2 ). I transformed the second term by part[ial] int[egration], thus getting rid of the derivatives of g, replaced δ /(q 2 ) + m2 by −δ(q 2 + m2 )/q 2 + m2 and so got, using rather clean methods π (2π)3 Bµν (0) = −2 m2 δµν g(−m2 ) 2 From your formula I get a factor 3 instead of 2. I’m pretty sure you’ll ﬁnd some snags in my above considerations. After the last few days’ hunt for the wrong signs and other mistakes in my notes I feel rather dim and so would be very grateful for any sort of hints, kicks and suggestions. Once more many thanks and the best wishes, M. Chr´etien

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[549] Gerry Brown to Rudolf Peierls [Birmingham], 27.2.1952 Dear Prof, Thanks for the letter of 19th February.525 Since I want to keep you informed of what I’m doing, I’m writing in considerable detail, but am sending a CC to Salpeter so the eﬀort will not be wasted in case you are not interested. a) I took the Fourier transform of this term coming from two transverse photons: and found the interaction to be 3 1 i m Ry −imr12 −imr ) − 2 me + 4πδ(r12 ) − 3 (1 − e M π mc r12 r12 where the real part gives energy corrections. (The imaginary part doesn’t give simply transition probabilities, but also hangovers from the second order Hamiltonian.) It is easy to evaluate the eﬀect on the energy in hydrogen in which case one obtains 1s: −4.54 Mc. 2s: −0.46 Mc.

p states: of order α or less

The latter ﬁgure is precisely what E2 S526 gets from adding up the log contribution from the case where the intermediate states consist of states with both particles in negative energies, and another term where only the electron goes to a negative energy state. The ﬁnal two terms on the RHS of (1) always cancel so that one is left only with the 1 Q.P. : 3 (1 − e−imr ) r12 this is equally well 2 525 526

Letter [546]. E.E. Salpeter.

sin2 (mr/2) 3 r12

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b) I checked the calculation that Ravenhall and I made for the eﬀect of pair production of the ﬁne structure:

and got an answer twice as large as what E2 S would have gotten if he had evaluated his term for this case. (I don’t like this factor 4 in the denominator of a projection operator.) He doesn’t actually evaluate this, but evaluates the diﬀerence between this term and the term one would get evaluating the corresponding Breit term. (negative energy states instead of pair production.) Now in the way things were done in Breit, Brown and Arfken,527 the Dirac function was inserted for the electron. Hence no corrections of order m/M were taken into account in evaluating the ﬁne structure, and one should simply add the m/M corrections from pair production to our results. (The non m/M -dependent corrections will be the same any way one looks at it.) In the end, I get the same answer as E2 S to add on to B2 A. I’m checking this carefully, however. c) The simplest way to handle the retardation of the Coulomb potential seems to be to go back to the old fashioned perturbation theory as done by Ferrell and Salpeter. I’m checking their work carefully and am trying to put things into a neat form. I can’t ﬁnd in E2 S’s work any terms from

Coulomb transverse 527

G. Breit, G.E. Brown and G.B. Arfken, ‘The Eﬀect of Nuclear Motion on the Hyperﬁne Structure of Hydrogen’, Phys. Rev. 76, 1299–1304 (1949).

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these seem to me to come in this order. I’m almost sure that they do not in his work, because one can get all of his results [. . . ]528 from non-relativistic functions for the case when one +rp hat on is exchanged and no reference is made to the possibility of pair production. (This latter seems to be important for HFS). This ought to complete the FS of hydrogen to this order, and I’ll have all factors collected before you get back. d) Simultaneously I’m carrying through the calculation of FS and HFS corrections in positronium, which are not much diﬀerent except that in a) positrons go down to negative energy states and b) etc. The connection of this perturbation scheme with the BS eqn. is no[w] fairly obvious to me: the perturbation scheme is simply a development in powers of the coupling constant of the BS eqn. (Or better, a development in terms of the part of the Hamiltonian assumed to be small). To date I have not had to know the fourth components of the two particles any more accurately than their rest-mass energy; if one wishes to know the fourth components more precisely, it seems desirable to go back to the BS eqn, altho this too can be done (from my point of view) a bit more visually and therefore it is perhaps easier to write things down, altho that is a matter of taste. I consider it an advantage not to work in the CM system and to use Feynman’s integration tricks; after one is more or less accustomed to them it ought to go easier — I don’t know. Yours sincerely, Gerry [550] Rudolf Peierls to Gerry Brown [Princeton], 28.2.1952 (carbon copy) Dear Gerry, I spent a useful day at Columbia yesterday, and met Kroll. He told me that Karplus & Co had also worked out the correction to the hydrogen 528

Missing in manuscript.

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hfs, treating both the Dirac and the anomalous moment as if they were given by Dirac theory. The correction factor is 1+

m 3α m log π M M

The best experimental determination of 137 from the hfs, without the correction is now 137.03652 I don’t remember the exact limit of error, but I would guess it is about 100 unites of the last quoted digit, or perhaps somewhat less. The best determination from the ﬁne structure, which is done with P states and therefore does not involve any correction, except for the Schwinger moment correction, (which, of course, is allowed for), is 137.0348 ± 0.0015 We discussed the question how one should allow for the hfs corrections. If one imagines these worked out from a non-relativistic equation, one should get them almost right, since that equation is correct to ﬁrst order in 1/M , and will therefore merely leave the argument of the log uncertain. Now such an equation, which would describe the meson part of the moment through a Pauli term, should be right except for the uncertainty of the log, and also except for structure eﬀects which, however, are likely to be even smaller than the uncertainty of the log. Tomorrow, Karplus is coming here to talk about positronium, and I hope to learn a lot, though whether I can transmit what I have learnt is the next question. I have now understood a lot more about commutation laws. Concerning the question whether the Lagrangian L + λA and the Hamiltonian H −λA are always equivalent, the position is as follows. In order to avoid complications about the construction of the unmodiﬁed ordered Lagrangian and Hamiltonian, I have restricted myself to the case in which L is quadratic in the ﬁrst time derivatives, the quadratic term having constant coeﬃcients. There may also be a linear term, whose coeﬃcients may be arbitrary functions of the wave functions: 1 i 1 L = Cαβ φ˙ α φ˙ β + (fα φα + φα fα ) + (gα φ˙α − φ˙α gα ) − V 2 2 2

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where f, g, and V are functions of the φ. I have not written here the dependence on the space coordinates, but this gives no complication. I can then prove the modiﬁed Hamiltonian and Lagrangian are equivalent to ﬁrst order, if the modifying term is either one of the φ or one of the φ˙ or, of course, any linear combination. This is enough to derive my form of the commutator between φα (x, t) and φσ (x , t ), but not for a more general function. To construct the expression for a more general A, it ˙ 529 (i) is still true without further is also correct (i) for Aφ (ii) for Aφ[..] restriction. (ii) is, however, not true, unless the f and g are further restricted. If f and g happen to be linear in the φ this is certainly suﬃcient. f may be quadratic in the φ, provided there are certain symmetry properties, which mean essentially that fα is the derivative of a cubic function of the φ with respect to φα . I don’t believe one can make the g quadratic and still have the equation right independently of the f . It is likely however, that one can have a more general case in which there are certain relations between the f and the g, but this is still too complicated for me. That this is not idle fussing can be seen by taking, in a problem of one degree of freedom, the Lagrangian 1 1 ˙ 3 ) − V (q) L = q˙2 + (q 3 q˙ + qq 2 2 Then the theorem in question is not true if A contains a term q˙3 or higher. Hence both your and Dyson’s proof would seem to be a bogus. In the actual cases of physical interest the f are never more than quadratic (e.g. interaction of charged scalar or pseudoscalar mesons with the electromagnetic ﬁeld) but I am not quite clear how generally they satisfy the required identities. The charged meson case contains both f and g terms, and therefore is not transparent. I have, however, written everything out for that case, and it seems to be all right. There is just a hope one might save the general theorem nevertheless if in the case of cubic f , for example, there are several ways of writing the Hamiltonian which all give the same unmodiﬁed equations of motion, but diﬀerent modiﬁed ones, and the theorem might then hold for one 529

Missing in carbon copy.

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of these form[s]. But I doubt it. This is quite academic, provided the theorem does hold in the cases that occur in practice. (Also academic is the question whether the breakdown of this theorem necessarily means a breakdown in my general expression for the commutator, but I suspect it does.) In all this, I have referred only to Boson ﬁelds. In Fermion ﬁelds, where the Lagrangian is linear in the ﬁrst time derivatives, everything is much easier, and there are, as far as I can see, no restrictive conditions. I also believe that, once I have straightened out the Boson case, the case of mixed ﬁelds, will give no trouble. However, these limitations show that one will have to learn a good deal more before one can be conﬁdent that the method will apply without trouble to non-Hamiltonian systems. Yours sincerely, [Rudolf Peierls]

[551] Rudolf Peierls to M. Chr´ etien [Princeton], 1.3.1952 (carbon copy) Dear Chr´etien Thank you for your letter with a lot of useful formulae. I am glad we agree more or less on the result of the calculation for ﬁnite p (your notation). You may well be right about the sign of the last part, I had checked mine, but I am never sure about signs. The reason for omitting the term in the second derivative of g was the following: you can interchange s and σ, the eﬀect of which is to change the sign of p in the argument of g. At the time you may also change the sign of q, which is a variable of integration, and by then you have reversed the whole argument, its second derivative is also even, so the function has not changed. However, the s-[. . . ]530 factor outside has changed sign. It is, I think quite legitimate to use the properties of the δ-function 530

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to reduce your expression to mine, as long as p = 0, since then the denominator does not vanish (or vanishes only in special cases, which do not contribute very much) but as you say one must be very careful in the limit p = 0 In stating that the answer involves g (−m2 ) I had also been careless about this, and had also used your identity δ (x) = −δ(x)/x. As my coeﬃcients were then, one could then cancel everything but a term pr gρ δ(p + m2 ) = 2pr pν g (p2 )δ(p2 + m2 ). If you use Lorentz invariance, you can argue that this product vanishes if µ = ν and that the integrals involving squares of the components are equal. Then the integral can be expressed in terms of p2 g (p2 )(p2 − m2 ). However, I checked the coeﬃcient in this derivation again in order to explain it to you, and I cannot make it come out the same way. I must have made an algebraic error. It does not matter anyway, because I no longer believe the identity, see below. I have checked that with your signs and coeﬃcients one gets in the same way something proportional to g(−m2 ). However, I do not understand how you can get a ﬁnite answer from this. If one integrates over the time component of q ﬁrst and thereby eliminates the [..]531 function, one gets apart from factors d3 θ/ Q2 − m2 where Q is the space part of q, and I do not see how this can come to anything but inﬁnity. The “rather clean methods” by which you did this were presumably something like ﬁeld theory, but this means attributing a ﬁnite value to a divergent integral by a convention, and if we can possibly help it this is to be avoided, because we are going to all this trouble just in order not to have to use recipes for divergent integrals. We cannot help some of this, because any four-dimensional Fourier transform of an invariant function is in some sense divergent, since an integration over each hyperboloid gives inﬁnity, so one must not do this integration ﬁrst. But I still hope we need not use conventions on other places. At any rate the Fourier transform if done the wrong way gives merely an indeﬁnite answer not simply plus inﬁnity. In any case, 531

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something must be wrong, since any expression which depends only on g(−m2 ) must be identical with the corresponding result in the local theory and there one knows that a reasonable convention can make the vacuum polarisation zero or inﬁnity, but never ﬁnite. Now about the identity δ1 (x) = −δ(x)/x. One can get this in two ways (perhaps more). One would be to take the correct identity xδ(x)+ δ(x) = 0 and divide by x, but that is not very convincing. The way I did it was to say δ(x) can be written as

1 1 1 − δ(x) = 2πi x + i x − i →0 because if this is multiplied by any function which is analytic near x = 0, and integrated, the integral reduces to the integral of 1/x times the other factor over an inﬁnitesimal countour around the origin. On the other hand, the principal value of 1/x can be deﬁned as

1 1 1 + 2 x + i x − i →0 Hence, 1 δ(x) = x 4πi

1 x + i

=

2

1 + x − i

→0

1 1 1 1 ∂ − = − g (x) 4π ∂x x + i x − i 2

I just notice that my identity is not the same as yours, but diﬀers by a factor 12 . However, we really have no business to take the t[w]o inﬁnitesimal imaginary parts equal. One should really use a small in representing the [. . . ]532 function and say δ in representing the principal part. In that case the answer will depend on the order in which they go to zero, and by putting in an arbitrary ratio between them one can get almost anything. 532

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There is also a more physical reasoning why one should not put p = 0 before carrying out the integration. Take as an example an expression like g(q − ps). Since g only depends on the square of the four vector, the argument is q 2 + sp2 − 2spq. Since this term is multiplied by a delta function of (p − q)2 m2 , the argument of g can be reduced to −m2 +2(−s)pq−(1−s2 )p2 . The last term is unimportant, but the second shows that as one integrates over q, the argument of g will increase indeﬁnitely as q increases in certain directions, for any ﬁnite p, however small. On the other hand, if we put p = 0 the argument of p remains constant. The diﬀerence would be unimportant if the integral converged well, so that only small values of q contributed anyway, but since it does not, the point may be of decisive importance. It will certainly help to reduce the integral, so far I have only looked at single terms, but there it seemed that even this eﬀect was not suﬃcient to give divergence, since the integration over the component of q at right angles to p was suﬃcient to give divergence, unless the integration over the component parallel to q, taken by itself, were to vanish. This certainly is not true if one treats each term separately, but there might be hidden cancelations. I was proposing to work out the integral for ﬁnite p with a speciﬁc function g. The McManus function is very suitable, since the number of its poles is small, so that one could use contour integration. But the discussion of the contours at large distance will give some trouble, and also in this kind of work one has to be sure of one’s signs, and so far I have not felt capable of doing this. Would you feel like having a look at it? If all this fails, one may still be able to argue that the non-gaugeinvariant part should be eliminated by regularization. This could be interpreted as a “realistic” regularization, since meson ﬁelds will give a similar term of opposite sign (cf. Feldman, Phys. Rev. 76, 1369, (1949)).533 This would then allow us to calculate the next term, the charge renormalization, which now certainly ought to be ﬁnite, since for this term realistic renormalizarion does not help. But I cannot pretend that this thought makes me very happy. Another approach is to say that, since the theory is gauge invariant, the B term must vanish if it is ﬁnite. It might be possible to see that it 533

David Feldmann, ‘On Realistic Field Theories and the Polarization of the Vacuum’, Phys. Rev. 76, 1369–1375 (1949).

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cannot be inﬁnite, by looking at the expression in coordinate space. At ﬁrst this seems diﬃcult, because one knows little about the properties of g−1 in coordinate space. But here again the McManus function provides a useful illustration, since its inverse is a diﬀerential operator. Using this, I thought at one time I could convince myself that the expression could not diverge, but I am no longer sure of this, since one has to worry about all sorts of cases, for example that in which the singularities of the two S functions lie on each other’s light cone &c. If you can see through this mess, it would be quite suﬃcient to know that the term is not inﬁnite. Yours sincerely, [Rudolf Peierls]

[552] Rudolf Peierls to P.A.M. Dirac [Princeton], 3.3.1952 (carbon copy) Dear Dirac, I am afraid I have not carried the investigations of the generalized commutation laws as far as I should have mainly because I was most interested in the question how one could apply these to non-Hamiltonian formalism. I am still held up by some aspects of this problem though there exists a[t] least one case of a non-Hamiltonian theory where everything seems to go through all right. I have however just recently resumed the study of the validity of these relations in theories where the canonical scheme applies, and I can make the following statements: 1. In classical theory, where one need not consider the order of the factors, the expression Dab − ba (in the notation of my Bombay lecture) deﬁned a generalized [. . . ]534 Poisson bracket which can generally be proved to coincide with the ordinary P.B. when the quantities a and b refer to the same time. D

534

Missing in carbon copy.

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2. In a non-standard case (in your terminology) these generalized P.B. are still unambiguously deﬁned. I have not yet given any general proof that they are equivalent to the canonical ones since I ﬁnd the several existing method[s] for treating this case in general rather hard to follow. I have, however, looked speciﬁcally at the case of the electromagnetic ﬁeld, and at the case of vector mesons, without coupling, and shown that the equivalence holds. The same is still true in quantum theory, since the uncoupled equations are linear and the question of the order of factors does not arise. 3. In the case of quantum theory and non-linear equations, my commutators are derived from an ordered Lagrangian, whereas the canonical scheme starts from an ordered Hamiltonian. For the comparison one must therefore have a method of constructing an ordered H and ordered L which give the same equations of motion. This cannot be done in all generality, but one can do it for a Lagrangian of the form . . . . . . d3 rCαβ ψα ψβ +fα ψα + ψα fα + i(gα ψα − ψα gα ) − V where Cαβ are constants (I have so far assumed a non-vanishing determinant, and thus restricted myself to the standard case again) fα gα and V may depend in any manner on the ﬁeld variables [..]535 but not on their time derivatives. If I then form Dab − Dab where a and b are functions of the ﬁeld variables at times t1 and t2 respectively, I can still prove equivalence with the canonical P.B. in the limit t1 = t2 (i) if a is one of the ψα or its time derivative (ii) for an arbitrary a provided that the fα and gα satisfy certain identities which need further clariﬁcation, but which seem to hold in all cases that occur in practice. For instance, it is suﬃcient that the f and g are linear in the ψ. This still excludes, for instance, the case of mesons interacting with an electromagnetic ﬁeld. But I have looked at the case of a charged scalar meson ﬁeld coupled to the electromagnetic ﬁeld, and the 535

Missing in carbon copy.

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identities are still all right. I can construct cases (with apparently no physical importance) in which the identities break down, but the only means that an auxiliary theorem I have used in the proof fails, and the general expression for the commutator might still be all right. In any case (i) is suﬃcient to obtain the commutators between the ﬁeld variables themselves. As you see, I have no clear proof, yet that covers vector mesons coupled to other ﬁelds, but I think it is most unlikely that any special complications will turn up. I think it is the most attractive feature of these commutation laws that they seem to work so universally, without specifying the nature of the theory in any way. For example, in vacuum electrodynamics, one can use them to derive directly the commutators between the ﬁeld strength at any two points in space-time, without ever deﬁning a vector potential. But of course one still needs the vector potential to describe the interaction with matter (I have some vague ideas how one might eliminate the vector potential there, too, from the deﬁnitions and work with ﬁeld strengths alone, but it is not yet clear whether this will work.) I am spending a most useful and enjoyable term at the Institute, many people here ask about you frequently and send their greetings to all of you. Yours sincerely, [R.E. Peierls]

[553] Rudolf Peierls to Gerry Brown [Princeton], 3.3.1952 (carbon copy) Dear Gerry, I shall try to report on Karplus’s talk. The main impression was that an incredible amount of virtuosity was not only used in this calculation,

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but was really required to get over some of the snags. The mathematical technique used was that from a paper by Schwinger in the Proc. Nat. Acad.536 which is apparently more or less equivalent to BetheSalpeter. This is not very important. The main diﬃculty was that, in order to avoid diﬃculties we know only too well, one has to separate longitudinal and transverse photons. This makes the calculation non-covariant. Now one term in this calculation contains an infra-red divergence, which should be cancelled against another coming from a charge-renormalization graph. This, of course, diverges at high energies, and the subtraction of both divergences should be done co-variantly to be sure one gets a reasonable answer. The trick how this is done is not to notice that the wave function which appears in the questionable term, and which is the solution of the non-co-variant equation with longitudinal interaction only can be replaced by one in which transverse eﬀects are allowed for as well and which to the required order is covariant. This is done by adding in corrections which really come from other graphs. The wave function is constructed by applying an integral operator to the non-relativistic wave function. This creates small correction terms everywhere, and larger corrections near the origin. One then juggles the expression around, subtracting suitable things which are easy to evaluate until one is left with something that matters only at short distances. This is only one of many tricks, but it seemed the most impressive one. You probably won’t understand much of this exposition, I am not sure I do. The result is interesting by the absence of any logarithm, Oppenheimer felt sure that was due to the peculiar cancellation one always gets in positronium, because the g-factors of the two particles are opposite and equal, but Karplus was not at all sure whether he agreed with this. He gave a list of contributions from the various terms, expressed in φ2 (0): units of 2πα m2

536

J.Schwinger, ‘On the Green’s Functions of Quantized Fields: I’, Proc. Nat. Acad. Sci US 37, 452–455 (1951).

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1 σ1 σ2 3 (vac. polarisation) & vice versa (vertex) the second being an iteration of a ﬁrst − order graph (Pirenne) (This is the second − order aﬀect of the above)

0 1σ σ1 σ2 3π −

3α 1 σ1 σ2 2π 3

s2 /2 −

8 α s2 · 9π 2 α s2 −1 (1−log 2) 2 π

* 1

+1α−

Total splitting The bracket is 1 − 0.0052.

7 3

4α s2 π 2

1−

41 3 α + log 2 21 7 π

I don’t know whether you know how Deutsch’s experiment is done. He measures the Zeeman eﬀect, which is strictly second-order, because of the cancellation of the g factors. In the formula for the second-eﬀect everything is known except the splitting in the denominator. (one can see that all other levels are too far away to give any important contribution.) Deutsch derives a splitting of (2.032 ± 0.003) × 105 Megacycles. He did not, however, allow for the Schwinger correction to the magnetic moment, and if this is done the splitting becomes 2.037. Karplus gets 2.034, which agrees within the experimental error. In presenting his calculations, he had at one stage a formula [..]537 which he claimed to give the total correction to the hydrogen hfs, if one 537

Missing in carbon copy.

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puts the proton mass in. This is evidently the result I got from Kroll and quoted in my last letter, only there it was not clear which way the correction went (or what was being corrected, whereas the formula seems clear. In the positronium case this simply gives one of many terms. If the implication in your last letter (of Feb. 27)538 which has just arrived, is that you can calculate the positronium case by less formidable means, good luck to you. I am very interested in your account of what you are doing — I cannot follow all of it, partly because I am really not up to date, and partly because of the liberal sprinkling of expressions like ,,this term” &c. which I usually ﬁnd hard to hitch to anything. However, I hope this remark and the lack of any more constructive response won’t discourage you from continuing to let me know what you are doing. Best wishes, [Rudolf Peierls]

[554] Gerry Brown to Rudolf Peierls [Birmingham], 10.3.1952 Dear Prof, Thanks very much for your account of Karplus’s seminar.539 It helps things a lot. May I say ﬁrst of all that I haven’t gotten as yet where the I[nfrared] catastrophes come in — that is, in the calculation of the Lamb-shift terms, and I can well believe what you have to say about them, but I think that they can be handled in a fairly straightforward manner following some of Dyson’s ideas on the subject which he gave while here. I would be very grateful if you would check with someone on the sign of Karplus’s correction to the hydrogen HFS. By taking the next 538 539

Letter [549]. Letter [553].

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term in m/M in my exchange of two transverse photons, I get just the same term except that mine has a plus sign where his has a minus sign. (Mine would make the triplet state lie higher than the singlet still more). If my answer is wrong, then I think it is because I’ve omitted other eﬀects, since the whole process of getting this next term involves a simple expansion of an already integrated term and the ﬁrst term in this expansion agrees with Salpeter. This is just the order where, from Low’s argument, corrections to the HFS should ﬁrst come in. ((m/M )2 α3 Ry). You will be surprised to receive in not too long a time, a rather weighty contribution from me — a cyclostyled copy of this draft. I’ve added lots of things so that the ﬁne structure in hydrogen is corrected to the order that Salpeter does it, and am now putting in some calculations on positronium and will add a few comments on helium. The whole things is getting quite long, and if the cost runs too high in putting it out, I’ll share it with the dept., but we can talk about that when you get back here. I’ve also been putting in some comments on the use of my method as an expansion of the BS equation, since I think that the expansion is done in a much nicer form here than in Salpeter’s MS. I’m still not happy in any of the above about the terms where the unlike parts of the Coulomb potential and one transverse photon interfere. But I’m putting oﬀ consideration of that until I get the above stuﬀ in shape and then during vacation, will really get after this interference term. It seems to me that this term[s] should contribute to the HFS. Kynch thought that the hydro question that I added was too easy,540 so we decided to tack onto it as ii: (ii) Under what condition can a velocity potential or a stream function or both be used to describe the motion of a ﬂuid? I’ve discussed this brieﬂy in class and it seems to me that it takes some thinking. It is the only question on “philosophy” on the exam. At any rate, there is still time for me to take the whole thing out, if you disagree with the question. Sheila’s work is not going too well at present since she is looking into a lot of questions in screening and since most people around here 540 This refers to hydrodynamics examination paper for a course Gerry Brown was teaching.

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— except myself — have been pretty pessimistic about being able to estimate other screening from outer electrons, etc. to this accuracy. It seems to me that one important thing which has already been done is that we understand how much of the inner screening comes from magnetic and how much from Coulomb eﬀects. But she has enough to do until you get back. Your letter made me more anxious than ever for Radcliﬀe to jump into this Positronium Lamb-shift. I don’t think things are so tough that he can’t get something out of it. As soon as lectures are over next week, I’ll get together with Woodward and we’ll probably get something on the γ-rays written up. Probably one can even get a sensible answer out of the problem if what’shis-name has done a calculation of the zero-order-term. I’m not at all anxious for you to get back from the States because the information you’ve been passing on has been a tremendous spur in getting a lot of things cleared up esp. about interpretation etc. and I ﬁnd your letters much more intelligible than you think from your comments. I’m getting oﬀ the stats exam to you the end of this week. I think that there still is plenty of time — the questions are pretty straightforward to formulate. Sincerely, Gerry [555] Rudolf Peierls to P.A.M. Dirac [Princeton], 12.3.1952 (carbon copy) Dear Dirac, I should correct a statement I made in my last letter to you,541 before it leads to confusion. Under (3), when I talk about the case of quantized ﬁelds I said that the identities which ensure the validity of my general commutation laws for any two operators a and b were still valid in the 541

Letter [552].

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case of charged mesons interaction with the electromagnetic ﬁeld. This turned out to be incorrect, owing to an algebraic error. In fact, the identities are not satisﬁed in this case, and this not only invalidates the auxiliary theorem used in the proof, but the general expression for the commutator does not hold. The position is therefore the following. My method leads to the construction of a generalized Poisson Bracket [. . . ]542 a,b. The identity [..]543 where the square bracket denotes the commutator, is always valid if a is one of the ﬁeld variables, or its time derivative, or any linear combination of these. b may be anything. The rule is generally valid, including the order of factors, for any a for a restricted class of theories, but these do not cover all the cases of physical interest. However, once one knows the commutators between the ﬁeld amplitudes and their time derivatives, the rest can be built up in the usual way, so that I do not believe this limitation seriously limits the usefulness of the relation. I have nearly completed my paper on this subject and shall send you a copy when it has been typed.544 Yours sincerely, [R.E. Peierls] [556] Claude Bloch to Rudolf Peierls Pasadena, 14.3.1952 Dear Professor Peierls, I thank you very much for your letter.545 I looked again into the question of the microscopic non-localizability. I do not think that the Fourier transform of the form function need be analytic. I suppose you get the condition of analyticity from the requirement that the form function F 542

Missing in carbon copy. Missing in carbon copy. 544 R.E. Peierls, ‘The commutation laws of relativistic ﬁeld theory’, Proc. Roy. Soc. A214, 143–57 (1952). 545 Letter Rudolf Peierls to Claude Bloch, 26.2.1952, Peierls Papers, Ms.Eng.misc.b203, C.26. 543

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considered as a function of s = (x − x )2 should fall oﬀ very rapidly as s becomes large. If one assumes an exponential decrease it turns out that the Fourier transform has to be analytic, but I think that this requirement is too strong. In fact I assume only a decrease as an inverse power of s. From any criterium I could think of this seems suﬃcient. Moreover, I think that the contributions of the neighbourhood of the light cannot in the best of the cases fall oﬀ faster than an inverse power of the three-dimensional distance. It seems then natural to assume the same law on the other direction. If one accepts this assumption, it turns out that the Fourier transform has to have a ﬁnite number of continuous and absolutely integrable derivatives. It is then possible to have timelike components only in the Fourier transform, provided the function matches smoothly at zero. As regard convergence, one would expect that the part of momentum space deﬁned by the condition that all momentum vectors occuring in a self-energy integral [. . . ] have a ﬁnite four-dimensional length should be ﬁnite. This is all right for the following term

For this one, however:

the situation is not so nice. The vectors 1 and 2 have bounded components, but 3 and 4 have bounded components only if 2 is a time-like vector. This is why I make the assumption that the form function should have a Fourier transform with time-like components only. I must say that I am not very fond of this assumption. It makes many virtual transitions impossible, and I am afraid that it will lead to some unreasonable consequence. The fact, however, remains that, at least for interaction of the type ψ + uψ, the form function is unable to cut oﬀ all integrals at large momenta. There may, of course, be a less drastic way out of this

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diﬃculty. I wonder if the same thing happens with the interactions you are considering. I thank you very much for your advice concerning next year, and particularly for proposing a stay in Birmingham. I would, in fact, be very interested in spending some time there when I go back to Europe, and I hope this possibility will still be open by then. With kindest regards, Yours very sincerely. C. Bloch

[557] Gerry Brown to Rudolf Peierls [Birmingham] 18.3.1952 Dear Prof., I thought I would write you a short note describing the general state of aﬀairs. First of all, I didn’t mean the comment about your being interested in the details of my letters two weeks or so ago the way that you understood it. In this particular letter I mentioned a number of details and referred to work of Salpeter’s which I didn’t think that you had looked into in this much details; consequently I didn’t want you to waste time trying to follow something which might have been inadequately explained.546 For those particular details it might have taken a prohibitive amount of work to show where everything came from and since some of the comments were not very carefully thought thru, it didn’t seem to be worthwhile to explain them. (& some of them were meant for Salpeter.) The end of this week I’m sending you oﬀ a copy of my screed which is now micrographed. I wrote up only the part thru hydrogen with some notes telling how to apply these particular calculations to positronium since the change-over is trivial — mostly it just means setting M equal 546

Letter Gerry Brown to Rudolf Ms.Eng.misc.b.204, C.51 and letter [554].

Peierls,

7.3.1952

Peierls

Papers,

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to m, in the formluae already calculated. Now there are many parts of the screed which are not too well thought through, and on the whole it is not too consistent. However, the work was fairly involved and I wanted to get it together before the Easter vacations so that I wouldn’t be bothered with details over the vac and can really think thru some of the points concerned. I still get the opposite sign to Karplus in the HFS. On the whole I check Salpeter, except for a factor 2 which is in an insigniﬁcant term. I think there is no doubt that the method is correct, and I discussed the similarity of it to the BS method — which gives the same expression in every case I’ve looked up so far – and have managed to straighten up some sloppy points about “end-eﬀects” of the Coulomb potential on a somewhat ununderstandable way to be sure, but it is clear to me how they should be handled, and I’ll accept criticism gratefully on the exposition. With all of these apologies, I’m sending the work on to you and will send it so that it will almost certainly get there before you have to leave in case you want some light reading on the boat. I want to get back much more on this other work of smearing things when you come back, but during your absence seemed a good time to clear up a number of points concerned with this perturbation theory, which seems to me a pretty powerful method as far as pure formalism is concerned — the perturbation procedure of Salpeter is pretty messy altho his handling of the equation and pairs, etc. is really beautiful. The hydro has really been enjoyable. I messed up a couple of lectures at the beginning of the term or rather middle (wave motion of all things) and gave one ill-chosen problem sheet, but the last few weeks have been going very smoothly and I think that my lectures have been quite reasonable. I haven’t been stumbling in class much at all — not once for two or three weeks now. I like the students — most of them — very much. I’ve covered just up thru viscosity, but no sound, turbulence, shock waves, etc. One reason that everything has gone so well this term is that I’ve been in wonderful health — not even the trace of a cold thus far — and I feel quite happy about the lectures now altho it was a bit of a strain to begin with. I’ll be very happy for you to get back with respect to Sheila’s problem, which is coming out at the sides now. One trouble is that I’m

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the only optimistic person w[ith] r[espect] t[o] it and she’s getting a somewhat defeatist attitude. There are some rather complicated articles by Bertha Swirles547 (Mrs. J.)548 on much the same thing and they look pretty horrible. (1936)549 Still, I think that with a little sense as to where to look one can really begin to understand a bit about the dynamics of screening. Also, Radcliﬀe is not progressing too fast. I try to imbue him with optimism, too — in fact I spend a lot of my time doing just that about the dept. now — but he hasn’t understood a lot of things about bound states in Lamb shift yet. Gerry

[558] Gerry Brown to Rudolf Peierls [Birmingham] 25.3.1952 Dear Prof., Last week I sent oﬀ a mimeographed copy of my screed to you. I’m afraid it does not ﬁt your economy requirements, but on the whole the costs didn’t run very high and I’ll be glad to pay part of it. About the only factor in a longer screed is the paper – postage is negligible when sent by printed matter rates. I discovered in messing around today that the factor for the HFS is probably not right because I made a slip in a factor calculating the eﬀect of interference with the longitudinal part of the interaction (retardation of Coulomb potential.) All in all, I’m trying to straighten up several points concerning the HFS which is considerably smaller than the FS and contains a number of troublesome terms. I wanted to get everything 547

Bertha Swirles (1903–99), studied at Girton College, Cambridge and G¨ ottingen; received her Ph.D. from Cambridge in 1929; later she taught at Manchester, Bristol, Imperial and Cambridge. 548 In 1940, Bertha Swirles had married Harold Jeﬀreys. 549 Bertha Swirles, ‘The Relativistic Interaction of Two Electrons in the SelfConsistent Field Method’, Proc. Roy. Soc. A157, 680 (1936).

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I now know or think put together in a form where I could communicate with people intelligently and on the whole most of the screed is ok. In especial, I’m trying to square away this whole business of interference between unlike parts of the potential and transverse photons. I think this may contribute to the HFS in the order Karplus calculated and this may be a diﬀerence between his and my calculations. I think I now know how to do this, tho. When you have mimeographed copies of the commutation laws, could you please send a copy to Dr. P.R. Zilsel550 Physical Dept. U of Conn. Storrs, Conn.? My friend Aadne Ore 551 is coming thru the department for a week late in May or early in June and I wrote him to see if he would talk on positron aﬃnities, etc. He has done some exceedingly nice variational calculations of the Hylleras type. Woodward and I will be sending you a draft copy of a letter or something on γ-rays. The writing of this followed very much the RavenhallBrown pattern,552 except that John kept his temper. He objected very much to my anthropomorphisms and I to his formalities. But you can arbitrate. It isn’t very long. I don’t know whether you’re aware of the fact, or not (or whether we are perhaps not aware of some publications) but there seems to be no reasonable theory — even statistical — on screening in atoms and the work boils down pretty much to that described in Sommerfeld’s book, where he interjects a screening coeﬃcient which is determined more or less empirically. As I see it, our job is to get an idea of how this screening constant is constituted, since by deﬁnition it is the diﬀerence between the theoretical term value in an unscreened ﬁeld and the experimental term value. Thus, I’m not so sure one wants to separate oﬀ screening. 550

P.R. Zilsel was among Gregory Breit’s students at Yale at the same time as Gerry Brown was working with Breit. 551 Aadene Ore (1916–1980) was another one of Gerry Brown’s friends at Yale. He later worked at Chicago, Bergen and Oslo, increasingly working on physical chemistry. 552 See letter [507], note 343.

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Our terms give more or less a dynamic description (I mean they include magnetic eﬀects) of screening. It is nice to know how much of it comes from magnetic eﬀects etc. The present aim is to calculate the interaction of a 1s electron with the 1s, 2s and perhaps 2p shell in detail (or at least to get an answer for the interaction with the electrons concerned, and a relativistic answer.) Then to take care of the outer screening by some sort of statistical theory or something. This may be all wet — you don’t seem to be thinking this way. Anyway, we can have a good hash when you come back. I don’t think that Sheila will have wasted much time over it. Thus far only the 1s − 1s interaction has been calculated. Unfortunately I think that almost all eﬀects will go the same way with Z so that there can’t be much separating oﬀ. About the only personal news is that — on your wife’s recommendation — I decided, or rather we, to get married in June. Also your wife wrote you a long letter yesterday and put a shilling stamp on it, but forgot to mark “Airmail” so that, if you receive no letters for a bit, this is the reason why. Yours, Gerry

[559] Freeman Dyson to Rudolf Peierls Ithaca, 26.3.1952 Dear Peierls, Thank you very much for your letter and MS. First I must say, I did not know you were coming here Monday and Tuesday of next week. In fact, Bob Wilson553 asked me if there were any special time when I would be away from Ithaca because he was expecting you to come here and would arrange it so that you should come while I was here. I told him, any 553

Robert Wilson (1914–2000), had studied at Berkeley where he obtained his Ph.D. in 1940. After research at Princeton he joined the Manhattan Project. After the war he went to Harvard before, in 1947 joining Cornell University. In 1967 he assumed the directorship of the National Accelerator Laboratory.

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time would suit me, except March 31 to April 3 inclusive when I shall be giving talks in Toronto. I hope you can arrange to be here some time outside these days. I am sorry this confusion has arisen. If you want to stay longer in Cornell there is no reason why you should not stay with us. Anyway, I want to see you and you should consider yourself invited for any time you chose. I hope you will have met Verena while she is in Princeton. Then you may already have straightened out your plans directly with her. She is unfortunately still very sick and exhausted, she has not been at all in good health since we came to Ithaca. I hope this week in Princeton may have done her some good. Next thing I have to say is thank you very much for getting me the F.R.S.554 This means a lot to me especially to my parents and I feel greatly indebted to you for it. Now, to answer your letter itself. I read the paper carefully555 and found it most illuminating. I am glad you have ﬁnally written this work up in an adequate way. Many things in it are new and exciting, especially Sec. 6 and the Appendix. I agree that my proof of the equivalence of your Equations 3.4 and 3.3 is “phoney”. It rested on the idea that λ itself could be considered as an additional ﬁeld-variable with a canonical momentum which vanished identically. This argument seems to work all right for classical dynamics, but I never explored the complications that can arise with non-commuting quantities in the quantum case. I am sorry if I misled you and held up your work by making excessive claims for it. I feel, and have always felt, that it is very doubtful if any clear meaning can be attached to a quantized theory with a term like q˙3 in the Lagrangian. Your example shows just in what way the diﬃculties begin to show up in a case like this. For example take your equation (A.17a) p = q˙ + q 3 + 3λq˙2 δ(t − t ) 554

(A17.a)

Freeman Dyson had been elected Royal Society Fellow on 20th March 1952. Peierls’ paper on commutation laws of relativistic ﬁeld theory. See letter [555], note 544. 555

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which you use to deduce the discontinuity of q at t = t DA (q)t1 + 0) = −3q˙2

(A18)

Now if q is discontinuous at the time t1 , the value of q˙ there is in fact inﬁnite or indeterminate. So we have to argue that the inﬁnite term in q˙ is multiplied by λ and so gives no contribution to A.18 in the lowest order of λ. That is, we neglect the term ∞ × λ because λ is small! a procedure painfully familiar to us in quantum electrodynamics. But here I think one should be able to do better and take proper account of all the terms. I have not any clear opinions on the relation of these things to the Feynman quantisation method. I think it is in general the case that the Feynman method will be meaningful only when terms like q˙3 are absent from the Lagrangian, but I am not sure of this. Thus your examples might tell us something about the Feynman method and its limitations. Have you read an obscure paper of Schwinger Proceedings of the National Academy of sciences 37, 452, July 1951?556 Here he writes down an equation (8)

δ δL(x) = i

δ1

dx [L(x)δ L(x ) + − δL(x) δ L(x ) ]

δ2

which is in his notations almost the same as your commutation rule. However he does everything only formally and never stops to explain what anything means. I think his method will run up against just the same diﬃculties as yours if one applies it to Lagrangians other than the simplest (He concerns himself only with electrodynamics of particles of spin 0, 12 and 1). Looking forward to seeing you here. With many thanks, Freeman Dyson

556

See letter [553], note 536.

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[560] Rudolf Peierls to R.H. Dalitz [Princeton], 2.4.1952 (carbon copy) Dear Dalitz, Thank you very much for your letter.557 I spent the last few days at Cornell, and found that Butler also thinks now he can get his results in a simpler way. From your rather brief description it looks as if the two methods are very similar, if not identical. One should make sure, however, that the one characteristic feature of Butler’s calculation, namely the occurence of a linear combination of the Bessel function and its derivative comes out correctly. Butler apparently can get this if he applies dispersion theory to the interaction of the neutron wave with the nucleus. I do not agree, however, that the protons are unpolarized. Consider, for example, the ground state of oxygen 17. This is a D state, and its spin is probably 5/2. This means that the neutron in the d wave can be absorbed only if its spin is parallel to its orbit. There is therefore strong correlation between neutron spin and orbit. On the other hand the proton spin is strongly correlated with the neutron spin, and there is a (rather complicated) correlation between the proton and neutron orbits. I feel unable to say, without calculation, how strong a proton polarization this will produce, and it may well be possible to see from general arguments that i[t] should be small, but I do not think this is obvious, or is established by the argument you give. Butler also has an approximation method of allowing for the Coulomb ﬁeld, but I am not yet convinced that it is right. Thank you for your remarks about the ﬁnal year students. In general it is not our job to disqualify potential research students completely. Of course, if it is obvious that a man is incapable of doing research it is not in his interests to make him apply, or to make him spend a year on trying to get somewhere, but in case of doubt we should not stop him. 557

Letter R.H. Dalitz Misc.Eng.misc.b205, C.75.

to

Rudolf

Peierls,

19.3.1952,

Peierls

Papers,

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However, we have to put the names in an order of merit list. This is important because the number of DSIR grants is usually limited, and for this purpose the question is who shows the greatest promise on the basis of available knowledge. This list of merit can be revised after the examination; anyone who does very badly in the exam will usually have to go down in the list unless there are special circumstances. But normally the examination will not change our opinion much. I would guess that this year we can expect about three grants. My present impression is that the order should be: 1. Miss Brenner, 2. Marshall, 3. Wade, 4. Beasley. There is also a physicist, Thomas, who may want to come to us, I am not yet clear whether he would be on our quota. It would be very useful to have your comments on this order. It is particularly hard to compare Miss Brenner with the others, because she has already done a year’s research (or nearly) but it does not matter particularly, unless [s]he should go down to third place or worse, which does not seem likely to me. Yours sincerely, [R.E. Peierls]

[561] Rudolf Peierls to Claude Bloch [Princeton] 13.4.1952 (carbon copy) Dear Bloch, I have left your letter of 14 March for a long time without reply.558 This was partly in the hope that your promised typescript would materialize. You are quite right in saying that the condition on the form function with I stated in my last letter was too severe. We have restricted ourselves to functions of that kind, which, in fact have the property that “non-causal”eﬀects along the light cone decrease exponentially with the time diﬀerence, but it is true that this is not strictly necessary. I had 558

Letter [556].

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in mind largely the electromagnetic case where the Fourier transform of the form function must be unity for zero argument in order to ensure that the ordinary equations hold for long waves, and in that case it could vanish for space-like argument only if it were discontinuous, which would not do. However, it is not safe to generalize from this to our case. I have not made much progress with the apparent non-gauge invariant term. I was interested to see from your letter that the diagram which gives you the trouble in fourth order is, in fact, what in the electro-magnetic case would be a vacuum polarisation part, and this made me wonder whether my trouble and yours might be related. However, I would have to learn more about your calculations to be sure of this. It would also be very interesting to know whether the divergence you ﬁnd is in the sense of the integral being mathematically ambiguous, or whether it can be expressed as an integral over a quantity of constant sign, so that it must deﬁnitely be regarded as inﬁnite. I hope that when I get back to Birmingham in ten days time I shall join forces with Chr´etien, who has been doing the detailed calculation for my case, and that we shall soon have an answer. Yours sincerely, R.E. Peierls

[562] Rudolf Peierls to Robert Oppenheimer Birmingham, 2.5.1952 (carbon copy) Dear Robert, I saw to-day the people from Bristol who wanted to raise the problem of “zeta” mesons and can therefore clear up the mystery about what these particles are supposed to be. This term refers to cases which have been found in which two mesons are emitted from a start at an angle very much smaller than it is likely statistically and with nearly the same momentum. The Bristol people tend to interpret this as the emission of a short lived particle which then decays into two mesons with a reaction energy of a few MeV. You will probably have seen the note which

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Brueckner and Watson wrote about this559 pointing out that very similar features can be o[b]tained if there is an attractive force between mesons which would inﬂuence the probability of their being emitted with small momentum diﬀerence. There is, of course, only a quantitative diﬀerence between these two descriptions and the experimental data are as yet insuﬃcient to decide whether one is dealing with a sharply deﬁned energy or with a broad resonance factor as Brueckner and Watson suggest. In any case it seems very likely that the phenomena itself is real. While I am writing may I thank you once more for letting me take the “refresher course” at the institute which helped me to catch up with other people’s ideas as well as sorting out my own and also for the extremely generous arrangements, which made everything so easy. With kindest regards, also to Kitty, Rudi

[563] Wolfgang Pauli to Rudolf Peierls Zollikon-Z¨ urich, 14.8.1952 Lieber Herr Peierls. Ich habe mit einigem Interesse Ihre Arbeiten u ¨ ber die Deﬁnition der Poisson-Klammern gelesen. (1. Die im Bombay-Report560 , 2. das type-written Manuskript von Princeton561 — ich komme eben aus Les Houches zur¨ uck,562 wo ich u[nter] a[nderem] auch mit Rosenfeld diskutiert und diese Arbeiten ein 2. Mal wiedergelesen habe.) 559 Keith A Brueckner and Kenneth A. Watson, ‘Possibility of Obtaining Experimental Information Concerning the Meson-Meson Interaction’, Phys. Rev. 87, 621–22 (1952). 560 R. Peierls, ‘Commutation laws in relativistic ﬁeld theory’, International Conference on elementary particles (1951). 561 R. Peierls, ‘The Commutation laws of the relativistic ﬁeld theory’, Proc. Roy. Soc. A214, 143–57 (1952). 562 ´ ´ e de Wolfgang Pauli had lectured at the third summer school at the Ecole d’Et´ Physique Th´eoretique at Les Houches. See Pauli, Wissenschaftlicher Briefwechsel, IV/1, p. 693.

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Seit der Konferenz in Kopenhagen im Juni563 habe ich mich etwas ausf¨ uhrlicher mit den Formfaktortheorien (siehe Peierls-McManus,564 Møller-Kristensen,565 Cl. Bloch566 ) besch¨aftigt. In dieser Verbindung, besonders im Hinblick auf die M¨ oglichkeit, Ihren Formalismus auf die Theorien a` la Møller-Kristensen (=M.-Kr.) anzuwenden, habe ich zun¨ achst einige Fragen, die sich — unabh¨ angig von der Lorentzinvarianz der Theorie — auf alle Theorien mit Translationsinvarianz beziehen. 1. Sie sprechen in Ihrer Arbeit etwas leichtfertig von “nichtEs l¨ aßt sich jedoch leicht Hamiltonschen Theorien”.567 zeigen, daß alle translations-invarianten Theorien exakte Energieussen. Die gegenteiliImpulsintegrale Pµ (µ = 1, 2, 3, 4) besitzen m¨ gen Behauptungen von Møller-Kristensen sowie von Cl. Bloch sind unrichtig. Im Falle der reell-skalaren Mesontheorie, elektrischneutrale Mesonen in Wechselwirkung mit Formfaktor F (x − x , x − x ) mit Nukleonen (Spinorfeld), habe ich diese Integrale leicht streng ausrechnen k¨ onnen und habe sie k¨ urzlich Møller geschrieben. Davon gibt es noch ein ebenfalls in der Zeit exakt konstantes “Ladungs”-Integral Q der Nukleonen (entsprechend ¯ −iα mit konstanter Phase α). der Eichgruppe ψ → ψeiα , ψ¯ → ψe

563

Between 3 and 17 June 1952 the Council of Representatives of European States for Planning of an International Laboratory oversaw a conference in Copenhagen which was concerned with the recently founded laboraroty later known as CERN. 564 R. Peierls and H. McManus, ‘Electrodynamics without point singularities’, Phys. Rev. 70, 795 (1946); see also letter [396], referring to McManus’ work; H. McManus, ‘Classical electrodynamics without singularities’, Proc. Roy. Soc. A195, 323–36 (1948) 565 P. Kristensen and Ch. Møller, ‘On a convergent meson theory’, in International Physics Conference, 50–51 (1952); P. Kristensen and Ch. Møller, ‘Convergent SMatrix formalism with correspondence to ordinary quantum mechanics’, Phys. Rev. 85, 928–29 (1952). 566 Cl. Bloch, ‘On ﬁeld theories with non-localized interaction’, Kgl.Danske Vid.Selsk. 27, No 8, 1–55 (1952). 567 R. Peierls, ‘The commutation laws of the relativistic ﬁeld theory’, Proc. Roy. Soc. A214, 143–57 (1952); here pp. 153f.

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Die Relationen (f = beliebige Feldgr¨ oße) −

∂f = i[Pµ , f ], [Q, ψ] = −ψ, [Q, ψ ∗ ] = ψ ∗ ∂xµ [Pµ , Pν ] = [Pµ , Q] = 0 [Q, u] = 0, ↓ reelles Mesonfeld

m¨ ussen aus gruppentheoretischen Gr¨ unden exakt gelten. (N.B. Ich konnte zeigen, daß dies mit Ihrer Deﬁnition der Klammersymbole im Einklang ist. Siehe unten.) Was Sie mit “nichtHamiltonschen Theorien” meinen, wird dem p.t. Leser nicht erkl¨art. Man kann und soll unter Umst¨ anden allerdings quantisierte (oder klassische) Feldtheorien in nicht kanonischen Variablen schreiben, die Bezeichnung “nicht-Hamiltonsche Theorie” scheint mir aber deswegen allein nicht angebracht. 2. Die einzige Voraussetzung f¨ ur die Anwendbarkeit Ihres Formalismus scheint mir die zu sein, daß die Mannigfaltigkeit der L¨ osungen dieselbe ist wie f¨ ur Kopplungskonstante Null (freie Teilchen). Im ¯ x), ψ(x), u(x ), ∂u(x) im Sinne Falle M.-Kr. bedeutet das, daß ψ( ∂t der klassischen Theorie auf einen Schnitt t = const. als Anfangszustand willk¨ urlich vorgegeben werden k¨ onnen∗ und die weitere zeitliche Entwicklung eindeutig deﬁnieren. Es soll also nicht so etwas wie “run-away solutions” geben. Pais-Uhlenbeck haben ja gezeigt, daßdies erf¨ ullt ist, wenn der Formfaktor keine Null2 urde stellen bzw. Pole hat. (z.B. e−α ). (Im gegenteiligen Fall w¨ ich lieber sagen, daß der Anfangszustand im Sinne der Theorie ungen¨ ugend charakterisiert war als daß “die Feldgleichungen unvollst¨andig sind”.) W¨ are dies nicht so, so m¨ ußten M.-Kr. und Cl. Bloch mit ihrer St¨ orungstheorie sowieso einpacken (der letztere Autor schw¨ atzt Unsinn u ¨ber diesen Punkt in einer in Pasadena verfaßten Arbeit, von der er mir ein Manuskript geschickt hat).568 ∗ D.

h. es sollen keine supplementary conditions f¨ ur diese Gr¨ oßen bestehen. 568

Bloch had spent some time in Pasadena in 1952/3. The manuscript to which Pauli refers was not published.

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¯ ψ, u, ∂u auf einen Schnitt t = const. den AnDaraus, daß ψ, ∂t fangszustand bestimmen, folgt nat¨ urlich gar nicht, daß sie kanonische Variable sind: Nat¨ urlich sind sie es nicht, und weder Q noch P (Impuls, entsprechend µ = 1, 2, 3) haben die Normalform (beide bekommen Zusatzterme proportional zur Kopplungskonstante, die in der lokalen Theorie verschwinden). 3. Nun betriﬀt eine erste Frage die G¨ ultigkeit Ihres Lemmas ret B − Dav B = −Dret A + Dav A [A, B] = −[B, A] oder DA A B B Ihr Beweis, der explizite kanonische Variable verwendet, scheint mir nicht ad¨ aquat. Selbst wenn man f¨ ur A, B die Feldgr¨ oßen selbst einsetzt, geben sie keinen von der Hamiltonischen Form der Gleichungen unabh¨ angigen Beweis, der die Allgemeinheit der G¨ ultigkeit des Satzes in Erscheinung treten l¨ aßt. Ich m¨ochte Sie deshalb fragen, was Sie dar¨ uber wissen (bevor ich anfange, mich selber damit zu plagen). Dazu noch einige Bemerkungen zu Ihren Methoden. Insofern die Diﬀerenzen der gestrichenen und der ungestrichenen Feldgr¨ oßen nur in der ersten Ordnung Ihres Parameters λ ben¨ otigt werden, verwendet Ihre Methode die sogenannten “Equations de variation” (Pointcar´e).∗∗ Den DA B entspricht, im ¯ Falle, daß B eine Feldgr¨ oße selbst ist (wie u, ∂u ∂t , ψ, ψ wie bei M.-Kr.), das δx1 · · · δxk der Punktmechanik (siehe Whit— Sie haben aber die “Variationsgleichuntaker, 1.c.)569 gen” durch Anbringen der Inhomogenit¨ at (Quelle) bereichert und das ist vielleicht eine gute Idee. (Nat¨ urlich kann man das∗∗∗ (N.B. Die Diﬀerenz der selbe in der Punktmechanik machen.) ∗∗

Vgl. Whittaker, Analytical Dynamics, Chap. X, §112. d Es w¨are den Gleichungen f¨ ur dt δxr (Whittaker, p. 285) als ∂A ugen. Dann gibt es wieder eine avancierte Zusatzterm ∂xr hinzuzuf¨ und eine retardierte L¨ osung. ∗∗∗

569

E.T. Whittaker, Analytische Mechanik der starren K¨ orper, (Berlin: Springer, 1924), 287f.

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retardierten und der avancierten L¨ osungen der inhomogenen Variationsgleichung gen¨ ugt nat¨ urlich der gew¨ ohnlichen homogenen Variationsgleichung. Deshalb verh¨ alt sich diese Diﬀerenz auch so sch¨on stetig.) Ob homogen oder inhomogen, jedenfalls sind oßen wie die Variationsgleichungen linear in den DA f (f Feldgr¨ ¯ ψ, ψ, u etc.) und das sollte wohl erm¨ oglichen, Reziprozit¨ atss¨atze u ¨ber selbstadjungierte lineare Diﬀerentialgleichungen anzuwenden und so zu Ihrem Satz {A, B} = -{B, A} zu gelangen. Ich habe das aber noch nicht durchgef¨ uhrt. Dagegen habe ich f¨ ur B = Pµ die Df · Pµ ausgerechnet und u r t < t1 fand, daß sie brav die Spr¨ unge bei t = t1 machen und f¨ bzw. t > t1 Null sind, obwohl die (nicht kanonischen) Feldgr¨ oßen selbst viel komplizierter sind. Die Relationen f¨ ur [Pµ , f ] kommen ganz richtig heraus. 4. Ich habe absichtlich die Analogien zur Punktmechanik mit endlich vielen Freiheitsgraden hervorgehoben, weil ich nun auf den Begriﬀ “Integralinvarianz” lossteuern m¨ochte (Whittaker, §§113). An Stelle von “Integralinvariante” (bzw. invariante Diﬀerentialform 1. und 2. Grades) (M1 δx1 + · · · + Mn δxn ) der Punktmechanik tritt im Falle kanonischer Feldvariablen p(x, t), q(x, t) {Mρ (p(x), q(x))δpρ (x) + Nρ (p(x), q(x))δqρ (x)}d3 x ρ

mit einer endlichen ρ (die auch nur aus einem einzigen Term bestehen kann) und einem Integral u ¨ber den 3-dimensionalen Raum (an Stelle der Summe u ¨ber die δxr ). Das der Integralinvariante der Punktmechanik w¨ are nunmehr u ¨ber den Funktionsraum zu erstrecken, was immer Schwierigkeiten macht (es sei denn, daß man ein Kristallgitter mit nach oben abgeschnittener endlicher Zahl von Eigenschwingungen statt des wirklichen Raumes einf¨ uhrt). Aber man

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kann ja von einer zeitlich konstanten Diﬀerentialform sprechen, z.B. Mρ (x), Nρ (x) mit

δJ , δJ δpρ (x) δqρ (x)

identiﬁzieren, worin J

↓ ↓ Variantionsableitung

ein Integral ist. Z.B. kann man f¨ ur J das Impulsintegral P = ∂qρ 3 x) ∂x) nehmen. Dann kann man auch zu invarianten ρ d xpρ ( ¨bergehen. (Das u ¨ber Bilinearformen† in den δ (bzw. Ihren Dt) u den Funktionsraum ist vermeidbar.) 5. Ganz unabh¨ angig von Ihrem Formalismus war ich zu dem Schluß gekommen, daß das Existenztheorem von Lie-K¨ onigs, wonach die zeitlich-konstante Bilinearform sich immer auf die kanonische Normalform bringen l¨ aßt, es also kanonische Variable geben muß, sobald es Poisson-klammern gibt, auch f¨ ur Feldtheorien g¨ ultig sein sollte. Einen strengen Beweis daf¨ ur habe ich allerdings noch nicht gefunden, aber ich bin bereit zu wetten, daß es z.B. in der M.-Kr. Formfaktortheorie kanonische Feldvariablen geben muß: Diese w¨aren dadurch charakterisiert, daß die Impuls- und Ladungsintegrale in den neuen Variablen wieder die Normalform Pk =

∂ϕ ∂ν ϕ + pν ∂xµ ∂x ∗

3

d x,

Q=

ϕ∗ ϕd3 x

(Im Ausdruck dieser Variablen durch die urspr¨ unglichen k¨ onnen letztere zu verschiedenen Zeiten eingehen.)

annehmen, daß f¨ ur ϕ∗ , ϕ, pν , ν die kanonischen Kommutatoren richtig sind und daß f¨ ur Kopplungskonstante 0 diese Variablen ¨bergehen. In der ersten N¨ aherung der stetig in ψ ∗ , ψ, pu , u u St¨ orungstheorie habe ich das in der Tat veriﬁzieren k¨ onnen (linear in der Kupplungskonstante). † N.B.

Die Koeﬃzienten der Kovariante ist die reziproke Matrix zu den Poisson-Klammern.

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Ich m¨ochte also wissen: den Zusammenhang Ihrer Deﬁnition der Poisson-Klammern†† mit dem Begriﬀ “bilineare Kovariante” (bzw. die Verallgemeinerung dieses Zusammenhanges f¨ ur Systeme mit ∞-vielen Freiheitsgraden wie es die Felder sind). Meine das Theorem von Lie-K¨onigs verallgemeinernde Vermutung ist, daß immer wenn Ihr Formalismus anwendbar ist, die Theorie sich auch auf die Hamiltonsche-kanonische Form bringen l¨ aßt (auch dann, wenn Formfaktoren vorhanden sind).— Nat¨ urlich kann die explizite Durchf¨ uhrung schwierig und auch unn¨ otig sein! Das ist alles reine Mathematik, also Vorfragen, die u ¨brigens nicht direkt mit der Lorentzinvarianz zu tun haben. Die letztere wird f¨ ur lorentz-invariante Formfaktoren typische Konvergenzprobleme verursachen, wohl auch dann, wenn der Formfaktor wie bei M.-Kr. von drei (statt bisher nur zwei) Punkten abh¨ angt. Auch bin ich sonst aus physikalischen Gr¨ unden eher ziemlich skeptisch gegen¨ uber den Formfaktortheorien. Was ist Ihre Ansicht? (N.B. Die Eichgruppe der Elektrodynamik wird unm¨ oglich!) Viele Gr¨ uße Ihr W. Pauli †† Mit

Hilfe der inhomogenen “Variationsgleichungen”.

[564] Wolfgang Pauli to Rudolf Peierls Zollikon-Z¨ urich, 14.8.1952 (draft) Nicht abgeschickt weil unfertig! Lieber Herr Peierls! Ich schicke Ihnen noch einen Nachtrag, um an einem einfachen (rein klassischen — alles sind c-Zahlen) Beispiel aus der Punktmechanik klar zu machen, was ich meine. Ich betrachte 3 Massenpunkte mit den Koogen. Das ordinaten q1 , q2 , q3 , die sich auf einer Geraden bewegen m¨ Bewegungsgesetz folgte aus einer (in bezug auf die Zeit translationsinvarianten) Lagrangefunktion, die einen Integraloperator enthalten

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m¨oge. (Oszillator und Wand einf¨ uhren, um Dn zu beschr¨anken):

Ldt −

−g

ein Born Potential

↓ m [ (q˙12 + q˙22 + q˙32 ) − V (q) ]dt 2

dt1 dt2 dt3 F (t1 , t2 , t3 )ϕ[q1 (t1 ), q2 (t2 ), q3 (t3 )].

F h¨ angt nur von den zwei Diﬀerenzen t1 − t2 , t3 − t1 ab und ist eine (reelle) Funktion, die f¨ ur F (τ1 , τ2 , τ3 ) = F (−τ1 , −τ2 , −τ3 ) (Spiegelinvarianz; z.B. eine Gauss-Funktion). u r t = t0 Von ϕ und g setze ich nur voraus, daß qi (t), q˙i (t) f¨ willk¨ urlich vorgegeben werden k¨ onnen und eindeutig den weiteren Verlauf in Zukunft und Vergangenheit bestimmen sollen.∗ Die Bewegungsgleichungen lauten ∂V ∂ϕ[q1 (t1 ), q2 (t2 ), q3 (t3 )] +g dt2 dt3 F (0, t2 −t, t3 −t) =0 m¨ q1 (t)+ ∂q1 ∂q1 {N.B. F (t1 , t2 , t3 ) ≡ F (0, t2 − t, t3 − t)} und entsprechend f¨ ur q2 , q3 . Ihre inhomogenen Variationsgleichungen bei einer Quelle f¨ ur qj kann man schreiben ∂2V (j) + g dt1 dt2 dt3 F (τ1 , τ2 , τ3 )δ(t − tk ) md¨ qk (t) + ∂qk ∂qr ·

∂2ϕ dqρ(j) (tρ ) = δkj δ(t − ti ). ∂q ∂q r k ρ

(A)

Ihre Vorschrift ist nun die: man suche erst die retardierten L¨ osungen (j) j ur t → −∞, dann die avancierten L¨ osungen δqk → 0 f¨ ur δqk → 0 f¨ t → +∞ und setze (I)

[qk (tk ), qj (tj )] = δq

(j) k ret

−δq

(j) k av

Nun kommt alles darauf an, direkt einzusehen, daß die rechte Seite bei Vertauschung von (j, tj ) mit (k, tk ) antisymmetrisch ist. ∗ Ein

Beispiel ist q gleich dem Produkt q1 (t1 )q2 (t2 )q3 (t3 ).

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Ich habe das bis jetzt noch nicht so gesehen, aber auch nicht das Gegenteil. K¨ onnen Sie es zeigen? (N.B. Wenn ich dieses Beispiel verstanden habe, kann ich ohne weiteres dasselbe auch f¨ ur eine Feldtheorie mit Formfaktor wie die von M[øller]-Kr[istensen].) Was meine eigenen Behauptungen u ¨ber ein solches System betriﬀt, so sind sie folgende: 1. Es existiert ein Energieintegral m H = (q˙12 + q˙22 + q˙32 ) + v(q) 2 ∂ϕ[q1 (t1 ) · · · q3 (t3 )] . q˙k (tk ) +g E(t1 −t3 , t2 −t, t3 −t)dt1 dt2 dt3 ∂[qk (tk )] k

Man muß nun E gem¨aß der Gleichung bestimmen 3 ∂ ∂ E(τ1 , τ2 , τ3 ) [F (τ2 −τ1 , τ3 −τ1 )δ(τk )] = ∂τk ∂τk k=1 k

↓ h¨ angt wirklich von 3 Variablen ab

oder mit τ2 = τ1 + ρ, τ3 = τ1 + σ, τ1 ≡ τ ∂ ∂δ(τ ) + [F (ρ, 0)(δ(ρ + τ ) · · · δ(τ ))] F (ρ, 0) ∂τ ∂ρ ∂ ∂ E(τ, τ + ρ, τ + σ), + [F (ρ, 0)(δ(σ + τ ) − δ(τ ))] = ∂σ ∂τ 1 ∂ [F (ρ, σ)((r+τ )−(τ ))] also E(τ, τ +ρ, τ +σ) = F (ρ, σ)δ(τ )+ 2 ∂ρ 1 ∂ [F (ρ, σ)((σ + τ ) − (τ ))]. + 2 ∂σ Man sieht, daß bei festem ρ, σ (bei dieser Wahl der additiven Konstante in E) f¨ ur τ → +∞ und f¨ ur τ → −∞E → 0 gilt. ußten die Poisson-Klammern 2. Aus q˙k = [H, qk ], q¨k = [H, q˙k ], · · · m¨ im Prinzip folgen und sobald nur im Prinzip (f¨ ur irgendein t) qk (t) ucken l¨ aßt (etwa durch Potenzsich durch qr (t0 ) und q˙r (t0 ) ausdr¨ reihen in g, muß diese Theorie als ,,Hamiltontheorie” betrachtet werden und kanonische Variable sollen existieren.

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Also die Hauptsache ist mir der Beweis f¨ ur die Antisymmetrie der rechten Seite von (I) in k und j. Inzwischen werde ich weiter dar¨ uber nachdenken. Nochmals viele Gr¨ uße Ihr W. Pauli

[565] Rudolf Peierls to John Cockroft [Birmingham], 14.8.1952 (carbon copy) Dear Cockroft, As you probably know there has been some correspondence recently about the question of this country’s participation in the European nuclear physics scheme. I had not previously written to you about this, because my impression was, after the conference at Buckland House,570 that most people there held very similar views. However, as I have in the past been rather sceptical about the scheme. I ought perhaps to say what I feel about it now and from what conversations I had with others, I believe that my views are fairly representative of those held in the universities now. I had been doubtful about the prospect of this scheme previously because I was afraid it might divert attention from the possibility of a scheme providing travel grants to move physicists around as between different European countries, which would have been very much cheaper and easier and of very great value. I also felt that it would probably be better for this country not to be a direct participant in such a scheme, since according to the early plans the new laboratory was to have machines only comparable to those already under construction in this country, and in that situation it would have been better for the 570

Informal Conference held on 7 June 1952 at Buckland House near Harwell to discuss ‘High Energy accelerators for Nuclear Physics’. See report written by M. Snowdon, 7.6.1952; carbon copy in Chadwick Papers, CHADI, 26/2.

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limited eﬀort and scientiﬁc manpower available here to be concentrated on the jobs to which we were already committed. I also felt that there was some doubt whether with arrangements started on the government committee level the administration of the scheme would get into the right hands and whether it would not be tied up in red tape. Now it is clear that the scheme is going ahead and my ﬁrst objection is therefore no longer relevant. From the point of view of this country the situation is entirely changed if, as is now proposed, the laboratory will go for a machine considerably more ambitious than what is planned in this country. If it were possible to go for a really high energy this would make a large diﬀerence, not only to the prestige of European physics, but also to the prospects of retaining in the future the chance of training some really ﬁrst rate physicists, who would be attracted to the subject and stimulated by the prospect of being in the front rank of the development of the fundamental side of the subject. It is still a question whether on abstract considerations it would be possible and desirable for such a bigger machine to be built independently in this country, but I think everybody is agreed that if Great Britain were now to announce a plan to go ahead independently with such a scheme it would have politically most unfortunate results, even if it were economically possible. One could, of course, return to this possibility if it should turn out that the discussions for international co-operation on this project were to break down. As regards my last diﬃculty I am still not completely satisﬁed that in the end the set-up will be one in which the technical and scientiﬁc problems can be pursued without undue bureaucratic diﬃculties, but there seems a good chance that if this country were to come in, the prestige of our representatives would be such that they could take a decisive part in helping to develop the organisation and then things might go well. For this reason it seems to me very important that the question about our participation should be settled as soon as possible and that if we are going to come in at all, which I hope we shall, it should be done at a very early stage. The expense of joining in during the present preparatory stage, which is all that would have to be deﬁnitely promised at the present, surely is not a serious obstacle.

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At the Buckland conference it sounded as if decisions on this matter were being taken (or not taken) by committees in which the representation of modern nuclear physics was extremely limited. Presumably you know how this has developed in the meantime and perhaps is set up is now more satisfactory, but if physicists in the universities can do anything to make their views heard, I am quite sure that many of us would be prepared to state our views in whatever form and place was unlikely to be most eﬀective. I must apologise for writing such a long letter on things that I must assume that you are well aware of and if as I hope you can tell me that these points are being taken account of in the responsible quarters, I shall be quite satisﬁed with that. Yours sincerely, R.E. Peierls [566] Wolfgang Pauli to Rudolf Peierls Zollikon-Z¨ urich, 16.8.1952 (draft) Nicht abgeschickt weil unfertig! Lieber Herr Peierls! Das beiliegend vorgerechnete Beispiel aus der Punktmechanik l¨aßt alles im Detail hervervortreten, was ich in meinem letzten Brief nur in allgemeinen Worten ausgef¨ uhrt habe. Es ergibt sich daran anschließend eine mir wesentliche Frage betref¨ fend die Anwendbarkeit Ihres Formalismus. Ubertr¨ agt man diesen w¨ortlich, so hat man statt der Gl[eichung] (2) der beiliegenden Noten die inhomogen Variationsgleichungen ∂2V (j) ( )t δql (t) + g dt1 · · · dtk F (t1 · · · tk ) mδ q¨k + ∂qk ∂ql l

· δ(t − tk )

l

∂2ϕ δql (tl ) = λδjk δ(t − tj ) ∂[qk (tk )]∂[ql (tl )]

(2, Peierls)

zu bilden. Diese haben eine retardierte L¨ osung δ(j) qkret (t), die mitsamt ihrer Ableitung nach der Zeit f¨ ur t → −∞ verschwindet und eine

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avancierte L¨osung, die (ebenso ihre zeitliche Ableitung) f¨ ur t → +∞ verschwindet. Dann hat man ihre Diﬀerenz zu bilden δ(j) q ≡ δ(j) q ret ∼ δ(j) q av k

k

k

die eine (besondere) L¨osung der homogenen Variationsgleichungen ist. osungen h¨ atte man nun die Poisson-Klammern anzusetzen: F¨ ur diese L¨ [qk (tk ), qj (tj )] = δ(j) qk . Leider kann ich nun aber nicht einsehen, daß die rechte Seite bei Vertauschung von (k, tk ) mit (j, tj ) das Vorzeichen ¨andert, wie das Ihr “Lemma” behauptet. Bei kanonischen Variablen stimmt das ur die Gleichungen, wie sie da stehen — schon, aber allgemein — f¨ halte ich es nicht f¨ ur richtig. (Ich sehe aber keine allgemeine Beziehung osungen qk (t) bei zwischen δqlret und δqlav , da die nicht variierten L¨ Umkehr der Zeit kein einfaches Verhalten zu zeigen brauchen.) Auch ist der Passus Ihrer Arbeit, wo “die L¨ osungen” der urspr¨ unglichen Gleichungen mit denen der inhomogenen Gleichungen durch eine kanonische Transformation verbunden werden sollen, etwas unklar geschrieben. Nat¨ urlich kann man Gr¨ oßen mit denselben Vertauschungs-Relationen durch eine S-Transformation verbinden, aber dazu muss man schon wissen, was die VertauschungsRelationen sind. Im vorliegenden Fall sehe ich keine einfache Beziehung zwischen den Vertauschungs-Relationen der homogenen und der inhomogenen Gleichungen. Bitte schreiben Sie mir also, ob f¨ ur die Gleichungen “(2, Peierls)” Ihr Antisymmetriesatz f¨ ur die Diﬀerenz der retardierten und avancierten L¨ osung gilt. Sollte das nicht der Fall sein (was ich vermute), so w¨ urde Ihr Formalismus f¨ ur mich wesentlich an Interesse verlieren, und ich w¨ urde dann lieber brav bei den homogenen Variationsgleichungen bleiben (die ja auch alles Gew¨ unschte schon enthalten) wie in den beiliegenden 571 Notizen. Viele herzliche Gr¨ uße Ihr W. Pauli 571

Enclosed with the letter were notes about ‘Punktmechanik mit “nichtmomentanen” Bewegungsgleichungen’. See Pauli, Wissenschaftlicher Briefwechsel, IV/1, 705–707.

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[567] Rudolf Peierls to Wolfgang Pauli [Birmingham], 20.8.1952 (carbon copy) Dear Professor Pauli, Thank you very much for your two long and interesting letters.572 In the question of deﬁning non-Hamiltonian systems I meant really nothing deep, but I wanted to know how one should handle the quantum mechanics of non-local equations (non-local meaning simply equations containing form functions). I took it for granted, perhaps too easily, that for those equations one could not practically imply the canonical formalism and that one would not be able to do anything with them without having a new technique. The method which I have worked out is, of course, very far from being a usable one, but it gives at least some hope in that direction. However, I agree with you that one should specify more carefully in what way such systems diﬀer from the canonical scheme, (if at all). Turning now to the example, which is worked out in your note,573 and discussed in your second letter.574 I think I can assert that this is the case to which classically my method is applicable. This, as far as I can see, follows directly from section 6 of my Princeton paper,575 which is entitled “Non-Hamiltonian Theories”, as you point out without suﬃcient justiﬁcation, but which does carry through the proof of the anti-symmetry of the Poisson bracket without the use of canonical variables. I tried to-day to write out this proof for the speciﬁc system contained in your note, but it would cover several pages of algebra and contain nothing that is not evident from the few equations in my paper, so I think you will really ﬁnd those more satisfactory, but if you have any trouble in following the argument or any objection to its validity, I would be glad to give more detail. 572

Letters [563], [566]. Note accompanying letter [563]. 574 Letter [566]. 575 See letter [563], note 561. 573

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Further in the same letter you raise an objection to the argument used in section three of my paper, but this section was intended merely to prove that in cases where canonical variables exist the deﬁnitions of the Poisson bracket, which I have given, are correct, and for this case, the canonical transformation (3.7) does, in fact, explicitly provide the transformation from the original to the modiﬁed solutions of the system and its existence is therefore established. As I tried to make clear in the paper, there remains still an essential gap in the justiﬁcation of the general commutation law, the argument of section 3 is valid only for canonical systems and that of section 6 is valid only classically, that is to say regardless of the order of factors. I cannot therefore assert that I can quantize a non-local theory, except for a somewhat trivial case, to which I want to come back later. Given what you say one might think of approaching the problem of quantization by your method, which essentially depends on expressing the solutions of the ﬁeld equations in terms of the values of variables at any one time, but the trouble is that the expressions one then obtains will no doubt algebraically be very complicated and the question of the ordering of factors will arise, if one chooses the wrong ordering of factors, one will presumably get a theory which is not Lorentz invariant and since the whole procedure of solving in terms of the quantities at one time destroys the covariance of the description, it will be hard to make the right choice. Of course, the question of quantization does not really arise, if one is prepared to expand in powers of the coupling constant, since one then needs only two commutators between the free particle quantities (Yang-Feldman).576 But I would like to get somewhat beyond this power series, which may after all be divergent and I would like at least to be able to make some general statements about a theory without series expansion, even though one might not be able to obtain any particular solution without expanding. In this way I rather diﬀer from Møller and Kristensen and incidentally I never believed their statement that there was not an energy and charge operator in such a theory that is completely conserved. 576 C.N. Yang and D. Feldman, ‘The S-Matrix in the Heisenberg Representation’, Phys. Rev. 79, 972–78 (1950).

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Turning now to some points in your ﬁrst letter. I agree that the only condition for the validity of my formulae classically is that the introduction of the coupling should not produce new degrees of freedom, but as I have stressed before, this does not dispose of the problem of quantization. You ask my views about the value of non-local theories in general. This is somewhat linked up with the question whether in the existing ﬁeld theory one can divorce the renormalization from the series expansion and whether one can write ﬁnite equations (however complicated and implicit) which are rigorous, and which one then can solve, if necessary, by means of an expansion. If this is possible, then I would doubt whether one really needs non-local equations, that is to say whether one would ever have to put a form factor into the basic postulate. However, it seems to me certain that the equations which one would then obtain after eliminating the inﬁnities would in themselves contain integral operations, so that the experience of handling such equations would not be wasted. On the other hand it [is] also possible that such ﬁnite equations which contain all the physical results of the existing theory may not exist and that the only way to get ﬁnite equations without series expansion is to leave out some part of the integrations, which, in any case, refers to energy regions about which we know nothing and in which new things like the production of as yet unknown particles will change things. In other words I would like to be able to write down that part of the present theory about which we can really be sure, and I would like to do so in a ﬁnite, consistent, and Lorentz and gauge invariant form. This brings me to another point. You say that the use of form factors destroys the gauge invariance, but this is not necessarily true. That such integral expressions can be made gauge invariant, was pointed out by C. Bloch,577 though he put it in a rather complicated form. It is true ¯ 2 ) is not gauge invariant, but one can replace ¯ 1 )ψ(x that the product ψ(x it by ¯ 1 )eie ψ(x 577

x

2 x1

Aµ δxµ

ψ(x2 ),

(1)

Cl. Bloch, ‘On ﬁeld theories with non-localised interactions’, Kgl. Danske Vid. Selsk. 27/8, 1–55 (1952), here p. 46.

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where the integral goes over the straight line (in four dimensions) from x1 to x2 . Evidently (1) is gauge invariant. Its occurrence in the action principle does not give any new trouble that is not already present in any form factor theory. If one wants to use a series expansion, the only change is some slight algebraic complication, and the occurrence of higher powers of A in the action principle which have to be taken together with the higher order approximations for the lower powers. We have been playing for some time with an action principle of this kind that has attractive features, and which looks as follows: L=i

4

4

¯ 1) d x1 d x2 ψ(x

∂ ie x2 Adx γµ + M F (x1 − x2 ) e x1 ψ(x2 ) ∂xµ

+ hermition conjugate + Lf .

(2)

Signs and numerical factors are not guaranteed, units are such that h = c = 1, F is a form factor (depending on one distance only). The brackets are meant to indicate that the diﬀerentiation acts only on F , not on the other factors, Lf is the action of the electromagnetic ﬁeld by itself. The other term contains both the Lagrangian of free particles and coupling. The equations derived from (2) have the property that (a) in the absence of a ﬁeld they admit only the solution of the free-electron Diracequation, (b) in the limit in which the spread of the form factor goes to zero it reduces to the usual local theory. We have tried to apply this to some simple cases, using a power series in e, in particular we have looked at the vacuum polarization. The result is that the non-gauge invariant term is still divergent. I am fairly sure that the next term, i.e. the charge renormalization will be ﬁnite, but it is of course messy to try to deﬁne this term in the presence of the divergent leading term. The reason for this trouble lies mathematically in the fact that, considering the eﬀect of a potential with wave vector k one is left with a four-dimensional integration over a momentum p, which is restricted to be a real-electron momentum, i.e. p2 = m2 . The integrand contains

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the four-dimensional Fourier transform g of the form factor in the form g(p − sk) and for other similar arguments. Here, s is an auxiliary variable which runs from 0 to 1, and arises from the line integral in (2). If g is to be invariant, it will depend only on the square of its argument, i.e. on p2 + s2 k2 − 2spk

(3)

In the integration over p, p2 remains constant, and the k is, of course, given and ﬁnite. If k is space-like, as for a static potential, then pk is zero in a two-dimensional section of the three-dimensional integration. In that section the form factor therefore does not reduce the integrand, and so it can reduce the order of the divergence only by one, which is not enough. Now (2) is not the most general action principle of this type, and we are at present studying the most general case. However, I am not very hopeful, because the integrand can only be reduced by a more general function of the three invariants, of which (3) is a linear combination. Since, in the two-dimensional section of the integration, all three of these variables are ﬁnite, it does not look as if this can help to remove the divergence. The same is true in the theory of Møller and Kristensen, their contrary assertion is due to the fact that they work out the vacuum polarization only for external ﬁelds satisfying the free-meson equation, and hence have a time-like k. In that case, the situation is quite diﬀerent, and pk is always large if any component of p is large (provided p2 = m2 ) This means the self-energy of a meson will in their theory diverge when k is space-[like] which will happen in virtual states. I believe this to be connected with Bloch’s statement that he tends to get divergences in fourth order. From some remarks in your letter it seems to me that you will not be surprised about this trouble. This may well force one to abandon the non-local theories. We are discussing the following means of avoiding this conclusion:

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1. The divergence may just be the fault of the method of calculation, and there may be a reasonable way of looking at the answer which makes it evident that the non-gauge invariant term is zero. There are such cases in four-dimensional Fourier transforms, and one can write the most harmless expressions in a way which makes them appear divergent. But I am not very hopeful in this direction. 2. One may simply prescribe a method which preserves group invariance, and therefore make this term vanish, but this would remove the main point of a non-local theory. 3. One might expect this term to be cancelled by a “relativistic” renormalization, since the contributions to this term from diﬀerent kinds of ﬁelds do have diﬀerent signs. This does not make me very happy either. 4.578 The divergence may have something to do with the power series in e, and if one were to obtain the rigorous solutions of the equations this might be equivalent to a prescribed order of integration, which would remove the diﬃculty. This seems to me at the moment the most promising line, but it makes things very diﬃcult mathematically. Rather surprisingly it is possible to get the rigorous solutions (2) for the case of an external homogeneous magnetic ﬁeld, without specifying the shape of the form factor, and I am playing with these at the moment. Unfortunately it seems that the inﬁnite extent of such a ﬁeld introduces some new ambiguities (similar to those in the diamagnetism of free electrons) and I have therefore not been able as yet to calculate the induced current. Apart from these diﬃculties, I have been interested in the action principle (2) as an exercise in quantization. I have no idea what to do with the general class of interacting quantized ﬁelds. But at least in the very modest case of a classical vector potential everything goes through all right. One then has the simpliﬁcation that the action principle is bilinear in the ﬁeld variables, so that the Poisson brackets are c-numbers. 578

In the manuscript the numbering is inconsistent and the number 3 is used twice.

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One can then carry through the quantization in a covariant manner and ﬁnds that the wave function can be expanded in terms of c-number solutions which minimize (2), with coeﬃcients which can be given the usual interpretation of emission and absorption operators. However, each of these refers to the whole space-time picture and it appears rather arbitrary to relate them to any speciﬁc time. I admit that to quantize such a simple case is not much of an achievement, but it is at least one case where the non-local theory works. If you are interested I could send you details of how this goes through quite covariantly. In such a gauge invariant theory there is, of course, no diﬃculty deﬁning a current density, since this is simply the functional derivative of the action principle with respect to the vector potential. Hence also the expression for the total charge is unambiguous. I think one should deﬁne the energy momentum tensor in the corresponding way, namely by writing the action principle in terms of curvilinear coordinates and then diﬀerentiating with respect to the gik . This can be done for any of these non-local theories. By integrating over space, one can then deﬁne the expression for the total energy, which is presumably the same thing as the Hamiltonian. But I am not sure what one does with it. (It is, of course, exactly constant in time, not merely on the average). It would be interesting to know how this deﬁnition of the energy is related to yours. Just one more point: It seems to be possible, by treating an expression like (1) as a density matrix, and ﬁnding the equations for it, to get a formulation of the theory in which only the electromagnetic ﬁeld appears, but not the vector potential. There no question of gauge invariance arises, and there cannot possibly [be] any gauge-invariant term in the polarization. I have not got very far with this, however, because of some mathematical troubles. Any comments on all this would be most welcome. Yours sincerely, R.E. Peierls

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[568] Wolfgang Pauli to Rudolf Peierls Z¨ urich, 29.8.1952 Lieber Herr Peierls, Vielen Dank f¨ ur Ihren Brief vom 20.579 Meine Bemerkungen dazu haben zum Teil provisorischen Charakter. 1. Ihren Beweis von section 6 habe ich nun genau durch¨ uberlegt und sehe kein Hindernis mehr, ihn auf das von mir diskutierte Beispiel anzuwenden. Darin sind wir also einig. Es sind aber noch einige Fragen zur¨ uckgeblieben, auf die ich noch keine Antwort weiß. (j) osung (0 f¨ ur t → −∞) mit Sei DRet qk (t) die retardierte L¨ der Inhomogenit¨ at −λδkj δ(t − tj ) in der Variationsgleichung.1 (j) Dav qk (t) die avancierte L¨ osung (0 f¨ ur t → +∞) mit der(j) (j) (j) selben Inhomogenit¨ at und δk (t) ∼ = DRet qk − DAv qk diese osung der homogenen Variationsgleichung. Wodurch spezielle L¨ (j) ∼ δ(j) (tj ) charakterisiert? sind die Anfangswerte limt→t δ (t) = j

k

k

Bei kanonischen Variablen ist die Antwort so einfach, aber im allgemeinen Fall bin ich bisher nicht durchgekommen. Hier muß die mir noch fehlende Br¨ ucke von Ihrer Methode zu meinen Ausdr¨ ucken f¨ ur die bilineare Kovariante sein.2.1 Die Schwierigkeit h¨ angt nat¨ urlich damit zusammen, daß das “Anfangswertproblem” in den nicht-lokalen Theorien nicht explizit l¨ osbar ist und man hier, wie Sie es ganz richtig r¨ ugen — noch 1 In

den Index k kann auch die Raumkoordinate mit einbezogen werden, die Zeit schreibe ich aber extra. 2.1 Das Lemma von der Antisymmetrie der nach Ihnen deﬁnierten Poisson-klammern ist u ¨brigens a¨quivalent mit der Behauptung, daß die aus den beiden oben angef¨ uhrten L¨ osungen der inhomogenen (i)

(i)

Variat[ions]-Gl[eichungen] gebildete Kovariante D(DRet qk , DAv qk ) die nicht zeitleer konstant ist sowohl f¨ ur t → +∞ als auch f¨ ur t → −∞ verschwindet. 579

Letter [567].

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ganz in den Potenzreihen nach der Kopplungskonstante gefangen ist.2.2 Die Schwierigkeiten wegen der Reihenfolge von Faktoren ¨ beim Ubergang von der c-Zahltheorie zu der q-Zahltheorie im nichtlokalen Fall halte ich f¨ ur objektiv und tats¨ achlich vorhanden. (N.B. Bei Møller-Kristensen ist ein nicht ganz unwichtiger Fehler gemacht hinsichtlich dieser Reihenfolge in Ihrem Ausdruck ∂t0 f¨ ur ∂xµνν .) 2. Der Vorschlag von Cl. Bloch von einer Wechselwirkungsenergie die x µ ¯ 1 )eie x12 Aµ dx f (x2 ) Ψ(x ↓ gerade Linie

enth¨ alt, war mir wohl bekannt, ich habe ihn aber (vielleicht zu Unrecht) bisher nicht ernst genommen. Zun¨ achst hatte ich ein wenig Angst wegen der Identit¨ at zwischen den Feldgleichungen, die aus der Divergenzgle∂j ichung ∂xµµ = 0 entspringen. Diese Gleichungen folgen ja in der lokalen Theorie auf zweierlei Weise aus den Feldgleichungen a) aus den Maxwell’schen b) aus den Dirac’schen (b[e]z[iehungs]w[eise] bei Spin 0 aus den Klein-Jordanschen Gleichungen) f¨ ur das Materienfeld. Eine solche echte Identit¨ at wird auch in der nicht-lokalen Theorie bestehen bleiben, damit die Felder nicht u ¨berbestimmt sind. Nat¨ urlich kommt alles darauf an, daß der Stromvektor Jµ (x) richtig deﬁniert wird. Herr Cl. Bloch dr¨ uckt sich um diese Frage, da er die Aµ nur als a¨ußeres Feld einf¨ uhrt. Es fragt sich, ob bei der Deﬁnition des Stromvektors als Funktionalableitung des Wirkungs-integrals nach dem das Potential (S. 6 Ihres Briefes) diese Identit¨ at richtig 2.2 Bei

den Renormalisations-theorien hat Herr G. K¨allen hier in Z¨ urich einen ersten Versuch gemacht, von diesen Potentzreihen wegzukommen. Seine Arbeit ist gerade in den Helv. Phys. Acta erschienen580 Ihre Meinung w¨ urde mich interessieren. 580

G. K¨ allen, ‘On the deﬁnition of the renormalization constants in quamtum electrodynamics’, Helv.Phys.Acta 25, 417–34 (1952).

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herauskommt. Im Moment scheint es mir allerdings, daß das der Fall sein muß (wenigstens in der c-Zahltheorie) als Folge der Eichgruppe f¨ ur die Lagrange-funktion und die Feldgleichungen. Aber ich m¨ochte ganz sicher sein. Der zweite Einwand betriﬀt das m¨ogliche Auftreten neuer Divergenzen aus eie Aµ dxµ bei Quantisierung des elektromagnetischen Feldes. Wie ist es mit dem gew¨ohnlichen Vakuumerwartungswert eines solchen Operators? Entwickelt man die Exponetialfunktion in eine Potenzreihe, so treten doch voraussichtlich schreckliche Divergenzen (`a la Nullpunktsenergie) auf?† Das scheint mir immer noch so h¨aßlich, daß ich den Cl. Bloch’schen Vorschlag recht ungern mag. 3. Vakuum-polarisation Dies ist mir eigentlich noch wichtiger als die anderen unter 2) erw¨ahnten Punkte. In der Møller-Kristensen Theorie ist die Sachlage doch noch ein wenig anders als Sie es in Ihrem Brief schildern. Is ist richtig, daß M[øller]-K[ristensen] pl¨ otzlich sagen, der †† ¨brigens anzunehmen, daß das Vektor k sei zeitartig (ohne u außere Feld die kr¨ ¨ aftefreie Wellengleichung erf¨ ullt — es kann also nur “reine Dummheit” sein.) Aber im Z¨ ahler der Formel von M[øller]-K[ristensen] steht ein Faktor (p.k); das ist sehr bedeutungsvoll und d¨ urfte f¨ ur die Konvergenz der M[øller]-K[ristensen] Formeln f¨ ur die Vakuum-pol[arisation] im Falle raumartiger k wohl gen¨ ugen. Es fragt sich nun, ob das nur am skalaren Charakter des exponentiellen Meson-Feldes von M[øller]-K[ristensen] liegt, oder vielleicht doch allgemein ist. Haben Sie sorgf¨ altig nachgesehen, ob bei ur Ihrem Wirkungsprinzip (2) nicht am Ende auch der Ausdruck f¨ die Vakuumpolarisation f¨ ur (p.k) = 0 von selbst verschwindet? (Das d¨ urfte f¨ ur die Konvergenz gen¨ ugen). † Sie

sollten das ja wissen auf Grund Ihrer Untersuchungen u ¨ber das Wirkungsprinzip (vgl. p. 3 Ihres Biefes). †† Ich verwende die Bezeichnung Ihres Briefes. M[øller]-K[ristensen] haben L statt Ihres P , p statt Ihres k.

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Die Antwort auf diese letzte Frage interessiert mich besonders und vielleicht wird es sogar letzten Endes hiervon abh¨ angen, ob ich die lorentzinvarianten Form-faktoren ernst nehme. Denn von solchen besonderen Gl¨ ucksf¨ allen abgesehen, ist Cl. Bloch’s Argument, daß in h¨ oheren N¨ aherungen doch Divergenzen auftreten werden — entgegen dem Optimismus von M[øller]-K[ristensen] — ganz richtig. Diese diskutieren sehr stark die Ausdr¨ ucke unter dem Schutze der Voraussetzung, daß alle auftretenden Impulsvektoren bestimmten (nicht verschwindenden Massen) entsprechen. Nochmals vielen Dank f¨ ur Ihren Brief und herzliche Gr¨ uße Ihr W. Pauli

[569] Wolfgang Pauli to Rudolf Peierls Z¨ urich, 30.8.1952 Dear Peierls! I have one more question regarding the section 6 of your Princetonpaper:581 In order to prove the possibility of your deﬁnition of Poisson brackets one has still to show that the Jacoby identity [A[B, C]] + [B[C, A]] + [C[A, B]] ≡ 0

(I)

holds for your deﬁnition of [A,B].582 I am satisﬁed, if you prove it for the classical case, moreover it is suﬃcient to prove it for ﬁeld quantities φα , φβ , φγ themselves. — Of course I believe that it will be all right, but it is your business to give the proof (the Jacobian-identity being fundamental). Besides it, one needs the proof, that for all F s not explicitly depending on time one has ∂F = [F, H] ∂t 581

(II)

See letter [563], note 561. See W. Pauli, ‘On the Hamiltonian structure of non-local ﬁeld theories’, Nuovo Cimento 10, 648–67 (1953), here p. 656. 582

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But the latter was always trivial in the examples which I considered one has only to compute dH dt if the solution of the inhomogeneous variationalequation are inserted (see my last letter).583 So the missing point in your section 6 is just the Jacobi-identity. Please let me know about it. If this is completed, the Lie-K¨ onigstheorem asserts the existence of canonical variables for a ﬁnite number of degrees of freedom (But I think one can venture its generalisation to a system with an inﬁnite number of degrees of freedom.) This theorem is simply circumstance that in an arbitrary space without metrics, one can always transform a covariant antisymmetric tensor ﬁeld Jρσ (x), which fulﬁlls Jρσ ≡ −Jσρ

∂Jτ ρ ∂Jστ ∂Jρσ + + =0 τ ∂x ∂xσ ∂xρ

[expresses the Jacobi-identity δ1 J(δ2 , δ3 ) + δ2 J(δ3 , δ1 ) + δ3 J(δ1 , δ2 ) = 0∗ for 1 J(δ1 , δ2 ) ≡ Jρσ (δ1 xρ δ2 xσ − δ2 xρ δ1 xσ )] 2 to its normal form 0 −1 1 0 0 −1 1 0 .. . (with some trivial modiﬁcation if the determinant Det ||Jρσ || would be identically zero). ∂φρ σ One can, of course, if one wishes, put Jρσ = ∂φ ∂xρ − ∂xσ and then use the theorem of Pfaﬀ, that φρ (x)dxρ can be transformed into x1 dx2 + x3 dx4 + · · · x2n−1 dx2n (+ possibly dx2n+1 which does not occur, σ α σ follows for α Jρα [x , x ] = δρ from the Jacobi identity for ρ σ [x , x ]. It also follows from (II) that J(δ1 , δ2 ) is constant in time (“bilinear covariant”). (∗) It

583

Letter [568].

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if Det ||Jρσ || = 0). If you give a prove of the Jacobi-identity you have practically(∗∗) proved that all classical systems, which you considered in section 6 are Hamiltonian systems. Regarding troubles with orders of factors in the quantized systems, they will actually exist for arbitrary Lagrangian’s and I believe that the formalism can work only for particular Lagrangians. Best wishes, Yours W. Pauli (∗∗) Apart

from the epsilontic questions like treatment of space coordinates [...] as an index α etc.

[570] Rudolf Peierls to Wolfgang Pauli Les Houches, 1.9.1952 (carbon copy) Lieber Herr Pauli! Ihr Brief vom 29/8.584 erreichte mich in Birmingham gerade vor der Abreise in die Ferien, der n¨achste wurde mir nach Paris nachgeschickt. Ich bin jetzt auf einer Rundreise zur Riviera und vielleicht Spanien, und daher nur mit Verz¨ ogerungen erreichbar. 2 ¨ Uber die Eigenschaften des Ausdruckes ei 1 ADS habe ich im Falle quantisierter Aµ noch nichts bewiesen. Ich habe keine Angst vor der mu Identit¨ at ∂j ∂xµ ≡ 0, da diese doch automatisch aus der Deﬁnition folgt (sobald L eichinvariant ist) und unabh¨ angig von jµ (x) = δAδL µ (x) der Reihenfolge von Faktoren. ¨ Uber Vakuumsﬂuktuationen eines solchen nichtlinearen Ausdruckes weiß ich auch noch nichts, aber ich glaube, das kommt sp¨ ater. Man muß nat¨ urlich nur verlangen, daß die Fluktuationen von beobachtbaren Gr¨ oßen sind. 584

Letter [568].

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¨ Uber den anscheinend divergenten Ausdruck der Vakuumpolarisation versuchen wir noch immer, uns zu u ¨berzeugen, daß er wirklich verschwindet. Man kann schon Rechenvorschriften geben, mit denen die Integration Null ergibt. Aber das gen¨ ugt nicht. Es k¨ onnte sein, daß man eine eindeutige Vorschrift bekommt, wenn man (im Prinzip) die Gleichungen f¨ ur endliches e l¨ ost und dann entwickelt. Ich glaube, ich werde die Jacobi-Identit¨ at beweisen k¨onnen — im wesentlichen unter Benutzung eines Variationsprinzipes L + λA + µB und seiner L¨osungen bis zur zweiten Ordnung in λµ. Aber das muß warten, bis ich wieder zu Hause bin. Mit herzlichen Gr¨ ußen Ihr [R. Peierls] [571] Ed Salpeter to Rudolf Peierls Ithaca, 15.9.1952 Dear Rudi, We have been playing with J. Irving’s tritone and Alpha-p[artic]le wave f[unctio]ns585 and I want your advice on the following: We took the latest experimental values for the triplet and singlet ranges of the 2body potential and plugged it into John’s formulae (Phil. Mag., XLII, 338 (1951)),586 adjusted the well depths (separately for H3 & H4 ) (away from the ex[ponential] values in such a way as to get the correct binding energy out of Jock’s formulae. For H4 this required no faking of the experimental well depth for Yukawa and a 15% increase of depth for the exponential shape. We then calculated the quantity I am really after r 2 , where r is the distance of a nucleon from the total center of mass. We got r 2 ∼ 0.7 × 10−26 cm2 for Yukawa and 1.2 × 10−26 cm2 for exponential. 585

John Irving, ‘The Binding Energy of the α-Particle’, Phys. Rev. 87, 519–20 (1952). 586 John Irving, ‘Binding energies of three and four-particle nuclei’, Phil. Mag. 42, 338–50 (1951).

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I’d like to know whether your guess would be that r 2 really depends so strongly on potential shape or whether you think that the method merely is inaccurate? The only news I have are rumours of some (14) “T-tracks” which Salant found at Brookhaven.587 A heavily ionizing, probably doubly charged part[icle] comes to rest and emits two minimum ionisation tracks, extremely straight, in exactly opposite directions. They were found in high altitude balloon ﬂights (one ﬂight), were very common in this one ﬂight, but have never been seen before or after. ??? The Brookhaven Cosmotron is dismantled at the moment and they are getting it ready for systematic experiments in a few months time. As Oliphant probably told you, there is a possibility of my going to Canberra at the beginning of 1954. I haven’t made any decisions yet, but if I should decide to go, I would very much like to spend a few months at the end of 1953 (say October — or September — until X-mas in Birmingham before going Down Under. I am wondering what you think the chances might be for ﬁnancial support for such a term’s stay at Edgbaston? Greetings to all Ed. [572] Rudolf Peierls to Ed Salpeter [Birmingham], 20.10.1952 (carbon copy) Dear Ed, I am sorry that the usual post-vacation rush has prevented me so far from thinking about your question and therefore from answering your letter. I would say that on general principles one would not expect variation methods to give good wave functions, even though they give good energy values, in fact, their very advantage lies in that they give a good energy value from a moderately bad function. I would therefore not be in the 587

M. Blau and E.O. Salant, ‘T -Tracks in Nuclear Emulsions’, Phys. Rev. 88, 954–55 (1952).

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least surprised if the mean square radius, which after all is sensitive to the wave function, in particular to its asymptotic part, were sensitive to the assumptions. It is often stated of Irving’s wave function that it is arranged to have the right asymptotic behaviour. This, however, applied only to the functional nature of the tail, but neither to the coeﬃcient in the exponent, nor to the amplitude factor outside. Incidentally some later work by Irving, now in course of publication, indicates that even for the energy values his function is not quite as good as appeared at ﬁrst, he seems to have had some luck with the cases to which it was ﬁrst applied. Now about looking at the same integrals for the wave function of Svartholm,588 where the ﬁrst iterated function should be very much better, this at any rate has the right asymptotic form with the correct exponent, whatever else may be wrong with it. Now about your plans. I need hardly say that I would be delighted at any prospect of your visiting this department and that I shall do anything in my power to secure a reasonable grant for the purpose. About the only kind of grant I can count on are our ordinary Research Fellowships. It may well be that one of these will be vacant at the beginning of next session and I think there would be no trouble in persuading the University to appoint you for one term. The maximum rate provided for these is at the rate of £700 p.a. I don’t know whether you would regard this as a satisfactory order of magnitude, but I shall also see what can be done in other ways. Please let me know how your plans develop and in particular about the probability p of your being able to come here as a function of time t. We have this year again a particularly attractive and lively group, and about the only trouble at the moment is that we have so many postgraduate lectures, working parties and discussion groups that one has to keep a time table to prevent them clashing. With kindest regards to everybody, Yours sincerely, R.E. Peierls 588

N.V. Svartholm, The Binding Energy of the Lightest Atomic Nuclei, Stockhom: Lund, 1945.

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[573] Wolfgang Pauli to Rudolf Peierls Z¨ urich, 30.10.1952 Dear Peierls! I am writing to you just a few lines in a hurry before my departure to India on Nov[ember] 4.589 I thank you still for your letter from your vacation.590 Meanwhile I did not continue any work in the formfactor theory, but I may well resume it in Bombay. I would be, therefore, very grateful, if you could write to me at Tata Institute in Bombay, if you made some progress with your own work in this ﬁeld, particularly with the proof of the Jacobi identity, which you sketched in your last letter.591 With best regards Sincerely yours W. Pauli

[574] Rudolf Peierls to Robert Aitken [Birmingham], 26.11.1952 (carbon copy) Dear Vice-Chancellor. I am writing to make the points about housing that I mentioned to you the other day. I believe that some other Universities are doing more than we are in suitable cases. For example my opposite numbers in the Universities 589

Pauli was planning to spend the winter semester 1952/3 at the Tata Institute of Fundamental Research in Bombay. He had to cut short his commitment in India due to an illness of his wife and returned in Zurich in January 1953. See letter Wolfgang Pauli to Rudolf Peierls, 12.1.1953, Peierls Papers, Ms.Eng.misc.b212, C.237. 590 Letter [570]. 591 Pauli continued to work in this problem and gave a paper in Turin in March 1953 at a meeting on Non-Local Field Theories, which was later published as ‘On the Hamiltonian structure of non-local ﬁeld theories’, Nuovo Cimento 10 648–67 (1953).

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of Oxford and Manchester are living in houses which their universities are renting to them. In the case of Manchester this is a Professor who came over from the Continent and who probably otherwise would not have been able to come. Both these people moved into their houses a few years ago. I have no direct knowledge of anything like that having been done recently. From one other provincial University I understand that they control about 30 ﬂats which are rented to members of staﬀ, probably at some slight loss to the University. In that University also a good deal of help is being given to new people with ﬁnding houses. This included, for example, a University car which took a prospective new professor to see various suitable houses. Apart from the question of acquiring more property it seems to me that the ﬂats at present occupied by members of staﬀ would serve their purpose more adequately if the tenants were given to understand that they were expected to make way for new comers as soon as they can reasonably ﬁnd more permanent accommodation. Even without imposing any ﬁxed time limit I believe that an occasional reminder would make some of these ﬂats available more frequently than is the case now. In addition I would suggest that some machinery be set up by which the University would enquire about the housing needs and other problems of new staﬀ, particularly in diﬃcult cases, such as men with large families and low salaries, or in the case of staﬀ coming directly from abroad. In most cases they are now receiving help from colleagues in the same or related departments, but now and again this fails because the closest colleagues of a new member of staﬀ may themselves be new comers or may be less knowledgeable in problems of real estate than in the academic subjects. From my own experience in advising new comers I know that a little local knowledge may save the new comer a great deal of time and may help to save him from serious mistakes. Yours sincerely, R.E. Peierls

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[575] Ed Salpeter to Rudolf Peierls Ithaca, 10.12.1952 Dear Rudi, Thanks for your comments on Irving’s variational wave functions.592 I haven’t yet done any more about the problem. I’m afraid I have another question: One of our graduate students, Stan Cohen, has started (as a Ph.D. thesis) to calculate all the corrections, except the Lamb Shift, to the binding energy of a K-electron in a very heavy atom (say, U). I have just heard a rumour that one of your students (Shirley Brenner I believe) is doing — or has done — the same or a similar problem. If that’s true I would be very interested in details so that we can try to reduce duplication to a minium. My future plans are now somewhat more deﬁnite than before: I had almost decided to take the Chair at Canberra, but was rather worried about committing myself to a more or less permanent job of responsibility. In the meantime it has turned out that Dyson is going to the Princeton Institute on a permanent basis next September and so I got the chance of staying at Cornell on an Associate Professorship. To cut a long story short we decided to stay at Cornell but to go to Canberra for about a year either next September or sometime in 1954. All this doesn’t necessarily mean that we’ll live out our lives sitting on the ﬂeshpots of America, but I think we’ll stay at Cornell at least for a number of years. We still would like very much to come to B’ham for a while in the not too distant future. Coming for a term or year would be nicest but I couldn’t get another leave of absence very soon after my leave for going to Canberra. Another possibility would be coming for a summer sometime (for which I don’t need a leave of absence). An earlier possibility would be to come for just a month or so on our way to or from Australia, but I don’t know whether I could arrange that yet (and the extra fare might be a bit steep for such a short stay). An added complication is that Mika is expecting a baby in June 1953 — but I hope something can be arranged in spite of these complications. With best regards to all from Mika & Ed Salpeter 592

Letter [572].

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P.S. E.A. Power of University College is thinking of coming to the States for a year. There might possibly be some Research Associateship at Cornell. I’m wondering whether you know him, if so we would be interested in your opinion of him.

[576] Rudolf Peierls to John Cockroft [Birmingham], 12.12.1952 (carbon copy) Dear Cockroft, The Birmingham Post this morning had a front line item reporting that Flowers was about to be appointed as the Chief Theoretical Physicist at A.E.R.E., as usual they forgot the word ‘theoretical’ half-way through and also in the headline, which makes him the Chief Physicist at Harwell and some other parts of the report are equally silly. They quote as their source the New York Times and the New York Herald Tribune. The item is somewhat embarrassing for me because they also quote me in a statement about Flowers,593 which came about because their reporter rang me to say they understood a report from the Ministry of Supply was about to be released and they wanted to collect background information, but they would hold it until the release was authorized by the Ministry. I warned the man speciﬁcally that I could not conﬁrm the story and that I advised him not to accept it as true, but I thought it was in order to tell him what I thought of Flowers. I am reporting this to you to point out that things like that seem to be happening frequently, because information seems to reach the newspapers long before a decision has been formally conﬁrmed and even longer before it is released to the press. The situation seems to me very bad for the relations between the Ministry and the Press, to put everybody into embarrassing situations and to result in the Press printing 593

Brian Hilton Flower, who had completed his Ph.D. at Birminham, became head of the theoretical division at AERE, holding this post until 1958.

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stories in a distorted way (when the oﬃcial release comes it is then stale news and they do not bother to give the correct information). I know, of course, perfectly well that these matters are not controlled from Harwell, but I thought I would draw your attention to this in case you are able to pass it on to the appropriate quarters in the Ministry for a more reasonable procedure. Yours sincerely, R.E. Peierls

[577] Hans Bethe to Rudolf Peierls Ithaca, 15.12.1952 Dear Rudy: I have the feeling that I have owed you a letter for quite a while. In particular, you asked me about an International Conference in Birmingham594 next fall. You may have decided about this long ago. If you haven’t I want to point out the existence of an International Conference in Japan in September 1953,595 which you probably have been invited to. I don’t know whether you want to go, but in any case, a considerable number of people possibly will go, and it may therefore not be a good idea to run a competition.∗ I probably shall not go, but I have not decided yet. An additional reason for writing you is that a very good graduate student of mine Stanley Cohen, wants very much to go to England after he ﬁnishes his Ph.D. He has applied for a Fulbright but it is of course not clear whether he will get it. If he gets it, he would like to come ∗ This

letter was held up by a secretarial confusion. In the meantime I have learnt that the conference is going to take place, and in July, so there won’t be any interference. 594

Rudolf Peierls was organising the second of two international conferences in Birmingham for the autumn of 1953. 595 International Conference on Theoretical Physics, Kyoto and Tokyo, September 1953.

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to you. Some time ago you told me that you might have fellowships or positions of your own available for good Ph.D.’s from Cornell. This one I can recommend wholeheartedly. What are the possibilities for him at Birmingham? Naturally, his going there would be dependent on your reaction to the other letter enclosed with this one, but supposing you were at Birmingham he would be very anxious to come. There is another question connected with the same man. He is working on a good and accurate theory of the energy levels of electrons in heavy atoms. After he had gone quite a way in this calculation, we heard a rumour that a student of yours was working on the same subject. I think this is not necessarily undesirable because a lot has to be done on this problem and two diﬀerent people may ﬁnd diﬀerent approaches to it. However, I think you should know that this is going on and maybe the two people concerned should exchange their wisdom. We are making considerable progress on the scattering of mesons by nucleons. It is a straightforward application of pseudo-scalar coupling. The approximation made is that we consider only processes in which one additional meson is produced in the ﬁeld, or a nucleon pair, or both. We hope this is a good approximation but we have no proof for that. Apart from this approximation the problem is treated exactly, using a method similar to Tamm and Dancoﬀ.596 We can reproduce the essential features of the phase shifts of the important partial waves as measured by Fermi, et al. The only major discrepancy is for the S state of isotopic spin 1/2. We are only at the beginning of these calculations, so that much of it can still be wrong, and we have neither quantitative results nor a consistent theory. But it is very interesting and exciting. Hoping to hear from you soon, Yours sincerely, Hans Merry Xmas!

596

I. Tamm, ‘Relativistic interaction of elementary particles’, J. Phys. (USSR) 9, 449–60 (1945); S.M. Dancoﬀ, ‘Non-Adiabatic Meson Theory of Nuclear Forces’, Phys. Rev. 78, 382–85 (1950).

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[578] Hans Bethe to Rudolf Peierls Ithaca, 15.12.1952 Dear Rudy: This is to ask you whether it would be possible for you to come here to Cornell as a Visiting Professor for one year, namely the academic year 1953–54. Unfortunately, we are losing Dyson to the Institute of Advanced Studies. During his ﬁrst year here, he had the feeling that he did not work very eﬀectively; others did not. Particularly, during the summer he accepted some work which did not satisfy him. This fall he is working with very great eﬃciency on the scattering of mesons by nucleons; in fact we are all working with him.597 However, before this creative period started, he had come to the conclusion that a University with all its graduate students, examinations and other diversions would not permit him to devote his full energy to his work. He therefore asked Oppenheimer whether the standing invitation he had to the Institute could be converted into a permanent appointment. Oppie of course took up this suggestions most eagerly and made him an oﬀer which also ﬁnancially exceeds anything that Cornell University can match. We are very sorry to lose him, but ﬁnd it impossible to prevent it. We have oﬀered Ed Salpeter an Associate Professorship to take Dyson’s place at least as far as the teaching is concerned. Ed has accepted this position in preference to the Chair of Theoretical Physics at Canberra. However, he wants to visit Australia for one year and, for personal reasons, he would prefer this to be the ﬁrst year of his appointment, that is the next academic year. Oliphant has already oﬀered him to come to Canberra for one year as he wants to, but the exact time has not been settled yet. Salpeter has written to him, asking whether next year will be alright. Cornell University has agreed to give him a leave during his ﬁrst year [if] he can make his arrangement with Oliphant. 597

See letter [577]. A joint paper was published in 1954. F.J. Dyson, M. Ross, E.E. Salpeter, S.S. Schweber, M.K. Sundaresan, W.M. Visscher, and H.A. Bethe, ‘MesonNucleon Scattering in the Tamm-Dancoﬀ Approximation’, Phys. Rev. 95, 1644–58 (1954).

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This leaves us minus a professor of theoretical physics for this coming year. At the same time, it gives us an opportunity which especially Wilson and I have been seeking for quite a while. We have wanted for a long time to invite you to come here for a considerable period. The University has agreed to my approaching you on this matter. We can oﬀer you for the academic year a salary of $10,000. The University starts on September 21, 1953 and ends on June 8, 1954. I do not know, of course, whether you can get away from Birmingham for this length of time. However, I thought that perhaps it could be arranged if you started this long ahead of time. If you could come, all of us would be delighted. I am sure you would want to bring your family, and I am sure that suitable living quarters could be found. You would have to teach presumably one course each semester, 3 hours a week. You could choose among the set of courses ranging from three courses in classical physics through a year-course in quantum mechanics to some more advanced courses like nuclear theory. The other courses will be given by Morrison598 and myself. As you know, there is a lot of experimental work going on in the Nuclear Laboratory and I am sure you will ﬁnd the contact with this work interesting. You may have heard that Wilson is building a new synchrotron which is to give 1 to 1.5 Bev with a small amount of iron. We hope this will be working next summer so that the coming academic year may be a particularly interesting time. In addition, we are doing a lot of theoretical work and we hope, with Dyson’s help to bring meson theory into a shape such that it can actually be applied to the calculation of speciﬁc processes. This also ought to be in full swing by next fall. There are always a considerable number of young men who have taken their Ph.D.’s at other Universities and who come here with some kind of fellowship. This year we have three such people from the United States, plus a man from Turkey. In addition, we have three or four Research Associates who are paid by the Laboratory. There is a con598

Philip Morrison (1915–2005), obtained his Ph.D. from Berkeley in 1940. After his wartime work on the Manhattan Project, he worked at San Francisco State University, University of Illinois, Cornell University and M.I.T.

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siderable number of graduate students, some of whom are doing their theses in theoretical physics. Altogether, this makes quite a stimulating group. The group is usually quite international; for next year we expect to have a Frenchman, an Egyptian and presumably one or two Englishmen, and possibly an Austrian or a Japanese. I hope very much that all this will sound attractive enough for you to consider coming here. If you decide to do so, you would make us very happy. Especially I would like very much the idea of repeating the times of Manchester, 1933. Please let me know what you think of it. Yours sincerely, Hans [579] Rudolf Peierls to Hans Bethe [Birmingham], 16.12.1952 (carbon copy) Dear Hans, I am writing once again about a further possible link in the chain between Birmingham and Cornell. This time it is about R.D. Dalitz, who will be writing to you saying that he is applying for a Commonwealth Fund Grant and asking whether you are prepared to have him if he gets the award and also what the possibilities are of a Research Fellowship, or similar post at Cornell. As regards the ﬁrst part of the question I shall eat my hat if you do not say that you will be glad to have him, but as regards the second part you might like to know more about him. Firstly you met Dalitz when you were here last and I think we had some quite lengthy discussions with him, but I do not know how much detail you remember. Then he is, of course, also well known to Dyson and you should be able to ﬁnd out what Dyson thinks of him. As far as my own view goes I have an enormous respect for Dalitz. He is good at ﬁeld theory, for example when he worried about the internal pair creation in the Oxygen 16 decay, the papers by Feynman were quite new, and when he found that those would be useful for him he learnt the drill in a month or two and produced a reasonable answer. He knows

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a lot about nuclear physics, for example both the shell model experts here like Flowers, and the experimentalists, made a habit of consulting him frequently, much to their beneﬁt, but somewhat to the detriment of Dalitz’s own research output. He is good in talking to experimentalists and has constructive ideas, for example he realised that the pairs found at Bristol close to the stars represented the decay of a neutral meson into one pair and one photon, calculated this to show it gives the right magnitude and showed how this can be used to estimate the life-time. He volunteered last year to give a course on nuclear reactions, which was new to him then and he gave a ﬁrst rate course on this. As part of this he produced the elementary derivation of the Butler formula, which was noticed independently by several other people.599 It never occurred to him to write this up as a paper, this was just part of giving a good course of lectures. There was later some interest in the polarization of the protons, which on the Butler approximation is zero, and this came out more easily from Dalitz’s technique than any other and only then was I able to persuade him to write a paper on the subject. This year he is giving us a similar post-graduate course on meson physics, both for experimentalists and our own group. I had thought of giving this course myself to avoid overloading Dalitz, but he was keen on doing it and I am now glad that I let him, because he is doing a much better job that I could I have done.600 He is also a ﬁrst rate undergraduate teacher, though this will concern you less and one of his functions is to give our somewhat crazy courses in the Physical School, which as you may remember involves doing Maxwell’s theory in twelve lectures and wave mechanics in another twelve. The Physics Department have pressed me hard to keep Dalitz on this particular assignment, unless I can do it myself, because nobody else has done it so well. He is also running our Seminar and since he has taken it over I am for the ﬁrst time in the position of not having to worry about it, but just to ask who will be talking next week. 599 See letter R.H. Dalitz to Rudolf Peierls, 19.3.1952, Peierls Papers, Ms.Eng.misc.b205, C.75. 600 Dalitz later published research arising from his work on the τ -meson. R.H. Dalitz, ‘The Decay of the τ -Meson’, Proc. Phys. Soc. A66, 710–13 (1953).

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With all these activities and his sense of duty it is not surprising that he has not published as much as he might have, even though his output is quite creditable. Another reason for this is that he has set his heart on meson theory, where it is much harder to publish papers than, for example, on nuclei, where he could have got out a lot more. He has also very high standards and will not undertake a calculation by sloppy methods, perhaps he is even a bit too critical in this respect. One of the objects of trying to spend some time at Cornell would be just the hope of getting a more concrete programme in that direction. He has made himself so useful here that I am not at all happy at the thought of being without him, but of course it [. . . ]601

[580] Rudolf Peierls to Ed Salpeter Birmingham, 18.12.1952 (carbon copy) Dear Ed, Thank you for your very interesting letter.602 On the ﬁrst point you will have had the letter from Brown who explains in detail what we have done about it and I think the conclusion is that this is well in hand and is hardly worth pursuing further (it turns out in the end to be so simple that it would in any case not be the subject of a Ph.D. thesis) unless, of course, one either wants to get a still higher accuracy, which would be very diﬃcult or else wants to put more eﬀorts into dotting all the i’s and crossing all the t’s. We are quite happy about the approximations that Miss Brenner has made, with the possible exception of an estimate of certain second order corrections, which we are discussing at the moment. What pleases us particularly is that I have invented a trick which should reduce the problem of calculating the Lamb Shift corrections 601 602

Last page missing from manuscript. Letter [575].

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for this case to quite manageable proportions. This arose because we wanted to see whether one could use electronic computing equipment for this purpose, but it now looks as if it might in fact be quite manageable to do it here and hardly worth putting on a machine. If this is successful, it would at the same time also give the answer to the problem of the scattering of gamma-rays by a heavy element in which we are still interested. However, this idea is only about a week old, and we evidently have to sort it out further. As regards your own plans, you will of course always be welcome here for a week, or a month, or a year, though in the latter case of course it depends on what we can do in the way of funds. I suppose I should now wait until you tell me a little more deﬁnitely when you are going to Australia. We have just sent out invitations for a conference to be held here in July along lines similar to the 1948 conference, but devoted to nuclear physics as such. We cannot pay fares for this, but it might be an excuse to get your fare paid by someone else. However, it does not sound as if, from your own domestic point of view, June would be a particularly good time. As regards Power,603 I do not know him well personally, I do know that both Gunn and Massey think very highly of him, but you will no doubt get their opinions directly. My only direct contact with him was that I interviewed him for a job at Harwell, for which we would have taken him, if he had not preferred to go to University College, and I was his examiner for the Ph.D. which at Glasgow involves no oral examination, so I only had to read his thesis. This was quite a good piece of work, though to my taste rather too strongly based on perturbation theory and coming out with rather strong statements for pseudo vector and against pseudo scalar coupling, however, that is not much evidence either way. With kindest regards, Yours sincerely, R.E. Peierls 603

E.A. Power from University College London was contemplating embarking on research in the United States.

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[581] Freeman Dyson to Rudolf Peierls Ithaca, 26.12.1952 Dear Peierls, Thank you very much for your letter.604 I feel I owe you and your wife several letters. It is very good of Genia especially to continue taking so much interest in us. We all send our warmest good wishes for the new year to you and the whole department. I hope you had as merry a Christmas as we had. Probably you will some time run into Perkins who was here for the Rochester Conference, and he will tell you in some detail what went on there, if you do not get this information already from the proceedings which this time will be printed and given a wide distribution.605 It was a good and enjoyable conference, not so much because of any speciﬁc new development, but because of a general atmosphere of progress and optimism. Now to answer your questions about our meson-nucleon scattering calculations. We have not renormalized anything, and we have not instigated the order of magnitude of the many terms which we have omitted from our calculations entirely. On the contrary, our aim has been simply to take all those terms in the exact ﬁeld theory which in the Dancoﬀ approximation remain ﬁnite and unambiguous, and forget the rest for the time being.606 Speciﬁcally, we have thrown away the terms describing the proton self-energy (also the vacuum self-energy) and the meson self-energy. It is fairly clear how these terms will be handled in a more accurate calculation, by carrying out the usual renormalization in a covariant way before going to the Dancoﬀ approximation, but we have not seriously attempted to do this. We have not done the P1/21/2 and the S1/2 state at all. 604

Letter could not be located. Proceedings of the Third Rochester Conference on High Energy Physics, New York: Interscience Publishers, 1953. 606 F.J. Dyson, ‘The Use of the Tamm-Dancoﬀ Method in Field Theory’, Phys. Rev. 90, 994 (1953). 605

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Our justiﬁcation for all this is that we have ﬁnite equations which we can go ahead and solve, which contain in a qualitatively correct way the theoretical relativistic properties of the meson and nucleon, and which seem to give a good qualitative understanding of many features of the experimental results. The important thing is that, by actually solving these equations, we have learned a great many elementary facts about the consequences of any similar set of equations. So it is now much easier to see what will be the consequences of including in the interaction some of the many terms which we have neglected. So far our main numerical eﬀorts have been concentrated on the P3/2 3/2 state which is the only one with strong attractive forces. Hans Bethe has derived for this the formula (quoting from memory) tan δ [tan δ]Born approx.

=

340 − E 200 − E

E= kinetic energy of meson in c. of mass system in MeV. This is at 2 2 a coupling constant G 4π = 14. Making G a little smaller will put the 607 resonance at a higher energy. I will be very glad to hear what you think of all this. All good wishes, Freeman Dyson I am sorry there is no chance of coming to the conference in July. I am teaching Summer School in Berkeley this summer.

607

See also F.J. Dyson, ‘Mass Renormalization with the Tamm-Dancoﬀ Method’, Phys. Rev. 91, 421–22 (1953).

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[582] Rudolf Peierls to Hans Bethe Birmingham, 5.1.1953 (carbon copy) Dear Hans, Thanks you for your letter of 15th December, which arrived a day or two ago and for your invitation.608 This is most tempting indeed, I would love to stay at Cornell for some time and even more to have a chance of working with you again at leisure. However, I do not think it can be done. My group here still ha[s] such a rapid turn over that I am a very important element in its continuity. If I went away for a year I would probably have to start from scratch when I returned. In any case it would not be fair on the other members of staﬀ here, who would have to deputize for me and whose chances of getting some research done would suﬀer the most because they would loose my help and because they would have to do my work instead. It would also be unreasonable to leave just when the synchrotron in the Physics Department here is nearing completion (it might in fact be working) so that the experimentalists are at last beginning to think about mesons rather than about engineering problems. On the more formal side I could not expect to get study leave from the university so soon after spending a term at Princeton. I could presumably get leave of absence without pay, provided I could assure the university that the work of the department could continue satisfactorily, but I am not sure this would work ﬁnancially. However, the major diﬃculty is that I feel I can’t leave the other people here in the lurch. This is particularly acute next year when presumably Dalitz will not be here, because his presence made a lot of diﬀerence during my absence in Princeton. I certainly would not want to bring any pressure on him to postpone his departure since I think he needs a change of scenery. With all this, much as I felt tempted by the invitation, I think I must not accept. 608

Letters [577–78].

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Of course the situation may change with time and if the possibility of such an invitation might arise again some time later I would be very happy to look at it again. If at the present you are likely to be somewhat shorthanded I think you might ﬁnd my suggestion of having Dalitz with you quite useful. He would certainly be quite willing to do some teaching and to help look after research students and the like, provided this is not on such a scale as to prevent his doing physics himself. I think you would also ﬁnd that he is a very good person to discuss things with. Once more many thanks and kindest regards, Yours sincerely, [Rudi]

[583] Rudolf Peierls to Hans Bethe Birmingham, 5.1.1953 (carbon copy) Dear Hans, In reply to your letter about Stanley Cohen,609 I would of course be very glad to have him if he can get a Fulbright grant. Does he want, at this stage, a formal letter saying so? On the question of a local grant, this is not quite to easy, our Fellowships here are limited in number and I do not know how many vacancies I will have next year, if any, since the plans of one of two people who are holding such Fellowships at the present are not yet decided. I also expect some fairly strong applicants and therefore one would have to make out a fairly good case for Cohen, if he were to have any chance. From what you say it seems as if he has not published anything yet and while this does not rule him out, it would certainly need a very ﬁrm supporting statement from you. When the time comes to advertize our Fellowships, which is likely to be in two or three months, I shall let you know and perhaps you would then be good enough to tell me your opinion about him explicitly. 609

Letter [577].

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As regards his problem, we had already heard about this from Salpeter and Gerry Brown, who is looking after this work, and has sent a summary to Salpeter. The numbers of course are still changing a little, because one or two corrections of interest have turned up, at the same time our conﬁdence in the terms already worked out is increasing and the really surprising part of the situation is how simple it all is in the end. However, this work is concerned only with the K-absorption edge and we are not at present proposing to look at other energy levels. The main outstanding uncertainly in the K-absorption edge is the contribution of Lamb-shift terms and we think we have got a method which will make the numerical computation of this term possible and will at the same time give the results for the scattering of gamma rays in the K-shell of a heavy element, which I believe are still of interest. I am now in touch with Hartree to see if this problem can be done on the Cambridge machine. Yours sincrerely, [Rudi]

[584] Rudolf Peierls to Wolfgang Pauli Birmingham, 20.1.1953 (carbon copy) Dear Pauli! Thank you for your letter.610 I am very sorry to hear that your wife was ill in India, I hope she has completely recovered and I also hope that you had some chance of seeing something of India. I had not written to you since I had not found the proof for the Jacobi identities. I knew that the proof had to be quite simple, but I somehow could not see it. However, I have got it now, and I enclose a rough draft of it. I would like to consider this a little longer because the argument is very abstract 610

Letter Wolfgang Pauli to Rudolf Peierls, 12.1.1953, Peierls Papers, Supp., C.238.

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and one has to watch out that one knows what the symbols mean, but I am reasonably convinced that it is in order. I would be glad to know what you think. Otherwise on the subject of non-local theories our main progress has been to ﬁnd a method by means of which one can regard the action principle which contains an inﬁnite time integration, as the limiting case of a modiﬁed action principle extending over a ﬁnite time interval only. At least for the case of non-interacting ﬁelds we can write this in such a form that the ﬁnite action principle has reasonable solutions and one can in fact prove that they are the complete set of solutions, so that one avoids the ambiguity of the mathematics, which previously troubled me, but I cannot say how this will work with interacting ﬁelds. We are also in the process of writing up a paper on the results we have so far obtained.611 This still leaves a number of diﬃculties unsolved, but we have discussed the equations so often and with so many people that it seems more satisfactory to put down in writing what we know. Yours sincerely R.E. Peierls Appendix Proof of the Jacobi Identity If the bracket symbols deﬁned in the previous paper612 can be identiﬁed as the Poisson brackets, they must satisfy the identity {A, {B, C}} + {B, {C, A, }} + {C, {A, B}} = 0

(1)

In the present note I want to verify that this is indeed a consequence of the deﬁnitions in a classical theory, i.e. apart from the order of factors. It is suﬃcient to prove (1) for the case in which A, B, C are the ﬁeld amplitudes themselves. 611

R. Peierls, ‘The Commutation laws of relativistic ﬁeld theory’, Proc. Roy. Soc. A 214, 143–57 (1952). 612 Refers to the draft paper on commutation laws.

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I use the notation of section 6 of the previous paper, i.e. a symbol φα represents the value of a ﬁeld amplitude at some given space time point. The action integral L is assumed to be a function of all these φα and a sum α stands for the integration over space-time as well as the summation over components and over the diﬀerent kinds of ﬁeld. I shall further shorten notation by writing Lα for ∂L/∂φα , and Dαβ φ for Dφαβ . Then (1) requires that −

α γ

−

−

γ β

α

α β Dγ

− Dβ

−

D D

D

D

D

β α

γ β

D

+Dγ Dαβ − Dγ

α

β γ Dα

γ

D

D

+Dβ Dγα − Dβ

−

D D

γ β

D D

Dα Dβγ − Dα

β α

α γ

(2)

= 0.

The ﬁeld equations are Lµ = 0

(3)

D

and νµ as well as Dµν satisfy the equation, (using the summation convention): (4a) Lσλ Dβλ + δσγ = 0 D

Lσλ

λ β

+ δσγ = 0.

(4b)

Now the deﬁnition of the operator D acting on any function of the ﬁeld variables is ∂f (5) Dµ f = Dµν ∂φν and to generate a term of the type occuring in (2) we apply this rule to f = Dβλ : ∂ Dλ . (6) Dµ Dβλ = Dµν ∂φν β Now, for this purpose Dβλ is deﬁned as that solution of (4a) for which Dβλ → 0,

tλ − tβ → −α.

(7)

We may therefore regard (4a) as an identity, and may diﬀerentiate it with respect to any φ, say φν : Lσλν Dβλ

+ Lσλ

∂Dβλ ∂φν

= 0.

(8)

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Multiply by Dµν : ∂ Dλ = 0. ∂φν β

To solve this equation for the quantity (6) multiply by D

σ γ

+ Lσλ

D

Lσλν Dµν Dβλ

σ ν γ Dµ

∂ Dλ = 0. ∂φν β

(9) D

Lσλν Dµν Dβλ + Lσλ Dµν

σ γ:

(10)

But from (4b) remembering that Lσλ is a second derivative, so that Lσλ = Lλσ

Lσλ

σ γ

= −δλγ

(12)

∂ Dλ = Lσλν Dµν Dβλ γ σ ∂φν β D

Dµν

D

we have

(11)

(13)

inserting in (6) and using the identity D

Dσγ =

σ γ

(14)

{paper 1, equation (6.8)}, we have Dα Dβγ = Lσλν Dαν Dβλ Dσγ .

(15)

D

Note. It would appear arbitrary that we used σγ as a factor obtaining (10) and that we might have used Dγσ instead, since we would obtain the corresponding reduction by means of (4a) instead of (4b). However, we would then have obtained, instead of (15) the expression Lσλν Dαν Dβλ Dγσ ,

(16)

where α, β, γ are summation variables. Now the factor Lσλν is of a limited range, i.e. it gives a large contribution only if tσ tλ tn u are not very diﬀerent. This, however, does not prevent all of them being very large and positive, and the other factors do not decrease as tσ ∼ tλ ∼ tσ → +α The expression (16) therefore contains an integral

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which is likely to diverge. This objection does not apply to (15) since the factor Dσγ will decrease as {cf(7)} tγ − tσ → ∞ (15) gives us the ﬁrst term of (2) and with an obvious interchange of suﬃxes also the ﬁrst term of the second and third line. The last term on each line is obtained by reversing the time order, i.e. interchanging upper and lower suﬃxes in the D functions of (15). For the second term on the ﬁrst line we proceed in the same way, but with Dβλ replaced by λβ in (6). Therefore we obtain: D

D

Dα

γ β

= Lσλν Dαν Dλβ Dσγ .

(17)

In this case the alternative calculation analogous to (16) is also meaningful and we ﬁnd also D

Dα

γ β

= Lσλν Dαν Dλβ Dγσ .

(18)

For the third term we again reverse the order of time compared to (17) or (18), and for other lines we interchange αβγ cyclically. Thus we ﬁnd for (2), using only the relations (15) and (17): Lσλν {Dαν Dβλ Dσγ − Dαν Dλβ Dσγ − Dνα Dβλ Dγσ + Dνα Dλβ Dγσ +Dβν Dλγ Dσα − Dβν Dλγ Dσα − Dνβ Dγλ Dασ − Dνβ Dγλ Dασ +Dγν Dαλ Dσβ − Dγν Dλα Dσβ − +Dνγ Dαλ Dβσ + Dνγ Dλα Dβσ }.

(19)

Here the suﬃxes σλ, ν may be interchanged in the bracket, since the factor outside is a third derivative, and therefore symmetric. It is then evident that the terms in (19) are opposite and equal in pairs. This establishes the Jacobi identity.

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[585] Wolfgang Pauli to Rudolf Peierls Z¨ urich, 23.1.1953 Dear Peierls! I have just received your letter with your proof of the Jacobi-identity which I read with great interest.613 There is indeed a peculiarity contained in it, which should explicitly be emphasized: In the equation Dµ f = Dµν

∂f ∂φν

(5)

∂f is only unambiguously deﬁned, if a given function of the the symbol ∂φ ν φν regardless whether or not the φν satisfy the ﬁeld equations Lµ = 0 ∂f (3).∗ If, on the other hand, f is only deﬁned for solutions of Lµ = 0, ∂φ ν µ µ is only deﬁned apart from an additional term +Lµν Λ (Λ Lagrangian multiplier). This would give rise, on the right side of (5), to the additional term (see (4a)!)

Dµν Lαν Λα = −δαµ Λα = −Λµ which is entirely arbitrary. It was therefore not obvious for me a priori whether it is possible to deﬁne unambiguously the quantity Dµ Dβλ [see equation (6)], which enters the Jacobi-identity (2). It is, after all, a certain trick, to use the “variational equations” Lσλ Dβλ + δσβ = 0

(4a)

independent of the validity of the ﬁeld equations Lµ = 0 for the ﬁelds which enter Lσλ and Dβλ : One proceeds to deﬁne second variations of ∗I

assume of course that L given as function(al) of the φν before the ﬁeld equations were derived at all. 613

Letter [584].

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the variational equations in cases, where the varied “orbit” does not fulﬁll the “equations of motion”. ∂D λ

In this way, one reaches a deﬁnition of ∂φνβ [equation (8)], assuming L (hence Lσλν ) to be known (deﬁned) also for ﬁelds, which do not satisfy Lµ = 0. All this I do not consider at all to be an objection. On the contrary it is necessary to use a deﬁnition of Dα Dγβ in order to give to the Jacobi-identity a meaning. As the deﬁnition (8) — which leads to (15) — is consistent, it is reasonable to apply it. But, independent of the Jacobi-identity, it seems to me important to emphasize, that according to your formalism ∂f /∂φν has only an unambiguous meaning if f is deﬁned as a function of the φ’s, even if the latter do not satisfy Lµ = 0. My wife is much better now. In India we saw the temples of the island of Elephanta and in Ellora, Ajanta and Aurangabad. But we did not see Agra, Madras and Mysore, what was planned, due to the illness of my wife. Hope to get your paper soon. I intend to tell what I know myself in Turin in March.614 All good wishes Yours W. Pauli [586] Wolfgang Pauli to Rudolf Peierls Z¨ urich, 24.1.1953 (1st letter) supplement to my letter from yesterday Dear Peierls! I just saw, that the ambiguity in the deﬁnitions of cancels in the ﬁnal result. Consider the Poisson-Bracket [f, φn u] = (Dµν − Dµν ) 614

See letter [573], note 291.

∂f . ∂φν

∂f ∂φν

and of Dµν ∂φ∂ ν Dβλ

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∂f The arbitrary additional term in ∂φ is equal Λα Lαν but Λα · Lαν (Dµν − ν ν µ ) = 0 The Poisson Bracket [f, φν ] is therefore well deﬁned, even if f is only deﬁned for φ’s satisfying Lα = 0. — The reason is, of course, that (Dµν − νµ ) satisﬁes the homogeneous variational equations, in contrast to Dm uν and m uν separately. In the same way, the equation

D

D

D

D

γ ν µ )Dβ

+ Lσλ (Dµν −

D

Lσλν (Dµν −

ν µ)

∂ Dλ = 0 ∂φν β

in entirely unambiguous, in contrast to your equation (9). And so is D

γ α )Dβ

= Lσλν (Dαν −

D

(Dα −

γ λ ν α )Dβ Dσ .

But this would mean to write the 3d term −Dνα Dβλ Dσγ instead of −Dνα Dσλ Dγσ as you wish to do. I write therefore µλ Lσλν Dµν Dβλ + Lσλ Dµ Dβλ = Lσλ Λβ

↓ arbitrary Lagrangian multiplier

D

Lσλν

ν λ µ Dβ

+ Lσλ

D

and

λ µ Dβ

D

Multiply the ﬁrst equation with use σ γ Lσλ = δγλ ,

σ γ

= Lσλ Λµλ. β

↓ same multiplier

(A)

(B)

the second with Dγσ and subtract, Dγσ Lσλ = δγλ ,

D

One gets D

Lσλν (Dαν Dβλ Dσγ − Dνα Dβλ Dγσ ) = (Dα −

γ α )Dβ .

This is your ﬁrst minus your third term, a diﬀerence which is certainly unambiguous. It is anyway a certain arbitrariness to use the equation (A), (B) separately with the same multiplier Λµλ β . Hence a certain ambiguity, overcome only by a suitable deﬁnition, is still in your proof, if you try to avoid the form −Dνα Dβλ Dσγ of the third term.

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In the moment, I think, that your attempts to deﬁne uniquely ∂ Dλ ∂φν β

and

D

Dµν

ν µ

∂ Dλ ∂φν β

separately, not only their diﬀerence, needs a further study. Yours W. Pauli [587] Wolfgang Pauli to Rudolf Peierls Z¨ urich, 24.1.1953 [2nd letter] Dear Peierls! I hope that this is now my last addendum: I do not see any diﬃculty any longer with the proof of the Jacobi-identity, if this proof is arranged only slightly diﬀerently. Dβλ can be considered as only deﬁned for such ﬁelds which are solutions of Lµ = 0. Instead of diﬀerentiating Lσλ Dβλ + δσδ = 0

(4a)

with respect to φν I propose to replace φν by φν + λµ (Dµν − Dµν ) which is still a solution of Lµ = 0. Deﬁning ∂ (Dµ − Dµ )Dβλ ≡ − µ Dβλ ∂λ µ and diﬀerentiating (4a) with respect to λ one gets then Lσλν (Dµν − Dµν )Dβλ + Lσλ (Dµ − Dµ )Dβλ = 0 instead of your (9). Multiplying with Dγσ and proceeding as you one gets (Dα − Dα )Dβγ = Lσλν (Dαν Dβλ Dσγ − Dνα Dβλ Dσγ ) instead of (15).

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(There is no convergence diﬃculty as there is always at least one of the J indices σλν below and at least one above.) Changing in the last relation the time order and adding one gets for the Jacoby-identity (2) the form (slightly diﬀerently from your (19)). In the second and third term Dγσ and Dσγ are transposed compared with your (19) Lσλν {Dαν Dβλ Dσγ − Dαν Dλβ Dγσ − Dνα Dβλ Dσγ − Dνα Dλβ Dγσ ) + Dβν Dγλ Dσα − Dβν Dλγ Dασ − Dνβ Dγλ Dσα − Dνβ Dλγ Dασ + Dγν Dαλ Dσβ − Dγν Dλα Dβσ − Dνγ Dαλ Dβσ + Dνγ Dλα Dβσ } which of course cancels also due to the symmetry of Lσλν . I think that settles this case now. One shall not deﬁne and use more than it is really necessary; nobody needs to know what Dβλ is for ﬁelds with Lµ = 0! Yours sincerely, W. Pauli

[588] Rudolf Peierls to Wolfgang Pauli Birmingham, 13.2.1953 (carbon copy) Dear Pauli! Thank you for your dramatic sequence of letters615 which were very interesting. I must say that on considering my proof further I see no objection at all in regarding the ﬁrst order D-quantities as deﬁned even for ﬁelds which do not satisfy the ﬁeld equations. If they don’t then they cannot be real ﬁelds and the variation equations for D do not have the meaning of proper variation equations, but they are still perfectly valid mathematical relations and if we ﬁnd it convenient to use them in intermediate steps, why not? Of course, your method of proceeding is in order, too, and it is largely a matter of taste which one prefers. 615

Letters [585–87].

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I am now really interested in where we go from here. One questions to which you seem to know the answer, but on which I am not quite clear is: having now established the Jacoby identities, how much of the standard theory using Poisson brackets, is at our disposal and how can we prove it? Of course a much more interesting question is what do we do about the real case where the order of the factors matters? I have an invitation from Wataghin616 to lecture in Turin while you are there.617 I accepted with preasure in principle and wrote about dates, but meanwhile I have had a very bad bout of ﬂu and am still in bed, so I am not quite sure that I shall be able to travel. But it would be nice to be able to discuss some of these problems directly. With kindest regards, Yours sincerely, R.E. Peierls [589] Wolfgang Pauli to Rudolf Peierls [Z¨ urich], 17.2.1953 Dear Peierls! Many thanks for your letter.618 If you regard the ﬁrst order quantities as deﬁned even for ﬁelds, which do not satisfy the ﬁeld equations, it is arbitrary to start either with Lσλ Dβλ + δσβ = 0 as you so — or with

λ Lσλ Dβλ + δσβ + Λσβ = 0.

↓ arbitrary

616

Gleb Wataghin (1899–1986) Russian-Italian physicist who had worked in S˜ ao Paulo from 1934 until his return to Turin where he built a centre of theoretical physics after the war. 617 Peierls had agreed to lecture at the Turin conference on non-local ﬁeld theories which took place between 9 and 14 March 2004. 618 Letter [588].

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I do not see any reason to exclude the latter equation, which, however, gives something diﬀerent than the former, if diﬀerentiated with respect to φν . I thought it worth while to check, that this ambiguity has no inﬂuence on the result. I wrote down everything I know on energy-integrals, Poisson brackets etc. as a pre-publication manuscript, from which you will receive a copy very soon.619 I may publish it after the Turin lectures, after I shall know the reaction of you and some others. The draw back is the solution for the “initial-value-problem” for which I do not see yet any other possibility than the development in power series of the coupling constant. I hope very much, that you will be able to travel to Turin and that your ﬂu will be over in time. I proposed to Wataghin for my stay there March 8 till 15. Hoping to see you soon yours sincerely, W. Pauli

[590] Ed Salpeter to Rudolf Peierls Ithaca, 23.2.1953 Dear Rudi, I should apologize for not having answered your last letter620 and the invitation to the B[irming]ham Conference sooner. My main excuse is that I wanted to hear from Oliphant about our visit to Canberra before I wrote you. Since M.L.O. has been acting only as a sink but not a source for correspondence I’m writing anyway: I would of course love to be able to come to the July Conference, but Mika’s scheduled multiplication this summer unfortunately makes this impossible. As you can see from the above paragraph my Australian 619

Prepublication manuscript of his Turin lecture, later published as W. Pauli, ‘On the Hamiltonian structure of non local ﬁeld theories’, Nuovo Cimento 10, 648–67 (1953). 620 Letter [580].

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plans are still awfully vague. I think there is still a possibility that we might go to Canberra for a year in September but it’s getting a bit late. In any case I think there probably wouldn’t be time for us to go via England this summer. But if we should go to Australia in Sept. 1953 we might be able to return via England, may be early July 1954. I presume you won’t know for quite a while yet what your movements in Summer 1954 might be? In any case I’ll let you know when I know if, when and how we’re going to Australia. You mentioned in your last letter that you had hopes of calculating the Lamb Shift in heavy elements. If you have any preprints or something of that sort yet, we’d be very interested. I believe Julian Mack at Wisconsin621 is busy getting X-ray levels in heavy elements even more accurately than so far. So we thought it might be worthwhile for Stan Cohen to see how accurately he can calculate everything, except the Lamb Shift. At the moment, his idea is to calculate only K − L shell energy diﬀerences (exptg. this is probably still more reliable than ionization potentials). The diﬃculties in his calculations would then be somewhat diﬀerent from Miss Brenner’s, but if you have any preprints of her work, we’d be very grateful. There are some moves afoot to reprint Dyson’s Electrodynamics Notes (which are out of print at the moment), so if any of your students need some, we might have some again in a month or two. Greetings to All, Ed

621

Julian Ellis Mack (1903–1966), had obtained his Ph.D. from the University of Michigan in 1927; after research at the Universities of Michigan and Minnesota, he moved to Wisconsin where he eventually became professor of physics.

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[591] Wolfgang Pauli to Rudolf Peierls Z¨ urich, 17.3.1953 Dear Peierls! As soon as I came back, I found here a letter of Møller and Kristensen about the convergence questions, though — it seems to me — with a very negative result.622 They say “As regards the question of convergence we now agree with the general statement of Claude Bloch that, in order to be sure to obtain convergence to any power in g, one has to choose a form factor in momentum space G(l(1) l(3) ),∗ which vanishes whenever one of the (1) (3) (1) (3) vectors lµ , lµ or lµ + lµ is space-like.” They show that the matrix-elements between two states a, b of the operators occuring in the ﬁeld-equations are for instance of the form β Iab = G(Pµ2 , Kµ2 , Pµ Kµ )fab (p(a) + p(b) , P, K) · d4 K where

1 (3) (l − l(1) ) 2 and show that this is in general divergent unless G vanishes for all (1) (3) space-like P ’s. (For space-like lµ or lµ other matrix elements give analogous results.) (fab in general does not vanish for large values of any components of K.) They add, that their calculations of last summer, which gave convergence on fourth order were formally correct, but only valid for very particular values of the length’s λ (occuring in their special form factor) and that they think now that this has no signiﬁcance and adjoin Bloch’s result. ∗ Deﬁned

P = l(1) + l(3) mK =

by F (x , x , x ) = (2π)−8 l(3) )x } · dl(1) dl(3) . 622

(1)

(3)

G(l(1) , l(3) )·exp i{lx +lx −(l(1) +

Letter Ch. Møller and P. Kristensen to Wolfgang Pauli, 12.3.1953, Pauli, Wissenschaftlicher Briefwechsel, IV/2, pp. 68–71.

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But if one passes with such form factors — they continue — to λ → 0 (k·k) ) in momentum space in one gets additional factors χ(k) = 12 (1 − |(k·k)| the Green-functions, which then in the x-space satisfy equations 1 1 1 ( − m2 )D(x − x ) = δ(x − x ) − 3 2 π [xx]2 They ﬁnally make the remark: “It is not obvious that the non-localised character of this function could be reconciled with causality requirements even for large space-time intervals. We would be very glad for comments on this point.” I am personally certain that these formfactors of the Bloch-type which make the theory convergent will give rise to a macroscopically wrong time order of processes (acausality). If I remember correctly you said already the same in Turin and I would be glad if you could write to me soon your opinion on this point. I hope to ﬁnish my paper this week. All good wishes Yours W. Pauli For me it looks like a cemetery for the lorentzinvariant formfactor theory in its present form. Do you have any idea how to proceed?

[592] Rudolf Peierls to Wolfgang Pauli Birmingham, 23.3.1953 (carbon copy) Dear Pauli! Thank you for your letter.623 I am very glad to know the discrepancy between Møller and Bloch has been cleared up. This agrees with conclusions we had reached here, namely Chr´etien looked at the meson self-energy for a space-like wave vector and saw 623

Letter [591].

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that in that case not only Møller’s proof breaks down that the answer is ﬁnite, but one can actually see that the answer diverges. Since these terms will also appear in the second-order nucleon self-energy it is not surprising that there must be trouble. I do not, however, agree that the requirement of zero form factor for space-like argument in momentum space leads to all the trouble which Møller indicates. I believe that this happens only if one chooses the particular form of the form factor which Møller wants to have, for which there is no strong reason. Whether one may work with a form factor which is restricted in this way depends on other questions. For example if one takes the electromagnetic case and uses the old McManus theory624 in which the form factor just appears in the form ¯ )γµ ψ(x )d4 x Aµ (x) = 4π F (x − x )ψ(x with the wave functions taken at the same point, then correspondence with the classical equations for slowly varying ﬁelds requires that the form factor be normalized to unity for zero momentum. If this is coupled with the condition that it vanishes for space-like argument, one obviously ends up with a discontinuous function and this will give the kind of trouble which Møller reports. On the other hand in the form of the equations which I discussed in Turin,625 the correspondence with the usual theory for long waves merely requires that the form is normalized to 1, when the argument is time like and equal to m2 . This is obviously compatible with the form factor vanishing for space-like argument and it is possible at the same time to have any number of derivatives of the form factor in momentum space bounded (but not all derivatives) so that I think such a form factor would have reasonable properties, but it is not of course clear that in our form of the theory one would wish it to vanish for space-like argument at all. 624

See letter [396], note 80. These correspond with Peierls’ contribution to the Kyoto-conference published as R. Peierls, ‘Field theories with non-local interactions’, Kyoto-Tokyo-Konferenz, 24–39 (1953). 625

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Now in any case in the Møller-Kristensen theory I do not see that there is any normalization condition, since there is no classical limit for a meson ﬁeld about which any knowledge exists. I do not therefore think that one can jump to the conclusion that any choice of the form factor is prohibited, though I admit that a form factor which vanishes for space-like arguments sounds somewhat unreasonable and one would have to see what other trouble could arise from such a choice. I enclose a copy of a letter to Wataghin from which you will see that we are proposing to send a short paper on the properties of the form factors, which I think would be useful in connection with your paper.626 I shall of course send you a copy of is as soon as it is ready. Yours sincerely R.E. Peierls (handwritten comment by Pauli: This, however, does not settle yet the question of the time order of processes (causality) of macroscopic distances. I shall come back to it. Hope to hear from you again. Best regards, W. Pauli.)

[593] Rudolf Peierls to Nevill Mott Birmingham, 9.12.1953 (carbon copy) Dear Mott, Congratulations on your appointment.627 I had not heard about it yet, but I am exceedingly glad for Cambridge. How soon will you be moving? On the particular question of Scott. This is a most diﬃcult situation. You know him personally and I need not therefore stress how attractive, intelligent and generally educated a person he is. 626 Chr´etien and Peierls were about to publish their results in M. Chr´etien and R. Peierls, ‘Properties of form factors in non-local theories’, Nuovo Cimento 10, 668–76 (1953). 627 Nevill Mott had been appointed Cavendish Professor of Physics, an appointment he took up in 1954 and held until 1971.

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About his research. He was always interested in nuclear theory and before he took up his present post, he had a rather nice idea about explaining unsymmetric ﬁssion. I do not believe in fact that his explanation of this is right, but it was an interesting possibility, which had independently been suggested by Lise Meitner and he had followed it much further. However, since his appointment to his present job in which his particular assignment is to deal with nuclear theory, he does not seem to have got very much done. I saw one paper of his in which he tried to establish some semi-empirical rule in the shell model, but it was neither very convincing or constructive and I don’t think he has pursued it. I cannot remember whether this paper ever got published. Shortly after this he seems to have dropped nuclear physics and taken up some ﬁner points in atomic theory. What he has done about these problems seems quite competent, though not exciting. What has embarrassed me particularly is that at least two research students whom Scott was supposed to supervise on problems of nuclear theory, have come to the conclusion that they did not get very much help from him and have moved to Birmingham. One of these really blossomed out and has since done some ﬁrst rate work. The other one has just moved, but he has been put by Scott on some spectroscopic problem, which he solved alright, but was not very interested in and he seems greatly relieved now to be confronted with some proper nuclear problems. I do not think it would be fair to blame Scott completely for this situation, since, as you probably know the whole set up in Cambridge is not very satisfactory for theoretical research students. People seem scattered all over the place, there is no proper team work and I known of people spending years in Cambridge without ever discovering that they may have interests in common. But I had hoped that Scott might collect a few young people and get them interested in nuclear problems and this does not seem to have happened. Another thing that is evidently badly needed in Cambridge is to talk with the experimentalists about the interpretation of their work and the planning of new experiments. I have the impression that Scott has not been very much help in this respect, but no doubt you can ﬁnd this out more directly.

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As you see therefore I cannot give a very favourable opinion. I would like to stress that there might well be things that I have missed. For example he may well have had contacts in Cambridge with other people and that such contacts have led on or may lead to important and useful suggestions without actually publishing any papers on them. But merely I have not so far come across any evidence of this. There arises of course the important question of principle. To what extent one should over short periods make tenure of academic appointments dependent on the success of a man’s research work, but I am quite sure you are yourself well aware of this side of the problems. Yours sincerely, R.E. Peierls * 1 2 α s − 1 (1 − log 2) + 1α 2 π −

Total splitting

7 3

4α s2 π 2

1−

41 3 α + log 2 21 7 π

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8.

1954–1963:

Spreading the Seeds of the Birmingham Group

When Rudolf Peierls took up his Chair in Mathematical Physics at Birmingham, there was no theoretical physics to speak of. When he returned to his position from the US at the beginning of 1946, what little had been achieved in the pre-war years, had been put on hold between 1939 and 1945, and Peierls had to start virtually from scratch with his endeavour to create a viable centre of theoretical physics. By early 1954, his department had been ﬁrmly established on the international research and teaching landscape. After two international conferences in 1948 and 1953, after several years of successfully attracting some of the best research students and fellows, and after successful international exchanges both of ‘Prof’ himself and some of his staﬀ, Birmingham’s reputation had risen to a point where the recruitment of excellent staﬀ and students caused fewer headaches than in many other places.628 Among the young researchers joining Peierls’ department in the mid-1950s were Sam Edwards, who had completed his doctorate under Julian Schwinger at Princeton with work on the structure of the electron; Nina Byers, who came to Birmingham from Chicago, and the young South African Stanley Mandelstam. If it had been Peierls’ sabbatical at Princeton and the PrincetonBirmingham arrangements over Dyson’s research position, which had guaranteed an excellent ﬂow of information between Birmingham and the US in the early 1950s, later in the decade regular visits abroad of Peierls’ junior colleagues and exchanges arranged for advanced students and fellows facilitated a continuation of the information transfer in both directions. 628

In contrast, some universities in England and the US were struggling with recruitment and funding. See letters [599], [610].

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Dick Dalitz, who had joined Peierls’ group in 1949, and who had already made a name for himself in particle physics, spent two years in the US, mainly at Cornell and brieﬂy at Brookhaven and Princeton; his correspondence with ‘Prof’ demonstrates both the intensity of the latter’s involvement in his junior colleagues’ research work and research environments, as well as his interest in the success of their exchange visits. Dalitz had been working on various aspects of decay processes of the τ -meson629 and had hoped to make further progress in this ﬁeld at Cornell in 1953/4. But with Ed Salpeter on leave, he found the environment less conducive to progress than he had anticipated.630 However, despite this disappointment, it is evident that the opportunities arising from the presence of the 1 BeV synchrotron at Cornell and the possibilities of visits to other research centres in the US such as Brookhaven and Princeton proved beneﬁcial for Dalitz;631 but occasionally it required Prof’s advice to steer in the most eﬀective directions and to make the most of the opportunities which presented themselves.632 The Birmingham department itself was seen as an exceptional training ground for young scientists well beyond the United Kingdom. This is evident in the success of students and research fellows in securing interesting research and teaching positions throughout Europe and globally. 629

R.H. Dalitz, ‘On an Alternative Decay Process for the Neutral τ − Meson’, Proc. Phys. Soc. A64, 667–69 (1951); R.H. Dalitz, ‘On Polarized Particle Beams’, Proc. Phys. Soc. A65, 175–78 (1952); R.H. Dalitz, ‘Some Features of the Deuteron Stripping Process’, Proc. Phys. Soc. A65, 28–32 (1951); and R.H. Dalitz, ‘The Decay of the τ -Meson’, Proc. Phys. Soc. A66, 710–13 (1953). 630 Letters [594], [598]. 631 Letters [596], [602]. See also publications resulting from his research in the US: R.H. Dalitz, ‘Decay of τ Mesons of Known Charge’, Phys. Rev. 94, 1046–51 (1954); R.H. Dalitz, ‘Isotopic Spin Changes in τ and θ Decay’, Proc. Phys. Soc. A69, 527–40 (1954); R.H. Dalitz, ‘Isotopic Spin Changes in τ and θ Decay’, Proc. Phys. Soc. A69, 527–40 (1954); R.H. Dalitz, ‘Radiative τ -Meson Decay’, Phys. Rev. 99, 915–20 (1955); R.H. Dalitz and F.J. Dyson, ‘Renormalization in the New TammDancoﬀ Theory of Meson-Nucleon Scattering’, Phys. Rev. 99, 301–314 (1955); R.H. Dalitz, ‘The Sachs Exchange Moment’, Phys. Rev. 95, 799–800 (1954); R.H. Dalitz, ‘Charge Independence in Light Hyperfragments’, Phys. Rev. 99, 1475–77 (1955); M.H. Kalos and R.H. Dalitz, ‘Pion-Nucleon Scattering Calculations in the TammDancoﬀ Theory’, Phys. Rev. 100, 1515–22 (1955). 632 Letters [595], [598].

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Felix Bloch, on assuming the directorship at CERN, enquired about potential recruits for his establishment.633 Peierls’ reply gives a clear indication of the high calibre of some of his junior colleagues, Valatin, Feldman, Edwards, Swiatecki.634 Many of those who came to Birmingham as students, graduates or research fellows in the 1950s later ﬁlled lectureships and professorships around the globe: Dyson, Dalitz, Edwards, Brown, Byers, Flowers, Mandelstam, Bell, Matthews, Wilkinson, Lieb, Langer to name but a few. As a junior colleague commented in 1958 on what was generally known as the ‘sales campaign’ among students and staﬀ in Birmingham, it was one of the impressive features of Peierls’ leadership that he took an interest and played an active part in ensuring the success of his young colleagues.635 The rising numbers of staﬀ and students and their exceptionally high standard caused some logistic and administrative problems, too. As accommodation within the physics department was notoriously limited, huts had to be employed to deal with the shortage of space,636 and on one occasion, Peierls had to ask for permission to add a trailer in order to overcome the departmental space crisis.637 Even greater was the problem of ﬁnding recognition for the excellent research done in his department within the university. In an environment where promotion was often determined by long service and academic excellence was not necessarily seen as suﬃcient for rising through the ranks of the academic hierarchy, it was diﬃcult to retain staﬀ who were potentially attractive recruits to other universities. Two particularly pressing cases were Gerry Brown and Dick Dalitz. Both had joined the theoretical physics department around the same time, in 1949/50 and both, within a few years, had established themselves in their research ﬁelds internationally due to excellent research work. Similarly, both, in diﬀerent ways, had contributed immensely to the departmental life of Peierls’ group, in teaching undergraduates, graduates and in 633

Letter Letter 635 Letter 636 Letter 637 Letter 634

[603]. [604]. [657]. [684]. [622].

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taking on important administrative duties. With Peierls’ recommendation, Dalitz was promoted to a senior lectureship, but promotion to a professorship, which Peierls had hoped to secure shortly afterwards, came too late to convince Dalitz to remain at Birmingham, and he chose to move to a more attractive position in Chicago. A similar case arose when Paul Matthews negotiated a readership position with Imperial College, while his promotion to senior lecturer was still pending at Birmingham. In the case of Gerry Brown, Peierls hoped to be able to avoid a similar scenario of losing an excellent member of staﬀ largely because of the cumbersome administrative setup within the university. Brown had been put forward for promotion for senior lectureship in 1957, but had lost out to the then more senior colleague, Paul Matthews. By 1958, Brown’s international standing had increased to such a level that Peierls took the unusual step of putting him forward for promotion to a professorship, although promotion to senior lecturer level had not been ﬁnalised at that point.638 His initial enquiry to the dean of the faculty was met with some scepticism and the vice-chancellor replied indicating that Brown’s age (he was 31 at the time) and the fact that he was only a lecturer, would make the conferment of the title of professor diﬃcult, as would the fact that if ‘such a dramatic promotion were made the door would be opened to an embarrassing number of claims on behalf of other lecturers and readers in the university.’639 The reason given by the Vice Chancellor caused some consternation with Peierls, and he attempted to push Brown’s case further, not only by dismissing these arguments, but also by pointing to Brown’s academic brilliance, the more enlightened attitude of institutions such as the ETH Zurich, Harwell and other well-respected research establishments which did not consider young age as an obstacle to high achievement (and had fared very well in not doing so), and by indicating the likely eﬀect of a lack of recognition of academic excellence on Birmingham University in particular and the UK in general.640 638

Letter [647]. Letter [649]. 640 Letter [650]. 639

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More than two months after the initial enquiry, Brown ﬁnally received conﬁrmation of his promotion, not to professor or reader but to senior lecturer at the bottom of the scale641 which caused some indignation. However, later in the year, the university took the decision to promote him to reader, a step which made him ‘quite happy on the relative scale’,642 but which still meant that by moving away from Birmingham, Brown was likely to improve his position. And indeed, little over a year later he accepted a full professorship at NORDITA.643 Among the young researchers who joined the theoretical physics group in 1956 was Nina Byers, an American student who had completed her Ph.D. at Chicago under Wentzel. Even Pauli despite his notorious scepticism about female theoretical physicists had described her as a ‘very clever girl’.644 She was another ‘political refugee’ from the US who had been oﬀered a position at Washington, but objected to signing the required loyalty oath. Peierls, himself married to a female physicist and political refugee, had no objections to taking Nina Byers on, provided she compared favourably with other applicants for the fellowship on oﬀer. His judgement proved right, because not only did she become a valuable member of his group during her two years at Birmingham; she later moved on to Stanford and UCLA where she eventually became professor of physics. Vivid contacts to colleagues abroad and regular international travel made ‘Prof’ more aware than many of his colleagues that standing still in a fast-moving discipline such as physics, was tantamount to lagging behind. As he wrote self-critically to Freeman Dyson, what he had brought back from his trip to the Rochester Conference in 1954 was ‘the knowledge that we have been out of touch with what goes on in several important ﬁelds and we must try to catch up. This is in part because we have not read enough and in part because we have not kept up the correspondence with other people suﬃciently.’645 641

Letter Letter 643 Letter 644 Letter 645 Letter 642

[656]. [660]. [674]. [646]. [606].

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He exchanged views with some of his British colleagues, who — like him — felt that the UK was losing ground to other countries, in particular to the US,646 and he took advice from his Birmingham colleagues who were spending time in the US647 as well as colleagues who had chosen the United States as their work base, such as Freeman Dyson. In his correspondence with Dyson in particular, Peierls tried to gauge what the most promising steps would be to stop the brain drain to the US and indeed, how to encourage American scientists to consider working in the UK.648 But his concern was not only with the more advanced students. Peierls also devoted time to the consideration of undergraduate teaching in its diﬀerent facets. As external examiner to several other institutions and through correspondence with his own department’s external examiners,649 Peierls developed an acute sense of which teaching set ups were successful, and which courses produced the best understanding among students of his discipline and also what research facilities were needed to guarantee the scientiﬁc progress necessary to back up university teaching. He was happy to discuss his own experiences with other colleagues,650 and he was equally keen to make the scientists’ voice heard among the political decision makers, as his letter to Selwyn Lloyd at the Treasury demonstrated. In this he lobbied for better government funding of science in general and the National Institute for Research in Nuclear Science in particular.651 If Rudolf Peierls felt strongly on an issue, he was prepared to make his views known irrespective of whether this would cause diﬃculties for himself. One such example was the political rat-race that his friend Robert Oppenheimer found himself facing in the 1950s. In 1953, Oppenheimer had been suspended from the General Advisory Committee of the Atomic Energy Commission, which he had chaired since 1947, as 646

See letters [612], [618]. Letter [613]. 648 Letters [559], [581]. 649 See Peierls Papers, Ms.Eng.misc.b199, B.17, B.20. 650 See e.g. letter [641]. 651 Letter [692]. See also letter [618] to Cockcroft about university research facilities. 647

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concerns had been expressed about his loyalty and reliability, and his security clearance had been withdrawn. Oppenheimer appealed against this decision, and between April and June 1954 hearings were held to determine whether his clearance should be restored. The commission decided against a restoration. However, Oppenheimer continued to speak out on nuclear physics issues, and although he was never oﬃcially rehabilitated, in 1963 he received the Enrico Fermi Award, a U.S. government presidential award honouring scientists of international stature for their life-time achievement in the development, use, or production of energy. This served as a measure of reconciliation for what many perceived to be a grave injustice done to Oppenheimer. Peierls tirelessly spoke out in support of Robert Oppenheimer, and his letters to ‘Oppie’ are evidence of the deeply-felt indignation at the attacks launched against his friend. Being well aware of the reluctance of many to speak up for what is right and reject what is wrong, he expressed his hope that ‘[your] many friends in America will have the wisdom and the courage to give you active support’.652 Peierls himself had his share of ‘security troubles’.653 His contacts to left-wing colleagues, his friendship with people of communist persuasion, his marriage to a Russian, his close friendship with Klaus Fuchs, all led to him being viewed with a degree of suspicion by many. When he applied for a visa to attend a conference in the US, his application met with a long delay, as did his paperwork in connection with his sabbatical at Princeton in early 1952.654 In 1957 Peierls, who at the time was acting as a consultant for the AERE at Harwell, had his security clearance revoked at the request of the American authorities. Disappointed with the action of the Harwell authorities over this matter, Peierls resigned from his consultancy. Even before this episode, Peierls had been challenged by William Penney, then on the board of the United Kingdom Atomic Energy Authority, about his contact to Russian colleagues and in particular his intention of participating in a conference in Moscow. In a letter in 1956, Peierls expressed his conviction of the sacrosanctity of 652

Letter [597]. See Peierls, Bird of Passage, chapter 14. 654 Letter [529]. See also Peierls, Bird of Passage, p. 322. 653

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the ‘freedom of scientiﬁc enquiry, the freedom of exchange of scientiﬁc information, and of objective discussion with any scientist, regardless of person, nationality, or position as long as these do not interfere with his approach to scientiﬁc fact or argument’, a principle which was subject only to ‘the overriding requirement of national security.’655 As Peierls had already made clear in his memorandum on the lessons of the Fuchs case,656 he felt strongly that the victory of the liberal democratic system could only be achieved by open competition with other regimes and political systems. In his view, it was essential not to risk personal freedom in an endeavour to silence non-democratic voices, be they communist or in other ways totalitarian. In 1956, Peierls did attend an international conference in Moscow. There had been many signs that after Stalin’s death in 1953 and with the ascension of Khrushchev in the mid 1950s, contacts between Russian and Western scientists were promoted oﬃcially in the Soviet Union. Landau had been permitted to contribute to the Festschrift on the occasion of Bohr’s 70th birthday, Russian scientists were no longer prevented from publishing in English-language journals, and some were allowed to participate in Western conferences.657 Peierls welcomed the opportunity presented by the Moscow conference to re-engage in dialogue with Russian science658 and this gave him also the chance to renew his contacts with many old friends, above all with Lev Landau.659 The more liberal ﬂow of information from Russia brought the West into contact with Landau’s work, and his views on renormalized quantum electrodynamics was discussed widely among Peierls and some of his colleagues. Peierls engaged in an exchange with his old teacher allen, Pauli,660 who himself had discussed the topic with Gunnar K¨ Werner Heisenberg, Vicki Weisskopf.661 655

Letter [628]. Item [500]. 657 See Letter Wolfgang Pauli to Oskar Klein, 1.3.1955, Pauli, Wissenschaftlicher Briefwechsel, IV/III, p. 131. 658 International Conference on High Energy Physics in Moscow between 14 and 22 May 1956. 659 Letters [624], [640]. 660 Letters [614–616]. 661 See correspondence between Pauli, K¨ allen, Heisenberg, Weisskopf in Pauli, 656

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The contacts with Landau facilitated the ﬁrst English edition of Landau’s and Lifshitz’ seminal Course of Theoretical Physics, a set of textbooks which had only been available in Russian and which was to become one of the standard works of teaching and reference for generations of physics to come.662 Peierls clearly appreciated the fact that the restrictions to scientiﬁc exchange with Russian colleagues and friends were slowly lifted, and he attempted to encourage an appreciation in the west of the work done by Russian physicists. He asked Niels Bohr to use his reputation and standing in Russia to help Lev Landau travel to the West,663 and it was doubtless on his recommendation that Birmingham University invited him to accept an honorary degree in 1958.664 In 1961, Rudolf Peierls was interviewed by a journalist in preparation of a proﬁle to be published in the New Scientist. On reading the draft, Genia Peierls decided to write her own proﬁle and sent it on to the journalist in question. The honest and insightful letter gives an accurate description of ‘Prof’, and many of the characteristics have since become common currency among those interested in the history of 20th century theoretical physics. Most signiﬁcantly of all, perhaps, was Genia’s diﬀerentiation of scientists as either golfer or tennis player. The former, with Dirac being the stereotypical example, work by themselves without partners, collaborators or many students; the latter, and among those Genia named her husband, needed a partner to bounce ideas oﬀ and push each other to better performance.665 By the 1960s, Peierls’ impact through teaching and collaboration with younger colleagues outweighed the contributions he made independently. Also, his focus was shifting to political work and publications

Wissenschaftlicher Briefwechsel, vol. IV/III, May–August 1955. See also letter Pauli to Abrikosov, Khalatnikov, and Pomeranchuk, Pauli, Wissenschaftlicher Briefwechsel, vol. IV/III, pp. 322–29. 662 Lev Landau and E.M. Lifshitz had written a series of textbooks on theoretical physics, the English translation of which was subsequently published by Pergamon Press. L.D. Landau and E.M. Lifshitz, Course of Theoretical Physics, 10 vols., Oxford: Pergamon Press. 663 Letter [680]. 664 Letter [653]. 665 Letter [684].

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in the area of arms control. And, as some of the letters in this chapters show, he was also beginning to get involved in putting on record the history of nuclear weapons, a story that had been written largely by Americans in a political context which had no interest per se in explaining the role of British scientists in the eﬀorts to develop the atom bomb. Margaret Gowing, an economic historian who had worked under Keith Hancock on the civil history of the second world war, a mammoth 27-volume project, became historian and archivist to the UKAEA and researched the history of Britain and Atomic Energy, which led to a two-volume publication putting Britain’s research and development of nuclear energy into its political national and international context.666 Rudolf Peierls was happy to assist with her research, and the exchanges between the two in connection with Gowing’s work on Britain’s development of atomic energy667 was the beginning of a fruitful collaboration which later, on Gowing’s appointment to the Chair of history of science at Oxford, would continue with joint work on the history of quantum physics.668 Throughout the post-war decades, Peierls had been approached, on many occasions, about taking up chairs in other universities, both in Britain and abroad. Genia Peierls, in her proﬁle of ‘Prof’ explained some of the reasons for his commitment to Birmingham; he rejected offers, among others, from Cambridge, Manchester, Oxford, London and Edinburgh, because he felt committed to Birmingham University, he largely liked the administrative set-up and he appreciated the research environment in his own department. In the early 1960s, however, after lengthy negotiations with Oxford University, he decided to take up the Wykeham Chair of Physics in succession of Willis Lamb. This step provided a two-folded challenge: a challenge for Peierls himself to create an equally successful school at Oxford with its more cumbersome structures, and a challenge for the Birmingham department under Peierls’ 666 M. Gowing, Britain and Atomic Energy. 1939–1945, London: Macmillan, 1964; M. Gowing, Independence and Deterrence. Britain and Atomic Energy. 1945–1952, London: Macmillan, 1974. 667 Letters [687], [702]. 668 See chapters 9 and 10.

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successor Tony Skyrme to keep up its high standing and international proﬁle. Neither Peierls at Oxford nor Skyrme at Birmingham, despite some positive developments, were entirely successful in their endeavours.

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[594] R.H. Dalitz to Rudolf Peierls Ithaca, 1.1.1954 Dear Professor Peierls, Many thanks for your interesting letter. It is good to hear that things are working out so well this year. Your developments on the SF function sound very interesting and I should very much appreciate a preprint if these become available. I have heard of some studies of the SF function over here which may be of interest to you if you have not already heard more than I — for example Lee (Columbia) has recently obtained an explicit expression for SF in neutral scalar (ﬁxed source) meson theory669 with the result SF (t) = e+imt e−g

2

d3 keiωt /ω 3

m the observed mass

It is interesting that this SF may be expanded in powers of g2 for all values of g2 . The power series expansion of SF (E) clearly has branch points at E − m = µ, 2µ, 3µ · · · as it should, but I have not yet seen whether it has any other singularities. I have also heard that Kallen, starting from some very general properties which the vacuum should have in any satisfactory theory, has concluded that the most general form allowable for SF in electrodynamics is ∞ ∞ 1 F (M )dM G(M )dM + + SF (p) = \p − m p p m M − ie − \ m M − ie + \ This seems very reasonable, though I do not understand the signiﬁcance of the last term. I have not seen the work myself but have heard about it fourth hand. I am looking forward to the Rochester conference three weeks hence — we are hoping that the rumour that you are being ﬂown over to attend this conference has a very solid foundation.670 669

T.D. Lee and D. Pines, ‘Interaction of Nonrelativistic Particle with a Scalar Field with Application to Slow Electrons in Polar Crystal’, Phys. Rev. 92, 883–89 (1953). 670 High Energy Nuclear Physics Proceedings of the Fourth Annual Rochester Conference, 25–27 January 1954, Rochester: University of Rochester Press, 1954.

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The attendance at the Chicago meeting was not very large but there were many interesting people there. I was particularly interested in the widespread and deep scepticism that exists in the U.S.A. concerning γ5 meson theory. Outside Cornell there appears to be relatively little work and no belief on this particular case — far more typical seem to be the semi-phenomenological ﬁxed source studies of the type made by Chew and collaborators.671 People seem to be very impressed by the existence of heavy mesons and their possible bearing on all problems in meson physics — especially now that the π − + P → V0 + θ ◦ seems so well established at Brookhaven, although the cross section for this process seems to be relatively small. However, there even seems to be considerable interest in developing unitary ﬁeld theories as a result.

One speciﬁc result reported at Chicago which may be of interest in Birmingham was an energy spectrum for pions emitted at 32◦ Lab from 2.3 Bev protons on Be (Lindenbaum & Yuan)672 — I have sketched it 671

Geoﬀrey F. Chew, Department of Physics, Illinois. See e.g. G.F. Chew, ‘Renormalization of Meson Theory with a Fixed Extended Source’, Phys. Rev. 94, 1748–54 (1954); G.F. Chew, ‘Method of Approximation fort the Meson-Nucleon Problem when the Interaction is Fixed and Extended’, Phys. Rev. 94, 1755–59 (1954); G.F. Chew, ‘Improved Calculation of the P -Wave Pion-Nucleon Scattering Phase Shifts in the Cut-Oﬀ Theory’, Phys. Rev. 95, 285–86 (1954). 672 Luke C.L. Yuan and S.J. Lindenbaum, ‘Energy Spectrum of Negative Pions Produced in Beryllium by 2.3-Bev Protons’, Phys. Rev. 93, 1431–32 (1954).

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on the reverse side. This was compared with rough calculation using Fermi’s statistical theory and it was concluded that the low-energy peak was probably due to 3π production.∗ There has been a certain amount of interest lately in general statements which may be made on the basis of ﬁeld theory for threshold matrix elements, in the limit when the meson mass approaches zero. You have probably seen the Kroll & Rudermann discussion for photoproduction673 (and which points out very neatly that Brueckner’s pair suppression argument does not hold for one case which can be rigorously calculated, namely the scattering of light by protons in the Thomson limit).674 Fubini675 spent a few hours in Princeton last week and reports that Goldberger says that for zero energy and µ/M = 0, he can obtain the scattering matrix for positive pions on protons exactly in the γs theory (!) — he says that the result indicates that the “eﬀective coupling constant” for this case is 0.6 rather than 10. I understand a preprint will be available in a week or so.676 It is of course very doubtful whether these theories are even approximately similar to the physical situation where µ/M = 1/6, because of the terms of type µ/M (log µ/M )n which occur in a power series expansion at least — besides in this approximation the zero energy scattering is isotopic spin independent which is certainly not the case experimentally. ∗ However,

Shutt677 has no cloud chamber evidence for 3π production in N-P collisions. Shutt ﬁnds nature 2π/π production i.e. (π − , π o ) + (π + , π − )/(π − ) to be 94+26/32 (Neutrons ∼ 1.75 BeV.) 673

Norman M. Kroll and Malvin A. Rudermann, ‘A Theorem on Photomeson Production near Threshold and the Suppression of Pairs in Pseudoscalar Meson Theory’, Phys. Rev. 93, 233–38 (1954). 674 K.A. Brueckner, M. Gell-Mann and M. Goldberger, ‘On the Damping of Virtual Nucleon-Pair Formation in Pseudoscalar Meson Theory’, Phys. Rev. 90, 476–78 (1953). 675 Sergio Fubini (1928–2005), taught at the Universities of Padua, Turin and at M.I.T. Between 1971 and 1980 he served as a member of the CERN directorate. 676 S. Deser, W.E. Thirring and M.L. Goldberger, ‘Low-Energy Limits and Renormalization in Meson Theory’, Phys. Rev. 94, 711–23 (1954). 677 Ralph Shutt (1913–2001), particle scientist at the Brookhaven National Laboratory from 1947 until 1993.

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I believe the Dyson lecture notes have now been sent on to Birmingham. If there are any diﬃculties about paying for these I could easily pay for them (at any rate next month, certainly) and have the recipients repay me in sterling. The payment for the copies is not urgent. You asked me to let you know about my plans for next Session about this time. We still feel very new here, and a second term in the U.S.A. would be of far greater value to me than this ﬁrst year here. This would also ease the problem of saving the funds to pay for our transportation here and back across the Atlantic. Hence I would be grateful if you could explore the possibility of extending my leave of absence for a second Session. I am still unclear what I shall be doing next year and I would appreciate any comments you may care to make on the possibilities. I have not yet asked Bethe concerning positions here next year (in fact I have not seen him for some weeks, partly because he went down with the cold, but I believe he will be back from Los Angeles within a fortnight now) but it is my impression that it is expected that I shall be here next year. The only question then arising is whether it would be wiser for me to move on and extend my contact with American physicists — this of course depends on many unpredictable factors. It seems clear that Cornell has reached an all-time low this year — next year must be an improvement (incidentally it was touch and go whether even Bethe was here this session — he was very seriously considering a permanent post at the Institute). The fact that it seems to take us a long time to settle in a new place provides an argument for staying in Cornell, though we have to seek new housing next June in any case. I am supervising several graduate students at present, and owing to the lack of senior people, about half my time is spent also discussing problems with the younger research people — this consolidates what I already know but is a slow way of learning. On the other hand I have been oﬀered a position in Chicago for next year — Gellmann and Goldberger are both very stimulating; I have not yet gone into details concerning this oﬀer, Chicago is not a pleasant place and housing a family is diﬃcult according to those here who have recently come from there. The Institute is another possibility — I had recently felt that I wanted to get myself established in some line of research before going there, but perhaps I am too sensitive about this. A quite attractive

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oﬀer from Messel678 has also suggested the possibility of spending a year in Australia — I imagine though that he will be wanting to settle his permanent staﬀ and would prefer to look further rather than have a transient occupy the position just for a year. One thing I plan to do is to enquire from Bethe as to the possibilities of working elsewhere during the summer months — Brookhaven is one possibility which comes to mind and which is essentially appropriate for many reasons. Had you heard that several examples of K-meson decay have now been observed which may be interpreted as the alternative mode of decay of the τ -meson? Rochester has two examples of star K π µ e; In both cases the π energy is between 13 and 14 Mev. Barrett from Syracuse was down here the other day and looking over his events, I noticed that he also has a similar event, giving a 4 Mev meson.679 Have you looked at the data on heavy meson capture stars — one interesting feature is that in the three cases in which a π-meson is ejected, it has energy in the region 25–30 Mev, I had wondered if this would come from a V0 -formed with low kinetic energy in the capture process, trapped in the capturing nucleus and later decaying — I ﬁnd this extremely plausible now that Brookhaven had established the pro duction process π − + P V0 + θ 0 . Though it is not what I am here for, I would like to work a little on this capture process — unfortunately I have not yet been able to interest any of the graduate students in the problem. With very good wishes to all in the department, and best wishes to your family for the New Year, Yours sincerely, R.H. Dalitz

678 679

Harry Messel (1922–), Professor of Physics, University of Sydney, 1952–1987. P. Barrett, ‘K-Meson and Hyperon Decays’, Phys. Rev. 94, 1328–30 (1954).

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[595] Rudolf Peierls to R.H. Dalitz [Birmingham], 11.1.1954 (carbon copy) Dear Dalitz, Thank you very much for your long and interesting letter.680 As regards the physics it is very amusing how parallel are the thoughts of people in diﬀerent places. The result of Lee which you quote is part of the equations contained in the note by Edwards an myself, which is just ﬁnished.681 We are sending a preprint oﬀ to you to-day. In the course of these discussions we have also formed the conjecture that what [. . . ]682 should look like and this agrees entirely with what Kallen says according to you. I think everybody would be agreed now that one should incorporate heavier particles into a complete description, but I still feel that if any equations containing only nucleons and ions can be useful at all they should have pseudo-scalar coupling and at any rate it pays to learn more about the mathematical techniques that are required to solve this case, because it seems most unlikely that the modiﬁcations of the theory brought in by heavier mesons would eliminate any of the present diﬃculties. Other progress from here. Davison has done a rather nice piece of work showing how to turn the Feynman ‘sum over histories’ into a respectable mathematical operation.683 Radicati and I are trying to demolish Gell-Mann’s hypothesis that particles of spin 12 can have isotopic spin, but I am not yet sure whether this can be done.684 680

Letter [594]. S.F. Edwards and R.E. Peierls, ‘Field equations in functional form’, Proc. Roy. Soc. Lond. A224, 24–33 (1954). 682 Missing in carbon copy. 683 Davison had used orthogonal function expansion in the representation of Feynman path integrals. B. Davison, ‘On Feynman’s “Integral over All Paths”’, Proc. Roy. Soc. A225, 252–63 (1954). 684 M. Gell-Mann, ‘Isotopic Spin and New Unstable Particles’, Phys. Rev. 92, 833–34 (1953). 681

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Turning now to personal problems. I am very sorry to hear that Cornell has been so unsatisfactory. I am sorry because I feel in a large manner responsible for your choice, but there seemed to have been quite a number of unpredictable factors in operation. As regards the question of where to go next year I feel rather reluctant to express a ﬁrm opinion. Firstly because what advice I gave before seems to have been in the wrong direction and also because by now you have much more up to date information about conditions in the various places than I have. Cornell has of course the advantage that there is no removal problem, as you say, and life is likely to brighten up a bit with the return of Salpeter, however it all depends on how much time Bethe is going to spend at Cornell and the only way to ﬁnd this out is to ask him. I think it would probably pay to discuss the whole problem very frankly with Bethe. He will not mind being told that you are not entirely happy at Cornell and why. I have a feeling that you are unduly intimidated by Princeton. As regards the physics there, you know of course Dyson and you can make up your mind yourself how much you could get out of working with him. I do not know who else is there or will be there next year. The great advantage of the Institute of course is that they are so used to having people there temporarily they have regular housing under their control and from the practical point of view there is probably less trouble involved in moving to Princeton than almost anywhere else (perhaps even less than ﬁnding a new place in Cornell). Against that the disadvantage of Princeton is the absence of experiments and this is rather a pity because one of the things you like doing and do so very well is to talk with experimentalists. From this point of view the question depends a great deal on the future of experimental work at Cornell. I imagine now they are at the machine building stage again, but the question is where are they likely to be next year. From this point of view there are great attractions in Chicago and Chicago probably combines to a rare degree contact with ﬁrst rate experimental work and theoretical groups with ﬁrst rate initiative, but against that of course there is the housing problem. To some extent this is a ﬁnancial problem. If they pay you well enough it might not be

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so bad, also there might be some lucky chance, for example to get the house of someone who has gone oﬀ for a year on a Fulbright grant or something. (It need not of course be a physicist). Another place which would give you experimental information straight from the horse’s mouth is of course Brookhaven, but I have no idea what sort of jobs they have available and whether any of them would be open to people who are not U.S. Citizens. While I say this I just remember that Yang is there now for a year unless he is actually sitting at Brookhaven with a grant from the Princeton Institute, this would seem to answer my question. However, you would be largely on your own as regards abstract theory, as far as I know, unless Yang remains there. On the whole, if the job exists, I cannot help feeling that this might be the most attractive possibility. Perhaps it may seem to you that this puts you more or less into the same position as you were at Bristol, but this was many years ago and I think now it would be very much easier for you. I am afraid this is not much in the way of deﬁnite advice, but I really know too little about the factors which are involved. On the formal side I shall now transmit to the Faculty your request for a further year’s leave of absence. I think we agreed originally that this would be easy only if it was your intention to return to Birmingham at the end of that year. I do not think this should be understood as a ﬁrm promise, nobody would want to hold you to it if there were any radically new developments, but I think the Faculty would like to know what your present intention was in this respect. Perhaps you would make this explicit when you write next. I think I understand the position, but as I may be asked questions about it it might be just as well to have it explicitly. I see I have not commented on the possibility of going to Sydney. I must confess that after meeting Blatt685 who paid us a short visit just after you left, I feel most doubtful about the pleasures of that depart685

John Blatt (1921–1990), studied in Cincinnati and obtained Ph.D.s from Cornell and Princeton. After working at M.I.T. and the University of Illinois, he moved to Sydney in 1953, before becoming foundation Professor of Applied Mathematics at the University of New South Wales (1959–84).

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ment. Not only at Birmingham, but in all the places which Blatt visited in this country he seems to have left a trail of dropped bricks and raised eyebrows, if you will forgive a somewhat questionable metaphor. His plans seem to center largely around an enormous electronic computer. I would imagine that next year they will be largely interested in completing the arrangements for this and planning work that can be put on such a computer. Nevertheless it would of course be a reasonable way of getting to Australia for a year for which I know there are arguments. I imagine that facilities for doing work there will be good, and that there might be good students. No doubt George will by next year have started some good cosmic ray work. Only I have the feeling that on the purely theoretical side you might feel rather cut oﬀ. I should think it highly likely that Messel would not mind at all having you for a year, only how much he would be willing to contribute to your fare both ways is of course another question. Other local news that might interest you. Radicati has been elected to a Chair in Naples, and will be leaving about Easter. Redmond and None got married a few days ago. Clementel from Italy will probably join us at Easter. I shall not get to Rochester because for some reason the Navy is not willing to give me a space on a Naval Transport Aircraft. Transportation has been oﬀered to Moon, but for domestic reasons it is almost certain that he will not be able to go. With kindest regards, Yours sincerely, R.E. Peierls

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[596] R.H. Dalitz to Rudolf Peierls Ithaca, 9.2.1954 Dear Professor Peierls, Many thanks for your very helpful letter686 and especially for the papers which you sent. Your airletter also arrived this morning — I am sorry that I had delayed so long in replying. I am still somewhat unclear about my plans for next year — I have not formally promised to stay on here, but Bethe certainly expects this and I should ﬁnd it a little diﬃcult to tell him if it turns out that I decide to spend next year elsewhere. You may have heard from Redmond that there appears to be a great shortage of funds at Cornell for next year, very few of those theoretical people now here will be able to stay on next year — at present it appears that only Salpeter, myself and Kalos687 will be employed by the Lab., though it is possible that some people may come with outside support (this is not so common here of course). If I stay on I would plan to travel about as much as possible. This seems a good place to mention recent progress on the Cornell strong focusing 1 Bev. synchrotron. Last week the electrons were accelerated to 1400 turns, the limit of the frequency modulated acceleration. (there is a story behind this — in the original design a mistake was made and late in the construction it was realized that the machine was not even in the stability region — this was roughly and hurriedly corrected and construction went on. More detailed calculations then predicted that the machine was square on a resonance “— then we knew we were safe”, said Wilson!! and he seems to have been right.) The high power resonator necessary for the ﬁxed frequency acceleration which now takes over is in process of being installed and hopes are running very high — of course the particles still have a long way to go. 1.5 Bev is the aim — even assuming all goes well, there may still be quite some delay in getting results as these energies will need somewhat diﬀerent techniques. 686

Letter [595]. Malvin H. Kalos had studied at Illinois where he received his Ph.D. in 1952. He later moved his research focus to computational many-body physics, Monte-Carlo simulations and parallel processing. 687

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However, the cosmic ray group has been getting some experience with a hydrogen diﬀusion chamber which will be used in preliminary work with the synchrotron. Perhaps I should go on with a little more physics. The Rochester Conference was very interesting and well organised. Nucleon-nucleon polarisation expts. were the largest single topic — there seems to be general agreement that pp polarization is large (Oxley, at 220 Mev, ﬁnds 22 = 4% maximum pol. for pp, whilst for pd, the max. pol. is 45 = 11%!?) — dependence on angle was plotted by Harwell, and by Chicago (330 Mev. — this deﬁnitely needs F -waves interfering with the P ). In the np collisions (200–300 Mev) polarization of order 5% were reported at 45◦ c.m. angle. There was some controversy as to whether the large nucleon-nucleus polarisations were due to elastic scattering or to quasi-nucleon scattering. Brookhaven reported that for neutrons between 1.0 and 2.0 Bev. incident on a hydrogen chamber, they found 24 P P− , 30 P P− O and 95 P N+− events, but no triple production. Yang said to me that meson production for 1 Bev neutrons on Be9 is only down by a factor 5 on the results for 2 Bev− at 1 Bev. The maximum intensity both for π + and π − is at 300 Mev/c in Lab. (for 32◦ Lab. angle), the π + /π − ratio is about 8 at this maximum, in c.m. system the spectrum is close to the 2π shape, though the peak is at the slightly lower energy (c.m. kinetic energy ∼ 80 Mev.) Piccioni has now done direct measurements of total cross sections for π ± P scattering at 800 Mev. and feels sure that there is really a resonance in the T = 1/2 scattering at about this energy. Bethe feels that he understands the meson-nucleon phase shifts now, and in particular all the previous mistakes, and that he now has the only permissable set which gives a α33 resonance at 194 Mev. The corresponding Yang solution has a large α31 which reaches 180◦ at this energy, the Yang α33 also being 90 here. Fermi did not feel so sure, he has seen the data change too frequently. The main theoretical contribution was that of Goldberger — I suspect you will have his paper by now.688 Wich discussed the poles of 688

Marvin Goldberger had worked on renormalization in meson theory. See S. Dreser, W.E. Thirring and M. Goldberger, ‘Low-Energy Limits and Renormalization in Meson Theory’, Phys. Rev. 94, 711–23 (1954); See also M.L. Goldberger,

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the Feynman amplitude in the po plane following the kinds of arguments given by Gellmann – Low and by Kallen, and showed that these are such as to allow one to transfer to the imaginary axis and discuss the Bethe–Salpeter equation in a positive deﬁnite metric — this seems ﬁne for the eigenvalue problem.

Serber689 gave a very stimulating talk at the N.Y. meeting on the interpretation of high energy experiments. Collins690 sa[i]d in his talk that Brookhaven now operates at 2.8 Bev. with 5 × 109 particles per pulse — I was interested to note that they do experiments with beams of scattered neutrons as far as 40◦ oﬀ the internal beam. I appreciate that it is necessary for us to consider our plans for the next few years. I should mention that Bethe has raised with us the possibility of our making a more permanent stay in this country, he believes that the procedure for this is not so diﬃcult now. We feel that we are not able to make a rational decision about this at this stage, especially as we had things planned for a return to Birmingham. We do not feel unhappy about a return to Birmingham and no matter how ‘Causality Conditions and Dispersion Relations. I. Boson Fields’, Phys. Rev. 99, 979–85 (1955). 689 Robert Serber (1909–1997), studied at the University of Wisconsin where he obtained his Ph.D. in 1934; he worked at Berkeley, Illinois and became professor of physics at Columbia in 1951 where he remained for the remainder of his academic career. 690 George B. Collins, Brookhaven National Laboratory.

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things may develop, it seems to us that our proper course is to return to Birmingham in September 1955. This is deﬁnitely our present intention. I shall be seeing the Institute for myself next week as I will be giving a talk there on the τ -meson. Pais has asked me about spending next year there, but I do not feel much inclined towards this at the present. It is easy to rationalize our inertia now that there is a strong possibility of a 1 Bev beam shortly. In any case there are of course quite a few very good experimenters here who are in close touch with work going on elsewhere and with whom it is good to discuss the real world. Silvermann or Martin for example, or Creisen or Cocconi in the cosmic ray group. I have written up some further remarks on the τ -meson decay analysis, with a more general viewpoint and which I think people at Rochester would ﬁnd more convincing — on the present data (11 events!) it is rather plausible that the τ meson should have odd parity and even spin, so that 2π-decay could not compete — the experimental points just happen to lie in the regions which are unfavoured if 2π decay is allowed so that the small number of events does carry fair weight. Perhaps there are a triplet (τ + , τ o , τ − ) and a singlet θ o , forming a close mass doublet ?τ o and θ o then being distinct. Thompson has found a large number of θ o (about 15), but only one charged τ and two anomalous θ o (which might be τ o ). Very speculative!691 Otherwise I am still working on the T = 1/2 scattering and am beginning to understand the problem, which is really to carry out a renormalisation outside the framework of perturbation theory. None of the proposals published face up to this problem and Levy’s renormalisation doesn’t even give a ﬁnite result! A further complication is that in order to make any calculation practicable in my opinion, one needs to separate angular momenta ﬁrst and work covariantly. However, in new Tamm-Dancoﬀ, the terms have structure closely paralleling the covariant theory and maybe one will be able to make renormalisation which will convince other people besides myself.692 691

R.H. Dalitz, ‘Decay of tau Mesons of Known Charge’, Phys. Rev. 94, 1046–51 (1954). See also R.H. Dalitz, ‘Radiative tau-Meson Decay’, Phys. Rev. 99, 915–20 (1955). 692 See M.H. Kalos and R.H. Dalitz, ‘Pion-Scattering Calculations in the TammDancoﬀ Theory’, Phys. Rev. 100, 1515–22 (1955).

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Concerning Sydney it seems very odd to me for the physics dept.’s major project to be the construction of a large computer. Though it is nice to have one available, the department’s theoretical research may well have its direction determined by the necessity of justifying the computer which is not very healthy nor particularly interesting. I have turned down the possibility, though Valda was very much attracted (all fares paid! £A1800, 3 lectures per week, Sydney climate!). Blatt seems to have an extraordinarily high reputation in this country. It is good to hear that there are so many applicants for next session! I am sorry to hear that Blin Stoyle cannot stay longer — if Gerry were to relinquish his Fellowship, would this not make diﬃculties for him on my return — or is he now reaching the limit anyway? We were all unhappy that you were not able to come to Rochester — it was a very stupid business! With all good wishes from both of us to yourself and Mrs Peierls, Yours sincerely, R.H. Dalitz [597] Rudolf Peierls to Robert Oppenheimer [location unspeciﬁed], 16.4.1954 (carbon copy) Dear Robert, May I add this letter to the many that you must be receiving just now, expressing indignation at the attack on you which has just been made public.693 Of all the fantastic charges the one that shocked us most is the claim (if our press reports are correct) that to have defended by legitimate methods, views on such an immensely complex question as hydrogen bomb policy which diﬀered from the one that ultimately prevailed, must be regarded as evidence of improper motives. In a 693

In 1953, Robert Oppenheimer was suspended as Chair of the General Advisory Committee to the Atomic Energy Commission as an alleged security risk and he had his security clearance taken away, in part due to criticism from Edward Teller. In October 1954, he was unanimously re-elected director of the Institute of Advanced Study. In 1963, Oppenheimer was awarded the Enrico Fermi Award which was widely seen as a gesture of political rehabilitation.

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communist or Nazi state one expects as a matter of routine, the holders of minority views to be regarded, and treated, as traitors, but if this happens elsewhere it makes us despondent about the prospects of survival of free society. But one may still be optimistic about the ultimate outcome. May I remind you of the remark that cheered you when we met last, that no situation will ever again be as hopeless as things were here in the summer of 1940. From an objective point of view, our best hope lies in the fact that this time the attack is directed against someone who is held in respect and conﬁdence so universally by all who know him, so widely that his vocal supporters range over a ﬁeld that includes Einstein and Groves, whose tangible contributions are so well known and remembered, and above all who understands the real issues so well and knows how to put his views into words. I hope that your many friends in America will have the wisdom and the courage to give you active support. For us abroad it is frustrating to know that in this battle over alleged national issues, action which we could take would be of the most doubtful value; it seems we cannot do more than assure you how strongly our feelings are on your side, and that you know without being told. Yet, ultimately your battle is also ours. We are now eagerly awaiting the next round before the investigating committee. I wish I could feel conﬁdent that this will be able to operate in suﬃciently calm and dispassionate atmosphere to produce a just and fair report. In any case, a great deal of dust is going to be raised before this can happen. I feel that this letter is really quite unnecessary, because whenever we talked about anything from ﬁeld theory to human aﬀairs, you have known what I wanted to say long before I ﬁnished saying it. All I have written you could have said better for me, but I just had to write. We saw with pleasure that your name is on the programme for the Glasgow conference. Do you still plan to be there? Genia joins me in sending good wishes to both of you. Yours sincerely [R.E. Peierls]

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[598] Rudolf Peierls to R.H. Dalitz [Birmingham], 29.4.1954 (carbon copy) Dear Dalitz, Thank you for your letter.694 First of all as regards Weinberg. I have now written to him that we shall be ready to take him, I am sorry this has taken so long. We were very sorry to hear of your various trials and tribulations, and I very much hope that things will now run smoothly for you for a while. I am also sorry that the team at Cornell this year seems less congenial to you than it would have been in many other years. These are the statistical ﬂuctuations that are hard to predict. You probably have heard some reports about activities of our department here. The enormous crowd is beginning to show some signs of reasonable integration. We have animated discussions on ﬁeld theory which started with thoughts about Feldman’s results.695 This seems to give a clear indication of what the analytical form of a correct SF prime should be like and this we feel is going to be very helpful in developing a better approach to it. Then Edwards and I got on to approaching this in the sense of the Schwinger equation (in which the mass operator contains a functional derivatives with respect to the meson ﬁeld). One can take this quite seriously as a diﬀerential equation in functional space and solve it formally. The answer is expressed then as an integral over functional space, which looks very much like a Feynman sum over histories. We have at least learnt a good deal from the relation, though of course in itself it does not get much nearer to a practical solution. However, Edwards found that in a one-dimensional model (corresponding to particles which can have energies but no momentum) one can solve the problem exactly and obtain in fact a result corresponding without ideas 694

Letter [596]. G. Feldman, ‘Modiﬁed propagators in ﬁeld theory (with applications to the anomalous magnetic moment of the nucleon)’, Proc. Roy. Soc. A223, 112–29 (1954). 695

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of what its analytical form should be. This simple case could probably have been solved in other ways as well, but it is nice that it comes out in this way and it is also a good model on which to try out various approximations to see the kind of thing one is leaving out and how important it is. We also had some lectures by Skyrme, who it turns out has done something along very similar lines. In fact he derived some years ago, independently, the Schwinger equation with a mass operator though his notation was somewhat diﬀerent. He now has a variation principle in which the unknown function is the propagator, as a function of the co-ordinates, and of an arbitrary meson ﬁeld. His idea is then to put a suitable trial functions in and this seems very sensible, only I am not yet sure that he is able to guess trial functions which have any reasonable hope of success. Thank you for your information about the Dyson lecture notes. We made this known here, with the result that I think 15 members of the department want copies. Three of them have written individually and Matthews wrote a letter to the Secretary giving the remaining names. I don’t know what is the normal arrangement about paying for these, I think all the individual applicants could get permission through the bank to send the money, but if the copies will not be sent or reserved until the money arrives they miss the bus. Would you check up on this point and if necessary ask Bethe to advance the required amount for all of us. I imagine he would be willing to do so. We continue animated discussions with the physicists about meson physics and there is quite a good spirit. It is, however, a little depressing that it looks as if the synchrotron energy here is just about equal to the threshold for V production and that also for double [. . . ]696 production, one is still so close to the threshold that on arguments of Seitz space alone the yield should be very small. Beyond careful measurements of collisions between protons and mesons, and of course meson production, there seem to be very few fundamental experiments which can be done here. 696

Missing in carbon copy.

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Brown and Scheila Brenner have completed a machine run on high energy electron scattering, with various shapes of nuclear density distributions, but their evaluation still seems to require a lot of hard work. It looks as if the results are going to be much more sensible than would appear from the ﬁrst crude Born approximation results reported by Hofstadter.697 Mott asked the other day whether one should have an article in the Advances in Physics on meson theory. I told him that you might possibly be prepared to say something about the more phenomenological aspects, which you have discussed so carefully and which I believe are not dealt with fully in the existing articles by Gunn and Moorhouse.698 He is writing to you to see if he can persuade you to do it. With kindest regards from everybody, R.E. Peierls

[599] R.H. Dalitz to Rudolf Peierls Ithaca, 28.5.1954 Dear Professor Peierls, It seems a very long time since I wrote you last. I have been rather busy lately with a review article for Frisch which has taken me very much longer than I would have ever believed possible.699 How is the 697

R. Hofstadter, H.R. Fechter and J.A. McIntyre, ‘High-Energy Scattering and Nuclear Structure Determinations’, Phys. Rev. 92, 978–87 (1953); R. Hofstadter, B. Hahn, A.W. Knudsen, and J.A. McIntyre, ‘High-Energy Scattering and Nuclear Structure Determinations. II’, Phys. Rev. 95, 512–15 (1954). 698 John Currie Gunn and Gordon Moorhouse had been working on aspects of meson theory. See e.g. J.C. Gunn, E.A. Power and B. Touschek, ‘The Production of π-Mesons in Proton-Proton Collisions’, Phys. Rev. 81, 277–78 (1951); R.G. Moorhouse, ‘Pair Creation in Intermediate Coupling Theory’, Phys. Rev. 89, 958–65 (1953); R.G. Moorhouse, ‘Scattering of Neutrons by Ferromagnetic Crystals’, Proc. Phys. Soc. A64, 207–208 and 1097–1107, (1951). 699 R.H. Dalitz, ‘K-Mesons and Hyperons their strong and weak interactions’, Reports on Progress in Physics 20, 163–303 (1957).

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publication of your book coming along? I have been looking out for its advertisement but have been surprised not to ﬁnd any yet. I have settled some of my plans for next Session. First I made an attempt to get a job for the Summer at Brookhaven – however only US citizens may be employed by Brookhaven. However Bethe suggested that I should go work there on my present salary as a representative of Cornell. I felt that this would imply an obligation toward Cornell for the coming Session, but I accepted this as I hoped the visit to Brookhaven would be very beneﬁcial to me, Brookhaven being the major centre for theoretical physics in U.S.A. during the summer months. Therefore I did not apply to the Institute, but to confound me I received an invitation from Oppenheimer. I talked this over with Bethe, who suggested that I might consider going there just for a term, perhaps returning to Cornell for the summer. So I have arranged to stay in Cornell for the Fall and then to go on to the Institute for the Spring. For the Summer of 55 I will try to ﬁnd a Summer job in California — I have had several oﬀers for the year there, but Summer jobs don’t seem so easy to ﬁnd; still I am hopeful. From my experience during the year I should say that research positions still seem fairly plentiful, but that permanent positions seem rather scarce (though it may be necessary to hunt for these, and this, of course, I have not done — but none of those here who were looking for permanent jobs really found suitable ones). Term is practically at an end this week, and many people are now leaving — Bethe leaves tomorrow. My own plans are not in a healthy state at the moment. We have to give up our house next Tuesday, and we planned to leave Ithaca then. However, yesterday I learned that my clearance has not yet come through and that I can’t go on to Brookhaven until that comes through, if ever — I had understood that Brookhaven clearance was the merest formality. Life is so complicated. Since I last wrote I have attended the Washington Meeting700 and I am enclosing a few notes from talks by Wick and Cutkosky701 — they 700

28.–30.4.1955: Washington Meeting of the American Physical Society. Copy of notes about ‘Solutions of co-variant two-particle equations’ by Wick and Cutkosky and notes by Peaslee enclosed with the letter. See also G.C. Wick, 701

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have not made any progress with the Bethe-Salpeter equation for two spinor particles with ν = 0, which Goldstein considered and which appears to have no solutions — they believe this is an exceptional energy value (E = 0) and this is easy to believe. There was a great deal of talk about an event observed at Princeton, a heavy meson decay in which a product of π o -meson decays directly into two electron pairs — the evidence being fairly convincing. The π o → γ + e+ + e− decay is very commonplace these days — in fact I was told that a good check on absolute measurements of π o production processes is provided by counting the number of these pairs when the production is inside a diﬀusion chamber. I also enclose a few notes about some work by Peaslee on meson production in nucleon-nucleon collisions. He uses the obvious models for these energies, in which meson production results from isobar excitation, or alternatively the enhancement of the ﬁnal state meson-nucleon interaction due to the resonance in the (33) state is taken into account, and he is then able to make some statements about the π + , π o , π − rations to be expected. He has some interesting comments to make concerning the possible role of higher isobars T = 5/2, 7/2 · · · , which the strong coupling theory predicts and which would not be eﬀective in meson-nucleon scattering — these higher isobars may be important in 3π production etc. The present model can only explain why double production is enhanced above the statistical model, but similar mechanisms of excitation of higher isobars may modify the statistical model for higher multiplication also. How does it look for next Session in Birmingham? It was very encouraging to hear that you had a great ﬂood of applications. Do you think this is just a temporary ﬂuctuation — I had had the impression that money for research was becoming fairly scarce in Europe, has the situation changed? Certainly your problem is not one that exists over here — in fact the inﬂow of graduate students seems to have fallen by ‘Properties of the Bethe-Salpeter Wave Functions’, Phys. Rev. 96, 1124–34 (1954); R.E. Cutkosky, ‘Solutions of the Bethe-Salpeter Equation’, Phys. Rev. 96, 1135–41 (1954); and G.C. Wick and R.E. Cutkosky, ‘Spectrum of a Bethe-Salpeter Equation’, Phys. Rev. 101, 1830–31 (1956).

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a factor of two in the last few years and the Physics Dept. is becoming rather worried, especially since they depend very much on the younger graduate students for the undergraduate lab teaching. Also I was wondering whether any of the people coming were likely to be interested in renting our house — there [is] some faint possibility that Woodward and some others may take it over, but I should be glad to write to any others who may possibly be interested. At present I am writing up some work on a program for the calculation of T = 1/2 phases or meson-nucleon scattering which was ﬁnished up when Dyson visited Cornell for a week some time back — you have probably seen the abstract which I sent to Brum.702 The work uncovers more problems than it solves and I have no great hopes that it will lead to any accord with experiment. In the absence of better proposals it does seem worthwhile to see what phases the scheme leads to and Kalos and I have permission to use the AEC UNIVAC at NYU for this problem. Kalos is an experienced computer and I am hoping not to spend too much time on this program, although it would be a good opportunity to learn what can be done with these big machines and how. Our scheme does enable a practicable calculation of a renormalised vertex and self energy without power series expansion, but making the TammDancoﬀ approximation, and this is not without interest. I was hoping to get onto more physical problems again when I got close to the date at Brookhaven. Bethe’s book is still expanding and has reached about 800 pages703 — it has quite extensive sections on Field Theory, and goes on to explain practically every important type of meson process in detail, even strange particles · · · de Hoﬀmann feels like the sorcerer’s apprentice. Weinberg has now deﬁnitely accepted the Fulbright studentship in Copenhagen — I expect he has written to you about this some time back. 702 R.H. Dalitz and F.J. Dyson, ‘Renormalization in the New Tamm-Dancoﬀ Theory of Meson Nucleon Scattering’, Phys. Rev. 99, 301–14 (1955). 703 H.A. Bethe, F. De Hoﬀmann, S.S. Schweber, Mesons and Fields, Vol. 1. Fields, Evanston: Row, Peterson & Co., 1955; H.A. Bethe and F. De Hoﬀmann, Mesons and Fields, Vol. 2. Mesons, Evanston: Row, Peterson & Co., 1955.

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The family has been enjoying life very well here in the Spring — our country house has been extremely pleasant. With good wishes to you all in Birmingham Yours sincerely, R.H. Dalitz [600] Rudolf Peierls to Robert S. Aitken704 [Birmingham], 12.8.1954 (carbon copy) Dear Dr. Aitken, You said some time ago that you would be willing, during your visit to North America, to handle some items of business for the University departments. I am writing to explain to you one matter concerning my department, not with the object of asking you to raise it, but because I think it is conceivable that you may be asked about it by the Vice Chancellor of Toronto and in that event it would be better that you knew the circumstances. It concerns Dr. B. Davison, a fairly senior person now a guest in my department, for whom a post is being created in the Physics Department at Toronto. I suggest that you save yourself some trouble of reading the rest of this letter now until a question is asked about it. Mr. Davison is a senior member of the staﬀ at Harwell and has spent the present session here on paid leave (we would say study leave). He is anxious to return to Canada, where he spent several years during the war on atomic energy, largely for personal reasons (his wife was educated in Canada and has her family there). Watson, the professor of physics at Toronto knows Davison well from the war-time work and is anxious to get him there. Davison is a person of outstanding ability with an exceptionally wide knowledge of both pure and applied mathematics and the sort of person 704

Robert Stevenson Aitken (1901–1997), Vice Chancellor of the University of Birmingham (1953–1968).

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who can make a helpful and practical suggestion on almost any diﬃcult problem that is put to him. During the last year for example he has helped us make progress in a very highbrow and abstract ﬁeld that until then was completely unknown to him. I would before now have tried to ﬁnd ways and means of keeping him here, if it were not for his ﬁrm wish to go to Canada, and also the diﬃculty of creating a post of suﬃciently high standing to be comparable with his status of Civil Servant. There are some special circumstances which are in fact a large measure the reason why he will not return to Harwell. This is because he was born and educated in Russia, though he is by birth a British subject. His grandfather emigrated to Russia and his father kept his British nationality. Dr. Davison left Russia in 1938 when faced with the choice of leaving or giving up his nationality. But his parents are still there. About a year ago the authorities felt worried about having a person with his background employed in as sensitive a ﬁeld as atomic energy, not because anyone had any doubt in his loyalty or discretion, but because the record looks odd on paper and because there is at least the hypothetical possibility of his being exposed to blackmail through the fate of his parents. About that time when he did move to Birmingham the case received some publicity in the press, though these stories presented the picture quite fairly in not carrying any implication of his being regarded as unreliable in any sense. This publicity had been foreseen and before we agreed to his coming here I discussed the matter with Professor Humphreys, who also consulted the Pro-Vice Chancellor, who agreed that the possibility of press comment was no reason why we should not be glad to have him here, in fact I think it is correct that the publicity was in no sense adverse to the University. As far as possible questions in Toronto are concerned, the only things that are likely to matter are ﬁrstly that everyone who knows Davison here has the highest possible opinion of him as a scientist and secondly that as far as we know nobody has ever raised any doubts as to his integrity and that the interest of the press in his move to Birmingham was without embarrassment to us and extremely short lived. All these factors are of course well known to Professor Watson in Toronto, and the only reason why you might be asked about it would be to conﬁrm that these impressions correspond to the views held by his colleagues in Birmingham.

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I hope you will have a pleasant and not too strenuous trip. Yours sincerely, R.E. Peierls [601] Rudolf Peierls Robert Oppenheimer [Birmingham], 8.10.1954 (carbon copy) Dear Robert, A fair time has passed and a great many words have been uttered since I last wrote to you to comment on the fantastic situation in which you have been placed.705 There was little to say then that was not immediately obvious, the same still applies. The immediate occasion for this letter is that we had recently a news item saying that it is now conﬁrmed you would continue at your position in the Institute. This is gratifying but it makes me sad to think that we have reached a state of aﬀairs where we cannot even take this statement as a matter of course, but have to receive it with gratiﬁcation. I also have now had an opportunity to read all the many pages that have been covered with print over this business and my main reaction is to feel: If I should ever have the misfortune to have my biography laid open, dissected and discussed in this kind of manner I would feel proud to come out of it with so good an account of everything I did and with so little cause for regret. This remark, too, comes under the heading of the perfectly obvious, but nevertheless it may need saying. The reaction is rather diﬀerent to the testimony of some of our colleagues. Let us hope that the whole nightmare may now be forgotten, or at least put aside. I have some hope of attending the next Rochester Conference, though some of the paperwork may again go wrong as it did last year, but if I do, I very much hope to see you there. With kindest regards to you and Kitty, Yours sincerely, [Rudi] 705

See letter [597].

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[602] Rudolf Peierls to R.H. Dalitz [Birmingham], 12.10.1954 (carbon copy) Dear Dalitz, It lies heavily on my conscience that I have not yet replied to at least two of your interesting and welcome letters.706 We were very interested both in your general impressions of life in American Universities and of your trip across the country and also in the useful bits of information about physics. You probably know in a general way what is going on here. Radicati left in the Spring to take up a Chair at Naples. Blin-Stoyle returned to Oxford. He completed some rather nice work about the eﬀect on interconﬁgurational mixing on magnetic moments and other phenomena. The latest paper on this by him and Perks707 (whom I believe you only know as an undergraduate) has just got published by the Physical Society. This eﬀect seems to provide amongst other things an explanation for the anomalous magnetic moment of Bi209 . He also wrote a very nice and simple paper on hydrodynamics, giving the correct answer for the deﬁnition of rotons, on which a lot of nonsense had been published previously.708 We had hoped that this would be of some help in discussing the question of morticity in the motion of nuclear matter and we are still thinking about this, but have not got a deﬁnite answer. Redmond completed some rather nice work on intermediate coupling and has now gone oﬀ to a job at Columbia.709 This leaves us very sadly depleted on the nuclear theory side, but we are trying to build this up again, mainly with younger people and I am also getting a research fellow for one year from Japan, a man called Yoshida, who knows a lot about group theory. One of the nicer things that has come 706

Letters [596], [599]. R.J. Blin-Stoyle and M.A. Perks, ‘The Deviations of Nuclear Magnetic Moments from the Schmidt Lines’, Proc. Phys. Soc. A67, 885–94 (1954). 708 R.J. Blin-Stoyle, ‘Spin-orbit coupling and the density distribution in heavy nuclei’, Phil. Mag. 46, 973–81 (1955). 709 P.J. Redmond, ‘An explicit formula for the calculation of fractional parentage coeﬃcients’, Proc. Roy. Soc. A222, 84–93 (1954). 707

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out of nuclear theory is the work by Bowcock,710 who has been here for a year and is staying on, about the stripping process. The point is that in order to calculate the reduced width of the reaction from the observed diﬀerential cross sections, one can eliminate the correction, which was pointed out by Messiah and Horowitz.711 I always believed that they were right in so far as they showed that the total cross section in a d,p reaction was sensitive to the interaction of the proton with a nucleus, but I do not think it is safe to rely on their calculations to make the correction. Bowcock has now worked out a technique of getting this cross section reliably from the observed curve, without using any details of mechanism and this seems to be working nicely. On the solid state side Harper left in the summer for a C.S.I.R. job in Sydney, and Marshall whose work on antiferromagnetism came out very nicely, has now gone to Harwell. This leaves only two people on solid state to prevent this side from dying out. Sheila Brenner wrote a thesis on [..]712 -mesic atoms, mainly showing how one could link in a simple way the position of the energy levels with the information about the nuclear charge distribution. She has now gone oﬀ to a temporary teaching post at Swansea. The ﬁeld theory group continues to be even more active than before and the general trend is more and more towards methods using functional integration. In this respect Edwards has continued with simple problems which can be solved accurately and has just completed a paper dealing with the scalar charged case without recoil, by a method which is accurate both in the limits of weak and strong coupling and reasonably good in the intermediate case. It looks as if he will be able to handle the case with recoil by essentially the same method. Matthews and Salam have done some more joint work in the summer, which in particular shows what happens in the functional integration method if one includes the closed loops (i.e. vacuum polarization eﬀects), which

710

J.E. Bowcock, Department of Mathematics, University of Birmingham. J. Horowitz and A.M.L. Messiah, ‘The Mechanism of Stripping Reactions’, Phys. Rev. 92, 1326–27 (1953). 712 Missing in carbon copy. 711

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were left out in the paper by Edwards and myself.713 The result is very simple because one simply has to replace in the numerator of our expression the propagator for a single nucleon in a given external ﬁeld, by the corresponding Fredholm resolvent, i.e. to multiply the integrand by the Fredholm determinant and the same determinant has also to be added in the integrand of the normalizing factor in the numerator. This result is very reminiscent of the result of Matthews and Salam for an external ﬁeld,714 and in the latter case one obtains a convergent series whenever the Fredholm series is conv[erg]ent, even though the Born approximation might be divergent. This was the basis of the somewhat optimistic remark which I made in a letter to Bethe and which has evidently reached you. We are now, however, not quite clear what really follows from this, because although one is dealing with a convergent series in the integrand, the functional integration over all possible meson ﬁelds makes each term diverge if one integrates each term separately. These inﬁnities are just the ordinary vacuum inﬁnities, which have to be cancelled out, but if one does cancel them out, a few of the general theorems about Fredhol[m] theory remain and so we don’t know very much at the moment. Nevertheless I have the impression that the new form of the result should be powerful in opening up new possibilities, but we have not seen them yet. Valatin has completed his work on writing counter terms in the ﬁeld equations which have a deﬁnite meaning without reference to the power series, but he was troubled in doing this by the fact that inﬁnities remain in the basic commutation laws and therefore in the deﬁnition of a state. He is therefore now working on a deﬁnition of a state which makes no explicit reference to a space like surface and he has got some formal results so far which tried together with diﬀerent methods used by diﬀerent people and which looks promising. Feldmann has been getting on very well, in particular in helping the experimentalists sort things out and he, Matthews and I have given talks on various occasions trying to sell some of the ideas of the present theory to the experimental 713

Letter [595], note 681. P.T. Matthews and Abdus Salam, ‘Propagators in quantized ﬁelds’, Nuovo Cimento 2, 120–34 (1955). 714

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group. This has gone down so well that it has encouraged us to try as an experiment to put on in December a meeting of the Physical Society, which will consist of lectures taking two days, setting out the ideas of ﬁeld theory for experimentalists and non-specialist theoreticians. We have also got Salam to help with this and we hope that it will all work. The synchrotron continues to work well as an accelerator, but progress with deﬁning beams and getting clean conditions for experiments is still rather slow. The cyclotron has just been rebuilt, it was out of action for several months, but is now starting to work again, this time we hope it is a better engineering job. It was interesting to note from one of your letters that it is not easy to get good research students. We are under just as big a pressure as ever and I had great diﬃculty in keeping the number down to the same as last year, i.e. 27. In fact for a transition period of a few weeks we are one over. I have already ﬁve names down for consideration for next year and it looks as if we shall be in the same trouble again. You will have heard about the Glasgow Conference. It was on the whole quite instructive, but it was a pity that so many papers had been put on that in most sessions there was literally not a single minute for discussion. Your house is now inhabited by the four bachelors and while I have not had an occasion yet to inspect it, it looks as if it ought to survive the experience well and still be quite inhabitable by the time you come back. As things have turned out the time of your move to Princeton is probably fairly well chosen, because by then people should have had time to recover from all this fantastic loyalty Board business,715 which must have been quite upsetting and disturbing. With kindest regards, also to your wife, Yours sincerely, R.E. Peierls

715

See letters [597], [601].

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[603] Felix Bloch to Rudolf Peierls Geneva, 22.10.1954 Dear Peierls, You may have heard that I have recently taken on a position as the director of CERN and you may have further heard that I am planning to have some physics done here on completion of the machines. One of the important activities in this respect is of course the theory, and although the center of the CERN theory group remains in Copenhagen for a few more years, there will be also a nucleus of condensation here in Geneva. At the present moment we have Bernard here who came on the recommendation of Møller and works on the problems of meson production. We also have succeeded to have Abragam visiting us on a half-time basis and I am very happy that in this manner we have at least made a start. The only trouble is that I am anything but an expert in high-energy physics and that even if I were one I would have very little time for acting as such. Consequently, d’Espagnat feels a bit lonely here, and I should like very much to ﬁnd another man of his approximate age (32 years), experienced and interested to join us here very soon. The reason for writing this letter to you is to ask you whether you could propose somebody whom you consider suitable and likely to come within the next few months. While it would be preferable for the reasons mentioned above, to have a high energy theoretician, we would certainly also consider a man working in another ﬁeld, provided that he is good, that his interests are not too narrow and that he is otherwise a nice person. I should be most grateful to you, if you would give some thought to this matter and either recommend to us possibilities or tell us who else might be a good source of information. Thanking you very much in advance for your answer to this letter. I am, with best regards, your F. Bloch

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[604] Rudolf Peierls to Felix Bloch [Birmingham], 30.10.1954 (carbon copy) Dear Bloch, Thank you very much for your letter. I am very glad to know that you have taken up your new duties at Geneva and I only hope that the amount of time you will have to spend battling with red tape will not prevent you from thinking about more interesting problems. If in the course of your business you should visit this country, please don’t forget to come and see us at Birmingham. As to the question of a suitable theoretician for your staﬀ, I do not feel I have from your letter as yet a very clear picture of the kind of man who would be required. Probably the best thing therefore is if I mention a few names which come to my mind and describe their qualiﬁcations brieﬂy and perhaps you would let me have your reaction to them. 1) J.G.Valatin. Born and educated in Hungary. Now stateless. Age 36. He worked in Hungary mainly on molecular spectra, then spent some years in Paris when he got interested in ﬁeld theory. Spent about two years in Copenhagen and has been, for the last two years, a research fellow in my department. He is very mature and has an excellent and very wide knowledge of theoretical physics. His work on ﬁeld theory has at ﬁrst tended to be somewhat formal, but he is now thinking on some of the really important questions, in particular how to get up the renormalization process, so as to get away from series expansion and he has made some very interesting progress. He takes a very active part in our discussions. He has not had very close contact with the experimental high energy work here but I think he would do this well and his experience on the molecular spectroscopy where he did work very closely with experimentalists should be valuable. I can perhaps express my opinion of his judgment best by saying that whenever I get a paper on any part of theoretical physics to referee on which noone else here is obviously an expert and I want a second opinion, I ask Valatin to look at it for me.

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2) W.J.Swiatecki. Polish born, but was in this country during and after the war. Finished school here and got his university education here. He is a British subject. He took a Ph.D. in this department with a very good paper on nuclear problems, in particular on the nuclear surface energy. Then went for three years to Copenhagen, where he had a very bright idea about explaining the asymmetry of ﬁssion, but spent rather too long on diﬃcult calculations with which he was trying to prove that his mechanism would work. He has now been for a year in Uppsala, partly working with Waller and partly helping the cyclotron people with the design and interpretation of experiments. Particularly the work on polarization. This is high energy work in a sense, but of course the energies they have available there are not high enough to make mesons and he has I believe no experience of meson work. However, I believe he would take to that very easily. He has a wife and two children. As far as I know it was his intention to complete the present year at Uppsala and then to leave Sweden and settle down somewhere else. I cannot of course say what would be his reaction to an invitation to Geneva. He is aged about 29. He undoubtedly is a man of ﬁrst rate ability and a very good person to discuss with. He should by now have plenty of experience of talking with experimentalists. 3) G. Feldman, a Canadian. Aged 26. Took his Bachelor’s and Master’s degrees in Toronto and then did a Ph.D. here with a paper on ﬁeld theory, which has proved quite important and instructive. For the last year he has held an assignment here which requires him to work together with the people on the synchrotron team, getting for them all available data on meson theory and discuss the actual or possible experiments in the light of theoretical knowledge. This involves also explaining the ideas and results of the theories in language suitable for experimentalists and he has proved extremely suitable for this particular assignment. While he was doing this, he also continued theoretical work on ﬁeld theory and as a very active member of our ﬁeld theory group. Particularly for a man of his age he is exceptionally good and with him more than with anyone else I would particularly hope that you would fail to persuade him to go, because we would miss him very much. Not because he is necessarily so much

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better than the others here, but because he seems to well suited to his particular function here, that he would be hard to replace. His type of approach is perhaps characterized by his latest publication which is a letter to Physical Review716 pointing out that in attempting to produce anti-protons one should with an accelerator of the Berkeley type not look at the proton-proton collisions, but one should make mesons in protonproton collisions and then let the mesons collide with other protons, since in this way the threshold for nuclear pair production is lower. This of course is not a major piece of work, but it is a point he happened to notice which others seem to have missed. 4) S.F. Edwards. A graduate of Cambridge, who spent a year at Harvard with Schwinger, then a year at the Institute at Princeton and has now been here for a year on a fellowship. He is extremely productive in ideas on ﬁeld theory and he has developed since he came here some powerful methods of solving simpliﬁed problems exactly, which up till then I would have regarded as completely insoluble. I wrote a joint paper with him recently717 which sta[r]ted oﬀ the development and he has gone very much further since then. I put his name forward with some hesitation, not because of any doubt as to his quality. He is undoubtedly one of the most promising young men I have here at the moment, but he is so full of ideas and so fast in his work that it is very important for him to be in a large group where his ideas can be subject to discussion and it might not be in his interest therefore to join a Laboratory with fewer theoreticians at this present time. 5) Ravenhall, whom you evidentally know from Stanford. I have a high opinion of him, though he does not seem to have got very much done since he went to America and I do not quite know why. By now you probably know more about him than I do. I don’t know what his plans are, but I heard a rumour that he was considering returning to Europe. I would be interested in your reaction to these various possibilities. I should of course add that I did not think it reasonable to sound out any 716 717

G. Feldman, ‘Antiproton Production’, Phys.Rev. 95, 1697 (1954). See letter [595], note 681.

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of these people at this stage and have therefore no means of knowing which of them if any would be interested in the post. With kindest regards Yours sincerely, R.E. Peierls

[605] Nicholas Kemmer to Rudolf Peierls Edinburgh, 13.1.1955 Dear Peierls, I have long felt that a letter to you was overdue, but I must confess that the immediate impulse to write arises from the invitation that I am now sending to you. However, ﬁrst let me say a few words about what has been going on here. I cannot report much scientiﬁcally, but in other ways things seem to be getting going quite nicely, now. We are moving from our cramped quarters, that you are I am sure acquainted with, into a separate building, across the road, which will contain two lecture rooms, a library, separate oﬃces for each member of staﬀ and a number of quite roomy research rooms which will take from one to three students each. The building is an old one and is being thoroughly reconstructed internally at the moment. Our present guess is that we might be in it next October. We shall be quite full even when we start. The present staﬀ consists of Schlapp, Nisbet, Pursey and the secretary, and we have ﬁve people doing research. Two are beginners. We have Nataf from Paris as an I.C.I. Fellow, Higgs, formerly of King’s College London (just starting), who wants to learn ﬁeld theory, having previously done theoretical chemistry, and also just starting, Dedijer from Yugoslavia who, among other things, has been one of their representatives in CERN but now wants a year of peace to brush up his theoretical physics. There are also some possibles for next year. We have managed to get a promise of the periodicals library independent of Feather’s (on the book side, our library has been excellent since Born’s time).

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I, myself, am carrying on with the electrodynamics text-took that I am doing jointly with Lyttleton. As regards ﬁeld theory, I have not really kept abreast of the latest developments at all well, though now I have the new stimulus to start in the presence of Higgs and in the fact that Salam has insisted in making me co-author of a paper he has just written, to which I contributed a very small amount in very early discussions.718 We shall be sending out preprints very shortly, if you have not already seen the MS. from Salam. I feel all this is quite a good start, but there is one big problem that we are now concerned with and that is giving us a lot of thought — it is the question of a desirable syllabus for an Honours course of mathematical physics. We are just in the process of having a separate “Honours school” of math. physics recognized by the University. There is not much diﬃculty about the advanced courses (the actual Honours school) for these have existed in a very good form since Born’s time. But the initial stages of the curriculum which have to serve the Ordinary degree students as well, are causing us quite a big headache. At present our ﬁrst year is taught elementary statics and dynamics only, and none of the lecturers are really satisﬁed with the course, though they ﬁnd it hard to decide how to improve matters in view of the poor mathematical equipment of some of the students. I have a feeling that we could learn a lot from your experience and that the time has come to seek your advice. This is one of the reasons why not only I but Schlapp and the others, would be very pleased to see you here sometime. I am glad, however that I can oﬀer you a small further inducement to come, and I might say that the ﬁrst excuse is really unnecessary for me to extend to you this invitation. It is to give one of our Ritchie Lectures. I know that you have already given one of these, but to refresh your memory, let me say that these are Guest Lectures of a quasi-popular character. The audience consists of staﬀ and students of Mathematics, Physics, Chemistry and perhaps some Philosophy. It is usually held on a Friday at 5.15 [p].m. and the choice of subject is left completely to the lecturer. We can oﬀer you £15 for expenses. Of course Feather joins me in this invitation. 718

N. Kemmer and Abdus Salam, ‘On the relativistic equation for scattering’, Proc. Roy. Soc. A230, 266–71 (1955).

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You are quite free to choose your own subject though I might just make two suggestions: Firstly, I have hitherto kept away from anything on ﬁeld theory or nuclear theory, reserving such talks for a time when there were a few more people assembled here, therefore if you think of anything suﬃciently generally intelligible in either of these lines, it would be grand. But I should tell you that I have also recently written to Weisskopf with a similar invitation. I do not know whether he can manage to come, but if he does, it would be as well if the topics did not overlap too much. The two dates that would suit us best would be Friday, February 4th and Friday March 4th. We could possibly shift things if you could come some other week instead, and we are not absolutely tied to Fridays. I am sorry if the ﬁrst date gives you such short notice, but I am mentioning it just in case I hear from Weisskopf that he has chosen the same. If you would be kind enough to come, we would be very pleased to put you up at our home and of course we should like you to make your stay as long as possible. With best regards from my family and the department, Yours sincerely, N. Kemmer [606] Rudolf Peierls to Freeman Dyson [Birmingham], 17.2.1955 (carbon copy) Dear Dyson, Thank you very much for your letter.719 Your letter to Goudsmit720 does sum up the facts quite well. In the meantime I have also drafted a letter 719

Letter could not be located. Samuel Abraham Goudsmit (1902–1978), studied physics at Leiden and Amsterdam and received his Ph.D. from Leiden in 1927. He took up a faculty position at the University of Michigan, subsequently worked at M.I.T. and later was Chief of Scientiﬁc Intelligence of the Alsos Mission to investigate the German atomic bomb project. After a short period at Northwestern University (1946–48) he became Senior Scientist at Brookhaven (1948–70) and served as managing editor and later editorin-chief of the American Physical Society, founding, in 1958, its Physical Review Letters. 720

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to Goudsmit which is just waiting for Salam’s approval before it is sent oﬀ, but I imagine he agrees.721 In this I explain that we now accept the statement that the main result of the paper is implicit in Feynman’s papers, though I still maintain that it is very hard to recognize and the result is also obtained in the Russian paper which you mentioned to me, but there it is derived in a rather round about way through the Schwinger equation. I still believe the Matthews-Salam paper is still worth publishing,722 but since some redrafting will be necessary to acknowledge the connection with earlier papers and to emphasize what is really new there would be a good deal of delay involved in having the amended version referred again and we are therefore proposing to withdraw the paper from the Physical Review and have it published in this country. I still believe that it should be published somewhere and I am strengthened in this both by the fact that the recent paper by Klein723 using functional methods still juggles around with the most complicated Schwingeresque formalism and still misses the simplicity of the whole matter and also by a remark in one of Feynman’s earlier papers in which he says that nobody has ever worked out how to do the integration over spinor ﬁelds and that this ought to be done. As to the usefulness of the functional approach, it seems to me that Feynman’s recent work on the ‘polaron’ has again demonstrated its power and the remarks which Feynman made at Rochester724 also show that a good deal can be learnt that way.725 Edwards and I have talked a bit about that latter problem and are by no means convinced that Feynman’s answers are reasonable. The doubts are based on the question what region is of the greatest importance if one thinks that it is most important to represent things correctly in the immediate neigh721

The controversy refers to a paper of P.T. Matthews and Abdus Salam the result of which Dyson claimed were already implicit in Feynman’s work. 722 See Letter [602], note 714. 723 Abraham Klein, ‘New Tamm-Dancoﬀ Formalism’, Phys. Rev. 95, 1676–82 (1954). 724 Fifth annual Rochester Conference on High Energy Physics, 31.1.–2.2.1955. 725 R.P. Feynman, ‘Slow Electrons in a Polar Crystal’, Phys. Rev. 97, 660–65 (1955).

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bourhood of the nucleon, where [..] 726 tends to become very large. It looks as if the corrections are much less than Feynman claims. However, Feynman may still be right in placing more weight on the behaviour of [..]727 over somewhat larger volumes. I have no doubt at all that by sorting out these problems one can learn much more about the nature of the physical problem, though not necessarily solve it. Apart from this my belief in the functional method is very largely based on the success of Edwards ﬁnding sensible approximations. I would be very interested to know what you think of his paper on the charged scalar case, which exists in preprint form.728 This is still an academic case for which other methods work equally well, but he is now working on an extension of the same method to the correct pseudoscalar case with recoil and this looks very promising, at any rate I am sure that not all the possibilities of the method have been explored.729 I believe that the further formal development of this method is justiﬁed only when one knows it can be used, but already when there seems some hope that it may be simpler (I think it would be fair to say that some of your papers also represent formal developments of techniques that have not as yet proved themselves.) I do not see why you feel so apologetic about disagreeing. Physics would be a poor business if one was not allowed to disagree, particularly when this does not concern facts, but the outlook for the future. If I am optimistic about the functional method it is only in the sense of the deﬁnition that an optimist is a person who thinks the future is uncertain. I hope you have by now got over the ’ﬂu. I have been spared it this time. I got back just in time to ﬁnd my wife in bed with the children just recovered. One thing I have brought back from Rochester is the knowledge that we have been out of touch with what goes on in several important ﬁelds 726

Missing in carbon copy. Missing in carbon copy. 728 S.F. Edwards, ‘The nucleon Green function in charged meson theory’, Proc. Roy. Soc. A228, 411–24 (1955). 729 S.F. Edwards, ‘The Nucleon Green Function in Pseudoscalar Meson Theory. I’, Proc. Roy. Soc. A232, 371–76 (1955). 727

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and we must try to catch up. This is in part because we have not read enough and in part because we have not kept up the correspondence with other people suﬃciently. As you will have noticed I am a very bad correspondent, but we always appreciate very much hearing in particular from you what you think about the way things are going. I also share your impression of Lehmann. I am glad he is clear about the signiﬁcance of their paper. From reading the abstract one gets the impression that they claim far too much of it, but certainly it is an interesting beginning.730 With kindest regards, Yours sincerely, R.E. Peierls

[607] Rudolf Peierls to R.H. Dalitz [Birmingham], 28.2.1955 (carbon copy) Dear Dalitz, I am writing to bring you up to date on some possible developments which I have also discussed with other members of the department and which if they came oﬀ would concern you. I mentioned to you that last year I had been asked to move to Imperial College and shortly after my return this suggestion was again raised. Some of the practical factors had changed in the course of the year and I considered the question quite seriously. However, I have now again come to the conclusion that I do not want to go. Simultaneously with this, however, I was also asked in a quite preliminary way what would be my reaction to an invitation to go to Oxford. This is still quite vague, since the suggestion did not come from their selection committee and it is by no means certain that they would in fact ask me. At 730

H. Lehman, K. Symanyik, and W. Zimmerman, ‘Zur Formulierung quantisierter Feldtheorien’, Nuovo Cimento 1, 205–25 (1955).

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ﬁrst sight my reaction to Oxford was rather negative, but it has been changing gradually. The main cause being that I think I tended to overestimate the diﬃculties and disadvantages of Oxford at ﬁrst and also, particularly as a result of the study of the London proposition, I now feel more strongly that there is every prospect of the school here surviving my departure and from a national point of view if we succeed in having two good schools, one here and one in Oxford, this would of course be an improvement. Admittedly, nuclear physics is not exciting, but it is largely compensated by the proximity of Harwell, which is not a negligible factor. As I already told you I have been thinking of who would be likely to succeed me here and, in my opinion, you would be the best choice. Clearly this is not for me to decide and in fact it is a rule in the University that a professor who is resigning or retiring does not take part in the selection of his successor, except that people may ask for his views. What I say about this is therefore hypothetical in three ways: it is not sure I shall be asked to go to Oxford, it is not sure that I should accept if I was, (depending largely on whether they would be able and willing to meet various requirements I would have) and it would then not be certain what action would be taken by Birmingham. I do know, however, that the most senior members of the department while they would not like the idea of my going would, if I did go, be quite happy about the prospect of working with you and I am also satisﬁed that for the foreseeable future there would remain a good supply of more junior research people here, though not necessarily equalling the present numbers (I think it would be preferable for the beginning to cut down the numbers to something like half of the present size) and this is just about what I would guess would happen. I am telling you all this because it is obviously of interest and also to give you an opportunity of commenting if you like. You would not of course be committing yourself by anything you say at this stage, but when we talked on the same subject at Rochester it seemed such a hypothetical possibility that I did not particularly invite you to deﬁne your reactions. If for example your reaction was that you would not wish to take on the responsibility of running a department, this would be a factor I would like to know. As you know the department is in quite good

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shape and runs easily. You could rely on getting every cooperation both inside the department and the University. If you felt that in any case you would not want to settle for a long period in this country, this would be something else of interest and in that case I would be rather interested to know whether an appointment where to run a department would make it more or less likely that you would be willing to stay here. It would also be interesting to know whether in the event of my remaining here the appointment to a research professorship in the department would be more likely to attract you than either of the alternatives. (I am not yet certain what would be the prospects of getting such an appointment made, it looks as if this could not in any event be done for next session if I stay here, but it might be possible in the near future.) I might mention also that if I were to leave and you did not wish to take over, or the selection committee did not choose you, the next name that comes to mind would be Flowers. There may well be others, but no very obvious other possibility suggests itself. I would very much appreciate hearing your ﬁrst reaction to this fairly soon. It is all preliminary and should not commit you and it will not have any direct eﬀect on my decision (if a decision is called for), but it always helps in thinking about the future to know what your general reaction to such ideas looks like. With kindest regards, Yours sincerely, R.E. Peierls

[608] R.H. Dalitz to Rudolf Peierls Princeton, 17.3.1955 Dear Professor Peierls, Thank you for your letter. I am very anxious to know how your thoughts and plans are developing and I will try to give you some indication of my position by discussing brieﬂy the merits of the various possibilities. My views on these possibilities are by no means settled, as I believe you will understand.

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It will certainly be unfortunate for Birmingham if you decide to go to Oxford (if Oxford will not meet your conditions, they will be very foolish) — but I have little doubt that there you would have a greater and more direct inﬂuence on the state of physics in England than is possible at Birmingham. More promising research students should be available in greater numbers and these will be people one might expect to have more reason to stay in England. But, of course, I am very much out of touch with the way the department has been developing recently. I would consider seriously the possibility of running a department at Birmingham and I am not unwilling to contemplate a lengthy stay in England. However I am inclined to think that there would be rather little to hold the present senior people to Birmingham after your departure, and that better-paid positions in more attractive localities would soon draw them away. It is probable that the only research students available would be the few coming up through the undergraduate school, for outside students are generally attracted only by very well-known names. The health of the department would be strongly coupled with the success of the synchrotron group — if things turned out well, one could hope to build up a school with high energy physics as the main ﬁeld of interest. I do not have a good picture of their rate of progress at present, but it is my impression that real experiments are still a long way oﬀ; which is rather disappointing. I expect that there would be a good deal of support from the cyclotron group, which would be very stimulating and helpful. It is not clear to me how wise it would be for me to take on such a proposition at the present time. My main fear would be that the administrative work and the eﬀort of trying to stimulate other people would leave me with little energy and peace of mind to participate personally in much of the research work. Perhaps this is an unduly pessimistic view. I am also very much worried about the general health of physics in England; particularly by the lack of active experimental work and by continuing outﬂow of capable and active experimenters — I understand that A.P. French is leaving Cambridge for the States731 shortly 731

A.P. French took up an appointment at the University of South Carolina, Columbia.

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and also R.N. Wilson of Oxford732 and that D. Walker is returning to New Zealand, all good men leaving at a time when there is such a great shortage. Do these people leave because there are insuﬃcient senior positions available? Perhaps this is just a particularly bad period for England; there has been much wasted time and eﬀort in the abandoned machine programmes at Cambridge and Harwell and the previous machine building projects have not been outstandingly successful except for the Liverpool machine (which certainly stands in a very favourable position at present). It is indeed very much of a question whether it makes sense for a meson-physicist to work in England at the present time!∗ If you decide against leaving Birmingham, then I anticipate that I will be returning to Birmingham as we have discussed previously — a senior position such as you suggest would certainly be acceptable. Presumably this would be argued on the basis of the needs of the synchrotron group, and it would certainly be my intention to work in this direction, as you will, of course, realize. Incidentally, I have been meaning to ask whether there is anybody likely to replace Feldman next year. The Canberra position will presumably be ﬁlled during this year, and, if I ever intend to return to Australia, this would be the time to consider doing so. The group will be quite well-supported, sabbatical leave is on a quite liberal basis, and it is envisaged that the theoretical group would consist of about six or seven post-doctoral people together with four of ﬁve research students. Unfortunately very little stimulus can be expected from the machine project within the next ﬁve years, and the low energy nuclear physics is on a rather limited scale. Also there is no undergraduate school from which students would naturally ﬂow; the larger universities have their own theoretical groups. However I think ∗ Perhaps

this is rather too severe — it is largely a matter of one’s connections with the experimental groups, and they may really be quite good. 732

Richard Wilson took up a post at Harvard University.

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that, although it may not be easy to achieve much signiﬁcant work in physics there, at least in the beginning, one could play a useful role in stimulating interest in the more rapidly growing regions of physics and activity in more signiﬁcant experimental work. It is not an unattractive position, on the whole, but the situation seems somewhat unpredictable to me. I believe that I must apply for the position, although I may withdraw my application or, if the position is oﬀered to me, I may not accept in the end — at least I would not ﬁnd myself regretting later that I did not apply. Lastly, you may have heard that four positions are being made available at the University of Chicago in lieu of a replacement for Fermi.733 Senior positions have been oﬀered to Wick and Steinberger, I believe, and one of the junior positions is being oﬀered to me. The details of the oﬀer have not reached me; the oﬀer has been approved by the University but will not be made formally until approved by the senior theoretician to be appointed, presumably Wick. Owing to the uncertainties raised by your letter, I did not discourage the oﬀer out of hand. It is rather tempting, of course — I have much to learn in physics and I am well aware that one’s development is very much a reaction to the stimuli and inﬂuences which act on one — these would undoubtedly be very beneﬁcial at Chicago. The Institute has a good atmosphere, lecturing loads are quite nominal and one would have no reason for not getting along well with the research. It would certainly not be much of a life for the family, however — I must remark, incidentally, that I have no wish to spend my life in the States, but one could argue that several years further experience in such a position now may make me more eﬀective in England eventually, through my wider experience and wider contacts in the States, than would be the case should I return at the present time. Perhaps this is just sophistry? But this possibility deserves consideration — perhaps it may be feasible to have the oﬀer put oﬀ for a year. I am very much confused by the existence of the new alternative, and not least by the fact that people to whom I have mentioned this matter have taken it for granted that I would accept! 733

Enrico Fermi, who had been professor of physics at the Institute of Nuclear Studies in Chicago since 1946, had died in 1954.

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I regret that in writing to you I am still confused in my assessment of these paths to the future — it is not easy to visualize where each of them would lead, and it is not even completely clear where I would desire them to lead. However, I am hoping that these remarks will suﬃce to give you some idea of my attitudes toward the various possibilities. With all good wishes, Yours sincerely, R.H. Dalitz

[609] Freeman Dyson to Rudolf Peierls Princeton, 31.3.1955 Dear Peierls, Your point is well taken.734 However, I still stand by the statements I made in the review of Edward’s paper. The point he made is that if G(φ) ∼ C0 + C2 g2 + C4 g4 + · · · is the Green’s function of the Fermi particle in a ﬁxed c-number φ, then the Green function with quantized φ goes like Gq ∼ c0 + c2 (1!) + c4 (2!) + c6 (3!) + · · · The remark is quite general and applies with or without vacuum polarization, and this I considered the main contribution of the paper. Then he said in particular, if we use a cut-oﬀ theory without vac. pol. the Fredholm solution gives a G(φ) with a ﬁnite radius of convergence and therefore Gq is divergent. Now in the letter he says, for a cut-oﬀ theory with var. pol. the G(φ) will be convergent. It is not clear to me whether he also states that in this case he had proved that the G(φ) converges rapidly enough so 734

See letter [606].

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that Gq is also convergent; I assume this to be the case for a suﬃciently smooth φ. I do not consider that this result destroys the force of his earlier argument, because I assume that the G(φ) will in any case behave badly for suﬃciently rapidly varying φ. In other words, the convergence of G(φ) is certainly not uniform in φ. His general result, that Gq is more divergent than the worst possible G(φ), is likely to be useful for a proof of divergence of Gq also with vacuum polarization. I hope I have made this argument as clear as it is to me, which is not saying much. Thank you also for your long letter of February. I got Edwards’ paper on the charge scalar theory735 and have looked at it only superﬁcially. It seems to have some clever tricks, but I must study it much harder before I understand it properly. In general I think the test of such a method will only come when he puts in the recoil. Last week we had Chew736 here and he gave a 2 1/2 hour talk about his equations for the meson scattering. The most interesting new development is that it is proved that these equations can be mathematically deduced from only the following assumptions. (1) Unitarity of the S-Matrix (2) Causality (analytic property of the S-Matrix) (3) Goldberger symmetry between emission and absorption of mesons (4) Absence of recoil and nucleon-pair eﬀects (5) Neglect of 2-meson states 735 S.F. Edwards, ‘The nucleon Green function in pseudoscalar meson theory. I.’, Proc. Roy. Soc. A232, 371–76 (1955). 736 Geoﬀrey Chew had written several papers on diﬀerent aspects of meson scattering. See G.F. Chew, ‘Pion-nucleon scattering when coupling is weak and extended’, Phys. Rev. 89, 591–93 (1953); G.F. Chew, ‘Renormalization of Meson Theory with a Fixed Extended Source’, Phys. Rev. 94, 1748–54 (1954); G.F. Chew, ‘Method of Approximation for the Meson Theory with Experiment’, Phys. Rev. 94, 1755–59 (1954): G.F. Chew, ‘Comparison of the Cut-oﬀ Meson Theory with Experiment’, Phys. Rev. 96, 1669–75 (1954).

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So in some sense this Chew model is the most general possible within the limits of the ﬁxed-source problem. I am at present just working over the details to try and understand it better. In particular I do not consider I understand it until I see where the factors 29 , 79 etc. come from. As you can see, I did not go to Moscow.737 The reasons were complicated and not very creditable to me. The immigration people in Washington told me that they would not penalize me for going to a meeting in Moscow if it were purely scientiﬁc. But if any kind of political propaganda were attached to it, they would be forced by the McCarran Act738 to exclude me from the U.S. unless I could prove that I had no part in such propaganda. They said also that it would be practically impossible for me to establish such proof, and a declaration beforehand of my good intentions would not help. I was sorry to ﬁnd that my idealism was not strong enough to make me want to ﬁght this through. The recent remarks of Pontecorvo also did not help.739 Yours ever, Freeman Dyson

737

31.3.–7.4.1955: All Union Conference on Quantum electrodynamics in Moscow. The International Security Act of 1950, sometimes referred to as McCarran Act, allowed for the expulsion or deportation of people considered ‘dangerous to public safety’, in particular communists or communist sympathisers. 739 Bruno Pontecorvo (1913–93), had been working under Fermi in Rome and with the Joliots in Paris; he ﬂed to Spain and later to the US and eventually moved to Canada where he worked on cosmic rays, neutrinos and the decay of muons. In 1948, after obtaining British citizenship, he joined the British atomic project and became professor at Liverpool. In 1950, he voluntarily moved to the USSR he continued to work in nuclear research in Dubna. In 1955, he consented, for the ﬁrst time after his move to the Soviet Union, to appear in public, at a press conference where he explained why he chose to leave the West and work in the USSR. 738

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[610] Rudolf Peierls to R.H. Dalitz [Birmingham], 4.4.1955 (carbon copy) Dear Dalitz, I have put oﬀ replying to your long and interesting letter in the expectation that things would develop a little and I could write less conditionally.740 This has now happened. Oxford have not invited me (presumably because they knew that I would ask for more than they could aﬀord) and so at any rate for the present there will be no change here. On the other hand, the recommendation for your promotion to Grade I is well on its way and while it has not yet passed through all the stages I do not expect any complication. Of the various possibilities which you mention in your letter I am greatly disturbed by your invitation to Chicago, which must have a lot of attraction for you. I still hope of course that you will not decide to go there, but I must not try to disguise this hope as advice. However, I am glad to know that life in Chicago does not look perfect from your point of view. I assume of course that in any event you will be here next year. I cannot imagine that if you were interested in Chicago they would not be willing to wait for you for a year, since the post does not seem to involve any special duties which call for continuity. May I now comment in turn on the various points which you make in your letter. Some of them have been made less relevant by the fact that I am unlikely to leave, but they are of general interest in any case. Firstly I am not by any means sure that we are less well placed here than Oxford as regards the supply of students. Oxford does not have a very high prestige for science in general and in particular for mathematics, which is still the undergraduate course through which most of our entrants come. This was brought home to me particularly a few weeks ago when I interviewed a prospective student who on the advice of his school had put Birmingham as his ﬁrst choice, Liverpool 740

Letter [608].

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second and Oxford third, and he explained that he would not have put Oxford down at all except for the fact that he was short of some subject (I have forgotten whether it was Applied Mathematics or Physics) and that Oxford might take him even if the other Universities did not. This is perhaps an extreme case, but I still believe that we can maintain an undergraduate school containing a fair number of bright people and the main diﬃculty is the question of selection. We are still experimenting with our admissions procedure, but I think we shall get it to a point where we shall not miss many promising people. There certainly is no sign of our running out of research students. In fact on the contrary I have had this year to turn down more applicants for postgraduate places in the department (some as research students, some as post-doctoral research grants) than ever. It is true that a fair proportion of these always come from abroad, but it seems to me right that we should continue to have a proportion of such people because their presence gives us more variety and has a useful inﬂuence on local students. It may in fact be worth while to run over the present composition of the department, particularly concerning the people you do not yourself know. Of the people you know Matthews, Woodward, Field, Brown, Edwards, Valatin are still here and are remaining here as far as I know. They make a really powerful team. Feldman is going to Princeton and presumably will not return to this country, however, we cannot grumble as we have had certainly much help from him.741 Candlin, whom you do not know, but who is very good is going to the Institute with a Commonwealth Fund Fellowship and must return.742 I do not think he is likely to settle in America. Of the more junior people a Canadian, Schaefer, who is quite good and working with Brown on the numerical treatment of radiation corrections for heavy elements, will stay if he can get a grant.743 A bright young South African, Mandelstam, is staying 741 Gordon Feldman moved to Princeton, and later worked at the University of Wisconsin before becoming professor of physics at John Hopkins University. 742 D.J. Candlin, after his time at Princeton, returned to the UK. Later his interests moved towards computing and he became lecturer at Edinburgh. 743 Glen Schaefer (–1986), stayed on at Birmingham. He eventually published,

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on as a research student. He is very bright and quite likely to stay on in this country, if there is a job for him since physics in South Africa is not very attractive.744 Finally as regards ﬁeld theory there is a young American, Lieb, who will be here for another year.745 Then we have a South Korean and a Greek, who are nice people, but not ﬁrst rate. Two of our own graduates in their second year of research (one on solid state and one on nuclear theory), both of whom seem very promising. Two of last year’s graduates who are in their ﬁrst year of research, both on relativistic electron theory. One rather promising and the other more average. Two French men, both more interested in nuclear problems. One will be returning to Paris in the summer, the other will continue for another year. Finally there is Miss Dee, a Cambridge graduate who has started here on nuclear problems and is likely to continue and a Japanese research Fellow, Yoshida, who will stay another year if we can renew his Fellowship. This list omits a few people who are leaving this summer and therefore don’t concern you directly. Expected newcomers include Nicholson from Australia, who should be here within the next few days and who wants to do ﬁeld theory on a Canberra Fellowship; one of our own graduates (the present ﬁnal year is exceptionally small and except for this man exceptionally poor); there are two very promising Fulbright Fellows, one starting research and the other one with a Doctor’s degree; one Canadian, Vogt,746 now with Wigner, who seems very bright but whose fellowship is not as

among others, a joint paper with Gerry Brown and J.S. Langer, G.E. Brown, J.S. Langer and G.W. Schaefer, ‘Lamb Shift of a Tightly Bound Electron’, Proc. Roy. Soc. A251, 92–104 (1959). 744 Stanley Mandelstam (1928–) had studied at Witwatersrand and Cambridge and obtained his Ph.D. from Birmingham in 1956. He went on to do research at Birmingham, Columbia, and Berkeley where he eventually became professor of physics in 1963. 745 Elliott H. Lieb (1932–) studied at M.I.T. and Birmingham where he obtained his Ph.D. in 1956. He took on posts in Kyoto, Illinois, Cornell, at IBM, in Sierra Leone, Yeshiva University Northwestern University and M.I.T. before becoming professor of physics at Princeton in 1975. 746 Erich Vogt (1929–), later professor at the University of British Columbia, Vancouver and director of TRIUMF, Canada’s National Laboratory for Particle and Nuclear Physics.

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yet assured; one Italian and one other Japanese, both interested in nuclei; one Frenchman from Joliot’s group; one very promising man from Oxford, and possibly Felix Adler from Carnegie Tech, on a year’s sabbatical leave.747 This is all we shall have room for, but I have turned down a great number of applicants some of whom looked quite promising, though I have not in fact refused any serious application from this country. You are quite right that progress with the synchrotron experiments is slow, largely because we now know that the energy region available here is not one for new discovery, but one for precise experiments and that of course always takes time. Progress is, however, continuous and we are in the satisfactory position of being evidently useful to the physicists in keeping them informed and in discussing hypothetical experiments. What you say about experimental physics is quite true and is worrying everybody. We begin to feel that the lack of equipment is only one of many reasons and that perhaps the absence of a systematic training of the younger people in modern physics, including those parts not studied locally, has a lot to do with it, and in almost every University now measures are being discussed of remedying this. In particular Mott is proposing to start postgraduate courses and he hopes that Bethe, who will be there next year, will play a large part not only in giving such course, but in organizing a suitable scheme. Nevertheless there are still good people around and the standards and the spirit of the groups, particularly at Harwell and at Liverpool, are very high. My own feeling is that for theoretical work it is not absolutely necessary to be close to a group contributing to the latest discoveries, what is absolutely essential is to be in close contact with experimentalists who are alive and up to date and who can digest for us new experimental information that becomes available. This we have got in a large measure at Birmingham and if we do not have more of it it is very largely our own fault. In educating the experimentalists here and in maintaining contact with them Feldman has been very useful. There is no immediate pro747

Felix T. Adler, (1911—79) staﬀ member at General Atomic (1956–58), consultant at Los Alamos National Laboratory (1961–78), he served as professor of physics and nuclear engineering at the University of Illinois, Urbana between 1958 and 1979.

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posal to replace him. It would not be diﬃcult to get the same kind of grant again, but I have no suitable candidate. However, I do not think this is serious because our group is now generally in much closer contact with the Physics Department than used to be the case (there are for example weekly meetings on high energy physics which are attended usually by three or four of our people) and I expect of course also that your return will help matters in this respect. Our group is still weakest in the nuclear theory side where at the moment we are down to quite junior people, except for myself and except for the Japanese, Yoshida, who however still has diﬃculties with the language and therefore cannot yet pull his full weight. I ﬁnd it diﬃcult to keep myself up to date suﬃciently to guide people in the right direction, or even for example to work out a programme for our nuclear physics discussion meetings, which for that reason have lagged behind. I expect of the newcomers next year some will be able to help and of course your presence here will help further even though I imagine you will not want to work on nuclear theory yourself. Incidentally I have omitted to mention another useful fact, namely that we have an arrangement by which we can pay Salam’s expenses during any periods he can spend in Birmingham, during the Cambridge vacation. We regard this as an attractive arrangement and I am almost sure it will continue indeﬁnitely. The most interesting progress here recently is work by Edwards whose use of functional methods is approaching more closely to the possibility of a realistic solution for the full pseudo-scalar case with recoil. However, of course there are many diﬃculties and one can’t be sure until one actually has a solution which still looks a fair way oﬀ. With all best wishes, Yours sincerely, R.E. Peierls

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[611] Rudolf Peierls to Freeman Dyson [Birmingham], 7.4.1955 (carbon copy) Dear Dyson, Thank you for your letter.748 I think we would all agree at once with your remark that even allowing for vacuum polarization Edwards has not proved that anything converges. What seemed to me so instructive was that in the absence of vacuum polarization one can prove, or better one can make it plausible by very simple reasoning that the series diverges even if one uses the cut-oﬀ and therefore removes inﬁnities. Now this situation is changed by the vacuum polarization term so that the basis for this proof collapses and I would take this as an indication that the vacuum part has profound inﬂuence on the structure of the theory and one should not believe any conclusions derived from an approach which ignores it. This of course agrees so far with what Feynman said at Rochester, except that Feynman’s analysis always necessarily puts the vacuum correction in to the exponent, which would seem at sight a slightly dangerous procedure, since any zeros of the Fredholm determinant, if they are anywhere near the relevant region, would produce logarithmic singularities in the exponent which would give quite an erroneous impression of the diﬃculty. By the way, I should have mentioned in my last letter that the Matthews-Salam paper apparently is going to appear in the Physical Review after all.749 Our letter withdrawing it crossed with a note from Goudsmit saying it was being published, but changes have been made which stress more clearly the relations of the contents to the results of Feynman and other people. About the method of Edwards it is certainly true that their ultimate value cannot be judged until the whole thing has been done. However, since he wrote the note which you have he has added a number of very important further steps and there is in fact an outline of a full 748 749

Letter [609]. Letter [606], notes 723–24.

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treatment of the charged pseudo-scalar case with recoil. Of course it is only approximate and one has to ﬁnd out how great the errors are, however, the nature of the theory is again such that it is exact in the case of weak coupling and that it is extremely good if not rigorous in the case of strong coupling (rather like the method used in Feynman’s paper on polarons. The calculations also have not been carried out completely and these get exceedingly complicated. It is in part a question of what features of the propagator one wants to look at. The exact solution for the propagator would in any way really contain the whole of physics almost everything that can happen as a virtual process which will leave its trace in the propagator, but there are some ideas about how to proceed. One satisfactory feature is that there is no problem about renormalization at all stages the diﬀerent terms just split oﬀ cleanly and there is never an ambiguity. I think it is a pity you did not get to Moscow and particularly that in the end nobody from the West seems to have gone (possibly Kallen has gone but I have not yet heard), so at the moment it is the West which blocks international contact of scientists, certainly a most unsatisfactory situation.750 However, I am sure everybody will understand that in your case the risk of serious complication was extremely heavy and I think really everyone else in your position would have done just the same thing. I must say I don’t quite see why Feynman did not have the courage to go because it would in his case at most have resulted in some unpleasant publicity. I tried my best to persuade Salam to go and he almost went. With kindest regards, Yours sincerely, R.E. Peierls

750

See letter [609].

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[612] Rudolf Peierls to Nevill Mott [Birmingham], 18.4.1955 (carbon copy) Dear Mott, I am again late with my replies to various letters of yours on rather long term questions and I am trying to catch up with arrears. This is about your letter of 10th February751 in which you raise the general questions of how to improve physics in this country. I found, like Salam, that the Rochester Conference showed up a lot of things which are common ground in America and less well known here, but this did not depress me quite as much as Salam, because I have had this kind of experience many times before and know that there are compensations. However, it is quite true that physics in this country is behind that in America and not merely because of a lack of big machines. I do not know of any simple remedy. It is very largely a question of spirit and of ways of thinking, rather than of speciﬁc organizational measures which would be easy to take. For example it is I think generally true that we tend in this country to know less than we thought about what goes on in detail in other laboratories. This is a question of time only for the senior people, who are reluctant to go away for a day when it is not absolutely necessary. For younger people to spend a day occasionally at another university is not a serious problem and even the question of expenses is not serious. Many such visits are possible without being away overnight and fares are not all that large. Very often people also can arrange to stay the night with friends. The real trouble I think is that it just does not occur to people to do this except in special circumstances. Perhaps they do not know the right place to go to or with whom to talk. This in part is remedied by senior people and in this respect I think occasional meetings, smaller than the big international conferences, to which only a few of the research students can get admission, but large enough to bring together people from diﬀerent Universities. It would not be possible to 751

Letter could not be located.

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cover in such meetings all the interesting topics, but they could serve to establish contacts, which people could follow up on their own. However, a much more serious problems seems to lie with experimental physics. There is somehow a lack of leadership. There do not seem to be enough people who are really excited about the problems of high energy physics and who think of these problems on their own merits without necessarily linking them to an immediately practicable experiment. Perhaps it is not reasonable to this kind of interest to have survived or developed during the years when there was no chance of such experiments being done in this country. Perhaps it is a question of education and perhaps we are really short of leaders of the right type or perhaps we have failed to spot them and put them in the right positions. I think it is likely that all these answers are true to some extent and no quick remedy is evident. I should certainly be glad to talk more with you about these problems, although you will have seen from the above that my idea on the subject are far from being clear or deﬁnite. I shall next be in Cambridge on 25th May, when Ziman752 has asked me to talk to their Wednesday colloquium. I shall have to come up the night before and if you happen to be free on the evening of Tuesday, 24th May I shall be very glad to see you then. It may also be that I can stay up for the following night, but this is not clear yet. Yours sincerely, R.E. Peierls

[613] R.H. Dalitz to Rudolf Peierls Princeton, 18.4.1955 Dear Professor Peierls, I was very surprised to hear that nothing came out of your interest in the Oxford position (which suggests a sad lack of imagination at Oxford) — 752

John Michael Ziman (1925–2005), studied at Hamilton and Oxford where he obtained his Ph.D. After research in Cambridge he moved to Bristol where his research interest shifted from pure science to philosophy of science.

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my previous letter took it very much for granted that you would leave and should be understood thus. Thank you for your detailed letter. I certainly have no reason to expect that there will ever be a shortage of research students as long as you are there. I agree that it is very healthy to have research students from abroad, and it is also very interesting and pleasant for all concerned — my only point was that the possibility of a number of healthy and active schools of theoretical physics will depend on having suitable people stay in the country, and I am only sorry that more of the people who do stay have not been associated with a closely-knit and practical-minded school such as Birmingham. I am inclined to think that the disadvantages for a theoretical physicist working remote from active experiment depend a good deal on the nature of his work — if he seeks to account for low energy pion phenomena in terms of a meson theory, for example, the disadvantage is not very great. But if he has a direct interest in the phenomena themselves, he needs to know early what types of observations are becoming possible, how the current data is behaving — what it is interesting to discuss depends a good deal on what is experimentally feasible (although Wick — and experience — have taught me the principle “what is impossible today is still worth discussing now, for it will be done within two years”). Even if preprint communication were eﬃcient, (word-of-mouth is more the rule here), the phenomena have been thoroughly discussed by the experts on the spot before preprints go out. (Of course the Rochester Conference and the APS meetings are particularly helpful in this matter). However, there are always things which have been overlooked, and there are obvious advantages in being able to stand at a distance, especially for one who is not particularly quick-witted. I did not wish to stress this point unduly. I am a bit surprised now to look back at the heavy concentration of ﬁeld theory at Birmingham. I have wondered to what extent this can be correlated with the level of experimental activity in England, but I expect it is really just a ﬂuctuation. The organisation of academic physics on the States has greatly impressed me. In the best places, the graduate student training is very eﬀective and to the point; the students have a practical grasp of quan-

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tum theory and its applications to many ﬁelds of current interest, which has often surprised (and embarrassed) me — in comparison English students seem one-dimensional in their interests (in physics). At ﬁrst I was surprised at the fewness (low density!) of theoreticians here, but it is certainly right to encourage students to do experimental work with such facilities available here. I would very much like many English experimenters to see the courses which it is considered proper for a graduate student in experiment to attend here! The separation between graduate and undergraduate work seems very convenient for the senior people, also there are now so many research institutes and special laboratories, whose people have at most a few graduate courses to give, this tendency seems to be on the increase as machine projects are becoming too large for a University department to manage. I should mention here that I had a call from Chicago a few days ago — they are anxious to ﬁll this position and have no authority to hold over the oﬀer, so I turned it down. Another oﬀer a year hence may, however, be possible. Incidentally, Wick decided not to go, and Gell-Mann left for CalTech. I was not asking for advice on Canberra,753 but I would infer that you also think it rather unattractive. I feel that one should perhaps look to the future — Australia is growing rapidly and is actively interested in atomic energy development, ten years hence (say) such a position may have more to oﬀer than any position that may be available to me in England. Also it oﬀers complete freedom for research (although in some isolation) which is an unusual attraction. However, it is always hard to start from scratch, and there are special diﬃculties in this case; one cannot hope for ideal conditions and there is a challenge to see what one can do. But it is rather likely that I would not be acceptable for the position — however, if it were oﬀered to me, it would not be easy to turn down. I am rather sorry that it is coming up at this time. I must say that I have little feeling now for the degree of isolation which would be involved in working in Canberra. I was very interested indeed to hear how things stand in Birmingham at present.

753

See letter [608].

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I do not have much news of physics at the moment — people here seem rather remote from one another and there have been few visitors — but what little I have is enclosed separately. With all good wishes, Yours sincerely, R.H. Dalitz

[614] Wolfgang Pauli to Rudolf Peierls Z¨ urich, 6.5.1955 Are you — or some other from Birmingham — going to the conference in Pisa?754 I am not sure yet whether or not I shall go.755 Dear Peierls! I would like to write to you now my present views on renormalized quantum electrodynamics. Although everything is still conjecture, at least it turned out recently that Landau has the same conjectures as I. The papers in question all appear in “Doklady Akademii Nauk SSSR”, Autoren: L.D. Landau, A.A. Abrikosov and J.M. Khalatnikov.756 754

Between 12 and 18 June 1955 an international conference on elementary particles took place in Pisa. Pauli only decided to attend when it became clear that the conference would attract participation of many eminent colleagues from all over the world. See Pauli Wissenschaftlicher Briefwechsel, IV/3, pp. 232–4; see also Il Nouvo Cimento. Supplemento (1955) which published the most important papers of the conference. 755 Handwritten addition at the top of the letter. 756 L.D. Landau, A.A. Abrikosov and I.M. Khalatnikov, ‘On the removal of inﬁnities in quantum electrodynamics’, Doklady Akademii Nauk SSSR 95, 497–500 (1954); L.D. Landau, A.A. Abrikosov and I.M. Khalatnikov, ‘An asymptotic expression for the electron Green function in quantum electrodynamics’, Doklady Akademii Nauk SSSR 95, 773–76 (1954); L.D. Landau, A.A. Abrikosov and I.M. Khalatnikov, ‘An asymptotic expression for the photon Green function in quantum electrodynamics’, Doklady Akademii Nauk SSSR 95, 1117–1120 (1954); L.D. Landau, A.A. Abrikosov and I.M. Khalatnikov, ‘The electron mass in quantum electrodynamics’, Doklady

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1. 2. 3. 4.

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l.c. l.c. l.c. l.c.

95 95 95 96

(3), (4), (6), (2),

497, 1954 773, 1954 1177, 1954 261, 1954

Do you have this periodical in England and can you understand sufﬁciently Russian to read these papers? K¨ all´en, who was recently in 757 and had discussions there with the groups of Landau and Moscow of Tamm brought these papers to Copenhagen and they are going to have them translated there by the theoretical CERN division. I did not see these papers myself, but I read Landau’s summarizing article (for the Bohr festival book) “The quantum theory of ﬁelds”,758 where the four mentioned papers are also quoted. I don’t think that anything is really proved by Landau and his collaborators, and K¨ all´en also has this impression. Nevertheless, I am ready not “to bet”. Landau came to his ideas quite independent of Lee’s model (which he did not know at all). (I was inﬂuenced by it, but not by it alone.) Not the conjecture. Let e be the physical, e0 the mathematical electrical charge, and let us ﬁrst introduce a cut-oﬀ in momentum space at a ﬁnite momentum P destroying this the Lorentz-invariance of the theory. This I held essential in order that the renormalized qu[antum] el[ectro]dyn[amics] is at all deﬁned. Write then e20 , (1) e2 = 1 + e20 F (P, e20 ) Akademii Nauk SSSR 95, 497–500 (1955). English-language versions of these papers can be found in D. ter Haar, (ed), Collected Papers of L.D. Landau, Oxford, 1965, papers 78–81. 757 Gunnar K¨ all´en had been the only Western representative at the All Union Conference 1955 in Moscow, where he reported on the mathematical structures of the Lee-model renormalized ﬁelds. In Moscow, he had discussions with Landau and his Russian colleagues, and he returned to Copenhagen with copies of the above mentioned articles which he had translated into English for use by Western colleagues. See letter K¨ all´en to Pauli, 19.4.1955, Pauli, Wissenschaftlicher Briefwechsel IV/2, p. 201. 758 L.D. Landau, ‘The quantum theory of ﬁelds’, in W. Pauli (ed.), Niels Bohr and the development of physics, New York: McGraw-Hill, 1955, pp. 52–69.

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consider only real e0 ’s. Then it is proved that e2 /e20 < 1 or F > 0. Conjecture (both of Landau and mine): There is a lower bound for F whatever the real value of e0 may be F > µ(P ) > 0 and for large P the order of magnitude of µ(P) will be log P/m: µ(P ) ∼ log P/m

for large

P

From this conjecture it follows e2 <

1 . µ(P )

Mathematically it follows for the limit P → ∞, e2 → 0. Or, the other 1 it follows way round, for the physical value∗ e2 = 137 µ(P ) < 137, which blocks the possibility to pass to the limit P → ∞. If the conjecture in question is true, renormalized quantum electrodynamics would never be a consistent lorentzinvariant theory, a negative statement in which I now ﬁrmly believe (so does Landau). On the other hand one would still understand well that renormalized quantum electrodynamics is a good approximation to the physical reality, as the cutting-oﬀ momentum P is very large of the order of magnitude ∼ m(exp)137. (Landau made an interesting attempt to connect this cutting oﬀ boundary with gravitational forces.) It seems to me very important that more eﬀorts should be made by the experts of ﬁeld-quantization and of renormalization to prove or disprove this conjecture. I am not myself such an expert but I have talked with and written to someone, however until now their methods to attack the problem do not seem to me really satisfactory. ∗ Units

= c = 1, m = electron-restmass.

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One question is: can F (P, e21 ) (for a ﬁnite P) in the denominator of (1) be developed in a power series in e21 ? (This would certainly be better than to develop e2 itself in such a power series, as is known for some time already.) Thirring759 — the expert, which is locally nearest to me (Berne) — has certain doubts about it: he is afraid, that even for a ﬁnite P power series of F might have the convergence radius zero. But this may be a bit overpessimistic. I rather believe that for ﬁnite P the power series of F exists and even has the convergence radius inﬁnite. Only two terms of this power series are known at present (see: Jost and Luttinger, Helvetica Physica Acta 23, 201, 1950,760 which paper is also quoted by Landau) and both are positive. Jost already then guessed (and still believes in it now), that all coeﬃcients of this power series will turn out to be positive (at least for suﬃciently large P ). In this case one would of course have a lower bound for F in the hand (provided that the power series for F actually converges everywhere). I am sorry, this is all what I know about the problem of the range of consistency of the renormalized quantum electrodynamics at present. Dyson and the G¨ ottinger “Feldverein” for a while recommended a kind of “Vogel Strauß politics”, namely not to cut oﬀ and not to talk of e21 at all and only to use e2 . But this seems to me completely silly. Every statement of e2 can be translated into one of e21 and vice versa and if our conjecture is true the use of an e2 larger than µ(P ) would correspond to a non-real e1 -values (or to no e1 values at all) and will certainly give rise to pathologies (the details of which seem to me of no great interest). It seems to me urgent to ﬁnd a direct and eﬃcient method to verify or falsify our conjecture which concerns the use of a ﬁnite cut-oﬀ. 759

Walter Thirring (1927–), obtained his Ph.D. from Vienna in 1949. After research at Dublin, Glasgow, G¨ ottingen, Zurich, Bern, Princeton, M.I.T. and visiting professorships at M.I.T. and Washington, he became professor of physics at Bern, before taking up a professorship at Vienna in 1959. 760 R. Jost and J.M. Luttinger, ‘Vakuumpolarisation und e4 -Ladungsrenormalisation f¨ ur Elektronen’, Helv. Phys. Acta 23, 201–214 (1950).

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I am thanking Dr. Edwards very much for sending his letter to Metzer761 and his manuscripts.762 It will take some time until we have studied it thoroughly. It seems to me, that insuﬃcient attention has [been] given his papers to the renormalization of the coupling constant which I held to be decisive in all examples. All good wishes, Yours W. Pauli

[615] Rudolf Peierls to Wolfgang Pauli [Birmingham], 9.5.1955 (carbon copy) Dear Pauli! Thank you very much for your interesting letter.763 We had reprints of the four Landau papers and have spent a fair time studying them. As a result we believe on the whole that Landau is right, but his arguments in a typical Landau fashion tend to accept certain steps as plausible and certainly do not represent a rigorous proof. I certainly like your conjecture and I always felt very strongly that the fact that renormalization works in the frame work of the series expansion does not prove that the theory without cut-oﬀ makes sense. The possibility that such things may happen, was brought home to me particularly by playing with non-local classical theories. (I agree of course with your point that classical models can be quite misleading.) But in a paper by Irving764 which was done here, it was shown that if 761

Kurt Metzer, English physicist who spent some time at Zurich with Pauli. See Pauli, Wissenschaftlicher Briefwechsel IV/2, p. 869. 762 S.F. Edwards, ‘A Note on the divergence of the perturbation method in ﬁeld theory’, Phil. Mag. 45, 758–61, (1954). 763 Letter [614]. 764 J. Irving, ‘The eﬀect of the tensor force on the binding energy of the alpha particle’, Proc. Roy. Soc.A 66, 17–27 (1953); J. Irving and D.S. Schonland, ‘Energy of the ground state of Li6 ’ , Phys.Rev. 97, 446–450 (1955).

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one takes the McManus-type non-local equations seriously765 then while the series expansion looks alright and allows one after renormalization to go in each term to the limit, the physical results for the scattering of light of very high frequency depend not on the renormalized, but on the bare mass and therefore becomes nonsense when the cut-oﬀ momentum exceeds a certain value. I want to regard this merely as an illustration of what may happen. The classical theory is certainly no proof that it will happen. Edwards has come to conclusions766 which are very similar to yours and Landau’s except that he has looked more at mass than charge normalization and he can derive from very general arguments plausible results about the behaviour of the propagator for very high momentum, which in the case considered by Landau, agree exactly with Landau’s results and which would support your qualitative conjecture, i.e. the idea that one is not allowed to go to the limit in a fairly general type of theory. We agree of course that in Edward’s approach much remains to be done about renormalization. The reason why this has been omitted is in part because this is very diﬃcult, but there is another point. One cannot, of course, talk about renormalization without reference to a speciﬁc procedure for solving the equation. I believe a good deal of confusion has been caused by people starting from renormalization in the frame-work of series expansion and then jumping to the conclusion that the results have a meaning which is unrelated to the series. Now the experience with the type of method Edwards is trying has always been that whenever some simpliﬁed theory or some part of the whole theory is amenable to a mathematical solution, then at least the mass renormalization deﬁnes itself and there is no doubt about what should be done. For this reason it seemed more proﬁtable to concentrate on a method of solution rather than worry about renormalization If it is true that one must not go to the limit then of course we are forced back into theories of the non-local type. I am not too pleased with 765

See letter [396], note 80. S.F. Edwards, ‘A note on the divergence of the perturbation method in ﬁeld theory’, Phil. Mag. 45, 758–61 (1954). 766

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our previous attempts to handle non-local theories, but I have a feeling that one would get further with the following point of view: There are several possible ways of describing non-local equations, one is to use generalized Poisson brackets which I have tried to deﬁne, but then one is in diﬃculty with proving consistency and also it is not at all clear how one is to solve such equations, other than in perturbation theory. Another is to use the Yang-Feldman formalism767 as for example Møller and Kristensen have done,768 but then there is trouble, ﬁrstly about deﬁning a theory other than through a series expansion and also one is troubled by the question whether the ‘Bloch theorem’ is valid, a point on which the Japanese have thrown considerable doubt. Finally one can start from the Feynman integration over paths, which can immediately be applied to any non-local theory derived from an action principle, but the doubt in that case is whether the S-Matrix resulting from the theory is unitary. I do not believe any proof for the unitarity of Feynman’s S-Matrix has been given, except by showing its equivalence with the Hamiltonian formalism where this exists. Now if one believes that the equations one is handling are the ﬁnal ones they must be unitary. If one understands by the non-local theory simply that part of physics of which at the present time we have reasonable knowledge, omitting regions where new ﬁelds or new particles (or possibly, as Landau says, even gravitation) may be of importance, then the theory need not be unitary. In any theory from which possible virtual processes have been eliminated, one does not get a unitary S-Matrix. However, then there is still a requirement, namely that the total probability of all calculable processes should be less than one and never greater than one, since the lack of unitary rules results from throwing away things that may not happen. I see no clear way of deciding whether Feynman’s equations with any given non-local action satisfy such an inequality or how one is to restrict the actual principle to make them satisfy it. But certainly if one gives up the need for exact unitarity, one acquires more freedom and things might work better. 767

C.N. Yang and David Feldman, ‘The S-Matrix in the Heisenberg Representation’, Phys. Rev. 79, 972–78 (1950). 768 P. Kristensen and C. Møller, Mat-fys. Medd. 27, 7 (1952).

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It seems therefore that as on some previous occasions our conjectures are rather similar, if perhaps for diﬀerent reasons. Unfortunately I shall not be able to come to the Pisa Conference, because it happens at a time when we are busy with examinations, but Edwards is certainly going and probably Matthews, Feldmann and Valatin from here as well. I think you might ﬁnd it interesting to talk to these people. If you cannot get to Pisa, perhaps it would be a good idea to see whether Edwards could visit Z¨ urich on his way back. Yours sincerely, R.E. Peierls

[616] Wolfgang Pauli to Rudolf Peierls Z¨ urich, 3.6.1955 Dear Peierls, I have still to thank you for your letter of May 9th.769 Apart from reproduction of your well-known McManus complex it contained very important information. 1) That the Landau papers have been studied in Birmingham and that “on the whole you believe that Landau is right.” (I never doubted the “typical Landau fashion” of his arguments.) 2) That you like my conjecture. That for larger energies for all (however complicated) processes the Born approximation with the bare mass and charge holds, is the content of a general conjecture of K¨ all´en’s which is proved for particular processes only. I do not believe that in order to prove my conjecture, it is necessary to prove K¨allen’s conjecture generally. (N.B. In the Leemodel the latter is true.) — I think charge renormalization is well deﬁned, independently of any power series development. Your inequality for the total probability seems to me hopeless to prove in a theory with non-unitary S-matrix. 769

Letter [615].

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Although I know some interesting models for renormalization of quantized ﬁelds besides the Lee-modell, no decisive progress has been made in the problem to prove or disprove mine and Landau’s conjecture in quantum electrodynamics. I have now decided to go to the Pisa conference and I am looking forward to see there Edwards and the other people from Birmingham, which you mentioned. His majesty Julian I Schwinger will be there, too. I thank you very much for your book on quantum theory of solids.770 I give now a lecture on problems of quantum statistics, where I am also discussing in detail the theory of the de Haas-van Alphen eﬀect (just in order to learn it). I had used already the copy of your book in the library at this occasion before your dedicated copy has arrived.771 While I found physics always discussed ﬁne in your book, I also found that you thankfully followed my traces as a teacher by introducing many errors of signs. In order to diminish my greater depth in this respect I am enclosing a page with a list of errors in the formula of your book in connection with the de Haas-van Alphen eﬀect. I am looking forward to read the other chapters of your book. Yours sincerely W. Pauli [617] R.H. Dalitz to Rudolf Peierls Brookhaven, 4.8.1955 Dear Professor Peierls, I am writing this letter mainly to clarify my impressions of a long discussion which we had with T.D. Lee today on a bold synthesis he has suggested, which may have some elements of truth. I hope it may have some interest for you also. First a little background. Lifetime measurements for Kµ2 and Kπ2 by counter method are under way at Berkeley. I will not give details of 770

R.E. Peierls, The Quantum Theory of Solids, Oxford: Clarendon Press, 1955. Rudolf Peierls had dedicated the copy ‘To Professor Pauli who introduced me to the subject of solid-state theory, with compliments R.E. Peierls. Mai 1955.’ 771

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the method as it is quite similar to that used by the Princeton group and by Hyams at Manchester.772 With 82 Kµ2 and 25 Kπ2 counted (the delay time for the standard origin being measured), Alvarez believes that these lifetimes cannot diﬀer by more than 40%. The τ -lifetime has been measured again by exploding emulsion stacks at two distances from the source, with a result 1.0 × 10−8 sec (±30%). Also the joint, Kπ2 lifetime has been deduced from the decays-in-ﬂight observed along K-tracks coming into the emulsion — this is also 1.0 × 10−8 sec with a similar error. On the other hand, decay statistics of the τ -meson make it very unlikely that the τ could decay to 2π and be identiﬁed with the θ-meson. So, Lee’s starting point is that the τ and the θ should be diﬀerent but with the same “apparent lifeline”, and essentially the same mass (the K + , τ + mass diﬀerence is now < 3m3 according to Berkeley). Also there is a desire to link the Kµ2 , Kµ3 Ke3 decay nodes to the explanation of beta decay. Now what kind of intermediate meson could account for beta decay, which is S+T coupling in about equal proportion? To obtain tensor coupling a vector meson is needed — to agree with the shape of > allowed spectra, it must be heavy (∼ 1000 me ); three requirements have been long known. Lee suggests that this should be the θ-meson, a (1-) meson can readily give 2π decay. From µ-decay and beta decay, then gµν gP N and gev is not very far diﬀerent.

772

Bernard Hyams, at the time at Manchester University, joined CERN in 1957, where he remained until 1990.

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µν and to ev PN , to µν through Now θ + can decay to 2π through + through gev (this latter is something of a diﬃculty since θ → e+ +v has not been observed with certainty but possibly gev is somewhat less than the other links, this is not clear). But these decays are all fast taking the various g’s from beta decay etc. with lifetimes close to 10−14 sec. How then to account for the observed Kπ2 lifetime? Lee suggests that τ of (0-) and that the θ mass is a little less than the τ mass, say ∼ /me . Then

τ →θ+γ

(1)

is allowed, with probability lifetime depending on the mass diﬀerence

= mτ − mθ and the τ -meson radius. Lee supposes that this lifetime is 10−8 sec and that the tracking ratio τ → 3π/τ → θ + γ is 1/10 (the observed τ + /K + ratio). You will then see that the observed K + lifetimes are all governed by the lifetime (1), so that the “apparent lifetime” for Kπ2 , etc. is actually the τ lifetime. It is now supposed further that the θ particle does not appear directly in associated production. If it did, say π − + p → Λ◦ + θ o ,

(2)

and charge independence is assumed, π + + N → Λ◦ + θ + should go but θ + → π + + π o quite quickly (∼ 10−14 sec) and one fouls seem to have π + + βn → Λ◦ + π + + π o

(3)

is unassociated production. (However I do not believe that situation (3) has really been examined experimentally yet.) So Lee supposes, instead of (2) that (4) π − + p → Λ◦ + τ o and that τ o → θ o + γ could explain the appearance of θ o . Note that the mass diﬀerence mτ o − mθo may be quite diﬀerent from Λ above so the τ o , τ + lifetime can be completely diﬀerent — the observed “θ o lifetime” of 2 × 10−10 sec. would then really be the τ o lifetime and the

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τ o → 3π decay mode would no longer be able to compete with this (∼ 10−3 branching ratio). Many things still lie outside this scheme — the π − µ decay cannot go through S or T coupling, i.e. through a (1-) θ-meson. The Kµ3 and Ke3 decays do not appear naturally — if the neutral particle is a γ then they will be too slow and if it is a π, additional couplings are needed (e.g. a weak τ + → θ + + π o which then → π o + µ+ + ν). Alvarez is making an attempt to detect a ∼ 12 Mev photon in coincidence with the Kµ2 decay, but this has obvious diﬃculties. But this gives a picture so diﬀerent from anything that has been suggested before but which brings together at least in a rough way, some very diﬀerent aspects of our problems, that it certainly merits a good deal of thought. I might say that Lee does not ﬁnd it satisfying or anywhere near a ﬁnal picture, but hopes that some elements of it may be useful. The prospect of a τ − θ pair with masses and lifetimes so close certainly suggests a situation whose solution may seem rather strange to us! Life in very enjoyable here, although the humid heat is sometimes not easy to bear. Valda and the children are all very brown and enjoy being able to visit the ocean beach very frequently. The cosmotron has been running rather spasmodically. There was a maintenance shutdown, a failure in the fuse across the magnet circuit meant another 10day break and now there is a good deal of work on the machine concerned with the external beam project. I hope the problem of beam extraction is being pushed very rigorously at Birmingham — it seems the only hope for the synchrotron to make any really signiﬁcant contribution. Our departure now seems very near, and I have a great deal to do before the end of the summer — the weather, the seminar activities and the many interesting visitors all make steady writing a diﬃcult proposition! With good wishes to all, R.H. Dalitz

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[618] Rudolf Peierls to John Cockroft [Birmingham], 9.9.1955 (carbon copy) Dear Cockroft, I am writing about the question of the plans for a large accelerator. First of all I must apologise for failing to reply to Schonland’s letter at the right time. I misread the letter and was under the impression that replies were only expected later. However, if I had written at that time I would have advocated the high intensity machine at 2–3 GeV, in line with the conclusions reached at your meeting. Since then I think the case against the 12 GeV machine has been strengthened by the news of the Russian project, since it is most unlikely that the energy interval from 10–12 GeV will be critical, and one would surely expect that if for ﬁve years most of the interesting work will have been done up to 10 GeV, which can conveniently be carried out with a low intensity machine. I admit the force of Powell’s argument as regards negative K particles, but while this indicates some limitations of the work in the 2–3 Gev region, it does not in the light of the Russian programme justify the 12 GeV project. In addition I do not think one can be at all sure that in ﬁve years and later the interest will centre on negative K particles, but I think one can be sure that high intensity beams, which permit more accurate and more detailed measurements, for example of angular distributions of resonance curves and of secondary reactions will always justify themselves in any energy region. It is quite likely that new and exciting things will be found at the higher energies. It is probably true that at any time the most interesting physics will be done in the highest available energies, but clearly one cannot hope to reach, in a reasonable time, the maximum available energies, and it is just impracticable for this country to compete with the CERN and Brookhaven projects. Looking further ahead, no doubt in the distant future the questions will arise whether one can exceed the 25 MeV ﬁgure which looks like the practical limit at the present time. This will call for new ideas

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in accelerator design and the experience in thinking about the present high intensity 3 GeV machine, one is as likely, as by another method, to collect new ideas. Whether even with the most brilliant ideas one can hit on a design for energies above 25 GeV which would be within the means of the U.K. is of course doubtful, but it would be satisfactory if this country could contribute some new ideas which would allow such energies to be reached by some international project. I would also like to comment on Powell’s remark about the location of the machine. There is no doubt whatever that the new machine is too big to belong to any individual University and I see the strength of the case for it being placed at Harwell. Even if it were anywhere else it would necessarily have to be available to members of all universities and would have to be operated under some central authority. Any such arrangement raises serious diﬃculties which I think must be faced. It is of vital importance for this country that there should be a satisfactory arrangement for attracting to fundamental experimental physics a suﬃcient number of men of the highest ability, and of giving them the best possible training. The traditional method of ensuring this is to have good equipment at the universities, so as to attract to the Universities staﬀ of high calibre who can keep in touch with the undergraduate teaching, and who can themselves keep alive by being active in research. We expect the same people to supervise research students and to bring up these research students in a university atmosphere, where they can keep in touch with other branches of the subject and with other subjects. If the equipment necessary for work in the front line of physics is available only outside the Universities we will run the danger that the staﬀ will have their main interest away from their normal laboratories and will come to regard the Universities as places to do their routine undergraduate teaching. Equally, the research students (or junior staﬀ equivalent in status to research students) may spend most of their time at the accelerator station and we may lose the important and stimulating eﬀect of their presence in the Universities and also the eﬀect of the University atmosphere on their continued general education. In as much as they may regard high energy physics as the only interesting branch of the subject, they may see a post at this accelerator station as the only

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worth while career and may not be attracted by a teaching post, which would allow them openly to do their main work during short periods away from their base, and as a result the present danger of losing good young men to permanent posts in the United States would obviously be enhanced. I do not believe there is any simple way out and in particular I do not believe that the idea of attaching the machine to a particular University would either be possible or would represent a satisfactory solution to the diﬃculties, but the conclusion to be drawn is that in the near future very serious thought should be given to this situation and that we should try to think of all possible ways to mitigate the disadvantages. Yours sincerely, R.E. Peierls

[619] Freeman Dyson to Rudolf Peierls Berkeley, 11.9.1955 Dear Peierls, I said I would write again at the end of the summer, and as I am leaving here to-morrow I will do it now. I am glad to see your book is out,773 though I have not yet managed to get hold of a copy of it. Actually, no deﬁnitive “results” have come out of the big machine so far. When I went round asking people how it is going, they all said “Oh in another month or two we will have something.” The bottleneck with could chamber and plate experiments is of course the scanning. The one experiment which has been completed since the Pisa conference is a counter experiment to measure the lifetimes of Kµ2 , Kπ2 and τ . This works in the following way. 773

See letter [616], note 770.

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ABCDEF are scintillation counters. X is 3/4 inch copper absorber, Y is 14 inch absorber-radiator. (A − F ) means a particle stopping in A. If in addition we have (B + D − C − E) it is a Kµ2 (B − D − C + E) or (C + E − B + D) it is a Kπ2 (B + C − D − E) it is a τ . The Kµ2 will include some Kµ3 and Ke3 but these are known from the plate experiments to be only a few per cent of Kµ2 , so they are ignored. The delay between A and BCDE is measured for each event of interest. The results are Kµ2 lifetime (1 ± 0.3) × 10−8 sec. (1 ± 0.3) Kπ2 τ (0 ± 0.5) However, they say one should not believe the shorter τ -lifetime because the τ events are contaminated with protons which make the stars in A, ˇ and the Cerenkov selector is only 99% eﬃcient against protons. They hope to overcome this trouble in the next run. This seems to be a good experiment and it opens up a whole ﬁeld of counter experiments which one can now do with K-particles. But the main hopes of the radiation Lab. are being put into bubble chambers.

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You probably heard that they are designing a liquid–hydrogen bubblechamber 50×50×20 inches, which is to give precise information about all the hyperon-K-particle interactions with good statistics. A big program is being planned to scan the pictures and put the results onto Hollerith cards on a mass production basis, so that really big quantities of data can be eﬀectively used: All this will take 2–3 years to put into operation, but it seems very sensible. Apart from the Bevatron, the most interesting experiments have been the triple-scattering experiments done with the 350 MeV cyclotron. These probably were mostly already reported at Pisa, but they are continuing to get new results. They have now enough to analyse the P − P scattering into phase shifts with SPDF waves (9 independent phase angles) using the same method as they used for π-P scattering. There are at the moment 3 possible solutions. All this is only at one energy, and if it can be done at more energy values (which is diﬃcult) one will really learn something about the P − P interaction. I myself have worked this summer mainly on cleaning up the theory of spin waves. I considered only the simplest and most ideal case of a lattice of ﬁxed spins with the nearest-neighbour exchange interaction J

(Si ˙ Sj ). nn

It turns out that there is a lot of interesting mathematics in this. The problem of course is to deal decently with the fact that spin waves interfere with each other not more than 2S reversed spins can sit on the same atom. I succeeded in understanding this. The problem arose because there are two published calculations of the spontaneous magnetization of such a lattice, which disagree. One by Kramers and Opechowski774 gave 3

1 − c1 θ 2 + c2 θ 2 − · · · 774

¨ W. Opechowski, ‘Uber die Temperaturabh¨ angigkeit der Magnetisierung eines Ferromagnetikums bei tiefen Temperaturen’, Physica 4, 715–22 (1937); H.A. Kramers, Commun.Kamerlingh Onnes Lab. Univ. Leiden 22, Suppl. 83 (1936).

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where θ = (kT /J). The other by Schafroth775 gave 3

7

1 − c1 θ 2 + c2 θ 4 − · · · These are supposed to be low-temperature approximations, good when θ 1. 5 In fact they are both wrong. The third term is of order θ 2 when S = 12 . Aside from the practical applications of this work (which is rather negligible) I found it interesting as a kind of object-lesson showing how a non-linear ﬁeld theory might behave. We have here a theory containing precisely one dimensionless parameter θ = kT /J. All the thermodynamic functions of the system can be calculated as powerseries expansions in θ, and one feels then that the theory is essentially complete. But there are obviously physical eﬀects proportional to e−J/kT = e−1/θ which become dominant at high temperatures, which give zero contribution to every term of the power-series. So the powerseries are in no sense a complete solution of the problem. If you translate this into quantum electrodynamics and replace θ by α, the moral is obvious. This letter is getting so long I had better bring it to an end quick. Were you at Geneva? I would be glad to hear what you thought of this aﬀair.776 I hope you had a good summer and some respectable holiday. Verena and I succeeded in getting for a few days into the high mountains, which are just wonderful. Verena also turns out to be an excellent walker and scrambler. Our children are in good shape too, and we are enjoying them more and more. George astonished us at the age of 2 y. 1 month by telling his left and right with 100% accuracy. But he has now forgotten it again. All good wishes to the family. Yours ever, Freeman Dyson 775

M.R. Schafroth, ‘Self-Consistent Spin-Wave Theory for the Ferromagnetic Exchange Problem’, Proc. Phys. Soc. A67, 33–38 (1954). 776 In August 1955, at the Geneva Conference on the Peaceful Uses of Atomic Energy, Soviet scientists had the opportunity, for the ﬁrst time since the war, to demonstrate their progress in nuclear physics. The conference marked the beginning of the reconstruction of scientiﬁc East-West dialogue.

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[620] Rudolf Peierls to Freeman Dyson [location unspeciﬁed], 14.9.1955 (carbon copy) Dear Dyson, Thank you very much for your long and interesting letter.777 I have recently been so poor a correspondent that I might for once answer for return. I am very interested in what you say about spin wave theory because we have recently been interested in this ourselves. A very good student of mine, Marshall (I have forgotten whether you overlapped at all, but I don’t believe so) has done some very nice work on this. In particular debunking the conventional spin wave theory which replaces the spin matrices by some phoney boson creation and annihilation operators. He also showed that the answer of Schafroth was wrong, though he is not proposing to publish this, and we have always suspected the T 2 term in the expansion, but had not yet got round to doing something about the problem. Marshall’s main eﬀort has been on the problem of antiferromagnetism, where the position is much more diﬃcult since one does not even have any simple approximation for the state of lowest energy. He has a nice variational approach to this problem, which indicates that in the anti-ferromagnetic case the energy of the lowest ordered and the lowest disordered state are so close together that in any given model one would have to calculate extremely accurately to be sure which is which, and in addition the answer is likely to be very sensitive to secondary eﬀects (such as interaction between other than nearest neighbours, etc). The result, while disappointing from the point of view of a clean theory, ﬁts in quite reasonably with the experimental situation. His papers are being published in the Royal Society,778 but if you are interested I can see if he has a copy to spare. I have always known the importance in physics of the function −1 e x . It occurs in a wide class of problems in statistical mechanics in 777

Letter [619]. W. Marshall, ‘The structure of magneto-hydrodynamic stock waves’, Proc. Roy. Soc. A233, 367–76 (1955). 778

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describing the diﬀerence between a very close and discrete spectrum at high temperature, and the classical continuous spectrum. The anomalous diamagnetism at low temperatures is an important example. I therefore agree enthusiastically when you say one must be prepared for such things happening in ﬁeld theory, though of course this does not prove that they do happen. We have been talking a good deal about Pauli’s worries on the meaning of a renormalized theory in which the ‘bare’ coupling constant is imaginary. They are really two quite separate questions. The ﬁrst is whether it is established that in the ordinary theory the bare constants really do come out imaginary, or in other words whether there is an upper limit to the observed coupling constant or charge for an arbitrary real bare constant. Pauli’s belief in this comes mainly from the Lee model, which of course proves nothing. Landau is also very conﬁdent, but we are not altogether convinced of his reasoning. On this point there is an interesting new paper by Taylor in Cambridge779 inspired mainly by your review of the Landau paper.780 He has obtained the same result from the equations of Gell-Mann, and this probably is a valid proof, but we are still digesting some steps in his reasoning. Assuming this is so there remains the question whether it is a disaster that one has to start from an unreasonable ‘bare’ theory. If the situation is similar to that in the series expansion, then the bare constants never appear in any physical answer and it should therefore not matter what they are, but I agree intuitively with Pauli that if one works with such a theory there should be some disaster somewhere. Pauli is so sure of this that when questioned at Pisa he refused even to discuss the question, but if disasters happen one ought to be able to say just what kind of disaster will occur and exactly where it will mess up the theory. Apart from this we have tried to understand the now fashionable low energy approximations. Matthews and Feldman have succeeded in 779

J.C. Taylor, ‘Self-Energy Eﬀects on Meson-Nucleon Scattering According to the Tamm-Dancoﬀ Method’, Phys. Rev. 98, 201 (1955). See also J.C. Taylor, ‘The form of the divergencies in quantum electrodynamics’, Proc. Roy. Soc. A234, 296–300 (1956). 780 ¨ F.J. Dyson and H.Uberall, ‘Anisotropy of Bremsstrahlung and Pair Production in Single Crystals’, Phys. Rev. 99, 604–605 (1955).

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simplifying the arguments on this a good deal, but of this you will hear shortly from Feldman, who is on his way to the Institute.781 I am particularly interested to understand to what extent these results depend on the model, and to what extent they are purely phenomenological. I believe we are in danger of making the same error that was made for a long time in the nuclear two-body problem, where we now know that owing to the eﬀective range approximation we are dealing with results dependent only on two parameters, and that therefore any kind of interaction with two parameters (and not too unreasonable in certain ways) will agree with the experiments. There the situation was confused for many years by people working with speciﬁc models, and taking any agreement they found as a conﬁrmation of the model. We have also put a considerable eﬀort into understanding the philosophy of Brueckner’s treatment of the many body problem, and I gather from Bethe and Weisskopf that noone in America outside Brueckner’s group has taken his approach at all seriously. Our impression so far is that for the idealised case of an inﬁnitely large nucleus calculating only volume eﬀects, his approximation looks good; we have gone through all the steps of his rather long and somewhat confusing reasoning and are reasonable happy about all but one on which there remains some confusion. Of course one wrong step is suﬃcient to wreck the answer, but since all other arguments turned out to be right, we are still hopeful. On the other hand I do not think much of his attempts to treat surface eﬀects let alone the problem of a small ﬁnite nucleus. We hope to put some more eﬀort into analysing these Brueckner methods still further. Yes, I did get to Geneva. At ﬁrst rather reluctantly and at short notice, but I thoroughly enjoyed it. It was great fun to watch the reopening of channels in international scientiﬁc communication. I found it a great advantage there to be able to talk Russian, and to know some of the Russians personally. Their performance on accelerators is staggering. By now you will probably have heard about this. They not only have the famous 650 MeV synchro-cyclotron, which employs an extraction method similar to the Liverpool one, but even better, giving an extraction eﬃciency of 5%, but they also have completed, though 781

G. Feldman and P.T. Matthews, ‘No-Recoil Approximations to Charged Scalar Meson Scattering’, Phys. Rev. 103, 1870–73 (1956).

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not yet in operation, a 10 BeV proton synchrotron of the Bevatron type, very lavish in space and rather conservative in design. The experiments with the 650 MeV cyclotron and with Veksler’s electron-synchrotron (of I believe 250 MeV) seem very good and accurate, but I have heard of nothing exciting. It is interesting that their planning of the experiments does not seem to have been guided by as close a contact with theory, as has been the case in Chicago. Another interesting illustration of your Bethe book review. In other words they did not have Fermi there. For example they have measured their scattering of charged mesons, but as far as I know have not observed the charge exchange eﬀect and therefore could not make a complete analysis. Their cosmic ray work is in bad shape; they had essentially two groups of which one produced the phoney mesons of which you have heard, and the other one was too busy debunking them that they omitted the chance of looking for new particles themselves. Their theoretical team seems good. The only theoretician in Geneva was Markov, who is a very nice person, though what he is doing himself on non-local theory is not exciting, but he talked a bit about the attitude of the Landau and Tamm groups. Landau is very gloomy about the prospects of renormalization theory and present ﬁeld theory in general, whereas Tamm’s people are busy doing rough calculations by TammDancoﬀ method and the like. The most important thing is that contacts should now be very easy. It is clear that Russians will in future be able to come to conferences, that they will invite people (I have a ﬁrm promise of an invitation to Moscow as soon as possible), they will now start again to publish foreign language abstracts with their papers, and evidently also the bar on publishing papers in foreign language periodicals has been lifted. We told them about the present practice about sending out preprints, and they will consider doing the same. It will obviously be useful to include them in the distribution of future preprint. Where one does not know addresses they can always be sent care of the Academy of Sciences. The spirit at the Geneva conference was best summed up by a remark which one of the Russians is supposed to have made to an American colleague ‘You know we are so glad that we have been told to be nice and charming to you’.

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We had a very successful holiday in Dorset. For once the weather in this country was better than anywhere else. I never wrote to say how much we enjoyed the visit of your parents the other day. I was highly amused by your father remarking at the end that he had been very surprised to ﬁnd how young I was. With kindest regards, Yours sincerely, R.E. Peierls

[621] Rudolf Peierls to Wolfgang Pauli [Birmingham], 16.9.1955 (carbon copy) Dear Pauli, There exists a scheme by which the British Council (a government organization which promotes cultural interchanges with other countries) can invite foreign scientists to visit Universities in this country. I have just heard that, at our request, they have given approval for an invitation to be sent to you. I understand that a similar request has been made by the University of Manchester and I believe that Manchester are to send you an oﬃcial invitation to come to this country sometime during the academic year 1955–56 and to spend some time in Manchester and in Birmingham. I am writing for the moment only to say how pleased we are that this invitation is being sent and to hope that you will ﬁnd it possible to accept. As far as Birmingham is concerned I believe any time during the academic year would be suitable, except the Easter vacation (end of March to end of April), when I myself maybe away, and of course the longer you can stay the more we shall be pleased. Before you decide on dates it would be best to wait for the letter from Manchester. Yours sincerely, R.E. Peierls

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[622] Rudolf Peierls to Robert Aitken [location unspeciﬁed], 20.9.1955 (carbon copy) Dear Dr. Aitken, I am writing to let you know about a new diﬃculty I have met as regards accommodation for my people and the proposed solution. I have been trying very hard to limit the membership of my department for the new academic year to remain within the available space. This involves always some guess work since some people do not know until the last minute about their grants, and I was fairly pleased when the number turned out to be only one more than I had really room for. We can usually manage to squeeze in an extra one, particularly since one man is leaving at Christmas. However, since then I had a request from another American, who was going to Copenhagen for a year, but now would like to come here for a term ﬁrst. His qualiﬁcations are so good and he would be so useful to us that I was most reluctant to turn him down. To exceed our number by two would really be rather diﬃcult, but a reasonable solution would seem to be to borrow a small trailer belonging to the Physics department, which is not at the moment in use and which just makes an oﬃce for two people. I have discussed this with the physicists and it would seem possible to put this up in a suitable position near my hut, where it either will join two trailers already in use, or else will be fairly well hidden from view. I know you do not like these trailers about the place, but in this particular case it would only mar a corner of the University already not conspicuous for its beauty and would help us out of an otherwise very diﬃcult situation. I hope you will not object to this too strongly. [Rudolf Peierls]

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[623] Rudolf Peierls to Robert Aitken [Birmingham], 21.10.1955 Dear Dr. Aitken, I have now had time to consider your proposals for the Arts Faculty.782 While this may from the overall University point of view turn out to be the best solution, I have little doubt that from the point of view of University House it would have great disadvantages. If the furniture and equipment moved to the new hall were to remain there, this would handicap the planning of the new hall, which one would like to see done from scratch without being hampered by existing furniture. etc. If it were ultimately to return to the present University House, the two moves in short succession would mean a great strain on the staﬀ and particularly on the warden, and I visualize that particularly to get the building into shape after a few years’ use for another purpose by the Arts Faculty would be rather troublesome. The Warden has put an enormous eﬀort into making limits resources go very far, and a good deal of work has been done by her personally and by voluntary eﬀort of the staﬀ. It would be hard to ask for that to be done again. To get the place into shape again one would probably have to spend a great deal of money and this raises the question whether with the same amount of money one could not ﬁnd easier solutions. An obvious suggestion would be if the new building at Wyddrington could be obtained in time to use that for the Arts Faculty. Distance would be a disadvantage, but I don’t see anything unsurmountable in that. Second-hand buses are surprisingly cheap and it would not cost very much to run a shuttle service between this place and the Library, as well as any other sites in the district which might have to be brought into use. After all the present institute of Education is not located very closely either to Edgbaston or Edmund Street and there must be a great deal of traﬃc between these places which somehow or other manages to get along. 782

Letter Robert Aitken Ms.Eng.misc.b.198, B.10.

to

Rudolf

Peierls,

24.10.1955,

Peierls Papers,

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Presumably some thought has been given to other large houses in the neighbourhood which are available, or may become available in time. I believe there is one large house belonging to the University now being converted into ﬂats and possibly this could be held for the purpose temporarily until the Arts Faculty Building is available. I have also heard of a large house in Somerset Road, with ten bedrooms, which is not on the market for the remainder of its lease (I believe twenty years) and which would not cost very much to acquire. You mention in you letter the question of huts for lecture rooms. As you know I believe that huts make very bad rooms for large classes. Some of the Arts classes are as large as 200 and I have never seen a satisfactory hut used as a lecture room for so large a class. Possibly such large classes could be accommodated in existing departmental lecture theatres (e.g. Physics or Engineering), if the times could be ﬁtted in. I believe these rooms are not heavily used in the afternoons and perhaps the Arts Faculty could make it possible to have large lectures in the afternoon, or else the science departments here could share in some of the inconvenience. For smaller classes huts might be adequate, or possibly large rooms in houses we acquire might be suitable. The move of the Arts Faculty will of course also bring problems for the Refectory and Union. Here I imagine University House could make an important contribution. Since at present no lunches are served at University House, one could imagine, given the necessary additional facilities and staﬀ to use the kitchen and dining room to serve several meals to undergraduates, probably in two or three sittings. This would probably not cope with all the Arts students, but I would imagine that if in addition the Refectory and the Union accepted such additional numbers as they could manage, one might not be too far out. Finally I feel that before placing too great a hardship either on members of the Arts Faculty or on other parts of the University, one should be very clear of the argument for moving as soon as possible. There may be technical reasons why we cannot continue to use Edmund Street. I imagine another point would be that this will increase the urgency of a case for getting the Arts building complete. As regards this last point we would probably also have an unassailable case if we

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should show that it had in fact proved impracticable to move the Arts Faculty, and that therefore we had the beautiful new Library building and were not able to use it. Yours sincerely, R.E. Peierls [624] Rudolf Peierls to Lev Landau [Birmingham], 8.11.1955 (carbon copy) Dear Landau, Thank you very much for your letter.783 I am interested to hear that you are arranging for a translation of the Quantum Theory of Solids.784 Since this was published I have noticed one or two minor errors and misprints. Perhaps when you know the date of the translation going to press you could let me know so that I could send you an up to date list of corrections. I am also sending you a copy of another book, the Laws of Nature, which may amuse you.785 It is a more popular book written without any mathematics. We were very interested in seeing the papers by yourself and your collaborators about quantum ﬁeld theory, in which you show that with point interactions the real charge was zero, if the bare charge is to be real.786 The hardest point in this seems to be the question whether the perturbation theory, which has been used in deriving this result remains valid in the limit. The point is of course dealt with in one of the papers by Pomeranchuk,787 but we are still trying to understand this paper in detail. 783

Letter could not be located. See letter [616], note 770. The book, published by Peierls in 1953, appeared in Russian translation in 1956. 785 R.E. Peierls, The Laws of Nature, London: Geo.Allen & Unwin, 1955. 786 See letter [625]. 787 Iu.Ia. Pomeranchuk, ‘Zero Equality of renormalized charge in quantum electrodynamics’, Doklady Akademii Nauk SSSR 103, 1005–1009 (1955). 784

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It would, I think be most useful if there were an opportunity to discuss these and other unresolved questions of modern theory at greater length than is possible at a large conference and I am now trying for an invitation to one (or more) theoretical physicists from the U.S.S.R. to visit our department for several weeks. Needless to say we would be particularly glad, if you were able to accept such an invitation and we could arrange the time almost entirely according to your convenience. However, if you do not expect to be able to accept in the near future we would be glad to ask instead one of the other senior theoreticians, and in the choice of names would be glad of your advice. This of course would not exclude the possibility of my visiting Moscow, which you mention in your letter. With kindest regards, Yours sincerely, R.E. Peierls

[625] Wolfgang Pauli to Rudolf Peierls Z¨ urich, 25.11.1955 Lieber Herr Peierls, Leider kann ich im Fr¨ uhjahr doch nicht nach England kommen, da ich mich nun entschlossen habe von Januar bis etwa Mitte April (Beginn des Sommersemester in Z¨ urich) wieder zu Besuch ans Institute in Princeton 788 Das wird Sie sicherlich entt¨ auschen, aber aufgeschoben ist zu gehen. nicht aufgehoben. Im u ¨brigen ist die Feldquantisierung (trotz Landau, arts gekommen und Pomeranchuk789 und Taylor)790 nicht wirklich vorw¨ alle interessanten mathematischen Fragen (¨ uber die ich Kopenhagen 788

See letter [621]. After the death of Pauli’s father the latter was not tied to Zurich in the same way as before and could contemplate longer visits abroad, as his planned trip to Princeton. 789 L.D. Landau and I.J. Pommeranchuk, ‘On the point interactions in quantum electrodynamics’, Doklady Akademii Nauk SSSR 102, 489–92 (1955). 790 See letter [620], note 779.

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viel mit K¨all´en und Lehmann diskutiert habe), sind so unentschieden wie je. Nun noch eine Frage betreﬀend meinen jetzigen Assistent Dr. A. Thellung: Kann er im n¨ achsten Fr¨ uhjahr (nicht vor dem 1. April 1956) zu Ihnen nach Birmingham kommen? Ich war mit ihm sehr zufrieden und er hat eine l¨ angere Arbeit u ¨ber Quantisierung der Hydrodynamik ¨brigens fertiggestellt, die er nun zusammenschreibt.791 Dabei hat sich u gezeigt, dass die Resultate st¨arker von der Art des Abschneidens, d.h. hier von der atomistischen Konstitution der Fl¨ ussigkeit anh¨ angen als man zun¨achst erwartet hatte. Von Zeit zu Zeit ist bei meinen Assistenten ein Wechsel n¨otig, bei Thellung w¨ are vielleicht auch ein Wechsel des Arbeitsgebietes empfehlenswert und er selbst w¨ urde gerne zu Ihnen gehen.792 Was die Finanzierung von Thellungs Auslandsaufenthalt betriﬀt, so w¨ urde ich im Falle einer positiven Antwort von Ihnen versuchen, ihm ein Schweizer Forschungsstipendium zu verschaﬀen, welches etwa Fr. 500.- bis Fr. 600.- pro Monat betragen w¨ urde. Da mir das etwas knapp zu sein scheint, m¨ochte ich Sie gerne fragen, ob er aus irgend welchen Fonds bei Ihnen noch etwas dazu verdienen k¨ onnte. Mit freundlichen Gr¨ ussen Ihr W. Pauli

791 A. Thellung, ‘On the energy spectrum in quantum electrodynamics and the theory of He II’, Helv. Phys. Acta 29, 103–27 (1956). 792 Thellung spent two years between March 1956 and April 1958 in Birmingham, ﬁrst as research fellow and then as part-time lecturer, before he returned to Zurich to take up an appointment as professor of physics.

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[626] Rudolf Peierls to S.C. Redshaw [Birmingham], 30.11.1955 (carbon copy) Dear Redshaw,793 I promised to let you have a note about the case for further for Dr. Dalitz. You will remember that Dalitz was promoted to Grade I as from the beginning of this session, and that on the last round of meetings he was given the title of Reader, on the basis of very enthusiastic reports from three referees which you read out at the Board meeting. I feel that this still does not give him an adequate status corresponding to his merit. He is certainly by far the best man in my subject in this country, who does not yet hold a chair, and he compares very favourably with many who do. His approach to his work is a very personal characteristic combining an easy command of all the modern mathematical techniques with very good practical judgement, and a sense of the important. He is extremely critical and has very high standards. If in any problem of modern physics his opinion diﬀered from everybody else’s, including my own, I would bet that in the end he would be proved right. In addition the part of the subject which he has chosen for his own work at the present time is concerned with high energy phenomena and new unstable particles, which is the present frontline of physics, and is of the greatest importance, if only because very large amounts of money are being invested in using machines producing particles for such work, as the synchrotron in the physics department here, and the cyclotron at Liverpool, and more such machines are being planned. There is nobody else at all in this country whose knowledge and understanding of these problems can compare in the least with that of Dalitz, and who is capable of leadership. Since his return he has already has a profound inﬂuence over the planning of work in this department. We have put several research 793

S.C. Redshaw, professor of civil engineering at the University of Birmingham and dean of the faculty of science.

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students on problems which he raised, and he is taking the responsibility for the planning of their work. It will probably soon be necessary to add to this group by taking further students oﬀ the problems we had previously put them on, because the new work is of great importance. In addition to this he is an extremely good judge of experimental work and good in discussing the plans for experiments the interpretation of their results with the people engaged in such work, and he is a brilliant lecturer. Before he went to America two years ago he was not known to very many people in this country, and therefore the most enthusiastic support for his recent promotion came from America. Since his return he has visited several Universities in this country, and I gather has greatly impressed everybody on the[s]e occasions. I am sure that I could now ask any physicist in any of the leading laboratories for his opinion about Dalitz and get an opinion at least as favourable as my own. There is no doubt that as regards ability, achievement, personality, Dalitz is of professorial calibre. This in itself would not necessarily make out a case for creating a personal Chair for him here, because it might be argued that a man of such a standing is not needed in the department and that he should therefore be released to go to the next Chair which is oﬀered. However, it would be better for him if for a time he did not have to carry administrative responsibility and to worry about the organisation of undergraduate teaching, or the building up of a department. He is perfectly capable of doing the[s]e things but it would be better if for a few more years he could devote himself mainly to research, in which he can give a more unique service. But also from the point of view of the department a case can be made out. I think it is fair to say that this department is now the leading school of the subject in the country. It contains thirty people doing research, and places for research training are greatly in demand, both by applicants from within this country and by people from overseas. We have every year to turn down many good applications and even so our numbers are rising. Although I have some excellent senior people on my staﬀ, even so I still carry too much responsibility personally for various aspects of our work, and as a result some aspects of it tend to become neglected. This applies in particular to the more experimental and phenomenological

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aspects of high energy physics, which is Dalitz’ special ﬁeld. I am now bringing myself up to date by attending Dalitz’ lectures. I feel we have a strong case for strengthening our department by retaining for some years our best and most experienced man in an appropriate capacity. The situation is aggravated by the fact that Dalitz is very much in demand. He has an invitation to join the staﬀ of the Brookhaven Laboratory in Long Island as the senior theoretician on the high energy side. This is a very attractive appointment because Brookhaven is one of the two laboratories in the world now leading in this kind of research. He must decide on this oﬀer by about January. In addition he is being short listed for a new post as Head of the Theoretical section of the new European Nuclear Research Laboratory in Geneva, and he is being oﬀered a vacant post at Liverpool, which if Dalitz is interested would I believe be turned into a research Chair. There are many other attractive posts he could have if he wanted them. I want to make it clear that the existence of these competing oﬀers is not the basis of my case, but they do make it more urgent. Apart from these oﬀers there would be more time to consider the proposal, but unless something is done soon we are very likely to lose him, and particularly if he were lost to the United States I would regard this as a disaster from the national point of view. The progress of physics in this country is in danger by losing too many good people to America. To some extent this is unavoidable because of the attractive facilities available there, and the more rapid pace of progress in research. But it would be a misfortune, if, in addition we lost people by being too slow in recognizing their value, and giving them adequate status. We tend to give too much weight to age and seniority. Dalitz is now about the same age as I was when I took up my chair here. His standing in physics, his ability and his general reputation are quite comparable with mine at that time, as for the future I am conﬁdent that he will do more than I have done. I hope you will do what you can to help me in this problem. Yours sincerely, R.E. Peierls

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[627] Rudolf Peierls to Wolfgang Pauli [Birmingham], 1.12.1955 (carbon copy) Dear Pauli! Thank you for your letter.794 I am sorry you will not be able to visit us in the spring, but I hope you will come later. I have little doubt that the British Council would be glad to sponsor an invitation also in another year. We shall certainly be glad to have Thellung here. I see at the moment no possibility of ﬁnding here a grant which would add to his income, but a sum of 500–600 swiss francs a month sounds quite adequate. The cost of living here is much less than in Switzerland. I do not of course know whether he has any special requirements. If he is married or if he is the sort of man who cannot live without a motorcar, then it might be a little diﬃcult, but a lot of people here manage to live on considerably less. I would of course be glad to know later when he is proposing to come and roughly how long he intends to stay. The conclusions which you mention about the problem of quantum hydrodynamics sound very similar to those reached in a recent paper by Kuper and Allock795 in Liverpool. I suppose you know of their work. If you will be in America in the beginning of April I hope you will ﬁnd it possible to come to the conference in Rochester (3rd to 7th April).796 These conferences are usually very good. Yours sincerely, R.E. Peierls

794

Letter [625]. G.R. Allock and C.G. Kuper, ‘“Rotons” in quantum hydrodynamics’, Proc. Roy. Soc. A231, 226–43 (1955). 796 Between 3 and 7 April 1955 the sixth Rochester Conference took place. The meeting, for the ﬁrst time since the war, also included three Russian scientists. 795

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[628] Rudolf Peierls to William Penney [location unspeciﬁed], 6.3.1956 (carbon copy) Dear Bill, On the subject of your phone call this morning I think that I should write you a note explaining what is in my mind, so that you can consider my point of view before we meet on Monday.797 Let me say, ﬁrst of all, that I very much appreciate your call and the frank and courteous way in which you put the position to me. I want to ensure you that I have given the problem a great deal of thought, and do not take it lightly. It would distress me very much if I were to cause any diﬃculty or embarrassment to you and your colleagues in the Authority, but to my mind an important principle is involved on the other side, and this is what I want to explain. I regard our position in the cold war not merely a matter of national loyalty. We have in the west some important principles in which we believe very deeply. We tend to be a little ashamed to talk about them, but in the end most of us are willing to go to a lot of trouble about them and risk a lot for their sake. Very important amongst these is the freedom of scientiﬁc enquiry, the freedom of exchange of scientiﬁc information, and of objective discussion with any scientist, regardless of person, nationality, or position as long as these do not interfere with his approach to scientiﬁc fact or argument. This principle must, of course, be subject to the overriding requirement of national security. We have learnt to accept these limitations, and have succeeded in deﬁning in a workable way the ﬁelds in which research may still be free because it only serves the long-term aims of searching for the fundamental laws, from those ﬁelds which at present have to remain restricted. Amongst the many things for which we blame the Russian system is their fear of free and open discussion, their arbitrary restriction of 797

Rudolf Peierls wanted to attend the International Conference on High Energy Physics in Moscow between 14 and 22 May 1956, but his attendance was deemed a risk because of his role in the UK Atomic Energy Authority, Harwell.

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movement of individuals and, in the past decade, their method of letting dogmatic prejudices intrude in scientiﬁc questions. For many years I have been very conscious of two embarrassing incidents: One was, when, shortly after the war, scientiﬁc interchange of visits with Russia stopped completely, a left-wing physicist wrote an article to say that this was mutual. If western physicists were invited to a conference in Russia they would not be allowed to go. I was very angry over this statement which at the time certainly was untrue. But before there was any chance of proving him wrong, things had got to a point where he probably would have been right. The other is the fact that, because of the incident over the refusal to let physicists go to the Russian Academy celebrations in 1945, the Russians, and our left-wing colleagues, may claim that it was, in fact, the West which started the “Iron Curtain” for physicists. The government decision on that occasion can, of course, be defended, because at that time the most important secret was that there was a large atomic energy project in operation, and near completion, and it could have been compromised by a casual remark made in the best of intentions. But in consequence, it is bitter to have to swallow remarks by left-wingers or neutrals that our conviction of the importance of freedom of movement and of non-military information is not sincere. You may remember the passionate appeal for an open world which Niels Bohr wrote some years ago.798 I do not share his belief that such an appeal oﬀers a realistic chance of a solution of the problems of international tension. But I do believe in the importance of the principle both as an ultimate test of the state of international relations, and as something which matters for our own convictions. To put it in more practical terms. We have a lot to gain by keeping the scientiﬁc channels of communication open, now that the Russians are willing to open them a little way from their side. Russia is evidently in a transition stage of some sort, and even in a dictatorship informal public opinion has some sort of inﬂuence. The more opportunities there are of individuals meeting the better the chance of some Russians 798

See letter [507], note 348.

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realizing how the world looks from the other side. I don’t mean that a few Western physicists will cause a revolution in Russia, but if we can make a few of our Russian colleagues feel envious of the way we live, something is gained. One also should not underrate the importance of the eﬀect “of the neutral” countries. Lack of willingness to take part in open conferences will be a gift to communist propaganda amongst the scientists in Europe or Asia; the success or failure of communism in such countries may be more vital for the future than even the number of atomic weapons. You might say, it is reasonable that some physicists should attend such a conference, but why not send some others who do not have some embarrassing connections? There are several answers to this. In the ﬁrst place until a lead has been given, a younger man would need considerable courage to go. There was in fact a smaller conference on theoretical physics in Moscow last March.799 One of the Russian[s] in Geneva told me that they had deliberately invited younger people in order to avoid refusals (“they expect the senior people might be too busy”) but of four people invited from the West only Kallen from Sweden800 accepted. The others were too worried about possible repercussions, troubles about getting US visas in the future & c. It is therefore up to us senior people to show that it can be done, and to see what disasters will happen to us. Also, it seems rather a dangerous principle to set up that people that once have been connected with a weapons project may never again use their own judgement as to where they go, they might well further aggravate your recruitment problem. In a way, I am probably better qualiﬁed to go to such a conference than many other people. I know a lot about Russia, enough not to have any illusions about their system either before or after the present changes.801 I have many good personal reasons for hating their system 799

See letter [609], note 737. See letter [614], note 757. 801 After the death of Stalin in 1953 Nikita Khrushchev had become First Secretary of the Communist Party. After a period of consolidating his power, in February 1956, at the XXth Party Congress, he condemned the worst excesses of Stalin’s policies and initiated a thaw in East-West relations. 800

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like poison just as I had good personal reasons for hating the Nazis in Germany. I am not likely to be taken in by any propaganda to which members of the conference may be exposed. But just what I have seen of Russia, and of Nazi Germany, has taught me the importance of doing what you think is right without worrying about other people’s reaction and any unpleasantness that might come to you. More harm was done in Germany by the people who knew what was right but thought it expedient to comply with what was popular at the time, than by real fanatics. In Russia too, people have to live mainly by rules of expediency (though it took rather more pressure to reduce them to that state). It is therefore frightening to see symptoms of this in America. The whole Oppenheimer case was mixed up with the charge that he went to see a man who was said to be a communist – not that there was any rational reason why seeing him should do any harm, but he should not have seen him because that might have given some people the suspicion that he might be disloyal. For similar reasons some people in America may object to my going to this conference. I may well not get an American visa after that. But I would feel ashamed of myself if I refused to go for that reason. It is important to remind others, and particularly younger people, that one must do what is right even at the risk of unpleasant consequences. This may – in the long term, even beneﬁt our relations with the Americans. There are many people in America who are working for the right things, and the collapse of Senator McCarthy has demonstrated that they have some inﬂuence. A few cases in which outsiders show that they are not too intimidated by the disapproval of some Americans, if this disapproval is irrational, may actually strengthen their hand. I doubt if the public or the press either here or in America would take much notice of my trip; to them this is hardly diﬀerent from the Harwell team or the visit of the Russians to Harwell. As to the people in the A.E.A. who know that I was at Los Alamos, they must know that all the information I had there is quite stale, and could, if necessary be told how little classiﬁed information I have recently had from other sources. In addition they must appreciate that if I was disloyal I would not have to go to Moscow to give information away, and that after 16 years practice I have by now learnt not to slip up accidentally. I believe

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therefore that any objection they may bring up could only be on an irrational basis. I would certainly wish to minimize any trouble which I cause to anyone else, even, if necessary, to the extent of resigning from whatever tenuous contacts I have left with the Authority. I need not say that I would feel very sorry to give up this very long-standing connection, and the many very pleasant personal contacts it involves. But if you felt it might reduce the risk of damaging the interests of the Authority if at the time of the conference I was not actually in the position of a consultant it would undoubtedly be my duty to resign. You seemed surprised that I had already accepted the invitation. When I got a telegram in the middle of February announcing that the invitation was on the way, I wrote to Cockroft that I was proposing to accept, and suggested that he might pass this information on to whoever he thought should have it. About two weeks later when I assumed there had been time for any complaints I sent my acceptance. I did not want to delay it more. In view of the remarks by the Russian in Geneva which I quoted it seemed to [be] desirable to avoid the impression that this was something controversial. However, an acceptance is not irrevocable, and I shall be glad to hear your point of view. If you convince me that I ought not to go I can cancel the trip. But so far I have not seen a suﬃcient reason. I shall be in your oﬃce at 9.30 on Monday, unless I hear from you otherwise, With kindest regards Yours sincerely, [R.E. Peierls]

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[629] Rudolf Peierls to John Cockroft [Birmingham], 22.3.1956 (carbon copy) Dear Cockroft, I hear from Moon that you would like to know more about the programme of the Moscow Conference. I enclose a copy of the provisional programme which accompanied the invitation.802 In addition the letter of invitation said “At the Conference there will be in the ﬁrst place reports and discussions on the main experimental investigations about the interaction of elementary particles at high energies, which have been carried out with the existing accelerators in the USSR. In addition it is proposed to discuss theoretical papers which have a bearing on this ﬁeld, as well as certain papers on the study of elementary interactions of particles in cosmic rays”. They also invite contributions from visiting foreign scientists. It will be followed by a week’s visit to various Institutions, which are expected to include the Lebedev Institute, the Institute of Nuclear Problems, the Atomic Power Stations, the University of Moscow and others. This list does not seem to include the new 10 Bev accelerator unless this is one of the “others”. Yours sincerely, R.E. Peierls

[630] Nevill Mott to Rudolf Peierls Cambridge, 25.4.1956 Dear Peierls, Salam has come back with the suggestion that we might try to have the Rochester conference in England in the spring of 1958. Do you think it would be a good idea that we should have it in Cambridge under the scientiﬁc direction of yourself — if you are willing to do it — and 802

See letter [628], note 792.

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of such of your colleagues as we think ﬁt? If we had it here we would make a major eﬀort to ensure that the arrangements for lodging and entertainment were ﬁrst-class. The dates from Wednesday, March 26th, 1958 to Tuesday, April 1st would seem convenient though these would of course have to be arranged with the American committee. Shall we meet some time and discuss it? Yours sincerely, N.F. Mott P.S. Easter Monday, 1958, is on April 7th

[631] Nina Byers to Rudolf Peierls Chicago, 24.5.1956 Dear Professor Peierls, Thank you very much for your letter to Professor Wentzel. I do appreciate your sending it and am writing to thank you and to explain why my application was made so late.803 Prior to the time your letter arrived, I had accepted an instructorship at the University of Washington. I accepted the position on the advice of Professor Goldberger who returned from Rochester with the impression that I was quite unlikely to be oﬀered a position at Birmingham. Professor Wentzel had somewhat the same impression. Therefore it seemed advisable to accept the Washington oﬀer. I did so. Late in the afternoon of May 21, however, I became aware of the fact that there was a “loyalty oath” at the University of Washington804 803 Nina Byers had obtained her Ph.D. at Chicago in 1956 before coming to Birmingham; she continued her research at Stanford (1958–61) before joining the faculty at UCLA as assistant professor and later professor of physics. 804 In 1951, the Washington Legislature imposed a loyalty oath requirement for all state employees. In 1955, the statute was amended to require employees to swear that ‘I am not a subversive person.’ On June 1, 1964, after a legal challenge by the ACLU, the Supreme Court ruled that ‘the oath requirements and the statutory provisions on which they are based are invalid’ and concluded that the laws violated due process and were unconstitutional.

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and that it might become necessary for me to sign it in order to retain my job. This oath is one which I consider particularly objectionable and would not be willing to sign. I discussed this matter with Professor Wentzel telling him that I would like very much to come to Birmingham, he suggested that I cable notiﬁcation to the Registrar that I would like to apply for the Research Fellowship. I did so, and have sent a letter of application with details of education, research and teaching experience. The department at Washington has been informed about my feelings regarding the oath, and now of the fact that I am making an application for a Research Fellowship in your department. I hope this explains the last minute nature of my application and that it can still be given full consideration. [Nina Byers]

[632] Rudolf Peierls to Lev Landau [Birmingham], 6.6.1956 (carbon copy) Dear Landau, I am writing ﬁrst of all to thank you for the many interesting discussions and for your kindness in so many ways during the conference.805 I greatly enjoyed the visit and I feel only that it would have been even more useful if I (and some of the other foreign visitors) would have talked less and listened more. Since my return I have passed on to Pergamon Press the question of translations of the other books in your series and they assured me that they would be happy to publish also the translations of these volumes, and suggested that you should arrange to send copies of these books to them.806 805

Moscow Conference. See letter [628], note 797. Lev Landau and E.M. Lifshitz had written a series of textbooks on theoretical physics, the English translation of which was subsequently published by Pergamon Press. L.D. Landau and E.M. Lifshitz, Course of Theoretical Physics, 10 vols., 806

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I have also thought a little more on the position of ﬁeld theory in the light of your negative results, and one point I perhaps did not make clearly enough in our conversations is that all the present calculations are not attempts to solve the equations exactly (if anybody was close to an exact solution one would not need to argue whether the exact solution exists or not), but there are attempts at approximate solutions in which the method of approximation is inspired not by any mathematical understanding of the equations, but by physical arguments. It is therefore very well possible that they should turn out to be not approximations to the present equations of ﬁeld theory, which according to your argument have no sensible solutions, but to some sensible equations. This of course could be a sheer miracle if the approximations just consisted in mathematical tricks, but when one is dealing with equations of the type of Chew and Low807 which are at least in part based on general dispersion relations, it is not unreasonable that they might have more validity in the full theory which one writes down to start with. In the trivial sense this is obviously true of electrodynamics where the present perturbation theory no doubt has some validity and should be regarded as a series expansion of the solution of some non-local or otherwise more complicated theory. The case in meson theory is certainly much less clear, and it might also be that the present approximate work just leaves out some very essential pieces of physics, but I think it is worth continuing with such studies because they may well help to analyse the problem further and therefore to construct a better theory. We are sending oﬀ separately some modern English plays and also a children’s book. The plays contain some which have been very successful here. If we could know later which of them has been found suitable for translation, we could easily pick out some others of the same type.

Oxford: Pergamon Press. Not all the volumes had been completed at the time of Landau’s serious accident and eventual death in 1968, and Lifshitz and his pupils continued the project with the last volume completed in 1979. 807 G.F. Chew and F.E. Low, ‘Eﬀective-Range Approach to the Low Energy p-Wave Pion-Nucleon Interaction’, Phys. Rev. 101, 1570–79 (1956); and G.F. Chew and F.E. Low, ‘Theory of Photomeson Production at Low Energies’, Phys. Rev. 101, 1579–87 (1956).

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Children’s books are harder to choose because there is such an enormous variety. The one we are sending is particularly popular just now. There are many for younger children, a common type being the story of some animal and its family described in rather human perspective. There are literally hundreds of these. There are also many more serious books dealing with aspects of knowledge, nature, science, engineering for children. Which of these would be most interesting? With kindest regards, Yours sincerely, R.E. Peierls

[633] Rudolf Peierls to O. Hood Phillips808 [location unspeciﬁed], 6.6.1956 (carbon copy) Dear Hood Phillips, I am now writing to give you some notes about Bethe. Firstly about his work. Bethe is a pupil of Arnold Sommerfeld, who was probably the most famous and most successful teacher of theoretical physics in the last generation, and whose work was characterised by a very positive attitude with the emphasis on the solution to practical problems rather than on general principles. Bethe, whose attitude was strongly inﬂuenced by Sommerfeld, is now occupying the position in physics once held by his former teacher. The main impression his work makes is one of immense strength. There is hardly any branch of modern theoretical physics in which Bethe has not made contributions of vital importance. For example, some of his work on the theory of solids is now about 25 years old and still standard equipment for theoretical physicists. He developed a powerful method to clarify problems in the structure of alloys, he showed how to calculate realistically the stopping power of various substances for particles. He made important 808

Owen Hood Phillips (1907–86), Professor of Law at Birmingham University.

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contributions to the theory of nuclear forces and of nuclear reactions. He was among the ﬁrst to work out the corrections to atomic energy levels, which had led to the development of modern ﬁeld theory and he has assisted in an important way our understanding of mesons and their interactions with nuclei. This is by no means a complete list of the important things he has done. In addition he has written important texts, some as books, some as review articles, which are very characteristic in that each not merely reviews published work in a certain ﬁeld, but adds a new quantitative discussion and completes investigations which had not been done completely or not correctly, so that each such article represents a stage in the development of a branch of physics. During the war he was active in several ﬁelds, ﬁrst in radar and simultaneously in the theory of shock waves caused by explosions and later in atomic energy. He was the head of the theoretical physics division of the Atomic Weapons Laboratory at Los Alamos from its formation to the end of the war and to him must go a good share of the credit for the work of that laboratory. Those who have seen him at work get in the ﬁrst place the impression of immense strength. For him problems are there to be solved and not to be worried about, and there are few problems which have attracted his interest to which he would not ﬁnd a reasonable solution in a short time. He seems to talk and act slowly and deliberately, but knowing just what to do and where to go he does get there with incredible speed. One is sometimes reminded of the sensation of seeing an elephant run, when one is also struck by the speed of progress of an apparently slow and lumbering mode of progress. The story goes that he was once consulted by a colleague about a certain calculation and replied that this was well worth doing. “It would take you about a week to do it. It would take me two days”. Those who know him would realise that this was not a boast, but a statement of fact. I know that puns on names are generally frowned upon in such connections, but nevertheless you might like to know the story that Gamow, one of our colleagues who likes to make people laugh, once persuaded Bethe to contribute to some work he was doing jointly with a student by the name of Alpher, mainly for the pleasure of then publishing a joint

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paper under the authors Alpher, Bethe and Gamow, which he likes to refer to as the α, β, γ paper. I have also heard that in a seminar at a French University a research student referred to a diﬃcult problem which he said was so hard that “mˆeme le grand Bˆete” had been unable to solve it. In private life, Bethe was famous as a young man both for the quantity of food he could consume and for the slow and deliberate pace at which he went about it. In a way his appetite for food was similar to his appetite for physical problems. I assume that you have the usual facts about his biography. I might mention specially the fact that he has held his present chair at Cornell University since 1935, which for a physicist is rather unusual continuity. It may also be on interest that he worked in this country from 1933 to 1935, ﬁrst at Manchester and then at Bristol, after he had left Germany on Hitler coming to power, and that he is now spending a year at Cambridge where his presence has been a great source of strength through the ideas he has brought along and through the inspiring guidance he has provided for many students and colleagues. I am passing this letter on to Moon who no doubt will add any further points that I may have omitted. Yours sincerely R.E. Peierls

[634] Rudolf Peierls to Nina Byers [Birmingham], 10.6.1956 (carbon copy) Dear Miss Byers, I am writing to let you know that we are recommending your appointment to a research fellowship for the academic year 1956–57. This recommendation has yet to be conﬁrmed by the University authorities, but this is a formality, and you may regard the oﬀer as deﬁnite. The salary will not be less than £ 600 p.a.; it is just conceivable that we might get a little more, but I do not regard this as very likely. The appointment

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will be for one year in the ﬁrst instance but may be renewed. It normally dates from 1st October, but we could advance the date as far as 1st September, if that were more convenient for you. A fellowship of this kind is here subject to income tax. In a full year, tax on £ 600 amounts to approximately [..],809 but since the tax year begins on 5th April you may get the ﬁrst six months’ salary regarded as a full year’s income, with a considerable deduction in tax. The amount appears very low by American standards, I believe, however, that you would manage on this quite comfortably, if not in luxury. I doubt whether it would also easily cover your transatlantic fare, particularly if you stay in Europe only one year. I regret that we cannot make a grant towards your travelling expenses. You will be entitled to take part in our superannuation (pension) scheme, by which 5% of your salary is deducted, and another 10% added by the university. The total is used to purchase an insurance policy, which can be chosen in such a way that on surrender you get both your own and the University’s contribution back. This is optional and we can see later on whether this is worth your while. As you will have seen from the advertisement, the fellowship carries the obligation to do up to three hours’ of lecturing per week. Our assignment of courses has not been ﬁnally settled yet, but we may ask you to give a course on Potential Theory, which averages about 1 1/2 hours a week over the year, or one on Numerical Methods, which amounts to two hours a week plus some practical work. I would be glad to know whether you have had any experience in numerical work, and would be willing to consider this second course. If neither of these suggestions turn out to be suitable, there are still other possibilities. Our autumn term starts on 7th October, and I would hope that you could get here by that date. I would be grateful if I could know by 21st June whether you are willing to accept this oﬀer. However, if before deciding you have some further questions, please do not hesitate to let me know. Yours sincerely, [R.E. Peierls] 809

Missing in carbon copy.

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[635] Nina Byers to Rudolf Peierls Chicago, 17.6.1956 Dear Professor Peierls, I am very pleased to accept the position of research fellow in your department. I am not yet able to say when I shall arrive in Birmingham, and would like to ask you some questions in this regard. It is not clear to me whether my appointment would be for a full year or an academic year, and I would appreciate knowing whether I shall be expected to remain in Birmingham during the summer months. Most academic jobs here in the United States begin in September, and since at some later time it may be necessary to return to a job here, it might be advisable for me to request that my appointment begin in September. If you have a recommendation or preference regarding my time of arrival, I will be glad to make arrangements in accordance with it. I should like to arrive in Birmingham in suﬃcient time to prepare for my teaching duties. I have done little numerical work and am not aware of what the content of a course in Numerical Methods would be. Of the two courses you mentioned, my preference would be for the course on Potential Theory. However, I do want to say that, to a degree depending on the level of instruction, both of these courses would require preparation on my part. This I would be more than willing to undertake, but I feel that that could best be done in Birmingham. Therefore, I will appreciate any further information you can send me about my teaching duties. It is diﬃcult for me to say what I am prepared to teach as I do not know the content of the courses given, however, I will be glad to assume whatever responsibilities are given to me. I would like to close by saying that I am looking forward with great pleasure to my stay in Birmingham. Respectfully yours, Nina Byers

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[636] Rudolf Peierls to Nina Byers Birmingham, 21.6.1956 (carbon copy) Dear Miss Byers, Thank you very much for your letter of 17th June.810 I am glad to know that you are willing to accept the Research Fellowship, and we look forward to seeing you here next Autumn. I should have explained that our appointments always run for a full year. The reason being that our climate does not prevent research work being continuing during the summer, except of course for a reasonable period of vacation, which may be taken during the tenure of the Fellowship. If you ﬁnd it convenient to return before the full year is up, there would however, be no diﬃculty in your resigning before the oﬃcial termination. However, in that case your salary, which is paid monthly, would of course also terminate, except that it might continue beyond your actual date of departure if some part of that may be counted as vacation. It is not easy to make precise forecasts about the length of time that can be allowed in this way. Since the salary is not very generous and only just about covers your cost of living, you would not in fact lose very much by leaving early to take up another appointment. Your time of arrival should therefore be settled on what you ﬁnd most convenient. As regards the teaching I suggest that the Potential Theory course may be more suitable. The required level is not high, the main point is to make students familiar with simple partial diﬀerential equations with separation of variables and expansion in spherical harmonics, as well as simple problems involving images and the like. I do not think you will ﬁnd much preparation necessary. I shall shortly write in more detail about the contents of this course, but we are discussing slight rearrangements of some of the courses with which this is connected, so that I would rather leave the details until we know what is going to 810

Letter [635].

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happen. We still have to make another appointment and depending on this I may still produce an alternative suggestion, so I hope you won’t start working hard on Potential Theory just yet. Incidentally, at present our Potential Theory course starts only after Christmas, but under the proposed rearrangement it would start in October (9th October at the earliest) and go on at the rate of only one hour a week, so I do not think it is necessary, for that reason, to arrive much before the beginning of October. You will shortly receive a letter from the Secretary of the University oﬀering you the appointment oﬃcially beginning on 1st September, or such later date as you can take up your duties. Yours sincerely, R.E. Peierls

[637] Freeman Dyson to Rudolf Peierls La Jolla, 12.7.1956 If you happen to come through California on your trip, do stop here. We are 20 miles from the frontier. But it is a long way from Mexico City.811 Dear Peierls, Let me answer your letter at once before it gets buried.812 The question is a sensible one and gave me some worry when I was working out the theory. I don’t have a copy of the paper here, but I think I can explain it without referring to the equations.813 The point is that you must not put L = 0 at the beginning. You must take L > 0 and then go to the limit L → 0. This makes physical sense because the ground state is trivially degenerate when L = 0 but 811

Addition at the top of the letter. Letter could not be located. 813 F.J. Dyson, ‘Thermodynamic Behavior of an Ideal Ferromagnet’, Phys. Rev. 102, 1230–44 (1956). 812

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not when L > 0. You must arrange it so that the long-range order is kept pointing in the chosen z-direction. If you don’t do this then the deﬁnition of spin-waves is wrong from the beginning. Where this comes into the proof is easy to see. I ﬁnd for the eigenvalue an inequality something like (Vj − Vj+δ )2 + L Vj E − E0 > jδ

j

where Vj = δ + δj2 is the “potential” in the electric analog network when 2

some junctions are held at potential 2S. This is at least (2S) R assuming the potential at inﬁnity is zero. If the potential at inﬁnity is not zero, then the term L Vj is positive inﬁnite and the same result holds a fortiori, provided L > 0 to stop too many of the Vj from being large simultaneously. In your counter-example all Vj are equal 2. I ought to have explained this better in the published paper. I am sorry. I hope you have a ﬁne time in Mexico. I am enjoying my ﬁrst splash in the reactor business. Also I am splashing quite a lot in the Paciﬁc. Yours, Freeman Dyson

[638] Rudolf Peierls to Freeman Dyson [Birmingham], 7.9.1956 (carbon copy) Dear Freeman, I am sorry I have not replied to your letter of 12th July in which you comment so promptly on my query.814 While I was in Mexico I have been thinking of other things, and it has taken me until now to compare your letter with the equation in your paper and try and make sense of it. 814

Letter [637].

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I am afraid I am still completely in the dark, because you refer in the ﬁrst place to the external magnetic ﬁeld L and stress the importance of not taking this as zero. But in the counter example we have constructed it makes no diﬀerence whatever what L you assume because q is diagonal in the state considered; we just have to add to the energy the quantity q and the same appears in the inequality which this counter example tends to disprove. Your other remarks about the electrical network analogy seem, if I understand them right, to explain nearly why your proof goes wrong in the particular case. I have not followed this in detail because I had not really tried to understand the proof, but I think the counter example is still incompatible with the theorem you state in your paper, and presumably one has to add some qualiﬁcations to the theorem. The explanation in your letter does not seem to help us ﬁnd what is now the correct statement of the theorem. This is not quite an academic matter because since the theorem if correctly expressed does not apply to some of the unphysical states one must then show that these states are also excluded from your evaluation of the partition function with the “phoney” Hamiltonian or else something would have to be wrong. I am sorry to keep bothering you; by adequate research we could no doubt perhaps discover the answers ourselves, but it seems so much easier to ask the author. We had a wonderful time in Mexico. Thank you for your invitation to drop in, but the only time spent in the United States was a few hours in Idlewild each way. This was not quite suﬃcient. Yours sincerely, R.E. Peierls

[639] Freeman Dyson to Rudolf Peierls Princeton, 25.9.1956 Dear Peierls, Just got back from California and met the family here. We are in a new house and enjoying being together again.

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Let me again try to explain about this spin-wave problem. Now I have the paper in front of me and can refer to it. The answer to your question is very simple.815 Equation (40) on page 1235 of the Phys. Rev.816 paper holds unconditionally, for all states, including your counter example. In passing from (40) to (47) it is assumed (i) that L > 0, (ii) that the energy ( − E0 ) is ﬁnite. For your counter example the second assumption is invalid. So the correct statement of Eq. (47) should have a remark that we assume ( − E0 ) to be ﬁnite. I maintain that the statement is correct as it stands because in calling an eigenvalue of H we understand automatically that = ∞. As far as the physical application goes, this situation is completely harmless. The unphysical states for which Eq. (47) fails have − E0 = +∞ (by Eq. (40)) and so they make rigorously zero contribution to the partition sum. It is not necessary to use any device to exclude these states, except putting L > 0. I am glad you were happy in Mexico. The part of Mexico I saw made me less happy. I got bitten by a nasty-looking Mexican dog and so spent my last two weeks taking the Pasteur treatment for rabies. Otherwise I had a ﬁne summer. Yours ever, Freeman [640] Rudolf Peierls to Lev Landau [Birmingham], 26.9.1956 (carbon copy) Dear Dau, Thank you for your letter of 21 August.817 You don’t need to apologise for delay in writing, because as you know I am a very bad letter writer myself. 815

See letter [638]. See letter [637], note 813. 817 Letter could not be located. 816

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We have just received your corrections to chapters 9, 10 and 11 of Statistical Physics,818 chapters 1–8 have already gone to the publishers in their ﬁnal form. My son has put in all your corrections including the term “perfect gas” in place of “ideal”, except where it is a matter of the use of the English language without any ambiguity in the meaning. He showed me one new problem you have added, which relates to the expansion of a gas from a thermal insulated vessel into another vessel also insulated. This has been translated as you (or presumably Lifshitz) wrote it, but we could not quite understand it, because it did not state whether the second vessel is originally empty or just contains gas at a lower pressure and whether for example the expansion is adiabatic. We would probably have discovered the conditions by working back from the answer, but have not yet done so. If you have a copy of this problem you might look at it again. Any change of wording can be made in the proof. Since my son has now gone to America, it would be very helpful, if we could have a second copy of the Russian edition. If you can send one, could you send it either here or directly to my son (Mr. R.S. Peierls, Laboratory for Nuclear Physics, Cornell University, Ithaca, N.Y.) whichever is easier. I was very interested at the Moscow Conference819 in the reasoning by Ioﬀe on the questions whether the dispersion relations are valid in a non-local theory, provided it is compatible with macroscopic causality and we would like to study this question here further. When a written account of this work becomes available I would very much appreciate having a copy. With kindest regards, Yours sincerely, [R.E. Peierls]

818

L.D. Landau, E.M. Lifshitz, Statistical Physics. Course of Theoretical Physics, vol. 5., later published by Pergamon Press. 819 See letter [628].

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[641] Rudolf Peierls to N. Kemmer [Birmingham], 22.10.1956 (carbon copy) Dear Kemmer, Thank you for your letter.820 May I deal with the easy part ﬁrst? I shall certainly be glad to continue acting as External Examiner, in fact the ﬁrst year was the least convenient from the point of view of other engagements, and I know of nothing at the moment which would prevent me acting this time or the following year. As regards the reform of physics teaching, I agree with you that conferences do not achieve very much on a matter like this, but surely the next step is to see whom you want to get moving and in what direction. I assume that your correspondence shows that broadly speaking the diagnosis of the situation is clear. If you feel that there are still too many dissentients and it would be desirable to achieve greater unanimity, then indeed a conference would be called for. Accepting the analysis of the present situation who is to do what in getting an improvement. As I said previously I have no hope that one could, at the present time, get agreement for lengthening the University undergraduate courses to 4 years. As long as there is national service, and as long as people still are considering putting an extra year on the course at the other end to cope with inadequate preparation in the sixth form, or to cater for the people who have taken the wrong subjects at school, the chance of success in this would be negligible. The right remedies are therefore ﬁrstly in the Physics syllabus in each University, and in the institution of postgraduate courses. These need no agreement as between diﬀerent Universities, and propaganda has to be addressed to each University Department separately. I think you have already started this by circulating your memorandum, and independently of this there were already many beginnings in similar directions. Whether a report by a further committee would add much 820

Letter could not be located.

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to your memorandum I do not know, but I would be glad to take part in the writing of such a report if it were regarded as desirable. You were in your original memorandum suggesting some changes which would mean that postgraduate students would not be in the category of research students for their ﬁrst year, and thus not eligible for the usual grants. I still maintain that it is better to avoid this, and that in fact the right things could be done within the terms of most present grants. Where these terms are obsolete, for example where they provide grants for two years only, one should direct propaganda at the appropriate bodies. I have not recently met any such situation. Another matter is the provision of research staﬀ to conduct such postgraduate courses. This is again a matter for individual universities. Some may in fact have made provision for this in their present Quintennial estimates. Where this has not been done, it would I think be very diﬃcult to have it included now. The shift of responsibility of some of the teaching from mathematics to mathematical physics departments, or their equivalent, and this again is a matter which diﬀers very much from one University to another, and on which one can hardly hope to get a national policy. This is a battle which will have to be fought by such mathematical physics departments that exist already, or in their absence by physics departments. Your memorandum should have strengthened their hand. If the report or a conference would provide a further necessary support I cannot judge. Our own position in that respect is of course fortunate since we are quite satisﬁed with the distribution of duties in this University and the only unsolved question is how to ﬁnd more time for mathematical courses within the physics syllabus, a subject on which we nearly have to argue with our physics colleagues. If you want to get a report drafted by a committee you could either call an ad hoc committee on your own initiative, or that of your University, and perhaps to give it more authority circulating a proposed list of names to physics professors and other suitable people asking for comments on the choice and alternative suggestions. If you do not regard that as suﬃciently authoritative, I do not see how you can avoid having a conference and getting your committee elected at the conference. It may be that for example the Physical Society would be willing to set

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up such a Committee, if they were asked, but I doubt whether just the people you want to impress would regard the recommendations of the Physical Society Committee as authoritative or in any sense binding on them. A committee appointed by the Royal Society would carry somewhat more weight, but Royal Society Committees tend to get appointed in a haphazard way, and as a result people might still not like the report when it is produced. I have looked with interest at your new scheme of honours courses which on the face of it looks very good, but is hard to judge in detail because I do not remember exactly the various categories of students you have, and for example how many of these optional courses your mathematicians (as opposed to mathematical physicists) are supposed to take. One feature which looks a little odd is that introductory kinetic energy precedes the course on thermodynamics, but I suppose this means that the students have already met the elementary concepts of thermodynamics elsewhere. An interesting comparison of this scheme with our course is that you manage to get much more of the advanced work, such as electromagnetic theory and hydrodynamics into the third year, which corresponds to our second honours year. This must mean either that your students are harder worked than our’s, or that they do less pure mathematics in that year. Presumably the latter is a possible advantage of the fact that you get them from the beginning and can start them earlier on the mathematics that will later be required. Yours sincerely, R.E. Peierls

[642] Rudolf Peierls to Robert Serber [Birmingham], 6.12.1956 (carbon copy) Dear Bob, I am writing once more about a promising young man to see whether there would be a chance for him to spend some time in your Department at Columbia. He is Stanley Mandelstam, a South African aged

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nearly 28, who came to this country in 1952 after obtaining an engineering degree in South Africa and then completed the Cambridge course in theoretical physics in two years with excellent results. He then came here as a research student in 1954 and has just qualiﬁed for his Ph.D. which will be conferred this month. His work as a research student was concerned with formal ﬁeld theory and he has published two papers dealing with the nature of the solutions to the Bethe-Salpeter equation in which he made an excellent job of sorting out this problem and incidentally of putting right incorrect statements made by Goldstein.821 The ﬁrst of these papers was completed after one year’s research work and I would, in fact, have been quite happy to give him a Ph.D. on the strength of that one year’s work if our regulations had permitted it. During his second year he continued and extended this kind of work, and the second paper on this subject has just been published in the Proceedings of the Royal Society.822 I believe a reprint of this paper is on its way to you. During the current academic year he has turned to more practical things and he is tending now to make his main interest the phenomenological side and the interpretation of experiments. Indeed he holds this year a special post from Government funds with the particular assignment to collect data and to do calculations which are required for planning and interpretation of experiments in the high energy laboratory here. As an example of this, he is looking at the moment at the theory of the meson production in p − p collisions, combining phase-space arguments with the picture of the isobaric state and linking the results with experiments performed here. In this work he had a good deal of guidance and inspiration from Dalitz. He would like to spend some time in the United States both to widen his general experience and to get more contact with current experimen821

S. Mandelstam, ‘Dynamical variables in the Bethe-Salpeter formalism’, Proc. Roy. Soc. A233, 248–66 (1955). 822 S. Mandelstam, ‘Uniqueness of solutions of the Bethe-Salpeter equation for scattering’, Proc. Roy. Soc. A237, 496–512 (1956).

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tal work in high energy physics. Amongst the possible places his ﬁrst choice would be Columbia. As you will gather from the description I have given I regard him as a ﬁrst rate man, as yet with more experience on the formal ﬁeld theory than on the practical side of high energy physics, but with a strong desire and, in my opinion, the capacity of developing in that direction. On general ability I would rate him higher than Redmond, of whom I also have a high opinion. He is doing this year some undergraduate teaching for us, and he is doing it well. He would have no diﬃculty in doing a certain amount of undergraduate teaching, though I do not think at this stage he would want to consider a full time teaching post. He is a very charming and educated person. In case it is relevant I should add that he is single. I would be most grateful, if you could let me know whether there might be a prospect of ﬁnding him some kind of grant in your department. If it would help to have a second opinion I am sure that Dalitz would be willing to give him a recommendation. With kindest regards, Yours sincerely, R.E. Peierls

[643] Hans Bethe to Rudolf Peierls Ithaca, 15.2.1957 Dear Rudy: Excellent! We are all looking forward to your visit either before or after the Rochester meeting. As far as I know, there is not much reason for us to prefer one or the other time. It is possible that after the conference the Russian physicists will visit Cornell for a day or so, and in this case we would of course be very grateful if you would do some extra work as an interpreter. At present we expect the Russians to come but, of course, such things may change in the course of two months.

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Ronnie is doing ﬁne.823 He is starting some calculations on the production of K-mesons by gamma rays, in connection with the experiments which are just beginning on our synchrotron. He is a most pleasant companion to have at home. Yours sincerely, Hans

[644] Gerry Brown to Rudolf Peierls Copenhagen, 5.4.1957 Dear Prof, Thanks for your letter explaining the situation at B’ham.824 It’s pretty clear that you’ve done everything possible and that if the future business doesn’t come through, it’s not for lack of trying. My only information had come from the Dean’s congratulatory note, and it looked like things ended there. (Of course, maybe they still will.) I had thought of staying a month in the US and coming back around May 22nd or 23rd. I have to be [in] Uppsala May 27th, where I’m faculty opponent in the Doctor’s Exam of Yren. (Although his work is mainly experimental, I gather they just want me to put the value of it & information from it in some kind of perspective.) I had planned on only stopping part of a day at B’ham, but if it would be useful to stop longer, please let me know before I go to the U.S. & I’ll take a plane back earlier. My U.S. schedule ﬁlled up from one end & and this Swedish business came several days earlier than I had bargained for. I was somewhat apologetic to Aage about being away for so long, but, as he pointed out, I wasn’t really paid here for doing anything special. (And I think I’ve given more than my fair share of seminars etc. here.) 823

Ronnie Peierls had completed his undergraduate degree at Cambridge and had moved to Cornell to work with Hans Bethe. 824 Gerry Brown was on sabbatical working at Copenhagen. In his absence Peierls was working on his promotion to senior lecturer.

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I shouldn’t like to be misleading about the depth of my “Brucknerization” of the formalism. Actually, all I did was notice that in S = Sˆ + S ce γ=

S ce was obtained by S ce = oγ|t˜|oγ || propagator in a complex well, i.e.,

t˜ = v(r, s) − vˆ(r) + (v(r, s) − vˆ)

inc. channel.

1 ˆ −E H

where t˜ is simply the

(v − vˆ) + · · ·

and one can express t˜ in terms of two-body operators τα in a complex well. This is very single. Deﬁne: v(r, ξ) = vα (r, ξα ) A 1 v˜α {vα (r, ξα ) − vˆ(r)} ≡ v˜ = A

then t˜ =

t˜α +

1 β=α

t˜β

1 ˆ H−E

P0

t˜α + · · ·

α

where P0 is a projection operator which keeps the nuclear ground state from ever being repeated. Of course, this latter expression is obtained in the same way as t is expressed in terms of tα in the Brueckner-Watson formalism. If one now takes the 1st two terms in the expansion of the t˜α in terms of v˜α , then one gets just Brueckner’s expression for the optical model potential of the making o|t˜|o = 0 (Actually Brueckner, Francis & Eden).825 Thus, this is really almost trivial, although I thought 825

Brueckner, Francis and Eden had published a series of papers developing methods for discussing gross properties and detailed properties of the nuclear ground state. See K.A. Brueckner, R.J. Eden and N.C. Francis, ‘High-Energy Reactions and the Evidence for Correlations in the Nuclear Ground State Wave Function’, Phys. Rev. 98, 1445–55 (1955); K.A. Brueckner, R.J. Eden and N.C. Francis, ‘Nuclear Energy Level Fine Structure and Conﬁguration Mixing’, Phys. Rev. 99, 76–87 (1955); K.A. Brueckner, R.J. Eden and N.C. Francis, ‘Theory of Neutron Reactions with Nuclei at Low Energy’, Phys. Rev. 100, 891–900 (1955).

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it more diﬃcult ﬁrst, hence I’d arrived at it in a diﬀerent way. Now, Watson ﬁnds within the approximation of keeping the 1st term t˜ ∼ = tα Vˆ (r) = o|

tα |o

but since α = t˜α − vˆ as far as I know, this may not correspond to keeping only the ﬁrst term alone. However, in the case that t˜α can be expanded in v˜α we have, of course, tied up the conceptional points pretty well. One question keeps recurring to me. That is, at about what stage is the Watson type derivation — which starts with an expansion in successive nucleon-nucleon collisions — valid in its own right without further assumptions about the shape of the strength function (as you’ll remember, random phases have to be assumed to get back to perturbation theory; this is equivalent to assuming the strength function to be of Lorentz-form)? I suspect it becomes valid at the point where the pronounced maxima in the average cross section as a function of energy cease. In terms of a particle picture, this means that the particle is not reﬂected at the edge of the nucleus, but essentially passes over it only once, in which case an expansion of the Watson-type seems intuitively reasonable. But does this mean that the compound states can be built up out of several successive collisions, to a good approximation? This, of course, doesn’t follow. Otherwise, I’m mainly concerned now with ﬁtting together lots of pieces in problems, without any very deep conceptual points being involved. In fact, aside from the basis of the rotational model, most of the big paradoxes (strong and weak interactions, etc.) seem to have been worked out of nuclear physics and it seems to be rapidly getting to the stage of spectroscopic analysis. Of course, there are still some problems in spectroscopic analysis, which reminds me of the Lamb Shift. I’ve checked and rechecked all components of this calculation (which I could only have done with my vast amount of time here) and the answer remains ∆EK = 0.14αmc2 . This is just what one would guess by an order of magnitude estimate 4 (Z α4 ≡ 0.12) but is much larger than the 1/2 Ry or so that Stan Cohen

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was willing to allow to remain of the 2s − 1s level diﬀerence. Of course, the 2s level also is shifted — and I’d hate to calculate it — but one wouldn’t expect it to be shifted so much. The cancellation of inﬁnities by the counter terms & the internal consistency of the calculation come out so beautifully, that it’s hard to see how anything could be wrong. We’ve had a very peaceful Easter vacation. Traudl is very happy with C’haven customs, food, etc., so that she hardly complains. At ﬁrst I thought she must be ill. She’s been so enthusiastic to people at the Institute, that they suggest that we stay. Whereas I enjoy very much being an honorary Scandinavian, I don’t think I’d like to become an actual one. When things proceed further on the research fellowship and ICI fellowship business, please ask me further about Mavis. He’s full of ideas and a hard worker. I don’t ﬁnd his present political views and attitude unreasonable, and he’d be a real asset. Probably ICI would be better, since he’s likely to work partly experimentally. I have only indicated to him that he should apply — he has a CERN iron in the ﬁre. But I thought it best to make the whole business clear to you, from the start. Best regards, Gerry

[645] Stanley Mandelstam to Rudolf Peierls Columbia, 30.11.1957 Dear Professor Peierls, I have settled down in New York, and, on the whole, I am liking it very much. Needless to say there are many more “distractions” than in Birmingham, and I am ﬁnding no shortage of concerts, theatres or art galleries to which to go! On the physics side, it is certainly very useful to be able to get some of the latest experimental results in high energy physics as they come out. As you and others had told me, the department at Columbia is somewhat less integrated and informal than Birmingham, and, apart from seminars and colloquia, most of

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the activity involves individual groups rather than the department as a whole. The most interesting results of this department since I have been here, have been from Steinberger’s bubble chamber group.826 In case you have not heard them, they have shown pretty conclusively that the 1 spin of both the Λ and the is 2 (assuming that the K has zero spin). This was done by means of an Adair analysis — observation of the angular correlation between the planes of production and decay for K’s produced in the forward direction in π − p reactions —, and the spin is thereby obtained unambiguously. We also had a seminar by Adair, who claimed to have shown that, if the parity of the Λ and the is the same, the K is scalar relative to them. He did this by examining the angular distribution in elastic π − p collisions near the threshold for K-meson production.827 Although the data are not enough to determine the transition matrix at this energy, he nevertheless came to the conclusion that it was very probable that the inelastic production from an S-wave is less than 1mb. Most of the audience did not believe that one could get such a small upper limit from the relatively meagre data. If his analysis is accepted, then his ﬁnal result is very likely, since the data for the Kmeson production indicates that the cross-section for production into an S-state rises above this ﬁgure. There must therefore be production from a P -state into an S-state, and the parity of the K-hyperon system must be diﬀerent from that of the π − N system. Orear’s group828 has bee[n] looking very carefully for a mass-500 particle in cosmic rays, and we should have their results before very long. I am at the moment working on dispersion relations, and I am trying to adapt the method of Chew, Low and Salzman829 to be applicable to 826

See M. Chr´etien, J. Leitner, N.P. Samios, M. Schwarz and J. Steinberger, ‘pi− −p Electric Scattering at 1.44.Bev’, Phys. Rev. 108, 383–89 (1957). 827 See L.B. Leipuner and R.K. Adair, ‘Production of Strange Particles by pi− p Interactions near Threshold’, Phys. Rev. 109, 1358–63 (1958). 828 Jay Orear had obtained his Ph.D. in 1953 from Chicago working with Fermi, then became lecturer at Columbia University, later professor of physics at Cornell University. 829 G. F. Chew and F. E. Low, ‘Eﬀective Range Approach to the Low-Energy p-Wave

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the relativistic case in the one-meson approximation. The relativistic theory is much more diﬃcult than the static theory, partly because the crossing term mixes all the angular-momentum states, and partly because of the subtractions. I am hoping to treat these by considering the dispersion relations for the process N + N → π together with the usual relations for pion-nucleon scattering.830 The treatment of the non-physical region will require careful consideration. One thing which emerges from this sort of study is that the existence of crossing terms changes profoundly. It follows that there is really not much evidence for the inconsistency of local ﬁeld theory, since all the models (such as the Lee model) or approximations (such as the Landau approximation) which led to this belief leave out crossing. Goldberger feels the same way, and he pointed out to me that the high-energy behaviour of the theory is completely changed by crossing. He and his students are doing a lot of work on dispersion relations; at the moment they are examining nucleon-nucleon scattering, and also the electro-magnetic properties of the nucleon. As you probably heard, Sirlin831 took Ronnie’s boots to Cornell. I am returning your Bonamine, and thank you for it. Best regards to you, your wife and Gaby, Yours sincerely, S. Mandelstam

Pion-Nucleon Interaction’, Phys. Rev. 101, 1570–79 (1956); G. Salzman and F. Salzman, ‘Solutions of Static Theory Integral Equations for Pion-Nucleon Scattering in the One-Meson Approximation’, Phys. Rev. 108, 1619–28 (1957); George Salzman, ‘Nucleon Structure in the Static Theory’, Phys. Rev. 105, 1076–1083 (1957). 830 This eventually resulted in Mandelstam, S., ‘Determination of the Pion-Nucleon Scattering Amplitude from Dispersion Relations and Unitarity. General Theory’, Phys. Rev. 112, 1344–60 (1958). 831 Alberto Sirlin (1930–), obtained his D.Sc. from Buenos Aires in 1953 and his Ph.D. from Cornell in 1958 before moving to New York University in 1959 where he eventually became full professor (1968).

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[646] Rudolf Peierls to Felix Bloch [Birmingham], 12.12.1957 (carbon copy) Dear Bloch, I am writing to enquire whether there might be a job in your department in the next academic year for Miss Nina Byers, an American girl who has been with us here since October 1956. She is a native Californian, did her undergraduate work at Berkeley and her Ph.D. in Chicago under Wentzel. She ﬁnished there in 1956 and some of her Chicago work is published (Physical Review, 107, 843, 1957).832 In 1956 she came here on one of our University fellowships which are mainly research posts, though they involve a small amount of undergraduate teaching. Her interests here have been mainly concerned with strange particles and, more lately, with beta decay and parity. She has been one of our main experts on strange particles and has given a series of seminars, for example trying to help us understand the mysterious papers by Schwinger, reporting on the Venice Conference833 etc. She has also been investigating the decay of hyperfragments and is working out at the moment a suggestion, entirely due to her, that from the comparison of the rates of mesonic and non-mesonic decay, it may be possible to decide the spin of the hyperfragment (i.e. whether the hyperon likes to have its spin parallel or opposite to the odd nucleon). She has also looked after a research student who is working out the angular and energy distributions in these hyperfragments decays where three particles are seen in the ﬁnal state. Her main work at the moment is to explore, in the light of the most recent evidence, the model in which beta decay is a two stage process involving an intermediate particle and this is going well and I am sure she will be able to decide whether such a model is feasible, though we do not yet know the answers. 832 Nina Byers, ‘Interactions of Low-Energy Negative Pions with Nuclei’, Phys. Rev. 107, 843–49 (1957). 833 Padua-Venice Conference on Mesons and Newly Discovered Particles, September 1957.

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We have found her a most useful member of the department and a very good person to discuss problems with, and in a very closely-knit group she has been a very good inﬂuence on the work of quite a number of people. I would like to quote one particular illustration. When Pauli visited here last year and lectured on his ideas about lepton conservation in beta decay, she had some comments which she discussed with Pauli at length and he came back to me from this interview with the remark “This is a very clever girl.” I imagine you imagine Pauli’s attitude to female theoretical physicists and will therefore be able to appreciate this compliment. Miss Byers has also given a course of undergraduate lectures of about 2 hours a week and this has gone extremely well. It turned out that the class was much larger than we expected and contained some very undisciplined students, who in courses by other lecturers to the same group cause considerable turmoil. We would never have put an inexperienced lecturer in charge of this class if we had foreseen this situation, but in fact Miss Byers coped with it extremely well and no diﬃculties appeared at all. We would have been delighted to keep her here longer, but she understandably feels that she would now like to return to the United States and Stanford was her ﬁrst choice amongst suitable Universities. Miss Byers is not at this stage concerned with the security of tenure, and some research fellowship or associateship would be quite appropriate, but she would also be quite willing to take a job, involving some teaching within reason. I know that jobs in Stanford are very much in demand, but I would be very glad if you could let me know what the prospects are, if any. If there is a reasonable chance, she should no doubt make a formal application herself. I am very sorry I shall not be able to come to the very interesting conference you are holding shortly. I hope it will go oﬀ well.834 With kindest regards, Yours sincerely, R.E. Peierls 834

Stanford Meeting of the American Physical Society, December 1957.

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[647] Rudolf Peierls to F.R. Shotton [Birmingham], 6.1.1958 (carbon copy) Dear Shotton,835 I would like to propose that Dr.G.E.Brown in my department be given the title of professor, and I understand that, under the current procedure, the request should in the ﬁrst instance, go to you. Dr. Brown is aged 31. He is a graduate of Wisconsin and a Ph.D. of Yale, and he has been in this department since 1950, ﬁrst on American funds, then on a research fellowship and later as a temporary and then permanent lecturer. He has done and is continuing to do important work in several branches of my subject, and he has built up a considerable international reputation. Much of his work has borne fruit in the last year or two and at some recent conferences, it has become particularly obvious how much weight his opinion carries. He has supervised a large number of research students, nearly all of whom have worked on ideas which he initiated himself, and he has been extremely successful in bringing out the best qualities in them and inspiring them with his enthusiasm for research and at the same time in getting them to realise that hard work and perseverance are as important as elegant ideas and intelligent understanding of the subject. Dr. Brown is still grade 2. He was put forward for promotion to senior lecturer grade 1 a year ago, but was then competing with many others, including in this department, Dr. P.T. Matthews, who has since left us. I put Dr. Matthews ﬁrst at the time because of his greater seniority and reputation, but was already then in some doubt about the relative claims of these two men. Brown’s progress has continued at such a pace that today I would probably put him ahead of Matthews. It may appear surprising that I believe there is a strong case for a professorship for someone who has not yet reached the senior lectureship grade, and I should therefore explain why he was not considered earlier 835

F.R. Shotton, professor of Geology, Birmingham University.

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than last year for promotion. This is, in the ﬁrst place, due to the rapid rate at which his work has come along recently. My opinion has not changed at all much because I was always most impressed with him, though I do appreciate the great value of his recent work, but the point is that he has become so much better known through his recent papers outside the department and outside the university that it is now very much easier than it would have been some years ago to get outside opinions to conﬁrm my views. In addition, I believe now that I was too slow in asking for promotion, even on the evidence as it stood. I am sure that Brown deserved consideration earlier, and I was at fault in not realising this soon enough. The matter is of some urgency because I ﬁnd that Brown’s name is mentioned more and more frequently in connection with other appointments. For example, there is a chair of theoretical physics at Manchester, which will be vacant from next October, and I know that Brown is one of the two strongest candidates for this. I have been asked my opinion about his suitability for a major chair in Holland, and I have been approached by the senior professor at MIT to ﬁnd out if Brown would be likely to be interested in an associate professorship there. He is just leaving to spend 8 months at the Institute for Theoretical Physics in Copenhagen, and he is too conscientious a person to resign immediately after the end of his study leave, so I am virtually assured of his being here at least for the session 58/59, but he may well be faced with more than one oﬀer relating to the period after that. I would be greatly distressed to lose Brown from my staﬀ because of the help we get from him on many aspects of work here, as well as on practical matters and in teaching. I cannot hope to keep him here indeﬁnitely and sometime he will want to run a department of his own, but I believe that the set-up here suits him and that he would be willing to continue for some more years in the department if he were given adequate status. I would like to mention in this connection that I have recently lost two good men and in part, no doubt, because I was not able or did not try to do enough for them. These were R.H.Dalitz, who was promoted to a senior lectureship and for whom I had hoped to obtain the title of professor, except that a change in procedure delayed this proposal and

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in the meantime he had already decided to go to Chicago. In this case I was able, with the approval of Redshaw who was then Dean, to make it clear that there was every likelihood of this title being conferred to him, and I am sure the major reason for leaving in this case was the closer contact with work in his special line and the easier access to the latest data, which he could have in America. But he did at least hint that an earlier and more tangible recognition of his work might have inﬂuenced him the other way. In the case of Matthews, he started negotiations with Imperial College because he was oﬀered a readership there when his promotion to senior lectureship here was not yet certain. In his case the promotion was approved before he had to make his decision, and therefore here again the decision was made on other grounds. But is very possible in his case, too, that he might not have taken the invitation seriously if the promotion could have been assured earlier. In many ways I am more anxious to keep Brown for longer than was the case with the other two, because of the breadth of his interests, his ﬂair for handling research students and his willingness to take on any work or any chore that turns up, regardless of whether it happens to suit his particular inclination at the time. Mrs. Brake has letters about Brown from several people. In connection with his proposal to promote him to senior lectureship we had letters from Prof. Bethe at Cornell, and Prof. L. Rosenfeld of Manchester. Later he submitted a thesis for the oﬃcial degree, for which the external examiners were Prof. Rosenfeld and Professor H.S.W.Massey of University College London. Both reports, beyond recommending the award of the D.Sc. are highly enthusiastic about Brown’s work. All these letters and reports are available, and, if required, no doubt the same people would be willing to express and opinion on the merit of the case for a professorship and further opinions could be obtained if necessary. I hope you will regard this letter as making out at least a prima facie case, and will arrange for the matter to go further. Yours sincerely, R.E. Peierls

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[648] Rudolf Peierls to Hans Bethe [Birmingham], 8.1.1958 (carbon copy) Dear Hans, I am writing to mention the case of a very bright American, James S. Langer,836 who is expected to get a Ph.D. here this summer, and who is going to return to the United States after that. He is a graduate of Carnegie Tech. and came here immediately from his Bachelor’s degree in 1955. We do not usually expect students who have completed the undergraduate courses in an American institution to be ready for research straight away; however, Langer was unusually well-trained and unusually mature, and we found it reasonable to treat him on the same basis as one of our own graduates. He produced, under the guidance of Edwards and Matthews, a paper on the Eﬀect of Virtual Pairs of Strange Particles in the S-Wave Scattering of Mesons by Nucleons, which, as you may remember, Matthews summarized at the last Rochester Conference, and which is published. (Nuovo Cimento, 6, 674, 1957.) Since then, he has changed to more conventional nuclear theory, and has been working under the supervision of Gerry Brown. Here he has already made some very nice contributions to the derivation of the optical potential from the dispersion theory, following the work of Brown and De Dominicis,837 and I have every conﬁdence that he will produce a good Ph.D. thesis before he leaves us. He is a very charming person, speaks well and clearly, and has been successful in what little part-time teaching we asked him to do. He would like to continue for a time in nuclear theory and would be quite 836 James S. Langer (1934–), received his Ph.D. from Birmingham in 1958 before joining the physics department at Carnegie Mellon University in 1958. In 1982 he became professor of physics and a member of the Institute for Theoretical Physics at the University of California, Santa Barbara, serving as its director between 1989 and 1995. 837 G.E. Brown and C.T. de Dominicis, ‘Elastic Scattering of Low Energy Nucleons by Complex Nuclei’, Proc. Phys. Soc. A70, 668–80 (1957); G.E. Brown and C.T. de Dominicis, ‘Direct Interaction and Nuclear Dispersion Theory’, Proc. Phys. Soc. A70, 686–89 (1957).

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interested in a job which would involve some teaching, provided of course it left him adequate time to continue research. In considering his plans for next year, his ﬁrst choice turned out to be M.I.T., because of the connections of what he is doing with the main line of interest of some people there, and his second choice is Cornell. We have, of course, made an approach also to M.I.T., but the object of the letter is to ﬁnd out what the prospects would be in your Department. Yours sincerely, R.E. Peierls

[649] Robert Aitken to Rudolf Peierls Birmingham, 10.1.1958 My dear Peierls, Shotton has shown me your letter to him about the possibility of the title of Professor to Dr. G.E. Brown. We both think that it is very unlikely that the Committee concerned would recommend the conferment of the title. There is the obvious diﬃculty that Dr. Brown is young and still only a lecturer, and it would need evidence of striking brilliance to justify the title of Professor. There is the further diﬃculty that if such a dramatic promotion were made the door would be opened to an embarrassing number of claims on behalf of other lecturers and readers in the University. I wonder therefore whether you would like to consider again whether a proposal for a Readership would not be more appropriate? If eventually you decide to press for the Professorship, we shall of course set the wheels in motion, for the procedure was never intended to give the Dean and the Vive Chancellor a veto. Yours sincerely, Robert Aitken

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[650] Rudolf Peierls to Robert Aitken Birmingham, 13.1.1958 (carbon copy) Dear Dr. Aitken, Thank you for your letter of 10th January about the case of Dr. G.E. Brown. I would like, of course, to be guided by your advice and I would be reluctant to press a case of which you felt that the Committee would or ought to turn it down. However, I am intensely unhappy about the reasons which you give for regarding this as an unsuitable case, and I would be disappointed if these should be taken as representing the policy of the University. I would agree of course that evidence of quite striking brilliance would be required to justify the promotion to a professorship, and in my letter to the Dean I had tried to make it clear that Brown was indeed an exceptionally brilliant man. I hope that, if in the further consideration of the request other opinions were sought, both inside the University and outside, they would conﬁrm and amplify this view. Brown is indeed only 31. He is a year older than I was then I was appointed to my present chair, and he is about the normal age at which the best men in my ﬁeld are appointed to chairs. My subject may be somewhat exceptional in this respect. The progress depends on the young men and good people to establish themselves early. I might here perhaps quote a famous remark by an outstanding Russian theoretical physicist, who, when the name of a man came up of whom he had not heard and when he was told he was under thirty, said: “What, so young and already so unknown?” The other serious candidate for a chair in Manchester to whom I referred in my previous letter is about 33. Five years ago he was appointed to be the Head of the Theoretical Division at Harwell; a post which carries the status equivalent or higher to that of a professor and a considerably higher salary. This was done in part on my advice, and some doubt then was expressed about his age. He has proved an outstanding success and has fully justiﬁed the appointment. He is a good man, but except for the additional administrative experience he has acquired by now I would not rate him higher than Brown.

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I have in my department on a temporary basis, Dr. Thellung, a young Swiss who was last summer appointed to a second chair in the Department of Theoretical Physics in the University of Zurich, which as you no doubt know is a University of good standing. I do not know his exact age, but I believe he is several years younger than Brown. Incidentally, he has deferred taking up his appointment there until Easter so as to complete the period he was planning to spend here. This is a compliment to the standard of the department here, which I would not hope to maintain unless I could attract and adequately look after men of the quality of Brown. I might in this connection also mention that another visitor is an American, the senior professor of theoretical physics at the University of Louisiana, who has come here for a sabbatical year and for whom one of the chief attractions was the possibility to work with Brown. I referred in my previous letter to an enquiry I had from the University of Groningen in Holland about their vacant chair; the two names mentioned there were those of Brown and Thellung. You know no doubt of my concern now generally felt about young scientists being tempted away to the United States. In my own subject we have been fairly lucky in this respect, but the one serious loss is that of F.J. Dyson, probably the most outstanding theoretical physicist of his generation who is now at the Institute of Advanced Studies at Princeton. He was given his full professorship there at the age of 27. His reasons for leaving are complicated and probably unavoidable, but I often discussed with him the position of scientists in the Universities in this country on which he holds strong views. Some of his criticisms I had to admit as justiﬁed, but when he said recently that we were in this country too slow to recognize and regard special merit, even within the framework of the scales and conditions existing here, I objected violently and tried with some success to prove that he was wrong. I would not like to have to admit to him that his view was after all justiﬁed. We often critizise the Civil Service as an organisation in which seniority and coming in the correct way up the ladder is more important than merit, but it seems to be easier today to get exceptional promotion for a good man in the Civil Service than in the University. I have certainly seen within the atomic energy organisation (even when it was under the Civil

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Service) many cases of accelerated promotion which would have been unbelievable in the University. If we want to be guided primarily by seniority and carry out our promotions tidily and slowly we should be content to retain competent mediocrities and let the real outstanding men look for recognition in the Civil Service, in the European Nuclear Physics Organisation at Geneva, which is beginning to compete for good men, and, of course, in the United States. I suspect that if we were to lose Brown it would be a loss not merely from the local point of view in Birmingham, but also from the national points of view, because from his preliminary reaction to the Chair in Manchester and other openings, I have the impression that this department in Birmingham is the only place in his country which would suit him and that apart from that he would respond to one of the many enquiries that have already come from the United States and will continue to come his way. Finally, I would like to comment on your remark that a promotion of the kind I have asked for would lead to many other trends. I thought the purpose of the new procedure was to discriminate between genuine cases of exceptional merit and others. If the principle was not to give the one what others might ask for a special procedure would hardly be necessary. I do not think I have ever asked for an unreasonable concession and I would really have felt by now that if I had brought up a case which seemed to me to merit exceptional measure, that at least the possibility would be considered, as it might be an exceptional case. It is, of course, possible that in your reaction you had in mind not only reasons which you gave in your letter but that you also felt that the particular case was not strong enough to win the approval of the Committee, and that would alter the position considerably. In that case, I hope you will let me know why you regard the case as inadequate. If it would help to clarify the particular case, or the general points of policy, I would of course be grateful for an opportunity for discussing the problem with you personally. Yours sincerely, R.E. Peierls

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[651] Rudolf Peierls to Gerry Brown [Birmingham], 3.3.1958 (carbon copy) Dear Gerry, I owe you a letter on a variety of topics. To start with I have no particular comment on your draft paper.838 The model you propose is a little vague but so is really the whole problem and this is probably as far as one can go at the present moment. My only comment on wording is in the last paragraph but one “This can soon be checked” sounds as of you mean this is an experiment what will take no time. I think you probably mean “It will soon be possible to check this”. As regards the question of study leave or leave of absence, I doubt whether many people appreciate the subtlety of the distinction and I think “on leave” is quite adequate. If you wanted to stress the kindness of the University of Birmingham, I should think the proper place would be in an acknowledgment at the end in which presumably in any case you will refer to hospitality etc. in Copenhagen. I was very interested in your many various activities. You seem to manage to be quite as busy in Copenhagen as you are usually. As regards the Lamb shift, I was asked recently by Zienau of University College839 whether any more details of the calculation were available, since they were trying to use similar techniques for a diﬀerent problem and had got stuck with setting it up. When eventually something gets written up about it, it would be kindness to send them a copy. About the Geneva Conference,840 pressure is certainly very high 838 G.E. Brown, ‘Proton-Proton Scattering in the Bev Region’, Phys. Rev. 111, 1178–81 (1958). 839 S. Zienau was collaborating with E. Power on work that would lead to the so-called Power-Zienau transformation, later extended to the Power-Zienau-Wooley transformation. See E. Power and S. Zienau, ‘Coulomb gauge in nonrelativistic quantum electrodynamics and the shape of spectral lines’, Philos. Trans. R. Soc. A251, 427–54 (1959). 840 The 8th Rochester Conference took place in Geneva between 27 June and 5 July 1958.

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and it is not yet even settled whether this department will get a place in addition to mine. If we do we shall bear in mind that you shall not get a place at the Copenhagen list, and consider you as a candidate for our list. But, as you will appreciate, this will be a very tough question to settle and I do not know at the moment which horse to back. Mrs. Tuscott suddenly reported that she had ﬁnished the calculation for you, which somehow I had expected, from what she said, to take much monger. The results will be sent to you as soon as they have been copied to avoid the risk of their going astray in the post, even though it might be a small risk, and meanwhile we are seeing which other computation we can set up in a hurry, so as to go using Mrs. Tuscott’s help. The Physical Society wrote a rather silly letter about your last paper with Cyrano.841 I enclose this together with a copy of my reply. I have, however, still kept the paper here, ﬁrstly in case you are inspired by the referee’s remarks to make any changes (which I doubt), and secondly to see whether you think it would be useful to incorporate the result of Langer, which essentially amounts to a formal solution of your equation (2) for W , which I think you saw just before leaving. I do not want to press this point at all, but since we have the paper back anyway, I think we should at least consider the question. I have heard no more from Anne Dee since we saw her last, but she is coming up again in a week’s time and I shall let you know what the position is. I was going to continue writing more about what goes on in the department generally, but this would [d]elay the letter, particularly since with Aage Bohr around I would like to spend as much time as possible with him, so I had better close at this point and hope to report the general gossip later. Yours sincerely, R.E. Peierls 841

The paper was submitted in January 1958. It was published as G.E. Brown and C.T. de Dominicis, ‘The Optical Model at Low Energies and Dispersion Theory’, Proc. Phys. Soc. A72, 70–80 (1958).

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[652] Gerry Brown to Rudolf Peierls Copenhagen, 13.3.1958 Dear Prof, We’re just back from Norway — wonderful week of skiing and a week at Oslo University (where, of course, they are interested in the two-electron problems). I think that the referee (and I’m sure I know who it is) of my paper with Cyrano842 should take same Alka Seltzer, since he seems to have a bitter view of life. The amount of space wasted by the previous error plus correction was about 1 1/2 pages (which doesn’t mean we should have made it). Your letter was very much to the point on all the criticisms and since it’s such a good statement, I don’t think that anything would be gained by my adding to it. Thomas’ paper is so complicated that I’ve never been able to ascertain precisely what is included, but I’m sure that it’s not as complete a treatment as ours, although it’s much longer.843 I would prefer not to add Langer’s work to this paper, since it is not an integral part of the development and adding it would involve complications with time and with Cyrano. Further, I believe from what he writes that ultimately he’ll be able to make quite a nice contribution out of his work on several formal points, and his development could very well be part of this.844 I don’t want to make a strong bid for the Geneva Conference, since I hope to be going to a couple of other ones (Washington and Paris) which are just as much in my line. Further, I can probably arrange things so as to go to Geneva for a week or so at another time. I think, however, that it would be good, if you could report the Bev pp scattering work 842

See letter [651], note 841. R.G. Thomas, ‘Collision Matrices for the Compound Nucleus’, Phys. Rev. 97, 224–37. 844 Brown, De Dominicis and Langer, a year later, published a joint paper which developed the exact expressions for the amplitudes for scattering of a particle by a complex nucleus. G.E. Brown, C.T. De Dominicis and J.S. Langer, ‘Perturbation theory in nuclear reactions’, Ann. Phys. 6, 209–29 (1959). 843

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and any progress I make in meson production before then. I can provide you with slides. On Monday I’m oﬀ to Uppsala for a week, which promises to be most interesting. Best regards, Gerry

[653] Rudolf Peierls to Lev Landau [Birmingham], 14.3.1958 (carbon copy) Dear Dau, You will by now have received a letter from the Vice Chancellor of this University inviting you to accept an honorary degree, which would be conferred at our degree ceremony on 5th July. I am writing ﬁrst of all to express the hope that you will be able to accept and also to give you a little more explanation in case you are not familiar with our practice about honorary degrees. Such degrees are usually awarded to rather few people (something like 5 each year) who may be scientists or scholars of special distinction or to other public ﬁgures whom for one reason or another the University wishes to honour. Perhaps the best idea of giving you an indication of standard is to mention the names of those physicists or mathematicians who have in the past accepted such degrees from this University: Appleton, Aston, Bethe, Niels Bohr, W.H. Bragg, Chadwick, Cockroft, Madame Curie, Frisch, Larmor, Lorentz, Oliphant, Rayleigh, Rutherford, G.I. Taylor, Urey, E.T. Whittaker. We have never had in our list a U.S.S.R. scientist and I doubt whether an honorary degree has yet been awarded to a U.S.S.R. scientist by any other University in this country. I feel therefore that if you were able to accept this would be a symbol of value for the international cooperation between scientists. It is our custom to confer honorary degrees at the same ceremony at which our own students receive their degrees and, for this reason, the

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date is inﬂexible. Honorary degrees cannot be conferred in absentia. They are normally conferred by the Chancellor of the University who is usually a public ﬁgure associated with the University in a purely formal way. In our case the Chancellor is Sir Anthony Eden. Since he has recently been in poor health, it is not yet known whether he will be able to come this summer. If he is not there, his place will be taken by the Vice Chancellor, who is the administrative head of the University. The ceremony is quite short. It is usually divided into a morning and an afternoon session, and it would be fairly easy to arrange for you to be included in the morning or the afternoon, if either would be more convenient. I very much hope you will ﬁnd it possible to accept and it would of course be a great pleasure to see you here on that occasion. If you can come, the next question would be whether you can spend here a little more time than is necessary just for the honorary degree, and we would of course be extremely pleased to have you here for as much time as you can spare. This is slightly complicated by the fact that I shall be spending the week preceding the degree ceremony at the conference in Geneva and immediately after the ceremony have to leave for a summer school in North Carolina. So from our point of view it would be most attractive if you could get here during the week beginning 23rd June or earlier. However, even later other members of the department will be very happy to see you here, even though I would be disappointed to miss this occasion. However, all this is a separate question, and we shall be happy enough if you can only manage to get here for the degree day. I hear that the publication of the translation of “Statistical Physics” is at last making progress. My son reports good progress with the page proofs, which would be ﬁnished by now except that the alterations (required no doubt because of the long delay in publication) have necessitated second page proofs of some parts. With kindest regards, Yours sincerely, R.E. Peierls

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[654] Hans Bethe to Rudolf Peierls Ithaca, 20.3.1958 Dear Rudi: Thanks a lot for your letter of March 3.845 I am glad to hear that Jenkins and Langer have satisfactory oﬀers. We are in the meantime were saturated, actually somewhat more than saturated, because it is possible that two people may stay for part of the time whom I had expected to leave. So I am afraid I cannot make any oﬀer to Dabrowski or Burkhardt. Concerning your physics questions, we have indeed some results about the imaginary part of the nucleon-nucleus potential. If we assume that the eﬀective mass, the imaginary potential comes out to be about 1/2 Mev for slow neutrons, about 4 Mev at 14 Mev neutron energy. Both values are about half of the observed, and perhaps even somewhat less. So one has to assume a very large contribution of the nuclear surface, as you say in your letter. These results were obtained by Mr. Gordon Shaw.846 He ﬁrst considered the Born approximation with an exceptional potential, similar to the Italians, but doing the integrals more accurately. More recently he has taken the numerical results on the G Matrix of Brueckner and Gammel847 and deduced the imaginary potential from these.848 The result is only 20% higher than from the conventional potential with Born approximation. The 20% may be attributed to the fact that G is larger than v for an attractive potential, and also partly to the non-central forces. It is not clear to us, however, how strongly the result would 845

Letter Rudolf Peierls to Hans Bethe, 3.3.1958, Peierls Papers, Ms.Eng.misc.b202, C.18. 846 Gordon L. Shaw, obtained his Ph.D. at Cornell in 1959; he continued his research at Indiana University Bloomington, at the University of California, San Diego, at Stanford and at the University of California, Irvine where he became professor in 1968. 847 K.A. Brueckner and J. Gammel, ‘Properties of Liquid He3 at Low Temperature’, Phys. Rev. 109, 1040–46 (1958). 848 G.L. Shaw ‘Imaginary part of the optical model potential for neutron interaction with nuclei’, Ann. Phys. 8, 509–556 (1959).

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be inﬂuenced by singular potentials (a repulsive core was included by Brueckner and Gammel). For diﬀerent conventional potentials with the same eﬀective range and Platt strength parameter, the imaginary potential comes out to be about the same. One possible modiﬁcation may come from the eﬀective mass. Thou849 less has developed a theory of the actual one-particle energies in which he shows that these energies are considerably larger than the model energies used in the Brueckner theory. The correction comes mainly from the Pauli principle. Since Thouless’ correction is greater for low levels, it tends to increase the eﬀective mass for real nucleons. This seems to be contradicted by experiments on the optical potential but, if it were true at least near the Fermi energy, it would lead to an increase in the imaginary part of the optical potential which is proportional to about the square of the eﬀective mass. With best regards. Yours sincerely, Hans

[655] Rudolf Peierls to Gerry Brown Pisa, 25.3.1958 (carbon copy) Dear Gerry, Amongst assorted bits of news ﬁrstly I can report that your promotion to a Senior Lectureship (formerly Grade I) has passed the diﬃcult hurdles and is just waiting for formal conﬁrmation so it is still conﬁdential. I am writing mainly to explain that when you get the oﬃcial letter about this, you should not take this as evidence that nothing more is going to happen. Since any other action goes through a diﬀerent procedure 849

David J. Thouless (1934–), obtained his Ph.D. from Cornell; in 1959 he joined Peierls’ department at Birmingham; after further research at Cambridge he became professor at Birmingham (1965–78). He also did research at Kingston, Yale, and Seattle before taking up a professorship at Washington University in 1980.

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it was obviously prudent to go ahead with this step when we could. Further action is still in the mill. I never answered your question about Anne Dee’s work. She did come up recently but really had not done much since we saw her last. On going over the problem with her, I found that it was not really very complicated to extend this treatment to get the energy dependence. Since one evidently still is in the region of separated compound resonances, it is reasonable to treat the compound nucleus eigenfunction as approximately real. In that case all the matrix elements in your formalism take their phase just from the external wave functions, which are known. Anne is still trying to get her thesis in by May, but I doubt if she will make it. I am very interested to hear that you have Bruecknerizesd your formalism; when this is written up I hope you will send us a copy, since in the meantime I had started oﬀ Mondragon on doing this.850 However, he decided rightly that as a ﬁrst step towards this it would be wise to extend the formalism to full antisymmetry, and he is making some progress with that. I now believe this is not as hard as we had always thought. Langer has now quite a lot of promising lines, and it is just a question which one to do ﬁrst. One is connected with a rumour according to which Bethe has calculated the imaginary part of the potential for an inﬁnite nucleus by Brueckner method and ﬁnds it much smaller than usually assumed. He explains this by saying that the imaginary part is much larger near the surface. Langer has seen a simple way of calculating the imaginary part near the surface from a special model without too much computing, and this is clearly worth doing. Did you ever explain to Rosenfeld the facts of life about branch points and thresholds in the dispersion formula? Recently it has occured to me that it may well be that this diﬃculty can be overcome by the trick which Aage Bohr uses to derive the dispersion relations of ﬁeld theory, in which the part from the “unphysical region” appears as due 850

Alfonso Mondrag´ on (1932–), had studied in Mexico before joining department of mathematical physics at Birmingham where he obtained his Ph.D. in 1960. He returned to Mexico where he spent the remainder of his scientiﬁc career.

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to the behaviour of components which decrease exponentially in space, but which still should be causal in time. However, that is still a very vague thought, and I may perhaps think a little more about it in the peace and quiet of Pisa. Our sales campaign is going quite well. Jenkins, who is getting on quite well with Sam’s plasma problems, got an oﬀer from Brueckner by return of post, Nina Byers is going to Stanford, Schultz to Illinois, Hearing to McMaster. Burckhardt is still waiting to hear from Lee, and we are beginning to build up second and third lines of defence. Langer has an oﬀer from Carnegie Tec’ but is waiting to hear whether Wick is returning there or staying at Brookhaven. However, it may still be Hobson’s choice for him. Dabrowski now would also like to go to America, and I have written about him to Wigner, Dyson (since the Institute settle their grants later than anybody else) and Bethe, but have so far had not reply. By some strange ﬂuctuation we do not seem to get next year any of the usual post-doctoral visitors. It seems therefore all the more important to make good choices for the vacant Fellowship (Nina’s) which is just being advertised. I have tried to get Goldstone851 interested in this, but he won’t commit himself. Maximon852 is evidently interested. Do you know of anyone suitable? You might bear this in mind when you meet someone at the photonuclear orgy. If we ﬁnd more than one good candidate we may try to get an I.C.I. Fellowship as well. There are plenty of other things to report, but this is all I remember for the moment. Yes, did you notice that Bethe’s paper853 has now come out in the 851

Jeﬀrey Goldstone (1933–), obtained his Ph.D. from Cambridge in 1958 before doing research at Cornell, CERN, Copenhagen and Harvard. Between 1962 and 1976 he taught at Cambridge before taking up a professorship at M.I.T in 1977. 852 Leonard C. Maximon received his Ph.D. from Cornell in 1952. He went on to do research at Brown University, Manchester and Trondheim, before working for the National Bureau of Standards in Washington and the National Institute of Standards and Technology in Gatthersburg. He later became research professor at George Washington University. 853 H.A. Bethe, ‘Scattering and Polarization of Protons by Nuclei’, Ann. Phys. 3, 190–240 (1958).

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Annals of Physics, essentially as it was, acknowledging interesting correspondence from you? Did he ever reply to your arguments directly? Skinner has asked me for a letter about Ashmore, on the basis of your joint paper.854 Could you drop me a line explaining what his part was in the joint enterprise? We shall be here until about 25th April. Best wishes to all of you, Yours sincerely, [Rudolf Peierls]

[656] Gerry Brown to Rudolf Peierls Copenhagen, 25.3.1958 Dear Prof, I received a letter today from Dean Shotton today, saying that I am to have a senior lectureship & congratulating me (in a very nice way). However, it seemed to me to be implied in the letter that I would be appointed at the bottom of the scale. Maybe that is not so, but I would like to make my feelings on this clear. As you know, I enjoy working in the dep[artment] at Birmingham very much, probably for many of the same reasons that you do. I think, though, that I’ve got far behind almost all the young theoreticians in England who are doing reasonable work — ﬁnancially, I mean. Now the senior lectureship salaries were made to overlap greatly with the lectureship ones so as to make it possible to promote “promising young people” to senior lecturer. However, in fact, it seems to be just as hard as before to promote people, the quota system is adhered to, etc., so really the overlap is just a way of keeping the relative position of the senior lectureship down, ﬁnancially. One trouble may be that you haven’t had enough “ammunition”, i.e. job oﬀers from other places. If I am really being appointed to the 854

G.E. Brown, A. Ashmore and R. Nordhagen, ‘Elastic Scattering of 350 MeV Neutrons by Complex Nuclei’, Proc. Phys. Soc. 71, 565–73 (1958).

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bottom of the scale, I shall certainly go back to the States after a year in B[irming]ham. Several people have asked me in a vague way if I was interested & I don’t think it would be hard to get a reasonable job. I certainly have no complaints on grounds other than salary, and I hope that this will be o.k., but I thought I could speak quite frankly with you. I go from Burtonwood to the States at the end of next month, & will come through B[irming]ham for a couple of days on my way, since it would be nice to talk with people there. I haven’t ﬁnished working out any new ideas since coming back from Sweden, but I hope to have some progress this next four weeks. Best regards, Gerry I picked up a lot of interesting data in Uppsala.

[657] Gerry Brown to Rudolf Peierls Copenhagen, 27.3.1958 Dear Prof, Please tear up the letter which will reach you, being forwarded from Birmingham.855 Whereas the sentiments there are correct, they don’t seem to apply to the actual situation & I am very glad of that. You described the situation of leave spent in a charming place quite correctly when you said to Traudl that there are places one can go to and enjoy oneself, but that doesn’t mean one is unhappy to go home again. We are enjoying this nine months very much; on the other hand I look forward, also, to coming back to Birmingham, because I feel so much part of the community there, and appreciate so much the atmosphere we build for our students. I always appreciate this latter so much more while away where I see how little is done in integrate students. On the 855

Letter [656].

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other hand I am just succeeding in paying oﬀ personal debts incurred when we bought the house in England and, thanks to the estate, we are getting a car (Volkswagen) next month, so that the ﬁnancial aspects of living in Birmingham have been much on my mind. I realized in our Norwegian trip that if I could take Traudl out of England sometimes on trips that the dreariness of the weather etc. would be much less wearing. I hope, however, that I haven’t made it sound as if ﬁnances were of primary or even main importance in choice of job, and no suggestions I have received from America yet would seem interesting compared with a good Birmingham position. I have some comments on the possible vacant fellowship. The ﬁrst one is, don’t consider Maximon. He is one of the Americans who consider a primary part of his life to be esthetic, and is rather lazy as regards physics, although he is not lacking in natural intelligence. I have one suggestion and that is that Maris,856 who is here at the moment, is looking for a job. He would probably want to take quite a part in planning of experiments and their interpretation (He is basically a theoretician · · · was trained in Bopp’s group) in the Bev region · · · i.e., in connection with the synchrotron. There is, however, one thing that should be said. Namely, Maris has been a bloody idiot as regards past politics. Although originally Dutch, he volunteered in the German Army when the Russian war started. He does not believe in any of the things now that he did then, but he is probably still somewhat silly in political attitudes. Of course, he wouldn’t get into political discussions in the lab — he never does here. He is very easy to work with, and continually astounds me by his energy. He is now looking for a job in CERN, but he probably won’t get it, maybe partly because of his past. I think it may be well worth getting an ICI fellowship and asking the physics dep[artment] to support this as well. You might ask Aage Bohr for an opinion. Ashmore’s part in this joint paper was concerned with discussing how to set the problem up & with interpretation of the results — our 856

Theodor August Johannes Maris (1920–), received his Ph.D. from Munich in 1954. After research at Stockholm, Uppsala and Copenhagen, he started a research institute of physics in Brazil.

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jewel Stuttar[d]857 did the calculations. Ashmore contributed a lot to the ideas and he amazed me by his thorough criticism of anything I sent to him. I had to modify quite a bit of my work because of his criticisms. I was most impressed by his knowledge, and have been corresponding with him since about proposed experiments. His group of experimentalists has done an impressive array of experiments in the past year: all of these neutron experiments, analysis in coincidence in pp scattering, gamma rays from mu meson fusion and some others. He’s always kept someone in the group working on the theoretical interpretation and has kept up with this himself. I think that he may tend to be underestimated, because he’s quite a quiet person, but he seems to be an eﬀective leader of the group (which works independently). I discussed with Prof. Rosenfeld his formalism and talked about branch points, etc. He seems to think that he has a suﬃciently large region under the real axis free of these to carry out his expansion using the Mittag-Leﬄer theorem. The sales campaign seems to be coming out very nicely. This is always an impressive thing about Bir[mingham]. In conversation some time ago I mentioned to a research student who wanted to go to America in front of his Professor that U[niversity] of Penn[sylvania] wanted people. His Prof. said, “Oh, you must write there” to the student. No names!! I can only get transportation from Burtonwood to America. Therefore I’ll be back through England, probably before you are back, and plan to spend a couple of days in Birmingham, since I would like to discuss problems with Jon and Graham in particular. I have been concentrating mainly on photonuclear reactions these weeks since I will give a series of lectures at U. of Penn. (they will give me expenses, through which I hope to break even on my U.S. trip). The number of informative experiments which no one had tried yet is really amazing. 857

James Stuttart, who had studied mathematics at Birmingham, worked on numerical problems for several members of the department of mathematical physics and subsequently the computing department.

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Next week I give seminars here on the Lamb Shift and on High Energy Scattering. I’m getting a lot of experience in Public Speaking these days. Life continues to be very pleasant and Traudl and the children are really thriving. Best regards to all of you, Gerry

[658] Gerry Brown to Rudolf Peierls Copenhagen, 4.6.1958 Dear Prof., Mayers is certainly interested in a University job, but he’s going to the Mathematical Institute at Oxford next year as a lecturer.858 Probably he would be interested in coming to Birmingham later if we oﬀered him a better job, but I think he’s committed for next year. I have to write to him soon about our work together, so I’ll sound him out. He is undoubtedly a very good fellow, bright and conscientious. There are other good people ﬂoating around the Maths Lab at Cambridge. They have relatively few permanent posts there, and I have the impression that there are people who would like academic jobs. Most of the people I knew there some years ago already have good posts there or elsewhere. Your idea is a very good one for getting a wedge in — it has looked pretty gloomy as far as the computation group is concerned — and it would be a pity not to follow it through. There are very good prospects for getting machine time now, at least at Manchester. I wrote a letter to Graham.859 I don’t think that the paper is 858

D.F. Mayers took up a post at the Computing Laboratory at Oxford where he remained until his retirement in 1997. 859 Graham McCauley was collaborating with Gerry Brown on a paper on inelastic scattering.

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complete yet, although it is very nice in outline.860 Still, a bit more work will improve its value; it’s a tough situation also in the way that Squires has published before.861 I think that the one point we had — that the interaction with a single particle which is excited should not be counted in the optical model potential — is a nice one, and [I] think that the consequent 8% lowering of absorption might have an appreciative eﬀect, although there are, of course, other corrections to the absorption. I had a letter from Chris Batty862 who has now done over the Coulomb Interference work at 310 MeV in a very nice unif[i]ed way. I gather from him that Ohnuma has recalculated optical model amplitudes at 300 MeV from the nucleon-nucleon scattering amplitudes, and has found a value of c, the spin orbit coupling parameter of 2.0 (Gamma-Thaler) and 1.9 (Signell-Marshak).863 Bethe gets 1.2. We had settled on 2.0 from a combination of our work + a machine analysis of the Berkeley polarization by Bjorklund et al. (We said that the position of the max polarization depends only on c, and therefore, although they had a diﬀerent division into real and imaginary part than we, we could use their analysis to give us the absolute value. Our analysis gave (RP 2 − IP 2 ). Chris ﬁnds also better agreement with small angle polarization data using c = 2.0. Thus I think things are coming nicely together. We also still renormalize the experimental results by a factor of 1.07. But all of this comes right out of our calculations. There are still a few things to look at, and Chris is carrying on.

860 G.P. McCauley and G.E. Brown, ‘Inelastic Scattering of High Energy Nucleons by Complex Nuclei I: Semi-Classical Formulation’, Proc. Phys. Soc. 71, 893–903 (1958). McCauley later published a second part. G.P. McCauley, ‘Inelastic Scattering of High Energy Nucleons by Complex Nuclei II: Excitation of the 4.4 MeV Level of 12 C’, Proc. Phys. Soc. 73, 309–14 (1959). 861 E.J. Squires from Harwell had published a paper on a related theme. E.J. Squires, ‘The inelastic scattering of protons by C 12 ’, Nucl. Phys. 6, 504–16 (1958). 862 Chris Batty was working on the optical model parameters for the scattering of 310 MeV protons by carbon, and the modiﬁcation of Coulomb scattering by the absorption of protons in the nucleus. See C.J. Batty, ‘Optical Model Analysis of the Scattering of 310 MeV Protons by Carbon’, Proc. Phys. Soc. 73, 185–92 (1959). 863 Shoruku Ohnuma, ‘Nucleon-Nucleon Interactions and Polarization of HighEnergy Protons Elastically Scattered from Carbon’, Phys. Rev. 111, 1173–78 (1958).

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Czyz is a nice man,864 of the same group as Dabrowski and Sawicki. I think that his present work on the many body problem would ﬁt in nicely with the B[irming]ham work and he is personally easy to get on with, so it would not be a bad idea to give him a fellowship, but I don’t think he would be any help with teaching, although he could look after a graduate student or two. Like most of the Polish group, he has worked mostly over a desk and has had little experience in solving things through discussion. Thus, he is slow on the uptake. He would have a personal problem with respect to coming and that is, that he wouldn’t like to come unless his wife would. This means getting permission for her to leave Poland, where she is this year. This will probably be possible, but still seems to be rather diﬃcult. Life here is very pleasant at the moment. We have sunny weather and everything is in bloom. The Volkswagen performed magniﬁcently in the Uppsala trip, and Traudl is happy at the mobility. I think that having a car will change the complexion of her life greatly (I don’t ever get to use it; in fact, I can’t even drive it decently yet). Best regards, also to Mrs. Peierls Gerry

[659] Rudolf Peierls to F.W. Shotton [Birmingham], 13.6.1958 (carbon copy) Dear Shotton, I am writing about the problem I have already mentioned to you that Dr. S.F. Edwards in my department has been to interview at Manchester for a Grade 1 appointment and there is no doubt that the formal oﬀer of this will arrive within days. I have ascertained that in Manchester Grade 1 starts above the top of Grade 2, so that the oﬀer is bound to carry a salary of at least £1,500. 864

Wieslaw Czyz, later professor of particle theory at Jagellonian University, Cracow.

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Edwards is at present receiving £1,250. He has been granted a special increment as well as the normal one, so that he will be getting £1,350 next year. I do not think it would be reasonable to expect Edwards to turn down the oﬀer for Manchester without some assurance about his prospects here. I was under the impression that at this time of the year no salary adjustments can be considered. I am a little doubtful that now, in view of the suggestions made at the meeting last week, Faculty might reconsider Brown’s salary for adjustment, and if it were possible to raise the problem of Edwards also, I would of course be most grateful. However, if you feel that Brown’s case is very exceptional and that we would not consider Edwards now, I would like to tell him ﬁrstly that I shall ask at the appropriate time for a substantial merit increase to take eﬀect October 1959 which would I imagine consist of two extra steps bringing him with the normal increment to £1,575 in October 1959. I would further propose to tell him that, while I cannot ask for a promise, I would hope that the Faculty would take account of the fact that he had turned down this oﬀer from Manchester and of the embarrassment in which I would ﬁnd myself in the circumstances my request was refused. To put the matter into its right perspective I should of course explain that quite apart from the Manchester oﬀer, I am convinced that this salary would not be generous in view of Dr. Edward’s ability and achievements. He is another man in my department who is exceptionally gifted, original and productive. He is a man who in a few years time will be ready for a major chair. I would have tried to do more for him earlier, but I was ﬁghting other battles, as you know, and I thought I had still time to rectify this position. I would also not exclude, of course, the possibility of proposing Edwards next year for promotion to Grade 1, which he fully deserves, but I am concentrating on the salary question because it seems even harder to assess the prospects of his promotion to Grade 1 in the present competitive position. I am writing this letter to let you know what I propose to say to Edwards. While I appreciate that you cannot commit yourself or the

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Faculty, I would derive some comfort from the knowledge that you are aware of the position and do not regard my statement as unreasonable. Yours sincerely, R.E. Peierls

[660] Gerry Brown to Rudolf Peierls Copenhagen, 25.6.1958 Dear Prof., Thanks for the two letters,865 which I’m replying to separately, especially since you won’t have the chance to consider the physics one until later, probably. My impression is that the Reader’s scale starts a couple of hundred pounds above the senior lecturer’s one, and in the sense that is a very good position on the relative scale, it makes one quite happy. I feel that the University has done all that they could, considering the unfavourable report.866 I was most impressed by your last paragraph & and I tore up the letter, not discussing it with Traudl except to tell her that nothing further was going through, & I won’t mention any of this — in fact I think it best to operate on just this basis because any number of things can get in the way, although I don’t think it likely unless referees have to be consulted again. In the past I have told friends, who urged me to come to the States, in conﬁdence, that I hoped that something like the research chairs in the Liverpool and B[irming]ham physics dep[artments] would be created in ours & that therefore it made some sense to think about staying in England. I don’t think this will get to B[irming]ham; in any case, it is fairly natural for me to think of this. But in view of our talk in Birmingham & and your letter, it’s undoubtedly best for me to shut up 865 866

Letter could not be located. See letters [649–650].

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completely. In any case, I am really happy about a Readership, & I considered anything further only as a future prospect. I only thought that the bottom of grade I was hardly any progress. You’ll undoubtedly see Weisskopf in Geneva, & I’d like to ask you to thank him for the suggestion (I wasn’t able to talk with him privately here). I’m going to MIT. I was very impressed by the large group of competent & congenial people they had, and it would certainly be No. 1 on my list of places I’d go to, esp[ecially] since Weisskopf is such a nice guy personally as well. In many ways, however, we are just beginning to appreciate the charms of Europe, and I don’t feel ready to go back to the U.S. yet. If there are positions open there which I’d be suitable for, I’d think very seriously about them, but I wouldn’t want him to go to the trouble of piloting one through. Thanks very much for all of the trouble you’ve taken in these matters. I hope that you and Mrs. Peierls have a very good time in Colorado & that your conscience doesn’t hurt you too much for just enjoying yourselves & not raising the standard of mankind at one blow like Dyson. Best regards, Gerry

[661] Gerry Brown to Rudolf Peierls Copenhagen, 25.6.1958 Dear Prof., Physics! (light reading for the airplane journey). Very impressive lectures here by Marshak, which you’ll hear. K¨ allen has been trying hard to beat down Bohr & Mottelsohn’s dispersion adventure, but mostly he seems to have raised red herrings. Lamb Shift: I didn’t understand Cohen’s calculations in detail since he only sent me numerical results for diﬀerent terms. But he seems to have obtained a diﬀerent answer for the α1s × αi term, summed over all other electrons i, than we had. But I’m not sure that he didn’t lump any exchange terms for the Coulomb ﬁeld with this. Sheila & I estimated them to be 13Ry but they could actually be larger. We didn’t handle

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them very well. A fellow at MIT, Bob Nesbitt, looked at the 1/z 2 terms ∼ 5 Ry) or so by a guess), but also after challenging over estimate (< came to the conclusion that they are small. The net facts are: Cohen ﬁnds 22 Ry room for the L.S. taking present ex[trapolation] values. & I’ve heard that Mack & Co say that ex[trapolation] values are too high, so that there’s more room. This is quite a diﬀerent story for the 2 or 3 Ry allowed a couple of years ago. I should be disturbed, however, if we come oﬀ more than 10 Ry in the end, although I’d want to check through Cohen’s work before being unduly disturbed. Also, insofar as binding energies are almost additive & the 1/z 2 terms are small, I’d be happier to get too low than too high a value for the binding energy, but, as you say, one can’t prove anything. I’ve made progress on nuclear reactions. Mainly! In γp = p p ˆ aom aom ψm (R)ψˆm (R) only terms m = m come in when we choose m,m

vˆ according to our perception, and Pm γ¯p = In iπ D Em − E m where we can evaluate the RHS in either a velocity-dep[endent] or velocity indep[endent] well. We had this before, but I didn’t realize clearly that the criterion for one term on the RHS to reproduce (¯ γP /D) was that W/∆Em 1, where ∆Em is strictly the distance between states of the same angular momentum, I’ve run into trouble further on with identity of particles, but will just ignore this for the moment, hoping that Mondragon & Co. can take care of it. Incidentally, I’m talking to Watson, who is here these days. I will send drafts of papers on photodisintegration & nuclear reactions to Colorado. Best regards, Gerry

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[662] Nina Byers to Rudolf Peierls Birmingham, 14.7.1958 Dear Professor Peierls, Thanks very much for your letter, and for sending Chew’s report and the conference program. Chew’s report enabled me to ﬁll in a bit of the theoretical background for the proposed n − p scattering experiment for determining f 2 for Hutchinson which he reported on in the Saturday morning cyclotron meeting. (He is hoping to carry out the measurement of n − p back scattering, as you probably know.) As for Feinberg’s calculation — it seems to me that Feinberg is right, the integral is only logarithmically divergent, though I haven’t been able to completely convince myself because of all the algebra involved. Due to my lack of experience with such calculations, I haven’t found a way to boil it down to something simple. However, tomorrow I shall see Matthews and will check with him. The last few weeks Cottingham and I have been busy writing up this ∧ He5 decay. The results are quite interesting and generalize rather easily. We tried to get the paper ﬁnished before Cottingham left on his holiday, but didn’t succeed. However, the guts of it are done and it should be easy for us to ﬁnish it up in August. (I plan to go oﬀ for the ﬁrst week in August, return on the 21st, and leave for Scotland and the States September 2. I am planning to visit the Low Countries, Germany and Copenhagen.) The results (mentioned above) are that the formation of virtual states in the decay (Li5 in our case) dominates the energy and angular distributions. The distribution in energy shows diﬀerent characteristics according as to what is the level scheme of the nucleus in question,, whereas the angular distribution will always be peaked forward if there is any possibility of a virtual state for the proton and residual nucleus near zero energy. From examining in such detail the ∧ He5 case, we ﬁnd that case, we ﬁnd that we can to a certain extent say what characteristics might be expected from various level schemes. We will, of course, be very interested to hear your comments on the paper and hope you will ﬁnd it of some interest. In any case, I think it was in many respects a good problem for Cottingham, in spite of the

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fact that it was not as exciting a problem as he would have liked. I agree with you, he is a good man. Since there are neither speciﬁc indications for nor presently observable implications of the intermediate particle, I can easily see reasons for not publishing the paper. However, if you feel it would be of interest, I shall be glad to do the necessary things to send it to be published. Hope your family has arrived safely in Boulder and are enjoying their stay. Miraculously, the ﬁsh is still alive! We are all getting along quite well — the Chester baby is sleeping and eating his way into blooming babyhood. Caroline Chester is recovering gracefully, and Mrs Chester is feeding us and making life pleasant. There haven’t been any queries from the Royal Society about the proofs, yet. If there is anything that I can do for you while I am here I’ll be most glad to do it. Hope you are enjoying your stay. Best regards, Nina

[663] Gerry Brown to Rudolf Peierls Copenhagen, 22.7.1958 Dear Prof., It really would be a pity to let you have a pure vacation, so I am sending under separate cover a draft of a paper by Nicholson and myself.867 We made this short and sweet, since Marshak and Co. really scooped us.868 But I think it’s worth publishing; certainly a lot of work has gone into it. I would appreciate very much comments on this, so that I could get it ready for submission to the Phys. Soc. I am sending along a copy of 867

A.F. Nicholson and G.E. Brown, ‘Photodisintegration of the Deuteron at 130 MeV’, Proc. Phys. Soc. 73, 221–26 (1959). 868 J.J. de Smart and R.E. Marshak, ‘Photodisintegration of the Deuteron on the Medium Energy Range’, Phys. Rev. 111, 272–76 (1958).

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the mu/meson paper, which had not been pretty well checked.869 If you think that these are suitable, after some revision, it would be nice, if you could write letters communicating these to the Phys. Soc. and send them to me. I would like to get all of these businesses cleared up before returning to B[irming]ham, because I have some premonition that there will be quite a bit of work to do next year. I enclose a letter which I am sending to Bethe. It would be nice, if you could send it to him along with the rough draft of our paper in perturbation theory in nuclear reactions,870 since I think that he is particularly interested in this subject. Could you please send me your criticism of this paper before sending it onto him, so that I can work over my copy somewhat. I mean to make it clearer at several points as to what we are doing and why we are doing it as we do and what use it has, which seems to be unclear at the moment. In further correspondence with Cohen, I found out that the discrepancy between his work and the work of Sheila and myself lay mainly in the determination of the Coulomb potential from the outer electrons at the origin. It seems that our crude account of relativistic corrections to this was not accurate. Our calculations of magnetic interactions, etc. seem to agree to within a couple of Ry and he agrees that the magnetic interactions with closed shells are zero. We had a nice trip back through Germany after the Paris conference, but were happy on the whole to be back, since the time in Paris — although very enjoyable — was exhausting. We are enjoying our back yard here at the moment (yard in the American sense). All best regards from us, especially to Mrs. Peierls, who is soon one year older. Best regards, Gerry

869

G.E. Brown, L.R.B. Elton and F. Mandl, ‘Polarization of µ-Mesons Scattered by Mercury’, Proc. Phys. Soc. 72, 1137–41 (1958). 870 G.E. Brown, C.T. De Dominicis and J.S. Langer, ‘Perturbation Theory in Nuclear Reactions’, Ann. Phys. 16, 209–20 (1959).

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[664] Gerry Brown to Rudolf Peierls Copenhagen, 6.8.1958 Dear Prof., Thanks very much for your comments, esp[ecially] those on the nuclear reaction paper.871 I have changed the oﬀending parts · · · in particular the “harder to justify” was simply an unfortunate phrase, which I meant was simply that one had to average over a larger energy interval, before the average scattering amplitude can be derived from perturbation theory. This is simply because the strength function between the pure Brueckner type states and the true ones has a spread which may be a fair fraction of the single-particle giant resonance, although it is less by a numerical factor. Anyway, I think that I made this point clear in the last section that I sent to you and I have been struggling to make this and other things clear in the text. As far as the less important slips etc. I hope that Jim will go through the paper carefully; I just had a letter from him in Alberta, where he and his girl friend went from Colorado because her sister and brother-in-law got lost in Glacier Park, but they came walking out of the woods as soon as Jim came, which shows what a beneﬁcial eﬀect his presence had. I think that we make both types of perturbation theory stick, and certainly feel at the moment as if this is the ultimate that one can reach in justifying perturbation theory. In this philosophy, I now believe that a lot of things have to be taken more seriously and there are quite a number of things which I would like to work out next year. Thus, it would be nice to have some prospects of computational help and use of machines in view. In any case, we’ll do the best we can in getting hold of the Manchester and Oxford machines. The latter may be facilitated by David’s presence there. It will be nice to have a lot of manpower — most of these problems involve some calculation, although there is a lot of useful setting up to do ﬁrst, and they would seem to be ideal for beginning people. 871

See letter [663], note 870.

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The research fellow situation looks better. I read a joint paper by Verlet and Gavoret on Brueckner-Watson theory which was quite a nice piece of work.872 However, I agree that one can’t give him a fellowship without being unfair to Graham if he is only at about the same level. I’m sending a paper to you under separate cover by Chris Batty, which would seem to be more in your province to communicate than in Moon’s.873 He is working out in detail in this paper techniques we developed for treating Coulomb interference, in such a way as to remove the delicate parts — the answers are quite deﬁnite and unambiguous, and one gets at the whole problem in a uniﬁed way without getting various amplitudes piecemeal and throwing in interferences etc. You might communicate your criticisms to Chris when you get back to B[irming]ham, since you will precede me, although, if you have any major criticism, it would be best to wait until I’m back before doing anything. I’ve kept a pretty close check on the numerical procedure, etc. during the course of the work. Now that he’s learned about these things, he can do most of the optical model analysis for the experimentalists, which is pleasant. I have ﬁnished writing up the Lamb Shift,874 and ﬁnd that it is possible to write up in quite short form, since many of the renormalization integrals etc., are carried out in Jauch and Rohrlich875 in precisely the form we desire them, and I can just refer to the chapter and verse (although I would not like to carry the analogy with the bible much further.) As soon as I have it typed (I do all of my own typing here), I’ll send it along to you. With both this and Batty’s work, it might be useful to get Glauber’s criticism. The energy gap work here, which is largely being carried out by Belyaev, whom I share an oﬃce with, is coming quite nicely and looking 872 L. Verlet and J. Gavoret, ‘On the optical model for nuclear reactions’, Nuovo Cimento 10, 505–519 (1958). 873 See also letter [658], note 862. 874 G.E. Brown, J.S. Langer and G.W. Schaefer, ’Lamb Shift of a Tightly Bound Electron. I. Method’, Proc. Phys. Soc. 251, 92–104 (1959); G.E. Brown and D.F. Mayers, ‘Lamb Shift of a Tightly Bound Electron. II. Calculation for the K-Electron in Mercury’, Proc. Phys. Soc. 251, 105–109 (1959). 875 J.M. Jauch, F. Rohrlich, The Theory of Photons and Electrons, Reading/MA: Addison-Wesley, 1955.

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fairly convincing.876 In many ways, nuclei seem to be better cases than superconductors. I have been discussing the possibility of going to the U. of Minnesota next summer — they may be able to give me enough money to bring the family in comfort. In any case, we would like to discuss some of the practical problems involved with Mrs. Peierls before going very far into the negotiations. This would be quite nice, since it is fairly close to my home in S[outh] D[akota] and I could look up a lot of old friends. Also, the north woods of Minn. are delightful and there is adequate opportunity for swimming. Our summer, at the moment, is somewhat too “English” for our liking. I promised Traudl that we would go to the beach every nice day, but this doesn’t interfere with my work much more than such a promise would in England. We are really longing for some sun · · · we couldn’t really appreciate it in going through France, because we were always so rushed. I have been hearing a lot about gamma-ray scattering from Standing,877 the French group, Sood — who was here yesterday.878 Everything, C.S., polarization, etc. seem to be converging on our results, or is there something psychological there? The French group calculated the imaginary part of the Delbrueck amplitude following my suggestions, but ﬁnd that even at the high energy of 2.62 Mev it isn’t very large. Aage and B. don’t seem to think that the comments at Geneva were very damaging to their dispersion theory. I got the idea that there wasn’t much in speciﬁcs, except for Low. Best regards, also to Mrs. P. Gerry

876

S.T. Belyaev, Kgl. Danske Videnskab, Mat.-Fys. Medd 31, No. 11 (1959). Kenneth G. Standing, University of Manitoba. 878 P.C. Sood, University of Alberta, Edmonton. 877

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[665] Gerry Brown to Rudolf Peierls Copenhagen, 14.8.1958 Dear Prof., I had a frenzied letter from Angus Nicholson,879 and I think I’ve straightened that out (or rather, conﬁrmed his work), but I’ll repeat his argument because a) it surprised me at ﬁrst. b) it shows that at least some papers in the litt. are wrong. The dipole matrix element for el[ectron] trans[formation] without retardation is iω(i/∼ u ·∼ r /f ) with ∼ u the unit polarization vector. With u ·∼ r j0 (∼ k∼ r)/f ) but it retardation, the dipole matrix element is not iω(i/∼ is 1

0

iω(i/∼ u ·∼ r j0 (∼ k ·∼ r y)/f )dy.

I won’t repeat the argument, since the electric multiple moments are obtained by Sachs, p. 239 (Nuclear Theory) in a very general way, using only gauge invariance.880 He obtains for the total electric matrix element |Q|f with Q=

∞ l=1

1 u ·∼ r)(i∼ k ·∼ r)l−1 (iω) (∼ l!

= iω(∼ u ·∼ r)

∞ l=0

= iω(∼ u ·∼ r) = iω(∼ u ·∼ r)

1 0 1 0

1 0

1 dy(i∼ k ·∼ r y)l l!

ik · r y dye ∼ ∼

dy{Cl jl (∼ k ·∼ r y)Pl (cos θ)}.

(I have used a slightly diﬀerent notation from Sachs here). 879 880

See letter [663]. R.G. Sachs, Nuclear Theory, Cambridge, MA: Addison-Wesley, 1953.

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Since we found the eﬀect of retardation negligible taking j0 (kr) at our energy, this won’t change our results. (In fact, the correct retardation is just 1/3 of what we calculated.) Nicholson is writing up a thesis now & and I’ve had quite a bit of correspondence with him. I sent you by separate post yesterday carbons of the two Lamb shift papers. As you will see, I’ve been able to make them quite compact by referring to other people’s work.881 But I hope that they bring out all crucial points. Best regards, Gerry

[666] P.R. Kabir to Rudolf Peierls Calcutta, 19.11.1958 Dear Professor Peierls, I did not write thus far because I had nothing signiﬁcant to say. But I realised that if this were to be the only justiﬁcation for writing I should never write at all, and if I did not wish to appear ungrateful I should write at least to thank you for giving me the chance to come to Birmingham. I enjoyed my year there tremendously — perhaps too much! — and I regret only that I could not accomplish anything in the way of physics. I know now that I am probably not the sort that is likely to, and I do not ﬁnd the realisation too painful: I am only sorry that I may not have been able to fulﬁll what was expected of me. I had hoped that at least here, I could make myself useful in some way, but aﬀairs appear somewhat less ordered than I had imagined from my brief visit of a year ago. The Institute is huge, probably larger than the Physics Department at Birmingham, but there is very little 881

G.E. Brown, J.S. Langer, and G.W. Schaefer, ‘Lamb Shift of a Tightly Bound Electron I. Method’ Proc. Roy. Soc A251, 92–104 (1959); G.E. Brown and D.F. Mayers, ‘Lamb Shift of a Tightly Bound Electron I. Calculation for the K-Electron in Mercury’, Proc. Roy. Soc A251, 105–109 (1959).

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organisation and not much work seems to be done. Although I have been here over a month now, I have not succeeded in getting a desk for myself so I lead a cuckoo’s life sitting wherever I ﬁnd an empty place! Organised physics does not, of course, exist in India but there seems little likelihood of it developing either. It is a great pity that Raman, the only Indian physicist with both the enthusiasm and the ability to found a school of physics, has not been associated with a University for along time. Saha, the founder of our Institute was another, but he, unfortunately did not live long enough to make it a going concern. Otherwise, the men who run the physics departments in India seem either to lack the initiative to control the interference of the bureaucrats, or are too busy building their own small empires. It is little wonder then that the albedo for returning Indian physicists is about 0.9 (ﬁgure from an Indian newspaper). I hope to remain in the 10 per cent, not by any special virtue, but because I have had all the chances already I know that I cannot blame the surroundings, if I do not achieve anything. However, I do not enjoy living in Calcutta (the population is unoﬃcially estimated at 10 million) and I am thinking of applying for a job at the University of Kashmir where life will certainly be much more pleasant and physics probably only a little more non-existent. Life in general is not nearly as gloomy as I have pictured from the British newspapers — or is it just that I have reverted to the Indian viewpoint? — by which I mean that the government’s ﬁve-year plan has not imposed enough of the burden on the common man to make the situation much worse than before. In other words, things are not bad enough to make a revolution, or something like it, imminent. But there is the question, mentioned by Mrs Peierls and I now believe very pertinent, whether in India, it will ever be bad enough to rouse the people. Well, I hope matters improve so that I may have the pleasure of seeing you when you come to India again. With my deepest regards Praban Kabir

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[667] Rudolf Peierls to P.R. Kabir [Birmingham], 1.12.1958 (carbon copy) Dear Kabir, Thank you for your interesting and rather sad letter. Let me start with disagreeing with your pessimistic assessment of your own potentialities in physics. I certainly do not feel disappointed with your year in Birmingham. One should not follow the American practice of measuring progress directly by the number of papers published in any one year, and this applies particularly for someone like yourself, with a good taste for important and fundamental work who does not derive much pleasure from carrying out some minor and obvious routine calculations, perhaps on rather doubtful approximations. If one wants to get into fundamental work, this is a slow process. One has to acquire both breadth of knowledge and depth of understanding. And this takes time. It is harder to complete this process in isolation and this consideration was at the back of my mind in advising you to stay longer if possible though I appreciate of course the reasons that made you go back. We are in this department not always very good at producing concrete and soluble problems, and in a diﬀerent environment, you might have found a more concrete assignment which would have produced tangible results. But I do not think that the year was badly spent, because as a preparation for standing on your own feet it probably has given you an opportunity to broaden your approach and to get exposed to all sorts of diﬀerent pieces of physics. I hope you will not approach your work in your present Institute or in any new place you might move to in a defeatist spirit. I see no reason for that at all. I do not believe you will in the long run be satisﬁed with just doing your duties in the way of undergraduate teaching and will always wish to be connected in some way with new ideas. This of course is a situation which most of the time is bound to give one feelings of frustration and of doubts. Research is on the whole a very painful process from which one should discourage anybody who can live without it, but I doubt whether you can.

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I might put in at this point a piece of general advice, meant not as a criticism of your suitability for research but as something to bear in mind in your further developments. That is that you are sometimes inclined to look for an easy solution. If one sees a simple trick by which to get over an outstanding problem which has been on the books for some time, one should be suspicious. It does of course happen that such simple answers work and the best ideas in the history of physics have just been of this type, but usually success is not cheap, and the ﬁrst guess should always be that if such a problem had a cheap answer, somebody else would have noticed it before. One must of course equally be aware of overdoing the diﬃculties. It is surprising how often a problem that looks hopelessly insoluble will yield to the right method if one looks at it hard enough. Another point is that in the sort of frame of mind in which you seem to be at the moment, according to your letter, it always pays to try and play with something very concrete, for example analyse quantitatively some recent experiments on a topical question, even where the chances that this is being done already somewhere else by people closer to the source so that the results are likely to duplicate work done elsewhere and will not be publishable. It is a good way of keeping one’s hand in and of keeping one’s thoughts along concrete and quantitative lines. I would put into the same category the kind of work you did with Baldin,882 in which you test the possibility of a radically diﬀerent hypothesis. This, if carried through far enough, leads one to a better understanding of the kind of evidence there is for the usual picture and is therefore valuable, even if in the end the new hypothesis turns out to be untenable as I suspect will be the ultimate answer with the second neutral pion. Of course one must try to handle such a question without prejudice and to give all arguments for and against the hypothesis a fair chance. To keep going with such minor pieces of work even though they may not make a lasting contribution to physics is specially important if you want to look for an opportunity to work with a few research students, 882

A.M. Baldin and P.K. Kabir, ‘Questions of a second pion’, Nuovo Cimento 9, 547–50 (1958).

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of which there are bound to be some promising ones amongst the large crowds in Calcutta and elsewhere, if you can only discover them. This is very much worthwhile in that it nor only helps them but in return helps you yourself in keeping alive and up-to-date. For working with students it is quite important to have something they can get their teeth into and learn the right use of tools and the right physical judgements, even if they do not at once produce anything new. It has been my own experience that I could not keep going in physics at all without some younger people around me, mainly because it clears my own ideas if I try to explain them to someone else and because I can best test whether an argument I am trying to use is valid if I can get him to see objectively that the contrary view would not be satisfactory. If one has a student capable only of occasionally interjecting ‘Why’ ? in one’s exposition, this is a great help, but of course not every student is capable of this. From what you say it does sound like a good idea to try for the job in Kashmir, not only because life is no doubt more pleasant there but also because in a smaller place you will have a better opportunity of exerting some inﬂuence on the way things are run and therefore to create a satisfactory environment, even though the smaller place of course will have disadvantages. With best wishes, Yours sincerely, R.E. Peierls [668] Nina Byers to Rudolf Peierls Stanford, 26.2.1959 Dear Prof, Thank you for your letter. I wrote to Cottingham immediately after receiving it to say that I thought Nuclear Physics was a ﬁne place for the publication of our paper.883 In fact, I think it is probably a more 883

N. Byers and W.N. Cottingham, ‘Energy and Angular Distributions of Mesonic Hyperfragment Decays’, Nucl. Phys. 11, 554–68 (1959).

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appropriate place than Nuovo Cimento. Presumably, the manuscript went oﬀ to Nuclear Physics a week or two ago. Zachariasen and I have veriﬁed the logarithmic convergence of µ → e + γ decay rate, both by dispersion theory and perturbation theory. However, we do not feel that Feinberg’s value of 10−4 for the branching rate is unambiguously the order of magnitude one should expect on the basis of the intermediate particle theory. That number was obtained by cutting oﬀ the perturbation theory integral at the intermediate particle mass. The dispersion theory integral is also logarithmically divergent. If we cut it oﬀ at the intermediate particle mass, however, we would obtain identically zero for the decay rate! Of course, the method of cutting oﬀ is quite diﬀerent in the two cases, and the cut oﬀs must be given diﬀerent interpretations. Since, as you pointed out, the absence of this decay mode cannot be taken to be a deﬁnite indication that the model is not correct, I shall not belabor this point further.884 As you may have heard, Cassels and others have shown that the branching ratio is less than 10−5 .885 Upon hearing this, the people here at Stanford have decided not to look for µ → e + γ, because the equipment they have available at present is not suﬃciently sensitive to detect the process if it is so rare. I hope you are enjoying your New York visit. As ever, Nina

884

Byers and Zachariasen published the results in N. Byers and F. Zachariasen, ‘Magnetic moments of the muon’, Nuovo Cimento 18, 1289–90 (1960). 885 J.M. Cassels, D.P. Jones, P.G. Murphy and P.L. O’Neill, ‘Neutral Pions’, Proc. Phys. Soc. 74, 92–96 (1959).

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[669] Rudolf Peierls to Nina Byers [New York], 8.3.1959 (carbon copy) Dear Nina, Thank you very much for your letter.886 I am very interested in your remark that there is still some ambiguity about the radiative µ decay. But nobody will have much enthusiasm for a model until either the high value of the Michel parameter gets conﬁrmed, (so far the evidence seems fairly equally balanced) or one can get some other non-trivial result out of the model. This would be much easier if one had a good enough value of the Michel parameter from which to estimate the mass. There is in theory no reason why one should not explore what the possible consequences would be for various mass values, but this could take too much enthusiasm. I suppose that the one argument that led a lot of people to hope for an intermediate particle, namely the non-renormalizability of the Fermi interaction, does not help for this version of the theory, because a charged vector particle is also not renormalizable. However, the whole distinction between renormalizable theories and others may be due to misplaced emphasis on perturbation theory. On this point I found the recent letter to Phys. Rev. by Redmond and Uretzky very persuasive.887 I can picture you much better worrying over this kind of thing than over solid-state theory. Not that there is anything wrong with doing solid-state physics! The great excitement here at the moment is over the magnetic moment of the µ meson. This seems to be deﬁnitely greater than 1.00157 compared to the Schwinger value 1.00116. The magnetic moment now has a very small error, but there is still some doubt about the µ mass. The limit given is derived from an experiment showing that a certain line of the µ mesonic X-ray from a transition in µ + Phosphorus is 886

Letter [668]. P.J. Redmond and J.L. Uretsky, ‘Conjecture Concerning the Properties of Nonrenormalizable Field Theories’, Phys. Rev. Lett. 1, 147–48 (1958). 887

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above the K-absorption edge of lead, but several steps in this chain of reasoning need checking. If true it could be satisfactory that the µ diﬀer from the electron in something other that its mass. I am playing with a new idea about analytic behaviour, starting from my knowledge about poles on the “wrong” sheets of the Riemann surface (which are so slandered by Salam). This method works extremely well for nuclear reactions, and has already yielded a new derivation of the dispersion formula which is much simpler and much more physical than Kapur-Peierls and which I always wanted to get. I hope to extend this to high energy problems, but there are still some pieces missing. Anyway, I am learning very fast and enjoying myself enormously. I suppose your and Cottingham’s paper has now gone oﬀ for publication, but I haven’t heard.888 It looks as if he has a very good chance of a fellowship at CERN for next year, which I think would be right for him. I think I have succeeded in selling Jean889 to the Institute, but this is not ﬁnally settled yet, and in any case the real hurdle will be the visa. Houghton is going to join Walter Kohn at Pittsburgh, Graham McCauley to Cornell, Butler is going into industry or something. So this solves all sales problems for this year. (Chan got his grant extended to stay another year in Birmingham) and all the problems now are about people next year. We shall have an enormous group, including many postdoctoral visitors. And we shall have to turn down a lot of applications for Fellowships even before we have advertised them or taken any further steps to ﬁnd people. So last year was deﬁnitely a ﬂuctuation. I don’t yet know whether I shall be able to get out West, it looks doubtful at the moment. Since it seems hardly worth going that far for two or three days it would probably have to be in the second half of May, when lectures ﬁnish here. But I fear that by then too many other things will have piled up. Are you coming to the Washington meeting?890 888

See letter [668], note 883. Jean Yoccoz had been working with Peierls at Birmingham, and had moved on to the Laboratoire de Physique et Chimie Nucl´eaire du Coll`ege de France in Paris. 890 A meeting of the APS was taking place in Washington in May 1959. 889

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Is your mother still in New York? I was thinking of calling on her, but you made some mysterious remark about change of address and mail not being forwarded. Yours sincerely, [Rudolf Peierls]

[670] Nina Byers to Rudolf Peierls Stanford, 31.3.1959 Dear Prof, Thank you very much for your letter as a result of which I calculated (together with Zachariasen) the contribution to the muon’s magnetic moment resulting from the intermediate boson model. Since this model says that there will be a contribution from a diagram such as

this contribution is something like 107 times larger than the correction that arises in the usual four-Fermion theory. (It is proportional to the “beta-decay” coupling constant whereas in the four-Fermion theory one gets a contribution proportional to the square of this constant.) From dimensional arguments one can see that this contribution cannot be large enough to explain the anomalous moment you quoted; however, we hear that the value may well be in error — Dumond891 says that the value of the P bK-absorption edge used in the determination of the muon mass is questionable. Dimensional arguments lead one to expect an anomalous moment due to the intermediate boson of the order of 10−7 . As you might have guessed from the above diagram, this contribution is closely related to the matrix element for µ → e + γ. Gauge invariance requires that the matrix element for the µ → e+ γ must be of 891

Jesse W.M. DuMond, (1892–1976), professor of physics at Cal. Tech. 1938–63.

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the form ∼ σµν Fµν . It turns out that if the intermediate particle’s mass, M , is at least three times larger than the muon mass, the anomalous moment contribution is just twice the radiative decay matrix element, and √ therefore equal to 1.2 10−7 ρ, where ρ is the branching ratio µ → e+γ/ µ → e + ν + ν¯. Experimentally ρ ≤ 10−6 , and so this is for all present practical purposes negligible — if lepton number is conserved and muon and electrons of the same charge have the same lepton number. Alternatively one can take Schwinger’s point of view, namely that the lepton conservation prevents µ → e + γ. Remember his two two-componentneutrino theory which made the opposite assignment of lepton number and said that µ → e + ν1 + ν2 ? In this theory, the anomalous moment contribution will arise even though µ → e + γ doesn’t. We used this as an excuse to evaluate the integrals and found that the contribution to the moment is 0.46 × 10−8 ln(K/M )e/2mµ c, if we assume the boson couples with equal strength to muon and electron and that terms of the order of (mµ /M )2 can be neglected (K is the cutoﬀ parameter). This contribution is given by gµ2 m2µ /M 2 times numerical factors so one can say two more things about it; (1) it is 4× 104 times larger for the muon than for the electron and (2) if gµ = ge , gµ2 /M 2 = E, the four-Fermion theory coupling constant for µ → e+ ν + µ; if gµ = ge , gµ2 /M 2 = E(D/C) where D and C are the four-Fermion coupling constants for µ− + P → N + ν and N → e + P + ν, respectively. I don’t know now what are the limits one can put on D/C — people always way its order of magnitude as one. So much for exploring further consequences of the model — except that, since I’m in so deep already. I can’t resist calculating the crosssection for photo-production of pairs of these bosons. By the way, do you happen to know if one of the famous g − 2 experiments on the muon is under way anywhere. Zachariasen and I are wondering whether or not it would be facetious to publish our calculation on the muon moment — that is, whether contributions to the moment of the order of that given by the calculation might in the foreseeable future be experimentally accessible; presumably, they would only be accessible in a g − 2 experiment. Cottingham wrote to say that he was pleased with the changes I’d made in the paper, and would send it oﬀ to Nuclear Physics — so I

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presume it is in the works. Dalitz wrote a rather detailed letter to me when he got the preprint as a result of which I realized we had left in it a few misleading sentences which I hope can be changed in proof — and also that it might be possible to learn about the spins of certain hyperfragments by looking at the appropriate angular distribution when compound nuclear states are formed. This would be nice since it would be a direct way of checking on the spin assignments he makes as a result of his conclusions regarding the spin-dependence of the n-nucleon force. Whether this is really feasible can’t be decided without a much more detailed consideration of the compound nuclear states which might be formed; one must be able to reliably estimate overlap integrals to decide this question, i.e. one must have reliable order of magnitude estimates. It is the angular part of the integrals that is crucial here and I am wondering how reliable it is to use shell model wave functions for these. Jean was very nearly overjoyed with his oﬀer from the Institute. As a result of a letter from Levy, Schiﬀ was thinking of inviting him here — pending conﬁrmation from you. (I was asked my opinion and said little deferring on personal grounds.) Schiﬀ, assuming you felt you could recommend Jean, now thinks that he might like to have Jean come here for the summer. This new “Institute” the Air Force is ﬁnancing at Stanford is bringing with it considerable money for all sorts of visitors.892 It will certainly be fun to have Jean here on my own home grounds and [I] hope that the arrangements can be made. Did you hear from a girl named Evelyn Fox? She wrote me asking about what I thought of her going to you for a year while she works on her thesis. She is a research student at Harvard and the sister of an old friend of mine. I don’t know her at all, so I couldn’t say much except that it might be better for her to go on a postdoctoral fellowship and that, if she were seriously interested, she should contact you. Of course I had only the best things to say about the Math-Physics Dept. — judging from my own experience and what I hear from Schultz and others, it clearly is an incomparable place. The stimulation one got from working in a department so active on so many fronts seems not 892

The Air Force had ﬁnanced an Institute of Scientiﬁc Research at Stanford.

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to be available elsewhere. It seems that departments here in the States that are comparably active are certainly not comparably uniﬁed. We are all still hoping you will be able to come out here — if only for a few days. I’m sure from our point of view that it would be worthwhile, however, we can imagine that you must have many commitments and may not be able to manage it. I am going to the Washington meeting, and perhaps can see you there? My mother is in New York now. My stepfather had a quite serious heart attack some months ago — was in hospital for a long time and is now conﬁned to the apartment. They plan to leave New York for a while as soon as he is able to travel. The mysterious remarks regarding change of address and mail not being forwarded has two origins — (1) they moved to 150 Riverside Drive (but kept the same phone number); and (2) my mother never forwards my mail! As ever, Nina

[671] Sam Edwards to Rudolf Peierls Manchester, 15.5.1959 Dear Professor Peierls, I hope this letter will not wonder around the world chasing after you, but if it has my apologies. My main cause for writing is a personal one. You’ll recall that last year you suggested to me that I consider applying for the D.Sc. degree at Birmingham. Upon leaving I let it rest, but Flowers recently also suggested the worthwhileness of the D.Sc., so I wonder if I could raise the matter again. Is it still possible, and, since I have left Birmingham is it still good form to apply? Please let me have your opinion and any comments. As for physics I have been suﬀering somewhat from a split mind in carrying on several projects at once, but some, at least, are nearing fruition. In particular on the transport problem in metals etc. I can now see how to deduce the kernel of the Boltzmann Eq[uation] in the same kind of spirit as your exact formula work. The ﬁrst term is the

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familiar one, and the rest appear rather like the higher order self energy diagrams in ﬁeld theory. The diﬃculties of alloys appear quite explicitly, but there doesn’t seem to be any trouble with an external magnetic ﬁeld, which worries me as you mentioned this as a problem. What happens apparently is if G is the G[reen] F[unction] of the Schr¨ odinger eq. (without scattering) the usual Boltz[mann] E[quation] has a scattering cross section in its kernel which in terms of G and the particle scattering potential Φ is GΦGΦ symbolically. In the mag[netic] ﬁeld B, G becomes G(B) which involves harmonic oscillations but is still known in closed form and still one has G(B)ΦG(B)Φ. So the Boltz[mann]E[quation] can still be written down even when the Larmor radius ∼ m.f.path, for the corrections to this kernel have nothing to do with B[oltzmann]. Of course it (the Boltz[mann] E[quation]) still has to be solved, but I was under the impression that there was trouble to get it. Have I missed something? This approach also seems to make progress with plasma problems. The general excitement here is over the high energy machine project which will formally come to your notice soon, so I won’t describe the proposals of Devons here. But I hope something will come of it. Partly under this stimulus several people are starting work on high energy theory. I have got thinking again about the complex pole problem particularly after hearing Matthews expound the rather empty work they are doing on it. I didn’t think very far, but you may be interested in the thoughts. I’ve got to have a model, and since the one particle propagator is hard on the intuition I thought about meson nucleon scattering, say in the resonant p wave. This has to have a pole at ω = 0, branch at ω = µ, resonance, & be unitary, so the simplest model is cos θ k2 ς t(ω, ς ) = λα ω(1 − ωωα ) + ik3 − µ3 k2 + µ2 = ω 2 , λα , ωα characteristic of the resonant phase This has the pole at ω = 0, and also the complex pole near ω = ωα on the ‘wrong’ sheet, no singularities (ex. ω = 0 & branch) on ‘right’ sheet. But it has a lot of other poles (4 in fact). What do they mean? If

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one looks at a resonant s wave similarly there are less extra poles since one gets k rather than k3 underneath. So the spare singularities appear to be tied up with the expansion of t(ω, ς) in spherical harmonics, and this suggests that one has to look at the complex 4 volume of t(ω, ς) `a la Mandelstam to make sense of the whole thing. There are many wise men looking [a]t this, but they conﬁne their attention (I think) to the principal leaf (or what is the generalization of the principal leaf in the double complex plane), and there may be something useful to be squeezed out of a simple model. But I’m afraid I haven’t now the time to get very far. Have you looked at this lately? I expect you’ll be very busy when you get back, but if any of these points merit a discussion, I’ll be happy to come to Birmingham to talk. I expect I’ll see you in Harwell later as I hope to attend the accelerator meeting in July. Give my regards you Mrs. Peierls and my wife send regards. We are at long last getting our garden into order and hoping the scorching sun which now aﬄicts England will not burn everything up. Best wishes, Sam Edwards

[672] Rudolf Peierls to Sam F. Edwards [Birmingham], May 1959 (carbon copy) Dear Sam, Thank you for your letter.893 I am afraid the procedure for an Oﬃcial Degree at Birmingham works only for members of the staﬀ. There was some long argument about whether they have to be member of staﬀ when the thesis is presented, or at the time the degree is conferred, but here is no question that you cannot apply for such a degree after you have left. The only way in which you could qualify for a Birmingham degree now would to be ask to be registered retrospectively as a research 893

Letter [671].

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students for the last two years of your Birmingham period, and then to submit a D.Sc. thesis in the ordinary way. However, this would be undigniﬁed and possibly expensive, and it is not even sure they would agree to this retrospective registration. I imagine that after some time you will be eligible for a Manchester D.Sc. and while this, of course, is a very inferior degree compared to the Birmingham one, it may have to do. On the Boltzmann equation in a magnetic ﬁeld it may well be that you are right, and that if one starts from the exact eigenstates in the ﬁeld, and adds the lattice vibrations as a perturbation, nothing terrible happens. In the way you set out the procedure, the trouble I was expecting would take the form that in calculating the eﬀect of the collisions with phonons (or with impurities, which might be simpler to think about) one gets cross terms between levels with diﬀerent n (n is the quantum number determining the energy levels in the ﬁeld) and these are not small unless the collision time is longer than the Larmor period. If you can prove this does not happen, then that is, of course, a step forward. There may be a diﬀerence between impurity scattering and photon scattering at low temperatures. In the latter case, the resistance is given as a solution of a complicated integral equation (even for the isotropic case) and I seem to remember that the approach in the old paper by Titeica, who also starts from the exact solutions in the magnetic ﬁeld does not converge for zero ﬁeld to the solution of that equation. This may possibly [be] a diﬀerence between using perturbation theory in deriving the Boltzmann equations and in solving them. But it seemed very hard to see how in the limit of zero ﬁeld one could get the right equation. On complex poles I have got a lot further, and have just written up a paper of which I hope to have preprints by the time I leave here (30th May).894 I have sen[t] a very rough photostatic copy to Castillejo, so if you happen to be in Birmingham in the meantime, you may like to glance at it. This paper shows how to exploit the Riemann surface 894

Peierls was Visiting Professor in the Department of Physics, Columbia University between February and May 1959.

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in a non-relativistic problem, and how to get the nuclear resonance formula in terms of the actual complex eigensolutions of the Schr¨ odinger equation (this is what Miss de Winter was trying to do). It works fairly generally, except in the case of forces with Yukawa tails, then one gets new logarithmic branch points appearing on the unphysical sheets, and I do not think one should try to follow into the inﬁnity of new sheets starting there.895 My analysis relates to the partial wave amplitude, and there the nasty [l]ogarithmic branch point even sits on the sheet. The same trouble is found by the ﬁeld theory experts (Mandelstam, Goldberg &c.) in real problems as a cut along the negative real energy axis. I believe that if the scattering amplitude is expressed as a function of energy and momentum transfer the trouble does not come on the physical sheet but undoubtedly on the others. The complication makes me pessimistic of extending to high-energy problems the approach I have used, which involves a Cauchy integral round the whole of the Riemann surface. But I still believe it may be useful to extend one’s study at least some way into the wrong sheets, if only because the unitary relations which usually are troublesome to handle, turn into analytic equations. I have also discussed the π-nucleon problem with Weisskopf and Low. Francis Low convinced me that in that case the Riemann surface has an inﬁnite number of sheets. It is still true that the branch point at energy µ (counting the energy of a nucleon as zero) is of a simple square root kind. But there is al[s]o another square root branch point at −µ, except on the physical sheet. This does not connect the same pair of sheets as the other, so that by alternatively going around both these points you cover an inﬁnite series of sheets. The behaviour of the function in this respect is something like cos−i (E/µ) (E 2 − µ2 ) which, with a suitable choice of branches, can be made regular at −µ. I take it that the model you quote represents the cross section, so that the scattering amplitude is obtained by taking a Cauchy integral with this function over the positive real axis. This would show quite the same behaviour. 895

R.E. Peierls, ‘Complex eigenvalues in scattering theory’, Proc. Roy. Soc. Lond. A253, 16–36 (1959).

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This might not stop me from using my technique but it would mean going around all this series of sheets, and one would have to make sure that the process converges, and that one has enough information about what is going on on all these sheets (and indeed whether any new branch points occur on them). Weisskopf was particularly worried by the fact that the pole at ω = 0 (ω is the same as E) occurs in all four spin and isotropic spin states, although the bound state with which it is connected exists only for one of these. The answer is that in the other three states the pole does not arise from a bound state, but is a “redundant” pole in the sense of Ma, which arises from an exponential tail in the interaction. I shall certainly look forward to discussing these things with you, and I shall get in touch with you when I get back. I don’t yet know whether I shall manage to get to the accelerator conference at Harwell, since it seems to come rather closely before the Russian conference.896 Yours sincerely, [R.E. Peierls]

[673] Rudolf Peierls to Klaus Fuchs [Birmingham], 15.6.1959 (carbon copy) Dear Klaus, I see from the paper that you are soon going to be released. If you need any help in getting started in life, ﬁnancial or otherwise, or if you need advice, please let me know. I shall do what I can. Yours sincerely, R.E. Peierls

896

The Sixth Pugwash Conference took place in Moscow in 1960. It was the ﬁrst attended by Rudolf Peierls.

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[674] Gerry Brown to Rudolf Peierls Minneapolis, 22.7.1959 Dear Prof., I was very happy, indeed, to have the note from Barnes, saying that I had been promoted. This will make things very easy for us ﬁnancially this coming year, and I won’t have to do any more translating than I ﬁnd enjoyable. I am only somewhat sorry that I’ll be taking oﬀ after one year — I haven’t yet written accepting the Copenhagen job, but have made up my mind to do so.897 However, I feel less badly about it than might be the case, because you should be able to hang on to the position, and certainly I don’t feel that the department loses by my having the promotion. There is, also, a certain amount of pride involved, on my part, in receiving the promotion. I always take pains to indicate that I am not much interested in status, but I must admit that I was very pleased, and probably not only because of the additional salary. Life is very very pleasant here. I’ve seen a number of my family already, and many friends. Last weekend I dropped over to Madison, Wis. and stopped for a few days at the U. of Wisconsin. I’ve been doing a lot of swimming, which is almost necessary in the hot weather here, although I don’t feel the heat much, and scrupulously avoid airconditioned restaurants, since I get much too cold in them. The weather in Minneapolis is absolutely gorgeous, as I remember South Dakota, without the wind. I see quite a bit of Mark and Margaret Bolsterli898 and people here in general have been very friendly. Twice a week I give lectures on nuclear reactions and theory, for 90–100 minutes, so that I am not becoming intellectually muscle bound. I have been having correspondence with various people in the lab in B[irming]ham, and I don’t think that we need bother with very much. Tony Green’s work has really been excellent, and will be of great interest 897

Gerry Brown had been oﬀered a professorship at the Nordic Institute for Theoretical Physics, NORDITA. 898 Mark Bolsterli obtained his Ph.D. from Washington University before moving to the University of Minnesota and later Los Alamos Laboratory.

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to a number of experimentalists, anyway, so we will get something into shape for publication. This is the p − 2p problem.899 Don Sprung900 has been sending me progress reports, and the older part of the work he is doing — giving an explicit model for continuing the Gammel-Thaler potential up to 1 Bev — is very successful in ﬁtting available data (total, elastic and diﬀ. c.s.) and predicts polarization, which changes sign at about 50 degs., so that here is something quite deﬁnite to check. In spite of the spin orbit terms and absorption, the polarization reaches both 0.6 and -0.6. I have also had time to sit down and check some numbers relating to the vibrational levels Pratts was looking at. The usual method for calculating Slater integrals turns out to be clumsy, when one is looking at high-j orbitals and short-range forces, in that in this method (of Talmi’s) one has lots of cancellations to that things have to be calculated with fantastic accuracy — say 8 or so signiﬁcant ﬁgures. I can ﬁnd no other simple way. Therefore, I think that I’ll still try to carry this through, but will only do it, if Stuttard ﬁnds time in between important jobs, to do some of the accurate calculation, since this is very tedious. I now think that the problem was misconceived, since all accumulating evidence points to the Gammel-Thaler forces begin strong enough to provide considerable correlation (in radial variables, which is not taken into account in our method) between two interacting nucleons, and a zero order treatment, even though diagonalizing the secular determinant within the shell, is not suﬃcient. It is a pity that Pratts has wasted so much time, but on the other hand, he should have noticed that he was continually losing accuracy in his calculations, and those that he performed personally have very large errors in them. I have been having the luxury of playing leisurely about with a number of ideas which tickled me, e.g. introducing senirotti-type correlations into the zero-order Hamiltonian and then calculating the imaginary part of the optical-model potential. You will doubtless kill many of these ideas when I get back, but I like to see how far I can get with them. 899

See A.M. Green and G.E. Brown, ‘Direct Interaction in the p − 2p Reaction’, Nucl. Phys. 18, 1–13 (1960). 900 See below letter [681].

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The experimental people here have been very stimulating on questions of nuclear reactions and I’ve picked up lots of little new ideas. Best regards, also to Mrs. Peierls, Gerry P.S. Before formally resigning from the University, I would like to have a thorough medical examination, if this won’t inconvenience you. I feel ﬁne, but before leaving Britain’s excellent National Health Service, it would be nice to be sure. Incidentally, the University Health Service here has taken care — insofar as care had to be taken — of my foot. It is now out of cast and I can walk quite well.

[675] Rudolf Peierls to Nina Byers [New York], 6.8.1959 (carbon copy) Dear Nina, Thank you very much for your interesting letter.901 The situation about the “heavy boson” contribution to the µ magnetism is a little reminiscent of the old story of the wonderful rabbi who sees a Jewish boy eating a ham sandwich in front of his house on Yom Kippur. He is so shocked that he prays to God asking him to send lightning to make the house collapse on the sinful family. But the little boy hears and starts crying bitterly, and the rabbi feels sorry for him. He asks God not to destroy the house. And believe it or not, such was the power of the rabbi that the house did not collapse. Seriously, it is quite true that the anomaly is still doubtful because of the uncertainty in the mass (the magnetic moment seems wonderfully accurate) so that it is too early to get excited, and I personally would tend to bet against it. As regards g-2 experiments, Ledermann902 who 901

Letter [670]. Leon M. Lederman, (1922–), received his Ph.D. from Columbia University in 1951, where he stayed for another 28 years, from 1958 as professor. In 1979 he became Director of the Fermi National Accelerator Laboratory. 902

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is at CERN, is working on this, and I believe it is also being tried elsewhere. This, of course, is a hard experiment, but it should be possible to check whether there is an anomaly comparable with the magnitude of the Schwinger term. It might not be easy to call immediately for a further substantial increase in accuracy. It is a bit hard on experimentalists who are in the process of measuring a diﬃcult thing to an impressive accuracy if one tells them that what would really be interesting is to push the accuracy by another ﬁve orders of magnitude or so! I do think it would be useful to publish your conclusions, but I think the emphasis should be on the negative aspect: Although this model is capable of giving somewhat larger corrections than the fourfermion coupling, the result is still much too small to have anything to do with present experiments. This is worth having, because it may save other people the trouble of working it out, and also because on[e] never knows whether it might not induce someone to extend the argument so as to get some other result which might be of practical interest. But I would not suggest putting it forward as a practical test at this time. Incidentally, even if the necessary accuracy could be reached, one would have to know the higher order electromagnetic corrections (like Karplus & Kroll)903 and I don’t know to how many orders one would have to go to be sure of such small anomaly. So the theory may even be harder than the experiment. I am sure you can get a few sentences changed in proof in your paper with Cottingham.904 Only you must make sure you know who will get the proofs, presumably they will come to Cottingham rather than to you, unless you request otherwise, and since it would be undesirable to hold things up until he sends you the proofs to Stanford, you might brief him in advance about the changes you want to make. There seems to have been some confusion of Jean’s application to Stanford. He had accepted the Princeton oﬀer before he realized that there was a chance at Stanford, but there is probably a lot to be said for 903

R. Karplus and N.M. Kroll, ‘Fourth-Order Corrections in Quantum Electrodynamics and the Magnetic Moment of the Electron’, Phys. Rev. 77, 536–49 (1950). 904 See letter [668], note 883.

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the Institute anyway. I shall now write at once to Schiﬀ to back the idea of a summer invitation. There is, of course, still the worry about the visa, and even if he gets it in time to go to the Institute in the autumn. this does not necessarily mean it will come in time for the summer. I have heard from Evelyn Fox, and she came to visit me here. She seems very nice and sensible, and I can see her point for wanting to move. The setup at Harvard for graduate students does not seem ideal, at least it does not seem to suit her too well. So she is deﬁnitely coming to Birmingham. I am beginning to realize that I won’t be able to make the trip to out West, much as I would have liked to come. I haven’t yet decided whether to go to the Washington meeting, but probably I shan’t get there either, life is too short and these mass aﬀairs are not really very fruitful. Are you likely to call in New York when you are in the East? Yours sincerely, R.E. Peierls

[676] Rudolf Peierls to John Cockroft [Birmingham], 10.8.1959 (carbon copy) Dear Cockroft, I do know Stanley Mandelstam very well. He came to us in October 1954, after completing part III in Cambridge, obtained his Ph.D. here in 1956, and stayed on for another year on D.S.I.R. funds. In 1959, he went to Columbia at my recommendation and I have met him several times since then. He started oﬀ by writing in one year a paper, which would evidently have been worth a Ph.D. but for the fact that our regulations would not allow us to award a Ph.D. on one year’s work so he had to wait for a second year. These papers were intelligent and useful contributions to ﬁeld theory. In this third year here he made a phenomenological analysis of

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pion production in proton-proton collisions, which has since become the standard approach to the subject. His most outstanding work has been done since then. He initiated a new approach to dispersion relations in high energy physics, which has had a profound eﬀect on work in this ﬁeld. I think it is no exaggeration to say that no paper is being written now on the theory of high energy events which does not in some measure rely on Mandelstam’s paper. He is now working at Berkeley with Chew continuing the exploitation of these new techniques. He is clearly a man of outstanding ability and originality. He is also a very pleasant person. He is perhaps a little shy and therefore a little restricted in contacts with other people, but not to an extent which results in any awkwardness. I have discussed with him his plans for returning to this country and I am very anxious to persuade him to settle in Birmingham, where we could certainly oﬀer him a satisfactory position, but he has not yet made up his mind, and there is certainly no reason why you should not invite him to join Churchill College and, if you succeed, it will be quite a catch, though I shall naturally be sorry if he does not come here. I understand that the people at Berkeley are going to do their best to try and keep him there and make him return, but as far as I know, he is determined to come back to this country. Chew told me recently that he regarded him as by far the best young man who has been at Berkeley in the ﬁve years which Chew has been there himself, which is quite a strong statement. You may, of course, like to get the Berkeley opinion ﬁrst hand. Yours sincerely, pp. R.E. Peierls (dictated by Professor Peierls and signed in his absence)

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[677] Rudolf Peierls to Nevill Mott [Birmingham] 11.8.1959 (carbon copy) Dear Mott, At a recent conference in Russia I talked with E.M.Lifshitz (as you know this is the one at the Kapitza Institute), who it turns out would be interested in getting two review articles written and published and the Advances of Physics would seem to be his ﬁrst choice for this. One of these would be on “The general theory of Van der Waal’s forces” and the other on “Cosmological problems in general relativity”. He seems to have some interesting thoughts in both these topics. I gather that it is very much easier to arrange for such articles to be published abroad if the correspondence is initiated by an invitation from the journal to contribute an article giving the general ﬁeld if not necessarily the precise title, and I promised therefore to write to you and ask whether you regard either or both of these articles as useful and suitable for the “Advances of Physics” or whether, if you do, you would be willing to have a suitable letter sent to Lifshitz. I believe he would prefer to have the article translated from the Russian here, though I do not know whether this can be conveniently arranged. I have forgotten whether the Advances of Physics normally pay a fee to contributors. If so, Lifshitz would be quite happy to let the translator have the fee. But if necessary I think he would be willing to send an English text, though presumably this would need editing. While I am writing to you, I suddenly realise that I have never yet sent you my congratulations on your appointment as Master,905 the reason being that this happened and I only heard of it when it was already very stale news, and I did not even remember to shake you appropriately by the hand at our recent meeting. I don’t know whether in this connection you have ever seen the songs written for the 1953 Birmingham Conference. In case you haven’t, I 905

Nevill Mott had been elected Master of Gonville and Caius College, Cambridge in 1959.

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enclose a copy and wish to draw your attention to the last two lines on page 5. I heard with particularly great pleasure that you are continuing as Cavendish Professor, in spite of the new duties, which makes the reference in the song inapplicable, but it might still amuse you. Yours sincerely, R.E. Peierls

[678] Gerry Brown to Rudolf Peierls Minneapolis, 8.9.1959 Dear Prof., I am happy to be back here from visiting a number of people over the country. I really enjoy most of all sitting here, where the weather is quite pleasant, and does not get so hot and humid. It rarely reaches 95 here. The photonuclear conference in New Hampshire906 was most interesting, especially as people are now beginning to get good quantitative results. My talk there was embarrassingly successful, since I had meant it only as an introductory theoretical talk, and the model was meant to be only a schematic one. The model is, however, quite suggestive. In it, one diagonalizes an approximate secular determinant, the matrix elements of which come from the particle-hole interaction. Of the several unperturbed, nearly-degenerate particle hole states, one perturbed one goes up a lot in energy. Just this level carries the main dipole strength — 100 per cent of it in the simpliﬁed model. It shows in a pretty way the uniﬁcation of single-particle, collective and plasma-oscillation points of view in a calculable model. I also discussed the (p, 2p) model with a lot of people. Tony Green has probably informed you of his progress in this direction, and he is writing it up for an M.Sc. thesis.907 906 907

Gordon Research Conference on Photonuclear Reactions in New Hampshire. See letter [674].

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In Berkeley I had a long talk with Chew and he drove me down to Stanford. People in Berkeley and Stanford certainly have a very high opinion of Mandelstam, not only as regards the speciﬁc breakthrough he has made, but on his ability in general. I believe that you are coming more and more to the view that he might be suitable for the vacant job in Birmingham, and I must admit that this would probably work out quite well, especially as we have been weak on that side of things. Your wife may have been somewhat perplexed by my letter, especially if she interpreted it as an answer to hers. I’ve just realised that the letter I received was from her — the way in which she signs her name does not aid my interpretation; also I was expecting a letter from elsewhere dealing with the same subject. I have certainly had enough of being away from my family by now. However, Traudl writes in quite a cheerful vein. I gather that renovations are underway in the house and Traudl and the children plus Danish girl will be in Wales the 12th to 20th. She says that it would be most convenient for me to return the week after that. Therefore I shall probably be returning a bit later than I wrote to you previously. I have tried for reservations for the 24th to 26th. At the moment, the 24th and 25th are full up, and I have reservations for the 26th. In any case, I won’t be home much before the last week in September. If there seems to be any urgent reason that I should come earlier from the point of view of University matters, please let me know, since I could grab a DC7 or so back at almost any time, I imagine. However, I am happy to sit here a bit longer, from the point that my expenses, other than the airfare to England, are negligible and I can save a lot of money. Also, I am ﬁnding the company here very stimulating at the moment, and Eisberg is just due back,908 having been away all summer — not that that’s my fault. I hope that everything is going well in the department. The various developments in my work this summer suggest a lot of nice little problems. Best regards, Gerry 908

Robert Martin Eisberg, professor of physics at University of Minnesota, Minneapolis.

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[679] Lev Landau to Rudolf Peierls Moscow, 13.3.1960 Dear Peierls, A very close friend of mine is seriously ill and it would be very important for him to obtain a new remedy called “tebafen”.909 I would be very much obliged to you if you could send us 5 vials (each containing 100 pills) to the following address: Moscow, ... I hate asking you for trouble, but the doctors say that it is of utmost importance. I was told the remedy is not very expensive. With many sincere greetings to you and the family Yours L. Landau [680] Rudolf Peierls to Niels Bohr [Birmingham], 19.12.1960 (carbon copy) Dear Uncle Nick, During a recent visit to Moscow I had some conversations about the fact that Landau has never yet, since the war been allowed to attend any conference outside the U.S.S.R. or to go abroad for any other purpose. From these conversations I have formed the impression that there is no speciﬁc political reason behind this, but that for some reason the people in the administration on whom the decision depends do not approve of Landau and perhaps regard him as a bad inﬂuence on Russian physics. It is perhaps symptomatic that none of the honours recently bestowed on him abroad, such as foreign membership of various academies, have been mentioned in the press in the U.S.S.R., with the exception of the election to one rather minor body to which he was elected simultaneously with a number of other sci[en]tistst whose awards are usually reported. If this interpretation is correct, the only remedy would seem to lie in an approach at a suﬃciently high level, which might result in a 909

Drug for the treatment of pulmonary tuberculosis.

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reconsideration, so that people who have been guided by rather petty jealousies might be overruled. It has occurred to me that it might be extremely helpful if you were willing to raise this problem in a personal letter to Khruschev, provided that it would be transmitted through some channel, (perhaps through the U.S.S.R. Ambassador in Copenhagen), which would oﬀer a chance that Khruschev would see it personally. I do not of course know, whether perhaps you have already tried an approach of this kind and if so, there is probably no point in doing it again but I though[t] I would put this suggestion to you for what it is worth. The occasion of my visit to Moscow was the Pugwash Conference, which I found more constructive and interesting than I had expected. While I returned from this without undue optimism about the chances of general agreement on disarmament, one feels that the chances of this, or of some kind of agreement which would rel[ie]ve a major part of the tension, are not quite as remote as I had thought. I had, between the meetings, the opportunity of spending a little time with Landau who is in excellent spirits and who is working hard and with great optimism on the problem of ﬁnding better fundamental equations to describe interacting ﬁelds. He believes that such a new formalism would retain much of the structure of Feynman graphs as used at present but would bear no similarity to the present ﬁeld equations in Hamiltonian form. My wife joins me in sending to you and Mrs. Bohr, best wishes for Christmas and the new year. Yours sincerely, R.E. Peierls [681] Rudolf Peierls to Hans Bethe Birmingham, 6.1.1961 (carbon copy) Dear Hans, I am writing once again about a possible candidate for a post doctoral fellowship of some sort at Cornell. This is a bright young Canadian, D. W. L. Sprung, who in expected to complete a Ph.D. here next summer.

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He came to us in 1957 from Toronto with an excellent academic record and he struck us immediately as very bright and lively. His knowledge, however, was still deﬁcient in some ways, (this is not the ﬁrst time we have noticed this with a Toronto graduate. You will remember the problem of Schaefer, whom you examined here), and we therefore made sure that he ﬁlled in background while starting on research. This is the reason why he is taking four years over a Ph.D. His ﬁrst piece of work, on which he wrote a qualifying thesis, was done for Gerry Brown on an attempt to use WKB for the scattering of neutrons by a heavy nucleus at rather lower energies than was normally done. There were some reasons for hoping that this would prove possible but Sprung found that one ended up with small diﬀerences between large quantities so that the method was not practical. This work was intelligently and competently done and he should not be blamed for the negative result. He then turned at my suggestion to the idea of Brown by which the nuclear spin orbit force could be understood as the relativistic correction to the repulsive core, an idea which I believe I mentioned to you some time ago and which I ﬁnd very plausible. He did some rough and ready calculations on this, which are published in a paper by Sprung and Willis910 of which I am sending a reprint separately. Sprung has been entirely responsible for the theory in this paper, (under Brown’s supervision), Willis merely helped to organise the computing side. It was always clear that the approximations used in this paper are of doubtful validity and that it can be used only for general orientation, and Sprung is attempting to make a proper theory of this problem. Since it is essential to put in projectional operators to eliminate negative energy states, one comes out with an integral diﬀerential equation of the structure not unlike the Bethe-Goldstone equation. Sprung is exploiting the analogy to construct a solution. He is making good progress with this and I am conﬁdent that he will complete a respectable Ph.D thesis on this subject by the summer. It also looks as if this procedure will come out with a spin orbit force which at least is qualitatively of the right kind. 910

D.W.L. Sprung and J.B. Willis, ‘The Spin-Orbit Potential in Proton-Proton Scattering’, Proc. Phys. Soc. 76, 539–544 (1960).

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As a by-product of his numerical studies he discovered some errors in other people’s results and he wrote a little note about this of which I am also sending you a preprint and which is going to come out in the Physical Review.911 This of course is not deep but it does show that he knows his way around the numerical side. As a sideline he has done some teaching for us, giving a short course intended to introduce biologists to the mysteries of calculus and he has done this very successfully. Sprung is very intelligent, hard working and lively, he is also a very pleasant and businesslike person. He is not as powerful a mathematician as McCauley, but he knows what he is about and in my opinion he in a good man to have around. He plans ultimately to return to Canada, but he feels rightly that he would beneﬁt from another year or two in the United States before settling down. I think a period at Cornell would be a wonderful opportunity for him. He would I think also be very good at talking with experimentalists. He has already done some of this here in connection with proton-proton scattering and polarisation experiments. He has a wife and a child of just over a year. Please let me know what you think. I am sorry you were not able to come to the Pugwash Meeting at which according to rumours we were hoping to see you. You would have heard that on the whole this was quite useful and informative. We did not expect to solve any problems there, but on the whole I came back from there somewhat more optimistic about the chances of a reasonable agreement than I was before. With kindest regards to all of you, Yours sincerely, [Rudi]

911

D.W.L. Sprung, ‘Relativistic Formula for the Spin Correlation Coeﬃcient CKP ’, Phys. Rev. 121, 925–926 (1961).

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[682] Rudolf Peierls to Robert Oppenheimer Birmingham, 14.4.1961 Dear Robert, I am sorry we missed each other all the time at M.I.T. I hoped to make one or two remarks which I shall now make in writing. One is about Marion Gunther. Yang mentioned to me the problems he had and perhaps some of the past history may be of some relevance. When he was due to leave here in 1950, we had many protracted discussions on whether he should go home or stay. I refused to make the decision for him but pressed him to take into account the likely eﬀect on other people. He wanted me also to give him an assurance about the prospects of getting a post in a university. At that time it was not possible to give him an assurance with any conﬁdence. There was no doubt that he would be able to earn his living somehow, though not necessarily in a research post in a university which would attract him, and I made it clear to him that I felt it was a little frivolous to make such a decision on the basis of the kind of job he could expect to get here. In the end he decided to go but after he had left Birmingham he had a change of mind and applied to the authorities for permission to stay. This was refused and he left. I discovered later that one of the reasons for the refusal was the absence of a recommendation from me, but the information that he had decided to apply reached me only after he had left the country, though somewhat later than he had originally stated. I was of course very worried that all this might get him into trouble but it does not seem to have done so. I now hear that he is talking rather freely about his problem and this seems rather foolish on any account. Another matter is Salam’s proposal for an International Institute for Theoretical Physics.912 The grape-vine says that you are not very 912

Abdus Salam was discussing the establishment of a research centre for theoretical physics in Italy. In 1964, he founded the International Centre for Theoretical Physics (ICTP) in Trieste. It operates under a tripartite agreement among the

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enthusiastic about this and it seems therefore that our reactions are similar.913 My own feeling is that the objectives stated by Salam could be more eﬀectively met by a scholarship and fellowship scheme which would allow people from all countries to be sent to existing institutions, balancing the load of junior scholars in any one department by a suitable mixture of senior fellows who could help to keep an eye on them. In other words, what in my view would be useful, would be (at least in theoretical physics) a scheme that could do for everybody what the Fulbright Scheme and National Science Foundation, now do for United States citizens. It should of course include a possibility for suitable people spending periods in the U.S.S.R. etc. We are beginning to get at least in this country a small but regular ﬂow of Russian visitors coming for reasonable periods on quite an informal basis. The main obst[a]cle for an extension of this seems to be a lack of reciprocity which is painful for Russian feelings or prest[i]ge. I am planning to use my inﬂuence to persuade some suitable people to think of spending some time [in] Dubna or Moscow. I believe that many people would ﬁnd such visits worthwhile. The main trouble is that it has not yet become a habit and people tend to regard other plans as more obvious. Yours sincerely, Rudi

[683] Robert Oppenheimer to Rudolf Peierls [Princeton], 27.4.1961 (carbon copy) Thank you for your letter.914 I too was very sorry indeed that we saw nothing of one another; and resented very much that we were each singing for his supper in concurrent and separate sessions. Italian Government, UNESCO and IAEA with a mission to foster advanced studies and research, especially in developing countries. 913 See also letters [772–773]. 914 Letter [682].

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It was good of you to write me about G[¨ unther], and I am glad to know the early history. I must say that nothing of what you write adds to the sense of distress, exasperation, and horror that his recent behaviour here has induced in me. As for Salam’s institute, I do indeed agree with you. It seems to me that the needs of underdeveloped countries are being rather well met now as far as the highbrow reaches of theoretical physics go; and could easily be better met if you and we, and a dozen or so other places, were to stretch ourselves a little, and make a few more enquiries. I ﬁnd myself uninclined to make elaborate institutional arrangements the purpose of which might be to increase or deepen co-operation between Russian and Western scientists. I do not know the meaning of the recent changes putting the foreign relations of Soviet Science under a new bureau rather than leaving them with the Academy; but I doubt whether we should rejoice in this. What you are doing, and also Copenhagen and CERN, seems to me just right. We have tried, but with no luck. With warm wishes from both of us to Genia and to you, Robert Oppenheimer

[684] Genia Peierls to Mr Raison Birmingham, 16.7.1961 (carbon copy) Dear Mr. Raison,915 I have just read your proﬁle of my husband. I know how diﬃcult it is to write about a man after a talk of two hours, and how few people can project themselves. I am sorry that most of my husband’s lecturers and collaborators are away on holiday or at conferences, and that his former secretary has just left to get married! 915

Mr Raison was a journalist who had drafted a proﬁle of Rudolf Peierls to be published in the New Scientist.

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Perhaps, if I try to write my “proﬁle” of my husband it might be of some help to you to look at, although usually the collaborators and secretaries are more amusing and detached than a mere wife. I met my husband at a large conference in Russia. And I think I fell in love with him partly because of his “easy-goingness”. To compare to others he was a treat to look after. He ate everything, slept under any conditions. Insects did not sting him, germs did not attack him. He was game to try anything, to organize anything, take part in anything. It is true he was the youngest of the visitors, but even so the order of magnitude of his “un-fussiness” was quite diﬀerent. He is still very much the same, and does not mind discomfort, noise, children playing, phones ringing, bad beds, unusual hours, unusual meals, & c. Just as well as he goes around so much and usually in a great hurry. He is a very typical untidy professor. His pockets bulge with correspondence, theatre programmes, and railway and airline time tables, for the last six months. He immediately covers with a think layer of paper all available surfaces around him. His secretaries usually resign themselves to this state of aﬀairs, and I take a chance and tidy his study when he is travelling. He brings back so many papers that the place immediately looks the same, and he is quite happy. On the other hand he is a very untypical professor in the way in which he enjoys and pursues any line of activity or enquiry which comes his way. He as willingly will cook, camp, paint ceilings, write funny verse (on domestic topics or science or scientists) as work on one of his many problems. If you idly ask him an idle question, he is immediately ﬁred with the urge to ﬁnd the answer, and will go through endless trouble to ﬁnd out what is the world’s production of chewing gum or the price of a ticket to Timbuctoo. He is very much what I call a “tennis player”. This means he enjoys and thrives on the questions, problems, challenges which come his way from the contacts with his pupils and collaborators, from seminars, conferences and visitors. (The alternative type of scientist being the “golfer”, who works alone, and is only upset by external pressures and demands. This type often does more fundamental work, but does not have many pupils and does not communicate easily. The most typical golfer is Paul Dirac.)

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He is extremely critical and loves to prick the balloons of beautiful but unsound theories (here the training by Pauli probably played some part). His colleagues say that in the departmental seminar he often talks considerably more than the speaker. They complain that he has very deﬁnite dislikes and if he is against an approach (too formal or too “messy”) it takes a long time and arduous work to persuade him that they have a case. They say ruefully that in the process they are just as likely to change their approach as he his distrust. He is called “Prof” by everybody in his department, and, I think, very much liked. I am not so sure about the university as a whole. He does not pay suﬃcient attention to people’s pet aversions, hates fuss, Empire building; he does not understand intrigues and has no time for gossip, so probably misses many local complications. After working in his youth with such intellectual giants and such great personalities as Bohr and Rutherford he is impressed by very few people, and certainly no titles, rewards or positions. He gets more “kick” out of a conversation with a bright research student than from one with an eminent but somewhat stale man. You mention the “international community” of physicists in the late twenties and early thirties. It was indeed very international and quite extraordinarily closely linked personally. It was very much a family. Conferences were like family gatherings. They all were very young. Pauli, in his early thirties, seemed an oldish man, and Bohr at 40 a patriarch! In Copenhagen, there was a great tradition of putting on plays, operas and mock discussions. We were of this generation the ﬁrst to be married (I mean the generation of Bethe, F. Bloch, Weisskopf, Teller, Landau, Gamow, Rosenfeld, Casimir) and when our ﬁrst daughter was born, the announcement was pinned on the main notice board in Copenhagen. Now there are too many people and too many centres for this. The conferences are too large to be so personal, and one has no chance of personal contacts with half the people one wants to see. But in many places the departments of theoretical physics are still extremely friendly. I know the one in Birmingham best, and since we came to this country, there stayed in our house, for months or even years, Bethe, Frisch, Fr¨ ohlich, Fuchs, G.E. Brown, Dyson, Salpeter amongst others.

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At Christmas our living room is covered from ceiling to ﬂoor with Christmas cards and photographs from all over the world with news of new jobs, new children and new successes. You write that my husband is very attached to Birmingham. He is very happy in the university, which he considers one of the bestorganised seats of learning, and is extremely fond of his department. So much so that he refused chairs in Cambridge, Oxford, London, Edinburgh, Manchester & c., to mention only British universities. So I am resigned to die in Brum! For twelve years my husband existed in a medium-size ex-army hut and for one year a bright young American and a very enthusiastic Italian shared as oﬃce a trailer parked outside the hut, since inside there was no room for another desk or another piece of paper. The surprise of many eminent visitors to ﬁnd the largest department of theoretical physics in England and one of the largest in Europe in these grim surroundings was great, but everybody was happy. When they ﬁnally got a new building many were even worried that the old spirit would die. But it survived alright, and the diﬃcult, often nervous, and sometimes very “rough” boys and some from all over the world, from Brazil to Poland, from China to Sweden, settled down in an unbelievably friendly community. The new ones were looked after by the older hands. They are taken to the shops and restaurants, helped with digs, language &c. And in a year’s time, they are quite ready to welcome a new ﬂood. They come of all ages, of all backgrounds, of all stages of development. Some come for a year (or less), some for three. Some who come for a year stay for ten and end as professors, like G.E. Brown. This year there will be 40 or more. In the middle of all this my husband is turning around and around like a top, dictating hundreds of letters, lecturing, helping with troubles in many problems, interviewing, running to and from meetings. This is an ideal arrangement for a tennis player and he thrives on it. It also means he has little time, and many excuses for not starting outside projects such as large textbooks, or a book on education, which he could do very well. His two books were written under great pressure. One as a result of lectures at a summer school which had to be written up, the other, “The Laws of Nature”, as a tour de force, to help pay the college bills of our children, whose courses at Oxford and Cambridge

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overlapped for one year and nearly broke the family ﬁnances. It proved to be a great pot-boiler and has been translated into I don’t know how many languages (I believe 9 including Armenian) and still brings in some very welcome royalties. I don’t know how long he will be able to stay this present pace, but being very easy-going and not a perfectionist he manages so far. I think you will now have a more lively picture than after one luncheon. What else? Yes, he loves puns (anathema to me!) good thrillers (the house is littered with hundreds of them) ﬁlms, good theatre (for which in Birmingham we are fortunately placed), classical music. Goes to sleep every week night with the Times cross word puzzle, and on Sunday with the Observer’s Everyman. He reads all the law reports in the Times, and collects time tables of every description, which is very useful, as with so many guests passing through from all parts of the world, he usually can solve the most unusual travelling problems on Sunday night. He does not like to play chess and cannot even play bridge. He dislikes all card games, monopoly &c... He does not play ball games, but learned to water ski at 51. Likes skiing and sailing, but never gets time for either. Likes camping, motoring, colour photography. Is very good with the children and very patient with the cat. Hates new clothes, mauve colour, ﬂowery hats and “learning-by-doing” method in education. On TV he watches Maigret, Peter Ustinov, occasionally Monitor, and will watch Mort Sahl. Yours sincerely, [Genia Peierls]

[685] Egon Orowan to Rudolf Peierls Ivanhoe, 30.7.1961 Dear Peierls, I am very sorry to have burdened you with those two items; had I known the complications that might arise from the matter, I certainly would not have done so.

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As regards the appliance, my hypothesis is that Brooke may have mislaid my letter and, in the course of time, misremembered its contents. I wrote quite clearly that I had diﬃculties in ﬁnding a manufacturer and wondered if there would be one in Britain. The hypothesis is supported by the fact that Nature sent to Brooke, for refereeing, our Letter on the Rhesus C relationship. We sent the letter by air in January; it was printed in June or July (I have not seen it yet, that number of Nature is out of the library). Apparently the MS was lost for a few months. The largest U.S.A. surgical rubber ﬁrm seems very interested in the appliance, and a favourable solution may be imminent. The decisive point is the presence or otherwise of a person of suitable intelligence. The results of the tests continue to be overwhelming: it is not an overstatement that a new situation is at hand. I do not venture to reconstruct the Rolls-Royce situation. I have not received any communication from them. There is no need to contact the Accident Hospital; the danger points in cars have been studied on a very large scale by the Cornell Aeronautics Laboratory, and the results are on the desk of every automobile man. Five years ago, the No. 1 danger spot was the opening of the door locks in accidents, and the No. 2 the windshield. In the meantime, General Motors have introduced their new safety locks, and now No. 1 is the windshield. There is at present a bitter ﬁght between the tempered glass windshield and the interlayered windshield; neither is any good, nobody knows well enough which is better, but of course very weighty commercial interests are attached to both. Last week I had interesting talks with top people at GM in Detroit. They strongly disavowed the attitudes of their underlings; they said that they were fully aware of the importance of the problem and they had worked out a solution of their own which, they admitted, was far from the one I showed you. They urged me to continue pressure, suggested large-scale experiments with dummies, and the use of their experimental facilities. A few days earlier I had lunch and dinner meetings with a countryman of mine (Budapest) who has recently become Ford’s research manager on glass; these talks may continue in Detroit. Finally, I had a lunch at the Du Pont Country Club two days after Detroit with their business, research, and engineering men in the safety glass ﬁeld; it was extremely interesting and satisfactory. It seems

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that interlayered safety glass can only survive if it is hitched to the new design; otherwise its merits are not equal to its additional cost. I shall see the opposite side in October. Lawrence Pilkington, the Director of Research of Pilkington Bros., just invited me to see their new laboratory (and discuss glassy plans of non-automotive nature). On that occasion, I shall ﬁnd out his present views on windshields. In 1955, we spent a part of a Liverpool-London trip on this subject. I read many weeks ago that Rollce-Royce may have to give up car manufacture, as a consequence of altered tax regulations which permit ﬁrms to charge the costs of cars only to a certain limit far below the price of a RR. So this avenue may become a cul-de-sac. I hope Genia is no longer bothered by the nuisance of the disc aﬀair. I had a touch of it in the meantime and it was very unpleasant. But of course I am only a weak man. We are having interesting times in plasticity. We have to face the possibility that the major part of the dislocation hypothesis of the last 15 years may have to be scrapped, and that strain hardening etc. (incl. crack nucleation) are probably not due to individual dislocation interactions of the Lomer and Cottrell types but to far simpler and more general mass actions. It seems that we shall look terrible fools. With kindest wishes to all, also from Jolan, Yours sincerely, Egon Orowan You may have heard that my friend Vaughan Lewis (Caius; Lecturer in Geography in Cambridge; he took me to Switzerland and introduced me to geology) was killed in a car smash in Iowa in June (a few days after we had tea at the Window Shop here). With the safety windshield, his death might have been avoided. His driver was saved by the steering wheel. P.S.: I hope you will not assume from the above that I am travelling across the U.S. to discuss the windshield. Detroit was a Symposium at the GM Technical Center (This was the ﬁrst time I saw and heard Debye). Du Pont-Wilmington was my milk run (I am their consultant on safety glass etc.). The Ford meeting was here in Cambridge and Boston.

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[686] Rudolf Peierls to Egon Orowan [Birmingham], 2.8.1961 (carbon copy) Dear Orowan, Thank you for your letter.916 I am comforted by the conﬁrmation that I did not muddle things up, but evidently Brooke did. I shall certainly [be] glad to take this further if it is any use, but in view of what you report, this may not be necessary. I am puzzled, however, by your remarks about the Rollce-Royce problem and your complaint that they did not write to you, because this suggests that you did not receive my letter of 24th June which enclosed a letter from Rollce Royce to me which, in fact, had been sitting on my desk for some deplorably long time. I had delayed it in the hope of reporting on both matters together, but I had some diﬃculty in getting hold of Brooke. Their letter, of which unfortunately I did not make a copy, and do not remember even the name of the writer, said essentially that they were always very interested in new ideas, but they did not feel like taking up yours, because in an accident in which the passenger was thrown forward through the opening left in your device by the opening windscreen, he would almost certainly receive serious injury by hitting the edge of the dashboard or the frame of the windscreen. For this reason, they felt that a seat belt was a better solution. They also added that in their cars there was no suﬃcient space available between ceiling and roof to allow for your device. I am reproducing their argument from memory but I think my description is substantially correct. My comment on their reaction was that they might have a point because from the description you give, it is not obvious that one could expect the passenger to be thrown neatly into the net, as your drawing shows. Presumably you have considered the dynamical problem involved, but it is not clear what the argument is and in what proportion of the cases one might expect the one or the other thing to happen. 916

Letter [685].

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I also said in my letter that I was keeping your speciﬁcation here in case you want me to pass it on to anybody else, and it was in this context that I suggested later the approach to the Accident Hospital, because their views about the mechanism of injuries might be a good counter to the ideas of Rollce Royce, but it would mean ﬁrst going back to my friend on the Board to discover who was the writer of the letter. In any event, they were not as discourteous as it appeared, because since your letter and papers reached them through me it seemed perfectly proper that they should reply to me. The delay in their letter being sent onto you is not their fault, but mine, and the fact that it did not reach you must be blamed on the Post Oﬃce. It is quite true that the new rule about tax allowances has been a serious blow to the market for Rollce Royce cars in this country. I had not heard that as a result they were giving up car production, and it would surprise me, but nothing is impossible. If you like I could try Rover, who are conveniently located in the Birmingham area and who are always willing to try new things. They were, I believe, the only ﬁrm to make an experimental gas turbine tower, though it does not seem to have been a success. Yours sincerely, R.E. Peierls

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[687] Rudolf Peierls to Margaret Gowing [Birmingham], 30.10.1961 (carbon copy) Dear Mrs Gowing,917 I found your story extremely interesting reading, not only because it seems to me an excellent piece of writing, but also because it contained many bits of information that were new to me. It has taken me until now, however, to go through it carefully and to pick out points on which I could make useful comments and here they are, if they may still be useful. I am referring to your typescript by a decimal number, indicating page and line. 1.5 – the “climax”. The period was not really a climax for nuclear physics, which went on developing at an accelerating pace, though later somewhat retarded during the war years. 1939 was, of course, a key year concerning the practical uses of atomic energy and concerning our knowledge of the ﬁssion process, but the preceding period was a steady development towards an understanding of nature, which was in no sense consciously aiming at any conceivable practical application. The word “climax” therefore, does not seem to me appropriate, but I cannot think of just the right way of expressing the thought. 3.4 Here and in other places you use the word “mechanism” to denote the observable properties of the ﬁssion process, such as the particular isotope in which it takes place, the cross-section, the dependence on the neutron energy, the number of neutrons produced, etc. This is not usually meant by this term. To use it would denote the internal mechanics, i.e. what the various particles do in the nature of the process, the state through which a nucleus passes in the course of the ﬁssion etc. Work on this problem did not really get going until after the war and is 917

Margaret Gowing, an economic historian, had become historian and archivist to the UKAEA and researched the history of Britain and Atomic Energy, which led to a two-volume publication putting Britain’s research and development of nuclear energy into its political national and international context. M.Gowing, Britain and Atomic Energy. 1939–1945, London: Macmillan, 1964 and M.Gowing, Independence and Deterrence. Britain and Atomic Energy. 1945–1952, London: Macmillan, 1974.

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not ﬁnally completed. It might be better to say instead of mechanism, perhaps, the “details” or the “characteristics” or the “nature” of the ﬁssion process. 4.3 The name is Francis Perrin. 16 First footnote. The remark you quote was not in fact meant to be modest, and I think it was correct, but I meant the questions in a very speciﬁc form. In the development of science, it is usually far more important and for more diﬃcult to ask the right questions than to answer them. My own contributions have tended to be in the direction of answering questions rather than raising new ones, but on this occasion Frisch and I succeeded in posing important new questions. What I meant was to ask the following series of questions. • What would be the cross section for the collision of a neutron of various energies with a nucleus of uranium 235? • What fraction of such collisions will lead to ﬁssion? What is, therefore, the critical size of a mass of pure uranium 235? What would be the consequences of a chain reaction in pure 235? What would be the military value of such a weapon in relation to the very large eﬀort of separating the uranium isotopes? These questions seem obvious enough today, but they were not obvious at the time, and we did not at once formulate them, because one tended to regard the possibility of having large quantities of separated uranium as quite academic, and also one had done the sum, one might intuitively have expected the required quantity to be much larger than it is. Everyone therefore, tended to think of using mixtures of uranium and moderators to slow down the neutrons or of using large quantities of natural or slightly enriched uranium, Given the questions in the form I have stated them, anyone who was up-to-date in the subject and in particular had understood Bohr’s theory, would have given very similar answers, as your narrative shows, our conclusions were immediately accepted by all the nuclear physicists as the most probable answers, the only doubt and controversy relating to the degree of uncertainty with which one could accept them, (apart from of course the practical problems about the eﬀort needed to realise the project). What I was

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trying to convey, therefore, was that we did not know or understand more of the physics of the problem than other people, we “just” asked the right questions, but this statement is anything but modest. 28.23 Frisch “was transferred” to Liverpool. This term does not convey the relations of the period. Frisch was not employed by any Government Department. He held some kind of grant in the University of Birmingham and nobody could, or did, give him orders to go to Liverpool. The question was raised in discussion whether he would not be more useful in Liverpool, and Frisch accepted the suggestion that he should move there. I cannot even remember whether initially he was employed there on university funds, or on funds provided by the Ministry, but the decision to go there was his own, and this seems to be an important point in connection with the whole spirit of the entreprise which you very rightly stress in other contexts. 37. First footnote. This is slightly exaggerated. At the time I had no secretary, but could occasionally use help from secretaries in other Departments. The typing of the reports for the meeting in September, 1940, to which you refer was, in fact, done by Professor Oliphant’s secretary, and some other documents were typed by secretaries in other Departments. Secrecy came into it only because it seemed undesirable to spread this work over many Departments, and the secretaries in the Physics Department were too busy to do it all. 42.5 In connection with the practical diﬃculties of designing a separation plant, it should, I think, be mentioned (as you mention in other places) that the corrosive nature of uranium hexaﬂuoride, which is the only gaseous compound of uranium, makes this a project of unusual practical diﬃculty. 47. Footnote. This might be read to indicate that the term “hex” was in general scientiﬁc use at the time. It was, in fact, a cover name used at ﬁrst by American scientists, so as to avoid frequent mention of the term “uranium Hexaﬂuoride” in everyday conversation. It was one of many such cover names invented for reasons of secrecy. Before we took over this term from the Americans, we used in this country a variety of names, which I am afraid I cannot now remember. 48.22. The word “blue print” conveys an exaggerated impression and Simon himself would, I am sure, not have liked to see it used there.

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A blue-print would have to contain speciﬁc descriptions of all the components in their design, size and connections. It was much too early for that and the very important paper by Simon was no more than a rough sketch of the plant with many unknown features still to be settled. 50.17 — “directed”. This word in the context implies that, by comparison, the work in this country was closely directed. I do not think that is a good description. It was well-coordinated but there was at the time very little central direction as to what any particular person or group should do. The discussions of the committee and informal discussions between the groups would show up the need for doing something, and as a result one of the groups would just start doing it, using the Committee only as a means of making it known that the work was going on and where necessary, of course, to obtain the money or materials required. 58.5. As I recall, the reason for consulting the explosives experts and, in particular, G.I. Taylor was speciﬁcally that a report was received from America, written I think by Professor Kistiakozsky, giving arguments which tended to show that most of the energy of such a highly concentrated explosion would be absolved in generating heat in a very small region and that the intensity of the blast wave set up would be very small. 59.18 “Peierls for example”. I may have expressed this view at the time, but if so I had forgotten about it completely. My only recollection is that I regarded the idea as rather speculative, both because even less was known of the nuclear constant of plutonium than of those of uranium, and also because the project would require ﬁrst making a reactor go, which at the time seemed to require a large plant for producing heavy water to start with, and then extracting the new element from it. It therefore seemed to me that the lines on which we were already working were preferable, particularly as, at least in our group, we were already fully occupied with what we were doing, so that it would really come to a choice between the two alternatives, and I therefore did not attempt to go deeply into the question of the merits of plutonium. This was probably a wrong view, but it did not mean that I saw any reason to believe that plutonium should not be usable. However, my mem-

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ory may well be at fault and if someone has quoted me as expressing a strongly negative view that may well be correct. Finally, I would like to make a point which does not relate to any speciﬁc place in your text and that is the omission of a rather serious mistake we made at the time which certainly aﬀected progress, though its consequences are not easy to assess. I feel that particularly in view of the many ﬂattering references you make to the work of my group, it would not be fair to omit mention of a very major error. This concerns the question of the equilibrium time of a large part. In various places in the text you have mentioned the question of the time it would take a plant to start producing material of the right concentration. Since such a plant consists of many stages working eﬀectively in series, it was always clear that it might take some time before each stage had enough enriched material to allow the subsequent stages working, and it was important to make an estimate of this. A complete calculation of the way in which the concentration of each part of the plant would rise with time after it had started operating with ordinary uranium was a rather lengthy process and some preliminary answer was required. I therefore tried to make an intuitive guess of the formula which would give the equilibrium time, i.e. the time taken by the plant to approach normal working conditions, independent of the size of the components, the number of stages, etc. My guess was wrong in that my formula made the time rise much more quickly with a number of stages than in fact it does. The error inﬂuenced the early thinking about the design and it led Simon to think of a plant in which all the membranes for a group of stages were housed within the same shell as the compressor itself, so as to minimise the amount of gas circulating between stages. The prototype machine which was then built by Metropolitan Vickers was of that kind. It made the manufacture and operation of such a machine rather diﬃcult, and I doubt very much whether a full scale plant could have been built reasonably along those lines. The ﬁrst indication that something was wrong came when we saw from the American reports that they were thinking of a plant which, on our formula, would have a prohibitively long equilibrium time. During

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the famous visit of Urey and Pegram I expressed the worry to Urey, who said his experts, in particular Dr. Karl Cohen, had come to a diﬀerent conclusion about equilibrium times. I was not convinced as yet, but when I went to the United States early in ’42 I had an occasion for discussing the matter with Cohen, and then came to the conclusion that he was right. Meanwhile, because of the doubt, we had asked Prof. Hartree and his group in Manchester to make detailed numerical calculations on this problem, and while I was still in the United States I received a message that these calculations had yielded an answer which conﬁrmed Cohen’s and not my formula. From this point on, of course, the very restrictive condition on the design was dropped. It is hard to assess how far this, in fact, delayed work. It turned out that the main function of the machine built by Metropolitan Vickers was to give one experience in the handling of “hex” in factory conditions, and of the problems of impurities, vacuum testing, etc. and for this purpose it served as well as any other machine. Moreover, it may be that the original exaggerated fear of equilibrium time gave rise to various ideas in the design, aiming at greater compactness, which were in the end valuable. Any assessment of the consequences of the error are necessarily a matter of speculation, but that the error was made is a fact, and I think it belongs to your story. Apart from this, all my comments are, of course, only suggestions which you may or may not take note of as you see ﬁt. Yours sincerely, R.E. Peierls

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[688] Rudolf Peierls to D.J. Thouless [Birmingham], 17.12.1961 (carbon copy) Dear Thouless, You have probably also discovered that the last note of optimism about the inequality, on which we parted, was not so well founded. To make sure we agree, let me spell out how it now looks to me: We wish to evaluate the overlap integral which in the notation of my draft, is N=

1

dk dre− 2 µk

2 − 9 (k−k )2 + 1 r(k−k )− c r 2 2 2 2

For the purpose of discussing convergence we may simplify the algebra by putting k [..]918 0 We then discussed two methods of evaluation: (a) Integrate over r ﬁrst. This is always justiﬁed, since c is positive. The second integration then converges provided µ1 ≡ µ + a

1 >0 4c

which is our old inequality. (b) Integrate ﬁrst over k . Then the ﬁrst integration makes sense only if 1 µ + a > 0, i.e. µ1 > 4c which is more restrictive than the condition of (a). If this is satisﬁed then the second integration converges provided c+

918

Missing in carbon copy.

1 >0 µ+a

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which is by itself a harmless condition, and allows [..]919 to be very large and negative. When we discussed this at the board, we looked only at the second integration since in case (a) the ﬁrst integration is not dangerous. 1 method (a) works, and (b) already fails. Evidently, if 0 < µ1 < 4c In other words, the integral is not uniformly convergent, and there is doubt whether the answer (a) is valid, but it looks plausible. But if the ﬁrst inequality is violated, the change in the order of integration is of no assistance. On further consideration I have decided not to believe your idea that, failing the inequality, the results remain valid. This would go, in particular, for the energy. Now consider the expectation value of the Hamiltonian, assuming the weight function to be Gaussian. Provided that all the integrations converge, the result is: γ

β/2c + 4c2 α − β/2c 3γ E +3 −3 =1− E0 2C µ + 1/2c µ + 2a If we plot this, assuming α −

β c

−

γ 4c2

> 0, we get

Here E1 is E0 − 3γ 2c or the energy obtained without the second projection. In this case, there is a minimum in the region in which the curve makes sense, and two points for which E becomes inﬁnitely negative. The ﬁrst value for which this happens, is µ = −1/2c, here µ1 is still positive, while µ + a = a − 1/2c is of unknown sign. (For the oscillator 919

Missing in carbon copy.

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a = 1/4c). We would hope that at this point the integrals diverge, since otherwise the variation principle would say that E is −∞. If, on the other hand the inequality is violated, the shape of the curve is

Again we must talk ourselves out of the points near 1/2c and near −2a, and I ﬁnd it hard to believe that nevertheless the minimum, which lies even much further to the left should correspond to a physically real value. My impression is now that in this case one the right-hand loop of the curve is justiﬁed, and this has a minimum for µ = ∞. This means that for this value of the parameters the second projection gives no improvement over the ﬁrst (except for correcting the momentum dependence of the energy, which remains correct) so that of the family of wave functions considered for the internal motion, the old P − Y solution is still the best. This would be in line with your result that the diﬀerential equation for the weight function has no solution (except the δ-function must be a solution, but this is hard to handle). It is of course still possible that in a reasonable case the inequality is valid, but if my present point of view is right, there would be no mystery if it were violated. For non-zero momentum the best trial function would be the P − Y solution for momentum zero, times exp(ikx) I have not yet thought out what would happen in the rotational case, but I believe there is no disaster. If I am right this would call for some slight redrafting of the paper, since the reservation about the inequality should be made earlier and

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more deﬁnitely.920 This has delayed my checking the draft for typing, and I shall now try to get a photocopy made. Please let me have your comments. Yours sincerely, [R.E. Peierls]

[689] D.J. Thouless to Rudolf Peierls Cambridge, 8.1.1962 Dear Prof. Peierls, Thank you for sending me the copy of the draft of our paper.921 I have now ﬁnished the section of the axially symmetric rotator, and I shall send you a copy of it when I have one ready. For some reason I did not get your letter until I got back after Christmas. I agree that one cannot just take exp(− 12 µk2 ) with negative µ for the weight function and get a sensible answer by changing the order of the integrations, but it does seem to be possible to make an analytic continuation of such a function through the zero of 1/µ. The weight function always occurs in an integral, and so our requirement would seem to be that the weight function may be approximated by a well-behaved, not that it should actually be well-behaved. If we demand that the wave function be well-behaved, when the analytic continuation is made, we ﬁnd that µ−1 must not be too negative, since the integration over k’ multiplies each one-particle wave function by exp(−x2 /2µ), and this must not increase more rapidly than the original wave functions decrease. This would seem to allow µ to be large and negative, but not 920

In 1957, Peierls had published a paper, together with Jean Yoccoz, discussing the variational states of nuclei by using a variational method. (R.E. Peierls and J. Yoccoz, ‘The Collective Model of Nuclear Motion’, Proc. Phys. Soc. A70, 381– 87 (1957).) This was now being extended in his work with David Thouless which resulted in a paper published in 1962. R.E. Peierls and D.J. Thouless, ‘Variational Approach to Collective Motion’, Nucl. Phys. 38, 154–76 (1962). 921 Letter [688], note 920.

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to be small and negative, which is not a result we expect from a study of the overlap integral. We really want to make sure that our results obtained by analytic continuation do not depend strongly on contributions from large differences in k and r, since our Gaussian approximation assumes that such contributions are negligible; there is clearly a danger that these contributions may be important if µ is negative. The method I put in the appendix does give an analytic continuation to negative µ, and it does ensure that the main contributions to the integrals come from small k, to approximate the weight function. The series for the energy converges quite rapidly (it is essentially a geometric series in s), and a good approximation to the analytic continuation for the energy could be obtained by taking only a few terms of the series. This method does give only the branches of the curve outside the two singularities, and diverges between the singularities, I think. I suppose that the other branch, going down to minus inﬁnity at both ends, might be obtained by making a formal sum of a divergent series in Eq. (B5). I found a packet of copper nails on Julie’s cooker when I got it home in October. Do they belong to you? Yours sincerely D.J. Thouless

[690] Rudolf Peierls to D.J. Thouless [Birmingham], 21.1.1962 (carbon copy) Dear Thouless, Thank you for your letter and for the section on three-dimensional rotation.922 On the question of the inequality, I agree that my last letter was an aberration, and I probably had not remembered correctly what we 922

Letter [689].

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did in our last conversation. I think I can now convince myself directly that everything is all right, at least in the translation problem (and the generalization may not be quite trivial) without using any limiting process or analytic continuation. If I could manage to present this decently, I would prefer it to your appendix, which still is written in terms of a divergent series. Take the wave function of the translation problem, for total momentum zero of the form: (A) dr dkg(k)eik(r−x) Φ(x − r) I can introduce the Fourier transform of g in the form g(k) = dsG(s)e−iks Inserting this in the deﬁnition of the trial function one ﬁnds this to be (B) dsG(s)Φ(x − x − s) If g is of the usual form exp(− 12 µk) with a large negative [. . . ]923 , the form (A) for the trial function does not exist, or at least exists only subject to some instruction about the order of integration. Its Fourier transform also does not exist, but by continuation the function G(s) [. . . ]924 becomes exp(−s2 /2µ) which makes the trial function (B) perfectly sensible for large negative µ. In that case we may use (B) as our trial function directly, without regarding it as a transform of (A). Then, for example, the normalization integral becomes (ds)ds G∗ (s)G(s )Φ∗ (x − x − s)Φ(x − x − s ) Here the integral over the particle coordinates is trivially divergent since the integrand is translation invariant, but this can be put right by using 923 924

Missing in carbon copy. Missing in carbon copy.

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a cyclic boundary condition with period L (which is also needed in the other form). In order to have the normalization equivalent to that of () when both forms exist, the integral must be c s + s − (s − s ) L. exp − 8a 2 (apart from trivial factors 2π outside the exponential). I wasted some time proving this result directly, but I do not really think this is necessary, since one is just doing a Fourier transform of the overlap integral, which always exists since µ does not come into it at all. Doing the same with the energy overlap, one gets of course an integral equation for G which is all right for large negative µ. Questions: Do you like this way of looking at it, which of course is not substantially diﬀerent from what we discussed when you were here? Is it necessary to spell this out, or is it suﬃcient to point out that the trial function can be written in the form (B) and that it, and all results, can then be continued into the region where (A) fails? How does one do the same for rotation? There the Fourier transform of the weight H , which are function would bring in the eigenstates of your operator probably quite undesirable animals. Or is it honest enough to accept the analytic continuation by analogy with the translational case? I do not, of course, want to rule out the way you did it in the appendix, but one would then, I think, have to make it clearer why the divergent series is better than the divergent integral, and to show that the trial function deﬁned in that way is ﬁnite, which is no doubt true, but not so easy to discuss. Sorry to delay things further, but it would be nice to have this point tidy, and it is probably the last one. Yours sincerely, [R.E. Peierls]

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[691] Rudolf Peierls to Hans Bethe [Birmingham], 24.2.1962 (carbon copy) Dear Hans, I am writing this letter to kill two birds with one stone. The ﬁrst bird is to ask you if you could be good enough to write me a short letter giving me your opinion of Graham McCauley,925 who seems to be willing to come here next year. We know him, of course, but your opinion would be of help to the appointing committee and we need in any case some information about how his work has progressed since he went to Cornell. I also would like to say that I have read your famous Cornell lecture926 about disarmament etc. and I found it extremely interesting and a wonderfully sane and balanced presentation of the subject. One gathers that you have come in for some nasty attacks from various quarters as a result and I hope they were not too much of a headache. Someone sent me an article from an unidentiﬁed magazine (it looks like “Life”) with a nasty and vicious attack. I hope this reaction is not general. I was interested in one remark you make, namely, that one motive for supporting the idea of a test ban treaty was that it would preserve the technical advantage of the United States.927 I had not previously realised that this was a strong factor and it is certainly worth making the point clear to the American public that such a treaty would have been a good thing, but I am a little concerned over the eﬀect on Russian readers of your lecture and therefore, also indirectly on people talking with the Russians, which I shall probably have to do this summer at a Pugwash meeting, since it provides a good reason why the Russians felt justiﬁed in their reluctance to accept the test ban treaty, at any rate 925

Graham McCauley had done research at Birmingham before taking up a fellowship at Cornell. In 1963 he returned to Birmingham. 926 In 1958 Hans Bethe had headed the presidential study of nuclear disarmament and was an advisor to the United States at the Geneva nuclear test ban talks. 927 Similar ideas had already been expressed earlier by Bethe. H.A. Bethe, ‘A Case for Ending Nuclear Tests’, Atlantic Monthly, August 1960, 43–51.

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until their own tests have made further progress. However, if this was a factor in the situation it has to be admitted. Are you coming to the Pugwash Conference in Cambridge?928 With kindest regards, Yours sincerely, [Rudi]

[692] Rudolf Peierls to Selwyn Lloyd [Birmingham], 2.4.1962 (carbon copy) Dear Mr Lloyd,929 In your letter to me of 2nd February930 you were kind enough to comment on my service on the Governing Board of the National Institute for Research in Nuclear Science, and you expressed yourself satisﬁed with the way in which the Institute had taken shape and promised to provide an important service to the Universities. I am sure, from my observations, that you are right in this view, and I was looking back on my association with the developments of the Institute with considerable pleasure and pride. However, since then, this feeling has been shattered by the decisions about ﬁnancial policy for the Universities. This makes it look as if the spirit and understanding of Universities will be allowed to decay to a point where the facilities and support oﬀered to them through the National Institute will cease to have any real value. No doubt you and your colleagues are aware of the dismay with which the recent cuts have been received in the Universities, but perhaps 928

In 1962, British scientists hosted two Pugwash conferences, one in Cambridge and one in London. 929 Selwyn Brook Lloyd (1904–1978), Minister of Supply, Minister of Defence and Foreign Secretary between 1954 and 1960, when he became Chancellor of the Exchequer. 930 Letter could not be located.

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it may help the understanding of this reaction if I may be allowed to give my own personal version of it. Since returning to academic life after the war, I have devoted all my energy to building up my own subject, which has an important part to play, not only in the development of nuclear science, but in many other applications. Before the war this country had a few great men in this ﬁeld, but for reasons which I need not here elaborate, no adequate research schools. I have, I think, succeeded in creating a successful school here at Birmingham, and I hope I have played my part in encouraging the growth of other good centres elsewhere. All through the post-war period, these developments were carried out in diﬃcult circumstances. Buildings were inadequate, establishment was limited, progress on the experimental side, on which our theoretical work is vitally dependent, was delayed by the shortage of facilities, and, above all, our ﬁrst-rate people were tempted to leave the country by attractive oﬀers particularly, of course, from the United States. I myself had plenty of such temptation[s], made attractive not primarily by the better standard of living, but by the pull of large and ﬂourishing teams, stimulated by the rapid growth of experimental discoveries and by a buoyant spirit, which would have made my own progress in research incomparably easier and more fruitful. Nevertheless, I decided to stay, or return after short periods abroad. What has kept us going has been the feeling that the development of science in this country was urgently necessary, and that this need was being appreciated and that, by and large, the Universities were given as much assistance as was reasonably possible during the times of severe shortages in the post-war period. Since then, conditions improved to a certain measure. Buildings, staﬀ and facilities have been augmented, but the pressure of able young people demanding places has been so heavy that the Universities have been forced into increasing their student numbers to the limit of their new capacity so that our new buildings are still crowded and our staﬀstudent ratio, which vitally aﬀects the standard of teaching, has further deteriorated. The recruitment of staﬀ, even up to the limit of the present establishment, has been made diﬃcult by salary scales which, in spite

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of improvements, have slipped substantially below those in comparable professions, not to speak of those in wealthier countries overseas. A few years ago, while we were still busy trying to consolidate the situation following the recent expansion, we were requested, on the initiative of the Government, to consider a further substantial expansion of student numbers and, as we understood it, we were promised the necessary support in terms of money and buildings. The proposal was not easy to accept, because it called for a change of scale which meant rethinking the whole structure of the University methods of teaching and ways of maintaining personal contact between staﬀ and students, which had been automatic on the old smaller scale. There was, in fact, a strong section of University opinion, which was opposed to the proposed increase because of the belief that it would ruin the eﬃciency of teaching and education. I belonged to the section who saw a worthwhile challenge in the new proposals and who felt that with enough eﬀort we could make the new larger Universities work, and we succeeded in persuading our colleagues to accept this view. Since then, we have devoted much of our eﬀort to the required re-planning, and as the new numbers would evidently aggravate the existing shortage of ﬁrst-rate staﬀ, we started to work hard to encourage all suitable young men to remain in academic life and to start training for a University career, and we also started to attract promising young men from overseas, or to encourage those who were temporarily working overseas to make plans to return. Here again, we were kept going by the feeling that we were responding to an imaginative proposal by the Government, who had seen the need for larger Universities and were willing to pay the price for them. Our reaction to the latest reversal of policy must be viewed against this background. I think if a team of experts in public relations had been asked to ﬁnd the most eﬀective way of damaging morale amongst University staﬀ and hindering the recruiting of new staﬀ, they could hardly have thought of a more eﬀective scheme than to cut the grants to a point where it will be diﬃcult to meet the rising costs of existing activities, to oﬀer an adjustment to the salary scales of one-tenth of that shown necessary in a case made out by the Association of University

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Teachers, or one-seventh of that recommended by the University Grants Committee, who are not normally regarded as extravagant, and to add to all this the request that the Universities should go on expanding. My ﬁrst reaction to this announcement was an inclination to accept the next attractive invitation from America. On reﬂection, I have decided against this, at least for the present, partly because of the serious eﬀect such an example would have on the reaction of younger people, but particularly because I cannot yet believe that the new policy is permanent. I am still hoping that the importance of Universities for the future of this country will be recognised. But it must be understood that time is pressing. In industry the problem of allowing the scale of activity to ﬂuctuate in line with economic factors is well understood, and one knows the importance of retaining, even in periods of retrenchment, the key craftsmen, such as the tool-room staﬀ, and the key technical experts, both of whom need long periods of training and are hard to recruit once they have been lost. It must be understood that all members of the University staﬀ are comparable to the tool-room workers or key engineers in this respect, and if even for a short period we fail to attract to this profession all suitable young people of high ability, we may never be able to catch up and may endanger the academic standards of the future. Returning to the problem of the National Institute for Research in Nuclear Science, this is a place in which some of these diﬃculties are likely to become acute, because it will have some of the best University people working hand in hand with staﬀ from the Scientiﬁc Civil Service or the Atomic Energy Authority, and therefore, will bring home to them more acutely the discrepancy in pay and in facilities. Already now, to give only a simple example, my colleagues are painfully aware of the diﬀerence between the ease with which Government-sponsored staﬀ are enabled to attend important conferences overseas and their own diﬃculties in getting support for such essential visits on the minimum possible scale. I would not, of course, wish to imply that scientists in the direct Government service are being treated too generously. Their standards are more or less adequate, and it is the University man who is made to feel that his services are not being appreciated and that he is of no importance.

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We do appreciate the diﬃculties of the national economy, but the Universities have to play a vital part in providing for the future, and the present policy is as dangerous as that of a farmer who would sell his seed corn to balance a short-term deﬁciency. Yours sincerely, R.E. Peierls [693] Rudolf Peierls to Hans Bethe [Birmingham], 2.5.1962 (carbon copy) Dear Hans, This letter is probably quite academic, but one never knows. It all arises because I have been asked to move to Oxford to succeed Lamb, as you will no doubt have heard by rumour. The rumour will have further told you that I am going to accept, which is more than I know, because there are some problems to be settled, but it is quite possible that the rumour might be right. If I do go, it would be in October, 1963. It is, therefore, pretty clear that there will be no professor there during the next academic year, and this brings me to the point of my letter. At the Solvay Conference you mentioned that you were going to take a sabbatical year. You were then thinking of speciﬁc good places for speciﬁc good reasons, but just in case these plans have not completely worked out for some reason, maybe you should know that there is a fairly attractive place which should spare professorial salary for a year, without any particular chores. I have not mentioned any of this to anyone in Oxford, because it seems a very long shot, but if by any chance you were interested, I should be most surprised (and no doubt you would) if they did not jump at the idea. I have no great illusions about the prospects, but they do seem worth a one-and-threepenny stamp. Yours sincerely, [Rudi]

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[694] Hans Bethe to Rudolf Peierls Ithaca, 16.5.1962 Dear Rudi, Thanks a lot for thinking of me. However, as you already believed, your letter is academic. My sabbatical will be 1963–1064, and in addition, I don’t want to tie myself down to one place. But thanks anyway. I have already heard rumors that you had accepted Oxford, and I am glad to hear how matters actually stand — including the fact that the rumor may be right. There are also rumors about your successors in Birmingham. I know how diﬃcult it is to make such a decision; it is a pleasant agony. With best wishes, [Hans]

[695] Rudolf Peierls to Lev Landau [Birmingham], 24.5.1962 (carbon copy) Dear Dau We have just heard that you are much better,931 and it seems that you are now in a ﬁt condition to receive letters. This is wonderful news. Like all your friends, and that includes all physicists who have never met you but know your work, we were terribly shocked by the news of your accident, and were waiting anxiously for you to get better. We would have liked to write to you and send you our good wishes, but until now it seemed that letters were hardly what you needed. 931

Lev Landau had been injured seriously in a motor accident which had led to several doctors declaring him clinically dead. Remarkably, he regained consciousness and recovered to some extent, although he could never again carry out creative scientiﬁc research.

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One gathers that the doctors did their best for you, and it is comforting to know that medical science has made enough progress to mitigate at least the damage that the progress of automobile technology produces. It will still need patience until your recovery is complete, but the ﬁrst stages are the most important ones, and you now seem to be a reasonable ﬁrst approximation to your old self. I suppose it will be some time before you are back at work, but I can assure you fundamental physics has not yet been ﬁnished oﬀ by other people while you were not looking, and it is not going to be before you join in again. A lot more information is building up about the new resonances and this makes high-energy physics look like a much richer ﬁeld. People are ﬁtting all sorts of group theoretical patterns to them, and soon there may be enough information to check some of these speculations — I shall be surprised if they ﬁt. On the abstract theory, Regge’s conjecture is now the fashion.932 Just as a few years ago no paper was respectable that did not use the Mandelstam representation, everything must now be expressed through Regge poles and their trajectories. But it is a powerful method and seems to be just the right way to understand the behaviour at very high energies or momentum transfers. All our best wishes for your future recovery, and for patience which I am sure you will need plenty. Yours, [Rudi]

932

T. Regge, ‘Bound States, shadow states, and Mandelstam representation’, Nuovo Cimento 18, 947–56 (1960).

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[696] Sam Edwards to Rudolf Peierls Manchester, 3.8.1962 Dear Rudi, Thanks for your letter. I didn’t reply sooner since I went to a conference on which I gave a paper on disordered systems, so thought about them a bit more and decided to reply after. I didn’t think I’ve understood your point so perhaps we can talk a bit more about it sometime. I’ll be very happy if you do get a research student on it, for what I need is someone to talk to who isn’t an “expert” in solid state (why are those people so limits?), but can see the problem in perspective. I’ve got some new results but they haven’t solved my troubles, but you might like to hear them. If one has a random potential, then there ought to be a density of levels from −∞ to +∞. I can get an approximate method of getting this; and the density below the mean energy has an essential singularity in the interaction constant. For example in one dimension, free electrons have n(E)

So the conductivity, which one normally thinks of as a series in (m.f.path)(electron wave length) λ λ d 1 + β + ··· small σ=α λ d d actually also has terms like e− γλ which cannot be got from a graphical analysis.I think I can solve itexactly in one dimension the answer being −(η3 +Eη)/λ2 dη/ e−(η3 +Eη)/λ2 dη taking up the imaginary n(E) = dη η e axis through the saddle point. The method is to change variables from

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potential to density matrix in the functional integration. We tried to do things like that many years ago and failed, so I can’t be sure this exact answer is o.k. and anyway of course nothing works in 3 dimension. But the approximate thing is ok. But I still don’t see what the wave functions look like. This has been rather a side line of course, my main work being with the turbulence. Really exciting things have now come out of ﬁeld theory extension, for I have a new modiﬁcation which produces exactly standard ﬁeld theory. It is quite clear from this where the standard theory is inadequate on two counts: ﬁrst why it is divergent, and secondly why the normal Feynman diagram technique is not the right way to solve it. My previous work can be regarded as a special case of renormalization, but since it amounts to renormalizing → 0 the previous work now emerges as a way to get a sensible ﬁeld theory right from the start. The point I hadn’t realized is that it is possible to get normal ﬁeld theory, by averaging over degrees of freedom, without ever invoking quantization. Once one sees this (and it can be proved rigorously) everything else clicks into position. I’ve worked in detail on meson ﬁelds so far, but looking at fermions there are more mysteries to be unravelled particularly in the light of the superconductivity theories, but I’m still in confusion here. I’d like to tell you about this in detail sometime, but unless you have time free in the next three weeks, I am travelling through September so it had better be October or later. I’ve just spent a week at Culham933 & got acquainted with John Adams.934 He was telling me about how he hoped things would develop now you are going to Oxford. It all sounded very impressive and it is clear that Oxford (or rather the Oxford area) will become the leading centre in theoretical physics in this country. It would be foolish of me to oﬀer congratulations on your move, rather oﬀer congratulations to 933

In 1960, a purpose-built laboratory for the UK Fusion Programme was set up at Culham on a former Fleet Air Army Airﬁeld. 934 John Adams (1920–1984), was the director of the Proton-Synchrotron division at CERN from 1954. From 1971 to 1975 he served as CERN director-general and between 1976 and 1980 as executive Director-General. In 1961 he moved to Culham, where he worked as director of the Culham Fusion Laboratory; from 1966 to 1971 he was a member of the Board of the UKAEA.

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Oxford on getting you, and trust you’ll be able to go on getting your own way with the University since your acceptance shows that you’ve made a good start! Best wishes, Sam

[697] Rudolf Peierls to Freeman Dyson [Birmingham], 5.12.1962 (carbon copy) Dear Freeman, I have been asked to write to you to get your reaction to the following idea. You may have seen from recent circulars from the Royal Society that a number of new research Professorships have been established. A Committee of the Royal Society are now considering names for these, and your name appears in a prominent position on that list. The Committee therefore would like to know whether there is any chance of you being persuaded to accept such a Chair. At this stage I have no authority to make any deﬁnite promise, since there are more names on the list than there are Chairs. However, there is evidently every reason to suppose that if you were interested, an oﬀer was likely to follow. From what I know of your attitude and your commitments, I have no illusions about the prospect of your being willing to consider such a proposition, but there seems no harm in asking the question. I need to say that everybody concerned would welcome with enormous enthusiasm any chance of having you back in this country. The details of these new Professorships were explained in Circulars numbers 5 and 6 of 1962 from the Royal Society. In case your ﬁling system is not such that you can turn these up immediately, let me summarize the most relevant points. The appointments are made for a ﬁve-year period in the ﬁrst instance, but are renewable (and, no doubt, would, in fact, be renewed more or less automatically). The salary is in the range of £3,000 to £3,600. (University salaries are due for review

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and forecasts say that there will be, in one or two years, an increase between 10% and 20%. No doubt if the salaries of University Professors are adjusted, the scale of Royal Society Professors should follow suit). There is, of course, provision for superannuation and for the customary family allowance of £50 per child per year. In addition there is an allowance for the purchase of preprints and money for scientiﬁc, technical and clerical assistance, provided that the total does not exceed £6,250 per annum, and a further sum is available for research expenses. The Professorship can be held at any University in the U.K., subject, of course, to it being acceptable to that University. I have been asked to let the Royal Society Committee know your response to this by 14th January at the latest, and I would therefore be grateful, if you could reply in good time for this. It is clear that no ﬁrm commitment is required at this at this stage, but merely a statement that you might be willing to consider such an oﬀer. If so, it would also be useful to know at what University you would like to hold it, although this, too, does not necessarily have to be ﬁnally settled at this stage. Yours sincerely, R.E. Peierls

[698] Freeman Dyson to Rudolf Peierls Princeton, 21.12.1962 Dear Rudi, Happy Christmas to you and your family! Thank you very much for your letter. I am sorry you had to write it, knowing well that you would get a negative answer. But it is of course a pleasure to receive such a letter, and to know that even as a ɩɨɫɬɚɪɟɥɵɣ ɜɭɧɞɟɪɤɢɧɞ I would not be welcome in my own country. I had read with considerable enthusiasm the Royal Society Circulars describing these new chairs. It seems on the whole a good idea to have these positions scattered around among universities, instead of having them concentrated in Research Institutes as is the custom here (and in

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almost all other countries.). However, a position of this sort is clearly not the right thing for me. So long as I am capable of doing research, I may as well do it here. If ever I decide to leave this Institute, it will be because I grow too old for a research job and wish to move to a place where I have normal teaching and departmental responsibilities. And anyhow, I am not thinking of leaving here during the next few years. Mehta and I just ﬁnished writing the seventh and last of the series of papers on statistics of energy levels.935 It is a relief to have this out of the way. We both worked on the problem for two full years, and we both made a ﬁrm resolution not to work on it anymore. There is lots more to be done, but two years is enough for any one man to spend on it. Now that the energy-level stuﬀ is ﬁnally ﬁnished, I am hoping to return in a serious way to ﬁeld theory and try my hand at clearing up some of the current confusion. During the last week we had a ﬂurry of excitement about the Mandelstam representation. A young man called Kim936 who has been a student of Treiman937 claims to have proved that a certain perturbation theory diagram, viz.

gives a scattering amplitude not representable a` la Mandelstam even in the case of all masses equal. 935

The papers, written by Freeman Dyson (parts 1–3) and jointly by Madan Lal Mehta (parts 4–7) were published in the Journal of Mathematical Physics between 1962 and 1963. 936 Young Suh Kim, graduate student at Princeton 1958–61 under Sam Treiman, since 1962 at the University of Maryland, now as professor of physics. 937 Sam Treiman (1925–1999), obtained his Ph.D. from Chicago in 1952 before joining the Princeton faculty ﬁrst as instructor and later (1963) as professor, being appointed Eugene Higgins Professor of Physics in 1977.

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The experts are not yet agreed that Kim is right, and they are busily trying to check the algebra. To me the question does not seem to be of really crucial importance. But of course the Mandelstamologists are wildly excited, and a hundred Ph.D. theses are at stake. Apart from this recent excitement there is nothing to report in physics. Jost938 gave us an excellent course of lectures in Axiomatic Field Theory which whetted my appetite to do something in this area. But it is strictly a long-term investment. My various children are all ﬂourishing in various ways. George started to play the violin and seems to be quite good at it. Warmest greetings to Genia — Yours ever, Freeman

[699] P.R. Kabir to Rudolf Peierls Pittsburgh, 19.4.1963 Dear Prof. Peierls, A question about which I have been thinking for some time and to which I have not been able to ﬁnd a satisfactory answer is how to deﬁne a resonance, in the sense that it is generally used in high-energy physics nowadays. For two-body collisions, the answer is obviously when the phase-shift goes through π/2, if elastic scattering is the only process energetically possible. But as soon as we allow just one other channel, it seems to me that one has more than one choice. For example, we could say that phase shifts for either of the channels of the diagonalised S-Matrix goes through π/2, in which case each channel of the physical problem would contain a part, both in the scattering cross-section and in the reaction cross-section which would show a resonant behaviour at 938

Res Jost (1918–1990), at the time professor of theoretical physics at the ETH Zurich.

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the resonance energy. On the other hand, if one writes the diagonal element of the S-Matrix for the incident channel as e2i(α+iβ) (x), one is tempted to say that we have resonance when α = π/2. Of course, β also varies with energy and the position of a maximum in the elastic cross-section will also depend on its value; I have tried to examine the dispersion relation for the phase-shift, to see its eﬀect but could not obtain any useful conclusion. The two deﬁnitions I have given above are not equivalent; in fact, neither may be the right one for physical discussions. I shall be very grateful for your comments on this question. The particular question which made me think about this problem was to understand the reported values of the π − π cross section at the δ-energy. If this cross-section is actually only ∼ 6πα2 , and my second deﬁnition is the correct one, the σ2π→4π must be about 40% of the elastic cross-section at that energy. Detection of a δ - peak in 4π distribution would not be easy as in 2π distributions but should not be impossible. Knowing that Professor Yang would be at UCLA this coming summer, I had applied for a summer job there. Recently I came to know that you will also be there so my interest in going to Los Angeles is redoubled. I have not yet been told whether I can go — Professor Finkelstein wrote me that the decision would probably be made in May — but if you should happen to write to him and see ﬁt to put in a word for me, I am certain it would improve my chances greatly. With my deepest regards, Yours sincerely, P.K. Kabir

[700] Rudolf Peierls to P.K. Kabir [Birmingham], 8.5.1963 Dear Kabir, Thank you for your letter which arrived while I was at a Spring School in Italy. As regards the deﬁnition of a resonance in a many channel problem, my own tendency would be to use a deﬁnition in terms of poles on the unphysical sheet (or sheets) of the R[ie]mann surface, as

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discussed in my 1959 paper in the Royal Society.939 In that sense a pole lying close to the real axis, in other words close to the physical sheet, should obviously be interpreted as a resonance, and would correspond to an obvious peak in the cross section. If the pole is further away from the real axis the eﬀect will be less clear, and if it is very far the interpretation as a resonance clearly becomes useless. In other words, if one uses this kind of deﬁnition one has to make an arbitrary limit about the distance from the real axis which one allows. This is true already in a one-channel problem. If in the one-channel problem you base your deﬁnition instead on the condition that the phase should pass through one 12 π one has also to bear in mind that in general the phase will rise steeply, and then get down again, and from that point of view there is no qualitative diﬀerence between a case where it rises to some maximum a little less, and in that respect one is again making an arbitrary distinction. In the many-channel case one could still look for poles on the R[ie]mann surface, and the position would still be as before, except that the structure of the R[ie]mann surface may be more complicated, and also that the arbitrariness would perhaps be more severe. The natural generalisation of the other criterion has been discussed by Mandelstam and he gave a talk on this subject at the last Solvay Conference.940 He suggests that one should look at the eigen phases, i.e. the phases of the elements of the S-Matrix in a representation in which it is diagonal. These are then always real and a resonance would mean that one of them equals one 12 π. This seems to me to be better than your definition, because the diagonal element of the S-Matrix is in general not very signiﬁcant. However, the last two deﬁnitions are clearly equivalent if the oﬀdiagonal elements are small, and this would appear to be true in the case of pion-pion scattering, since in experiments on pion-nucleon scattering 939 R.E. Peierls, ‘Complex Eigenvalues in scattering theory’, Proc. Roy. Soc. A253, 16–36 (1959). 940 The twelfth Solvay Conference on Physics took place in Brussels from 9 to 14 October 1961. The general theme was Field Theory, and Mandelstam gave a paper on the two-dimensional representation of scattering amplitudes.

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in which the resonance shows up, the number of events in which two additional pions appear in the ﬁnal state, is very small. I would suspect that the discrepancy you notice is probably due to poor experimental accuracy in the ππ cross section. I am afraid I shall not be able to go to U.C.L.A. this summer. I had been in correspondence with them, but it had always been made clear that the chances of my coming were very small, and by now they have converged into zero. In the light of this I could not very well bring pressure on them as to whom they should invite, but I hope, of course, that you will manage to get there. [R.E. Peierls] [701] Rudolf Peierls to Tony Skyrme [Birmingham], 6.6.1963 (carbon copy) Dear Tony, I gather that you have had a letter from our Vice Chancellor, and I would like to add some personal comments of my own. You probably know of the principle which is held strongly (and rightly) in university appointments that a departing professor takes no part in the selection of his successor. This does not bar me from writing to you, but clearly makes this letter personal and informal. In the ﬁrst place, I want to say that I welcome the University’s action with enthusiasm, and I would be happy to know that the department would be in good hands. I regard it as very important that a good and strong department should continue here (though not necessarily in exactly its present form) since there is a vast potential of good young people who want to be trained, and in making plans for next year both here and in Oxford we face a diﬃcult choice how to ﬁnd places for all the promising people without overloading the resources of supervisors. The spirit in the department is still excellent. No doubt you know that Mandelstam is also leaving (for reasons not connected with my own departure) and there are other changes, but there remains a core

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of lively and enthusiastic young people, and we have recently ﬁlled two vacant posts with bright young people who were anxious to come in spite of the uncertainly about my successor. I should also say that the amount of administrative chores is rather less than when you last saw the department. I had come to realize that I was doing too much myself, and have deliberately arranged to delegate a number of functions. For example Gerry Field has been given a complete charge of all the undergraduate teaching arrangements, and this has worked excellently (as I knew it would) during the present academic year. This process of delegation can be carried further, but I made only those changes which I could be sure would be welcome to my successor. The university authorities would also be happy to consider more oﬃcial arrangements if they were felt to make the running of the department easier. I shall of course be glad to give more detail on all these points, or to answer any other questions that may be in your mind. It is not possible of course to consult other members of staﬀ at this stage, but several have volunteered the statement that they would be happy to work with you, and I am sure that goes for the others as well. So I shall keep my ﬁngers crossed, and I hope you will take the proposition seriously and ﬁnd it acceptable. With kindest regards to both of you, Yours sincerely, [R.E.Peierls]

[702] Margaret Gowing to Rudolf Peierls London, 27.6.1963 Dear Professor Peierls, I am sending you extracts from a memorandum941 I have received from Sir Henry Dale942 , which deals with the British scientists’ attitudes to 941

Memorandum on Mrs. Gowing’s Draft (Part III), 20.6.1963, Ms.Eng.Misc.b197, A.19. 942 Sir Henry Dale (1875–1968), pharmacologist. President of the Royal Society between 1940 and 1945.

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the use of the ﬁrst bombs against Japan. I have also had a discussion with Sir Henry. I certainly did not intend to convey in my draft any impression that the American scientists had better consciences than their British colleagues and I must certainly do something to remove this idea. But before I do any writing I am adopting the suggestion of Sir Henry himself makes (X on p. 4 of the enclosed paper). I should be very grateful for any considered statement you can make on this point. I realise it is extremely diﬃcult to ask people what their thoughts were twenty years ago (I know I have no real memories of my own thoughts over this stretch of time). And of course I feel bound to take account of the documentary evidence of the day, even though this happens to be of a negative character. For example, in the fairly full records of the two or three meetings of the technical committee in 1944 and 1945, there is no evidence that the use of the bombs was discussed, and as I have shown in the narrative XII, the prime concern of the British was that Britain should have her own stock of bombs as soon as possible. Moreover, in April 1945, a memorandum by Chadwick was submitted to Anderson’s Consultative Council which said inter alia but speciﬁcally that it was certain that bombs would be ready for use by August of that year. There is no evidence that anyone on the Consultative Council raised the question of their use. If you can think back on those days and give me any help on this I would be immensely grateful. Yours sincerely, Margaret Gowing

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9.

1963–1974: Oxford

Having been oﬀered the Wykeham Chair of Physics in 1961, Rudolf Peierls, after lengthy negotiations decided to accept in early 1962 and took up his appointment in the autumn of 1963. When asked about the reasons for his decision to move from Birmingham to Oxford, he would later refer to the need for change after quarter of a century at the same university. But it was more than simply the desire of change. Peierls liked the challenge. After successfully building a school of theoretical physics at Birmingham, he wanted to achieve something similar in Oxford. There, however, Peierls did not begin with a clean slate. Theoretical physics had had a long-standing presence with eminent ﬁgures such as A.E.H. Love, Sydney Chapman, both Seldian Professors of Natural Philosophy, and A.E.H. Milne (Rouse-Ball Professor of Mathematics). In 1945, with the amalgamation of the Electrical and Clarendon Laboratories, the Wykeham Chair had become a professorship of theoretical physics, held by Maurice Pryce until 1955, and after a short period of Victor Weisskopf and Dirk ter Haar as Visiting Professor and Reader respectively, in 1957 Willis Lamb was appointed to the Chair. As a consequence, unlike Peierls’ previous experience at Birmingham, on his arrival at Oxford, he joined a fully functioning set-up with Dirk ter Haar as Reader, Roger Elliot as leader of the theory of solids group, and David Brink guiding the nuclear theorists. Yet, there were also a number of new recruits, such as Dick Dalitz, who came to Oxford as Royal Society Professor, and Leonardo Castillejo who joined the department as lecturer. If Peierls’ role as a senior academic in the United Kingdom had already undergone some changes towards the end of his time at Birmingham, this change became even more pronounced during the last decade

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of his university career at Oxford. It is visible not merely in his publications but also in his correspondence as his exchange of letters with Nevill Mott shows. Nevill Mott, whom Peierls had ﬁrst met at Cambridge in 1933, had taken up a professorship at Bristol in the same year but returned to Cambridge in 1954 to become Cavendish Professor there, a title held until his retirement in 1971. Peierls and Mott had corresponded with some regularity over the decades, and while in earlier years much of their communications was taken up by research questions, in later years, in addition to their ongoing scientiﬁc work,943 they were more concerned with university administration, teaching reform and, increasingly frequently, their work for nuclear disarmament. In the letters throughout the 1960s and 1970s, they discussed questions ranging from optimising journal publications944 to the organisation of summer schools for graduate students.945 The key question for Peierls in most of these exchanges was how to best serve the progress of physics, be it in providing the best possible research environment, creating a viable framework for the dissemination of ideas and results through eﬀective publications, organising eﬃcient undergraduate teaching or be it in setting up university structures which allowed high-level training for graduates. All this could only be achieved, if the best scientists could be persuaded to remain in the UK and to devote their professional lives to research and training of a new generation of scientists. Being part of an outspoken trade union, was one way bringing inﬂuence to bear with this aim in mind. However, Peierls did not always agree with his union’s approach to change in higher education, and while Peierls was generally known to be a quiet and at times almost shy person, he did not hold back expressing an opinion, whenever he felt it would serve a useful purpose. One such occasion was his reaction to a ballot paper circulated by his union, the A.U.T., about direct action (in the form of strikes) proposed by the union as part of salary negotiations. In a letter to the General Secretary of the AUT, Peierls argued that short-term strikes were empty and costly 943

See letters [715–717]. Letter [706]. 945 Letters [720]. 944

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gestures only, with no eﬀect on government; that long-term strikes would hurt, above all, the students and therefore were unsuitable as a means of pushing staﬀ demands. In Peierls’ view the only appropriate action would be for university teachers to threaten to accept reasonable job oﬀers from abroad, if their grievances were not addressed.946 The letter is in many respects typical of Rudolf Peierls’ approach to solving administrative or political problems. He was a ﬁrm believer in the theory that action should be taken only if it had a reasonable chance of achieving something positive; and any such action should not be taken at other people’s expense. Peierls was selective in what good causes he lent his name to and in which cases he would use his own reputation and standing. Just as he had tried to use his inﬂuence to best eﬀect in supporting prosecuted friends in Russia under Stalin947 and as he had asked Niels Bohr to utilise his reputation to encourage scientiﬁc exchange with Russia in the post-Stalin era, he was equally robust in his explanations to Max Born of his reasons for not supporting the Jews in the Arab-Israeli conﬂict.948 He approached these kinds of problems as optimization problems. However, it was not his own personal gain which had to be maximised — he was quite prepared to make personal sacriﬁces in order to promote a cause which he regarded worth ﬁghting for, an attitude which he had already shown in his support of Oppenheimer,949 his memorandum on dealings with German scientists950 and the comments in the aftermath of the Fuchs arrest.951 Like Peierls, many of his friends and colleagues from student and research fellow days had moved into highly respected positions in prestigious universities and research institutes across the world. Their contributions to science were marked on occasions of signiﬁcant birthdays, and increasingly also retirement or death. Peierls was often asked for advice, information, or anecdotes about his friends and former colleagues. 946

Letter [723]. See Lee, Selected Correspondence, Vol. 1, pp. 524–26. 948 Letter [458–460]. 949 Letters [597], [601]. 950 Item [440]. 951 Item [500]. 947

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Among others, he wrote obituaries or recollections of Pauli, Bohr, Skinner, Oppenheimer, Heisenberg, Frisch, Dirac, Landau, Penney, Chadwick, Bell, Wiener, von Neumann and Bhabba, Tamm and Frenkel. And often he contributed recollections to collections edited by others, such as a volume edited by Richard Eden, to whom he replied at some length about his recollections of Dirac, a notoriously private person.952 His observations were astute, and the clarity of his reminiscences and his willingness to concede gaps and possible inaccuracies in his memories, made him one of the key witnesses, when historians of science were attempting to reconstruct the development of 20th century physics.953 Peierls’ knowledge of this period of rapid scientiﬁc progress and in particular his assessment of the development of nuclear weapons was in great demand in scientiﬁc publications, but increasingly, the subject was also discovered by the media. Radio programmes were broadcast, and tv documentaries produced, and his advice was thought on numerous of these.954 Among the more controversial productions was the BBC’s programme The Building of the Bomb, for which Peierls had recorded an interview. Although his interview was not used when the programme was screened in 1965, Peierls was disturbed by the inaccuracies of programme as a whole, and he took up the issue with the Director-General of the BBC, Sir Hugh Carlton Greene.955 Moreover, when the BBC and their producer R. Reid, planned a similar programme on the history of the H-bomb, Peierls warned his old friend Hans Bethe and thereby led to a more cautious co-operation of American colleagues with the BBC.956 Peierls’ publications in the 1960s and 1970s mirror the impression conveyed by his correspondence. Among his publications one ﬁnds those of general conceptional or explanatory kind, such as his writings on 952

Letter [725]. See also letter [738] and chapters 10 and 11. 954 Peierls helped with several programmes including BBC TV’s Series on Quantum Physics (1963), Ethical Responsibility (1964), BBC Radio’s The Bomb (1962), Growing Points in Physics (1966–67), A Fable in his Life Time — Paul Dirac (1972), NBC’s The Decision to Drop the Atomic Bomb (1964), ABC’s The Struggle for Peace (1966), CBC’s On Klaus Fuchs (1973). 955 Peierls Papers, Ms.Eng.misc.b219, D.23. 956 Letter [711]. 953

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the ‘laws of physics’,957 the development of quantum theory,958 nuclear matter,959 or Fermi-Dirac statistics;960 those of political content such as contributions in the Pugwash context,961 works on the relationship between science and politics,962 or, indeed, biographical contributions.963 Evidently, Peierls’ research had undergone a gradual change which had already been visible in his ﬁnal years at Birmingham and which accelerated during his time at Oxford. He had been among the outstanding ﬁgures of the last generation of universalists in physics, and unlike many of his colleagues of this generation, he refused to choose one narrow ﬁeld as a focal point of his attention and instead tried to keep his interests broad. The increasingly rapid pace of developments in subject areas such as particle physics made it diﬃcult to keep up with the trends in the discipline for anybody keen on dividing his attention between diﬀerent specialisations. In addition, Peierls felt that his age was beginning to

957

R.E. Peierls, ‘Wo stehen wir in der Kenntnis der Naturgesetze?’ Phys. Bl. 19, 533–39 (1963). 958 R.E. Peierls, ‘The Development of Quantum Field Theory’, The Physicist’s Conception of Nature (ed. J. Mehra), Boston: Reidel, 1973, pp. 370–79; R.E. Peierls, ‘An Examination of the quantum jumps in the growth of quantum mechanics’, Sci. American 216(1), 137–140 (1967). 959 R.E. Peierls, ‘Nuclear Matter’, Endeavour 22, 146–150 (1963). 960 R.E. Peierls, ‘Fermi-Dirac Statistics’, Aspects of Quantum Theory (A. Salam and E.P. Wigner eds.), Cambridge: CUP, 1972, 117–127. 961 R.E. Peierls, ‘Problems of Collective Security’, Proc. 13th Pugwash Conference, London: Francis & Taylor, 1964, pp. 259–264; R.E. Peierls, A possible use of “black boxes” in connection with a comprehensive test ban’, Proc. 16th Pugwash Conference, London: Francis & Taylor, 1966, p. 272; R.E. Peierls and C.F. Powell, ‘Pugwash and the World’ Proc. 18th Pugwash Conference, London: Francis & Taylor, 1968, pp. 209–212; R.E. Peierls, ‘Britain in the atomic age’, Bull. Atomic Sci. 26 June 1970, 40–46; R.E. Peierls, ‘A Ban on the Development of New Weapons?’ Proc. 19th Pugwash Conference, London: Francis & Taylor, 1970, pp. 280–283; R.E. Peierls, ‘International Aspects of the Pollution Problem’ Proc. 21st Pugwash Conference, London: Francis & Taylor, 1971, pp. 294–303. 962 R.E. Peierls, ‘The scientist in public aﬀairs: between ivory tower and the arena’, Bull. Atomic. Sci. 25 November 1969, 28–30; R.E. Peierls, ‘Physicists and politics’, The Times Lit. Suppl. 18.12.1969, 1442. 963 R.E. Peierls, ‘Lev. D. Landau’, Phys. Bull. 19, 147 (1968); R.E. Peierls, ‘J. Robert Oppenheimer’, Dict. Sci. Bio. (Sr. Ed. C. C. Gilliespie), 10, 213–218, New York: Scribner, 1974.

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make itself shown by the speed with which he was capable of picking up and utilising other people’s ideas and concepts.964 He still exchanged ideas with colleagues and former students and facilitated information transfer, but he did not feel able to contribute anything original to the subdiscipline. One such example is his correspondence with Prabahan Kabir, an Indian research fellow who had come to Birmingham from Cornell and later became professor at Virginia. An exchange of letters with Kabir965 encouraged Peierls to contact his old colleague and expert in the ﬁeld, Harold Urey with a query about elementary particles, in particular quarks.966 Peierls’ letter to Urey in November 1965 is interesting as an indicator of Peierls’ role at Oxford. ‘In our discussions about elementary particles,’ he writes, ‘we have run up against a problem which seems to me very interesting, but very hard. ... I am writing to ask for your views and, if possible, for your advice.’ After describing some aspect of the quark hypothesis, he adds: ‘In this letter I have only summarised the results of conversations with Dr P.K. Kabir, who raised this question with me in the ﬁrst place.’967 Peierls evidently still followed developments in elementary particle physics, but he saw himself as a facilitator of dialogue more than an active participant who gave the signiﬁcant impetus himself. This was a marked diﬀerence from his approach a decade earlier when he had determined the direction of a lot of the ﬁeld theoretical and nuclear physics research at Birmingham himself. Developments in other areas were less rapid at the conceptual level, if similarly spectacular with regard to the growing complexity of ever more sophisticated mathematical techniques needed to move forward e.g. in condensed-matter physics. In this ﬁeld, Peierls continued to supervise students and publish himself, for example on transport theory.968 If one area crystallised as the focal point of Peierls’ research it was nuclear

964

Peierls, Bird of Passage, p. 304. See Peierls Papers, Ms.Eng.misc.b210, K163. 966 Letters [712]. 967 Letter [713]. 968 R.E. Peierls, ‘Some Simple Remarks on the Basis of Transport Theory’, Transport Phenomena (eds. G. Kirczenow and J. Marro), Berlin: Springer, 1974, 1–33. 965

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theory. Peierls still supervised a signiﬁcant number of graduate students and he published, often with David Brink, Lecturer and later Reader in the theory department with whom he collaborated on a number of papers on nuclear structures.969 Correspondence with Christian Møller highlights another feature of Peierls’ research. He occasionally returned to old unsolved research problems that he had been working on in the past. One such problem was the question of momentum of light in a refractive medium, about which there had been a controversy among physicists since 1909 when Minkowski and Abraham had published their contrasting views.970 Møller had commented on the question in his book on relativity,971 but had left open the question whether he agreed with Minkowski or Abraham. Peierls and his student Michael Burt tackled the subject and published a joint paper in which they concluded — wrongly — that Abraham was correct.972 In 1976, Peierls corrected the errors973 and many years into his retirement, in 1985, he published what he later described as ‘what I hope is the last word on the subject’.974

969

R.E. Peierls and D. Brink, ‘Nuclear Structure and realistic forces’, Comments Nucl. & Part. Phys. 1, 32–35 (1967); R.E. Peierls and D. Brink, ‘Calculation of nuclear reaction matrix elements’, Comments Nucl. & Part. Phys. 1, 66–68 (1967); R.E. Peierls and D. Brink, ‘Calculation of nuclear structure directly from two-nucleon phase shifts’, Comments Nucl. & Part. Phys. 1, 146–50 (1967); R.E. Peierls and D. Brink, ‘Calculations with phenomenological forces’, Comments Nucl. & Part. Phys. 1, 32–35 (1967); R.E. Peierls and D. Brink, ‘A realistic Thomas-Fermi approach to ﬁnite nuclei’, Comments Nucl. & Part. Phys. 2, 28–32 (1968); R.E. Peierls and D. Brink, ‘The three-nucleon bound state’, Comments Nucl. & Part. Phys. 2, 92–96 (1968); R.E. Peierls and D. Brink, ‘Isobaric spin and dipole states’, Comments Nucl. & Part. Phys. 2, 180–181 (1968). 970 H. Minkoswski, Math. Ann. 68, 472 (1910); and H. Minkowski, ‘Die Grundgleichungen f¨ ur elektromagnetische Vorg¨ ange in bewegten K¨ orpern’, Nachr. Ges. Wiss. G¨ ottingen 1908, 53; M. Abraham, ‘Zur Elektrodynamik bewegter K¨ orper’, Rc. Circ. Mat. Palermo 28, 1 (1909); M. Abraham, Rc. Circ. Mat. Palermo 30, 33 (1910). 971 Ch. Møller, Theory of Relativity, Oxford: Clarendon, 1964. 972 M.G. Burt and R.E. Peierls, ‘The momentum of a light wave in a refracting medium’, Proc. Roy. Soc. A333, 149–156 (1973). See also letter [742]. 973 R.E. Peierls, ‘The momentum of light in a refracting medium’, Proc. Roy. Soc. A347, 475–91 (1976). 974 Peierls, Bird of Passage, p. 305.

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Rudolf and Genia Peierls had always enjoyed leading a nomadic existence, and during their Oxford years, both before and during retirement, they continued travelling large parts of the world. The longest period away was a sabbatical in the US in 1967. Peierls revived his contacts with the University of Washington in Seattle, which he had visited for a summer workshop in 1962 and in 1967 he spent six months there as a visiting professor. His two previous long-term absences from his permanent employer, then Birmingham University, his sabbaticals at Princeton in 1952 and Columbia in 1959 had initiated elaborate correspondence with this colleagues ‘at home’. In 1967, this was far less pronounced. At Oxford, he was far less involved in the day-to-day running of the department and in particular in teaching of both undergraduates and graduate students. Although he communicated with Dirk ter Haar throughout the period of his leave,975 the exchange was nothing like the lively debates that had taken place with Dalitz and Brown in earlier years.976 While on the other side of the Atlantic, Peierls not only visited some of his children who had by then settled in the US,977 but he also attended the New York meeting of the American Physical Society, where he met many of his old friends and colleagues, not least Hans Bethe.978 The trip to Seattle also gave Peierls the opportunity to revisit a problem on which he had worked on in the late 1930s. At a symposium on dislocations at Seattle, he discovered, much to his surprise, that a paper in which he had discussed a simple model suggested by Egon Orowan of the structure of an edge dislocation979 had become a classic in this research ﬁeld. Peierls’ student, Frank Nabarro later extended the argument and corrected a major algebraic error in Peierls’ original paper,980 and the phenomenon became widely known as the Peierls-Nabarro force. 975

Peierls Papers, Ms.Eng.misc.b207, C.128. See chapters 7 and 8. 977 The three older Peierls children, Gaby, Ronnie and Kitty had settled in North America. 978 Letters [718–719]. 979 R.E. Peierls, ‘The size of a dislocation’, Proc. Phys. Soc. 52, 34–37 (1940). 980 F.R.N. Nabarro, ‘Dislocations in a simple cubic lattice’, Proc. Phys. Soc. 59, 256–72 (1947). 976

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In 1967, his close friend Robert Oppenheimer had died of throat cancer, and Rudolf Peierls wrote several obituaries. He also supported Oppenheimer’s wife Kitty, when she decided, with the help of Robert Serber, Oppenheimer’s long-time assistant and friend, to write a book about her husband in the early 1970s.981 Rudolf Peierls and Hans Bethe had been in continuous correspondence since their student days in Munich in the 1920s. The ﬂow of letters was only interrupted at periods when both worked and lived at the same location as in Manchester in 1933/34 or at Los Alamos during the Second World War. Several times, one or the other would try to convince the friend on the other side of the Atlantic to join him for a prolonged period of work together, for instance in the early 1960s, when Peierls approached Bethe to come to Birmingham as visiting professor in the gap year between his departure and his successor’s arrival. Similarly, in the early 1970s, Peierls invited him to join the physics department at Oxford.982 As on previous occasions, tempting as Bethe found the oﬀer, he declined, as he tended to use his sabbatical leaves travelling to various places, this time to Seattle, Copenhagen and Munich.983 Rudolf Peierls had lost contact with a number of his own friends and family friends from his Berlin days during and after the war. Obersch¨oneweide, the Berlin suburb where Peierls had grown up, was in the Eastern part of the city which, during the Cold War, was cut oﬀ from the West, and so contacts were even more diﬃcult than they were with those friends who had settled in West Germany. However, some of the contacts survived or were revived, often as the result of Peierls’ name going through the national and international press as a result of receiving an award, an honorary doctorate, a medal or the knighthood in 1968. One such incident occurred in November 1963, when Peierls received a letter from Maud Juliusberg. She was the wife of a good friend of his from school, and he speedily replied reminiscing about his days as a young boy in Berlin.984 Similarly, in 1974 he reestablished 981

Letters [733–34]. Letter [735]. 983 Letter [736]. 984 Letters [707–08]. 982

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links with Franz Jacobsohn, a childhood friend whom he had last seen in 1953985 and the two remained in contact until Jacobsohn’s death in 1986, exchanging letters and visits.986

985 986

Peierls, Bird of Passage, p. 14. Letter [743].

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[703] Rudolf Peierls to Margaret Gowing [Oxford], 23.8.1963 (carbon copy) Dear Mrs. Gowing, Please forgive the inordinate delay in my replying to your letter of 27th June in which you asked for comments about the thoughts of British scientists about the use of atomic bombs.987 I had to try and reconstruct my recollections which, as you say yourself, is very diﬃcult, and before I could do so I got caught up in my move to Oxford. I certainly agree with Sir Henry Dale that, in general, British scientists were not in a position to inﬂuence the tests. Of those who were at the time in this country, most did not know what the acute problems were or they did not even know how close the project was to completion. The group in Los Alamos certainly did know that others were getting ready for operational use. We were fully informed about all technical matters but not of anything of strategic relevance; such a knowledge was conﬁned to very few individuals and they were all American. This, however, does no mean that we had no views on the matter. In trying to say what were my own views at the time I ﬁnd it diﬃcult to keep these separate from thoughts that have come to me or have clariﬁed themselves in the intervening period, but I shall try to summarize my thoughts at the time as well as I can. I certainly realised, as did all of us who had the information, the enormous importance of using it for the long-term good of humanity and for eliminating war. This made it obvious that the Allies who, at that time, had a monopoly of this weapon, would not try to use it to gain world domination but should make it available to international agencies in the interests of a peaceful and orderly world. I did write in a memorandum about this a little later,988 just after the end of the war, at a time when Attlee and others were visiting Washington, and I sent this to Anderson in the hope that it might be of some use in the discussions which were then taking place. 987 988

Letter [702]. National Archives (NA): Public Record Oﬃce (PRO)/CAB 126/1.

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I have no copy of this memorandum and I do not know whether it even reached Anderson. I suspect if one read this memorandum now, it would sound terribly naive. Like many of the other people I certainly had no idea at the time of the diﬃculties in getting international agreement on such matters, which became so painfully clear later on. However, it was not as clear to me as it evidently was to Sir Henry Dale that the Allies ought to forego any use of the new weapon for ending the war. To understand this one must remember that none of us realised how close Japan was to collapse at the time. We were not told that the date for the invasion of Japan was set and could not be altered (looking back this sounds surprising but it is probably true that the people who knew of the new weapon did not, in fact, have the possibility of interfering with the progress of the military machine unless they brought the war to an end by the use of an atomic bomb. Evidently, an invasion of Japan would have been extremely costly and probably would have destroyed more Japanese lives than did the use of the bombs. The war was still going on; there was ﬁghting and attacks on cities, including the famous ﬁre-raid on Tokyo which caused more casualties than either of the atom bomb raids. It was clear to us that to drop an atomic bomb once one had one was a very easy thing to do and might therefore be done lightheartedly and wastefully. I remember thinking that the most desirable action would be to drop an atomic bomb on some uninhabited place for demonstration and then ask for a Japanese surrender. I do not believe that a mere statement that such a weapon was available without a demonstration would have had any eﬀect; it could so easily have been considered a bluﬀ. I remember some discussions on this point, though I could not say whether they took place before or after the event. In these it was pointed out that a demonstration might be ineﬀective, because, for example, in the tests in New Mexico there was nothing to show what had taken place unless one had the readings of the instruments, or could interpret the signiﬁcance of the large area of glass where the sand had been fused by the intense heat. There was no crater there, as would be caused by high explosive. This, of course, was in the desert. A demonstration over a

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forest area might have been more eﬀective; one over a region containing at least a few houses would certainly have been more eﬀective, even if the houses had been uninhabited, but it would not have been easy to ﬁnd a target where there were houses but no people. It might have been necessary to choose an area which had some population and therefore to cause casualties though, of course, not on the scale of a raid on a city. Basically our attitude was that we did not know the facts about the war situation or about the needs and that this was a policy decision to be taken by the statesmen and the military leaders. We felt that we should trust them to take this decision in a responsible spirit. Looking back I feel that this conﬁdence was excessive — not in the goodwill of the leaders, but in their imagination and their power of understanding an entirely unprecedented situation. It was also clear to us that for taking the right decision the Authorities had to understand fully the nature of the new weapon. We had never any doubt that they did for two reasons: in the ﬁrst place we trusted our senior American colleagues, including such men as Oppenheimer, to transmit the technical facts with suﬃcient clarity; secondly, it was unbelievable that a government who would have backed a project costing two thousand million dollars and a vast amount of scarce resources and manpower would do so without realising the nature of the result it was intended to produce. I still believe that the basic scientiﬁc facts were known and appreciated. It must also be remembered that the scientiﬁc staﬀ at Los Alamos had worked extremely hard to carry out a very diﬃcult project an it is not surprising that part of the reaction to the ﬁrst use of the atomic bombs included a feeling of pride that their achievement should have succeeded in ending the war, and of elation. I did notice that for many people there, both British and American, the ﬁrst reaction to the news was an enthusiastic cheer as to any victory in battle in which one has played a part, and I must admit to having a little of this feeling myself at the time. This is as near as I can get to a summary. If you would like me to elaborate on any particular points I shall try to do so. Yours sincerely, R.E. Peierls

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[704] Margaret Gowing to Rudolf Peierls London, 29.8.1963 Dear Professor Peierls Thank you very much indeed for your letter and all its reﬂections, which help a good deal. Somewhat to my surprise, the book989 has got over the oﬃcial hurdles pretty easily and has now gone to Macmillans, so I hope it will appear in 1964. May I repeat my plea for photos, especially of people, if you have any? I have collected a few but would welcome more — of you and Frisch together, of your Birmingham group, or of the Los Alamos British people (including anything recognisable from the English farewell party and play). Incidentally, in a recent letter Oliphant says: “The British did not owe their interest in slow neutron piles to the French. Frisch had the idea of the heterogeneous reactor early in 1940, and it was elaborated by Peierls. What Halban and Kowarski brought was the value of heavy water as a moderator.” Is this true as far as you and Frisch are concerned? I am pretty clear from the documents that although a lot of people knew about slow neutron reactions the U.K. would never have pursued the business during the war if it had not been for the French. I should like to repeat my thanks for all the help you have given me in the writing of this book, and also to wish you a happy life at Oxford. Yours sincerely, Margaret Gowing

989

See letter [687], note 917.

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[705] Rudolf Peierls to Margaret Gowing [Oxford], 20.9.1963 (carbon copy) Dear Mrs. Gowing, Your letter of 29th August arrived here while I was in Yugoslavia.990 I am very glad to hear that your book has been cleared for publication so quickly, and I am looking forward to seeing it in print before long. I have very little in the way of pictures, if any, but I shall have another check and let you have within the next week or so anything relevant I ﬁnd. On the point arising from Oliphant’s letter I have no recollection of Frisch suggesting the idea of the heterogeneous reactor though it is quite possible that this may be correct and that either I have forgotten such a discussion completely or that Frisch never happened to mention it to me. No doubt Frisch himself would remember. However, I certainly did not elaborate the idea. I was aware of the point from an American report written, I believe, by Fisk991 and somebody else. This was brought by Fisk on a visit to this country — I should think during 1940, though I may be wrong in the date, and I had a copy of it for some time; this was a general review of the reactor problem and mentioned the heterogeneous reactor and the arguments for it. I spent a little time convincing myself that the arguments were sensible and I probably discussed the idea with Oliphant but I myself made no contribution. Later, when Halban and his colleague arrived, we found that they had thought of the possibility independently. I do not think, however, that in the minds of the British scientists this idea was at all crucial at the time. It must be remembered that it was by no means clear that critical conditions could be obtained in a natural uranium reactor 990

Letter [704]. Charles Brenton Fisk (1925–83), had worked on the Manhattan Project before completing a physics and engineering degree at Harvard in 1949. He later switched his studies to music and became an accomplished organ builder. 991

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with a graphite moderator. Nobody knew at the time the absorption of pur[e] graphite for slow neutrons. Commercial graphite at the time would have been hopeless and it was a very hard problem to discover how much absorption was due to impurities, and it took a very great eﬀort on the part of Fermi and his collaborators to show that it was even probably that a reactor with natural uranium and graphite could be made. It seemed much more certain that heavy water would be a possible moderator and its absorption was known to be so small that it would not be necessary to go to a heterogeneous system though this might still be done for practical convenience. The decision of Halban’s group was to concentrate on heavy water so as to avoid the uncertainties and diﬃculties involved in a graphite project in spite of the cost of producing heavy water. I do not believe that anyone questioned this decision here at the time. I myself always regarded a reactor as a long-term project of no immediate military importance until the idea came up of using a reactor to produce plutonium. This view was shared fairly generally and I do not believe that without the appearance of the French team any work would have been done in this country even though the idea of the heterogeneous reactor was certainly known. Yours sincerely R.E. Peierls

[706] Rudolf Peierls to Nevill Mott [Oxford], 1.11.1963 (carbon copy) Dear Nevill, I do agree that it would be very desirable to do something about physics publications in this country, and I would be all in favour of your discussing the matter with Hodge, if you are willing to do so.

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I have for some time been disturbed by the growing tendency of physicists abroad to ignore papers published in this country, and consequently a tendency for authors to send their papers for publication abroad. For example, I ﬁnd that in many university departments in the United States the Royal Society Proceedings are not in the departmental library though they would generally be found in some university library, and that even when they are there people do not look at them. In other places one ﬁnds that the Physical Society Proceedings are not available. The basic reason is, in my opinion, the wide spread of subject matter in the Royal Society Proceedings, as a result of which a physicist will usually ﬁnd that there is at most one paper in each issue that he can understand. As one possible remedy I suggested a few years ago that Section A of the Proceedings might be further sub-divided; with the present amount of material in it this could easily be done without unduly delaying publication It still seems to me that this would be one sensible solution, though it raises problems as regards subscription rates for the whole or parts of the present Section A; this proposal, however, was turned down by the Oﬃcers without consulting Council. Incidentally, I raised at the same time the suggestions that the Proceedings be made available to bona ﬁde scientists for their personal use at a lower subscription rating, amounting to a little more than the marginal cost; everybody thought that this was a good idea and would be quite feasible, but nothing has been done. As regards the Physical Society Proceedings there are, I think, two reasons why people abroad do not pay enough attention to them. One is that the Royal Society Publications do still carry a higher prestige so that many authors who have papers they regard as exciting or important, will try to get them into the Royal Society Proceedings, and this gives the Physical Society Proceedings some of the ﬂavour of a journal for the second best papers. If somehow one could achieve a combination of both journals more attention would come from physicists abroad and, in turn, this would attract some of the good papers now published in foreign journals.

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If the facts are in doubt it might be worth collecting some statistics about the number of papers from laboratories in this country being published abroad, excluding papers that are being sent to certain journals for special reasons (e.g. as part of a series or as containing comments on papers published there previously). Yours sincerely, R.E. Peierls

[707] Maud Juliusberg992 to Rudolf Peierls Berlin, 9.11.1963 Lieber Herr Peierls! Sie werden sich gewiß wundern, wer Ihnen heute einen Brief schreibt! Ich weiß nicht, ob Sie sich noch an die Familie Juliusberg aus Obersch¨oneweide erinnern, wenn es auch sehr lange her ist. Ich las mit sehr großem Interesse von Ihren sch¨onen Erfolgen und daß Sie ein ber¨ uhmter Mann geworden sind, wozu ich Ihnen herzlich gratuliere. F¨ ur mich bleiben Sie immer noch Rudi Peierls, der Freund meines vor vor 5 Jahren so fr¨ uh verstorbenen Heinz. Er bekam ganz pl¨ otzlich Lungenkrebs und hinterließ seine Frau und seinen sehr begabten und t¨ uchtigen Jungen und ein Jahr darauf starb mein zweiter Sohn Wolfgang, der große Betriebe in K¨ oln und Bonn aufgebaut hatte (B¨ ussing Betriebe), wobei er sich kaputt gemacht hatte. Nun habe ich noch meinen j¨ ungsten Sohn, der Ingenieur bei der Hochbahn in Hamburg ist, leider unverheiratet aber meine ganze Freude. Mein Mann starb vor 8 Jahren, fast achzigj¨ ahrig. Wir hatten die b¨ ose Hitlerzeit u ¨berstanden wenngleich mein Mann seine Stellung bei der AEG, seine Pension, und sein kleines Verm¨ogen verlor. Dann ganz ausgebombt bekamen wir eine kleine Wohnung im sch¨ onsten Vorort von Berlin Zehlendorf, ganz im Gr¨ unen, und mein Mann hat noch 10 sch¨ one Jahre hier verlebt. Nun 992

The Juliusberg family were neighbours in Obersch¨ oneweide. Maud’s husband worked in the AEG factory of which Heinrich Peierls had been director. Her son Heinz was a good friend of Rudolf Peierls’, when they were school age.

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habe ich Ihnen unsere sp¨ atere Lebensgeschichte erz¨ahlt und ich w¨ urde mich sehr freuen, wenn Sie Zeit h¨ atten und Sie w¨ urden mir u ¨ber Ihre Familie berichten. Sind Sie verheiratet, haben Sie Kinder? Ist Alfred verheiratet mit Kindern, und wie geht es Anni mit Familie in Amerika? Erinnern Sie sich noch, dass Sie mal in den Sommerferien mit mir und meinen Kindern in Schwartau bei L¨ ubeck waren, als Ihre liebe Mutter schon sehr krank war? Das ist ein langer Brief geworden, ich hoﬀe, ich habe Sie in Ihrer kostbaren Zeit nicht sehr gelangweilt! Seien Sie in aller Frendschaft herzlich gegr¨ ußt

von Ihrer Maud Julisberg

[708] Rudolf Peierls to Maud Juliusberg [Oxford], 23.11.1963 (carbon copy) Liebe Frau Juliusberg, das war eine sehr große Freude, von Ihnen einen Brief zu bekommen. Ich bin schon sehr vergesslich, aber nicht so sehr dass ich mich nicht mehr an Ihre Familie erinnern sollte. Nat¨ urlich erinnere ich mich noch an die Ferien bei L¨ ubeck, kurz vor (oder nach?) dem Tode meiner Mutter. Ein Nachmittag w¨ ahrend des ersten Weltkrieges ist mir auch noch sehr klar im Ged¨ achtnis. Ein Feuer im Kabelwerk n¨ aherte sich einem Munitionslager, und die erwartete Explosion gef¨ ahrdete unser Haus. Ich wurde daher in Ihre Wohnung geschickt, und dort wie u ¨blich sehr gastfreundlich empfangen. Meine Familie blieb ruhig zu Hause. Aber dann bekam ich pl¨ otzlich grosse Angst und Sie mussten sich sehr bem¨ uhen, mich zu beruhigen. Es tut mir sehr leid, von dem so verfr¨ uhten Tode von Heinz, und seines Bruders zu h¨oren. Im ganzen hat Ihnen oﬀenbar das Schicksal das Leben nicht leicht gemacht, und trotzdem kann man zwischen den Zeilen Ihres Briefes noch immer die Lebensfreude erkennen, an die ich mich noch von der alten Zeit so gut erinnere.

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Sie fragen, wie es uns ergangen ist. Ich studierte an mehreren Universit¨ aten: Berlin, M¨ unchen, Leizpig, und dann an der Technischen Hochschule in Z¨ urich. Dort blieb ich dann noch f¨ ur drei Jahre als Assistent eines der gr¨ ossten Physiker unserer Generation. Auf einer Reise zu einer Tagung in Russland lernte ich eine Russin kennen, die ich bei meinem n¨achsten Besuch ein halbes Jahr sp¨ ater geheiratet habe. Dann musste sie in Russland zur¨ uckbleiben, und wir wussten nicht, ob ich wieder das Visum bekommen werde, um nach Russland zur¨ uckzufahren, oder ob meine Frau die Erlaubnis bekommen w¨ urde, mir nachzukommen. Aber nach sechs Monaten war ich wieder dort und wir konnten beide in die Schweiz gehen. Anfang 33 war ich mit einem RockefellerStipendium in England, und beschloss hierzubleiben. 1937 hatte ich dann das grosse Gl¨ uck, eine Professur in Birmingham zu bekommen, und ich bin dort bis jetzt geblieben; aber 26 Jahre in einer Stelle ist schon sehr lange, und ich habe jetzt gerade eine Stelle in Oxford angenommen. Vor dem Kriege hatten wir zwei Kinder, eine Tochter und einen Sohn. Als wir 1940 erwarteten, dass die Nazis bald England erobern w¨ urden, schickten wir die Kinder nach Kanada, wo sie mit anderen Kindern von englischen Universit¨ atslehrern von kanadischen Universit¨aten eingeladen worden waren. Sp¨ ater hatte ich mit der Entwicklung der Atomenergie zu tun, und 1943 wurden wir nach Amerika geschickt, um mit den Amerikanern dar¨ uber zusammen zu arbeiten. 1946 kehrten wir dann nach England, und zur rein akademischen Forschung zur¨ uck. Wir hatten dann noch zwei T¨ ochter, die jetzt 14 und 15 sind. Die grossen Kinder sind schon ganz erwachsen, und leben beide in Amerika. Mein Sohn ist auch theoretischer Physiker, und hat einen Jungen von zwei Jahren. Meine Tochter hat ein kleines M¨adchen. Alfred lebt auch in England. Er heiratete noch in Berlin ein Russin (das scheint eine Familienkrankheit zu sein), und hat seit etwa 1935 eine Stellung bei einer Telefonfabrik in der N¨ ahe von London. Er hat keine Kinder, aber seine Frau hat eine Tochter aus erster Ehe, an der er sehr h¨ angt. Annie geht es auch gut. Sie und ihr Mann leben noch immer in demselben Haus bei New York, in das sie bei ihrer Ankunft in 1936 eingezogen sind. Ihre Kinder sind nat¨ urlich schon von zu Hause weg,

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und zwei Nichten ihres Mannes, die Annie viele Jahre erzogen hat, sind auch schon verheiratet. Mein Vater verliess Deutschland erst in 1939, und nach einer kurzen Zeit in England ging er nach Amerika, wo er in der N¨ ahe von Annie wohnte. Er war dann schon nicht mehr sehr gesund, und er konnte sich nicht mehr an die neue Sprache, und das andere Leben gew¨ ohnen. Er starb in 1945. Else, seine zweite Frau, die Sie wohl auch kannten, starb vor einigen Jahren. Ich habe nicht mehr sehr viel von alten Obersch¨oneweidern gesehen, aber jetzt bekam ich einige sehr nette Briefe von fr¨ uheren Mitsch¨ ulern, und einen von Klaus Thomsen, dem Sohn unseres Hausarztes, den Sie sicher auch kannten. Eine andere interessante Verbindung ist dass Frau Professor Goeppert-Mayer, eine Physikerin, die gerade vor ein paar Wochen als Nobelpreistr¨agerin in den Zeitungen erschien, und die ich gut kenne, eine Verwandte der Familie Haberstamm ist, und daher als junges M¨ adchen oft in Obersch¨ oneweide war. Nochmals vielen Dank f¨ ur Ihren Brief und herzliche Gr¨ usse. Ihr [Rudi] [709] Rudolf Peierls to Alexander Dorozynski Oxford, 7.2.1965 (carbon copy) Dear Mr. Dorozynski, Last summer you sent to my wife a section of the typescript of your book about Landau,993 and requested her comments. She found it very diﬃcult to reply, because the picture that emerged of the early days bore little resemblance to the facts. There were a number of actual errors, but in addition the whole picture did not really come out right. It was clear that you had tried very hard to assemble the facts, but it is very hard to re-create an atmosphere from a few conversations. We discussed what to do, whether to point out to you only the factual mistakes, or to 993

Alexandre Dorozynski, The Man They Wouldn’t Let Die, New York: Macmillan, 1965.

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attempt to suggest improvements in a more general way and as a result we put oﬀ writing. We have now had an opportunity of seeing the galley proofs of the book, and ﬁnd, in addition to the errors we have already seen, many more serious mistakes in other parts. I do not know how far the production process has gone, but if there is an opportunity of correcting these errors, I you will try to get this done. It would be very unfortunate, if the book was published with all these mistakes, some of which no doubt result form misunderstandings, but many from gross carelessness. Evidently we have noticed mistakes only in the parts of the story which we know, I hope that in presenting the parts about which you were told by Mrs. Landau and by his friends and colleagues in the USSR you have been more careful. Errors there could evidently cause them considerable embarrassment. I enclose a list of errors. Since the corrections at this late stage, if at all possible, are likely to be diﬃcult, I have tried to limit this to the most serious ones. I have ignored obvious misprints, which presumably have been dealt with. The references are to a set of galley proofs headed “Bank 30-Slide 1· · · ” and showing reference 31143-110n14×23c. Yours sincerely, R.E. Peierls [710] Rudolf Peierls to Robert Oppenheimer Oxford, 9.10.1965 (carbon copy) Dear Robert, Your impression of the B.B.C. group seems to have been worse than mine. They spent some time interviewing me although they did not, in the end, use any of this in the programme, and they seemed to have some understanding of what they were talking about. However, this was after their trip to America, and they have probably learnt something in the process. I was all the more shocked how casual was their attitude was to facts.994 994

The BBC produced a programme entitled ‘The Building of the Bomb’ which was

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I am glad people spoke well of the Oxford Conference,995 but I deserve none of the credit which you generously oﬀer. The Conference was in, but not of, Oxford. It was organised entirely by the people at the Rutherford Laboratory. I was not even a member of the Conference since pressure on places was very heavy as usual and it did not seem fair to take up a place which might go to a younger man. I did listen to some of the talks when there were places, including that of T.D. Lee, who was wonderfully persuasive, though it remains to be seen whether this is the right story. Also Gell-Mann and while this was as lucid as attractively presented, as one would expect, it left me horriﬁed at the state of this particular piece of physics with symmetries which are not symmetries when any particle starts to move. When this particular fashion passes it will not be regretted. With kindest regards. Yours sincerely, Rudi [711] Hans Bethe to Rudolf Peierls Ithaca, 5.11.1965 Dear Rudi: Thank you very much indeed for your letter of 24 September concerning the BBC program about the history of the atom bomb,996 and their plans for a similar history of the H-bomb. I am very grateful to you for putting me on guard about my interview with Mr. Robert Reid of the BBC.997 Normally, I am used to giving such interviews quite innocently. After receiving your letter, I made him promise to submit to me any material that he may quote on the basis of our interview. screened in March 1965. Peierls was disturbed by inaccuracies and distortions in the ﬁnal version of the programme and took the matter up with the producer and with Sir Hugh Carleton Greene, the Director General of the BBC. See Peierls Papers, Ms. Eng. Misc. b202, C.19 and Ms. Eng. Misc. b219, D.23. 995 International Conference on High Energy Physics, 1965. 996 Letter could not be located. 997 Robert Reid was the producer responsible for the programme ‘Building of the Bomb’, screened earlier in the year. See letter [710], note 994.

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I believe your protest has had its eﬀect on Mr. Reid. In order to avoid similar troubles, he is going to eliminate all personal quotations, and all personal appearances of the characters in the drama. Instead, he is writing a script much of which he has showed me for my comment. It seemed on the whole fairly good, but I was able to correct [two] or three mistakes in fact. He took these corrections very gracefully. At many points I would have given diﬀerent emphasis, but I did not ﬁnd much that troubled me greatly. In the meantime, Mr. Nath will have appeared in Oxford. It took him much longer to ﬁnish than I had thought. Also, I was rather disappointed by his general knowledge of physics which came out in his ﬁnal examination. He is quite ignorant of the more elementary parts of physics, not only classical but also elementary quantum mechanics on the level of Schiﬀ. On the other hand, he did a good job on his thesis. It will do him good to teach, and I hope he will have to learn some of the more elementary parts of physics in the process. I am sorry I recommended to you a man who turns out to be less well trained than I thought he was. Otherwise, life is busy but happy. Henry has started studying at the University of Wisconsin, and seems to be managing quite well. He gets good grades, is interested in his work, and seems to have lots of friends. With best regards to you and Genia, Yours sincerely, Hans [712] Rudolf Peierls to Harold C. Urey [Oxford], 26.11.1965 (carbon copy) Dear Urey, In our discussions about elementary particles we have run up against a problem which seems to me very interesting but very hard, and, as far as I know, you are the only person who is likely to be able to make some intelligent suggestions about it. I am, therefore, writing to ask for your views and, if possible, for your advice.

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The problem arises from the hypothesis ﬁrst due to Gell-Mann that there might exist so-called “quarks”. I shall summarize brieﬂy the facts relevant to the present question. Very possibly these are quite wellknown to you, and I hope in that case you will forgive me. According to the hypothesis these quarks would be particles of fractional charges equal to one-third or two-thirds of the electron charge. A nucleon which consists of three of these, and a meson of one quark and one anti-quark. Since fractional charges have never been seen they would have to be very heavy so that they are hard to produce. The smaller mass of nucleons and mesons would then be due to very large attractive potential anergy which almost cancels out the rest of the components. From the fact that they have not yet been observed their mass should be at least three Bev but certain other features of the theory make it likely that it would be even larger — probably as much as 10 Bev. Even at 10 Bev they should occasionally be produced in the passage of cosmic rays through matter, but the rate would be so small that a direct observation of the event, or of the track of such a particle, would be hopeless. The point is, however, that once produced they would be virtually stable because having a fractional charge they could not annihilate except with each other, and their density, for example on the earth, would be so small that they would live practically for ever. There would then be on the earth a certain number of these particles practically equal to the number produced over the age of the earth, and the question is where would they end up. Strictly speaking, only one kind would be stable because they could transform into each other by beta-decay and we do not know whether the positive or negative variety would be stable. If the negative ones are stable they would obviously be attracted by nuclei, and probably form a new kind of nucleus. However, even if their nuclear forces should turn out to be repulsive, they would end up in a kind of Bohr orbit around the nucleus which at that mass would be not much larger than the nucleus itself, and the probability of transition to a neighbouring nucleus by panel eﬀect would be completely negligible, even over a geophysical period. They would, therefore, remain tied to the nucleus near which they have come to rest. If the positive ones were stable the position is

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less clear because once they have come to rest they would never get near any nucleus and it is hard to visualise what their properties would be. Some of these, however, still might be captured by a nucleus in ﬂight. It is also possible that even if the negative ones are unstable against betadecay in free space they would become stable once they are attached to a nucleus because the energy diﬀerence might be less than the very considerable binding energy. It is therefore a plausible, but not certain, consequence of the quark hypothesis that there might exist a small number of atoms whose nuclei contain one quark, and which not only would be distinguished by an enormously large atomic mass but particularly by a fractional charge. The question is now whether since this spectroscopic or massspectrometric technique had veriﬁed the existence of such objects, and this of course depends on the concentration one might reasonably expect. One can make a rough estimate of where quarks would stop after being produced in the atmosphere by primary cosmic rays, and the conclusion is that most of them would stop in about the ﬁrst metre of depth of solid material. To give a rough idea of the order of magnitude, if one assumes that all quarks produced during the life of the atoms were still to be found in the ﬁrst metre of depth their concentration would be about one in 1014 atoms. This is, of course, quite an academic ﬁgure, because there would be no place on the earth where a meter deep surface layer had remained undisturbed for all this time, though in practice the concentrations would be even smaller. However, the atoms carrying a quark would have very unusual chemical properties characterised by the fact that with their fractional charge they could never be electrically neutral. Presumably the number of electrons in such an atom would vary leaving the atoms sometimes slightly positive sometimes slightly negative, and therefore presumably the atom would be liable to various kinds of homo-polar compounds, but, in particular, its electrochemical properties would be weird. It seems possible, therefore, that such atoms might be enriched by very considerable factors in certain substances, and if one could only guess where to look, one might, in fact, have detectable concentrations by some further enrichment process.

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However, the diﬃculty is to know where to look. It might be feasible in any one chemical reaction to make a rough estimate of the likely fate of these peculiar atoms. However, we are concerned with a question of what happened to all the common elements in all possible chemical reactions that have taken place over geophysical periods so as to get the ﬁnal solution of the peculiar atoms, and without some inspired guess this looks quite impossible. I should be very glad to know what your ideas are about this problem. I should, of course, make it clear that the quark hypothesis is far from established but just for that reason if a search looked feasible it would be of the greatest importance. I need not stress that an actual discovery of quarks would be of major importance, but even the negative result of a search in circumstances where a positive result could plausibly be predicted would be of value to elementary particle physics. In this letter I have only summarised the results of conversations with Dr. P.K. Kabir, who raised this question with me in the ﬁrst place. With kindest regards. Yours sincerely, R.E. Peierls

[713] Harold C. Urey to Rudolf Peierls San Diego, 6.12.1965 Dear Peierls I am ﬂattered that you come to me to ask a question in regard to the quarks, and I have discussed the matter with some of my colleagues. It would seem to me, in view of what you say, that you should look at the iron meteorites which have been exposed for up to a billion years or thereabouts to space radiations of all kinds, then they arrive at the earth landing substantially cold, and they should contain these curious chemical substances. Neither I nor my colleagues have the slightest idea as to how we would look for them — how we would concentrate them.

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I am sorry to say that no one with whom I have talked has come up with any inspired guesses as to where to look for these curious types of atoms. However, we will keep the problem in mind and write to you again if anything occurs to us. It is most diﬃcult to detect atoms that are present to less than a part in a hundred million, this being approximately the limit of detection except for radioactive substances. When you mention 1 in 1014 as the probably concentrations, it is very discouraging indeed. It was nice to hear from you again. Frieda and I send you our best wishes for Christmas and the New Year. Sincerely yours, Harold C. Urey

[714] Rudolf Peierls to Hans Bethe [Oxford], 14.12.1965 (carbon copy) Dear Hans, It is ages since I received your letter of 5th November.998 You need not feel apologetic about Nath. He seems an extremely nice person and is making himself useful though he still has to spend a good deal of time on ﬁnishing his thesis. His teaching will not start till next term and I was glad to have your warnings as to know what possible diﬃculty to watch for. I talked recently with him about his plans. His original intention was to return to India next year, but he has had second thoughts about this in the light of various reports, and he now feels that he has to mature some more before it would be wise to go back. In the light of this his ﬁrst choice would be to try and return to the Unites States next year. One of the reasons being ﬁnancial; he would like to send some money 998

Letter [711].

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home eventually, and on an English salary that is not so easy. His ﬁrst choice would be Cornell, and he told me he was about to write to you to enquire about the possibilities. Alternatively, he might stay here, but it is not yet clear whether there will be funds to extend his appointment here which was made for only one year in the ﬁrst place. This doubt does not reﬂect any lack of interest in having him here for longer but only shortage of money in general together with the need for supporting some other people who are already here and looking after people whom we should like to have for special reasons. I thought it would be useful to make these remarks to explain the situation since otherwise the fact that he already is thinking about leaving might create the impression that we do not like him or that he is unable to settle down. Both these impressions would be quite misleading. Yours sincerely, [Rudi]

[715] Nevill Mott to Rudolf Peierls Cambridge, 25.7.1966 Dear Rudi, I am working at the moment on conductivity in disordered lattices, and I note that a good many papers are appearing which assume that one can describe the conduction process, even at the absolute zero of temperature, in terms of a mean free path which is small compared with the interatomic distance. I believe this to be nonsense and that one has to do with a hopping process here and therefore with a form of conductivity which goes to zero with the temperature. I think this, too, is fairly clear if one looks at the whole process from the point of view of the Kubo-Geenwood formula. You in your book have been a good deal concerned with the inconsistency of theories of conductivity in which the time of relaxation is

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short (though not as short as this!) and I wonder if you have given any thought to the problem. I should enjoy discussing it with someone such as yourself and wonder if you are in Oxford during the next weeks and would be free to have a talk next time I am over in the area. Yours sincerely Nevill

[716] Rudolf Peierls to Nevill Mott [Oxford], 26.7.1966 (carbon copy) Dear Nevill, I would certainly agree with you that the conductivity in a disordered lattice usually cannot be handled in terms of a mean free path and that a mean free path short compared to the lattice spacing does not make much sense. I think it is also true, as you say, that in such a case the conductivity should vanish at ﬁrst temperature because the Coulomb interaction between the electrons tends to keep them in their place unless enough of them are displaced already. This is a point which I believe you made a long time ago. The trouble is that while it is very easy to say how one should not proceed, I have found it extremely diﬃcult to choose a model of this kind in which one can get anywhere near a convincing solution. As you know, Sam Edwards has some powerful techniques for such problems, but they always require some simplifying assumptions, and it is not easy to judge their physical signiﬁcance. I must confess I was always thinking about this problem without the Coulomb complications although I know they were there, and your letter prompts the question whether perhaps, the low temperature limit when few of the electrons have enough energy to pass each other, might give a basis of a sensible approximation. I should certainly be delighted to talk about this if you are in the neighbourhood. I expect to be abroad from 7th August until about

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23rd September though, owing to various complications it is not yet clear whether I shall get away. Until 7th August I expect to be here with the exception of tomorrow, 27th July, and 4th August. If you are likely to be around here this week or next week, perhaps you would give me a ring to agree a date. Yours sincerely, R.E. Peierls

[717] Nevill Mott to Rudolf Peierls Cambridge, 27.7.1966 Dear Rudi, Many thanks for yours.999 I was not thinking in terms of Coulomb interaction between electrons, which at suﬃciently large interatomic distance turns a metal into an insulator, as was ﬁrst suggested by Wigner in 1938 and as I have discussed with a rather diﬀerent model. I was thinking solely in terms of non-interacting electrons. I have been asking myself what happens to a disordered lattice as the interatomic distance increases and as one goes over to the situation which, if one were dealing with a crystalline lattice, one would call tight binding. For small interatomic distance, the considerations which Heine and the Chicago School have brought forward about pseudopotentials apply. The nearly free electron approximation is a good one, and the mean free path is given by Ziman’s theory.1000 Both experimentally and theoretically the mean free path in liquid metals, for instance, can be quite long. As one increases the interatomic distance, the mean free path will drop and will eventually become comparable with the interatomic distance. What I think happens next is that the states become localised and the conductivity from here on is a hopping process, which needs essentially thermal activation and interaction with phonons. I think 999 1000

Letter [716]. See J.M. Ziman, Electrons and Phonons, Oxford: OUP, 1960.

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Sam Edwards is of the same opinion he has had a shot at applying his techniques to the problem without suﬃcient success to persuade him to publish. It still seems to me uncertain. If you are interested in this kind of problem I would like to come over to talk about it. I will next be near Oxford on Saturday, August 13th, but then I think you will be away. I could well drive over one day in the previous week. I should enjoy discussing this and other things. Yours sincerely, Nevill

[718] Hans Bethe to Rudolf Peierls Ithaca, 20.1.1967 Dear Rudi: I thought it might be useful to co-ordinate our talks at the New York meeting to some extent. In the main I am planning to give a speech very similar to the one at Gatlinburg of which I enclose a copy.1001 However, I want to put a little more emphasis on the statistical theory of the ﬁnite nucleus. Mrs Nemeth1002 has made some progress about solving the integral equation for the density which I want to report. In addition, I want to talk for about three minutes on the use and justiﬁcation of the local density approximation in the theory of the ﬁnite nuclei, by which I mean both a Hartree-Fock and a Thomas-Fermi theory. I use the local density approximation essentially as deﬁned by C.W.Wong,1003 not Brueckner, Gammel and Weitzner.1004 1001

Hans Bethe gave a paper at the International Conference on Nuclear Physics, Gatlinburg, Tennessee, 1967. See Proceedings of the International Conference on Nuclear Physics, Gatlinburg, Tennessee, 1967, New York: Academic Press Inc., 1967. 1002 Judit Nemeth, had worked with Hans Bethe at Cornell before taking up a post in Budapest in 1968. See J. Nemeth and Hans Bethe, ‘A simple Thomas-Fermi calculation for semi-ﬁnite nuclei’, Nuclear Physics A116, 241–55 (1968). 1003 Chun Wa Wong obtained his Ph.D. from Harvard in 1965 before taking up a post at University of California, Los Angeles. 1004 K.A. Brueckner, J.L. Gammel and H. Weitzner, ‘Theory of Finite Nuclei’, Phys. Rev. 110, 431–45 (1958).

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I hope all this does not interfere with your talk; if it does, please write me and I will change my talk accordingly. Yours sincerely, Hans

[719] Rudolf Peierls to Hans Bethe [Oxford], 24.1.1967 (carbon copy) Dear Hans, Thank you very much for the advance information about your talk in New York. I see no reason to ask for any change in your selection of topics (a) because there is not much overlap, and where there is it will probably lead to constructive discussion, (b) because I had in any case kept my plans ﬂexible in order to ﬁt in with whatever you are going to say, and (c) above all because all you say is interesting and worth saying and I would not be able to say it. I do not have a previous manuscript with which to return your compliment, and of course I don’t have my New York talk written down. I am still sorting out things to some extent, but roughly speaking what I want to do is the following: First I want to make some general remarks about why one wants to do this kind of thing. One hears remarkably often the view that all this is a waste of time because once ﬁeld theory has been put in order, one should just solve the many-nucleon problem in interaction with pions and everything else, and all the answers will come out. Of course, the exponents of such views will be at other sessions, but one may give a little moral support to the people who may be there. Then I want to make some brief remarks about the forces, and there will be a little overlap, because I want to comment both on the question of Many-body forces, and on non-local and other non-conventional forces. Here I shall not disagree with you, but place the emphasis a little diﬀerently, so that I am quite happy about your remarks preceding mine.

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After that I want to turn really to ﬁnite nuclei, say around oxygen, and the approximations one wants to make there are really complimentary to your Thomas-Fermi philosophy (which is not saying one might not even get useful information about oxygen via TF) except that your reference to the use of the local density approximation by C.W. Wong & Co. presumably gets close to my subject. I shall not try to review all the existing calculations, and give numbers — the real reason is of course that I am too lazy to collect all the detailed information, but I rationalize this by the argument that it is a little too early for such a review because the answers have not yet settled down suﬃciently. I do want, however, to discuss methods a little. It seems to me that many of the eminent authorities are too hypnotized by the Brueckner expansion. For example, the Brueckner reaction matrix for a ﬁnite nucleus is a horrible animal to deﬁne and to write down if known let alone to calculate. The separation or reference spectrum methods, or a judicious combination of them allow one to calculate this beast approximately, but if one goes beyond the crudest approximation, all the diﬃculties and complications of the Brueckner matrix are still there. If one uses physical intuition to approximate to some of the harder quantities it may be very hard to say how one should correct for the errors involved, or at least estimate them, because it is not clear what has been left out and what the next term should be. I believe it is useful to have a formalism in which it is quite clear what has been left out and in which one can see what terms in the expansion would have to be taken into account to deal with this. This view is also taken strongly by C.W.Wong.1005 Of course it is also important that the approximation be reasonably convergent — a series of which you have to calculate ﬁfteen terms is not much use. My impression is, for example, that Wong tends to go too far in writing too many manybody eﬀects into the deﬁnition of the one-particle states which causes all sorts of trouble (e.g. lack of orthogonality of the states) without 1005

See Chuan Wa Wong, ‘Application of the Reaction Matrix Theory (1). The Calculation of Nuclear Reaction Matrix Elements’, Nuclear Physics 91, 399–32 (1967). See also Chun Wa Wong, ‘Spin-Orbit Splitting in the Conventional Spherical HartreeFock Theory’, Nuclear Physics A108, 481–92 (1967).

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evidence that this really pays in terms of more rapid convergence. One can see that this reduces the size of some higher-order terms, but since one cannot have a series without higher order terms it does not matter to increase them somewhat, as long as they do not become larger in order of magnitude. A similar question relates to the self-consistency. One is tempted to require full self-consistency in the Hartree-Fock spirit. This can be stated by requiring the matrix elements from the ground state to oneparticle excitations to be zero. One can use a much simpler model potential (e.g. harmonic oscillator for a light nucleus like O 16) and keep the diﬀerence amongst one’s correction terms. The matrix elements for one-particle excitations are then non-zero, but they are usually very small, and it does not look as if they would make higher-order terms appreciably larger. What one gains is a much greater ease in evaluating, for example, second-order terms. You will see that this is largely a commercial for the approach we are developing in Oxford. However, we have so far only very partial results available, and this is more a programme than a calculation. However, I think my plea for ﬂexibility is more general than this. I hope this will give you some idea of what I propose to talk about and I think you will agree that there will be no serious demarcation dispute, as the trade unions would say. I am not too happy about the attempts to push this kind of discussion into the newspapers, because nothing sensible or intelligible will result. I refused to prepare a press release about my paper, but I felt I could not refuse to take part in the press conference on the Wednesday morning where I imagine I shall see you, presumably with not much greater enthusiasm. Yours sincerely, [Rudi]

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[720] Nevill Mott to Rudolf Peierls Cambridge, 23.10.1967 Dear Rudi, Proposal for Summer Schools in the Long Vacation for research students working in solid state in universities in the U.K. 1. This letter is to ask whether you would be sympathetic to an attempt to organise summer schools, extending over a period of, say, three weeks, for students taking a Ph.D. in experimental or theoretical solid state physics. The proposal is that a school should be organised each year, probably changing from one university to another, and the best talent available should be recruited from the host and other universities to give the instruction. The aim is partly economy of eﬀort; an audience of 40–80 students might be the aim, much larger than most universities can assemble for a postgraduate course. Also some of us think that, if it became normal practice to attend such schools, one or more concentrated courses might be to the advantage of students and might lessen the need for the constant interruption of research by postgraduate lectures. Those of us who have attended Continental or American summer schools have been impressed by the enthusiasm for information that can be engendered when all members of a group have a common interest. At this level it seems possible to absorb the content of about 20 lectures a week and still retain some semblance of humanity. 2. We have in mind lectures at two levels. (a) A course in late July or August for students directly after their ﬁrst degree. This could deal with quantum mechanics, formal theory of electrons in solids, some special topics and perhaps statistical mechanics. (b) Courses in any of the vacation periods on more advanced special topics, e.g., superconductivity, many body theory, defects in solids, techniques of electron microscopy.

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3. Lecturers would naturally be paid a fee; students would need maintenance costs. Support from the S.R.C. would therefore be essential. It is felt that a strong case could be made, even in a time of ﬁnancial stringency, since this is a method of using our teaching resources in a more rational and economical way. 4. I am sending this letter to some Heads of Departments specialising in solid state and related subjects and others and if we obtain a reasonable degree of support Professor Pippard1006 and I are willing to explore the letter with the S.R.C. Yours sincerely, Nevill

[721] Rudolf Peierls to Nevill Mott [Oxford], 30.10.1967 (carbon copy) Dear Nevill, I am writing in reply to your letter of 23rd October about the proposed summer schools in theoretical physics.1007 I have discussed this with senior members of the Theoretical Physics Department, but not with the people in the Clarendon. Our reaction is that we would very much welcome such summer schools if the details would be worked out satisfactorily, but we are not sure that of the two levels you envisage the lower one would be very useful in the form in which it is proposed. These doubts arise from the fact that the introductory material is probably taught better in an extended course over one of more terms, which gives the students a better chance of digesting the material and of 1006

A. Brian Pippard (1920–), Cavendish Professor of Physics at Cambridge University 1971–82. 1007 Letter [720].

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doing some reading between lectures, than in a very concentrated dose. It is also true that for most departments it would make sense to have such a course themselves, bearing in mind that at this level one can, if necessary, take experimentalists and theoreticians together; and also such a course could well be given to students interested in solid state physics together with those working in other areas (we already encourage our theoretical research students in nuclear and particle physics to take a basic course in solid state physics). It may be true that there are still a few departments in which the numbers are so small that a course even at that level would be wasteful, but I think you would ﬁnd that the larger departments, certainly including Oxford, would not want to send their students to a summer school at this level, and therefore the problem would look very diﬀerent from the second-level course. I can also see considerable diﬃculty in having such a course during the summer before students start on their postgraduate work. As you know, the ﬁnal decisions about the acceptance of students and about their grants are only taken during July, and there always remain a few cases in which matters are only settled during August and September. In some cases also the question of the ﬁeld of study is delayed, particularly for theoretical research in which the question of laboratory space does not arise. For many students the present practice of having a break after ﬁnals seems desirable, whether this is in the form of a long holiday or travel, or perhaps vacation work in industry or research establishment. Finally I would imagine that it would be diﬃcult to get all the overseas students to this country in time for this course. The result would therefore be inevitably that there would always be some students who would miss this course, and, even if their numbers are small, the need to cater for their requirements would complicate matters. If my guess is right that only a limited number of smaller departments would wish to make use of this course, you might well consider whether some other timing, for example the Christmas vacation, might not have advantages. We would, however, like to give strong and indeed enthusiastic support to your proposal of a course at the higher level, and there seems very little to add to the points already made in your letter. The only remark I personally would not agree with in that letter is the reference

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to the interruption of research work by lectures courses. Of course, such interruptions are often a nuissance, but I think we must educate our students to accepting this kind of thing as necessary and to realising that research workers must throughout their career be ready to get new ideas and new information from lectures and meetings, and that this cannot be replaced by going to a summer school for a few weeks. However, this remark seems incidental to the problem. You are probably right that the best arrangement would be for this course to be held at various universities in turn, and we would be willing to do our share in this. On a point of detail: it would probably be useful to have some kind of mechanism for the experience gained in running such a course in one place to be passed on to others, so that, while they should of course have the freedom to arrange their course according to their own ideas and according to local circumstances, they should know about practical diﬃculties that have been found in other places and measures to overcome them. One other point I have learnt from participating in various summer schools is that there is often a tendency to bring in a fair number of senior people in order to make the course attractive and that this can result in asking too many of them to give very short sets of lectures, which it is then diﬃcult to co-ordinate to the best advantage of the students. In my experience the best arrangement is to have a very small number of people giving the basic courses, so that they can give a systematic coverage to the subject, and this need not exclude asking other senior people to be present to take part in discussions and perhaps give a few seminars. Presumably such a course would in the ﬁrst place be national, so as to ensure places for all the U.K. students for whom the course is appropriate; but this would not necessarily exclude admitting some foreign students if they want to come and if there is room for them. Yours sincerely, R.E. Peierls

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[722] Rudolf Peierls to Sir Folliot Sandford [Oxford], 23.10.1968 (carbon copy) Dear Sandford,1008 I see from a study of the Statutes that my Chair is the only Schedule B Professorship which does not carry the “special allowance” to heads of departments, with the exception of the Regius Chair of Medicine, which no doubt is exceptional also in other ways. I do not know whether this reﬂects an impression that the burden of running this department is particularly light, though it hardly feels that way to me. When I came here in 1963 (at rather a reduction in my salary) I was told that it was at that time impossible to make any change in the situation, because the amount of money provided for covering these allowances was fully committed. I assumed — though I admit this was not stated at the time — that the questions would be kept under review. I was therefore somewhat surprised to ﬁnd that another Chair was added to this Schedule in 1966. In any academic appointments I have held previously it was never necessary, or proper, to raise any queries concerning one’s own salary, and I am still writing this letter with some reluctance. One reason why I decided to do so is the thought that if this anomaly was not rectiﬁed when my successor will have to be found, this would add to the diﬃculties facing the Electors. In saying this, I would not, however, wish to imply that I am capable of suﬃcient detachment to be satisﬁed if the problem is solved just in time for my successor. Incidentally, the Statues still provide (1967 Statutes, p. 50) that the Dr. Lee’s Professor of Experimental Philosophy shall assign adequate accommodation in the Clarendon Laboratory to the Wykeham Professor of Physics. I think it is about time this Statute was deleted, since I would be rather unpopular with Bleaney, if I insisted on my rights under this clause. Yours sincerely, [Rudolf Peierls] 1008

Folliot Sandford, Registrar of the University of Oxford.

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[723] Rudolf Peierls to K. Unwin [Oxford], 12.2.1969 (carbon copy) Dear Mr Urwin,1009 I am returning my ballot paper about “direct action” with entirely negative replies, and I feel I should write to you a word of explanation. My reason is not that I am opposed in principle to direct action by university teachers, but that all the forms of action listed in the ballot paper are unsuitable. Some, like the proposal of a one- or two-day token strike, are essentially empty gestures which could cause no particular distress to the D.E.S., the Government, or anyone else. Some, like the proposal of a longer strike, would hurt students more than anyone else. Some of the proposals ingeniously, manage to combine both features. I was able to think of only one form of action which would be likely to impress the authorities as a real threat — that is, for a large number of university teachers to sign a statement that if certain grievances or complaints were not remedied by a speciﬁc date, they would accept any reasonable oﬀer of a post abroad. Of course, not every university teacher has, or can obtain, reasonable oﬀers, but it is well known that the number of those who can and who mostly are refusing such oﬀers out of a sense of obligation is very considerable and includes some of the most valuable members of the universities. This would be a weapon which should not be used lightly, and of course statements would have to be genuine. It would not do to bluﬀ, because if the bluﬀ is called and people do not in fact leave, we would look ridiculous and any future threat of action would have no credibility. I doubt whether I myself would agree to participate in this kind of action merely over the question of salaries, particularly when my own salary is involved. However, if the A.U.T. were willing to conduct a ballot asking how many people would participate in such a declaration, given a suﬃciently serious complaint, and obtained a substantial 1009

Dr. K. Unwin, ﬁrst General Secretary of the Association of University Teachers, appointed in 1959.

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number of positive answers, this fact alone might impress the Authorities as a danger signal in a way that none of the proposals of the present ballot paper can, in my opinion, possibly do. Yours sincerely, [Rudolf Peierls]

[724] C.H. Paterson1010 to Rudolf Peierls Oxford, 30.6.1969 Dear Peierls, Some time ago, as you may recall, you raised with the Registrar the question of instituting a departmental allowance for the Wykeham Professorship of Physics. It was not feasible to take this up at that time since the “allowance structure” is dependent on the ﬁgure ﬁxed from time to time for the basic rate of professorial stipend and so can only be reviewed in the context of general supplementation exercise. The opportunity of such a review having now occured, Council and the General Board have examined the question whether any modiﬁcations in the present pattern of allowances at Oxford should be made, and in this context have speciﬁcally considered the position of the Wykeham chair among others. I write now to let you know that in the light of up-to-date comparative statistics showing, for all departments concerned, expenditure on departmental account (from university and outside funds), numbers of academic and non-academic staﬀ, and student numbers, they have decided that no allowance should be instituted at this time and no changes made in the pattern of existing allowances. Yours sincerely, C.H. Paterson

1010

C.H. Paterson, Secretary of Facilities, University Registry, Oxford University.

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[725] Rudolf Peierls to R.J. Eden [Oxford], 14.2.1970 (carbon copy) Dear Richard,1011 On your request for recollections of Dirac, there is rather little I can contribute about discussions on physics. As you know, his normal reaction to a question of physics is to answer “yes” or “no”, if the problem is solved in his view, or “I don’t know” if it is not. This does not easily generate an argument. I did see a good deal of him, however, and heard more from others, mostly of a personal rather than professorial nature. I shall write down what I can remember, and leave you to pick out what may be relevant to your purpose. I was of course familiar with Dirac’s work long before I met him. In fact, my ﬁrst serious assignment as a student was to report to Sommerfeld’s seminar on the papers by Dirac and Jordan on transformation theory,1012 which were then new and which nobody had understood as yet. I still remember the impact of the elegance and simplicity of Dirac’s approach, once one had got over the ﬁrst shock of delta-functions, bracket notation and other unconventional tools. I ﬁrst met Dirac in 1928 when I was a student at Leipzig, and he came to give a seminar talk, presumably on the relativistic wave equation. I do not remember the details, but I do remember noticing that his presentation in the talk was step-by-step the same as in his paper; this I believe, was general and reﬂected the fact that in writing his papers he had considered carefully the best way of presenting the material, and there was therefore no reason to change it. In the evening I was detailed to take the distinguished visitor to the theatre. I do not remember what the play was, or whether Dirac made any comments. I do remember struggling to keep conversation 1011

Dr. Richard J. Eden, Cavendish Laboratory, Cambridge. Dirac and Jordan. P.A.M. Dirac, ‘The Quantum Theory of Emission and Absorption of Radiation’, Proc. Roy. Soc. A114, 243–65 (1927); P. Jordan, ‘Zur Quantenmechanik der Gasentartung’, Z. Phys. 44, 473–80 (1927). 1012

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going, which seemed to me my duty as a host, but not doing very well. Another diﬃculty appeared when he entered the theatre, where it was then a rule that you had to leave your hat and coat in the cloakroom. Dirac would not believe me, or did not concede the management the right to make such an unreasonable rule, and announced ﬁrmly that he would take his hat and coat (or perhaps only his hat, as it was summer) with him to the great embarrassment of a very law-abiding German student, also conscious of his obligations as host. To my great surprise and relief, the attendants did not object. My next encounter with Dirac was in the autumn of 1928 when, at the end of a holiday in England, I spent a week or so in Cambridge and called on Dirac, boldly presuming on our meeting in Leipzig. He was kindness himself, arranged for me to use the Cavendish library and introduced me to R.H. Fowler. As far as I remember no physics was discussed between Dirac and myself, but probably at that stage I did not even try. I did try when I was back in Cambridge in the summer of 1933. One of the problems I was working on was the inﬁnities in the vacuum polarisation obtained from Dirac’s electron-positron theory and a proposal I had for obtaining inﬁnite answers which seemed physically justiﬁed (for renormalizing, we would say today). This, I felt, was close enough to Dirac’s interest to hope for some helpful comment. I do not remember any details of our conversations, but they got nowhere. I am sure this was basically because he did not know the answer to my problem, and speculating aloud on things one does not know is against his nature. It would be wrong, however, to give the impression that he was at that time silent or remote. He was interested in things around him and ready to ask questions, and to answer direct questions. On subjects other than physics, he would be quite willing to propose possible answers or guesses when he did not know. All the time we were in Cambridge (summer of 1933 and the academic years 1935–1937, I cannot keep apart events from those two periods) he was most considerate and never failed to oﬀer to my wife and me seats in his car when he was going to a meeting in London. We were at ﬁrst apprehensive because of the stories which were going

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around Cambridge that the speed of his car (like that of the Dirac electron) had only two eigenvalues, zero and full speed. However, we felt very safe in his car — no doubt he had decided to study the art of driving as seriously and as eﬀectively as he studied everything else. The story goes that early in his driving career he was involved in a minor accident with a woman and a pram, in which someone got hurt. A friend who was a passenger in Dirac’s car, phoned for the police and an ambulance, took the names of witnesses &c. Afterwards Dirac asked him whether he had been in an accident before, and when told not, asked: “How did you know what to do?” His comments in general conversations were often characteristic of his way of thinking which always comes as a quite unexpected surprise until you realize that his is the simplest and most logical reaction, where everybody else’s thoughts by habit or association take a more complicated, perhaps less logical turn. (All this can, of course, be said about many of his papers). At one social gathering at our house, there was talk about the fact that practically all the children born to physicists at Cambridge at that time were girls, and someone said “It must be something in the air”. Some time passed, and the conversation was beginning to turn elsewhere when Dirac remarked: “Or in the water.” About that time, it is said Dirac arrived in the house of friends for dinner, but the hosts were late returning themselves, so he waited in their sitting room where the grandmother was knitting. There was a long silence, the old lady being quiet and Dirac not given to idle conversation. He watched her knitting for a while, and then announced: “There must be two ways of doing this.” This is true, of course, but he had not known and deduced it from ﬁrst principles. A faith in the orderly nature of the world is indicated by the story that in Copenhagen he was once told to watch Pauli, who was putting on weight. This was more by way of a joke, but Pauli accepted the spirit of it and asked Dirac how many lumps of sugar he could take in his tea. Dirac said: “I think one is enough for you”, and after a pause: “I think one is enough for anybody”. Some more thought and “I think the lumps are made in such a way that one is enough for anybody”.

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On this or another visit to Copenhagen Dirac was helping Niels Bohr draft the English version of a letter or paper. Bohr liked to march up and down while he thought, so Dirac was writing down the draft at Bohr’s dictation. At one point Bohr said he did not know how to end the sentence he had started, whereupon Dirac put down his pen and said “I thought we were taught at school you should never start a sentence before you know the end of it.” (this led to some friends, including, I believe, R. de Konig, sending Dirac a picture postcard with the words “you should never start life before you know the end of it”) In his own papers he would, of course, always know how each sentence was to end, I doubt whether their text changed much from the ﬁrst draft. I was told that the very rapid publication of his papers was in part due to the fact that he knew the dates when the issues of the Proc. Roy. Soc. were going to the printers and always arranged to ﬁnish at the right time. He could, as I said, become interested in almost anything, and that was true also in physics to a much greater extent than one would believe. In about 1934 he invented a method of isotope separation. The idea was to make a jet of gas turn a corner, past a sharp edge so that the centrifugal force would cause separation of the components. He not only conceived the idea, but decided to verify it experimentally. Kapitza allowed him the use of a compressor in the Mond Laboratory, and the device was tried initially on a mixture not of isotopes, but of air with a heavy organic compound. When I saw the experiment there had been as yet no evidence of a diﬀerence in composition between the two output tubes, but by feeling the tubes, one could easily check that one was hot and the other cold, showing that something non-trivial was happening in the junction. When Kapitza had to stay in Moscow and his equipment was sent on, Dirac’s experiment was interrupted. During the war, however, a group in Oxford studied the feasibility of the method for separating uranium hexaﬂoride. They found it worked perfectly well, but less eﬃciently than gaseous diﬀusion, and it was therefore not pursued. When this work was started, Dirac was invited to Oxford to discuss the method. I was present at the meeting in the Clarendon Laboratory (there may have been more than one meeting) and I remember that the experimentalists expected a highbrow and

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abstract mathematician who would know the kinetic theory of the eﬀect, but would not know one end of an apparatus from another. They were most impressed by Dirac’s eminently practical and helpful remarks. Dirac’s experiment also provided the occasion for one of my favourite episodes, though I do not know whether this is more a story about Dirac or about Wigner. Wigner and I happened to visit Cambridge on the same day, and we both called, separately, in the Mond Laboratory and saw Dirac with his apparatus. Later Wigner complained that Dirac was so secretive about his idea; he had refused to explain it. I was surprised by this, since my impression was diﬀerent, I had actually guessed what the principle might be, but Dirac had shown no hesitation in showing that my guess was right. A little more probing brought out that the relevant conversation consisted of one exchange. Wigner had said “It must have been very diﬃcult to make the little brass piece?” (A brass T piece, with the gas mixture entering at the stem and the fractions coming out of the arms, was clearly the heart of the device). Dirac’s answer was “No, that was fairly easy”. He had given a straight answer to a direct question. Wigner, on the other hand, had asked for information and had been refused. I bet Wigner that, by asking directly for the principle, he would have got the explanation. The bet could not be settled, because when he asked Dirac whether he would have responded to a direct question he said, of course, “I do not know” — his frequent answer to a hypothetical question. I believe that this is all I can recall about the early days, but let me add two much more recent stories. One comes from Tyabji,1013 an Indian who had retired as a lawyer, but had come to try to do a Ph.D. under Dirac’s supervision. (He has since died.) He discovered that Dirac was an ardent E.M. Forster fan, but had never met him, although both had lived in Cambridge for many years. Tyabji, who knew Forster, invited both for dinner. After they were introduced, Dirac asked: “What happened in the cave?” Forster replied “Nothing.” This 1013

S.F.B. Tyabji has worked on the symmetrical energy momentum tensor of Dirac’s electrodynamics. See S.F.B. Tyabji, ‘The Energy Momentum Tensor in Dirac’s New Electromagnetic Theory’, Nature 170, 116 (1952).

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answer satisﬁed Dirac and he did not take the initiative again for the rest of the evening. The other is told by my daughter who came to live in Cambridge in 1956. When she visited Dirac’s, Mrs. Dirac suggested that she might invite some young people to meet her, perhaps some students. She asked “Paul, do you have any students?”, to which he answered: “I had one, but he died.” As I write this, I realize more and more that little, if any, of this is suitable for your purpose. However, I am glad to have written it down, and you can pick out what you want. Yours sincerely, [Rudolf Peierls] P.S. I ﬁnd I have omitted one story I meant to include, although you may get it also directly from H.R. Hulme.1014 Hulme was walking with Dirac in a Cambridge street in the early thirties, and apologized for a rattling noise in his overcoat. He explained that he had a bottle of throat lozenges, of which he had taken some because he had a cold. ”So the bottle is not longer full and it rattles”. Dirac considered this statement for a while and then commented: “I suppose it makes the maximum amount of noise when it is half full?” I was very anxious to get the date of this, in relation to the date of the ﬁrst work on hole theory. It would be nice to think that the “hole” idea had grown from thoughts about Hulme’s bottle of tablets. However, Hulme says that date must be 1934±2, and the paper about hole theory was published in 1931. Pity.

1014

H.R. Hulme (1909–1991), obtained his Ph.D. from Cambridge in 1932 and stayed on as a fellow of Gonville and Caius College; after research at Cambridge and wartime work at the Royal Observatory and the Admiralty he became Chief of Nuclear Research, at Atomic Weapons Research Establishment, Aldermaston, 1959–73.

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[726] Hans Bethe to Rudolf Peierls Rehovoth, 22.2.1970 Dear Rudi, We have now made our plans for the English visit.1015 If it is all right with you, we should like to come to Oxford at the very beginning. We expect to arrive in London on April 22, about noon. Then we want to visit two old aunts of Rose’s who live near the Airport. After dinner we should like to take a taxi from there to your house so that we should get there by about 9:30 p.m. or 10:00 p.m. on April 22. Would this be all right with you? We should then stay until Saturday, April 25. Then we want to go to Werner Sachs. He may come to collect us in Oxford, or else we shall take the train. Since both the taxi and Werner do not know the geography, would it be possible for you to draw a map how to reach your house from some clear landmark in Oxford? In your recent letter you kindly oﬀered to pay some travel expenses for me. I should be grateful, if you could. This would involve taxi, and if possible all, or part of the airfare from Germany to England and back. This trip is not included in our fare around the world. Of course I should be glad to give a talk on Nuclear Matter if you are interested. Looking forward to seeing you and Genia. Yours sincerely, Hans

1015

Hans and Rose Bethe were travelling around the world in 1970, and on tour they visited England.

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[727] Rudolf Peierls to Hans Bethe [Oxford], 28.2.1970 (carbon copy) Dear Hans, Thanks you for your letter. The dates you suggest are ﬁne. We wish the visit could be longer, but I can see the problem. On the 22nd April I think it would be easiest if we came to collect you, presumably around 8 or 8.30 p.m. if you let us know the address. It is really quite near, and that way we could have another hour or so of your company. In case something intervenes which prevents us coming, I enclose a map showing where we are. In that case you should tell the driver to come through Henley, which brings you on to our map by the red arrow. You then follow along the Oxford ring road the signs to Abingdon and Newbury, and from there the map should be adequate. We would be very happy, if you could give a talk on “Nuclear Matter”, probably on the Thursday afternoon. This could be done on one of three levels: either to our theoretical seminar, which is for all theoreticians, including elementary-particle and solid-state people as well as people working on nuclear theory; alternatively, it could be in our nuclear theory discussion group, where you could really take your hair down; or it could also be a meeting of the physics colloquium which normally includes all the experimentalists, both nuclear and otherwise. Please let me know which of these settings you prefer. I guess that the theoretical physics seminar might be the most appropriate. It is conceivable that we might arrange a meeting for the Friday afternoon rather than Thursday, because David Brink is returning from a visit to Orsay about that time and he would regret having to miss your talk. One minor complication is that Genia and I are supposed to go to a dinner in college on Friday evening. This is an annual event, which it might be awkward to get out of, and as it happens, this applies to Cook as well. However, Oxford is full of people who will be delighted to be your hosts for that evening, so there is no problem.

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We can certainly take care of your fare from Germany etc. Looking forward to the occasion. Yours sincerely, [Rudi]

[728] Rudolf Peierls to Christian Møller [Oxford], 19.3.1970 (carbon copy) Dear Møller, I am writing in reply to your circular about the future location of the Institute.1016 My comments on your question must be very general, because I have not had occasion to visit Copenhagen for many years and I am not familiar with all the factors. It is undoubtedly true that to a visitor it has been an attraction that the Institute is located so centrally in Copenhagen, and that by just walking out of the door one feels part of the life of the city, Equally, for those who were able to live reasonably close to the Institute, the proximity of work and home, and of other amenities, has been an advantage. Recently, of course, housing for visitors has been more diﬃcult in Copenhagen, as elsewhere, and I believe already now many members of the Institute both short-term and permanent, live in suburbs and do not have the advantages that were available in the old days, when one could expect to ﬁnd a place to stay within walking distance of the Institute. After the proposed move, of course, distances will be much greater than they are now, but I do not think you need fear that this will have a serious eﬀect on the desire of visitors to come. The Institute has such a unique position in Theoretical Physics that people will come to it wherever it is placed (when I speak of the Institute I mean of course the Bohr Institute and Nordita together). I have tried to think 1016

Christian Møller, director of NORDITA, earlier in March 1958, had sent a circular to old collaborators of the Niels Bohr Institute to enquire about their views on the possible move of the Niels Bohr Institute and NORDITA to Roskilde.

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of similar problems in other places, and perhaps the nearest example is Orsay whose distance from the city is probably somewhat less than comparable to what you describe, and where the move has certainly not resulted in either a feeling of isolation or in any reduction of the ﬂow of visitors, I do not of course wish to imply any close similarity in the nature of the institutions. If you do move, you will of course face some new problems which will need attention. The perennial problem of ﬁnding housing for visitors will take a new form, depending on whether there is a supply of suitable housing either near the new institute or at the right end of Copenhagen, or possibly in between, and in connection with such housing, the question of schools at various levels (and languages), shops, etc. will arise, but presumably one can ﬁnd answers to these problems. To sum up, the move will undoubtedly bring with it some minor disadvantages, but it is my impression that these would be entirely acceptable, assuming of course that there are compensating advantages in having a more convenient site for the building of the Institute and for other parts of the University. Yours sincerely, [R.E. Peierls]

[729] Rudolf Peierls to Sam Edwards [Oxford], 13.6.1970 (carbon copy) Dear Sam, Thank you for your letter.1017 I am glad to hear that you are making progress with studying the possibilities of a large summer school. I certainly did not want to give the impression that I am opposed to such a scheme in general. What I do feel strongly is that a concentrated dose of instructions in such a school is greatly inferior to a good system of teaching people 1017

Letter could not be located.

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throughout the year in their own department.∗ I agree with you that at present many departments are not able to provide satisfactory training or simply do not do so. It may therefore indeed be valuable to provide a big centralised and short-term operation as a second best. I do, however, oppose compulsion, because it can have adverse eﬀects on those departments (and I do not agree at all with you that we are the only one) which do give their students a good training. There is also another danger that has to be watched. A general scheme might induce departments to feel that this is now taking care of the problem, and reduce the incentive to put their own house in order. This would be disastrous. Another danger I can see is that the shortage of time available for a summer school would undoubtedly lead to pressure for specialisation. I am sure that either from the start or in the course of time the scheme would develop in a way in which elementary particle students, nuclear physics students, solid state students, etc. were given separate courses and this could further entrench narrow specialisation. Incidentally, one should not oversimplify the problem by assuming that a satisfactory training necessarily involves organised lecture courses. This is one possible method, which is eﬃcient when one is dealing with large numbers, and probably necessary when one has a small staﬀ-student ratio. A perfectly viable alternative (which after all is the method by which my generation and many later ones were brought up is by personal contact with a good teacher and reliance on reading and discussion under guidance. This requires, of course, that the number of students supervised by one person could not be excessive and that the supervisor should be willing to give time and thought to their needs. It also requires, of course, that an adequate proportion of the teachers should have the necessary breadth and depth of understanding and the capacity for transmitting it. I agree with Bethe’s remarks about the quality of American graduate schools; but it would be a fatal mistake to attribute this to certain ∗ But

an advanced summer course can, of course, usefully add to this — though that is a diﬀerent scheme and more like existing summer schools.

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speciﬁc features of their courses and to believe that by imitating those features we could reach the same standard. You will remember the arguments we had in Birmingham who reasoned that Cambridge and Oxford undergraduate courses had undoubtedly high standards; they are residential universities; therefore to approach their quality all provincial universities must provide halls of residence. I recall that you were as emphatic as I was in pointing out the fallacy of this argument. American postgraduate lecture courses have to be seen in their context. In part they replace the ﬁnal stages of our undergraduate course. Where they go beyond this they are not always very good. For example, when I was in Columbia in 1959 I was appalled by their system. The strength of their postgraduate system arises primarily from the quality and enthusiasm of their staﬀ. In part these are the result of a system which presses ruthlessly for quality, with very ﬂexible provision for making appointments and promotions very diﬀerent from our basic philosophy of “wage for age” and early security of tenure. Their system has, of course, its dangers in that the unorthodox easily get under the wheels, as Willis Lamb1018 nearly did and possibly would have done if he had not possessed private means. One must also remember that in America there is a vast number of second-rate universities, some without graduate schools, and some with graduate schools of very poor quality; and the leading ones, which we all know, rose to their present position by an evolutionary process of survival of the ﬁttest. At present America has also severe troubles about professional unemployment and this is aggravated by a tendency that the graduate training is regarded by student and teacher as a preparation for work in a narrow ﬁeld. More American Ph.D.s than ours are willing to think of a job in industry, but if a nuclear Ph.D. goes into industry he expects to work there on nuclear physics, and his training has probably neglected classical physics and led to a feeling of contempt for this, more eﬀectively than for his counterpart in this country. 1018

Willis Lamb (1913–2008) received his Ph.D. from Berkeley in 1938. He continued research at Columbia University where he later became professor. After appointments at Stanford and Harvard, he became Wykeham Professor of Physics at Oxford in 1956. In 1962 he took up a professorship at Yale.

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So I believe one should think about our training from ﬁrst principles and not give too much weight to isolated features of the American system. Yours sincerely, [R. E. Peierls]

[730] Rudolf Peierls to Christian Møller [Oxford], 1.7.1970 (carbon copy) Dear Møller, Thank you for your letter.1019 We were, of course, very distressed to hear about your illness, and the later cancellation of your visit to Queen Mary College suggested that this was taking longer than expected. I hope that by now you have fully recovered from whatever the trouble was. From our point of view the cancellation was, of course, a disappointment, but otherwise caused no particular diﬃculty. I very much hope that we may regard the visit as only postponed. As I think I mentioned, we had previously a talk by Landsberg1020 on a similar subject, who mentioned the points on which he believed you disagreed, and we found his arguments on those particular points (if not others) rather convincing, so that we were looking forward to the opportunity of hearing your side. Another point on which I would very much have liked your opinion concerns the old question of the momentum of a light wave in a refracting medium, on which a student of mine1021 has done some work, inspired by someone in Italy who is trying to do an experiment on this 1019

Letter could not be located. P.T. Landsberg obtained his Ph.D. from London in 1949. After lecturing at Aberdeen, Landsberg took up professorships at Cardiﬀ (1959–1972), Southampton (1972–1987) and a research professorship at Gainesville, Florida (1984–1988). 1021 The student referred to here was Michael G. Burt. 1020

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question.1022 In your book on relativity1023 the questions appears to be left open whether the answer given by Minkowski1024 or that by Abraham1025 is right. The ﬁrst would give for the ratio of momentum to energy the result 1/c , in other words the value n, whereas Abraham predicts c /c2 or 1/n. Here, of course, c is the velocity of light in the medium. Our conclusion is that Abraham is right, and this follows very simply from the fact that one can prove the stress tensor to be symmetric in all circumstances. The answer is also given by Landau and Lifshitz,1026 though I am not sure that their argument is fully convincing.1027 When my student’s work is written up we shall send it to you and we would appreciate your comments. I believe you have a second edition of your book ready, and if in that connection you have views on the question I would of course, also be very interested.1028 Yours sincerely, [R.E. Peierls]

1022 Burt and Peierls published a paper on the problem in 1973. M.G. Burt and R.E. Peierls, ‘The momentum of a light wave in a refracting medium’, Proc. Roy. Soc. A333, 149–156 (1973). 1023 Christian Møller, Theory of Relativity, Oxford, Clarendon, 1964. 1024 H. Minkoswski, ‘Die Grundgleichungen f¨ ur Elektromagnetische Vorg¨ ange in bewegten K¨ orpern,’ Math. Ann. 68, 472 (1910); and H. Minkowski, ‘Die Grundgleichungen f¨ ur elektromagnetische Vorg¨ ange in bewegten K¨ orpern’, Nachr. Ges. Wiss. G¨ ottingen 1908, 53. 1025 M. Abraham, ‘Zur Elektrodynamik bewegter K¨ orper’, Rc. Circ. Mat. Palermo 28, 1; M. Abraham, Rc. Circ. Mat. Palermo 30, 33. 1026 L.D. Landau and E.M. Lifshitz, Electrodynamics of continuous media, London: Pergamon, 1960, §56. 1027 Burt and Peierls wrongly concluded that Abraham’s prediction was correct, because of an error in the use of the relativistic expression for energy ﬂux. This error was later corrected in R.E. Peierls, ‘The momentum of light in a refracting medium’ Proc. Roy. Soc. A347, 475–91. The correct answer is presented in R.E. Peierls, ‘Momentum and pseudomomentum of light and sound’, in F. Bassani, F. Fume, M.P. Tosi, Highlights of Condensed Matter Theory, Amsterdam, Elsevier 1983, 89 and 237–55. 1028 The second edition of Møller’s book on the theory of relativity appeared in 1972.

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[731]Christian Møller to Rudolf Peierls Copenhagen, 25.9.1970 Dear Peierls, Thank you very much for your letter of 1st July,1029 which I should have answered earlier, but for several reasons, particularly the preparations for the International Conference on Gravitation and Relativity here in Copenhagen, I have been rather busy during the summer.1030 My present views on relativistic thermodynamics are perhaps not so far removed from those of Landsberg, and will be found in the new editions of my book on relativity, which is now being printed at the Clarendon Press.1031 Under separate cover I send you my latest paper on the subject which more or less contains what I wanted to say in my intended talk in Oxford this summer. With regard to the old controversy between Abraham and Minkowski,1032 investigations by I. Brevik1033 1. Minkowski’s tensor 2. Discussion of various tensor forms (Nordita publications nos. 323 and 3401034 ) have convinced me that the separation between the matter part and the electromagnetic part of the energy momentum tensor to a large extent is a matter of taste. For some problems, one separation may be natural, 1029

Letter [730]. The Conference on Gravitation and Relativity took place in Copenhagen in July 1971. 1031 See letter [730], note 1023. 1032 See letter [730], notes 1024, 1025 and 1027. 1033 Iver Brevik, Institute of Theoretical Physics, University of Trondheim, later published his results more widely in I. Brevik, ‘Experiments in phenomenological electrodynamics and the electrodynamic energy momentum tensor’, Physics Reports 52, 133–201 (1979). See also I. Brevik, K. Danske Vidensk. Selsk., Math-fys. Meddr. 37, 11 and 13. 1034 Between 1958 and 1977 NORDITA published a series of research papers, the Nordita publications. 1030

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and for other problems, it is more appropriate to make the separation in a diﬀerent way. However, for the description of light passing through a transparent medium, the Minkowski tensor still seems to give the appropriate description since the velocity of the energy according to this tensor has the well-established properties of the velocity of a light ray. Symmetry is of course an essential property of the energy momentum tensor for the closed system of matter plus electromagnetic ﬁeld. However, for a part of the system, like the electromagnetic ﬁeld in a dialectic, the corresponding energy-momentum tensor need not be symmetric. It will be a pleasure to read the mentioned work of your student when it is written up, and I shall also let Mr. Brevik have a look at it. With best regards, Sincerely yours, C. Møller

[732] Rudolf Peierls to Hans Bethe [Oxford], 20.5.1971 (carbon copy) Dear Hans, I am a member of the Scientiﬁc Advisory Committee of the French Institute of Advanced Study at Bures, of which you will know.1035 The Institute is active in mathematics and theoretical physics. On the physics side its permanent members, as you may know, are L. Michel and D. Ruelle. Negotiations are now going on to secure international support for the Institute and, as a result, it may well be possible in the near future to appoint two more physicists on a permanent basis. I am trying to collect suggestions of suitable names. 1035

´ The Institute des Hautes Etudes Scientiﬁques had been founded by L´eon Motchane in 1958 as a European counterpart to the Institute for Advanced Studies at Princeton. In 1963 Peierls was invited to join the Scientiﬁc Advisory Committee on which he served until 1974. See Peierls Papers, Ms. Eng. misc. b224, F.12–15.

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So far the orientation of the work has been somewhat abstract, partly because the present and former members were somewhat inclined that way, partly because the presence of ﬁrst-rate pure mathematicians tends to attract people with formal interests, for example Wightman 1036 is a regular visitor there, but the visitors cover a wide spectrum. New appointments might well be people ﬁtting in with the present image of the place, but alternatively it would be an interesting idea to broaden the range by using the two new places, if they can be conﬁrmed, for bringing in people with slightly diﬀerent, and perhaps more practical emphasis. The posts are attractive; they correspond in status to full professorships. The salaries are higher than those of say, English chairs, but not as high as American ones. One knows that at this time there may be people in established positions, for example in the United States, who nevertheless want to change, but it is very hard to know where they are, and for this reason I have been encouraged to use the grapevine to ensure that people like yourself are aware of the possible existence of these posts, and might let me (or Michel, or Ruelle) know if you happen to hear of someone who might be interested. Yours sincerely, [Rudi]

[733] Kitty Oppenheimer to Rudolf Peierls Princeton, [date unspeciﬁed]1037 Dear Rudy, After an essential period of adjustment I believe that at last I am ready to write a book about Robert. During the time it has been taking shape, 1036

Arthur S. Wightman (1922–) obtained his Ph.D from Princeton in 1948, where he eventually became professor of physics. 1037 Letter probably written in January 1972.

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other, and very inaccurate, books have been written; one of these hodgepodgers of fact and fancy is, I am told, even being used as a source book. I would like to go into Robert’s life from as early as possible to the end. For that I will need the help of all his friends; any letters they can provide or lend me, and above all their memories of times and discussions with him. I must rely entirely on these until 1939. After that my own memory will help my way, but still not without the aid of his friends. It has been pointed out to me that I will need a physicist for that enormous part of Robert’s life. Dr. Robert Serber1038 has been suggested by my friends and he has most kindly consented to help. He was with Robert from 1934, ﬁrst as research assistant, then as collaborator and friend. Many of the letters to me at the time of Robert’s death showed an insight and a sensitivity that makes me conﬁdent of real contributions, long or short, from most of Robert’s friends. I spoke to one of our grand old men of physics who oﬀered no correspondence nor any stories, but said: “Kitty, I want to write twenty or so pages myself”. Such a response is even more than I hoped for and in return gives me courage to send you this letter. The above letter to pertinent and impertinent people. My love to you and Genia, Kitty

1038

Robert Serber (1909–1997), obtained his Ph.D. in 1934 from the University of Wisconsin; he then worked with Oppenheimer at Berkeley and later became associate professor at Wisconsin and professor at Berkeley before taking up a professorship at Columbia University in 1951 where he stayed for the remainder of his academic career.

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[734] Rudolf Peierls to Kitty Oppenheimer [Oxford], 18.1.1972 (carbon copy) Dear Kitty, I am very pleased to hear about your project of writing a book about Robert. One would have been, in any case, pleased to look forward to this, but this feeling is enhanced by the large amount of rubbish which has been written. I am certainly happy to help in any way I can. I suspect this will not amount to very much. I shall write down any conceivably relevant things which occur to me. If you want me to elaborate on any of them I shall try, and if any further points occur to me later, I presumably can still add them. I ﬁrst met Robert one summer in Zurich, when I was working with Pauli, and he was visiting for something like a summer’s semester. This was probably 1929. Unfortunately, I do not remember anything that is signiﬁcant. I was then keen on sailing, and quite often rented a boat on the lake. On a few occasions I persuaded Robert to come along. I probably would have forgotten even that, except that I have some photographs taken on the sailing boat which I shall send along as soon as I can get them copied. Otherwise I remember being rather awed in Robert’s presence, as he was so obviously a man of the world, and I still remember with embarrassment when at some party I failed to grasp the point of an anecdote he was telling, so that he explained the point in words of one syllable. He did so, of course, perfectly politely without any hint that I was being dense, but that did not make it any better. I also remember Pauli saying that Robert was travelling with his own carpets and pictures to make any digs he was in more habitable. I do not know whether this was supposed to apply to the short stay in Zurich, nor do I know whether the whole remark was accurate or whether Pauli was exaggerating, but at least it shows Pauli’s impression at the time. I believe I did not see Robert again until 1942. Our paths might conceivably have crossed at some conference, if so, I have no recollection.

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In ’42 I was sent over to discuss atomic energy, and in the course of that travelled to the West coast to spend a day or two with Robert. These brief discussions were very impressive, because none of the people I met during my travels through the United States at the time had thought as clearly about the possibility and implications of a weapon. We had in England devoted a great deal of simple thought to this, and I was rather surprised that nobody in the United States seemed to have looked at the technical implications at all (with the possible exception of Fermi who was rather reticent about it, but might well have known the answers). As a result of these conversations I may have played some part in the subsequent development. After my visit to Berkeley I received a request to come for a second visit to Chicago to talk to Arthur Compton. He wanted to see me because he had heard that I was rather dissatisﬁed with the arrangements for looking at the weapons physics (this was at the time when Gregory Breit interpreted his duty as “Coordinator of Rapid Rupture” by locking all the documents he was given in a big safe, and making sure that nobody else had the combination or the documents). Compton wanted my comments on what needed doing, and if a person was to be put in charge, who it ought to be. The conversation led to the suggestion that it might be Robert. My memory is hazy as to how precisely it came up, but I believe it was mentioned by Compton who asked what I would think of the idea. It is not impossible that he had just invited suggestions, and that I ﬁrst mentioned Robert’s name, but, if so, it was evidently something he had already thought about. It goes without saying that I was highly enthusiastic about this suggestion, though how far this inﬂuenced Compton’s position I cannot say, of course. My next encounter was in 1943, then the exchange of information about atomic energy between the U.S.A. and the U.K. which had been interrupted was just being resumed, but with severe limitations. Robert was rather irritated by these restrictions; in the end permission was given for him to talk to me, this conversation took place in the presence of a witness, and must have been quite uncomfortable for him, because he could mention to me only some matters, and would have liked to tell me the rest. At least he was able to explain that he was not telling all he knew.

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Then a visit to Los Alamos. Later, as you know, we moved to Los Alamos. There is nothing to report about our eighteen months there that you don’t already know, except one episode which in the light of later history seems particularly interesting: Some time, I believe, in 1945, Lord Cherwell than a British Cabinet Minister visited Los Alamos. Robert was busy all day showing him round. At one point he rushed past me in the corridor to take an urgent phone call, and as he passed me he just had time to claim “that guy will never understand a thing.” This, however, is not the point of my story. In the evening you gave a party in honour of Cherwell, and it was intended that I should be amongst the invited (I was then in charge of the UK mission at Los Alamos, so this was fairly obvious). However, because of an error in the oﬃce I was never invited. Next day, Robert came to apologize for the omission, and added: “this is very embarrassing, but there is only one comforting though in this situation: it might have happened with Edward Teller.” I took this as a compliment, as it was no doubt intended, but looking back it has quite interesting implications. In later years I saw Robert on many occasions in various places, as you know, but I do not think I can add for that period anything to what you know, or will hear from others. A possible exception is a remark he made when Genia and I saw him Princeton for the last time. The conversation turned to the history of his troubles with the A.E.C., and the point came up, perhaps he ought to have resigned from the General Advisory Committee when his recommendation about the hydrogen bomb was overruled. He then, a little later, made a remark in a slightly diﬀerent context, but quite evidently still having the earlier point in mind. He then referred to the attitude “as long as I ride on this particular train it is bound to go to the right destination.” This is all for the present, except the pictures, and it is not very much. May I now come to you with a request myself? I have just been persuaded to write about Robert for the Dictionary of Scientiﬁc Biography, which seems a serious project. This, of course, will be on a very diﬀerent level, and mainly about his inﬂuence on physics with some mention of

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his part in public aﬀairs, and even less his personal history. However, I wonder whether you would be willing to look at the draft of this, when there is one, to tell me about anything that sounds wrong to you. Yours sincerely, [Rudi] P.S. Here are a few more thought conceivably worth mentioning. One is a rather neat illustration of Robert’s courtesy and attention to detail. When I spent a semester at the institute in 1952, I had originally imagined that the size of Princeton being what it is, there was no need to have a car. One evening there was a party at your house, and when the party broke up, Robert evidently remembered that I had no car, and noticed that all the other guests were neighbours, so he went to get his car out to drive me home. I protested, insisting that I liked walking and at this particular point would quite like some fresh air. He disposed of this with the remark “I shall drive you home and then, if you want to go for a walk you can.”’ (Next day I bought a car). His interest in people, and his awareness of so many seemingly unimportant facts about them, which is illustrated by this anecdote, contrasts in a way with his absolute intolerance in matters of style and taste. This is brought out in the classical, and very widely known story with which, I am sure, you are familiar of his remark to the man who ordered his steak well done “why don’t you have ﬁsh.” It also goes together with the fact that with all his consideration for the possible desires of guests, when he oﬀered one coﬀee there was never any milk or cream, though of course, it would appear when asked for (I hope I am not being discourteous here in case this was your doing and not Robert’s!). Another area of great intolerance, of course, was on the intellectual level, including physics, where he certainly did not suﬀer fools gladly, and could be quite devastating to people presenting confused or inadequate arguments, including sometimes young seminar speakers who did not deserve it. However, I should not embark here on the subject of Robert’s physics.

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[735] Rudolf Peierls to Hans Bethe [Oxford], 8.2.1972 (carbon copy) Dear Hans, I believe Dick Dalitz is writing to you to explore the possibility of your coming to Oxford in 1973–74 as a Visiting Fellow of All Souls College. I am writing to add my own voice to his, and saying how enthusiastic we would all be about such a proposal, if indeed it needs suggesting. I think you know what is being done in the department, and what kind of people are around, though I would be happy to go into details if you wish. On the practical side, apart from housing which no doubt will be looked after by the college, we would, of course, make arrangements of ﬁnancial support. The most obvious way of doing so is through a “Senior Visiting Fellowship” granted by the Science Research Council. I have, in fact, at my disposal a research grant which goes on until 1973– 74, the subject of which is “Nuclear Dynamics”. If you were interested in taking some interest in nuclear problems while you were here (which would, of course, not stop you from being interested in other matters as well!) we would conﬁrm the arrangement forthwith from an existing budget, but if this is not in line with what you might like to do, I have no doubt we could get a separate grant for the purpose, or change the terms of reference of the existing contract accordingly. The fellowship could carry a full professorial salary (currently £5, 472 p.a.) if you are not receiving a salary from other sources in respect of the same period. If you receive some of your Cornell salary, they would pay only the diﬀerence which is not likely to amount to much unless any partial support from Cornell could be arranged to relate to part of the time only, in which case we could pay for the rest of the period. Assuming you would receive a salary which would preclude us from paying you a salary from this end, we would still be able to pay your fare, and a subsistence allowance meant to cover extra costs of living away from home, which has to be computed in each case, but would come to something like £1, 000 for a year, and proportionately

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more for a shorter period. This subsistence would not be taxable; any salary we can pay might or might not be subject to U.K. tax depending on whether your appointment here can be classed as a teaching post, which it might be, if you are willing to take some interest in our graduate students. In that case, it would come under the bilateral convention on such matters. Whether it is liable to U.S. tax, of course, I would not know. I should apologize for this mercenary sounding exposition; it is in any case clear that if you came here, it would not be to make a proﬁt, but it is just as well to be clear about what is involved. I was grateful to you for bringing Mikkel Johnson1039 to my attention. I was about to send him an invitation when he withdrew because of an oﬀer from elsewhere, but such is life. Yours sincerely, [Rudi]

[736] Hans Bethe to Rudolf Peierls Ithaca, 15.2.1972 Dear Rudi: Thank you very much for your letter of 8 February.1040 It is a very nice oﬀer, and it would be nice to spend some leisurely time with you. However, rather than being too early, it is already too late. I have already made arrangements for the three coming academic years. In the fall terms I shall still be teaching at Cornell, and for the spring terms I have accepted invitations to Seattle, Copenhagen, and Munich respectively. How I will feel after that, I cannot tell at present, but I have the feeling that I will by that time be somewhat tired of travelling, and will like to stay at home for most of the time. 1039

Mikkel B. Johnson had obtained his Ph.D. from Carnegie Mellon University in 1970. After research at Cornell, he took up a post at the Los Alamos National Laboratory in 1972, ﬁrst as a staﬀ member and since 1991 as a fellow. 1040 Letter [735].

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So thank you very much again. You have worked it out so beautifully, but I am afraid I shall not be able to come. However, I hope to come for a short visit during my semester in Copenhagen. With best wishes. Yours sincerely, Hans

[737] Nevill Mott to Rudolf Peierls [Cambridge], 2.3.1973 Dear Rudi, I am writing a book on metal-insulator transitions and I want to get the history right.1041 I have always thought A.H.Wilson was the ﬁrst to state clearly the diﬀerence between metals and insulators in terms of full and empty bands. But is this correct? Did either you or Bloch state this ﬁrst? I would be most interested in your views. Yours sincerely, Nevill I know you are retiring. I hope you enjoy retirement. I ﬁnd it most agreeable.

[738] Rudolf Peierls to Nevill Mott [Oxford], 2.3.1973 (carbon copy) Dear Nevill, I am not quite sure what is the answer to your historical questions, partly because I ﬁnd that one must never rely on one’s memory of such matters. 1041

N.F. Mott, Metal-Insulator Transitions, London: Taylor & Francis, 1974.

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I have not searched the literature, but I believe the relevant paper of Wilson was written in 1931 (there m[ight] be an earlier one).1042 I do remember that when I saw those papers it seemed to me that they were labouring the obvious, and that the explanation of an insulator as having one band full and the next empty was an obvious part of what everybody had been saying for the past year or two. It was certainly obvious to me and to Felix Bloch, and probably others. However, my views at the time on what was obvious to everybody were certainly not the standard ones, and the papers I wrote at the time were hard to read just because I went so far in refraining from insulting the reader by explaining things that surely were obvious. My ﬁrst paper (Z. Phys. 53, 255, 1929[)], about the anomalous Hall eﬀect discusses the fact that there is asymmetry between the case of a few electrons near the bottom of a band, and that of a few holes near the top.1043 This is almost the same as saying that if there are no holes there is nothing left to conduct, but this sentence does not appear in the paper. In the summary of a conference talk (Phys.Z. 30, 273, 1929) I give an almost intelligible account of the anomalous Hall eﬀect and show a picture in two dimensions of an almost ﬁlled band, but it does not say that you get an insulator when you ﬁll it completely.1044 At that time I was still unhappy, because it was clear that there were bands, and the possibility of ﬁlling them in the tight binding limit, because Bloch had demonstrated this. On the other hand, in the case of weak binding one seemed to have a continuous spectrum, and since the truth was between these two extremes it did not seem clear whether one was right in assuming the existence of bands or otherwise. This diﬃculty got resolved in my mind only when in my paper in the Annalen 4,121,1930 I gave the argument that even a weak periodic potential will cause breaks in the energy surfaces. This was then used by Brillouin 1042 A.H. Wilson, ‘The Theory of Electronic Semi-Conductors’, Proc. Roy. Soc. A133, 458–491 (1931). 1043 R.E. Peierls, ‘Zur Theorie der galvanomagnetischen Eﬀekte’, Z. Phys. 53, 255–66 (1929). 1044 R.E. Peierls, ‘Zur Theorie des Hall-Eﬀektes’, Z. Phys. 30, 273–74 (1929).

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in his theory of zones.1045 The object of this argument was to show that there would always be breaks, because they existed in the two limits, and that it was therefore reasonable to believe in the existence of band gaps, and therefore of substances with a positive hole eﬀect, and therefore also insulated. In other words, it seems to me quite likely that Wilson’s papers are the ﬁrst in which these statements are made, but it is hard to be sure, since hearing this statement from anyone else at the time would not have sounded to me in any way interesting or memorable. Will you also ask for the recollections on this point of Felix Bloch? Thank you about your comforting remarks about retirement. I shall retire in the summer of 1974, and I expect I shall enjoy the change, but detailed plans are still rather hazy. Yours sincerely [Rudi]

[739] Nevill Mott to Rudolf Peierls Cambridge, 6.6.1973 Dear Rudi, I do not know if you know of work in Friedel’s laboratory on onedimensional metals, namely K2 Pt(CN)4 BR0.30 xH2 O by Comes and others. I have just been in Paris and have been given preprints. The point is that this seems to show a Peierls distortion as described on p. 108 of your book “Quantum Theory of Solids”.1046 This at least is the model which the French physicists favour; the evidence is that at room temperature, where the material is more or less metallic, there is an anisotropy of 105 between conduction along the chains and perpendicular to them, and at low temperatures a small energy gap opens 1045

R.E. Peierls, ‘Zur Theorie der elektrischen und thermischen Leitf¨ ahigkeit von Metallen’, Ann. Phys. 4, 121–48 (1930). 1046 R.E. Peierls, Quantum Theory of Solids, Oxford: OUP, 1955.

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up. There is some x-ray evidence for the distortion, but this seems not deﬁnite. The point I wanted to ask you is whether you would consider that, even if the lattice were rigid, a charge density wave ought to form with the same wave length and produce the same eﬀect, rather than in the spirit of Ovenhauser’s work, which surely ought to be right in one dimension. I would very much welcome your comments, and if you want to see the work I am sure that Dr. Comes would send you preprints (unless you already have them). Yours sincerely, Nevill

[740] Rudolf Peierls to Nevill Mott [Oxford], [date unspeciﬁed] (carbon copy) Dear Nevill, Thank you for your letter of 6 June.1047 I did not reply immediately because I was not familiar with Overhauser’s work. If one is concerned with one-dimensional system then, I believe, both Ovenhauser’s argument and mine apply. They both essentially say that it is energetically favourable to modify the ﬁeld in such a way that a new zone boundary is created at the edge of the Fermi distribution. Both the lattice and the electrons themselves will tend to do so, and since a lattice distortion will cause a loss of translational symmetry in the electron distribution and vice verse, it seems hard to distinguish the eﬀects. The characteristic thing about one-dimensional case is that one can prove that this eﬀect must exist (apart from zero-point ﬂuctuations of the lattice). This, at least, applies to my argument. I have not studied 1047

Letter [739].

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in detail Overhauser’s paper which proves that the eﬀect is always there even in two or three dimensions. In proving that the eﬀect caused by a lattice distortion necessarily leads to a lowering of the energy, I did not, of course, intend to say that it could not also happen in two or three dimensions, and, indeed, we all believe that solid hydrogen forms a molecular lattice, and the picture would ﬁt this well. Incidentally, the proof of the instability works only in a true onedimensional model, and not in a three-dimensional lattice with a very strong asymmetry, because in the latter case the Fermi surface would still be something like a very ﬂat1048 which could at most have a thickened order contact with a boundary zone, but could not coincide with it. I would agree with you that it is not easy to settle from ﬁrst principles which is the dominant mechanism. Incidentally, when Morrel Cohen was here recently he talked about a case where the “Peierls deformation” had been observed. I do not remember the substance he mentioned, or who had done the work, but I had the impression that this was not the same case as that mentioned in your letter. If Morrel Cohen is still in Cambridge, it might be useful to ask him about this. Yours sincerely, [Rudi]

[741] Freeman Dyson to Rudolf Peierls Princeton, 9.11.1973 Dear Rudi, I hope you are out of the cast and hopping around as usual by now. We enjoyed very much seeing you here and hope you come back soon.1049 1048

Missing in carbon copy. While visiting Seattle in the summer of 1973, Peierls had slipped on a mountain path and torn a ligament. 1049

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I did not solve the problem of the photo momentum. I still think about it with a feeling that a really clean understanding of the experiments is needed, before one can trust any formal arguments. In the meantime this article arrived from Ginsburg.1050 See especially the last three pages. Do you agree with this argument? At least he seems to have understood the formal relation between Abraham and Minkowski quite clearly. But he does not go into the details of speciﬁc experiments. I would be glad to hear your reactions. I am still deep in the spectrum problem of correcting a telescope mirror to cancel atmospheric distortion of the image. The prospects of doing something spectacular in this way look quite good. Greetings from Imme to you and Genia — Yours Freeman

[742] Rudolf Peierls to Freeman Dyson [Oxford], 21.11.1973 (carbon copy) Dear Freeman, Your letter made my bad conscience more acute.1051 I should have written long ago to thank you and Imme for being so nice to us, and to report that after another month, ﬁrst on crutches and then in a walking cast (but still no driving) my foot is now practically back to normal and fully usable. I should also have returned the article which you lent me, and this is going oﬀ separately now. I was putting oﬀ writing because I hoped to be able to report a suggestion of a physicist interested in reactor safety, and some lines I followed did not lead anywhere. In case this is still interesting, I am still trying to ﬁnd a suggestion. 1050

V.L. Ginzburg, ‘The laws of conservation of energy and momentum in emission of electromagnetic waves (photon) in a medium and the energy momentum tensor in macroscopic electrodynamics’, Usp. Fiz. Nauk 110, 309–319 (1973). 1051 Letter [741].

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On the question of the momentum of light I have learnt one very important thing: the statement on which we are relying heavily about the symmetry of the stress tensor is a relativistic argument, and requires that in the matter part of the tensor the transport is taken to include the transport of rest energy. Indeed, for free particles, the momentum density mv clearly requires mc2 v in the energy transport. If the mean velocity of the atoms is non-zero there is therefore a term which we would normally include in the energy ﬂux of the light wave. Our assertion that the momentum density must be equal to the Poynting vector divided by c2 is, therefore, wrong. The question is then how big is the mean velocity of the atoms during the passage of a light wave? In a gas at zero pressure, assuming the atoms to have only an electric polarisability and to be non-magnetic one can do the sum very easily, and the extra momentum accounts for just one half of the diﬀerence between Abraham and Minkowski.1052 I do not think this is an error in calculation, but the answer does not seem to ﬁt with the text book derivation of the “Abraham force”, but this must be that the derivation assumes the usual result for the force on a charge or current in a refracting medium and I suspect there is a snag there. In a realistic liquid or in a solid there are other complications. In particular, if one considers the response of an elastic solid to the mechanical force of a small light pulse (i.e. smaller than the solid body) one ﬁnds a situation analogous to the Cherenkov problem since the pulse travels with a velocity much greater than sound velocity, and it should, therefore, continuously emit sound wave. I ﬁnd this a surprising conclusion, but haven’t been able to get away from it. I haven’t yet got a number for the amount of energy carried by these elastic waves, nor have I thought out the consequences for the momentum. Thank you for sending the reprint by Ginzburg which I also return separately. Much of his discussion is confused because he mixes up conservation of wave vector with that of momentum, and his comparison of the classical and quantum case is not very deep. 1052

See letter [730], notes 1024, 1025 and 1027.

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However, he does make some clear statement towards the end about the role played by the Abraham force in the usual treatment, and that I found helpful, although it evidently is not new. As you see I understand much less than I did during our conversation, but the state of confusion is such that I hope to get things sorted out shortly. Yours sincerely, [R.E. Peierls]

[743] Franz B. Jacobsohn to Rudolf Peierls Heidelberg, 28.9.1974 Lieber Rudi, Ich habe mich halb d¨ amlich gefreut u ¨ber Deine Karte aus Bankok. Ich h¨ atte allerdings schon l¨ angst einmal schreiben sollen. Aber ich habe die Altersgrenze leider noch nicht erreicht und es sieht auch nicht so aus, als ob ich sie jemals erreichen w¨ urde. Also wurstele ich weiter, und die Korrespondenz kommt dabei zu kurz. In meiner Branche arbeitet man bis 85, falls einen nicht vorher der Teufel holt. Also Du bist in Sidney. Ich kenne es nur von einem kurzen Aufenthalt von etwa vier Wochen und das ist nun schon zehn Jahre her. Ich habe es in allerbester Erinnerung als eine Stadt, in der man leben kann. Ich hoﬀe, es macht auf Dich den gleichen Eindruck. Wirst Du dort lange sein? Und was wird inzwischen aus Eurem H¨ auschen? Dass Du u ¨brigens unsere alte Kate nicht hast ﬁnden k¨ onnen, erstaunt mich nicht: das Haus an der Suriwongse Road ist sofort nach unserem Auszug abgerissen worden und durch ein großes Hotel ersetzt worden. Das war auch die Ursache unseres Wechsels, den ich u ¨brigens nie bereut habe. Ich denke, Du wirst Dich nunmehr einigen Problemen widmen, die Dich schon immer interessiert haben. Bekommst Du auch Geld daf¨ ur, zumindest ein Stipendium? Also lass mal ein wenig h¨ oren. Ich selbst stecke meine Nase in andrer Leute Sachen, indem ich Vertretungen u ¨bernehme f¨ ur meine Kollegen, die krank oder erholungsbed¨ urftig sind oder es jedenfalls glauben. Das bringt zwar nicht soviel

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wie eine eigene Praxis, l¨ asst mir aber Zeit f¨ ur ein paar Wochen Ruhe zwischendurch. Devise: k¨ urzer treten oder f¨ ur einen alten Nautiker wie Dich: halbe Kraft voraus! Sonst werden wir a¨lter aber nicht sch¨ oner. In Heidelberg wohnen wir bequem, ruhig und ger¨ aumig. H[eidelberg] ist durchaus keine Weltstadt, aber immerhin kein Dorf. Mein Bruder Robert lebt in Berlin, wo er noch etliche Bekannte hat und es geht ihm gut. Wir sehen uns von Zeit zu Zeit. Im u ¨brigen lassen wir die Inﬂation an uns herankommen, wir sind ja geschult. Und was kann man tun? Ich h¨ orte gerade sehr viel Schlechtes u ¨ber Australien von Freunden in Sydney, die kleine Gesch¨ aftsleute sind. Solchen geht es aber zur Zeit u ¨berall nicht gut und sie leiden unter der modernen Sozialpolitik in jedem Lande. Das ist vermutlich unvermeidbar, ebenso wie die G¨ otterd¨ ammerung bei den Akademikern. Es fragt sich nur, ob es irgend jemandem hilft. Die allgemeine Hilﬂosigkeit ¨ der Okonomen wird nur von ihrer Arroganz u ¨bertroﬀen, mit der sie die Dinge dieser Welt regeln, in der vagen Hoﬀnung, es wird schon alles weiter gehen im alten Sinne. Hoﬀentlich behalten sie recht. Ich f¨ urchte, wir sitzen bald mal wieder auf einem Scherbenhaufen, wenn diesmal noch soviel u ¨brig bleibt. Aber das nur in Parenthese. Vorl¨ auﬁg geht es uns noch Danke und da wird man ja sehen. Also, lass Dir den Sonnenschein von Sydney munden, wenn Du an die Wintermisere von England denkst! Denen geht es wirklich noch viel schlimmer als uns hier. Solltest Du in absehbarer Zeit mal wieder nach Europa kommen, erwarte ich, dass Du in Frankfurt den Zug nach Heidelberg nimmst, es ist nota bene nur eine (1) Stunde Fahrt. Aber vorher schreibe ich nochmal, damit das Interval nicht allzu gross wird. Viele liebe Gr¨ usse auch an Deine Frau und den Rest der Familie. Auf wieviel Enkel hast Du es eigentlich schon gebracht? Wir protzen mit neun! Nur wir sind so verdammt weit voneinander entfernt, dass man sich ¨ausserst selten sieht: 2 S¨ohne in USA, Californien und Maine. Eine Tochter in Kenia. Man wird sich langsam fremd. Ich nehme an, bei Euch klappt es besser: Ihr seid wenigstens in demselben Land. Na, wir haben uns ja dieses Leben nicht ausgesucht. In diesem Sinne viele herzliche Gr¨ usse und Geburtstagsw¨ unsche soweit am Platze. Dein Franz

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10.

1974–1986:

Retirement — Two Birds of Passage

Despite the marked diﬀerence in their characters, Genia and Rudolf Peierls had many common interests and certainly one common passion: travel. In the twelve years between Rudolf Peierls’ retirement from his Chair at Oxford in 1974 and Genia’s death in 1986, the two rejoiced in the opportunities provided by the more ﬂexible work arrangements, which Peierls’ semi retirement made possible and the opportunities which the plentiful invitations to far ﬂung places brought. The travel schedule was truly astounding with regular visits to the University of Washington, Seattle, where Peierls took up a part-time appointment which resulted in him visiting Seattle between February and May each year until his retirement, at the age of 70, in 1977. Other places visited between 1974 and 1996 included Sydney, UCLA, UBC (Vancouver), Princeton, Oregon, Mexico, Pisa, Coimbra, Copenhagen, Finland, Russia, Italy, Stanford, Japan, Virginia, Toronto, Yugoslavia, India, Greece. Often the visits were initiated by invitations from abroad to give lectures or seminars and frequently Peierls was also asked to take up temporary residence as a visiting professor. The contacts came about, more often than not, as a result of links through former doctoral students or research fellows, who had moved on to become the next generation of professors or researchers in key positions. For example, the Peierls couple when touring the US following ‘Prof’s’ ﬁrst longer stay at Seattle in the spring of 1975, visited a former student and by now close friend, Nina Byers. She had advanced to a full professorship at UCLA, and in retirement the Peierls remained in contact by correspondence and regular visits.1053 One such letter is a good example of the way in which 1053

See letters [745], [747], [755–756], [760], [764], [768], [782], [814–815], [827].

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Genia and Rudi Peierls complemented each other in the way they communicated with others and mixed socially. While Nina Byers’s ability as a scientist had led Pauli to the infamous compliment that she was a ‘very clever girl’,1054 she was a notoriously bad time keeper, which led to a variety of problems and inconveniences for herself and others. Genia Peierls, never one to mince her words or indeed hold back with advice — wanted or unwanted — after Nina Byers had missed a visit to Oxford for such reasons, drafted a letter to Nina. This was copied, corrected, commented on and sent to Nina by Rudi.1055 Genia’s comments were characteristically frank: ‘After the disaster of your Oxford visit, or nonvisit, I think you will see an immediate need to reform. As I said on the phone, 50+ is a very good time for a reform, rethinking, and turning over a new leaf. · · · I think the main trouble is that you expect people to be “supportive”, and are upset when they are not particularly so. I don’t see any need for anybody at 50 to be supported. You ought to support others. When one is young, inexperienced and makes terrible blunders one needs support. And when one is getting very old and tottery. Otherwise one cannot expect it. And that probably is the root of your many troubles. A crazy young girl may be appealing, but a crazy middle-aged woman is irritating. This is a fact of life.’ Blunt as the letter was, it did not aﬀect the cordial relations between the Peierlses and Nina. Letters, phone calls and visits continued! While travelling took up far more time of the Peierls couple than in previous years, it still left plenty of time for reviving contacts with old friend which had been dormant for years and sometimes decades. Among those friends were some from school and student days in Germany, such as Heinz Rudolph,1056 Hans Thorner,1057 and Franz Jacobsohn.1058 It was diﬃcult to keep up with the whereabouts of Rudi and Genia, and conversely travelling made it diﬃcult for the couple to keep up with regular correspondence. Therefore they started sending annual 1054

Peierls, Bird of Passage, p. 240. Letter [782]. 1056 See Lee, Peierls Correspondence, Vol. 1, p. 12. 1057 See Lee, Peierls Correspondence, Vol. 1, letter [10]. 1058 See references in Lee, Peierls Correspondence, Vol. 1. letters [13], [72–73]. 1055

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circular letters at the end of the year which were included in the Christmas cards. Often these circulars rekindled communications, such as the correspondence with Ilse and Hans Thorner, old student friends who had settled near London.1059 Another contact was re-established as a result of a trip to Bangkok en route to his ﬁrst visiting professorship after his retirement, a threemonths assignment in Sidney. A distant cousin and close friend from Berlin, Franz Jacobsohn, had moved to Bangkok during the war and settled there for many years after the war before moving back to Germany in retirement; and the stop-over in Bangkok was a welcome excuse to send Franz a postcard, which restarted their correspondence and eventually resulted in a meeting in Heidelberg after not having seen each other for several decades. The circular letters also led to renewed communications with Peierls’ best friend from school, Heinz Rudolph.1060 After initial short replies to the annual reviews of 1977 and 1978, in February 1979 Heinz sent Rudi a long letter with his personal recollections of and experience during the war years.1061 Correspondence continued, following a pattern of Rudi sending his annual circular and Heinz replying early in the new year, and as with Franz Jacobsohn, eventually, the two met in 1992, when Rudi paid Heinz a visit on one of his trips to Germany.1062 A recurring nuisance for the Peierls family, above all for Rudolf Peierls himself, were the continued attempts of some to link him to Soviet espionage circles. As a German-born Jew with Russian wife and numerous friends in the Soviet Union and communist contacts elsewhere, as a close friend of Klaus Fuchs’, and as a nuclear scientist with access to classiﬁed information relating to atomic weapons, Rudolf Peierls (and his wife) had been subjects of suspicion throughout the Cold War. He had been under secret service investigation from 1938, when he had re-entered the United Kingdom after a visit to Russia, and naturally remained so throughout the war and beyond, until his ﬁle was closed in 1059

Letter [774]. Letters [750], [753], [851–52], [861], [875–76], [881], [940]. 1061 Letter [753]. 1062 See ‘Dear Everybody’, 12.7.1992. Family Possession. 1060

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1953. This exhaustive Security Service investigation over ﬁfteen years uncovered no evidence of any wrongdoing on the part of Peierls; quite the contrary. In 1948, after espionage suspicion had ﬁrst fallen on Klaus Fuchs, and Peierls was closely scrutinized, an MI5 oﬃcer minuted, ‘not only have we nothing against him, but he is a man of very good sense.’1063 Further investigations in the early 1950s in the aftermath of Fuchs’ arrest and conviction led to the categorical conclusion that ‘there is no substantial doubt about the loyalty of Prof. Peierls.’1064 The alleged discovery of possible spies or the naming of good ‘candidates’ for the identities of hitherto unidentiﬁed spies had been a popular past-time among several historians and journalists, and the Peierlses found themselves at the receiving end of such allegations on several occasions. As one commentator remarked in this context, ‘not only is a lie half way round the world before the truth has got its boots on, but a charge of espionage against a former knight of the realm is better news than a reasoned denial.’1065 With British libel laws allowing any such accusations being aired without legal repercussions, Rudi and Genia were accused posthumously, but also — by accident — allegations about Rudolf Peierls were made in writing in the late 1970s, when he was still alive. The journalist Donald McCormick, alias Richard Deacon, had written a book entitled The British Connection, to be published by Hamish Hamilton, about the alleged activities of Russian revolutionary agents in Britain. It contained many unsubstantiated allegations, and it also contained some defamatory passages about Rudolf Peierls, whom the author apparently believed dead. With details being mentioned in a prepublication, Peierls was able to serve a writ, and an out of court settlement was reached with the defendants (Donald McCormick and Hamish Hamilton) acknowledging that there was ‘no foundation for the grave allegations made against Sir Rudolf and to apologise unreservedly for the fact that they came to be made in the book.’1066

1063

NA: PRO KV2/1658. NA: PRO KV2/1662. 1065 Brian Cathcart in New Statesman, 7.10.2004. 1066 Statement in Open Court, copy of transcript in possession of Peierls family. 1064

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The publishers agreed to pay substantial damages, and Peierls decided to donate these to the British Pugwash Movement.1067 Peierls still followed many broad conceptional developments in physics, and he continued to engage in debates, when he held strong views about fundamental questions. One such example is his correspondence, in the 1980s, with John Bell.1068 After graduating from Queen’s University Belfast in physics and mathematics, in 1949 Bell joined the UK Atomic Energy Establishment at Harwell, from where he was seconded to do some research work in Peierls group in 1951. It was in this initial year at Birmingham that Bell produced his version of the CPT theorem which states that the combined operation of charge conjugation (in which a particle is replaced by its antiparticle) parity reversal and time reversal is a symmetry operation that leaves the system unchanged. After obtaining his Ph.D. from Birmingham and several years of research, mainly in nuclear physics, he moved to CERN, where he spent the remainder of his scientiﬁc career. While from then on particle physics was the subdiscipline with which he earned his keep, Bell’s real passion was quantum theory, and he investigated the implications for nature of the theory. This led him to criticise the quantum mechanical interpretations, speciﬁcally the so called ‘Copenhagen interpretation’ and to suggest some alternatives. Peierls rejected both Bell’s objections to the standard interpretation of quantum mechanics, and Bell’s alternative approaches. This led to a lively exchange over the next three years,1069 which, however, did not lead to a resolution of the controversy. Peierls’ ﬁrst hand knowledge of a signiﬁcant period in 20th century science, his personal insight and his plentiful recollections were an often-sought source of wisdom for historians, science historians and journalists. Frequently, he was asked for interviews, for comments on ideas for books or TV and radio programmes, for comments on drafts 1067

Letter [757]. John Steward Bell (1928–1990), joined UKAERE in 1949, obtained his Ph.D. from Birmingham in 1956. In 1960 he moved from Harwell to CERN where he spent the rest of his career. 1069 See letters [762], [765–766], [777], [787], [789]. 1068

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or he was approached to review books on various science or science historical topics. He commented in detail on Montgomery-Hyde’s book on Klaus Fuchs,1070 and on Bethe’s reﬂections on Los Alamos,1071 he took issue with John Hendry’s presentation of physics at Cambridge in the 1930s,1072 discussed Roger Stuewer’s article on Niels Bohr, and he criticised Andy Humphrey’s draft of a documentary on Klaus Fuchs to name but a few examples.1073 Peierls took his role as evaluator seriously and did not pass judgment easily or light-heartedly. This is evident in much of the correspondence surrounding his biographical contributions and his obituaries. A particularly poignant example is his attempt to do justice to one of his teachers and subsequently a most controversial ﬁgure in German wartime science: Werner Heisenberg. Peierls held very strong views about the attitudes and actions of those scientists who, reluctantly or not, cooperated with the Nazi regime. This was evident in his memorandum on German scientists, circulated in 1948.1074 It is telling of Peierls’ attitude that, despite his rejections of the actions of many of his German colleagues, he was instrumental in bringing about dialogue on a scientiﬁc plane after the war. As Ed Salpeter described his experiences in the early post-war years at Birmingham: ‘The early postwar years in England were also memorable for observing the bigshots in theoretical physics at conferences that Peierls organised. It was particularly interesting to watch the ﬁrst time Werner Heisenberg met Peierls, Bethe, Frisch, Oppenheimer, Pauli, Dirac and others after the war. It was a strained atmosphere.’1075 Although Peierls had formulated his own views on German war-time science, he strove to understand what made people co-operate with a murderous regime, and in particular what made Werner Heisenberg, his much respected teacher, collaborate. Peierls

1070

Letter [767]. Letter [786]. 1072 Letter [795–797]. 1073 Letters [812–813]. 1074 Item [440]. 1075 E.E. Salpeter, ‘A Generalist looks back’, Annu. Rev. Astron. Astrophys. 40, 1–25 (2002), here p. 5. 1071

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review of Physics and Beyond1076 shows him grapple with this question, as does his review of David Cassidy’s biography of Heisenberg1077 and the correspondence surrounding the obituary of Heisenberg, which Peierls wrote for the Royal Society Memoirs.1078 Heisenberg’s widow, who naturally had a very diﬀerent perspective on her husband and especially on his war-time experiences and actions, applauded Peierls’ fairness in providing a balanced and just picture.1079 Peierls encouraged her to publish her own recollections — more evidence of his desire to see as complete a picture emerge as possible.1080 In the mid-1980s, Peierls was again confronted with Heisenberg’s role in war-time Germany, when Paul Lawrence Rose consulted him in connection with a book on Furtw¨ angler, Heidegger and Heisenberg, as three paradigms of German “conscience” during the Third Reich.1081 Peierls took great pains to answer the queries accurately and the letters exchanged between him and Rose are revealing in that they demonstrate that Peierls was quite prepared to see his own convictions overturned by new evidence or reinterpretation of old evidence. In his answer to Rose’s question about whether Heisenberg knew the critical mass of U235, he described how he initially thought that Heisenberg did not, but was later convinced by new evidence, that Heisenberg had in fact had an understanding of the amount of uranium needed for a nuclear bomb.1082 In a later letter, he commented in some detail about a misguided interpretation of Rose who had put forward an explanation according to which Heisenberg had known about the order of magnitude of the critical mass but had assumed a greater mass could be assembled without explosion.1083 While Peierls took issue with some of Rose’s 1076

R.E. Peierls, ‘Atomic Germans’, N. Y. Rev. Books, 1.7.1971, 23–24. R.E. Peierls, ‘The Uncertain Scientist’, N. Y. Rev. Books, 23.4.1992, 43–45. 1078 R.E. Peierls and N.F. Mott, ‘Werner Heisenberg, 1901–1976’, Biographical Memoirs of the Fellows of the Royal Society 23, 213–51 (1977). 1079 Letter [749]. 1080 Letter [751]. 1081 Letters [803–804]. 1082 Letter [805]. 1083 Letter [811]. 1077

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explanations, he found the gist of the argument put forward by Rose convincing, namely that Heisenberg had no idea how to assemble a nuclear bomb.1084 However, after several more detailed exchanges, after a thorough examination of Heisenberg’s papers on the subject and after a discussion with Mark Walker1085 Peierls ﬁnally reverted to his initial interpretation of Heisenberg’s development of thought about the feasibility of nuclear weapons.1086 In other instances, too, Peierls tried to compare his own recollections with those of others, or attempted to reconcile diﬀerent versions of the same historical event. In letters to Hans Bethe, he endeavoured to throw light on some details of the thoughts on the compound nucleus,1087 in correspondence with Abdus Salam he tried to recapitulate the origin of Salam’s famous neutrino paper,1088 and in letters with numerous historians of science he clariﬁed many controversial issues.1089 ‘Prof’ had always tried to keep in touch with his Russian friends, colleagues and in-laws, and his additional time for travel and leisure facilitated this. Often Peierls provided the ‘semi-Western’ angle on biographical material concerning Russian colleagues or he liaised between Western and Russian colleagues in other history of science projects or even human rights issues. For instance, he wrote his recollections of Igor Tamm, one of his earliest acquaintances and teachers in Russia for an edited collection by Vitaly Ginzburg, Tamm’s successor as head of the Academy of Science’s physics institute (FIAN),1090 and he supplied David Shoenberg with his recollections of Kapitza1091 as well as Victor Frenkel with recollections about the latter’s father, Yakov

1084

Letter [819]. Mark Walker was writing his doctoral thesis at Harvard on the German atomic war eﬀort. Peierls communicated with him at length between 1984 and 1992. See Peierls Papers, Supp. D.74. 1086 Letter [826]. 1087 Letters [758–759]. 1088 Letters [772–773]. 1089 Letter [809]. See also Peierls Papers, Supp. D.66–D.77. 1090 Letter [746]. 1091 Letter [806]. 1085

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Il’ich.1092 Similarly, he communicated with Lifshitz regarding a contribution about Landau in a book on the history of sold-state physics, edited by Nevill Mott.1093 Among other scientists who he communicated with or about were I.Y.Pomeranchuk,1094 Semyon Shubin1095 and Lev Shubikov.1096 Peierls remained concerned about human rights issues in the Soviet Union, and followed the news from the other side of the Iron Curtain closely. But as in the past, he was careful about open involvement, when he judged intervention as hopeless or counterproductive, as in the case of the Soviet mathematician and human rights activist Naum Meiman.1097 He and Genia had planned visiting Moscow and Leningrad in the autumn of 1986, a visit eagerly awaited by both in view of the changes brought about by the advent of Michail Gorbachev. However, Genia had been unwell and had undergone surgery to have a benign brain tumour removed in 1985, an operation which had given temporary relief. She spent a comfortable year and Rudolf and Genia spent a ‘glorious’ holiday1098 in Greece in June of 1986. But amid preparations for their Russian trip,1099 Genia’s condition deteriorated, and she died on 26 October 1986. Around the time of Genia’s ﬁnal illness, Peierls’ autobiography was published: Bird of Passage was the ﬁtting title of a book which was endearing to many and a little disappointing to some. In a light-hearted manner, the book retold interesting parts of the history of physics in the ﬁrst half of the 20th century and the many personal anecdotes made entertaining reading for many colleagues and friends. But the attempt to give a mention to a vast number of acquaintances in the nicest possible 1092

Letter [807]. N.F. Mott (ed), Beginnings of Solid State Physics, London: The Royal Society, 1980. 1094 Peierls Papers, Supp. D.94. 1095 Peierls Papers, Supp. D.100. 1096 Peierls Papers, Supp. D.101. 1097 Letters [792–793]. 1098 See letter [831]. 1099 See letters [836–37]. 1093

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way, as it was Rudolf Peierls’ style, made the book less gripping as it might have been, had the author been a little more selective. However, the book gave rise to a large number of letters from those friends who keenly devoured the book after its publication in the autumn of 1985, only a year before Genia’s death.

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[744] Wilhelm Eveking to Rudolf Peierls Darmstadt, 12.4.[19]75 Lieber Rudi Peierls! 1925 haben wir in Obersch¨ oneweide letztmalig die Schulbank gedr¨ uckt, soweit ich mich erinnere. Versuche die Mitabiturienten ausﬁndig zu machen, haben erwartungsgem¨ass zu keinem grossen Erfolg gef¨ uhrt. Ob so etwas wie ein Treﬀen im Laufe des Jahres zustande kommen wird, ist fraglich. Vielleicht wird der eine oder andere von der Schulzeit nicht mehr viel wissen wollen. Eine Liste der ermittelten Anschriften f¨ uge ich bei. Deine Adresse wurde mir von der Deutschen Physikalischen Gesellschaft aus “Who’s who 1973–74” mitgeteilt. Ich selbst bin seit 1/4 Jahrhundert in Darmstadt ans¨assig und habe hier f¨ ur die chemische Industrie geschuftet. Seit zwei Jahren f¨ uhre ich das bescheidene Dasein eines Pension¨ars. Ich w¨ urde mich sehr freuen ein Lebenszeichen von Dir zu bekommen. Dein Wilhelm Eveking

[745] Rudolf Peierls to Nina Byers [Leiden], 1.1.1976 (carbon copy) Dear Nina, The occasion of this missive is to send you a copy of my letter to MacKenzie.1100 Thank you very much for your initiative in this operation. We look forward to being there in just a year’s time. After leaving Seattle last summer we spent three weeks in Mexico, and enjoyed ourselves enormously, in spite of the increased smog and the crazy traﬃc. Then Genia went back to Oxford, and I joined her a 1100

Kenneth Ross Mackenzie (1912–2002), professor of physics at UCLA. Rudolf Peierls was planning to spend the ﬁrst three months of 1977 at UCLA.

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week later after talking at a conference in Seattle. We had August and September in Oxford, and it was very pleasant to be back after almost a year, so the time passed very quickly. The department seemed in good shape though somewhat thinly populated, as usual in the summer. Chris Llewellyn Smith (of whom I caught only a ﬂeeting glance) is a live wire, and a powerful inﬂuence on the students. Did you see in November that Dick1101 got the Hughes Medal of the Royal Society? During the last academic year the state of near bankruptcy of the University Chest caused a moratorium on all new appointments, which included the university element (CUF) of the Somerville post. But in the summer when the pressure eased slightly, this was cleared and the job was advertised. To everyone’s surprise the college did not appoint Ann Eggington,1102 but a woman from Culham, whose ﬁeld is really plasma and who may be more distinguished than Ann Eggington, but more as an organiser and collector of data. As a result, Ann will be without a job after next autumn (at least that was the situation in October, I would not have heard if something had come up since). In talking to her about things she might try for it occured to me that in American Universities women now may have some advantage under the “aﬃrmative action” programmes. However, I do not know how far this applies to the post-doc positions for which she would presumably try in the ﬁrst instance, and how far to women who are non-residents? Since October I have been Lorentz Professor here, and we live in a small but pleasant ﬂat reserved for the Lorentz Professor. We are having a great time exploring the old parts of Leiden and all the many towns almost within walking distance, and the many exquisitely arranged museums. At the moment Jo and Chris are spending their Christmas holidays with us. Jo decided to become a full time student at Cambridge under 1101

Dick Dalitz, at the time Royal Society Professor at Oxford, had been awarded the Hughes Medal for his distinguished contributions to the theory of the basic particles of matter in 1975. 1102 Ann Eggington studied at Munich, the University of Sussex and Oxford before joining the UK Civil Service working at the Departments of Energy and of Trade and Industry. She is currently Head of the Europe, Middle East and Africa Division in the Oﬃce of Global Energy Dialogue at the International Energy Agency in Paris.

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a mature student scheme. She got her acceptance by Lucy Cavendish, a newish college, just as she was leaving Cambridge. Kitty and Chris almost came here for a weekend, but at the last minute Kitty, who is expecting a baby in April, had some complications so she went into hospital instead of coming here, but now things seem to be well under control, and she will be back at work in the new year. Her husband just decided to accept a three-year job in Vancouver from next summer, so they will keep the family banner ﬂying on the West Coast. We leave here on 30 Jan. and after re-packing and re-organising ourselves in Oxford, ﬂy to Mexico on 4 February and to Seattle on Feb. 18. How are things with you? Did you buy the house you were looking at, or any house? I am sending this to the UCLA address for safety. Best wishes to you and Art, Yours sincerely,

[746] Rudolf Peierls to V.L. Ginzburg [Oxford], 2.10.1976 (carbon copy) Dear Ginzburg, I enclose a short note about Tamm, which I hope will be suitable for your collection. I also enclose a photograph taken at the Odessa Conference in 1930, to which I refer in the text. I have mentioned it in my note in such a way that there is no need to publish the picture, but if you like you may include it. In case you want to do so, I enclose also a negative (not the original one, lost long ago, but one made from the original print.) You may also be interested to know that I was the author of the Obituary Notice for Tamm in Nature.1103 If you like this and would like to reproduce it in place of the enclosed note this would be all right. 1103

Professor Igor Tamm, Nature, 232, 142 (1971).

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I have checked with the Editor of Nature that they would not object to this being reprinted. I very much like your idea of publishing recollections of Tamm, and I hope your request will bring enough material to make this worthwhile.1104 With best regards also to Professor Feinberg, Yours sincerely, Rudolf Peierls Recollections of Igor Tamm My recollections of Igor Evgen’vich Tamm are vivid, but not extensive, since I never worked with him, or spent much time in his company. The ﬁrst thing one noticed about him was his liveliness and agility. This included his quick reaction and lively interest in any problem in physics as well as outside, his quick understanding of what one was trying to say, and even physically his restless and rapid movement. I cherish a photograph taken while he lectured at the Odessa physics conference in 1930, where I met him for the ﬁrst time. I did not have a very powerful camera, and while there was enough light to show all other faces in sharp focus, Tamm is only a vague blur. But as one soon discovered, his speed was no sign of superﬁciality. He had a deep understanding of physics, both old and new. At a time when many young physicists, full of enthusiasm for the new quantum mechanics, felt that anything done before 1926 was old-fashioned and useless, he knew how to combine a ﬂuent mastery of the newer method with a sound appreciation of the old, and one could always learn from him about the connection. In many later encounters I learned to appreciate his deep understanding of human aﬀairs, to which he brought the same modesty and humility with which he approached a problem in physics. Once he had formed a conviction about what was right and what was wrong, he acted on it with as little hesitation as he would have about physical truth. This 1104

Ginzburg eventually published a collection. V.L. Ginzburg, Reminiscences about I.E. Tamm, Moscow: Nauka, 1981.

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emerged also in the Pugwash Conferences, where our common concern was with the preservation of peace and the survival of mankind. At these meetings his presence was always an inspiration. I visited him for the last time in the summer of 1969, when his health was already severely aﬀected by his illness, and he was very uncomfortable. His movements were now slow, but his mind moved as rapidly as ever. In spite of his troubles, about which he would never occur to him to complain, he was working hard in a calculation relating to some new idea in fundamental physics. The world would be a better place, if there were more people like Igor Evgen’vich. [Rudi]

[747] Nina Byers to Rudolf Peierls Los Angeles, 28.10.1977 Dear Prof, Thanks so much for your last letter.1105 As soon as I ﬁnish writing this letter, I shall go home and enclose in it more pictures — this time of the house. It is lovely and quite fun to live in. Of course, it still isn’t ﬁnished; but the interior is very nearly done and the man who is going to do the last bit of outside construction has just promised to appear and begin in earnest day after tomorrow. That last bit is the deck to be built outside the font of the house. Hopefully arrangements will be made in the coming months for you and Genia to return to LA for the winter quarter of 1979 and ﬁnally I feel conﬁdent that by then the house will actually be ﬁnished! As our chairman is continuing to carry on his experimental programs at both Los Alamos and Berkeley, he divides his week between UCLA and these laboratories — we therefore do not know exactly when we will see him and when he will approve our recommendations. But it seems quite likely you will be receiving an oﬃcial invitation to return as 1105

Letter could not be located.

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visiting professor for winter quarter of 1979 sometime in the foreseeable future. I am still planning to take a sabbatical leave in the fall quarter of 1978 and hope to spend most of it in Oxford. Philippa Foot1106 is here now, and she assures me Somerville will have me back in some capacity. I haven’t yet corresponded with anyone there about it. (Philippa is now only peripherally attached to the college.) I hope also I could have a desk in the department. Should I write to Dick about it? I’m waiting a bit so that I am absolutely sure we’ll come before asking. Art is somewhat in a state of ﬂux. He has pretty much decided he really doesn’t want to start up a new business after all — still he is loathed to burn his bridges. If indeed he is not in the business, we can be away for all of the fall quarter. He is presently doing quite a lot of construction on our property; fences and other landscaping. He is working full time at that and sorting out in his mind what he’d like to do next. I think he feels that in order to live in the style to which he likes to be accustomed, he will have eventually to resume paid work. Unfortunately present times are such that accrued capital shrinks in value at an alarming rate. Speaking of paid work — thank you for asking me about Paul Frampton.1107 I am worried about him. He has remained here in spite of the fact that he has been asked to vacate his oﬃce. Indeed his things are now in a small room which is something more like a closet than an oﬃce. Still he comes round quite a lot. He doesn’t say much, but I understand from Abers to whom he has spoken that he has a rather good job offer of a job at Ohio State University and that they are in a process of trying to get his visa renewed. It has expired and he needs the renewal in order to be able to be paid a salary in this country. The job is not a 1106

Philippa Foot (1920–), had been associated with Somerville College since her undergraduate days in the early 1940s. An inﬂuential thinker in moral philosophy, she held positions at Cornell, Berkeley, MIT, Princeton, New York and Stanford and settled at UCLA in 1976 where she was appointed the ﬁrst holder of the Gloria and Paul Griﬃn Chair in Philosophy in 1988. 1107 Paul Howard Frampton (1943–), had obtained his Ph.D. from Oxford in 1968. After working at the University of Chicago, CERN, Syracuse University, UCLA, Ohio State University and Harvard, he joined the University of North Carolina in 1981 and eventually became Rubin professor of physics in 1996.

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tenure track job — but I believe it is one that is meant to last at least ﬁve years. Also, apparently he has the opportunity to go to Trieste — again not a permanent position but still a paid position. He seems to have said he’ll go there if his visa is not renewed. It is not clear why he remains here if Ohio State works on his visa renewal. I was told they would like him to come and work in their place. Though they couldn’t pay him a salary until the renewal is in hand, they oﬀer him all facilities and a welcome. Ernie says Paul says he doesn’t want to have to move twice and so only considers a move to Ohio after getting his renewal of visa. Ernie also says Paul has never said he actually would go to Ohio State. Presumably, however, he has told the people in Ohio State that he will come to them. He doesn’t seem to want to talk about any of these things with the rest of us, so I don’t know much ﬁrst hand. Somehow I feel it will be nice for him to receive a letter from you. I think the above information is fairly reliable. (Trouble is Paul says diﬀerent things to diﬀerent people.) It is the best I can do to inform you what is going on. How is your health? I hope you and Genia are both well. We miss you two here and look forward to seeing you next year. Best regards and love to you both. As ever, Nina [748] Rudolf Peierls to Margaret Gowing [Oxford], 13.1.1978 (carbon copy) Dear Margaret, Thank you for your letter.1108 I agree with your view that it would be worth while to collect material on the history of solid-state physics, and at any rate to record the recollections of the older people in the ﬁeld, before it is too late. 1108

Letter could not be located.

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I believe something along these lines is being done in America, and it may be worth while to ﬁnd out more about this, to see how far they are doing what needs to be done, and whether anything further might be done in collaboration with them, or had better be independent. Of course you may know all about that already. My own information comes only from the fact that, at a conference in Minneapolis last May on the history of Nuclear Physics, I was asked by a girl from the history of science department (I believe) of the University of Illinois, for an interview about the early days of solid-state physics, and we duly recorded an interview of about 30 minutes or so. In fact we had two tape recorders going, because she had been commissioned to get such a tape for some project and she also wanted to keep a copy for her own work. I have forgotten the nature of the project; it could have been the one run by the American Institute of Physics started by Charles Weiner.1109 I have also forgotten the name of the girl, but she was accompanied by Gordon Baym,1110 a physicist from Illinois, so I could easily write to him and make the connection. I have a vague idea that I was going to be sent a copy when the tape was transcribed, but I am not sure about that. If you would like me to ﬁnd out more, please let me know. Regardless of what may come of this, I shall certainly be glad to help with anything you decide should be done. Personally I would ﬁnd taping more convenient than writing, but I would be willing to do either. My general experience is that for best results it helps to have a discussion, either in the form of question and answer, with the questioner knowing some background, or a conversation between two or more people of the old generation who might remember diﬀerent aspects of the story. Either helps to jog one’s memory. If it is useful I could have a shot at a ﬁrst draft list of people to 1109

The American Institute of Physics oversaw a project ﬁnanced by the National Science Foundation to establish an Archive for the History of Quantum Physics (AHQP). See www.amphilsoc.org/library/guides/ahqp/index.htm. 1110 Lillian Hoddeson and Gordon Baym interviewed Rudolf Peierls on 20 May 1970. See R.E. Peierls, interview by L. Hoddeson and G. Baym, 20.5.1970, Niels Bohr Library, American Institute of Physics, College Park, MD. US.

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be included — I suspect it will turn out that the majority are in the United States, and that may be another reason for collaborating with the American project. With belated good wishes for 1978. Yours sincerely Rudolf Peierls

[749] Elisabeth Heisenberg to Rudolf Peierls Munich, 8.4.1978 Dear Mr. Peierls, Erlauben Sie mir bitte, daß ich Ihnen in deutscher Sprache schreibe. Mein Englisch ist nicht sicher genug um auch schwierige Sachverhalte genau widergeben zu k¨ onnen. Aber da Sie freundlicherweise auch deutsch geschrieben habe[n], nehme ich an, daß Sie das Deutsche doch ohne Schwierigkeiten verstehen werden. ¨ Zuerst m¨ochte ich Ihnen herzlich danken f¨ ur die Ubersendung Ihres 1111 Ich habe ihn mit großem Interesse geleArtikels u ¨ber meinen Mann. sen und mich auch u ¨ber Vieles sehr gefreut. Die Schilderung, die Sie von ihm gerade aus seiner fr¨ uhen Zeit geben, ist sehr freundschaftlich und lebendig. Auch in Ihren Auseinanderseztungen mit den so problematischen Jahren w¨ ahrend des Hitlerregimes und im Kriege sp¨ ure ich deutlich [ihre] Fairness und Ihr Bem¨ uhen ihm Gerechtigkeit widerfahren zu lassen. Gerade deswegen wage ich es, an einigen Stellen eine andere Meinung zu a¨ußern. Gerade in dem einen Punkt muß ich Ihnen sehr widersprechen: mein Mann hat nie auch nur einen Augenblick daran gezweifelt, daß Deutschland den Krieg verlieren w¨ urde und er hat nie auch nur entfernt gew¨ unscht, Deutschland k¨ onnte den Krieg gewinnen — das weiß ich aus unz¨ ahligen Gespr¨ achen, die wir gef¨ uhrt haben. Ich habe im letzten Jahr versucht eine Arbeit u ¨ber meinen Mann zu schreiben und habe alles aufgeschrieben, was ich u ¨ber seine politi1111

R.E. Peierls and N.F. Mott, ‘Werner Heisenberg (1901–1976)’, Biographical Memoirs of the Fellows of the Royal Society 23, 213–251 (1977).

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sche Haltung und seinen politischen Lebenslauf weiß.1112 Da wir immer in lebendigem Kontakt und Gespr¨ achen zusammen gelebt haben, sind mir seine Vorstellungen sehr vertraut. In dieser Arbeit habe ich ein Gespr¨ ach niedergeschrieben, das wir im Kriege gef¨ uhrt haben, nachdem die deutschen Truppen Frankreich erobert hatten. Ich war damals [tief] beunruhigt, Hitler k¨ onnte den Krieg gewinnen. Ich m¨ ochte Ihnen dieses Gespr¨ach, das mir wegen seiner besonderen Brisanz sehr genau im Ged¨ achtnis geblieben ist, aus meiner Arbeit abschreiben: Heisenberg hat nie einen Augenblick daran gezweifelt, daß Deutschland diesen schlimmen und verbrecherischen Krieg verlieren w¨ urde, ja verlieren mußte, selbst zu einer Zeit, als der Schein anders vermuten ließ, als sich die deutschen Truppen mit Siegeslorbeer schm¨ uckten — selbst da ließ er sich nicht t¨ auschen. Damals fragte ich ihn, selbst tief beunruhigt, ob er wohl glaube, daß Hitler den Krieg doch gewinnen w¨ urde. Heisenberg war ganz ruhig und sicher und sagte: “Er wird sicher nicht siegen. Es wird so werden wie ein englischer Diplomat es einmal formuliert hat, als man ihn fragte, wie der Krieg ausgehen w¨ urde: ‘Die deutschen Heere, so sagte er, werden durch Europa ziehen wie ein Messer durch die Butter; aber irgendwann werden sie zum Stehen kommen — und dann haben sie den Krieg verloren.’ So wird es werden, Du kannst ganz sicher sein,” setzte er nochmal dazu. Wir wagten damals nicht mehr, solche Gespr¨ ache zuhause zu f¨ uhren. Wir waren sicher, daß unsere Gespr¨ ache abgeh¨ort wurden und nicht nur die Telefongespr¨ache. So mußten wir auf die Straße gehen, um sicher zu sein, daß wir nicht belauscht wurden. Wir gingen bei diesem Gespr¨ ach unter den bl¨ uhenden japanischen Kirschb¨ aumen der Naunhofer Straße in Leipzig in einer duftenden Fr¨ uhlingsnacht. So weit meine Aufzeichnungen. Wenn Sie dies akzeptieren k¨ onnten, w¨ urde Ihnen auch vieles andere in anderem Licht erscheinen, auf das ich in diesem Brief aber nicht weiter eingehen will. 1112 Elisabeth Heisenberg eventually published her own assessment of her husband’s life and work. E. Heisenberg, Das politische Leben eines Unpolitischen. Erinnerungen an Werner Heisenberg, M¨ unchen: Piper, 1980 (later published in English as E.Heisenberg, Inner Exile. Recollections of a life with Werrner Heisenberg, Boston: Birkh¨ auser, 1984).

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Im Juni kommt Weißkopf nach M¨ unchen. Ich will ihm dann meine Aufzeichnungen zu lesen geben und h¨ oren, was er dazu sagt. Drucken will ich sie voraussichtlich nicht lassen. Wer wird meiner Darstellung schon glauben? Trotzdem glaube ich, daß sie Manches klarer machen w¨ urde, Manches, an dem heute noch herumger¨ atselt wird. Mit bestem Dank und freundschaftlichen Gr¨ ußen! Elisabeth Heisenberg

[750] Heinz Rudolph to Rudolf Peierls [location unspeciﬁed], 18.4.1978 Lieber Rudi! Du glaubst gar nicht, wie sehr ich mich u ¨ber Deinen Brief vom Februar urlich wollte ich Dir gleich antworten, doch sollte gefreut habe.1113 Nat¨ die Antwort, wie es sich geh¨ort, ganz ausf¨ uhrlich sein. Lange Briefe zu schreiben erfordert Zeit, und so verz¨ ogerte ich das Schreiben immer wieder. Inzwischen war ich f¨ ur einige Tage in Berlin zum diesj¨ ahrigen Klassentreﬀen am 18.3., das ich im vorigen Jahr wiederbelebt habe. Die Zeit, Dich davon zu benachrichtigen und Dich dazu einzuladen, war zu kurz. Ausserdem wusste ich nicht, ob Du Zeit und Lust gehabt haettest, zu dem Treﬀen zu kommen. Jetzt plagt mich das Gewissen, Dich so lange ohne Antwort gelassen zu haben, so sehr, dass ich Dir wenigstens diese Zeilen schreibe, mit den beiden Beilagen∗ schicken m¨ochte und dem Versprechen, mich bald ausf¨ uhrlich zu melden. Bis dahin herzlichst Dein Heinz R. ∗ Die

vom Jahre 1950 war von der ersten Zusammenkunft nach dem Kriege, der lange keine zweite folgte. 1113

Letter could not be located.

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[751] Rudolf Peierls to Elisabeth Heisenberg [Oxford], 24.5.1978 (carbon copy) Dear Mrs Heisenberg, Thank you very much for your interesting letter,1114 which reached me with some delay, because of my nomadic life. I hope you do not mind my replying in English — although German is my mother tongue, it got rusty in 45 years, and I can express myself better in English, which you understand very well. I found your letter, and particularly your account of the conversation, of fascinating interest. Your recollection of this conversation, and the details of its setting, does sound very convincing. In our article we did not presume to judge what Heisenberg’s view of these problems was. You may have noticed that in the two places where this is mentioned, we left room for doubt: In the ﬁrst paragraph of p. 232, about this conversation with his colleagues in America, we leave it open whose memories are the more reliable. In any case, here the discrepancy is only about what is said — and it might well have been dangerous to express his thoughts to comparative strangers even abroad. In the last paragraph on the same page, we say only:“it is reasonable to assume that he wanted Germany to win the war”, and we do not claim to know. It was not our function to decide what his views were, or indeed whether he had ﬁrm and settled views. In diﬃcult and emotive questions it is only human to hold, and to express, diﬀerent opinions at diﬀerent times. Whatever the answer, your recollection can make a most important contribution to the record, and I hope you will decide to publish them. You express doubt whether people will believe you. If one can judge by the one piece you sent me, it would be very hard not to believe you. I was relieved to hear that you found the spirit of our memoir acceptable. Yours sincerely, Rudolf Peierls 1114

Letter [749].

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[752] Nevill Mott to Rudolf Peierls Cambridge, 23.10.1978 Dear Rudi, The proposal has been made from several sides that a meeting would be held for physicists who were involved in the early developments of solid-state physics, with a view to putting on record the history of the subject.1115 Professor Margaret Gowing (History of Science, Oxford) Professor Rudolf Peierls and I are organising a three-day meeting to be held at the rooms of the Royal Society, London, starting probably on 23rd April 1979. Our plan is to cover the theory of electrons in solids up to, and perhaps including, the war of 1939–1945 and perhaps some developments immediately afterwards, but not the important work on superconductivity (BSC theory) or the development of the transistor, which we believe has been adequately treated elsewhere. In addition we want to include early work on defects in solids and particularly dislocations, and since the experimental veriﬁcation of their predicted properties extends into the early 1950’s, we would feel that our time limit should be around this subject. We hope that some or most of those invited would be willing to put their recollections on paper, and I include some preliminary notes which I have written myself. At the meeting I hope we could discuss these and that each author would feel that he could amend or lengthen what he had written in the light of the discussion, with a view to ultimate publication. As regards where the history would be published, no decision has been made as yet. We hope to have some funds available for travelling and hospitality. People who have already agreed to come include Dr Frederic Seitz and Dr Cyril Smith. Professor Bethe has promised to write a memoran1115

The symposium was held 30 April to 2 May 1979 at the Royal Society. Participants included J. Bardeen, B. Coles, A.H. Cotterell, P.B. Hirsch, H. Jones, N.F. Mott, F.R.N. Nabarro, R. Peierls, H. Rosenberg, A. Seeger, D. Shoenberg, F. Sondheimer, A.H. Wilson, E. Braun, M. Gowing, L. Hoddeson, and K. von Mayenn. Audio-recordings of the meeting are kept in AIP, Niels Bohr Library, AV C-79-(5–12).

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dum but is not able to attend the meeting. In fact, we shall, I expect, consider several memoranda whose authors are not able to come. I write to ask whether you would be interested in coming to this meeting if travelling expenses are available, and whether you would be able to write a few notes before the meeting, for considerations there. We very much hope that you will be able to help us in one of these ways. Yours sincerely, N.F.M. [753] Heinz Rudolph to Rudolf Peierls N¨ urnberg, 24.2.1979 Lieber Rudi! Als ich endlich dabei war, Dir einen ausf¨ uhrlichen Brief zu schreiben und bereits eine halbe Seite beisammen hatte, kam ein Anruf aus Berlin, dass unsere Tochter u ¨berraschend ins Krankenhaus musste. Da sie ausserdem am kommenden Montag (26.) einen Umzug vorhat, der nicht mehr aufgeschoben werden kann, muss ich jetzt gleich nach Berlin fahren. Nach meiner R¨ uckkehr h¨ orst Du mehr von mir. Nur soviel noch, dass unser inzwischen klein gewordener Kreis von ehemaligen Klassenkameraden am 24. M¨arz wieder zu einem Klassentag in Berlin zusammenkommt. Wenn Du Lust und Zeit hast, eine Reise nach Berlin zu machen, w¨ urden wir uns sehr freuen, Dich bei dieser Gelegenheit wiederzusehen. Als Treﬀpunkt haben wir die Mampe-Stube am Kurf¨ urstendamm wieder vorgesehen und als Zeit abends so um 19 Uhr. F¨ ur heute herzlichst Dein Heinz R. N¨ urnberg, 24.2.1979 Lieber Rudi! Nach langer Zeit und nachdem Du sicher meine Gr¨ usse mit Fotos zu Weihnachten erhalten haben wirst, will ich mich endlich ausf¨ uhrlicher

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melden. Den Grund, dass dies erst heute geschieht, wirst Du noch aus diesem, meinem Bericht ersehen. Zun¨achst nochmal herzlichen Dank f¨ ur Deinen “Lebenslauf” von vorigen Jahr. Vieles davon, n¨ amlich den Anfang, kannte ich allerdings, zumal wir uns bis 1930 oder 31 in Abst¨ anden immer noch sahen oder doch in brieﬂichem Kontakt standen. So schriebst Du mir einmal, nachdem Du wieder einmal in Russland gewesen warst, lakonisch, Dir w¨are schon im¨ attest mer die Ahnlichkeit zwischen жена und Женя aufgefallen. Du h¨ die Konsequenz daraus gezogen und w¨ arest seit kurzem verheiratet. Auch die Geburt Deiner ersten Tochter teiltest Du mir noch mit. Ich antwortete Dir stets, h¨orte aber schliesslich nichts mehr von Dir, auch nachdem ich Dir in Abst¨ anden mehrere Male geschrieben hatte (das muss schon 1937) gewesen sein. Vielleicht war es eine Briefzensur; denn auch Briefe von Herbert Lange aus Amerika waren in dieser Zeit ge¨ oﬀnet worden, erreichten mich aber immer. An dieser Stelle musste ich mitten im Schreiben meines Briefes seinerzeit unterbrechen, weil ich den telefonischen Anruf erhielt, dass unsere Tochter in Berlin pl¨otzlich mit einer akuten Blinddarmentz¨ undung ins Krankenhaus gekommen war und ich f¨ ur sie ihren unmittelbar bevorstehenden Umzug in eine neue Wohnung machen musste. Ich schrieb Dir das damals in wenigen Zeilen aus Berlin. Nach meiner R¨ uckkehr beabsichtigte ich, meinen Bericht an Dich fortzusetzen. Und er sollte ganz ausf¨ uhlich werden, das hatte ich mir von Anfang an vorgenommen, nachdem ich Deinen Brief erhalten hatte. Wobei mein Brief zugleich so eine Art von Lebens-R¨ uckschau f¨ ur mich selbst werden sollte. Wegen der beabsichtigten Ausf¨ uhrlichkeit musste ich mir daf¨ ur nat¨ urlich gen¨ ugend Zeit und Ruhe nehmen. Und daran fehlte es immer wieder, weil stets andere Dinge dazwischen kamen, die tats¨ achlich oder anscheinend dringender waren. Und wie das nun mal so mit den guten Vors¨ atzen ist: Man verschiebt sie. Zun¨ achst um Tage, dann um Wochen; aus den Wochen werden Monate und daraus schliesslich Jahre. Und dabei wird die Gewissenslast wegen der Verz¨ogerung immer dr¨ uckender, auch wenn ich mich in Abst¨ anden mal kurz bei Dir (einmal mit einem Foto) und dem Versprechen meldete, mich noch ausf¨ uhrlicher zu a¨ussern

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Bis dann schliesslich der Zeitpunkt kommt, wo es heisst: Jetzt ist es aber genug mit der Tr¨ odelei! Mag kommen, was will, jetzt bleibt alles andere liegen, und es wird endlich geschrieben! Und dieser Zeitpunkt ist jetzt da. Also: Ich entsinne mich noch an Deinen Brief von Anfang M¨ arz 32. Darin stand u[nter] a[nderem], dass Du mir wahrscheinlich das letzte Mal im Sommer 31 geschrieben h¨attest. Was stimmt; denn Du schriebst mir 31, dass Du im August in Russland warst, mit Deiner Gattin eine Reise in den Kaukasus machtest und sie dann mit Dir nach Z¨ urich ausreisen konnte. “Genia hat schon viel deutsch gelernt.” Die letzte Nachricht, dass Du nach Manchester gehen wolltest, so f¨ allt mir eben ein, erhielt ich 1934. Dann riss der Faden ab, und ich konnte Dir mangels Deiner Adresse auch nicht mehr schreiben. Nun zu mir. Auf der T[echnischen] H[ochschule] hatte mir der Professor Kock vom Lehrstuhl f¨ ur HF-Technik schon vor Erreichung der daf¨ ur erforderlichen Semesterzahl erlaubt, im Labor zu arbeiten; so oft ich wollte. Ich wurde dann bald Hilfsassistent. Die nach Beendigung des Studiums vorgesehene Assistentenstelle trat ich, als es soweit war, aus Anstand an einen fr¨ uheren Assistenten ab, der als Familienvater gerade seine Industriestelle verloren hatte. Wir befanden uns ja mitten in der Weltwirtschaftskrise. Schon w¨ ahrend des Studiums gab mir der Professor gelegentlich vom Lehrstuhl angeforderte Untersuchungen und Gutachten zur Bear¨ beitung, f¨ ur die ich zu meiner Uberraschung sogar bescheidene Honorare erhielt; den Hauptanteil erhielt nat¨ urlich der Professor f¨ ur seine Unterschrift. Du kennst das ja. Durch Vermittlungen und Empfehlungen ergaben sich nach und nach weitere derartige und andere Arbeiten, ohne den Weg u ¨ber den Lehrstuhl, so dass beim Ende des Studiums — trotz, oder vielleicht gerade wegen der Wirtschaftskrise — weitere Arbeiten vorlagen und laufend neue hinzukamen. Und so ergab es sich automatisch, dass ich bei dieser T¨atigkeit blieb. 1932 fand unsere Familie endlich wieder eine grosse und komfortable Wohnung in einem gepﬂegten Haus in der Spreestrasse in Niedersch¨oneweide. Hier konnte ich mir ein Arbeitszimmer mit Labor als beratender Ingenieur einrichten. Durch Zuweisungen vom Lehrstuhl erteilte ich nebenbei technischen Privatunterricht und hielt Kurse f¨ ur angehende Radiotechniker ab, was mir viel Spass machte. Dazu ein Kuriosum: Der

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bekannte HF-und Radio-Fachmann Dr. Erich F. Huth, der nach einem u ¨berstandenen Schlaganfall wieder Anschluss an seine Technik suchte, wurde durch Empfehlung des Lehrstuhls mein “Sch¨ uler”. Er starb aber bald. Nach dem politischen Umschwung von 1933 dr¨ uckte ich mich vor der “berufsst¨ andischen Einordnung”, auch “Gleichschaltung” genannt; wie ich aus Ablehnung der neuen Machthaber auch nie einer Naziorganisation angeh¨ ort habe. In der Industrie h¨ atte ich quittieren m¨ ussen, weil es da bald unm¨ oglich war, nicht wenigstens der “Arbeitsfront” der NSV (Volkswohlfahrt, oder wie das hiess) und a¨hnlichen der vielen dutzenden harmloseren NS-Organisationen anzugeh¨ oren, denen sich der Durchschnittsb¨ urger nicht entziehen konnte, ohne sich missliebig oder verd¨ achtig zu machen. Was unter Umst¨ anden gef¨ ahrlich werden konnte, nach dem Grundsatz: wer nicht f¨ ur uns ist, ist gegen uns. Im Beruf bem¨ uhte ich mich gewissenhaft, termingerecht und (wichtig!) preiswert zu sein, wobei ich nach meinem heutigen Empﬁnden, oft zu bescheiden war, aber dadurch weiterempfohlen wurde. Ich nahm auch ausgefallene Auftr¨ age an, die oft interessant waren, oder solche, die f¨ ur nicht oder nur schwer realisierbar galten, deren L¨ osung mir aber, wenn ich sie einmal u ¨bernommen hatte, schliesslich doch immer gelang. Wenn ich jetzt zur¨ uckdenke, w¨ urde mir heute im Alter der Schneid fehlen, manche damals ausgef¨ uhrte Arbeit zu u ¨bernehmen! Als Unikum f¨ allt mir gerade ein, dass ich 36 oder 37 u ¨ber einen Mittelsmann f¨ ur eine s¨ udamerikanische Regierung (Kolumbien?) eine Lauschzentrale entwarf und lieferte, mit der aus mehreren Zellen gleichzeitig die Gespr¨ ache von Gefangenen untereinander mit Kopfh¨ orern oder u ¨ber Lautsprecher abgeh¨ ort werden sollten. In der Jugend ist der Elan, wohl zu recht gr¨ osser. Gelegentlich bekam ich Kunden der AEG u ¨ber meinen Vater zugewiesen, deren W¨ unsche nicht zum Gesch¨ aftsbereich der AEG geh¨ orten oder ausgefallene Einzelw¨ unsche waren, die dem Kunden aber erf¨ ullt werden sollten. Bei der Leipziger Feuer-Versicherung erstellte ich ab 1937 Gutachten f¨ ur Brandschadensf¨ alle von Nachrichten- und Radioger¨ aten. Ich hatte also reichlich zu tun, was sich auch ﬁnanziell bestens auswirkte. Allerdings habe ich hin und wieder auch mal nachts durch-

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arbeiten m¨ ussen und jahrelang, bis 1938, keinen Urlaub genommen bezw. nehmen k¨onnen, mit Ausnahme von einer Gesch¨ aftsreise nach Heidelberg, die ich um einige Tage verl¨ angerte. Mit Wehrmachtsauftr¨agen direkt oder indirekt hatte ich nie etwas zu tun. Unser j¨ ahrliches Klassentreﬀen zum Abiturtag am 21. u[nd] 22. M¨ arz hielt ich als Traditionswahrer bis in den Krieg hinein aufrecht. Die Politik wurde dabei u ¨bergangen; von den politischen Witzen abgesehen, die u ¨berall zirkulierten. Nur einmal, 1934, als ich mir in einem anderen Zusammenhang die Bemerkung “sogenannte nationalsozialistische Bewegung” nicht verkneifen konnte, sprang Gr¨ uner auf und hielt mir eine emp¨orte Philippika: Meine Worte w¨ aren dazu angetan, dass der Betreﬀende eins in die Schnauze verdiene. “Alles, was Du bist, alles, was Du hast, verdankst Du dem F¨ uhrer!” Ein solches Verhalten und einen solchen Unsinn hatte ich von Gr¨ uner am wenigsten erwartet. Es beleuchtet aber die damalige Situation. Hoﬀentlich hat er sp¨ater einmal umgelernt. 1936 heiratete meine Schwester. 1939 bekam sie ihre einzige Tochter. Heute hat sie drei Enkelkinder. Mein Schwager, mit dem wir uns gut verstanden, sah durch seine beruﬂichen Beziehungen die auf uns zukommenden Gefahren klarer. Er warnte mich immer, mit meinen ¨ Ausserungen vorsichtiger zu sein. Dabei wusste er immer die neuesten politischen Witze. Im Nov[ember] 69 ist er an Krebs gestorben. Schon beim Klassentag 1937 oder 38 gab B¨ uttner uns allen den Rat, so wie er selbst an dreimonatigen Wehrmachts¨ ubungen teilzunehmen, um dadurch stufenweise in h¨ ohere Dienstgrade aufzur¨ ucken. Als Sicherheit f¨ ur alle F¨ alle. Er kannte die Lage wohl besser als wir anderen. (Parteigenosse?) Sein Rat wurde wohl nicht ernst genommen. Nur Gerhard Kirschke meldete sich sp¨ ater, als Schutzmassnahme, zur Wehrmacht. Er machte anschliessend, 1939, gleich den Polenfeldzug mit, wurde aber bald entlassen. Es war damals eine schwere Zeit f¨ ur seine Mutter und ihn. Die f¨ uhrenden Nazis wurden ja immer u ¨berm¨ utiger und verr¨ uckter. Nach der Kristallnacht im Nov[ember] 38 sah ich die Leute betreten und wortlos (wer wagte damals noch was zu sagen) an den zerschlagenen Schaufensterscheiben vorbeischleichen. Ich fand niemanden, der f¨ ur diese Taten Verst¨andnis aufbrachte, nicht einmal Parteigenossen. Und

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als der Polenfeldzug begann, war die Allgemeinheit trotz der propagandistischen Vorbereitungen betroﬀen und niedergeschlagen. Am 30. Sept[ember] 40 ereilte mich auch das Schicksal: Ich wurde zu den Luftnachrichten eingezogen. Zum Gl¨ uck in B[erlin]-Grunewald. Auf einem Sportplatz exerzierten wir Rekruten mittleren Jahrgangs, und in dem Gemeinsaal unter einer Kirche am Hohenzollerndamm war unsere Unterkunft. Wir hatten fast durchwegs a¨ltere, vern¨ unftige Ausbilder, die uns nicht “schliﬀen”, sondern uns in einem Vierteljahr gerade deswegen eine umfassande und gr¨ undliche Ausbildung gaben. Theoretisch bekamen wir als Angeh¨ orige einer Flugmelde-Kompanie mit der ganz ungew¨ ohnlich grossen St¨arke von etwa 2500 Mann, die u ¨ber einen grossen Bereich bis Pommern verteilt war, eine Spezialausbildung als “Flugmelder”. Vor dem Fahneneid, nat¨ urlich auf den “F¨ uhrer”, hatte ich mich gedr¨ uckt. Als sich das herausstellte, musste ich mit neu hinzugekommenen Rekruten diese Prozedur nachholen, wobei ich nat¨ urlich schon verd¨ achtig war. Als kleiner Mann gelang es mir, mich in die hinterste Reihe zu stellen. Aber der vereidigende Hauptmann sah mir unverwandt auf den Mund. Ich bewegte tonlos und schwach meine Lippen und sagte mir hinterher, dass ein so erzwungener Eid kein Eid ist, wenn es unter den Umst¨ anden (nicht gesprochen) u ¨berhaupt auch sonst einer war. Nach der Ausbildung wurden wir auf sog[enannte] Flugwachen verteilt, wo wir den Flugverkehr (Feindeinﬂ¨ uge) zu beobachten hatten. Feindeinﬂ¨ uge aus England gab es seit einem Jahr damals schon h¨ auﬁg, besonders in mondhellen N¨ achten, wenn auch die Sch¨ aden im Verh¨ altnis zu den sp¨ ateren Kriegsjahren noch nicht gravierend waren. Die Bev¨olkerung musste aber in die Luftschutzkeller und kam am n¨ achsten Tag unausgeschlafen zur Arbeit bezw. die Kinder in die Schule. Zur gleichen Zeit wurde umgekehrt auch London laufend bombardiert. Zwar hatte G¨ oring als Oberbefehlshaber der Luftwaﬀe fr¨ uher einmal gross-spurig erkl¨ art, er wolle “Meier” heissen, wenn ein feindliches Flugzeug nach Berlin k¨ ame. Doch wer wollte ihn jetzt “Meier” oder besser “Obermeier” nennen, ohne nicht gleich nach dem Heimt¨ uckegesetz liquidiert zu werden.

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Das Reich war mit einem Netz von Flugwachen u ¨berzogen. Im weiteren Bereich um Berlin herum waren es etwa 90, davon in der Stadt selbst vier, je eine in den 4 Himmelsrichtungen. Jede Flugwache war mit etwa 10 Mann besetzt, deren Aufgabe es war, st¨andig den Himmel nach Flugzeugen abzusuchen und einer Zentrale, dem Flugwachkomando (“Fluko”) in allen Einzelheiten telefonisch zu melden, so dass man sich dort ein Bild u ¨ber die Flugbewegungen, besonders bei Feindeinﬂ¨ ugen, machen konnte. In 4-st¨ undigem Turnus bezogen immer 2 Mann die Wache, wovon der “Sp¨ aher” mit Auge und Ohr den Luftraum beobachtete und der andere am Telefon sass, um eventuelle Meldungen des “Sp¨ ahers” sogleich ans “Fluko” weiterzugeben. Beide wechselten sich st¨ undlich ab. Im Winter trug der Sp¨ aher einen dicken, schweren Schafspelz und steckte in dicken Filzstiefeln, nat¨ urlich ohne Ohrensch¨ utzer, w¨ahrend der Melder dicht dabei und vor K¨ alte gesch¨ utzt in einem kleinen Verschlag vor seinem Telefon sass. Ich hatte das grosse Gl¨ uck, nicht auf irgendeine Wache weit weg von Berlin geschickt zu werden, sondern ich kam zur Flugwache B[erlin]Nord, die sich im Kasinoturm neben dem Stadtbahnhof Frohnau befand. Bei 10 Mann Wachbesatzung ergab es sich, des man nach ein paar Tagen 24 Stunden wachfrei hatte oder sogar auch mal 48 Stunden. In dieser Freizeit fuhr man nach Hause. Und so konnte ich noch beruﬂich einiges arbeiten. Ende M¨ arz 1941 wurde ich u ¨berraschend ins “Fluko” Berlin versetzt. Als erstes wurde ich dort belehrt, dass das Fluko die wichtigste milit¨ arische Anlage Berlins sei, weshalb ich u ¨ber Lage, Einrichtungen, Dienstbetrieb und alles, was mit dem Fluko zusammenhing, absolutes Stillschweigen zu bewahren h¨atte. Auch Angeh¨ origen gegen¨ uber. Andernfalls drohten, wie damals u ¨blich, schwere Strafen. Ich musste mich dazu schriftlich verpﬂichten. An dieses Gebot hielt ich mich begreiflicherweise. Nachdem ich noch dem Flukof¨ uhrer, einem Hauptmann, vorgestellt worden war, durfte ich in das “Allerheiligste”. Das “Fluko” befand sich in mehreren unterirdischen Bunkerr¨ aumen unter und teilweise hinter einem Postgeb¨ aude in Schmargendorf. Dadurch war es gut getarnt. Zugang hatte man durch eine unauﬀ¨allige, schmale Kellertreppe des Postgeb¨audes und eine Stahlt¨ ur, hinter der

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sich ein Gang zu den Bunkerr¨ aumen auftat. Eine Wache kontrollierte den Zgang. Der Hauptbunkerraum war die “Leitstelle”. An einem langen, schwach halbmondf¨ ormigen Tresen (erh¨ oht) befanden sich die einzelnen Arbeitspl¨ atze. In der Tresenmitte sass der Wachoﬃzier, der mehr eine milit¨ arische Anwesenheitsfunktion hatte und bei Feindeinﬂ¨ ugen in den Arbeitsablauf der eingespielten Soldaten kaum eingriﬀ oder sie, wenn er noch sehr jung war, h¨ ochstens nur nerv¨ os machte. Dem ge¨oﬀneten Halbrund des Tresens gegen¨ uber war eine die ganze Wandﬂ¨ ache bedeckende Landkarte von Deutschland angebracht, die von einer Art Plexiglas u ¨berdeckt war. Bei Feindeinﬂ¨ ugen wurden auf dieser Karte alle Flugbewegungen und deren Formationsst¨ arke aufgezeichnet und entsprechend den laufend eintreﬀenden Meldungen st¨ andig korrigiert. In einem der Leitstelle anschliessenden gr¨osseren Bunkerraum waren mehrer Dutzend Nachrichtenhelferinnen untergebracht; die meisten dienstverpﬂichtet, einzelne hatten sich freiwillig gemeldet, um sich unangenehmeren anderen Dienstverpﬂichtungen zu entziehen. Es waren alle Altersklassen vertreten, darunter viele Studentinnen. Ausserdem gab es noch einen Funkraum und eine Luftschutzwarnzentrale f¨ ur die Alarmierung der Bev¨ olkerung, und selbstverst¨andlich noch Nebenr¨ aume. Unsere eigentliche Unterkunft, wo wir uns w¨ ahrend der “Bereitschaft” aufhielten, befand sich in einer spartanisch eingerichteten Villa in der Hubertusbaderstrasse. In ruhigen N¨ achten ohne Feindeinﬂ¨ uge spielte die diensthabende Wachgruppe im allgemeinen in kleinen Kreisen Karten in der Leitstelle. Die Nichtkartenspieler lasen meistens oder schrieben oder unterhielten sich ged¨ ampft. Bei den Nachrichtenhelferinnen war es a¨hnlich; manche machten Handarbeiten. Sobald aber die ersten Meldungen von Feindeinﬂ¨ ugen eintrafen, wurde es in den Bunkern schlagartig lebendig, und die eingespielte Besatzung wimmelte wie ein Ameisenhaufen durcheinander. Nachrichtenhelferinnen brachten laufend die von ihren Kameradinnen aufgenommenen Meldungen in St¨ ossen von Zetteln in die Leitstelle, wo sie von den einzelnen Platzinhabern eiligst ausgewertet wurden; denn die Flugzeuge anderten ja sehr schnell ihren Standort. ¨

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Der wichtige “Fernplatz” hatte zu entscheiden, welche Meldungen an welche benachbarten Flukos weiterzugeben waren. Was durch ein Epidiaskop in den “Weitergaberaum” erfolgte, wo die jeweils zust¨andigen Frauen sie ablasen und sofort weitergaben. Der “Nahplatz” hatte die Flugabwehr (“Flak”) zu verst¨andigen, damit sie z.B. nicht irrt¨ umlich deutsche Nachtj¨ ager beschiesst. Der “Auswerteplatz” liess die wichtigen Fl¨ uge auf die grosse Wandkarte u ¨bertragen, so dass jeder in der Leitstelle die Luftlage u ¨berschauen konnte. Ein Vierter, der “z.b.V.” (zur besonderen Verwendung), hatte die unangenehme Aufgabe, Unklarheiten durch R¨ uckfragen zu kl¨ aren oder sonstige Pannen im Betriebsablauf zu beseitigen. Wegen des Zeitdruckes und auch sonst war das nicht immer einfach, weshalb dieser reihumgehende Posten nicht beliebt war. Es herrschte so w¨ahrend der Feindeinﬂ¨ uge eine gewisse Spannung. Wegen der vielen Menschen — oft fanden sich noch der Kompaniechef und weitere Oﬃziere ein — und der zahlreichen Lampen war es in der Leitstelle recht heiss und stickig, trotz eines Ventilators. Das machte mir sehr zu schaﬀen, besonders, wenn ich gerade “z.b.V.” und st¨ andig in Bewegung war. Ich hatte das Gl¨ uck, im Fluko in einen Kreis angenehmer Menschen gekommen zu sein. Das galt f¨ ur die Soldaten, die alle schon in meinem Alter oder etwas ¨alter waren, und auch f¨ ur die Nachrichtenhelferinnen. Zu meiner Gruppe geh¨ orten selbst¨andige Gesch¨aftsleute, ein Amtsrichter, ein Richter vom Landgericht, der Dichter Wolfgang Weyrauch und ein Musiklehrer. Wir verstanden uns gut. Die Politik wurde vorsichtshalber nie ber¨ uhrt. Jede unserer insgesamt drei Wachgruppen hatte nach einigen Tagen Dienst ab dem Nachtdienst um 8 Uhr morgens bis zum n¨achsten Morgen frei; zwischendurch auch bis zum u ¨bern¨ achsten Morgen, also 48 Stunden frei. Da wir alle aus Berlin waren, konnten wir dann nach Hause. Auf diese Weise war es m¨ oglich, dass die Selbst¨ andigen ihre Gesch¨ afte weiterf¨ uhren konnten. W¨ ahrend ich zum Klassentag am 21.3.40 noch vier Mann zusammenbringen konnte, fand sich auf meine schriftlichen Einladungen zum 20.3.41 nur noch Peschke ausser mir zum Treﬀpunkt ein. Am Morgen des 9. April 41 — ich hatte gerade meine freien Tage angetreten und war bei einem Gesch¨ aftsfreund — rief mich dort meine

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Mutter v¨ ollig aufgel¨ ost an: Mein Vater war auf dem Wege zum B¨ uro gleich nach 8 Uhr in der Stadtbahn einem Herzversagen erlegen. Ich fuhr sofort zum Bahnhof Alexander-Platz hin, wo ich ihn in einem Abstellraum unter einer Treppe auf einer Bahre liegend vorfand. Er hatte uns verschwiegen, wie schwer herzkrank er war, obgleich wir das eigentlich an seinem blassen Aussehen und seinem sonstigen Verhalten l¨angst h¨ atten bemerken m¨ ussen. Der wenige Schlaf durch die n¨ achtlichen Fliegeralarme werden sein Ende auch beschleunigt haben. Er konnte sich nie mit den politischen Verh¨altnissen nach 1933 abﬁnden und sprach nur von den “Verbrechern” und dem “Oberverbrecher”. Nach Beginn des Russlandfeldzuges wurden Soldaten gesucht, die bereit waren, Ofﬁzier zu werden, wobei die bildungsm¨ assigen Voraussetzungen zutreﬀen mussten. Das war bei allen meiner Wachgruppe der Fall, aber es meldete sich niemand. Wir hatten einfach keine Lust dazu und wollten ausserdem in unserem Fluko zusammenbleiben, in welchem wir im Verh¨altnis zu anderen Soldaten ein angenehmes Leben hatten. Nur ein TabakGrossh¨ andler von uns gab seine Meldung ab, nach langem Besinnen, weil er sich nach dem Kriege einen gesch¨ aftlichen Vorteil davon versprach, Oﬃzier gewesen zu sein. Ein a¨lterer, reifer Wachoﬃzier unserer Gruppe, ein sympathischer Oberleutnant, mit dem ich mich gut verstand, verriet mir nach einiger Zeit, dass der Kompaniechef mangels gen¨ ugender Meldungen einfach von sich aus mehrere Soldaten ohne deren Wissen f¨ ur die OﬃziersLaufbahn gemeldet hatte. Darunter auch mich. Das empfand ich als ein starkes St¨ uck und hatte wegen der Heimlichkeit einen geh¨ origen Zorn. Auf meine Frage an den Oberleutnant, was dagegen zu tun w¨ are, antwortete er lapidar: “Garnichts!” Als ich im Oktober 41 meinen ersten 14-t¨ agigen Urlaub bekam fuhr ich in die bayerischen Alpen, nach Ruhpolding. Schon nach 10 Tagen wurde ich zu einem Lehrgang zur¨ uckgerufen, nach dessen erfolgreichem Ende ich zum Gefreiten bef¨ ordert wurde. Ende November 41 wurde mir vom “Spiess” der Kompanie mitgeteilt, dass alle Ingenieure nach ganz oben gemeldet werden mussten. Diese sollten zu einer Ingenieureinheit versetzt werden. Ich sagte ihm, dass ich gerne weiter im Fluko bleiben m¨ ochte. Worauf er meinte, das w¨ are ihm sehr recht und das liesse sich wohl

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machen; denn ich w¨ are doch eigentlich Dipl.-Ing., in dem Befehl w¨ are aber von “Ingenieuren” die Rede, so dass man annehmen d¨ urfe, mich betr¨ afe die Anordnung nicht. So war mein Verbleiben im Fluko f¨ urs erste gerettet. In einer ruhigen Fluko-Nacht sagte mir der nette Oberleutnant, “Viol” sein Name, ich w¨ are als Hochfrequenzler eigentlich im Fluko ganz fehl am Platze. Es g¨abe Ger¨ ate, mit denen man Flugzeuge durch Richtstrahlen orten k¨ onne, und da geh¨ ore ich in Wirklichkeit hin und w¨ are auch in meinem Element, wenn ich auch verst¨ andlicherweise gerne im Fluko bleiben m¨ ochte. Am 22. 12.41 traf zu Hause f¨ ur mich ein Brief vom ReichsluftfahrtMinisterium (RLM) ein. Ohne Anrede lautete sein Inhalt: “RLM ben¨ otigt Ihre Truppenanschrift”. Der Spiess meinte, jetzt w¨ are ich die l¨ angste Zeit im Fluko gewesen. Auf meinen Hinweis, wegen der Geheimhaltungs-Verpﬂichtung dem RLM nicht antworten zu wollen, um weiter im Fluko bleiben zu d¨ urfen, rief er den Bezirk als vorgesetzte Stelle an. Dieser entschied, dass ich unbedingt dem RLM antworten m¨ usse. Was ich dann auch schweren Herzens tat. Zun¨ achst passierte jedoch noch nichts. Als das Fiasko des Winter-Feldzuges 41/42 in Russland begann, wurde die Bev¨olkerung aufgefordert, warme Sachen jeglicher Art f¨ ur die auf den Winter nicht genug ausger¨ usteten Soldaten zu spenden. Das geschah in einem u ¨berraschend hohen Masse. Die Bev¨ olkerung gab, was sie nur irgendwie entbehren konnte, obgleich schon alles an Kleidung und Lebensmitteln knapp war und auf Karten zugeteilt wurde. Auch wir Fluko-Soldaten gaben von uns aus jeder eine Schlafdecke her, weil es uns doch viel, viel besser ging als den armen Teufeln an der Ostfront. Aber leider: Kein Soldat vor Stalingrad erhielt von der Sammlung auch nur ein einziges St¨ uck. Und viele Soldaten gingen in dem grausen Winter erb¨ armlich zu Grunde, weil die Sammlung zu sp¨ at aufgerufen wurde und noch sp¨ ater oder garnicht die Ostfront erreichte. Heute r¨ uckschauend kann man sagen, dass nach dem Winter 41/42 die milit¨ arische Lage mehr als kritisch geworden war, da auch die Luftschlacht u ¨ber England verloren war, wenn man es richtig besah. Die h¨ ochste milit¨arische F¨ uhrung wusste das sicher. Aber Goebbels’ Siegespropaganda t¨ onte weiterhin, wenn auch die Bev¨ olkerung nachdenklich geworden war. Ende Januar wurde ich als Auszeichnung mit

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einem Oberfeldwebel und einem Unteroﬃzier zu einem 10-t¨agigen SchieLehrgang in die N¨ ahe der Schneekoppe geschickt was zugleich als Erholungsaufenthalt galt. Ich lernte dort das Schielaufen, habe es aber bis heute nicht wieder ausge¨ ubt. Als ich zum Fluko zur¨ uckkehrte, hatte sich dort — sicher unter dem Eindruck der milit¨ arischen Lage — manches zum Nachteil ver¨andert. Die bisherige allgemeine Grossz¨ ugigkeit war durch ein u ¨berstrebiges milit¨ arisches Reglement ersetzt worden. Als einzelne Beschwerden wegen der inzwischen wirklich unzureichenden Mittagsportionen kamen, sprach der Flukof¨ uhrer vor versammelter Mannschaft von Meuterei. Dabei wurden die Oﬃzie, entgegen der sonstigen Gewohnheit in der Wehrmacht, im Fluko durch den Essenverteiler (um sich anzuschmieren) reichlicher verpﬂegt, was sie aber wahrscheinlich nicht wussten und ihnen wahrscheinlich keiner sagte. Abgesehen von dem netten Kameradenkreis, fand ich das Fluko nicht mehr so anziehend wie fr¨ uher. Am 26. Februar 42 war es dann soweit: Das RLM versetzte mich zur “Erg¨ anzungs-Abteilung f¨ ur Soldaten im Ingenieurdienst” nach B[erlin]n-Adlershof. Ich schied recht ungern von meinem Kameradenkreis, und dieser bedauerte ebenfalls die Trennung vom “Rudi”, wie man mich auch sp¨ ater — bei Milit¨ar immer nannte. Und es tr¨ ostete mich wenig, dass mir der Verpﬂegungs-Unteroﬃzier zum Abschied noch ein halbes Kommisbrot zusteckte, der immer so nette und zivile “Spiess” mir aufrichtig versicherte, die Kompanie liesse mich ungerne gehen, k¨ onne aber gegen das hohe RLM nichts machen, und der sonst so distanzierte, um nicht zu sagen unnahbare Kompanie-Chef mir — entgegen jeder milit¨arischen Etikette — die Hand reichte und mir f¨ ur meine Dienstleistungen dankte. Mit dem Oﬃzier-Vorschlag hatte er sich nun auch verrechnet. In B[erlin]-Adlershof kam ich in ein Barackenlager voller Soldaten aller Dienstgrade. Man wusste garnicht, was man mit den vielen Menschen anfangen sollte. Da die Unterk¨ unfte nicht ausreichten, konnten diejenigen, die in Berlin wohnten, nach Dienstschluss mit einem DauerUrlaubsschein t¨ aglich nach Hause fahren. Das bedeutete f¨ ur mich nur die Fahrt von einer Stadtbahn-Station, n¨ amlich bis “Sch¨ oneweide” (3 Min.), um zu Hause zu sein.

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Der sog[enannte] Dienst bestand im Vertr¨ odeln der Zeit, wie Revierreinigen, M¨ obeltransporten, Schreibstubenarbeiten u.a. Zwischendurch gab es auch mal Exerzieren mit langen Exerzierpausen und vorzeitigem Ende. Wer geschickt war und irgendeinen Grund f¨ ur eine Besch¨aftigung fand, war von diesen “Diensten” befreit und konnte so einen Teil seiner Milit¨ arzeit beispielsweise in der Kantine verbringen. Jeder Neuank¨ ommling erhielt 3 Fragebogen, f¨ ur deren Beantwortung er unter Befreiung vom “Dienst” mehrere Tage Zeit hatte. Die Fragen bezogen sich auf Lebenslauf, Ausbildung, beruﬂiche T¨ atigkeit und letzten Verdienst vor der Einberufung. Es erfolgte dann nach einiger Zeit ¨ eine fachliche Uberpr¨ ufung durch einen Stabsingenieur, der bei den Sol¨ daten als arrogant bekannt war. Im Verlaufe meiner Uberpr¨ ufung f¨ uhlte sich der Herr oﬀensichtlich bald fachlich unterlegen, steckte zur¨ uck und schlug einen freundlichen, um nicht zu sagen unterw¨ urﬁgen Ton an, wie das bei solchen Naturen u ¨blich ist. Wie vorauszusehen war das Ergebnis: Zuteilung zu den Hochfrequenzlern. Als dann zuf¨ allig der f¨ ur die Hochfrequenz zust¨ andige, Stabsingenieur, mit Namen Six, das Zimmer betrat, wurde ich — von meinem Pr¨ ufer u ¨ber den gr¨ unen Klee gelobt — von diesem gleich hocherfreut in Empfang genommen. Hochfrequenzler waren, zumal gute, sehr begehrt. Doch dann fand erst noch eine ¨ 9-t¨ agige milit¨arische Uberpr¨ ufung statt, bei der sich zeigte, wieviel besser im Vergleich zu den anderen meine Kenntnisse und Fertigkeiten dank der guten Grundausbildung und des Gefreitenlehrgangs waren. Darauf wurde ich zu einem bereits laufenden Lehrgang abkommandiert, der f¨ ur diejenigen Elektroingenieure gedacht war, die nicht auf Hochfrequenz spezalisiert waren, und mir deshalb nichts einbrachte. [Heinz Rudolph]

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[754] Rudolf Peierls E.M. Lifschitz [location unspeciﬁed], 30.5.1979 (carbon copy) Dear Zhenya, I am writing to ask for your help in the following project: About a month ago there was a small conference in London, called on the invitation of Nevill Mott, to talk about the early history of solid-state physics, concentrating on the development of electron theory from the ﬁrst applications of quantum theory until the time of the Second World War (and also about dislocations in a somewhat later period). The idea was to get the recollections of those who participated in those developments and are still alive. Many of them were present at the meeting, others sent memoranda. There were also some historians of science present, to help in organising the material.1116 It is hoped to publish all the material collected at this meeting. It would be too unbalanced if no mention was made of those who are no longer alive. We already have notes of the work of E.C.Stoner and of R. Pohl. We expect to have some notes on the work of Frenkel, and of the Joﬀe school. It would obviously be desirable to have a note on Landau’s contributions to this area, and nobody could be better qualiﬁed to write this than you are. Would you be willing to write such a note, and if so, how long would you expect it to take you? Mott and all others interested in the project would be most grateful for your help. With warmest greetings, Yours sincerely, Rudolf Peierls I am writing this during a visit to the USA, but I am soon returning to Oxford, so please reply to Oxford.

1116

See letter [752], note 1115.

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[755] Nina Byers to Genia and Rudolf Peierls Los Angeles, 23.7.1979 Dear Rudi and Genia, As it is by now clear, we didn’t make it to Oxford for Somerville’s Centenary celebrations.1117 I had planned to attend the neutrino ’79 conference in Bergen1118 and then stop in Oxford on my way back. I had hoped to see you then. The Bergen Conference began just after school here ﬁnished, and a few days before I was to leave my ankle swole up and became very painful. I accused Art of kicking me in bed but he defended himself by pointing out that if he had done me so much damage he would himself at least be bruised. Since I had not fallen or otherwise hurt myself, the malady was a mystery – until it was diagnosed as gout. I was dosed with colchicine and the soreness and swelling went away. So gout it was. I don’t think that is a serious disease, but it was suﬃcient to cause me to decide not to go to Bergen. When I was able to walk more comfortably, I thought about going just to Oxford for the Centenary. But I decided that it would be better to contribute the money it would cost to the Somerville Library Physical Sciences Fund. So that is what I did — and I also sent a gift for the SCR and funds for an ice cream and cake party for the children of the Somerville Creche. And a journalist from the Los Angeles Times. So I am looking forward to seeing the pictures and reports from the festivities. How are you and what are your travel plans now? Art and I are due to spend the Fall quarter in Cambridge where I have been appointed some kind of fellow at Harvard. Will you be at the East Coast in September, October or November? (By the way, did Sam MacDowell come to see you in Stoney Brook?) In December we have said we would accept an invitation from Nguyen van Hieu to lecture in his institute 1117 Nina Byers had close connections with Somerville College in Oxford. She had been John Simon Guggenheim Memorial Fellow (1964/65), Fellow and Tutor in Physics (1967–1968) and Visiting Fellow (1968–1972 and 1978–1985). 1118 International Conference on Neutrinos, Weak Interactions and Cosmology, Bergen, 18–22. June 1979.

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in Hanoi.1119 Then in January we should be back in Santa Monica. Our place is idyllic. I love being there — the air is so sweet-smelling and the surroundings are so peaceful. It is a haven from the rest of Los Angeles! So we have a pleasant place to live and still access to a major metropolitan center. I feel we are very lucky. Art is enjoying his retirement, and (hopefully) I am adjusting to it and married life in general. I’m sorry not to have seen you this summer, and hope to see you soon. Best regards and love — As ever, Nina

[756] Rudolf Peierls to Nina Byers [Oxford], 26.8.1979 (carbon copy) Dear Nina, Thank you for your letter which is by now over a month old.1120 We were sorry you could not make it, and even more so to hear of the cause. Gout is a nuisance. It used to be thought of as associated with middleaged gentlemen given to drinking port in clubs — but it seems that in these times of equal opportunity no male prerogative is sacred. Gaby had expected to come to the Somerville jubilations, but also did not make it because she was in a complicated case, and could not get away. She came later and had a holiday visiting family and numerous old friends around this country. We have been back from Stony Brook since June, and are just about to take oﬀ again. (Institut Jozef Stefan, P.O. Box 199, 61001 Ljubljana, Yugoslavia) where [we] will stay until the end of October and then we 1119

Nguyen van Hieu (1938–), obtained his Ph.D. from Hanoi University in 1962 where he spent most of his scientiﬁc career. 1120 Letter [755].

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go for three months to Copenhagen. After that we come back to Oxford brieﬂy, since I have to give lecture here at the end of January, and we leave our car here. After that our travel plans get complicated. We shall be in Sao Paulo for three months from early March, and have decided to go there via Vancouver, to visit Kitty again. This means that on the way from Vancouver to Brazil we shall practically pass L.A., and so perhaps we could stop for a weekend if you were about. This would be middle or end of February, and according to your letter you may be home. As you were prevented from calling on us it would be ﬁtting if we called on you instead (ref. Mohammed and the mountain). We had some excitement here, because a book was published about Soviet inﬂuence in Britain, which claimed to know of many people who belonged to that network. The very incompetent author was careful to write mainly about dead people, to avoid the risk of libel suits, but for some reason he was sure I was dead, and wrote a lot of nonsense about me. So of course I sued him, and the case got settled out of court in record time, with the book withdrawn, author and publisher apologizing in court, and a very handsome sum in damages. We did not see Sam MacDowell in Stony Brook — they had been away and heard of our being there only a day or so before we left, but he later appeared in Oxford, and spent an evening with us. Greetings to Art, and good luck with all your travels. Yours, [Nina]

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[757] Rudolf Peierls to Joseph Rotblat [Copenhagen], 8.12.1979 (carbon copy) Dear Joe, Enclosed at last the donation to British Pugwash from the proceeds of my libel suit.1121 I am sorry it took so long, but with my nomadic way of life there was some delay in the “damages” being paid into my account, and more delay in my getting conﬁrmation of this. It has occurred to me that you might prefer the money to go into SEAS, but if this is to be done on a 7-year covenant basis, there is a snag that at my age it is by no means sure that all seven payments will be made, so Pugwash might lose. Also, the money comes from untaxed income, and while one could claim it to come from other income, I am not sure how far the claim for tax relief would run into complications. However, if you feel strongly about this, I suggest you delay paying in the cheque until the implications can be explored. I shall be at this address until 27 January, and then brieﬂy in England for a week or so. I just spoke on the phone to Michael Kaplan, whom I found in the Pugwash Oﬃce after chasing him via Geneva, about a thought that might conceivably make a contribution to the Tehran crisis. No doubt he told you about this. Here everybody is very agitated about a ﬁlm made from the idiotic “Intrepid” book that you probably know of. The ﬁlm apparently treats Niels Bohr in a more fantastic way than the book. He is shown working on heavy water for the Germans in Norway, in a lab guarded by German security, and realised what he is doing only after he gets a letter from 1121

The journalist Donald McCormick, alias Richard Deacon, had written a book entitled The British Connection, to be published by Hamish Hamilton, about the alleged activities of Russian revolutionary agents in Britain. This book contained some defamatory passages of Rudolf Peierls, whom the author apparently believed dead. In an out-of-court settlement with the publishers, Peierls not only received an apology and assurances that the passages in question would not be published, he also received substantial damages, which Peierls donated to the Pugwash Movement.

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Einstein, which prompts him to ﬂee to England! The ﬁlm has not yet been shown here, but people have seen advance showings. Luckily the papers have come out strongly in defence of Bohr’s reputation. If you hear of this turning up in England I would be glad to know. Here the title of the ﬁlm is, I believe, “Operation Death”.1122 Yours sincerely [Rudi]

[758] Hans Bethe to Rudolf Peierls Ithaca, 2.1.1980 Dear Rudi: Thanks for your letter of 12 December.1123 Unfortunately, I cannot solve the mystery of Niels Bohr’s idea about the compound nucleus.1124 I am pretty sure that I did not send a copy of my paper on the one-body theory of capture of neutrons to Copenhagen. However, I gave a talk about it at the American Physical Society meeting in February 1935 which was heard my many people, and I subsequently discussed it quite a lot with other physicists here in the U.S.1125 It could well be that some account of my paper could have travelled to Copenhagen through one of the many physicists with whom I discussed it. 1122 The 1979 ﬁlm, directed by Peter Carter, was shown under the title ‘A Man Called Intrepid’. The screening of the ﬁlm in Copenhagen led to Genia Peierls standing outside the cinema for three days protesting about the factual inaccuracies in the presentation of Niels Bohr. 1123 Letter could not be located. 1124 Rudolf Peierls was working on the ninth volume of the Collected Works of Niels Bohr, (the volume was later published as R.E. Peierls (ed.), Niels Bohr. Collected Works, Vol. 9, Amsterdam: North Holland, 1986) and for this purpose he was researching in Copenhagen. His query was in connection with the introduction for this volume. 1125 The meeting took place between 22 and 23 February 1935 in New York. Bethe presented a paper in which he based a subsequent publication. H.A. Bethe, ‘Theory of Disintegration of Nuclei by Neutrons’, Phys. Rev. 47, 747–59 (1935).

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As far as I remember, I did not participate in the conference in the autumn at Copenhagen. I was there during the summer for one month. It may well have been September, but I do not recall the exact time. I remember several seminars in which Niels Bohr participated, but I don’t recall any remark by Bohr which indicated to me the germ of the compound nucleus idea. Very likely I might not have noticed it even if he gave some indications. About Contemporary Physics: Unfortunately I have far more writing in the near future that I have time to do. On the supernova work with Gerry Brown, I promised to write a more popular account for the volume to celebrate Willy Fowler’s 70th birthday so I can’t very well publish once more in Contemporary Physics.1126 On nuclear matter, I have not done anything in recent years, so there are much more competent people to write about it, such as John Negele and Pandharipande. So, I am afraid, for the time being I cannot oblige. It was good to hear that you are enjoying Copenhagen, and that you were for some time living in paradise, in the Nationbank’s guest ﬂats in Nyhavn. Both Rose and I are wishing Genia and you the very best for the New Year. The enclosed circular letter tells you about our experiences in the year just passed. Yours sincerely, Hans In the meantime, your account of the last 5 years arrived, and we enjoyed it very much — but what a travelling life you have! A happy and perhaps more sedentary 1980 to you both! Where shall we meet again? Denmark ’81? Brazil ’80?

1126

H.A. Bethe, ‘Supernova Theory’, in C.A. Barnes, D.D. Clayton and D.N. Schramm (Eds.), Essays in Nuclear Astrophysics, New York: CUP, 1982, 439–66.

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[759] Rudolf Peierls to Hans Bethe [Copenhagen], 15.1.1980 (carbon copy) Dear Hans, Thank you for your letter.1127 I think I have resolved the main mystery by the brilliant idea that there were two seminars, one as described by Wheeler in April ’35, and another as described by Frisch later in the year, the latter being the one at which the report was about your paper. This removes all contradictions, except for some details which Wheeler may well be inaccurate. I have put this solution to Wheeler, and am waiting to see if he is willing to buy it. The other part of the mystery will have to remain unsolved. Our travel plans for the immediate future involve travelling South from Vancouver, stopping at Stanford from 18 to 29 February, then heading to Sao Paulo, Brazil, where we are due on 6 March. We plan to call at Los Angeles, but there seems to be time to drop in on Santa Barbara, where I gather you and Gerry Brown will be at that time. I have just written to Gerry asking him to look at the schedules and phone me in Vancouver when he — and you have got organized in Santa Barbara. Too bad about Contemporary Physics. Perhaps we can try some other time. Thank you also for your Annual Report. We did not know about your operation, and it was good to read that all went well, and that it has been worthwhile. Love to Rose, also from Genia, Yours sincerely, [Rudi]

1127

Letter [758].

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[760] Rudolf Peierls to Nina Byers Sao Paulo, 13.4.1980 (carbon copy) Dear Nina and Art, Genia and I cannot recall whether or not we wrote to you since our visit to your place. If we did, put it down to our increasing senility. Our trip here was satisfactorily uneventful, and we settled down easily. S˜ ao Paulo is much more attractive than its reputation suggests. It is lively, full of charming people, with high-rise buildings spread over a vast area, many of them quite interesting architecturally, and made more varied by the hilly terrain. The level diﬀerences are also cleverly used to disentangle streams of traﬃc by underpasses, overpasses, bridges and tunnels. The traﬃc density is fantastic even so; we live near a main street, with a post oﬃce just across that street. But most of the time it is impossible to cross without walking to the next lights and back along the other side, roughly a ten minutes’ expedition. We are staying in an apartment hotel near the downtown area with rudimentary cooking facilities, and with an excellent Italian restaurant around the corner, who will send orders up at 20 minutes’ notice. We spent a weekend in Rio, where, on the invitation of our old friend Guido Beck, I gave a talk, and we were shown the whole city. We enjoyed the visit, but just as we were getting ready to catch our night train back, Genia collapsed with a high temperature, and only a very powerful injection by the local doctor put her into a ﬁt state to travel. She had a violent virus infection some kind of ‘ﬂu’, which, with the heat (near 100F) produced complete dehydration. Since then, i.e. for the past three weeks, she has been under the weather, very weak, and with various side eﬀects, e.g. paralysis of a facial nerve, which is temporary but unpleasant. Now things are improving, though it will take her still some time to get back to her normal self. So we have not seen as much of Brazil as we expected, but at least we have sampled some aspects which are not normally on the visitor’s schedule. Genia spent three days in hospital, to ﬁght her dehydration by I.V. saline, and by local custom each patient is accompanied by a

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relative or friend, so I stayed in Hospital, too. Their nurses are very good, but as nobody in the hospital spoke anything but Portuguese, there were some problems in communication. But the Nussenzveigs and other friends were wonderful, and appeared at all times. The Institute is huge, and I have so far sampled mainly the Mathematical Physics Department, which contains a number of very bright young people, and I have met a few from Nuclear and Solid-state physics. Nussenzveig is now, for his sins, the director of the whole Institute, but seems to take this in his stride. This gives him the use of the director’s car and chauﬀeur, and I have proﬁted from this by being collected and returned in style. But by now I have mastered the local bus system, and in fact there are frequent bus lines practically from door to door. The buses are fast and temperamental, they like to take corners on two wheels or however many there are on each side, and in town there are separate bus lanes (in which the density of private carts and taxis is slightly less than in the rest of the road) We hope you have been spared further cloudbursts, and the leak in the roof has been located and dealt with. Thank you very much again for the pleasant days, and for giving up your bedroom. We enjoyed your company, right to the plane gate. With all good wishes to both of you, Yours sincerely, Rudi [761] Hans Bethe to Rudolf Peierls Ithaca, 1.7.1980 Dear Rudi: Thank you ever so much for your two letters (and also Genia’s) from Sao Paulo.1128 The advice on living conditions was most useful, and especially your advice on energy. 1128

As the Peierls couple were spending a lot of time traveling, much of the correspondence was written by hand and therefore without carbon copies. As a result, fewer of the letters have survived.

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Following your advice I will stress the development of hydroelectric power, and state that this is likely to be cheaper than nuclear. But I am supposed to talk about nuclear power, and give my usual talk about safety, waste disposal, and weapons proliferation. On the latter point, I suppose the Brazilians will be somewhat touchy. We have had a good spring although I had an awful lot of brief travels between April and now. We are leaving a week from today for Estes Park, Colorado, then on the 27th for Peru where we shall be joined by Monica, and on August 4 to Rio. We expect to be back in Ithaca on August 17. Thanks once more for your very nice letters, and we remember happily your visit on March 1 in the rain. Next spring we shall again be in Copenhagen, and will be one week in England, probably some time in May. We hope to see you. All the best, and love to Genia, Yours sincerely, Hans

[762] John Bell to Rudolf Peierls Geneva, 20.8.1980 Dear Professor Peierls, Thank you for your letter.1129 Your remark “I am not aware of any other description of what the wave function is for” reminded me that once I heard you tell of a man who was asked “Do you believe in polygamy” and replied “Yes, and what’s more, I have seen it![”] I have seen other interpretations of the wave function. In particular there are the “realistic” interpretations of de Broglie and Bohm and Everett. I enclose a paper setting out what I think of these. To ﬁnd some others I went to the library and browsed through what we have on quantum mechanics. One ﬁnds very few explicit statements that could be relevant. Moreover 1129

Letter could not be located.

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in talking to university colleagues I ﬁnd that, rather generally, like the authors of text books, they are uneasy about questions of interpretation, and refer to them as little as possible in their lectures. So our students learn quantum mechanics the way they learn to ride bicycles (both very valuable accomplishments) without really knowing what they are doing. But occasionally you do ﬁnd some remarks in the books. Soviet authors seem obliged to denounce any suggestion of subjectivity in the wave function. I enclose quotations from Blokhintsev and from Landau and Lifshitz. I also enclose, for fun, a quotation from Kemble. Kemble is an extreme subjectivist. He thinks the wave function is unreduced if the observer loses his notebook, and so has less knowledge than before! I cannot believe that you would endorse this. I think that “the wave function represents our knowledge” has to be carefully interpreted. In the course of making such an interpretation one concludes (I think) that the wave function is determined by the macroscopic setup — whether the observer has taken notes or not, or lost them — and is in this request quite analogous to a classical electromagnetic wave. It is then the word “macroscopic” that one must gloss over to avoid the pit. As regards non-linearity restoring determinism, and destroying the foundations of quantum mechanics, I think I could live with this! So long as the veriﬁed experimental predictions are reproduced I would be happy. I would be happy also with the even more radical destruction of the “foundations” that you yourself envisage in connection with life. In a general way I would say that I am very grateful to those who taught me how to do quantum mechanics, as to those who taught me how to ride a bicycle. But the diﬃculty of formulating QM in a sharp way convinced me that it is a vaguely perceived fragment of something else — it points beyond itself. I was happy where I could read you as to some extent sharing this view. With best wishes, John Bell

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[763] Joseph Rotblat to Rudolf Peierls London, 22.9.1980 Dear Rudi, Many thanks for your letter1130 and your comments on my letter to the Times. I wrote the letter in response to the leading article, and this referred directly to P.D. 591131 as a counterforce strategy. The main thrust of my letter was of course to point out the fallacy of a limited nuclear war. I received a number of letters from people unknown to me to express their support for my views. I know of at least two letters to the Times but not accepted for publication, possibly because they expressed support for me in very strong terms. The fact that so many people bothered to write to me is a sure indication that the threat of nuclear war is being taken much more seriously than in the past. But I am not certain about the best way to use this feeling to exert pressure on the government. I hope we shall have a chance to talk about these matter when you return to Oxford.1132 Yours sincerely, Joe [764] Rudolf Peierls to Nina Byers [Oxford], 9.10.1980 (carbon copy) Dear Nina, Thank you for your letter.1133 We seem to have lost the issue of the London Review of Books with my Dyson review, and they don’t give 1130

Letter could not be located. P.D. 59 was Jimmy Carter’s presidential decision, in July 1980, which outlined his counterforce strategy. 1132 R. Peierls spent September 1980 in Copenhagen. 1133 Letter could not be located. 1131

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reprints, but I found a carbon Copy of which I enclose a Xerox. This is as published, except perhaps for some slight stylistic corrections, and the title, which they changed, quite irrelevantly, to “Nuclear Family”.1134 Distressed to hear about the dry rot. Was this cause or eﬀect of the leak in the roof? Genia recovered by the end of our stay in Sao Paulo suﬃciently for a brief trip — one day in the magniﬁcent baroque town of Minas Gerais, and a few days in Salvador, the ﬁrst Portuguese settlement, now with a lot of black culture from the former slaves. Then we had a pleasant week in Brookhaven with Ronnie and Julie. We got back in June, and in July, Genia’s sister, Nina, joined us again. She will come with us when we go to Paris on 1 November. I went to a Pugwash Conference in Holland in August, and from there for a month to Copenhagen to ﬁnish (or nearly ﬁnish) with the Nuclear Physics volume of Bohr’s Collected Works. I was a little worried about leaving Genia, who was still shaky and tired, but it was a comforting thought that Nina was there to help. A week after I departed, Nina developed bad back trouble and was ﬂat on her back and needed nursing. However, Genia managed it all without disaster, and in a week or so Nina was o.k. again. With all good wishes to you and Art — and the house. Yours, Rudi [765] Rudolf Peierls to John Bell [Oxford], 13.11.1980 (carbon copy) Dear Bell, I am sorry I never yet acknowledged your letter of 20 August,1135 but I wanted to try to make some intelligent comments, and I could only now 1134 1135

R.E.Peierls, ‘Nuclear Families’, London Review of Books, 19 June 1980, 9–10. Letter [762].

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ﬁnd the necessary period of leisure to try to understand your point of view. I enjoyed reading the preprint you sent, although I disagree with most of what you say; but listening to diﬀerent views is a good way of making one’s own ideas more precise, provided the exposition is clear and imaginative, which yours certainly is. I shall try to explain where and why I disagree, and as I am doing this, to clear my own ideas, this letter may get rather long. But it will not be longer than your preprint, so I hope this is all right. There are two parts to my argument: I do not accept that the present theory is unacceptable, and I do not like the alternatives you discuss. Let me start with your objections to quantum mechanics. Call it the “Copenhagen interpretation” if you like, though I have still not seen any alternative that makes any sense; I have seen various schemes adding unnecessary words to the normal interpretation. First I shall comment on various statements in your preprint. P. 1 In spite of my respect for Dirac, I ﬁnd the third of the phrases which you quote very badly formulated. It gives the impression that a physical change takes place in the system; in fact all that changes is our knowledge of it. I agree with you that many distinguished theoreticians talk about these matters rather loosely, and this contributes to the diﬃculties experienced by people who want to learn the subject as you point out. “· · · are we not obliged to admit that more or less “measurementlike” processes are going on · · · ” The answer is NO, for any sensible deﬁnition of “measurement”. A measurement necessarily has two ingredients. (1) a device causing a correlation between the variable to be measured and something readily observable, say a “pointer”; (2) some observer “to see” the position of the pointer. You will remember the discussion in my book on the point. I do not follow your references to “good” and “bad” measurements. I am able to classify measurements only in two respects: Firstly accuracy. In the case of a discrete variable, like a spin, I can imagine a perfect measurement, e.g. a Stern Gerlach experiment which tells us with certainty that a spin is up and not down (Real Stern-Gerlach experiments come very close to this ideal). For a continuous variable, say a momentum, there must always be a ﬁnite error, and even for a

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discrete variable there may be an error. If no other information is available, the state of knowledge after the experiment must be presented as a mixture (density matrix) rather than a pure state (wave function). If there is some previous information available which is not destroyed in the process of the measurement, the description after measurement may still be a pure state (e.g. wave packet). The second classiﬁcation is according to the completeness of the measurement. For a system with N degrees of freedom, we can, in principle, measure N commuting observables. (I do not include discrete variables in the count, because the counting then becomes ambiguous, but the principles remain). In general, an experiment measures only some of these variables, and this is then an incomplete measurement . While even for a macroscopic system a complete measurement is possible in principle, it is, of course, hopelessly unrealistic. An incomplete measurement, again, leaves us with a mixture, unless suﬃcient previous information is carried along. (This of course never happens for a macroscopic system.) For purposes of exposition it is often convenient to simplify matters by talking about a perfect and complete measurement, leading to a pure state, although this is usually an unrealistic idealization. However, quantum mechanics has room for all measurements, however inaccurate and however incomplete. So where are the “bad” measurements? P. 2 Non-linearity. I am sure (and I suspect you agree) that one cannot expect non-linearity which will cause a collapse of the wave function as a result of a measurement. This would mean that from an accurate knowledge of the initial wave function we should be able to predict the outcome of the measurement, and this is not sensible. I do not believe there is a need for any non-linearity (or any other change) to make macroscopic systems behave classically. Quantum mechanics already accounts for the practically classical behaviour of large systems to the accuracy required. Of course the classical view of macroscopic systems is much simpler, and therefore preferable where applicable. Would you want to introduce modiﬁcations into mechanics to make a large solid behave as a continuum and not only approximate it? I also don’t accept the idea for which you quote Rosenfeld that we need classical behaviour in large objects to describe gravitation. We have to learn how to quantize gravitation, but I am willing to bet heavily that this will not involve

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non-linearities in the wave function. As regards consciousness, and life in general, I believe that its description will call for a modiﬁcation or rather enrichment of our concepts, but the idea of non-linear terms is much too naive. It is more likely that the concept of a wave function will have to be replaced by something deeper, rather than a change in the equation for a wave function. Otherwise it would resemble the prequantum attempts to resolve the diﬃculties of classical radiation theory by non-linear terms in Maxwell’s equations. P. 6 “· · · the placing of an inevitable split, between quantum system and observing world, is not a matter of indiﬀerence”. In the successive correlations set up by any measurement process, some may involve complications (like the possible interatomic interactions in your photographic plate) or they may still involve quantum corrections. A classical discussion of the result of the measurement is then not possible unless the split is placed beyond the point where this happens. Usually, this is followed by a large number of steps (light scattered by the pointer — light reaching my retina — retina activating a neutron · · · ) which function classically, so that within that range the placement of the cut is immaterial. However, I do not accept the view, expressed by some, that this classical part of the chain is essential in principle. We know that the human eye can respond to a very small number of photons, and there is no reason against the assumption that we might be able to see a single photon. This would still be an observation, but no part of it would behave classically. (I do not know whether the transmission of the nerve impulse to my brain would then still be classical.[)] P. 8 Interpret the quotation from Bohr at the bottom of the page as saying that the information we receive from a measurement is no diﬀerent in quantum mechanics from what it is in classical mechanics. I ﬁnd that something has happened, or that it has not happened. It does not mean that any part of the measuring apparatus must necessarily function classically (cf. the example of looking at a single photon, above). Or if this is what Bohr means, then I disagree. PP. 8–9 You claim that the quantum mechanical description of the world involves both a wave function and classical variables. This is a confused statement of the position. A complete description would be

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in terms of a single density matrix, in which all information that has been obtained is included. If all the degrees of freedom of all parts of the apparatus were included in this it would be prohibitively complicated, as would be the full account of all molecules of a gas in classical statistical mechanics. Hence in practice we are forced to make approximations in both cases. All this was rather negative comments on what you say — now let me make some positive statements about the contemporary theory. In my view, a description of the laws of physics consists in giving us a set of correlations between successive observations. By observations I mean really what can we see, or if you like a little more generality, what our senses can experience. That we have senses and can experience such sensations is an empirical fact, which has not been deduced (and in my opinion cannot be deduced) from current physics. I am not willing to speculate about the nature of the extension that might lead to such a deduction, or whether this should properly be called a modiﬁcation of physics or an addition of a diﬀerent discipline beyond physics (just as Maxwell theory was beyond mechanics and not a modiﬁcation of it). Classical physics can equally be regarded as giving correlations between initial and ﬁnal observations. There is, of course, the diﬀerence that the classical correlations are in principle deterministic whereas quantum mechanics gives you only probabilities. As you discuss quite properly, this means that predictions are ﬁrm only for many repetitions of the same experiment, but in many cases a single experiment can be equivalent to such a repetition to a good enough approximation, if parts of the system are practically non-interacting. We can predict the result of a scattering experiment with a particle beam because the particles in the beam don’t interact. In this way physics, and in particular quantum physics, is like a grammar book which deﬁnes all possible sentences you might pronounce, or write down, leaving you the choice of which one expresses what you think. We can envisage a book containing all possible solutions to the Schr¨ odinger equation; we then have to chose the one corresponding to our initial observation. The list of solutions exists, without reference to any observer, or even if nobody is there to look; it takes an observer to pick out a particular solution, as in classical physics.

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Your account of Everett-De Witt (which does not resemble the impression I had of their papers — I must look at the papers again in the light of your account) seems to me in full agreement with my description; except that they (or you) call any solution in the list a “universe”, and the choice of a particular solution corresponding to the initial observation becomes a choice between “universes”. This is, as you say, just a matter of words, and the use of the word “universe” or “world” seems to me quite unattractive. Apart from terminology I see no diﬀerence between my view and your version of Everett-De Witt, or between either and conventional quantum mechanics. Now about the pilot wave theory. It seems to me unattractive because of the appearance of trajectories, which are necessarily unobservable and seem entirely redundant. But there is a particularly ugly feature of this theory: In ordinary quantum mechanics a uniform mixture such as an unpolarized electron beam is a deﬁnite and useful concept. In such an unpolarized electron beam there is no way of saying whether it is a random mixture of electrons with a spin + or − in the z direction, or such a mixture of electrons with opposite spins in some other direction or a mixture of right and left helicity. All such unpolarized beams are identical. Yet on the pilot wave theory the distribution of trajectories would depend on the way the mixture is built up. This would of course not lead to any conﬂict with observation, since the trajectories are not observable, but it seems to me to be a very ugly feature of the theory. Your account of Everett-De Witt reminds me of a speculation which I read when I was a child, about the “universal library”: One may think of books as limited to a certain size, say 500 pages, particularly since a longer book could then be divided into several volumes. With a ﬁnite number of symbols to the page, and a ﬁnite alphabet (plus empty space, plus some mathematical symbols) the number of possible books is ﬁnite, if very large, and one could imagine a library containing all of them. The article pointed out that, even if the librarian could move with the velocity of light, you would be very fortunate of you retrieved the book you ordered within a lifetime. What I did not realize until much later was that having such a library would be quite useless, even if the problem of rapid retrieval were solved, because selecting a book from it is completely identical with the process of writing it (You have

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to decide what is to be the ﬁrst letter; then the second, & c.[)] The Everett worlds have something of the redundancy of this library. I would be very interested in your reaction to these points. I shall be here until the end of December, and then for two months at the Institute de Physique Nucl´eaire, Orsay. I apologize for the numerous typing errors — I am using a typewriter with a very weird keyboard. Yours sincerely, Rudolf Peierls

[766] John Bell to Rudolf Peierls Geneva, 28.1.1981 Dear Professor Peierls, Thank you for your letter.1136 I hesitated to reply only because nearly every sentence in your letter could be the occasion for a lengthy discussion. An adequate reply would not be a letter but a book! I will take up only two points where it seems to me some agreement should be possible. More or less ‘measurement-like’ processes are going on more or less everywhere. I still think so. Your criteria of “pointer” and “observer” are more or less always met. I have the impression, as I write this, that a moment ago I heard the bell of the tea trolley. But I am not sure because I was concentrating on what I was writing. Maybe I really heard it. But if so it was faint, indicating that the trolley is still distant. The strength of the sound was a ‘pointer’ ‘measuring’ the distance of the trolley. Other ‘pointers’ will be people passing my open door towards the trolley when it ﬁnally reaches the nearby corner. But they might be going to a lecture. This sort of thing is going on more or less all the time more or less everywhere. The clouds in the sky are ‘pointer’ to humidity. As I write I am aware of a small portion of the sky, but only in the tail of my eye. I could go to the window and look more deﬁnitely. 1136

Letter [765].

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Probably someone not far away is gazing through the window. More likely he is daydreaming than making meteorological observations. But ‘Measurement’ more or less. From this to the Stern-Gerlach experiment, it seems to me, is only a matter of degree. As I remember the output of the original experiment, it looked something like this.

Two more or less distinct cresents. A more modern experiment will surely do better, but residual gas scattering, if nothing else will give residual confusion. Remembering also that the silver grains have ﬁnite size, and take a ﬁnite time to form, it seems clear to me that the ideal instantaneous experiments of the text-books are not precisely realised anywhere anytime, and more or less realized more or less all the time more or less everywhere. I think then the status of such ‘measurements’ should be like that of the ideal reversible heat engines of old fashioned thermodynamics — with an honourable place in phenomenology, but no place in fundamental theory. The second point that I would take up is the need for ‘classical’ variables. A complete description you say would be in terms of a single density matrix. But I think you will add to the density matrix a “probability interpretation”. ‘Probabilities’ of what? That certain classical variables take certain values? Even if you insist on ‘measurement’ with what else can you specify the results? If you could really identify your measurement situations and measurement results, then I would identify all such results as a set of values of what I could call classical variables, specifying actual history as distinct from the set of possibilities and even probabilities. With best wishes John Bell

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[767] Rudolf Peierls to Montgomery-Hyde [Oxford], 5.3.1981 (carbon copy) Dear Mr Montgomery Hyde, I have been abroad until now, and have only just been able to read your book.1137 I must say I am quite shocked by many inaccuracies and the general careless attitude to the facts which it reveals. I am leaving the country again tomorrow morning, and therefore cannot explain all my objections in detail, but I feel I want to write at least a short letter to report my reaction and give a few examples. I shall be back in early May and may then be able to write more fully. By far the most serious misstatement is on p. 50, relating to the distinguished physicist Lise Meitner. You say, without quoting sources, that she passed information to the Russians. This is complete nonsense, if only because she had no information to pass. She made indeed important contributions to the understanding of ﬁssion, but all the results were published immediately. It is also not true that Russian agents had helped her to get out of Nazi Germany, the help came from Dutch colleagues. It is painful to see such a slur on the memory of a person of the highest integrity. The whole summary of the developments on pp. 50–51 is quite garbled, but I will not now go into details. On p. 122 you have now eliminated the statement that I saw Fuchs in Berlin, but substituted “a British scientist who prefers to be anonymous”. The scientist was, in fact, Nicholas Kurti, F.R.S., and I have checked that he has never expressed any wish to be anonymous. Since the story his conversation with Fuchs is known to many people, your statement is likely to be an embarrassment, and may even be libelous. If you do not know who it was, why not say so? On p. 89, there is the comment alleged to be made by my wife, to which I objected already when I saw that passage in the extracts from the proofs you sent. The ﬁrst two sentences represent what she may well have said, but the ﬁnal sentence gives the whole quotation a completely 1137

H. Montgomery Hyde, The atom bomb spies, London: Hamish Hamilton, 1980.

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diﬀerent meaning, and I am sure she never said or intended that. What is bad here is the use of quotation marks for a passage which is not quoted verbatim from anywhere. On p. 131 you have Pontecorvo staying with Seligman. My friend, Mrs. Seligman tells me that he never stayed with them, because there was no room in their small house. On p. 132 you have a wrong version of Pontecorvo’s remark to her, which also was not made after a game of tennis, and there was never a farewell party given by the Seligmans for the Pontecorvos. In the picture section you include Pontecorvo’s portrait under the heading “Three who spied for the Soviet Union”. In fact, as the text of your book makes clear, you do not know — and I do not know — whether he did spy or not. Statements of alleged fact should not be made without a basis. I hope these examples explain my reaction. All these episodes are of course incidental to the main subject of the book, which is mostly presented in terms of quotation from the record. Taken at face value these are very interesting and contain much that I was not aware of. But in view of the casual treatment of the facts in the parts I do know about, I am bound to feel some doubt whether these passages are correctly quoted and fairly selected. Yours sincerely, Rudolf Peierls [768] Rudolf Peierls to Nina Byers [Oxford], 28.7.1981 (carbon copy) Dear Nina and Art, We delayed mailing the change-of-address card with the intention to write a letter with it, but life, and our “moving experience” proved too much, so in the end no letter and no card.1138 1138

Genia and Rudolf Peierls moved from their House on Boar’s Hill to a more centrally located ﬂat in Northmoor Road.

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By now we are more or less installed in our ﬂat, which we like very much. Everything is unpacked, and most objects are in their right places, most of the pictures are on the walls, and all the boxes have gone. The ﬂat is in a large house, about 1905 vintage, divided well into four ﬂats, so the rooms are large, and the ceilings high, and there is a large garden which we can enjoy but are not responsible for. We had come back from our trip around the world in early May, and within a week, Genia had found this ﬂat, and we had decided to buy it. The paperwork took the lawyers some time, and we ﬁnally got possession of the ﬂat on 17 July, and had promised to move on the 20th, to allow the new people to come into Farleigh by the time they had sold their house. This did not leave much time to get things done. Luckily the ﬂat was in excellent shape — the previous owners had got it all repainted and modernised, mostly in suitable colours, without ever moving in, so we needed to make only a few changes. So we moved in on the Monday and by the Saturday the place was quite civilised. But this was a very strenuous time, and Genia, who of course did most of the work, was quite exhausted at the end. By now, we have slackened our eﬀorts at imposing ourselves and are beginning to enjoy ourselves. We still have a spare room, so if you are passing this way, we can accept bookings. Japan was very interesting, and we saw a lot without getting rushed or over-tired. We also met many nice people and made friends with some. We managed to see two out of the three famous beauty spots (Miyajimi and Matsushima Bay), which is not doing too badly for three weeks, and we were at the cherry blossom time at each place, except at Sendai in the North, where we were too early. Then Nepal was much more exciting than expected, with vast amounts of beautiful and delicate carving covering every old house, every temple, and every palace — and there are lots of both. Then Kashmir was like a dream, beautiful, comfortable and peaceful. Since then I have been at a Pugwash symposium in Rehovot, and we both went to Chicago where I got a degree. But now we don’t go anywhere until September, when we go for 6 weeks to Seattle, and then for another 6 to Virginia, at the invitation of Pasha Nabir.

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So that’s our immediate past, present, and future. Love, [Rudi] [769] Rudolf Peierls to Nevill Mott [Oxford], 19.12.1981 (carbon copy) Dear Nevill, I entirely agree with you that one should discuss nuclear policy for this country. The problem is how to get a group ready for some serious discussion and writing, and also containing enough senior people to carry some weight. On the merits of the problem I am not satisﬁed that a “no-ﬁrst-use” declaration is the answer, because 1. In present circumstances it would not carry much credibility, and if it is not regarded as reliable it might be counter productive. 2. I do not believe that nuclear weapons would in fact be used against a conventional attack, but some uncertainty on this point may be useful in inspiring caution and discouraging adventures. In other words, if (1) above is wrong and the declaration is credible it would not necessarily be desirable. I think the central issue is, in fact, the present NATO strategy which provides for the use of tactical nuclear weapons in the event of a conventional attack which cannot be halted by conventional forces. As long as this is the strategy, a no-ﬁrst-use declaration would have to be either dishonest or a recipe for defeat. This strategy is disastrous, because there is no reason for believing that the borderline between tactical and strategic weapons can be held. The deﬁnition of “tactical” and strategic weapons is too vague, and the Russians have never admitted that there is a qualitative diﬀerence. If any nuclear weapons are used in Europe, the result is likely to be escalation to total destruction of Europe. A limitation which might

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well be maintained is to limit the destruction to Europe, i.e. not to attack the territory of either of the superpowers, as for example Alva Myrdal has stressed.1139 One can well imagine both the US and the USSR observing, in their mutual interest, the integrity of each other’s territory. Once this is properly understood in Europe, it must mean either a change in NATO’s strategic thinking, or the end of NATO. What is the right answer for NATO? If it is true that the present conventional forces are too weak to resist an attack by the Warsaw Pact forces — there are people who disagree with this, and I do not know the facts — the only answer is to build up conventional armies. This is expensive and politically unpopular, particularly if it requires reintroduction of conscription in the UK and the US. Hence, the present strategy is the seemingly easy way out. All this has been said already much better by Mountbatten and by Zuckerman. If one can get rid of the present NATO doctrine, the “no-ﬁrst-use” declaration will become unnecessary. I would be interested in your comments. It now seems that I shall go to Copenhagen only on 19 January, so I shall be happy to see you here before or after your Harwell meeting. Would you like to stay overnight? Yours sincerely, R.P.

[770] Nevill Mott to Rudolf Peierls Cambridge, [December 1981] Dear Rudi, Do we really disagree? We agree that the present NATO strategy is disastrous. Therefore — unless you believe in unilateral conventional 1139

Alva Myrdal (1902–1986), prominent member of the Swedish Social Democrat Party who made major contributions to the promotion of social welfare before engaging prominently in the promotion of disarmament as the leader of the non-aligned nations during the Geneva disarmament negotiations.

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disarmament – the only possibility is to prepare to resist the Russians with conventional arms. On nuclear weapons I am saying that we should not throw them away, but keep enough to “deter” the Russians from using theirs, but abandon the present policy. For SDP, I thought that a never-the-ﬁrst policy might gain support, but I haven’t managed to arouse any interest locally among SDP members. Will the Warsaw Pugwash go ahead now?1140 I’ll telephone you later about coming to see you. Yours, Nevill [771] Rudolf Peierls to Nevill Mott [Oxford], 31.12.1981 (carbon copy) Dear Nevill, We do agree on basics, as you say, but there are questions of practical approach which are not negligible. I believe that a no-ﬁrst-use declaration before a revision of NATO resources and strategy would be completely lacking credibility. It also carries a ﬂavour of unilateralism, which would make it hard to accept certainly for our present government. I believe therefore that one must start with a re-examination of NATO doctrine. It might in fact be true that there is no disastrous weakness in our conventional forces, but I doubt if one can get the military people to admit this, if it is true. They have for too long insisted on the contrary view. It is therefore likely that abandoning the nuclear response to a non-nuclear attack would require strengthening conventional forces. This would not carry the stigma of unilateralism, and might well ﬁnd more sympathy amongst politicians. It could of course be made clear that the purpose of such build-up is to eliminate the need to rely on tactical nuclear weapons, and that a 1140

On 13 December 1981 martial law had been imposed by the military government in Poland under General Wojciech Jaruzelski.

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no-ﬁrst-use rule would be accepted once the build-up had proceeded far enough. I agree that it would be very desirable for the SDP to have a view on these matters. Perhaps one could get there with the help of Brian Flowers, who is now one of the SDP Lords. I propose to talk to him about this when I see him, or write to him if I don’t see him soon. As regards the Pugwash meeting, nobody can predict what things will be like in Poland in August. I would guess that the government would be anxious to have the conference, unless they still feel at the time that it is not safe to let so many nosy foreigners in the country. It could also be that the Pugwash Executive Committee will want to cancel, if they don’t like the way things are in Poland, but in general it has been in the spirit of Pugwash to be ready to meet anybody and talk with anybody whether we like them or not. Yours, [Rudi] [772] Rudolf Peierls to Abdus Salam [Oxford], 3.1.1982 (carbon copy) Dear Salam, There have lately been many occasions when I had to compare my own recollections of various events with those of other people involved, and I have learned how often diﬀerent people’s memories are completely diﬀerent. One example of this is the account you have given in several places of our early conversations which preceded your paper about the neutrino helicity. The one description I have seen most recently, and which seems the most detailed, is in your Wolfson lecture. Before explaining how our recollections diﬀer, let me make clear that these variations in no way aﬀect the status of your paper or the value of the contribution it made, nor would they imply any signiﬁcant part played in it by myself. I do not remember asking about the neutrino mass in your PhD viva, though the question may have come up. However, we came back to the

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subject much later, when I told you about my speculation on whether the state of a single photon was physically well-deﬁned, or whether it might be indistinguishable from a case of three (or more) photons travelling colinearly. I had concluded that the state must be well-deﬁned, because gauge invariance prohibits the decay of a photon into three, and I decided therefore there must exist some quantity, conserved by gauge invariance, which would have a diﬀerent value for a single photon from that for any other state. But I had not then (and have not yet) succeeded in constructing this quality. Of course, if gauge invariance is not exact, this question does not arise, because then the photons would have a ﬁnite mass, and any state with several photons would have a larger mass. This discussion led on to the question of the neutrino, and we concluded that if the neutrino mass is zero, and if a single neutrino is a well-deﬁned object, there must be again some conservation law to deﬁne it. When we met again (I don’t remember whether this was the next day during the same visit or on a quite diﬀerent occasion) you produced the idea that what was then called γ5 invariance (i.e. helicity) might give the required conserved quantity. It was immediately clear that this would involve a violation of parity. This was not a shocking idea, because at the time Dalitz’s conclusions were known, and people had wondered whether these could be explained by abandoning parity conservation. You then suggested that we might publish a joint note about this (or perhaps you suggested adding my name to a note you had already drafted), but I declined. The reason was not that I regarded the idea of parity violation as absurd but that I felt the reasoning was not compelling enough to back such a drastic conclusion. After all the argument depended on the neutrino mass being exactly zero. In the absence of any symmetry forbidding a mass, the neutrino might be expected to have a self-energy, but since it seemed to only have weak interactions, one would have expected its self-mass to be very small, well below the experimental bound then available. You will see that the diﬀerence in our recollections is of no great historical importance. It just intrigues me. Of course it is quite possible

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that my recollection is incorrect (it would not be the ﬁrst time). But it seems particularly clear because the question of how to identify a one-particle state was a hobby of mine for some time, and you were the only person to show a serious interest in it, even though you took it to what seemed to me an unwarranted conclusion. Yours sincerely, [Rudolf Peierls]

[773] Abdus Salam to Rudolf Peierls Trieste, 19.1.1982 Dear Professor Peierls, I appreciate your gracious letter.1141 Memory can play tricks and it is subjectively selective. I may be wrong about the events, but I believe you did ask me about the neutrino mass as early as 1952 in the Ph.D. examination. I think the question came up in the context of a possible inﬁnite renormalisation of mass. (You may recall my thesis was about renormalisation theory. In fact, I believe you said: “Since you are such an expert on matters of renormalisation, can you answer me the following question · · · ”) In the language of to-day a zero mass would be “unnatural” for neutrino if there are inﬁnite renormalisations to be found. I distinctly remember you[r] question about photon decaying into photons of smaller energies collinearly. I believe we discussed the question of gauge invariance placing restriction on the process and leading to stability. I also recall looking at the related phase space. I agree this question came later in time, when I started visiting the Birmingham department at your kind invitation after 1954. It is interesting that my memory has no record of the same question being discussed about the neutrino, though it is a very natural question. (This is what I meant by selectivity of one’s memory.) 1141

Letter [772].

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Regarding the events leading up to γ5 -invariance and after, I believe I did specially travel to Birmingham (after the Seattle conference) to show you the note I had written. I did very much want you to be coauthor and I believe I am right in thinking that you felt like Pauli and aesthetically disfavoured parity violation. With hindsight, one can see that one needs both zero mass as well as lepton conservation to motivate two-component theory, but at that time I was assuming implicitly that lepton number is conserved. In this sense you are right as to the reasoning not being compelling. I remember us travelling together by train for the opening of Britain’s ﬁrst reactor at Calder Hall. I recall our continuing the discussion on this and related matters throughout the journey. In fact, if I close my eyes, I can even now see you and I sitting in blue plush seats opposite each other, and I am sure I hung on every opinion you expressed — as indeed I do now. And I think I am right in thinking that certainly a part of the idea was the shared prejudice with Pauli in favour of parity conservation. Regarding the question of the small mass for the neutrino, because of the smallness of the weak coupling constant, let us recall that the four Fermi interactions for the neutrino gave a quartic inﬁnity in those days. Even if renormalisation ideas could be used, and a meaningful ﬁnite part extracted, I think the role of a small non-zero mass (and this not aﬀecting the nearly 100% polarisation of the neutrino) became clear after the two-component theory. Once again, I would like to pay a tribute to your penetrating questionings about neutrino mass, so far as my thinking is concerned. I was indeed disappointed when you declined to join as the author of the note. I even wondered for a while whether I should publish it at all. In the end I simply acknowledged your having raised the question about neutrino self-mass in the acknowledgments. I do sincerely hope that my words at the Wolfson lecture conveyed nothing but reverence for you and my deepest aﬀection for you (and Mrs. Peierls, to whom kindly convey my best regards). Yours sincerely, Abdus Salam

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[774] Ilse and Hans Thorner to Rudolf and Genia Peierls London, 23.1.1982 Dear Genia, dear Rudi, Many thanks for your circular letter. It has given us much pleasure. Your ‘retirement’ appears to be quite active and productive. The image of Genia standing with a large poster in front of a Cinema to defend the good name and image of Niels Bohr must have been a sight and I am sure it succeeded to rouse a lot of publicity.1142 I am glad that she still has her old — or rather young — determination. We are also very interested to hear what has happened to your children. Families have a tendency to spread out and appear in all sorts of places of this globe. You may ask what happened to us. As you see from the addresses — I wrote both above this letter in the hope that you may use one or the other to come to see us. Jordans is only one hour’s drive on the M40 from Oxford and we are here every weekend. Although we are still living at the same addresses, life has not stood still. The most obvious thing is that we also have become older and Michael — our son — is pressing me to retire. The great attraction of retirement for me would be that I would be more mobile; but the nature of my work is that it depends on seeing patients. That is not for practical that is therapeutic reasons. I mean the patients — but my theoretical work is depending on them and on contact with them. If I give up seeing patients, I am entirely dependent on literature, and that is far removed from the original facts and observations. Our observations are not of the same ‘objective’ nature as the results of physical experiments. If you make your own observations you can take the subjective factor into account. Naturally the nature of my work has changed. Instead of seeing patient, the accent of my work has shifted to teaching and lecturing — but there is not enough time to get away from here. If I take a month that is already a lot of time because one cannot leave patients for too long. Apart from London there are several centres where I go more or less regularly; Rio de Janeiro, but I have to stay 1142

See letter [757].

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there at least one month if I want to achieve anything — Germany which I can do in a long weekend, and Italy, mainly Florence, where I stay some time but we can combine this with a stay in our cottage which is only 2 hrs away from Florence. Another place of attraction for us is Charlottesville — you can imagine how amused we were to read of your stay there — I think our stay may have overlapped. The reason of attraction to Charlottesville is that Michael is Associate Professor of Medicine there. They have a delightful house in Ivy which is about 10 miles from Charlottesville but easily get-at-able from his hospital and his laboratory. He has been there for about four years and is about to become full professor. Somehow he made a name for himself by his research in the endocrinology of the pituitary and the endocrinology of neurotransmitters. So we tackle similar problems from diﬀerent angles, but I am afraid my own knowledge of his area is very limited, but I am following his work and career with interest. He also travels a lot. It seems that the printed word which once was a revolution in the world has had its eclipse: we still use and need the printed word, but the demand for personal communications has grown immensely. Naturally modern transport encourages this. As we are at the children. Madeline is here in London. She is married and has four children between 14 and 9. It is very interesting and happy to see their progress. Daniel is the eldest; he is very musical and he declines to become a musician. I quietly agree with him. Music is wonderful as a hobby but very demanding as a profession. I hope he can ﬁnd his feet in some other ﬁeld that will allow him also to make use of his musical abilities. He has absolute pitch and enjoys composing. The second one is a chess champion and goes to the Merchant Taylors’ School. The youngest boy is also going to the Purcell School which has a strong musical bias which he enjoys very much. The very youngest is a girl, and we are looking forward to see which way she will develop. Madeline herself plays her cello. She is a free lance now and plays a good deal with the BBC symphony orchestra and also a good deal of barock music. She has a barock cello and travels a lot also. She will be one month in Provence with her cello and hopes to be able to take with her two of her children while we take the other two and two from America with us to Italy. (Our cottage is really an old Italian house

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(1717) and as so many Italian houses much bigger than one would like them to have nowadays. So the four children and we two are not yet able to ﬁll the house). Ilse also ‘retired’ as an optician and to her surprise she enjoys her retirement a lot, as she ﬁnds a good deal to do. Since she has now taken to driving, she also has increased her radius. She has taken to driving because she realized that we are quite immobile, particularly in Italy, if we cannot use the car. So as we both drive chances that we are immobilized have become smaller. But the weather once played us a trick. We were surprised by a snow fall in winter and it was really impossible to get away. We eventually managed to get away by using our suitcases as sledges and went down the hill on them. In the village we found a good soul who drove us to Pisa where we could take an aeroplane home. Of course the best place of transport for the place where we are is a mule. But I have not yet had the courage to get one as we are not there long enough. You cannot park a mule unless there is someone who is willing and able to use it in your absence. Should I succeed in making up my mind about retirement we shall have to come to a decision about the mule too. I hope your perambulations will also lead you back to Oxford. If you have time and the inclination we would be very glad to see you here. I shall add my telephone numbers to the addresses so you can get in touch with us. With kindest regards and the best wishes for 1982 Yours, Ilse and Hans [775] Nevill Mott to Rudolf Peierls Cambridge, 14.2.1982 Dear Rudi and Genia, I do apologize for leaving a pull-over behind. Thank you so much for sending it. Arising out of our discussion, I have written to Adam Roberts (Reader in International Politics, Linacre College) saying I would like

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to meet him. After that I must consider the best way of trying to inﬂuence SDP in this direction. A local group (I’m getting pessimistic on forming one) — contact Brian Flowers and/or Zuckermann. Then I shall see Ruth Adams next month, with an article for the bulletin + see if there is any hope of an Oxford-based study group (or rather if Robert’s group would turn towards persuading SDP). I hope you both have a very good trip to Australia. I am just oﬀ for a week in Germany; purely physics! Yours, Nevill

[776] Franz Jacobsohn to Rudolf Peierls Heidelberg, 10.4.1982 Lieber Rudi, Ich habe mich halb d¨ amlich gefreut, mal wieder etwas von Dir zu h¨oren; schon daraus kannst Du entnehmen, dass Deine Hyphothese, ich w¨ are irgendwie kommunikationsfeindlich, im Ansatz falsch ist; ich bin 50 % nicht gegen Korrespondenz, die restlichen 50 sind allerdings zuweilen bedauerlicherweise durch sogenannte Schreibfaulheit ung¨ unstig beein¨ ﬂusst. Ubrigens warnte mich Hilde Hamburger, die bei der Abfassung der Karte dabei war, dass Du prinzipiell niemals antwortest. Es muss also an der Familie liegen. Jedenfalls f¨ uhle ich mich durch die bewiesene Ausnahme hoch geehrt. ¨ Ubrigens war die von Dir erw¨ ahnte Beilage mit dem Bericht u ¨ ber Deine Lebensumst¨ ande leider nicht beigelegt;1143 aber oﬀenbar bist Du in Deiner Branche immer noch sehr t¨ atig und das freut ein’ denn ja auch. Ich betreibe auch noch immer meine alten Tricks, die man mir vor 50 Jahren eingepr¨ ugelt hat und stehe als freiwillige Feuerwehr, allerdings 1143

This refers to the circular letters which Peierls usually enclosed with his Christmas and New Year correspondence.

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nur gegen ein Honorar meinen Kollegen bei, die entweder krank sind oder vom Fernweh ergiﬀen in der weiten Welt herumstreunen. Leider ist im vergangenen Jahr meine liebe Frau Else verstorben und ich bin etwas allein und vereinsamt, was auch die Kinder nicht ausgleichen k¨onnen. Aber jedenfalls sollten wir uns einmal wiedersehen nach jetzt etwa 12 Jahren. Also in M¨ unchen oder hier in Heidelberg bei mir. Gastzimmer steht bereit, K¨ uche wird allgemein ger¨ uhmt, Keller ist gepﬂegt. Nach Hause kommst Du via Frankfurt-Flughafen. Wie w¨ are das? Gib mal kurz Laut, wie wir alten J¨ agerleute zu sagen pﬂegen. Herzliche Gr¨ usse auch an Genia, die hoﬀentlich mit von der Partie ist (was macht die Puppensammlung?); mein Bruder Robert dankt f¨ ur die u ¨bermittelten Gr¨ usse und m¨ochte das Kompliment erwidern. Und da gerade Ostern ist, was man in unseren Kreisen auch Pessach nennt, auch dazu entsprechende Gr¨ usse und W¨ unsche! In diesem Sinne Dein Franz Da Euer Postamt das Problem der Adresse mit ﬂiegenden Fahnen gel¨ ost hat, schreibe ich heute unter voller Identit¨ at. Lasst Eure Fahnen nur nicht allzu hoch im Winde ﬂattern; man hat hierzulande schlechte Erfahrungen damit gemacht!

[777] Rudolf Peierls to John Bell [Oxford], 27.4.1982 (carbon copy) Dear Bell, I enjoyed your lecture last week very much, although I disagreed with much of it, because I can now see your point of view more clearly and that makes it much easier to reply. First of all about the standard interpretation. Dirac’s wording of the axioms is wrong (nobody is infallible, not even Dirac!) It is not the

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system which “jumps” when a measurement is made, but our knowledge of it. One other rather common error (I don’t remember whether Dirac also makes this) is the assertion that the system necessarily is found after a measurement in the eigenstate of the quantity being measured, with the eigenvalue found by the measurement. For example, the normal way of measuring a momentum is to scatter light from the object and observe the Doppler eﬀect. But this necessarily changes the momentum of the object and it is not what the measurement indicated. What is essential is that the measurement settles both the value of the momentum before and that after the measurement, and they do not have to be identical. You say there is nothing to describe a bad measurement. But of course there is. A typical ‘bad’ measurement is an observation of the position x with error δx. Here x can be as large as you like, making this a very bad measurement. If nothing was known about the particle beforehand, then the state of the particle after the measurement will be a density matrix of the form f (x)(x − x ) where f (x) is unity when (x − x1 ) does not exceed δx, and zero otherwise; x1 is the result of the measurement. More generally, if the state of the system is given by a density matrix [. . .],1144 then the probability of a bad measurement giving the value a1 is [. . .].1145 The trace of [. . .],1146 where [. . .]1147 is a suitable matrix. For a good measurement [...]1148 where us is the eigenfunction of eigenvalue a1 . Obviously, for a continuous variable all measurements must be ‘bad’ the perfect measurement is a limiting case. Let us now turn to the continuous scattering experiment. I think it is not in the least unreasonable that such continuous scrutiny should prevent the system from developing normally, because we know from the uncertainty principle that this involves a continuing drastic interference with it. If you want a homely analogue it should not be “a watched kettle never boils”, because that does not involve any physical interference. A 1144

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better analogue is if you keep examining your students all day every day they will not learn anything. Or better, if a surgeon cuts open a patient continually he will not recover. Besides this, I am not even sure the thing is feasible. Certainly not for a continuous variable, because, as I have pointed out, only “bad” measurements are possible. If you increase the accuracy of the experiment, you also decrease the time for which the wave function remains approximately unchanged, because the mean square velocity increases. So the double limit looks terrible, but I have not examined it. For a discrete variable there are cases in which the state after the measurement is not the same as would give the measured result, and then the problem does not arise. There are other variables whose measurement necessarily takes time, and then again it does not work. In the transition to classical conditions, one must take into account not only that the measurements made are very “bad”, i.e. that the error greatly exceeds the limits imposed by the uncertainty principle, but also that we are then always concerned with many degrees of freedom, of which only some are observed. This is important in problems like Schr¨ odingier’s cat (or the equivalent problem of John Bell in CERN and London). Averaging over a large number of unobserved variables destroys the coherence, and therefore the objectionable interference between the dead and the live cat does not exist. That this is essential can be seen from the fact that Schr¨ odingier’s devise involves a counter and a trigger. Both are essentially thermodynamic devices, in which irreversibility is essential. This involves the presence of many atoms, and this will be enough to destroy coherence. I cannot similarly analyze the John-Bell problem, because it is not speciﬁcally formulated. You further objected to a lot of terms occurring in the usual interpretation such as “measurement”, “observable”, etc. I think all these terms are perfectly clear if one does not stick too pedantically to the wording of the axioms by Dirac, or by any other person. Axiomatics is complicated, and the axiomatics of Newton’s mechanics took centuries to get clear. But in any case I ﬁnd your term Be-ables much more objectionable. I see no clear deﬁnition of this, which does not use the concept of “existence”. In the everyday use of the word, existence is synonymous with “in principle observable”. But your be-ables include

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some things which are not in principle observable. This seems to me an unnecessary encumbrance of the theory. About alternative theories: You seem to like the de Broglie-Bohm idea. Apart from the fact that it has not been extended to relativistic conditions and does not seem suitable for electromagnetic phenomena (and you did not sound very hopeful about such extensions) it is ugly in that one has to carry the arbitrary choice of the point variables from the beginning of time, although they do not matter in that a diﬀerent choice, with the same wave functions, would lead to the same observable eﬀects. It is also ugly that, as I mentioned previously, one gets a diﬀerent description of an unpolarized electron beam according to whether one thinks of it as made up of equal numbers of electron[s] with spins in the x and −x direction, or of the same in the y or −y, etc. You did not seem to like the idea of non-linear terms much, so maybe I don’t have to state my objection. But it is that if non-linear terms had the eﬀect of causing the collapse of the wave packet, you would have a deterministic theory in that form a knowledge of the initial wave function, the Schr¨ odinger equation would tell you not only that the wave packet collapses, but where it collapses. This seems to be nonsense. These are really comments on your lecture. I have looked again at your last letter, but I think the points made there have been dealt with, except the last paragraph which I still do not understand. Yours sincerely, Rudolf Peierls [778] Freeman Dyson to Rudolf Peierls Oxford, 10.5.1982 Dear Genia and Rudi, It was a great disappointment not to ﬁnd you here.1149 But your letter to-day makes up for it to some extent. It is good that you stay active rather than vegetating here in Oxford. 1149

Freeman Dyson was visiting Oxford. Genia and Rudolf Peierls spent the month of May in Grenoble.

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I wanted to talk with you about lots of things, especially Katrin.1150 You know now how much she needs help and how hard it is to give it. I am deeply grateful to you for taking the time to spend a day with her. Your visit did help. I had recently a long letter from Katrin, more frank and open and sensible than she has been for a long time. Thank you also for relaying Katrin’s message about Imme. I know it is deeply felt. I was lucky to see a lot of the Ahlforses in Jerusalem. I don’t know if you know them. Lars Ahlfors won the mathematics prize. He is from Finland and his wife from Austria. Wonderful people, rather similar an age and temperament to the two of you. During WW2 they were living in Z¨ urich and knew Verena and Hans Haefeli very well. Erna Ahlfors took care of Katrin when she was a baby, until she was two years old and Verena dragged her oﬀ to Peru. Erna was very fond of Katrin and wanted to know what had happened to her, She stayed in touch with Hans Haefeli in Luzern, but Hans also did not happen what had happened to Katrin since she remarried and cut oﬀ communications with Verena. The Ahlforses are both 100% sure that Hans is really Katrin’s father. They say they saw it at ﬁrst hand, that Verena’s romance with Paumgartner was mostly invented by Verena after the fact in order to make Hans miserable, that the physical resemblance between Katrin and Hans was obvious to everybody when she was a baby. I said, in that case, why does Hans cut himself oﬀ from her so completely? They said it is not true, as I had thought, that Hans’ wife forbids him to make contact with Katrin. The reasons he cut himself oﬀ were, ﬁrst, that he believed the story about Paumgartner, and second, he was so wounded by the long bruising he took from Verena that he needed to forget Verena and everything connected with her. So I said, the Ahlforses should by all means try to persuade Hans that the time has come for him to contact Katrin, that a little attention from him would mean a lot to her. As I know Hans to be a decent fellow I think there is a good chance he will listen. What I would like now is to have some feed-back from you about 1150

Katrin was the daughter of Freeman Dyson’s ﬁrst wife, Verena, born before Verena and Freeman married.

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what can and cannot be done for Katrin. I know you talked on the phone with Imme when I was away from Princeton. She enjoyed talking with you, but unfortunately the conversation was not recorded. Apart from meeting the Ahlforses and Vicki Weisskopf, the trip to Jerusalem was exciting in other ways. The Knesset ceremony was on Sunday and on the day before (the Shabbat) I was invited to Birzeit University in the West Bank to give a science talk. The university had been closed by the Israelis the month before after an Israeli oﬃcial had been beaten up by some students. So I went and walked around the empty buildings and left a friendly note on the blackboard in the room where I should have spoken. The buildings are lovely and the labs well equipped for teaching science. A remarkable achievement for the West Bank people. I suppose it is comparable with the way the Hebrew University was in the 1930’s and it has a similar symbolic meaning for the West Bank people. I gave my talk to the Birzeit Faculty in a private house in Ramallah, no students being allowed to attend. The next day when we came to the Knesset I knew I had to stand up and speak out for Birzeit. I felt like a fake old testament prophet coming to Jerusalem to tell the king how to behave. But I remembered Amos Chapter 7 verses 14–17 and that helped. The target of my remarks was not President Navon but Minister of the Interior Burg who was sitting beside him. Burg is a real tough guy and looks like a gangster. I had a serious worry that when Burg heard what I said he would declare that the state of Israel had been insulted and walk out. That would have put me in a very bad position. So I made my remarks brief and calculated that he would be taken by surprise and would not have time to react. As soon as I ﬁnished, there was a stony silence, Burg looked anxiously at Navon and then there was loud clapping from a young Israeli choir who were to sing at the end of the ceremony. The choir saved me. After they started to clap, most of the audience joined in, and then I sat down and Gerart t’Hooft started his speech. Afterwards I had strong reactions, some angry and some enthusiastic, from the Israelis. But the main thing is that I broke the conspiracy of silence which surrounds Birzeit. I heard from Birzeit that they were allowed to reopen on April 16 and so far as I know they are still open.

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Other news: Our 14-year-old Rebecca went for three weeks on a high-school trip to Venessieux (suburb of Lyon) not far from where you are. She lived with a French family and ended up giving a talk in French to her class in the Lyc´ee. It was an outstanding success. Rebecca learned a lot about life, e.g. her hosts and the whole surrounding district are solidly communist and still they are not very diﬀerent from the Americans. Afterwards, Rebecca’s opposite number H´el`ene came to stay with us in Princeton and that was the main reason Imme could not be with me in Jerusalem. As you can imagine almost the only subject of conversation at the Oxford high tables where I am eating is the Falklands. I am selﬁshly glad that for this problem, unlike Birzeit, I do not feel any personal responsibility. I am glad you went to see George. He writes to say the plans for publishing his book miscarried and it will probably end up as “one of those unpublished early manuscripts that turns up years later inside an old trunk.” At least he has a sense of humour! I ﬂy back home on May 21. Very sorry to miss you here. Yours ever, Freeman [779] Rudolf Peierls Freeman Dyson Oxford, 29.6.1982 (carbon copy) Dear Freeman, Thank you very much for sending us the text of your lectures, which we were sorry to miss. They were, as expected, brilliantly presented, and set one thinking.1151 1151

Dyson had given a series of lectures at Brasenose College in May 1982. These were later published as ‘Bombs and Poetry’, in Sterling M. McCurrin (ed.) The Tanner Lectures on Human Values, Vol. 4, Salt Lake City, University of Utah Press, 1983, 81–145.

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I do not agree with all your arguments. I agree most emphatically with what you say about battleﬁeld nuclear weapons. I wrote a piece on this in the Bulletin, which you may have seen, but I enclose a copy.1152 I did not have, of course, the unbelievable US Manual which you discovered, and I also did not make the point that they were more liable to be used because they are vulnerable. I do not agree, however, that there is any possibility of ABM schemes being sensible. Quite apart from the possibility of counter measures, the schemes that were discussed when ABM was popular involved nuclear weapons being exploded near the likely targets, and as there are always some failures, some of these will fall on the targets and do the damage the enemy missile failed to do. Because the time for interception is so short, ABM must have a split-second ﬁring system, which no doubt would result in their being let oﬀ on false alarms, and cause damage and fallout when there is no enemy attack. I also do not believe that your perspective of non-violent resistance is right. There are, of course, cases, in which this can have a powerful eﬀect, for example again an occupying force whose morale is weakening, as was the case in India. But the example of a small French town is very special, because there action coincided with the presence of an exceptionally reasonable German oﬃcer. There were some of those, of course, but there cannot have been many. Such acts of courage are very important as examples, to maintain the spirit of the subjugated people, but the occasions when they can achieve anything against a real dictatorship must be few. Of course you conclude in the end that passive resistance is not practical. Another question on which I have at least serious doubts is your statement that the Russians have a counterforce strategy. You base this on a statement by Grechkov that the Soviet arms are intended against the military potential of the enemy. Now this is the kind of statement that is always made. No government likes to say that their plans are to slaughter civilians. The remarkable thing is that in the West, and in particular in the USA discussion is so open that these things actually get admitted. I may have missed other evidence 1152

R.E. Peierls, ‘Limited Nuclear War?’, Bull. Atomic. Sci. 38 (5), 2 (1982).

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of the Russian intentions, but I would certainly not give weight to that one. Your positive proposal is to get support for a more sensible and more moral point of view by the slogan “Live and let live”. Perhaps you are right. It is always unpredictable what slogans may capture the imagination of the public, but I fear this is too sophisticated in its implication. I believe at the present time one should put strong pressure against tactical nuclear weapons and for a no-ﬁrst-use declaration, as you do. I understand that now McNamara is taking this line. Another important argument is to show that no security is lost by a unilateral reduction in strategic missiles, a point also made by Hans Bethe. For this it is important to show that the idea of a counterforce strike is just science ﬁction. Even discounting the submarine deterrent (someone might invent an eﬀective means of ABM) or bombers and cruise missiles, the thought of staking national survival on the eﬃcient functioning in a very short time-interval of numerous high-technology devices, seems to be utterly unrealistic. There was in a recent bulletin a serious analysis of the prospects of a counterforce strategy, which impressed me as sensible. I think more eﬀort should be devoted to this question. Of course, eliminating the reliance on tactical weapons, making a noﬁrst-use declaration, and reducing the stockpiles of strategic weapons to the “nuclear umbrella” or minimum deterrent, will not get rid of nuclear weapons and therefore will not answer the moral case you make so eﬀectively. But it would be a step towards sanity, and would make it easier to talk about future sensible measures. With best wishes, Yours sincerely, [Rudolf Peierls]

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[780] Franz B. Jacobsohn to Rudolf Peierls Heidelberg, 2.10.1982 Lieber Rudi, Besten Dank f¨ ur Deinen Brief und die darin enthaltene frohe Botschaft.1153 Aber leider kommt immer was dazwischen und diesmal ist es meine Abwesenheit von Heidelberg. In 3 Tagen fahre ich nach USA, um meine Herren S¨ ohne und deren zahlreiche Sippen heimzusuchen und bleibe zwei Monate unterwegs. Auch die viel beschriebene Duplizit¨ at der F¨ alle kommt dazu. Ich fahre aus ekonomischen Gr¨ unden via London; daher wollte ich unterbrechen und Dir ins Haus fallen. Denktste! Ich darf in London den Flugplatz nicht verlassen und 3 Stunden auf Anschluss nach Boston warten. The best laid ways of mice and men oder so! Ich hoﬀe, es geht Dir gut im alten Vaterland. Leider kann Heidelberg Ende Oktober recht schlechtes Wetter haben, allerdings machen wir f¨ ur prominente G¨ aste Ausnahmen, da wird man ja sehen. Eins steht leider fest: Wir werden uns nicht sehen, leider! Wenn irgend m¨ oglich, komme ich mal im Sommer nach England; wir werden das noch diskutieren. Es tut mir leid zu h¨ oren, dass Deine Schw¨agerin so krank ist, dass Euer Leben dadurch ausser Balance ger¨ at. Hoﬀentlich l¨ asst sich wenigstens dagegen etwas tun. Lass von Dir h¨ oren, wenn es mal geht. Ich bin Anfang Dezember von meiner sentimental journey zur¨ uck. Alles Gute und beste Gr¨ usse auch an Genia. Dein Franz

1153

Letter could not be located. Jacobsoshn is likely to refer to Peierls visit to Germany in 1982.

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[781] Rudolf Peierls to Abraham Pais Oxford, 4.10.1982 (carbon copy) Dear Pais, You may remember that a long time ago you asked me about a letter which Oppenheimer wrote to me in 1942, giving a report about the work of his group on the critical size and eﬃciency of a nuclear bomb. I could not remember such a letter, but this did not prove anything. I then found a reference to such a letter in the book by Margaret Gowing “Britain and Atomic Energy 1939-1945”,1154 but it seemed that this was based on papers in Washington, from which it was clear that the letter was written and handed to the British oﬃce in Washington, but it did not guarantee that it actually reached me. If it did, it would be in my wartime papers, which are kept in the archives of the U.K. Atomic Energy Authority. I delayed looking for it, because I thought it would involve spending a long time looking through unsorted papers, but when at last I asked the archivists about it, they immediately produced the letter and my reply. Both are still technically secret, simply because they have not been looked at for declassiﬁcation. I shall now ask that the whole collection of papers be considered for declassiﬁcation. I am told that this will take about a year. If this particular letter is found to be declassiﬁable, which seems likely, there is therefore hope that by the beginning of 1984 you will be able to see a copy of it, that is if you are then still interested. We enjoyed seeing you both in Oxford. With best wishes, Yours sincerely, Rudolf Peierls

1154

See letter [687], note 917.

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[782] Rudolf and Genia Peierls to Nina Byers Oxford, 7.10.1982 (carbon copy) My dear Nina, I was waiting for your letter, but when Art called two days ago, he told us that you were still thinking about writing one. So, gallantly, I am writing one ﬁrst. After the disaster of your Oxford visit, or non-visit, I think you will see an immediate need to reform. As I said on the phone, 50+ is a very good time for a reform, rethinking, and turning over a new leaf. At the moment you are very unsettled, very “insecure” and very dissatisﬁed with your own performance. So it is a doubly appropriate time for turning over a new leaf. I think the main trouble is that you expect people to be “supportive”, and are upset when they are not particularly so. I don’t see any need for anybody at 50 to be supported. You ought to support others. When one is young, inexperienced and makes terrible blunders one needs support. And when one is getting very old and tottery. Otherwise one cannot expect it. And that probably is the root of your many troubles. A crazy young girl may be appealing, but a crazy middle-aged woman is irritating. This is a fact of life. So, my love, stop waiting for support and start to organise yourself. You are bright enough to see the need for it, and the technique is to start in small doses. For instance, just for the sake of self-training, say that every day you will have breakfast at a deﬁnite time, I don’t know, 8 a.m. or whatever, and see that you really have it every day on the minute. It will be very hard for the ﬁrst three days, but afterwards elementary. It needs a lot of intellectual eﬀort, timing how long it takes to wash, to dress, to make coﬀee, etc. It may even be great fun, because the nicest thing in life is to master oneself. Once you can train yourself to do one thing, you go for another. Write down your appointments. Think them out beforehand as systematically as you would think about physics and organize yourself so that you won’t have to rush. Have a pocket alarm and put it on 15 minutes to zero hour, and then at zero hour, so that you can get from

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one occupation to another without much last-minute rush. Please write it down and do it. Don’t say you cannot do it; you jolly well can, and it must be done on your own without any support from anybody. One always can if the incentive is good enough. And you must realize that if you want to change your occupation you simply have to start with that sort of thing. I assure you it is very amusing and rewarding, and on the whole more useful and more fun than improving your driving or tennis-playing. One must learn to do things in very small bites at a time, so that one can really achieve something in a short time. These things with appointments and being on time. Do it for instance at half a day to start with. Another great help in life is automatic actions and reactions. For instance, it does not take anything out of you to clean your teeth every morning, or to comb your hair. You do it without thinking or taking decisions. One must reduce as many things as possible to such automatic actions. It will be very easy for you to be on time, if you automatically leave 15 minutes before you have to depart, to go to the loo, etc. But be ruthless, and for a week or so force yourself to drop everything and not to be late – soon it will be automatic. You ask, what shall I do, I am tired of ﬁeld theory etc. Train yourself, conquer yourself, and then see what else is available. Most certainly don’t rub your wounds and expect anything from UCLA. Give your lectures and if you want physics, go and play at Cal.Tech. a couple of times a week. It is great fun to see what brilliant minds are doing. Otherwise, clear the decks and don’t get involved in too many things. Because your major trouble is that the thing you are doing, or are interested in at a given moment seems to you the most and only important thing. That is obviously very hard on you and on your environment, and obviously wrong, as you realize when another thing takes your fancy. You don’t need any headshrinker or anything of that kind. You may, being 52, need some hormones. Try to time yourself in the four-weeks’ cycle, when you feel specially tired, or depressed, or mad, and see if there is any problem. In my long life, I had to change myself many times: one can do it, and one must do it. I think that for a few months the kind of self-

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discipline, planning etc. will be invaluable. And learn not to change plans every three minutes. Stick to what you have decided to do, and see that you do it. Just remember your non-visit to Oxford. Rudi will copy this letter. Art liked our ﬂat, I am sorry that you haven’t seen it. My sister is better as far as the spastic colon and the depression go, but she has awful anemia, although she eats a lot of iron, so one has to start to chase another hare. I am pretty tired but still quite all right. Love to you both, Yours Genia Dear Nina, The above is faithful, and I hope, legible copy of Genia’s letter, faithful, that is, but for details of spelling and grammar. But with the substance I fully agree. I would like to underline two points already made by Genia: One is that one cannot aﬀord to have a single-track mind. Life is often like a university time-table, where one has to stop one lecture when the bell rings, and start another, on a diﬀerent subject, and with diﬀerent students. It would be more convenient if such interruptions did not happen, but they do. By ignoring them and sticking to the business one has started, one creates confusion; and getting out of that usually takes more adjustment than to follow the bell in the ﬁrst place. The other point is about decisions. You know about APEX tickets. Once you have bought one, you cannot change your mind. Or rather, you can, but it costs a lot of money. Now most decisions about practical matters are like that. Changing you mind does not always cost money (Though it often does) but the cost is in wasted time, and above all in irritating the people around you. In terms of wear and tear on your and other people’s nerves the cost is quite comparable or greater than forfeiting an APEX ticket. So it is a good idea to treat any decision, once made, as an APEX decision, to be changed in the case of real disaster, but never just because one now feels one prefers another ﬂight. I had a very amusing time in Rome, as Art no doubt has reported. In a week’s time I am to go for a month to Munich. Love to both of you, Rudi

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[783] J.M. S´ anchez-Ron1155 to Rudolf Peierls Madrid, 8.10.1982 Dear Prof. Peierls: I am writing to you because while carrying out some historical research at the Einstein Archives in Princeton regarding Spain’s oﬀer, in 1933, to Einstein of a chair at Madrid University, and which he accepted, I came across some material connected with you. Einstein and the Spanish Government agreed to create not only Einstein’s Chair but also a research institute to be directed by Einstein. For this purpose a second chair would be created, to be occupied by a scientist who would take up permanent residence in Madrid (it was not clear whether or not Einstein would spend the entire year in Madrid). Well, I found a letter of Max Born to Einstein’s intermediary on this subject, A. Yahuda1156 dated 17 September 1934, where your name is suggested as a possibility for the post. I was wondering whether you were aware of the fact that you were being considered for said position or if you were approached regarding this and by whom. Thanking you for your kind attention, I remain Sincerely yours, J.M. S´ anchez-Ron

1155

J.M. S´ anchez-Ron, Department of Theoretical Physics, Madrid University. Abraham Shalom Yahuda (1877–1951) had studied Semitics at Heidelberg and Strassburg and later in Berlin. He served as professor at the University of Madrid between 1914 and 1922. 1156

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[784] Rudolf Peierls to J.M. S´ anchez-Ron Oxford, 14.10.1982 (carbon copy) Dear Dr. Sanchez-Ron, Thank you very much for your interesting letter.1157 The answer to your question is that I had no idea that my name was being mentioned for a professorship in Madrid, and that I was not approached about it. I assume that Max Born, knowing that I did not have a regular position at the time, assumed that I would be interested, and did not tell me about it in order not to raise any false hopes, in the event of this suggestion not getting anywhere, which seems to have been the case. I am trying to think whether I would have accepted the invitation if it had been issued at the time. I liked Spain which I had visited brieﬂy in 1932,1158 but might have been concerned about the language diﬃculty and about losing contact with modern physics. As far as I remember history, September 34 was before the Spanish Civil War. If I had been invited, and negotiations had dragged on until after Franco came to power, I would certainly have refused (and anyway the invitation would then probably not have been conﬁrmed). Yours sincerely, Rudolf Peierls [785] Nevill Mott to Rudolf Peierls Cambridge, 11.12.1982 Dear Rudi, Good to hear you on the phone. On W. Heitler, my notice in the Times appeared today; I want to do a more adequate one for Inst[itute] of Phys[ics] — + perhaps I’ll oﬀer to do the R[oyal] S[ociety]. I’ve 1157

Letter [783]. Between completion of his work at Zurich and the beginning of his Rockefeller Fellowship in Rome and Cambridge, Rudolf and Genia had spent some time in Spain in the late summer of 1932. 1158

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written to Thellung, Margaret Gowing, and others. Extraordinary how he disappeared from our knowledge. I wonder whether at Zurich he got entirely taken up with Sc[ience] and religion.1159 Now Pugwash. I got involved because Richard Wiggs, who ran the “Anti-Concorde Project” wanted to run an “anti-bomb project”. I tried unsuccessfully to get him to run it on a “never-use-ﬁrst” line, introduced him to Rotblat et.al., but we’ve come unstuck because he doesn’t want to talk about defence at all. Anyhow, I think he’s missed the bus for a project. Now — of the political parties, SDP is nearest to what I think according to David Owen’s spe[e]ches. When I ask, e.g. Lord Penny – what new policy is he says “it will have to come from the grassroots”. I wrote the enclosed note hoping — as new publicity promises — that local discussion groups would be set up on defence, education, etc.etc., but although the locality is full of CND people, I’ve not succeeded in forming any group with CND sponsorship. The local SDP seem v. sluggish. But I’ll go on trying. [I am involved with them in education]. I’ll be in Chicago in March, will see Ruth Adams + others + will write the Bulletin an article. Now, what about Pugwash? Gutten... is too busy to answer letters. Whether you or I go to Warsaw — don’t we need a UK study group to look at U.K. defence policy, study how much “never the ﬁrst” is a practical policy? There must be much literature on it. I’d love to discuss with you whether there is any chance of forming such a group. I discussed it brieﬂy with Joe. It should of course include anyone going to Warsaw. I have to go to Harwell on Jan 13 + could see you en route back (or the day before): Or if you’ll be in Copenhagen then, I could run over to see you earlier. Yours, Nevill 1159

Nevill Mott wrote the biographical memoir for the Royal Society. N.F. Mott, ‘Walter Heinrich Heitler (1904–1981)’, Biogr. Mem. Fell. Roy. Soc. 23, 141–151 (1977).

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[786] Rudolf Peierls to Gordon Baym Oxford, 5.2.1983 (carbon copy) Dear Gordon, Thank you very much for your letter, and for the copy of the Bethe Article, which I had not seen before.1160 You ask me for comments on Bethe’s account. I have no contact with any of the work after the war, with which most of Bethe’s article is concerned. So any comments I can make relate only to his part 1. With the wartime story I am fairly familiar, and my recollection does not diﬀer from Bethe’s in any way. One reﬂection on the personal relationship between Oppenheimer and Teller: My impression, though not supported by any precise facts, is that Teller was very anxious to have Oppenheimer’s respect, not just as a physicist, which he undoubtedly had, but as a person. Oppenheimer initially quite liked him, but regarded him as a primadonna. I treasure an anecdote which in retrospect, is a very amusing illustration of the relationship. You may know this story — it is, for example in the Alice Smith — Charles Weiner collection of Oppenheimer letters. Some time in 1945 Lord Cherwell visited Los Alamos. He was then a British cabinet minister, and this made his visit rather oﬃcial. In the evening Oppenheimer gave a party for him, to which I evidently should have been invited, as I was then in charge of the British contingent in Los Alamos. But Oppenheimer’s secretary slipped up, and I was not invited. When Robert discovered this the following day, he came to me to apologize. “This is terrible”, he said. “but there is one element of comfort in this situation: It might have happened with Edward Teller.” I arrived in Los Alamos in the summer of 1944 (I believe in June) and, as Bethe says, I took over the group concerning with the details of the implosion (I think it was called “hydrodynamics group”) and I knew that Teller had abandoned this work to think about the “super”. 1160

Possibly G. Baym, H.A. Bethe and Ch.J. Petrick, ‘Neutron Star Matter’, Nuclear Physics A175, 225–272 (1971).

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These are the only comments that come to mind, but if you or Lillian have any speciﬁc questions, I shall try to answer. With best wishes to you both. Yours sincerely, Rudolf Peierls

[787] Rudolf Peierls to John Bell Oxford, 13.2.1983 (carbon copy) Dear John, I was asked recently to referee a paper of “Foundations of Physics”, a journal of which there does not seem to be any copy in Oxford, replying to a paper in that journal by Herbert, who proposes a Gedankenexperiment to use an ERP setup to transmit signals faster than light. I found that the reply had missed the point and should be rejected, but this prompted me to think a little more about the problem, and I found that it was very simple.1161 I enclose a short note about this. I assume you would agree with this. With your better knowledge of the literature on this subject, I wonder whether you know of any place where this argument has been given before. I ﬁrst tried to prove that in general any measurement with unspeciﬁed result does not alter the state of the system, but this, of course, is not true, since it will, in general, destroy some phase relations. However, this is also not required for the consistency of quantum mechanics. For this it is suﬃcient that an “unspeciﬁed” measurement of one system does not state of another system with which it is correlated. After your remarks at the conference at the Rutherford Laboratory about Einstein’s views and determinism, I re-read the Born-Einstein letters, including Pauli’s comments on the point. Pauli certainly emphasizes that the issue is not determinism, but the concept of “reality”, 1161

N. Herbert, ‘FLASH — A superlumninal communitcator based upon a new kind of quantum measurement, Foundations of Physics 12, 1171–79 (1982).

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on which you and I disagree. But when Einstein says: “God does not play dice”, in other words probability should not enter in the fundamental laws, I see no way of escaping from determinism. I would like to make a distinction between determinism and predictability. If there existed hidden variables, these might follow deterministic laws, but as they would be hidden, we could never know their values and therefore could not predict the development with complete accuracy. Do you think this situation would satisfy Einstein? If so it would boil down to the semantic question what one means by determinism. Yours sincerely, Rudolf Peierls [788] Rudolf Peierls to Channel Four [Oxford], 16.2.1983 (carbon copy) Dear Sirs, The recent talk by Dr. Edward Teller on your “Opinion” series calls for a reply. He is a very experienced and persuasive advocate of a continued arms race, but his arguments contain essential fallacies. The ﬁrst fallacy is that piling up an insane amount of nuclear weapons gives increased security. Teller argues that the Soviet government are cautious and will not start an attack unless they are sure of victory. I agree, except that nobody can ever be absolutely sure of anything, so I would like to substitute “reasonably certain” for “sure”. But he then implies that a superiority in the number and explosive power of nuclear weapons would ensure victory. Since even the “inferior” American stock of nuclear weapons is enough to inﬂict terrible damage in retaliation, he must believe that superiority in numbers would give the possibility of a “ﬁrst strike”, i.e. of an attack which would wipe out all American missile bases before they could retaliate. This idea leaves out of account the existence of submarine-launched missiles, for which at present no eﬀective defence system exists or is expected to be developed or of air-borne cruise missiles, which would be airborne by the time the attacking missile arrives.

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But even if new measures could be developed to put submarines and planes out of action, the idea of a ﬁrst strike is pure science ﬁction. It would involve the almost simultaneous launching of a huge number of missiles, which would have to reach their targets with pinpoint accuracy using guidance systems which, if they depend on radar, are open to jamming and other interference, and if they are inertial or depend on map reading, cannot be tested in realistic conditions. In the heat of battle nothing functions as in the laboratory or in the computer simulation. We remember the “infallible” bomb sights available during the Second World War, which were technically perfect, but did not prevent planes from hitting the wrong city, or their own forces. No government would make the survival of their country depend on the success of such a speculative operation. The arguments about the relative numbers and explosive power of the contesting sides are based on a failure to think rationally about nuclear weapons. Nuclear weapons are not battleships, and a superiority does not guarantee victory, as long as the “weaker” side has enough to inﬂict unacceptable damage on an aggressor. One can argue how much is enough, but there is no doubt that the present stockpiles are vastly more than enough. While unilateral disarmament is dangerous and unrealistic, unilateral reduction is safe and desirable. A second controversial claim by Dr. Teller is that there exist eﬀective means of defence. Anti-ballistic missiles have been discussed at great length, and most experts are agreed that they could perhaps intercept some missiles, but never all, and that if they are expected to intercept 80% (which seems wildly optimistic) a potential enemy would counter this by increasing the number of his missiles ﬁve times. As an alternative he mentions a new system, which he is not allowed to talk about. I fully agree with his protest about too much secrecy being counter-productive. But I cannot rely on his assurance of the wonderful eﬀectiveness of this new invention. Teller is a great scientist, whose fertile imagination has made many important contributions to the progress of science, but he also an inveterate optimist about technical possibilities. Yours faithfully, Sir Rudolf Peierls

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[789] John Bell to Rudolf Peierls Geneva, 24.2.1983 Dear Rudi, Thank you for your letter and note.1162 I do of course agree with the note. While the idea is known to most people in the business, it is surprisingly diﬃcult to ﬁnd it set out explicitly in the literature. The only reference I can give you immediately is: P. Eberhard, Nuovo Cimento, 46B (1978), 392, Appendix D.1163 But I am sure I have seen it in other places before. If you need more references I will search harder. As regards “God does not play dice’, I think it is relatively early Einstein. While he continued to regard the diﬀerential equations of general relativity as the most hopeful model, I think that determinism was not ﬁnally the root of his continuing dissatisfaction with quantum mechanics. If you look at his contributions to “Albert Einstein — Philosopher and Scientist” (Ed. Schilpp),1164 written when he was 67, you will ﬁnd in the passage on quantum mechanics little on determinism and much on the absence of any description of the “real factual state” of an individual system. It is true that he thinks that the successor theory will not be of “statistical character”. I think this means that it will describe individual systems and not just ensembles. I do not think it means necessarily deterministic dynamics, which is not necessarily implied by relativistic individual kinematics. And I do not exclude the possibility that Einstein emphasised diﬀerent things on diﬀerent days or with diﬀerent people. He was only human. The Pauli intervention is particularly valuable to me because quoting it I can get across the point that a yearning for determinism is not the root of my dissatisfaction with quantum mechanics. I accept your distinction between determinism and predictability. But then I think that predictability is not an idea that was ever enter1162

Letter [787]. P.H. Eberhard, ‘Bell’s theorem and the diﬀerent concepts of locality’, Nuovo Cimento 46B, 392–419 (1978). 1164 P.A. Schilpp (ed.), Albert Einstein, Philosopher – Scientist, Illinois, Evanston, 1949. 1163

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tained even by classical physicists. That we could know the co-ordinates of all the molecules in a box of gas and use them to predict the times at which individual molecules subsequently emerge from a small hole, or the Brownian motion of a small body seems to me absurd. As regards the Universe as a whole, I vaguely remember reference to a theorem, perhaps by Popper, that in a classical world no part could “know” the whole. Perhaps because it would have to know itself, and that it knew itself · · · It would have to contain not only an image of the world, but also an image of the image, and an image · · · However, that may be theoretically, predictability is not a possibility that I would entertain myself. That in no way diminishes the interest for me in whether the increase of entropy and the apparent randomness of Brownian motion are compatible with underlying determinism. I do not see how the question of whether the world is deterministic or not could be settled. The world is given to us once only and we do not know what would have happened, either certainly or with some probability, with diﬀerent initial conditions. However, the question of whether a theory is deterministic or not is answered by inspection of the equations. (if it is well formulated). And the question of what price must be paid if we replace it by a theory of diﬀerent character seems to me to be interesting. I think that the semantics of the word “hidden” is (are?) more obscure than that of the word “deterministic”. Are you hidden? Or is your letter at least a partial revelation? Or does the letter only reveal itself? Is it not legitimate to see a scintillation on a screen as a partial revelation of a pre-existing co-ordinate of something? I think we invent concepts, like “particle”, or “Professor Peierls”, to make the immediate sense of data more intelligible. The de Broglie Bohm version of quantum mechanics, despite its unattractive features, is for me an indication that quantum mechanics could be made more intelligible. With best wishes, John

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[790] Rudolf Peierls to Franz Jacobsohn Oxford, 4.5.[19]83 (carbon copy) Lieber Franz, Jetzt fahren wir in einigen Tagen mit dem Wagen nach Italien, und es w¨are sch¨on, wenn wir auf dem R¨ uckweg u ¨ber Heidelberg fahren k¨ onnten, und Dich besuchen. Das w¨ urde ungef¨ ahr am 17. July sein. Ich bin noch nicht ganz sicher, ob wir das machen k¨ onnen, und jedenfalls k¨ onnen wir nicht sehr lange bleiben, etwa einen Tag. Aber ich m¨ ochte gerne wissen, ob Du um diese Zeit in Heidelberg bist, und ob es Dir passt. Bitte schreib mir entweder zwischen 14. und 2. Juni an die Scuola Normale, Piazza dei Cavieri 7, 56100 Pisa, oder zwischen 28. Juni und 16. Juli nach Villa Monastero, 22050 Varenna, Italien. Mit besten Gr¨ ussen, Dein [Rudi]

[791] Franz Jacobsohn to Rudolf Peierls Heidelberg, 11.5.1983 Lieber Rudi, Ich habe mich sehr u ¨ber Deinen lieben Brief gefreut und noch mehr u ¨ber die Aussicht, Dich und Deine Frau mal endlich wiederzusehen.1165 Ich bin am und um den 17. Juli in Heidelberg. Gib mir nur kurz vorher noch einmal Bescheid. Kannst Du u ¨ber Nacht bleiben? Platz ist genug da und die Icebox ist voll. Inzwischen beste Gr¨ usse und Alles Gute! Dein Franz 1165

Letter [790].

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[792] David Shoenberg to Rudolf Peierls Cambridge, 20.6.1983 Dear Rudi, I tried to telephone you recently but go[t] no reply, so am sending this letter which I hope will eventually reach you somewhere in your far ﬂung empire. There are two points: 1. I recently got a rather distressing handwritten letter from Meiman1166 (forwarded to me from Omaha, Nebraska without any covering note) and I enclose a translation of it. Do you think something could usefully be done to keep his plight in the public eye (and more importantly let the Soviet authorities know that he is not forgotten)? Possible actions might be a letter to “The Times” signed by one or two authorities in Meiman’s specialty or some sort of telegram to Soviet high-ups, (e.g. Aleksandrov and/or Andropov). I have also written to Atiyah1167 on these lines since I know he is sympathetic. 2. On receiving the latest list of those about to be elected Foreign Members of the RS this morning it occurred to me to wonder whether Sakharov might not be a serious contender if he was put up for the RS. I know too little about his scientiﬁc achievements to judge, but I do recall reading an article about him some time ago which claimed that he had outstanding scientiﬁc achievements to his credit, quite apart from the classiﬁed work. His diﬃcult position might be helped if it was known he was a candidate and even more so if he were elected. Am I right in thinking that a 1166

Naum Natanivich Meiman (1912–) Soviet mathematician and human rights activist who had been in conﬂict with the Soviet authorities over his outspoken advocacy of freedom of speech and democracy. 1167 Michael Atiyah (1929–), mathematician, had studied at Cambridge and later taught at Oxford, Cambridge and Princeton. He later became Master of Trinity College, Cambridge (1990–1997) and President of the Royal Society (1990–1995) and President of the Pugwash Conferences (1997).

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reasonably strong case might be made? If so, would you be willing to take the initiative? I am also writing to Denys Wilkinson on this question. With kind regards, Yours sincerely, David Shoenberg

[793] Rudolf Peierls to David Shoenberg Varenna, 6.7.1983 (carbon copy) Dear David, Your letter caught up with me at last at the summer school here.1168 The situation described in Meiman’s letter is indeed very sad, and it is not clear that anything eﬀective can be done about it. I agree that some kind of publicity would be useful to make the Soviet authorities realize that Meiman’s case is being watched in the West, and can earn them some bad publicity. One diﬃculty is what facts to quote in writing, and what to say about the source. I am, on the whole, against writing letters in protest over cases in which one only knows rumours, and where the facts might be quite diﬀerent. This does not arise here; Meiman’s letter rings true, though he could perhaps be exaggerating some details. But obviously one should not say publicly that the information comes from his letter — this might do him harm. Probably one must say: “We understand · · · ”. Of the two alternatives you mention I think the letter to The Times (or equivalent) is better, since a letter to Andropov would probably never reach him, and Alexandrov probably does not care. I believe Meiman was in the news some time ago; I do not remember the details but it was then pointed out that he is in bad health, I believe a 1168

Letter [792].

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weak heart, and if one can collect those facts, they should be mentioned again. As regards Sakharov, I do think it would be a good idea to propose him as Foreign Member. Until fairly recently I was under the impression that his published contributions to physics were not comparable to his classiﬁed work, and his political activities, but I heard his name mentioned in a recent conference as having made quite substantial contributions. When I return home about 21 July I shall try to ﬁnd people who really know. I think the proposal would have to be very carefully prepared, because people might easily get the impression that he is being put forward because of his public stand, and this would be controversial, so there should be a very clear citation. Yours sincerely, Rudolf Peierls The Nuclear Physics administrator, who handles my mail when I am away made a gallant eﬀort to read your signature, and came up with “Slevenkey”. It made no diﬀerence, of course.

[794] Rudolf Peierls to Franz Jacobsohn Oxford, 4.8.1983 (carbon copy) Lieber Franz, Wir h¨ atten schon lange ein Lebenszeichen geben sollen. Aber ich fand hier nach R¨ uckkehr einen grossen Stoss von Korrespondenz, denn die italienische Post funktioniert ja praktisch u ¨berhaupt nicht. Unsere Reise nach Calais was sehr schmerzlos; wir kamen sogar in einem Tage bis nach Calais, sodass wir nach einer Nacht in einem netten Hotel in der N¨ ahe schon Platz auf einer F¨ ahre am Morgen bekamen. Freilich gab es Nebel, und die F¨ ahre fuhr sehr langsam, aber das habe ich schon lieber als Zusammenst¨osse von F¨ahren im Nebel, wie die das vor einiger Zeit bei Harwich gemacht haben.

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Dann kam schon bald unsere Tochter Gaby mit ihrem Sohn aus Amerika zu Besuch, als Ferien, und um Genia’s 75. Geburtstag zu feiern. Ihr Flugzeug war beinahe halbwegs u ¨ber den Ozean, als ein Motor versagte, und sie ﬂogen den ganzen Weg nach New York zur¨ uck. Nochmals vielen Dank f¨ ur die Gastfreundschaft;1169 wir werden Dein Hotel und Restaurant sehr warm den Reisef¨ uhrern empfehlen. Aber vor allem war es eine grosse Freude, Dich wieder einmal zu sehen, und mehr von Deinen Abenteuern zu h¨ oren. Einige von diesen hatte ich schon geh¨ ort, aber da scheint es ja noch einen unersch¨ opﬂichen Brunnen von solchen Geschichten zu geben. Du solltest das wirklich mal aufschreiben. Oder wenn Du nicht gerne schreibst, kannst Du es schon auf einen Tape Recorder diktieren. Du solltest auch schon mal zu uns kommen. Ich weiss, das ist unbequem wegen des Visums, aber das muss sich doch schon machen lassen, vielleicht wenn Du mal aus einem anderen Grund in die Grosstadt fahren musst. Den automatischen Teekessel haben wir nicht vergessen. Es stellt sich heraus, dass der auch in Deutschland verkauft wird, aber die einzigen Lieferanten, die wir entdeckt haben, sind sehr weit von Heidelberg. Also werden wir einen von hier schicken lassen. Die Fabrik sagt, es gibt einen Herrn H. Roth, St¨ urzelberger Str. 35, 4041 Zons/Rhein, der das reparieren kann. Ich hoﬀe, Du wirst ihn nicht brauchen. Mit besten Gr¨ ussen Dein [Rudi] [795] John Hendry to Rudolf Peierls London, 17.11.1983 Dear Sir Rudolf, I understand from Margaret Gowing that you were not exactly happy with my talk last week. This does not come as a surprise, but it is 1169

Rudolf and Genia Peierls had visitited Franz Jacobsohn on their way back from Italy to England.

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a source of some regret, and I wonder if I might brieﬂy explain what I was trying to do and apologize for the ways in which it may have backﬁred. Since my book will shortly become available (and I should be happy to lend you proofs if you wish) I shall not go into details.1170 Any historical interpretation is open to criticism of course, not least my own, but I hope I have accumulated suﬃcient evidence to back up my speciﬁc statements I made. On the talk in general, the main apology I should like to make is for the mode of presentation, which was apparently far more arrogant than I either intended or realised. This was partly, I think, an unconscious raising of the defences, but it was also perhaps a mistake to use my own research as a basis of a plea for the importance of history. It never occured to me to do otherwise (one does generally talk of one’s research after all) but in retrospect it would have been much better to use someone else’s work. I did not wish to blow my own trumpet and to be seen as doing so, which I must have been, could only harm my case. So far as the overall thrust of the talk is concerned, the reason for my placing such an extraordinary emphasis on underlying philosophical themes (and I did try, perhaps unsuccessfully, to make clear that this was only part of the story) is that I think it’s in precisely this context that the historian of science can do something that the scientist cannot. Whether or not that’s valuable is of course another matter. But I cannot see much point in presenting a perspective with which scientists would agree: they might think “well, the history of science is not so bad after all”, but it would also make the historian redundant, except perhaps as a comforter or entertainer. Finally, I should just like to say that while I do, obviously, think that the philosophical content of the history of science is important, this is an historical judgment applied to a few very untypical scientists. I don’t think it’s true of the majority of scientists, or even of the majority of great scientists: it’s not true for example, of Heisenberg and Dirac in this century, or someone like Kelvin in the last. I don’t think I made this restriction suﬃciently clear. Yours sincerely, John Hendry 1170

John Hendry, Cambridge Physics in the Thirties, Bristol: Adam Hilger, 1984.

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P.S. On a couple of scientiﬁc points to which I have answers at hand: 1. I agree with you that there was no great wave/matrix mechanics divide, and I didn’t mean to give the impression that there was. I only brought up the statement as a means of questioning such categorisations. But see the Pauli letters v.1., nos 152, 153, 163, 164, especially 164, where Heisenberg talks about entering a battle on those lines. 2. The collaborative eﬀort I referred to was I think Pauli-HeisenbergDirac on transformation theory. If so this was of course a question of collaboration in discussion, not one of joint papers. I should also perhaps have mentioned Jordan’s independent work in the same direction.

[796] Rudolf Peierls to John Hendry Oxford, 27.11.1983 (carbon copy) Dear Dr. Hendry, Thank you for your letter.1171 I am sorry my reply is late, but I have been fairly busy. On the minor points of detail: It seems I misunderstood your reference to a division between supporters of wave and quantum mechanics. My impression was that you implied there was such a division. As regards Heisenberg’s letter No. 164, it has to be borne in mind that this was dated 31 May, and that in June he submitted a paper in which, while making disparaging remarks about wave mechanics in the beginning he uses wave functions for his arguments in later sections. I believe the explanation is that he was confusing the formalism of wave mechanics with Schr¨odinger’s interpretation of the wave function as a physical object. On this there was indeed a division for a short time, with Schr¨ odinger and Sommerfeld opposing Bohr and Heisenberg. 1171

Letter [795].

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As regards transformation theory, there may have been consultation between Pauli and Jordan, thought the relevant paper on this subject is by Jordan alone, but I know of no evidence that there was any consultation with Dirac, either in correspondence or personal. Another point of detail: I believe you implied that Pauli turned to quantum mechanics only after completing his big article on relativity. As far as I know he did his calculation in the hydrogen molecule ion at the same time as writing the article, although this work, which constituted his PhD thesis, was published only later. I cannot remember whether I noticed any other little points like that. They are certainly of no great importance; I mentioned them to Professor Gowing only to say that they did not increase my conﬁdence in your major thesis. On this thesis, i.e. the inﬂuence of Pauli on the genesis of Heisenberg’s quantum mechanics, I would like to keep an open mind, until your book appears, so I can see your reasoning in detail. A rapid glance at the Pauli-Heisenberg correspondence did not seem to support your point of view, but I may have missed something. I am rather intrigued by the remark in your letter that the historian has to come to diﬀerent conclusions from the scientist in order not to [be] redundant. When this applies to the choice of emphasis, it makes sense, but it is a rather dangerous principle to apply to discussions of causal relationships. Your remark in the discussion that scientists might not always be conscious of what inﬂuenced them, reminded me of an old German story of an edited version of Goethe’s letters. In one letter the aged Goethe said: “The woman I loved most was X”. To this a footnote by the editor said: “Here the poet is mistaken. The best-loved woman was Y”! Yours sincerely, Rudolf Peierls

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[797] John Hendry to Rudolf Peierls London, 6.12.1983 Dear Sir Rudolf, Thank you very much for your letter of 27 November.1172 As you might imagine, I am not without sympathy for the editors of the Goethe letters, but I do take your point! I am pretty conﬁdent that my interpretation will stand up to the historical evidence, but at the same time I’m quite sure that other, quite diﬀerent interpretations would also do so. Indeed, I don’t think anyone can ever claim to decide as a matter of historical fact, what someone “really thought”. Whereas in the type of history I have been doing in my new post at the London Business School, the emphasis must clearly be upon ﬁnding out what really happened — on historical evidence and historical fact — I think intellectual history is rather diﬀerent. There, I believe, the historian’s task has more to do with the raising of diﬀerent possibilities many of which might ﬁt the evidence than with giving any pseudo-deﬁnitive account. My work on quantum mechanics is intended as a supplement to the standard accounts — albeit one supported by a fair consensus of historians — and not as a replacement, and I hope that I have made this clear in my writing. That I have not yet mastered the art of making clear all the qualiﬁcations when I speak about my work is a cause of some concern. Yours sincerely, John Hendry

[798] Egon Orowan to Rudolf Peierls Belmont, Mass., 11.1.1984 Dear Genia and Rudi, I am full of admiration for word-processors which, instead of ignoring people who never (well, hardly ever) answer, let them have the news 1172

Letter [796].

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they enjoy reading, without deserving the pleasure. The pleasure is slightly increased by the admiration of the size of the world in which you move so Brownianly while I make maximum use of my sitting organ. I am sending this letter to Vancouver where you will be during the next three months; I am sure it will ﬁnd you; and now I begin with a brief reciprocation. Jolan spends the winter, as usual, with her sister in Gainesville, Florida, where they have a house in common, entirely devoid of steps and provided with a spare sister (and her husband) in the same street some ﬁve minutes walk away. Jolan left Belmont later than usual because she hoped to ﬁnd here a cardiologist who would agree to another mitral valve operation (the ﬁrst was in 1959 and it was to last for about ﬁve years; more than 20 years later she is relatively well, but not in operable state). I am fairly ﬂuent at reading dynastic tables in the Encycl. of World History, but I have become a bit shaky in your family table, except of course Ronnie and Gaby. Evidently they have all made brilliant careers. My Susi is no longer 7 years old; last year she became 40. She and her husband Dave (Martin) live about half way between Boston and Gainesville, on the Washington side of Baltimore. Dave teaches in a Washington college and Susie directs the library of John Hopkins U. They both do their best to keep the airlines of the world busy; last year they were in Australia, giving lectures (mirabile dictu, always at the same U. at the same time), meeting relatives and koalas etc. I have switched oﬀ my contact with my earlier ﬁeld which is now terribly grazed oﬀ, and I hope I am now in the last round of a MS on a new subject, economics (of which the earlier versions were economics and paleonomics), inseparable from socionomy which was founded so long ago that nobody remembers anything about them any more. In Cambridge I was lucky to learn from an expert (Sir Ronald Fisher who preceded me in the Junior Research Fellowship at Caius); he is no longer alive, and the only man who was a little close here (a charming ancient Russian named Sorokin), though not of Fisher’s calibre, also died many years ago. So I am enjoying solitude, surrounded by precambrian forms of life in the primeval ocean.

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Your attendance at Los Alamos reminded me of a charming remark; Tisza lent me some weeks ago a book by Wigner and forced me to read a few papers in it. There is a paper on the 20th birthday of the Chicago pile from which I learned a charming detail. When Fermi stopped the pile, Wigner produced a bottle of Chianti and he wrote, “As we drank the wine from paper cups, we sent up silent prayers that what we had done was the right thing to do.” No wonder he was an addict also of epistemology, mind and body and similar things. What Tisza wanted me to read, however, was an address on relativistic invariance and quantum phenomena; Cobalt behaves like Norwegian beer (you know the question: “What is written on the bottom of the beerbottles in Norway?” Answer (Swedish): “Open other side”) Conclusion: The universe has antiparity. I had a particular pleasure a few weeks ago. I excavated among old strata, and I found the enclosed photo of Genia. If you have an enlargement, will you return the enclosure at your convenience; if not I shall have it enlarged and return the original or the enlargement, whichever you want. I think the picture is lovely. I think I have exhausted whatever could be written down without a word-professor. I hope you will have an enjoyable time in Vancouver and, in particular, in the Butchart Gardens. Kindest regards and best wishes for the New Year. Egon I have just found an Australian photo of Susi, complete with koala, taken by Dave. I’ve kept the photo of Mummy + the other one. Can you let him know. J.

[799] Hans Bethe to Rudolf Peierls Ithaca, 13.1.1984 Dear Rudi: Accidentally, I just received copies of my letters to Sommerfeld, including some from 1930–1934. In the early letters I address him as ,,Lieber

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und sehr verehrter Herr Professor”, In later letters, I just address him ,,Lieber Herr Professor”. Good luck for your historical researches! Yours sincerely, Hans

[800] Rudolf Peierls to Hans Bethe Santa Barbara, 2.2.1984 (carbon copy) Dear Hans, Thank you very much for your note with the authoritative answer to my query.1173 This agrees with my recollection, and also with the published letters from Pauli to Sommerfeld. Viki’s recollection must be wrong, and I have written to him to say so. We have now arrived here after working our way down the Coast in improving weather, and ﬁnd this place as beautiful and the Institute as lively as expected. We hope our paths may intersect again in the summer. With best wishes, Yours, Rudi

1173

Letter [799].

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[801] Rudolf Peierls to Egon Orowan Santa Barbara, 8.3.1984 (carbon copy) Dear Egon, Thank you for your letter,1174 which found its way from Vancouver to England, where Joanna is dealing with our mail, and caught up with us here. But the pictures stayed in England, so it will be April before we can admire them and check them with our ﬁles. But we should have replied to your letter long ago — you are evidently familiar with the obstacles to this. Please accept our apologies. We were in Vancouver only a short time to spend Christmas and the New Year with Kitty (# 3 in the dynasty you queried, and married to an oncologist here) but not in any university or wherever you sent your letter. We then worked our way down the West Coast, stopping in Seattle, Stanford and Los Angeles, and now are spending February and March here. We have been very lucky with the weather: since we arrived in California we have not had a drop of rain. This may be bad for the local farmers and gardeners, but it suits us ﬁne. We are spending weekends on gentle walks in the mountains around here. So you have turned from the plastic ﬂow of metals to the turbulence of the economy. This seems a subject which is suﬀering from the invasion of the computer. The modern fashion in economics seems to be to get carried away with computer modelling, when the complexity and fascination of the computer makes one forget the uncertainty of the basic assumptions. In conversations with the experts I usually ﬁnd them at ﬁrst disinclined to believe that there are any basic assumptions involved, and when ﬁnally convinced, to assert that the results don’t depend on them. I am sure you are not that kind of “expert”, and I am happy that someone is looking at economic problems with less disregard for common sense! Your Norwegian beer bottle reminded me of the story (apologies if it is an old friends) of the British Navy during the ﬁrst world war, 1174

Letter [798].

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when their torpedo heads came in boxes labelled: “This box contains a torpedo head. It must be carried upside down. The bottom has been labelled ‘top’, to avoid confusion”. We were interested in the account of your family. Florida does not seem to have been exactly balmy during this winter, I hope Jolan has not found this too tiring, I also hope she ﬁnds a surgeon to give the wanted relief. With best wishes Yours Rudi [802] Egon Orowan to Rudolf Peierls Belmont, Mass., 12.3.1984 Dear Genia and Rudi, Please accept my apologies for thanking for you letter so fast;1175 I have three excuses: 1. the pleasure of your letter 2. the diﬃculty of shooting letters at a moving target; and 3. the shock generated by your interpretation of my “economics”. (the title of the book should be “the End of the Economic Age”). No, you need not worry: I do not computerize the froth of whipped ﬁgures. I just want to help a little these unfortunate people who do not see what is going on, from the smoke screen of economics which is particularly dense in English-speaking countries as a consequence of Adam Smith’s after-eﬀects. Today even a correct economics would not apply; but the misfortune is that the “classics” are based on trivial mistakes. Genia mentions Polanyi who was hooked on poor old Keynes; being a chemist he did not notice that Keynes’ “General Theory” was based on an algebraic error. He wanted to calculate the number of the 1175

Letter [801].

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employed workers from an equation, and did not notice that his equation was an identity satisﬁed for any number. (In fact, no economist has noticed it to this day). The unfortunate habit of calculating the tonnage of the ship from the weight of the captain arose in 1870 when an Australian assayer and a Viennese lawyer invented the “marginal theory” and believed that it was the explanation of what value was (the obvious “marginalism” was in fact published in 1728 by Gabriel Cramer (Cramer’s rule) and two years later by Daniel Bernoulli, without non-sequitur conclusions). Of course, no economist understood the matter and no noneconomist dared to read it, except perhaps Dodgson (Lewis Carroll); this may have been the origin of the two verses in “The Hunting of the Snark”: (the Beaver’s lesson from the Butcher): Taking Three as the subject to reason about A convenient number to state – We add Seven, and Ten, and then multiply out By One Thousand diminished by Eight. The result we proceed to divide, as you see, By Nine Hundred and Ninety and Two: Then Subtract Seventeen, and the answer must be Exactly and perfectly true.

You may know that Dodgson rigidly refused to answer any question about the meaning of the Snark; he had a superhuman intuition, for a few years later Francis Ysidro Edgeworth became Prof. of economics at Oxford, the man who wrote a book “Mathematical Psychics” in which he added and subtracted pains and pleasures with a contemptuous disregard of the axioms of arithmetics. The fact is that nobody knows about the Black Hole of Economics, because those who are not repelled by it are swallowed up and become economists, and the others turn away with disgust. But the general ignorance of economy has led to the present fast approach to state bankruptcy in U.S.A. With best wishes, and the hope that the whales have not swallowed you up. Love, Egon

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[803] Paul Laurence Rose to Rudolf Peierls Jerusalem, 20.3.1984 Dear Sir Rudolf, I hope you will forgive my writing to you for advice (or perhaps I should say imposing an interrogation on you) about some matters arising from your very interesting joint-authored obituary on Heisenberg in the Biographical Memoirs of the Fellows of the Royal Society, 1977.1176 Perhaps at this remove your memory may have faded on many matters of the obituary, but I feel a duty to consult you in the preparation of a chapter on Heisenberg forming part of a book of mine on Furtw¨ angler, Heidegger, Heisenberg as three paradigms of German “conscience” during the Third Reich. Any help you may be able to oﬀer would be warmly appreciated. 1. There was no mention in your piece, of the sharp polemic with Goudsmit. There still seem to me to be some unresolved matters arising out of this polemic of which I have encountered echoes on R.V. Jones Most Secret War, pp. 473 and 483, footnotes. Goudsmit seems perhaps to have been right that Heisenberg greatly overestimated the size of the uranium bomb to judge from Jones’ account of the secretly reported conversations of Heisenberg with his colleagues at Farm Hall in August 1945.1177 (This corroborates Groves’ account in Now It Can be Told, pp. 335f, that Heisenberg believed that two tons of ﬁssionable material would be needed for a bomb).1178 Jones seems to attribute this mistake to both an error of scientiﬁc principle (p. 473) and an error in diﬀusion theory (p. 483). Goudsmit also argued that Heisenberg never recognised that the uranium bomb was founded on the principle of a fast neutron reaction, and in this he was implicitly supported by Kenneth Jay’s 1176

R.E. Peierls and N.F. Mott, ‘Werner Heisenberg’, Biogr. Mem. Fell. Roy. Soc., 23, 213–251 (1977). 1177 R.V. Jones, Most Secret War, Sevenoaks: Coronet, 1978. 1178 L.R. Groves, Now It can be Told, London: A. Deutsch, 1963.

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introduction to Gowing’s Britain and Atomic Energy,1179 p. 30. which stated that “the diﬀerence in eﬀectiveness of slow and fast neutrons · · · was never appreciated by German scientists”. The Germans indeed, to judge from the documents I have seen, do not seem to have been as fortunate in their assumption of the ﬁssion cross-section of uranium 235 as you and Frisch were in your memorandum (Gowing, p. 390) If Jones is right about the diﬀusion paths used by Heisenberg in 1942 and 1945, that would certainly explain why he was so pessimistic about being able to extract enough U235 for a bomb. Might I ask you for comment on this matter which is one about which, as a pure layman, I feel a keen lack of conﬁdence? (One complicating problem is that Irving in his Virus House,1180 p. 100, quotes a German report of March 1942 from Diebner and Bagge’s book which suggests that the Germans were after all working from a more correct approximation of the critical mass of U235. I am, however, somewhat sceptical about the evidence for this claim in view of my acquaintance with Irving’s other historical writings.) 2. On p. 236 of your memoir you mentioned Heisenberg’s habit of making tactless remarks. For my purpose, the kind of remark you cite is very revealing and I would be most interested in hearing of any similar comments you might be willing to report. I should say that my main purpose is an examination of German concepts of “morality” as represented in the sensibility of the three thinkers under study. (Incidentally, I wonder if you would care to name any particular physicist to whom the remark was made? It wasn’t Born, was it?) 3. Regarding the visit of October 1941 to Niels Bohr, I have heard from other sources that Bohr was hostile in advance to Heisenberg’s visit, having heard that the latter had defended the German invasion of Poland in another tactless remark. These accounts also 1179 1180

See letter [687], note 917. D.J.C. Irving, Virus House, London: Kimber, 1967.

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assert that Heisenberg sought to persuade Bohr that a German victory was inevitable. Would you be able to comment? Once again, I do apologise for troubling you with these somewhat precise queries, but I must admit I feel somewhat at a loss to answer the technical problems myself. Yours sincerely, Paul Laurence Rose P.S. I wonder whether it might be possible for you to send me a copy of your 1971 review of Physics and Beyond which appeared in the New York Review of Books.1181 That particular number is — astonishingly — not held in Israel and the references in the ensuing correspondence about the “paradoxes” to be found in the book have aroused my curiosity. I must say that I think that the paradoxes in Heisenberg’s account of his work during the Third Reich arise out of his peculiar morality.

[804] Paul Laurence Rose to Rudolf Peierls Jerusalem, 6.4.1984 Dear Sir Rudolf, I hope you will excuse this rather hasty follow-up to my earlier note of 20 March (and trust that your reply has not crossed in the post),1182 but I have been giving a great deal more thought to some of the loose ends in the Heisenberg matter about which I wrote to you and think I have come up with a tentative solution which solves a great many of the outstanding problems (while doubtless creating new ones). The diﬃculty is that the solution depends to a very great extent on technical details and again I should appreciate your advice. 1181 1182

R.E. Peierls, ‘Atomic Germans’, New York Review of Books, 1 July 1971, 23–24. Letter [803].

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To sum up very quickly, it seems to me that the “2 ton” critical mass of U235 which Heisenberg said on tape on August 1945 was required for a bomb and the 15 kg. critical mass estimate, which he presented to a colloquium a week later on 14 August can be reconciled by only one explanation, namely that throughout the war Heisenberg had failed to realise that in pure U235 the ﬁssion cross-section for fast neutrons was large enough to permit explosive ﬁssion in a critical mass of reasonably small proportions, that is in kilograms rather than tons. This I deduce from Gowing’s book1183 (p. 42) was an error that Chadwick also made in early 1940 but which he was about to revise when he learned of your memorandum. Bohr also seems to have entertained the same error until 1943. What more natural then, that Heisenberg should have fallen into the mistake? Goaded then, in August 1945 by Hahn (as Bagge has told me) into explaining how the bomb worked, Heisenberg may well have re-thought the whole matter over and presented a more realistic answer about the critical mass at his colloquium the next week. This is summing things up very crudely and I am consulting physicists here about the actual details and calculations. However, I would be most interested to have your comments on the following issues since they may well throw light on Heisenberg’s working mind. 1. How did you arrive at your estimate of the ﬁssion cross-section assumed in the memorandum? Was it purely on theoretical grounds? If so, what were they? (Were you aware of Tuve’s 1939 measurements as reported in Bohr and Wheeler’s article in the Physical Review, 56, 1939, p. 444?).1184 2. What do you know of Chadwick’s growing scepticism in early 1940 about the Tuve measurements? Was he disturbed for the same theoretical reasons that had led you to your more accurate estimate?1185 1183

See letter [687], note 917. See Lee, Peierls Correspondence, Vol. 1, letter [305], note 1147. 1185 See Lee, Peierls Correspondence, Vol. 1, letters [305–306]. 1184

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3. Could Heisenberg have arrived at a true ﬁssion cross-section for U235 from the data published in Haxel1186 (enclosed)? Would these data have resulted in a critical mass of 15kg? (Any comments on the Haxel material, in particular on the last two sentences, would be appreciated very much indeed, if you should have the time to spend on it). I am sorry to bother you a second time with my conjectures, but it seems to me (in my lay ignorance on many of the technical matters) that it may be possible to clear up most of the contradictions surrounding this very murky issue which is one, you will understand, which concerns historians as much as physicists, and yet is not one that may well only be ﬁnally resolved by such ﬁrst-hand testimony as yours. Yours sincerely, Paul Lawrence Rose

[805] Rudolf Peierls to Paul Laurence Rose [Oxford], 9.4.1984 (carbon copy) Dear Dr. Rose, Thank you for your interesting letter.1187 I shall try to answer your questions. Firstly, did Heisenberg know the approximate size of a U235 bomb? I originally believed that he did not but changed my mind as I studied the evidence. In this I was particularly inﬂuenced by a passage in Armin Hermann’s book Heisenberg, published by Rohwolt 1976.1188 On p. 71 he describes a meeting on 4 June 1942 under Albert Speer. Heisenberg is asked how big would be an atom bomb, and he indicated with his hands a size about like a pineapple. The account of this meeting 1186

Attached to the letter is a chapter entitled ‘Der Beitrag der schnellen Neutronen zur Neutronenvermehrung im Uran’ by Otto Haxel. 1187 Letter [803]. 1188 Armin Hermann, Werner Heisenberg, Reinbek: Rohwolt, 1976.

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was given to Hermann by Telschow, the general secretary of the KaiserWilhelm Gesellschaft. I regarded this account as plausible, and in line with Heisenberg’s own description in his book. It also seemed to me that a physicist of Heisenberg’s calibre should be able to make a reasonable estimate. Others missed the point, because they never thought of isotope separation as a realistic possibility, But in Germany, Harteck and others had pressed the case for isotope separation, and it would be very surprising that Heisenberg would not have asked himself what would be the critical size of U235. Of course he could have been wrong. As regards Goudsmit, I enclose a copy of a letter from him commenting on our memoir, of which I had sent him a copy. You will see that he essentially agrees with us. However, there was no emphasis on the question of Heisenberg’s knowledge; I had asked him to comment on the moral questions. The memoir to which he refers, was written for publication. I regret I have no record of where it was published. Most of it deals with Heisenberg’s scientiﬁc achievements. I enclose a copy of the pages dealing with Heisenberg’s war work and the general assessment, which will interest you, though not in connection with the question of size. If R.V. Jones is right, then my view was wrong.1189 However, Jones’ ﬁrst quotation is a summary (via Irving) of a qualitative statement by Heisenberg, aimed at explaining the situation in simple terms. The footnote on p. 483 is based on his recollection of the famous transcript. He quotes Charles Frank as saying that perhaps the distance assumed by Heisenberg was half as large as Jones quoted. (4 instead of 8 cm). This would reduce the critical size by a factor of 8. The essential point seems to me that Heisenberg decided that the isotope separation was too big a job to be done in wartime, and as he says in his book this was true since the bomb was not made by the Americans with their greater resources, and without the diﬃculties arising from bombing etc. before the end of the war in Europe. If he overestimated the amount required this would make the argument stronger. 1189

See letter [803], note 1165.

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The statement by Kenneth Jay, in the introduction to Margaret Gowing’s book that the Germans did not appreciate the importance of fast neutrons for a bomb, was certainly wrong. I was originally inclined to the same view because of the absence of a concerted weapons project in Germany. Jay does not give any reasons for this statement and if Jones is right in quoting Heisenberg’s arguments, then Heisenberg was evidently (though possibly wrongly) working out the critical size for fast neutrons. The “tactless” remark quoted in the memoir was made to Sir Francis Simon and his wife, in their house. I discussed this at length with Lady Simon, suggesting various interpretations or misunderstandings which might have made the remark less tactless, but she was extremely positive in her recollection. You ask about other, similar, remarks. Of others I know only from hearsay. It is reported that Heisenberg met the Swiss physicist Scherrer towards the end of the war, when it was clear that Germany was losing the war, and both indicated that they knew this. Then Heisenberg said “Es w¨are so sch¨on gewesen · · · ” Another remark of which I heard very indirectly was at a gathering at which Lise Meitner was present, and at which the subject of Nazi atrocities came up. Heisenberg is reported to have said “In any period of great spiritual renewal there is bound to be violence” (I am not sure this is the actual wording). I have no direct knowledge of the Heisenberg-Bohr encounter. You will note the comments in Goudsmit’s letter. I sent a draft of our memoir to Aage Bohr, asking him to comment in particular on our account of this encounter, and I enclose a copy of his reply. I enclose a copy of my review of Heisenberg’s book. Yours sincerely, Rudolf Peierls 10.4.[1984] Your second letter arrived just after I had written the above.1190 I agree 1190

Letter [804].

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that if indeed Heisenberg’s ﬁrst estimate was in the 2 ton range, he might have revised it in the light of questioning and after the knowledge that the bomb had, in fact, been made. I am still not convinced about the high estimate. I have never seen the transcripts of the Farm Hall conversations,1191 but I believe the main point was that at the ﬁrst news the Germans scientists refused to believe that this was really an atom bomb. This suggested that they had not understood the principle. But it is equally plausible that it simply meant that they did not believe that the Americans could have managed the technological eﬀort to build an isotope plant. It is characteristic arrogance that it never occured to them that anyone could have got further than they did. Now on your speciﬁc questions: 1. We made our estimate of the ﬁssion cross section of U235 purely on theoretical grounds. It was clear from theory, as well as from general experience on other nuclei that the cross section for fast neutrons would be the geometrical size of the nucleus, i.e. a few times 10−24 cm2 . The Bohr-Wheeler theory suggested that practically the whole of this should lead to ﬁssion, i.e. that the cross section for capture and inelastic scattering should be small. The last turned out to be an exaggeration, hence our underestimate of the critical size. I do not remember whether we paid attention to Tuve’s 1939 measurements. If we did, we evidently were not convinced. 2. Chadwick was never very communicative. I do not recall hearing any comment on Tuve’s measurements.1192 1191 Several published versions of the transcripts exist. See e.g. Jeremy Bernstein, Hitler’s Uranium Club: The Secret Recordings at Farm Hall, New York: Woodbury, 1995. 1192 Peierls’ recollections on this point are not accurate. Chadwick alerted him to Tuve’s measurements in a letter in June 1940. (Lee, Peierls Correspondence, Vol. 1, Chapter 5, letter [305]). The results had been reported at a meeting of the American Physical Society and were not published subsequently. Peierls himself was doubtful about the accuracy of the measurements. (See Lee, Peierls Correspondence, Vol. 1, Chapter 5, letter [306]).

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3. The article by Haxel is concerned mostly with ordinary uranium. Here there is no ﬁssion produced by neutron energy below 1MeV, and the discussion is aimed at deducing from the experiments the eﬀect of neutrons above this energy. This discussion does not contribute to any understanding of the 235 cross section. He refers to 235 only in the last few sentences, but refrains from giving numbers because the data are too uncertain. What is puzzling is that he mentions the uncertainty in the number of neutrons per ﬁssion, which is indeed relevant, and also the inelastic (presumably capture) cross section, which is not very important, unless he takes it for granted (as we did) that the sum of inelastic capture and ﬁssion cross section adds up to the geometrical. I cannot see in the article anywhere information about the fast neutron cross section of U235. Yours [R. Peierls]

[806] Rudolf Peierls to David Shoenberg Oxford, 6.6.1984 (carbon copy) Dear David, I promised to write to you what I remember of Kapitza.1193 On reﬂection I ﬁnd I do not really have much to say, but here it is. First about Pugwash conferences. He attended a number of these, and his contributions to the discussions were always brief, pugnantly expressed and reminding us of the basic issues, the stupidity and danger of the arms race, the diﬃculty of getting agreement on disarmament when this was evidently in everybody’s interest, etc. He rarely took part 1193

Piotr Kapitza had died on 8 April 1984, and Shoenberg was preparing the biographical memoirs for the Royal Society. D. Shoenberg, ‘Piotr Leonidovich Kapitza’, Biogr. Mem. Fell. Roy. Soc. 31, 325–374 (1985).

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in the arguments about technical details, but his interventions always felt like a breath of fresh air. In physics, as you no doubt know, he also always had his eye on basic principles and in pursuing these was not afraid of unconventional methods. Outside of physics he also thought broadly. He once explained to me his observation that, physicists could be divided into two types, the ﬁrst like Rutherford and Niels Bohr, keeping abreast of the latest developments in their subject until they die, and others, like Einstein, Schr¨ odinger or Dirac, losing touch with mainstream very early. He pointed out that the ﬁrst type was always surrounded by young pupils or collaborators, whereas the second had few if any pupils. (It does not follow what is the cause and what is the eﬀect!) I need not tell you about his friendship with Rutherford, but perhaps you don’t know the story (which I have third hand) of his inviting a Russian statesman — I think it was Bukharin — to dinner in Trinity, for the fun of making the introduction “Comrade Bukharin — Lord Rutherford”! I suppose you know the anecdote of his encounter with a swan in his early days in Cambridge (which got so hopelessly mangled in Jungk’s terrible book). A story that does not reﬂect directly on Kapitza may yet be of interest: When it had been decided to sell Kapitza’s equipment to the Soviet Academy, the problem arose how to move the big generator. To get it out of the Mond Laboratory, one had to make a hole in the brick wall. But after that how could it be carried to the port? Cockroft and other people pondered and sought a lot of advice, without any easy solution, until it occured to them to phone the removal people, Pickfords, giving the weight and the dimensions of the object. The answer was: “Quite easy, we shall send a low-loader”. The problem was solved. I suspect, but you will know this better after rereading his papers, which I have not done, that in the early planning of his work on magnetism Kapitza believed, and persuaded Rutherford to believe, that this would show up some new fundamental laws concerning the properties of matter, rather than abstruse and surprising consequences of the general

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laws of quantum physics. But I do not remember any clear evidence for this. That is about all I can think of. If anything more occurs to me I shall let you know. Yours, Rudi

[807] Rudolf Peierls to Victor Frenkel [Oxford], 17.6.1984 (carbon copy) Dear Victor Yakovlevich, Your letter to Genia arrived while we were on a visit to America, and therefore I have only now been able to write a few lines about your father. I hope the enclosed is suitable in form, but I do not know how you want to quote it in the volume of reminiscences. If you prefer a diﬀerent form, please let me know. We have not seen Fr¨ ohlich recently, so we were very interested in the news about your family and yourself. With best regards, Yours sincerely, Rudolf Peierls I am glad I have the opportunity of saying a few words about my recollections of Yakov Il’ich. I ﬁrst met him at the Odessa Conference of Soviet physicists, to which a dozen or so foreigners were invited. For a young man of 23 this was therefore a great occasion, and I am sure I owed my invitation to him. He had no doubt seen some of my papers, and found them interesting. I owe him a great debt of gratitude, not only for the privilege of getting to a very interesting conference and my ﬁrst visit to the Soviet Union, but for the occasion on which I met my wife (in fact I think it was Yakov Il’ich who introduced us on the Lusanovka beach).

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I knew his name, of course, and many of his papers on diﬀerent subjects, particularly on solid-state physics, where our interests overlaped most. I also had heard of him from Landau and Gamow, when they visited Zurich. So it was like meeting an old friend; I believe our meeting would have had this character anyway, because of his great charm, and great informality. After the conference he arranged for me to travel to Karkov, Moscow and Leningrad, where I met him again. He then invited me to come to a longer visit next spring, to lecture at the Physico-Technical Institute, although he was going to be in America that time. On one of his visits to Berlin (perhaps in 1931, but my memory is a little vague) I was also visiting my parents there and brought him to lunch in their house. They were captivated by his warmth and friendliness though their background was very diﬀerent, not at all academic. During the nineteen thirties, we met again many times, mostly during my visits to the Soviet Union, the last being to the nuclear physics conference in Moscow in 1937. On all these occasions it was a pleasure to discuss physics with him, and one could always learn from these conversations, as also from his writings. Many of his papers were on subjects on which I was also trying to think, but others, such as his work on the theory of liquids, I came to appreciate only much later. I also admired his strong defence of quantum mechanics against obscurantist attacks. During the war and in the early post-war years the exchange of information with the Soviet Union was not very eﬃcient, and we heard of his untimely death only much later, with sadness at the loss of a great physicist, a great teacher and a great person.

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[808] Paul Laurence Rose to Rudolf Peierls Jerusalem, 26.6.1984 Dear Sir Rudolf, I am so sorry to be so long in replying to your two informative notes.1194 I have in fact been worrying at the Heisenberg problem all the time and only ﬁnally came to what seems to be the most plausible (to me) solution a couple of weeks ago. This is based on quite a bit of unpublished and fragmentary material but it seems to make sense. Broadly the matter of the ﬁssion cross section estimates seems to be largely irrelevant to the question of why Heisenberg made such a mistake with the bomb. (That he did so is clear from Groves’ and Jones’ citations from the Farm Hall transcripts and has been conﬁrmed to me last week by Charles Frank). The real reason for the mistake is one of scientiﬁc principle — in December 1939 Heisenberg speculated about the bomb as an extension of reactor theory that was fundamentally ﬂawed by the belief (sustained for the next six years) that a chain reaction in a pile would be selfregulating and that the temperature would stabilise without cadmium regulators at 800 degrees C. I’ve explained most of this in the enclosed paper which I gave here a fortnight ago and which I hope ties up most of the loose ends, speculative as it may be. Anyway, the general conclusion is that Goudsmit was right and that Heisenberg was always thinking of the bomb as a slow neutron reaction in which a huge mass of U235 had to be used in order to overcome the problems of neutron escape and the premature rise in temperature which would shut down the reaction (very close to Frisch’s original position perhaps in his 1940 Chemical Society report but skewed by the peculiar ideas Heisenberg had about temperature stabilisation). The paper is very rough and I shall be cleaning it up when I get back to Australia next week. In the meantime if there are any criticisms you might wish to make of it at this stage I should be very glad to have them. 1194

Letter [805].

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Incidentally I beneﬁted from discussions with several physicists here including Issachar Unna who sends his best wishes. My address in Australia is: Dept. of History University of Newcastle NSW 2308 Australia Yours sincerely Prof. Paul Lawrence Rose P.S. I shall write again in more detail from Australia.

[809] Roger H. Stuewer to Rudolf Peierls Minneapolis, 5.7.1984 Dear Sir Rudolf, Thank you very much for my comments on my Bohr article and for sending me sections of your introduction.1195 Actually, I should say that meanwhile I have also heard from John Wheeler, and included among the materials he sent me for consideration was a complete copy of your introduction, so that I have now read it through from beginning to end. I was much impressed with it and the enormous amount of work you have put into it. You have persuaded me that your interpretation of the origins of Bohr’s compound-nucleus theory is indeed reasonable — it certainly accounts for the otherwise inexplicably long delay between April and the end of 1935 before Bohr wrote it up for publication. I therefore have changed my account accordingly, with full reference to you in the text. I also have altered slightly my sentence on Professor Yamanouch in view of your interesting letter from him. 1195

This refers to Peierls’ introduction of the ninth volume of Bohr’s Collected Works, which he had edited. See letter [758], note 1124.

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Turning to the other points you raise, my reference for the in Nuclear Physics in Retrospect,1196 p. 276, where Wheeler recalled: “Bohr · · · left with Rosenfeld, crossed the campus to Fine Hall still without a word and there, Placzek and I joined them, explained in the idea that had just come to him · · · ” My guess, in view of Rosenfeld’s own account is that Bohr ﬁrst explained the idea to Rosenfeld alone, then to Rosenfeld, Wheeler and Placzek. This also seems to be more consistent with Wheeler’s earlier account in Physics Today, 16 (October 1963), p. 42, where he seems to imply that Bohr ﬁrst explained the idea to Rosenfeld alone. In any case, I now have changed my account in line with my guess above. You may have noticed, incidentally, that the proton-electron mass ration changed over time from 1846:1 to 1836:1. I have tried to clarify a bit further the importance of the EllisWooster experiment, which was that it eliminated the possibility that βrays were being emitted with discrete energies but then lost some energy through secondary processes when passing through an electron cloud, thus showing that they were being emitted directly with a continuous distribution of energies. The continuous spectrum itself, as you correctly suggest, was indeed observed much earlier by Chadwick in 1914. My references to Bloch, Bethe, and Weisskopf receiving oﬀers of jobs in America while in Copenhagen are the interviews that were conducted with them by Charles Weiner and his colleagues. I enclose copies of the relevant pages, which show that they were all actually in Copenhagen when the oﬀers came through. As for Frisch’s move to Birmingham, I have decided to simply delete this passage on him as not central to the paragraph. You are also correct about Delbruck being in Berlin in 1936 — I evidently made a mental slip, somehow confusing him with Bloch. Since, as I indicated above, I now have read your own introduction through completely, I hope you do not mind, if I call your attention to a few minor points in it that I noticed as follows: U235 discussion

1196

Roger H. Stuewer (ed.), Nuclear Physics in Retrospect: Proceedings of a Symposium on the 1930s, Minneapolis: University of Minnesota Press, 1979.

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p. 51: Gamov ﬁrst visited Copenhagen in 1928–9 not 1929 (he conceived the liquid drop model still in 1928). p. 52: I think you might wish to cite the earlier English edition of Gamow’s book, Constitution of Atomic Nuclei and Radioactivity, Oxford: Clarendon Press, 1931) rather than the 1932 German translation. p. 56: (and ref 68a): Wheeler was actually at the University of North Carolina, Chapel Hill, in 1937, so I wonder if his notes were not taken there instead of Princeton. p. 77: Frisch’s recollection about relaying the news of his and Meitner’s interpretation to Bohr just as Bohr left Copenhagen is certainly incorrect. His letters to Meitner in January 1939 deposited in Churchill College, Cambridge (which I cite) are very informative on this point. I would enclose copies, but there is a big stamp on them that says I cannot reproduce them without permission. However, I am quite certain that the Archivist there, Miss Marian Stewart, would help you in this matter. The dates of the most important letters are 3.1.1939, 8.1.1939 and 17.1.1939. (Also, Frisch’s experiments evidently took three days, not two.) p. 95: I do not think that Bohr had the U235 idea by the time he went to the Washington Conference. This would conﬂict both with Wheeler’s account and with the fact that Placzek arrived in Princeton on February 3. p. 101: Wheeler gave the April 1939 APS talk, not Bohr. Sincerely yours, Roger H. Stuewer I enclose reprints of a couple of articles that may interest you.

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[810] Rudolf Peierls to Roger H. Stuewer Oxford, 18.7.1984 (carbon copy) Dear Dr. Stuewer, Thank you very much for your letter of 5 July, which I found on my return from a conference.1197 Of your points concerning your article I would like to take up only the question of Bethe receiving the Cornell oﬀer in Copenhagen. The interview of which you kindly sent a copy, shows indeed that he received the letter from Cornell while in Copenhagen, but this was only a brief visit of a month, in between temporary appointments in Manchester and Bristol. He had gone to Copenhagen to talk physics, not to ask for Bohr’s help to get a job. I doubt whether in his case, Bohr had anything to do with the job oﬀer (unlike so many other cases). This is not the impression one gets from your description. Thank you also for the helpful remarks about my Introduction to Bohr’s Nuclear Physics papers. I have corrected the date of Gamow’s visit, and changed the reference to the English edition of his book. I have also deleted the reference to Princeton on p. 56. (I have a vague recollection of Wheeler referring to lectures in Princeton, but it does not really matter where they were given). I have also changed the reference to Bohr mentioning the 235 idea to Fermi at Washington. You were evidently right — Rosenfeld’s account makes it clear that the idea was then new. Bohr argues with Fermi in Washington about theoretical methods, not about results. I had already discovered that Wheeler gave the talk about the joint paper, and changed the text accordingly. I shall try to get hold of the Frisch-Meitner letters and see how to cope with the discrepancy. Yours sincerely, Rudolf Peierls

1197

Letter [809].

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[811] Rudolf Peierls to Paul Laurence Rose Oxford, 22.7.1984 (carbon copy) Dear Prof. Rose, Thank you for your interesting letter and paper.1198 You put forward a novel solution, but I am not convinced that you are right. I cannot make my objections very speciﬁc, because the copy you sent does not include a list of references. Broadly speaking you say that Heisenberg knew, more or less, the correct order of magnitude of the critical size for U235, but he believed that a mass only somewhat greater than critical would not explode violently, and that for a bomb one would have to have several tons of U235. Now this would be too crazy an idea to think that Heisenberg could have believed it. Assume the critical size is 12 kg, and you want to assemble even 1 ton, i.e. almost 100 times the critical mass. To store such a mass without the chain reaction starting, you have to divide it into about 100 pieces, and keep these at a large distance from each other. To set oﬀ such a bomb, you would then have to push all these pieces into a compact mass, in a time so short that the chain reaction will not be started by a spontaneous neutron before the assembly is ready. If this were possible at all, it would be an enormous engineering feat, and I would expect that the diﬃculty of achieving this would have been mentioned somewhere besides the problem of procuring such a large mass of U235. In fact I would not be surprised if Heisenberg and Co. had then decided that a bomb was just not feasible. My recollection of the remarks by Jones (whose book I do not have in front of me) is that they relate to arguments about the critical size and suggest that Heisenberg, at least at times overestimated the size, but not to the eﬃciency of the explosion. You seem to tie the error to Heisenberg’s belief that a reactor working with thermal neutrons would be self-stabilizing. This is by no means 1198

Letter [808].

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as “absurd” a reasoning as you call it. Brieﬂy speaking, as the temperature rises, the kinetic energy of the neutrons goes up, and in the region of thermal energies the ﬁssion cross section decreases with increasing energy. It is therefore a very reasonable conclusion that such a reactor would be self-stabilizing, and I believe that in the case of the heavywater reaction of Heisenberg this would indeed have been correct. Some kinds of reactor do not show this stability. The reasons for this are complicated, and have to do with the resonance absorption, a phenomenon not yet known to Heisenberg. So he was by no means crazy when he expected his reactor to be stable. He did show, of course, the typical arrogance in trusting his theory so strongly that he would have started a reactor without shutting it down if necessary. But this would never have led him to believe that a fast-neutron system would have temperature stability. There is no reason to expect the cross section in the fast neutron regime to vary much with energy, and in any case since there is no moderator, and the neutrons do not have much chance of making collisions which would change their energy, a rising temperature of the whole system would not cause much change in the energy of the neutron. Incidentally, about the “disastrous measurement” of Bothe’s (p. 3) the position is more complicated. The best graphite commercially available, still contains impurities in so small amounts that they cannot be detected by chemical means (or could not in 1940), yet making an important contribution to the neutron absorption because some of the elements involved had enormous neutron absorption cross sections. One therefore had no means of telling whether the graphite one was working with was pure enough or whether further puriﬁcation could still improve it — one had to guess. Bothe made the wrong guess, as did the members of G.P. Thomson’s committee in this country. Fermi had the right hunch, and insisted on attempts being made to purify the graphite further. So, if my recollection is right, Bothe did not make the wrong measurement, he made a wrong guess. Another minor point: Jungk did not believe everything he was told. Sam Goudsmit told me that he had spent half a day (or was it a whole day) showing Jungk documents which proved that his view was wrong,

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yet Junck repeated the same wrong statements in his book. So he shows some selectivity in what he believes! I look forward to your reaction to my points and to your list of references. Yours sincerely Rudolf Peierls

[812] Andy Humphreys to Rudolf Peierls Oxford, 13.8.1984 Dear Sir Rudolf, Thank you for your letter of the 5th of August1199 and please accept my apologies for this delayed reply, but I was on location in Plymouth for all of last week and will be in Glasgow all of this week. You are quite correct to question some of the points listed in my outline structure and it is only by working with people such as yourself that I can hope to achieve the authenticity that I declared at the outset must be achieved. However, the secretive nature of the subject poses many problems for accurate veriﬁcation. I have made certain assumptions based on published works, in order to tell the story in an informative and interesting way. There are details in my outline which I have always been aware needed checking and this letter and your cooperation, for which I am grateful, are part of this process. There are several books which have helped me in my research, one of which is Andrew Boyle’s “The Climate of Treason”.1200 Regarding Blunt assisting Fuchs without Fuchs’ knowledge, I refer to this passage in Boyle’s book: “To what extent Blunt took risks in discreetly assisting Dr. Klaus Fuchs and Dr. Alan Nunn May remains a tantalising question”. I have tried to check this yet without success, but feel there is suﬃcient circumstantial evidence to include it in the ﬁrst draft stage. 1199 1200

Letter Rudolf Peierls to Andy Humphreys, 5.8.1984, Peierls Papers, Supp., D.54. A. Boyle, The Climate of Treason, London: Hutchinson, 1979.

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Item 63 where Philby and Blunt allow Fuchs’ arrest in the belief that this would be far more damaging to the Atlantic Alliance than permitting his escape, I consider to be a justiﬁed assumption as Philby, given his position at the time, must have been aware both of Fuchs’ activities as well as the endeavours of the FBI and MI5. In his book, “My silent War”,1201 whilst not whole heartedly reliable, [he] does indicate this when referring to an MI5 agent Peter Dwyer, who helped to sort out which of you was the traitor. Incidentally, Robert Lapere of the FBI wrote and guided me to a 1980 issue of Newsweek which reports that Fuchs was revealed by diﬀerent means involving codebreaking. Much of this also stands for your query over Item 28 except that I assume when you and Fuchs journeyed to America you would have had conversations about the nature of your future work. Many books refer to Fuchs’ changing attitudes to Russian/Stalin policies, but most seem to be based on Alan Moorehead’s book – “The Traitors”.1202 However, there are also references to this, but not clear reasons, in Magistrates’ Bow Street hearings. “The Traitors” expresses the point of view that as Mexico was a communist staying post, Fuchs may have contemplated defecting during his visit to Mexico City in 1945. I hope I have answered your queries adequately and please can I express my apologies as I can imagine how irritating it must be for a stranger to write to you about your activities, but I am pleased to communicate with you and not via books. When we met, I vaguely asked you about a document which was written by a woman about Fuchs who knew him well and sent copies to several people. The woman was Margret Hager and I wonder whether you received such a document and if so, could I see it? Thank you again for your co-operation I look forward to hearing from you. Your sincerely, Andy Humphreys 1201 1202

Kim Philby, My Silent War, New York: Grove Press, 1968. Alan Moorehead, The Traitors, New York: Dell, 1965.

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[813] Rudolf Peierls to Andy Humphreys Oxford, 15.8.1984 (carbon copy) Dear Mr Humphreys, Thank you for your letter.1203 I appreciate that the items in your draft were only provisional, to be checked out further. But the approach is to put up some speculative theories and to see how for the evidence is compatible with them, rather than, as a documentary would, look at the evidence without prejudice to see what theories one is led to. Either approach has its merits, and basically it is a conﬂict between objectivity and entertainment. The truth, as far as it can be ascertained, is often very dull. When Shakespeare or G.B. Shaw write about Caesar and Cleopatra, their plays contain many items for which they have no evidence, and many of which conﬂict with the historical truth. Yet, these are great plays. One diﬀerence is that they refer to the distant past. When writers like Hochhut dramatize recent events, some of whose protagonists are still alive, this is much less well received. Another diﬀerence is that television carries a much stronger illusion of reality than the stage. I had the experience of professional historians accepting as a fact things seen in TV “faction” in the absence of any evidence. This illusion would be enhanced by the proposed interspersed interviews. However, the main point is that it is just not in my nature, or perhaps in my training, to work in this way, and I cannot agree to participate in your project. I do not mind answering questions about facts, provided my help is not acknowledged in any way that implies my support for the approach. On the details you quote Boyle asking a question. You do not mention the nature of the circumstantial evidence suggesting an answer. My query to item 28 related to the idea that Blunt was responsible for Fuchs being sent to America, which I am sure is nonsense. We might 1203

Letter [812].

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indeed have discussed the use of the bomb on Germany, though with considerable uncertainty, but we did not. Again, Moorhead raises a speculative possibility of Fuchs considering an escape via Mexico, but this is no evidence, and evidence would be very hard to get. I do not ﬁnd it in the least irritating that others comment on my activities; this is unavoidable once these have been in the public domain. The spirit in which this is done can be irritating, but this seems to relate more to other people’s activities. I have no recollection of a document from Marget Hager, and don’t believe I ever saw it. In any case, I do not have it now. Finally, there are the errors of fact in your draft, including some items which I doubt but without certainty: Introduction: I was not aware that Fuchs was deported to East Germany. This can presumably be checked. He was not the head of the atomic energy laboratory, except after the defection of Barwich. I do not believe “Institute for Nuclear Physics” is the correct title. 14. Fuchs was not at that time interested in nuclear physics, or in splitting atoms. Nobody was discussing an atom bomb. I doubt if he studied “Das Kapital” in private or otherwise. 22. The name “Tube Alloys” came into use only in late 1941. 24. I have already queried Blunt’s involvement. But my application was made as soon as Fuchs agreed to join us, and I presume his approach to the Soviet Embassy was after that. What is meant by Blunt being responsible for my interest? 25. I have never seen Fuchs drunk. He drank heavily on occasion, but could take it. 27. He must have transmitted information based on other people’s work. He was not illogical enough to claim this as his own work. 32. Los Alamos is in New Mexico, not Arizona. 42c. Again: he never got drunk. 47. We never “inspected” Harwell.

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56. In the windscreen event, Fuchs was driven by a colleague. He did not explain at the time why he was so shattered. Yours sincerely, Rudolf Peierls

[814] Nina Byers to Rudolf Peierls Santa Monica, 28.8.1984 Dear Rudi, If you have the time, I would appreciate very much your comment on the enclosed article. If you remember, the LA Times Sunday edition has an Opinion section in which they print contributed articles (for which they probably pay a nominal fee), editorials and Letters to the Editor. This article appeared in that section. If you would care to correct or add to it, I’m sure a contribution from you would be of interest to many people not only me. If you felt like writing something for publication, I think it very likely the paper would publish it. Tony Day (Anthony Day, Editor of the Editorial Pages) is a good guy and probably very intelligent. If you send something for publication, I think you should send it to him with a covering biographical sketch so that he would be sure to know who you are. I spent the month of July in Germany — two weeks in the west and two in the east. It was very interesting, I met many physicists active in the peace movement; am enclosing the G¨ottingen Appeal and declaration which were issued at the end of the G¨ottingen meeting. The initial signers of the appeal were all speakers at the plenary sessions. Before arriving in G¨ ottingen, I spoke in Karlsruhe and Dusseldorf; in Karlsruhe at the University in a meeting attended by over 800 students, and in Dusseldorf at a meeting in a church organized by a group of physicists and astronomers who are also conscientious objectors. These latter young scientists told me about the organisation of conscientious objectors that has been in existence in Germany for nearly a century; it was begun before the ﬁrst world war and was a forerunner of the War Resistors League.

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After G¨ ottingen I went to work at Desy. It was good to do physics again and to be working among gem¨ utliches volk (for a change) who are also good physicists. The university theoretical physics group occupies the 5th and 6th ﬂoors and the lab group the 3rd and 4th of one of the taller buildings. I stayed in the lab appartment on site. Art was not with me, he decided he prefers not to travel with me on working trips. Then I went with Hans and Inge Joos in their car to the Leipzig “Rochester” Conference. It was a very interesting day trip. We left early in the morning and stopped at Eisenach and Weimar on the way. Unfortunately it took some two or three hours to pass the border and we didn’t have time for Nauemburg, where there is, according to Hans, very beautiful sculpture. Weimar was lovely. If there had been war damage, that had been repaired but otherwise it is unrestored and looks old and authentic — one could easily imagine Goethe walking in its treelined main street. And we had dinner in a grand old hotel called I think, the Elephant which had a beautiful old well cared-for garden. But there are so few people out in the streets. Houses are unpainted and the country seems underpopulated. Leipzig is anomalous, of course, because of the trade fair. It is relatively lively even bustling in the late afternoon — and there are so many new, now bad looking buildings; and many of the ones from before the war are restored and look like restored buildings in the west. The Conference took place in the University and the plenary sessions in the Zoo! It was very well organized; the plenary sessions in a very large auditorium with good projectors and loud speaker system. And it was fun, when you wanted to talk with someone to have a walk down a path through the zoo. The Conference was interesting for me both for physics and politics. A. Uhlmann, one of the local conference organizers and a Professor at the University, organized under University auspices a Colloquium on Peace and Disarmament. He invited me and I. Chuvilo, Director ITEP in Moscow, to speak. I declined to be the “other side” to Chuvilo, but in the end spoke from the audience. As a result physicists actively engaged in trying to improve the situation working both in west Europe and East Germany contacted me and inter alia two very interesting outcomes

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emerged. One was an invitation to visit an antiwar museum/peace library in a church in East Berlin, and the other was the evolution of a statement enclosed herewith. The framers felt it was important to issue a statement explicitly holding the USA and the USSR responsible for the arms race. They hoped this would be published in the local press, I don’t know whether it was or not. In any case, Chuvilo struggled to get the explicit mention of the USSR removed; we were adamant and ﬁnally he went along. After Leipzig, Anna Kernan and I rented a car and drove to Berlin. We stopped in Dessau and Potsdam. San Souci is really grand; and the Bauhaus and the Schloss in Dessau are certainly worth a visit. The Schloss has a grand collection of paintings; I particularly enjoyed the Flemish section. They have great paintings there. On our day oﬀ during the Conference, we went to Dresden and Meissen. The Zwinger in Dresden is magniﬁcent. In general the museums in East Germany are worth going there for, the Pergamon and the Bodemuseum in East Berlin are fabulous. Although the Pergamon ranks just behind the British Museum and the Louvre in the extent of its collections, the display is superb. I believe the Soviets built the present museum in the middle ﬁfties as a showcase for the ancient works of art they removed from Berlin and then returned. The reconstruction of Greek temples and friezes, of Roman and Babylonian streets and gates, of Assyrian and Hittite scu[lpt]ures is excellent and skylighted by translucent ceilings, I had only one day there; enjoyed it enormously, I hope to return to the Pergamon soon — perhaps next spring with Art. We are beginning to get our plans together for next summer term in Oxford. Our marriage is really diﬃcult, but we try to hold it together. Also life in physics in the UCLA physics department is diﬃcult. Herman Feshbach and his committee wrote an excellent report in which they reported the department is in deep trouble. I’m not sanguine about its ability to pull itself up. I think the only way that can be done is for the University to appoint a strong chairman or woman who can give the department leadership and bring into it scientiﬁc leadership. Anyhow, this is a very long letter. You are probably getting tired of reading, and I must alas go into my oﬃce. I am sending this to you in the Department because my purse was stolen (again; here in Santa

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Monica) and I have lost your home address. Otherwise I would have addressed it to you and Genia. Please give her my best regard. I hope you and she are well. My love to you both. As ever, Nina

[815] Rudolf Peierls to Nina Byers Oxford, 9.9.1984 (carbon copy) Dear Nina, Thank you very much for your interesting travelogue, both about the Leipzig Conference, about which I also heard reports from others, and about your travels in East Germany.1204 At the Pugwash Conference in Lapland I saw a West German appeal for a treaty against anti-satellite weapons, and signed it. I don’t think it was identical with the one you sent, but in the same spirit. It is obvious to any sane person that such a treaty would be desirable, but your friend Reagan may feel that it would rule out some aspects of his Star War schemes. The article about the Soviet atom bomb contains the usual amount of errors for a journalist’s presentation, but on the whole gives a fair picture of the development. I am not an expert on the subject, but from my own knowledge I can list some of the errors. Stalin did not purge Jews from physics because he did not want to hamper the atom bomb developments. (Landau remarked that here the atom bomb proved a defensive weapon). Before 1939 Soviet intelligence did not tap Western scientists for information on nuclear matters, because none was secret. I do not believe you can get more plutonium than U235 out of a given mass of uranium, but I could be wrong. Kurchatov could not in 1944 1204

Letter [814].

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“come up” with the idea of using graphite as a moderator, since the idea had been discussed widely, and he must have known from intelligence sources of Fermi’s success with this. Manfred von Ardenne was a maverick not connected with the main German project. Gustav Hertz (not Herz) and Heinz (not Hans) Barwich no doubt made some contribution to the Soviet project, but did not play a “key role”. I do not want to contribute an article on that subject, since these details are not important, and since I do not know many of the other facts. For a full assessment of the article, or of the government report on which it is based, one should ask Holloway, an historian from Edinburgh, who is spending a few years at Stanford and is writing a book abut the history of Soviet atomic energy. We are delighted that you and Art will be here in the summer term. A rumour in the theoretical physics department says you might want to come in Hilary term instead. At that time Oxford is likely to have much less pleasant weather. We are going to Paris at the beginning of December, and plan to stay for about two months. So even if you come in Hilary term, we shall overlap for most of the time. All my sympathy for your lost purse. Losing an address list is a traumatic experience. I now keep several copies of our address list, which with the word processor is no trouble. A little while ago I read your review in Physics Today and liked it. But what possessed you to say I was an adviser to the British government? Love and greetings to Art Yours Rudi

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[816] Rudolf Peierls to Lord Kearton Oxford, 17.9.1984 (carbon copy) Dear Kearton, I would like to ask you for advice on some very naive thoughts concerning the mining dispute. I seems obvious that any solution must involve concessions by both sides, and it is not easy to think of a concession which the Coal Board could reasonably be expected to make. I can see, however, one step which might be acceptable. That is for the Board to agree not to close any pit at less than, say, ﬁve years’ notice. Remember that the present row started with the decision to close one pit in a few months’ time which had previously been described as still being workable for ﬁve years. Such a measure would cause some ﬁnancial loss to the Coal Board, but this would not be a continuing loss since in the long run adequate forward planning would allow due notice to be given. I do not believe that the ﬂuctuations in price or demand would make this amount of delay disastrous. After all, it takes several years to bing a new mine into production, and if the short-term future was that uncertain, it would never be a reasonable proposition to start a new investment. On the other side the longer notice would allow miners time to decide whether to accept a transfer or voluntary retirement, and it would make it possible to consider ways of mitigating the disturbance of the aﬀected communities. These ideas may be naive, but sometimes naive thoughts can be more acceptable than sophisticated ones. I am writing to you because with your industrial experience and good sense you may be able to judge whether my thought is quite foolish or might have a chance. In the latter case there is a question how it might be brought to the attention of the people involved. I do not think it would make any sense to raise the suggestion through the media. Do you have any advice on how to go about this? Do you have any contacts? Forgive me for inﬂicting these questions on you, but in the present disastrous situation even a long shot would seem worth exploring. Yours sincerely, Rudolf Peierls

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[817] Paul Laurence Rose to Rudolf Peierls Newcastle, NSW, 30.11.1984 Dear Sir Rudolf, I hope you will forgive my long-delayed reply to your most informative letters1205 but the preparation of the documented paper which I thought you should have has taken far longer than anticipated owing to the problems of departmental business here. I don’t dwell on the conclusions in the paper except to say (1) that Sir Charles Frank’s letter about the back of an envelope calculation conﬁrms the hypothesis reached in my draft of the paper in early June and (2) that the paper reconciles the Groves and Jones excerpts of the Farm Hall material and the captured German papers. (Incidentally I have had an oﬃcial source conﬁrm Groves’ report of the Heisenberg remark that two tons of U235 would be required for a bomb). One thing which I really should have written to you earlier is that the rough state of typing of my draft sent to you may have misled you in some matters. While typing the draft for a meeting, I was forced to change my conclusions by the evidence coming to hand and it is possible that some of the paragraphs outlining my earlier thoughts — and meant to be suppressed — were not clearly marked so in the draft you have. Yours sincerely, Paul Laurence Rose

[818] Nevill Mott to Rudolf Peierls Cambridge, 24.12.1984 Dear Rudi, Various people particularly Margaret Gowing are suggesting that I should publish an autobiography, and Margaret tells me that you are writing yours, and have some kind of subsidy. Could you tell me about 1205

Letter [811].

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this, and who will publish it? I think I would do it if any publisher thinks it worth while. There is the Sloan Foundation which did Casimir’s. CUP did Robert Frisch’s Taylor & Francis did the English edition of Max Born’s (which sold well). Anyhow — I’d be very interested in your plans and the kind of book you mean to write. With best wishes to you both Nevill

[819] Rudolf Peierls to Paul Laurence Rose Bures-sur-Yvette, 27.12.1984 (carbon copy) Dear Professor Rose, Thank you very much for your letter of 30 November and for your revised and expanded manuscript.1206 This still leaves a few points which I want to consider, and perhaps look at some of your references, but basically you have convinced me that Heisenberg had no idea of how a bomb would work and I am amazed at his degree of misunderstanding of the issue. The key is as you say in his paper G39. Here he takes it for granted that the neutrons in a pure U235 bomb will be in thermal equilibrium with the atoms. There is no reason to suppose this, because each neutron makes at most one or two collisions with U nuclei before being captured to produce ﬁssion, and in these collisions will lose only less than one per cent of its energy. It seems that either he assumed that one would still use a moderator (but whatever for?) which would justify your comment that he was thinking really of an exploding reactor, or he was so accustomed to having the neutrons in thermal equilibrium that he took this for granted without troubling to think how they would get there. Incidentally, he does not seem to be concerned with the uranium evaporating and getting dispersed as its temperature rises, which would 1206

Letter [817].

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stop the reaction. At least there is no indication in the extracts you quote that he understood this. However, I disagree with some of your comments and reconstructions of Heisenberg’s arguments, because they are based on misunderstandings of Heisenberg’s arguments. I shall try to list the most important of these: • p. 12 bottom. You quote the formula for the required radius [. . .]1207 from G39, without speciﬁcation that here [. . . ]1208 is to be taken as the diﬀusion length for thermal neutrons. It is not clear how to evaluate this, because in pure U235 the diﬀusion length would be equal to the mean free path for ﬁssion, and for thermal neutrons this would be very small indeed. If a moderator is present everything would depend on its speciﬁcation. • p. 9 last few lines. Here you seem to misinterpret Jones. When you say that “the neutron escape from the surface would cut oﬀ the chain reaction” this is precisely the consideration which goes into the question of critical size, and by deﬁnition the critical size is that for which the escape from the surface is balanced by the release of neutrons inside. The further statement that “the last atom to ﬁssion” has still to be inside before the expansion stops the reaction has to do not with the critical size, but with the extent to which a chain reaction proceeds, a question apparently ignored by Heisenberg. • p. 10 addendum (1) One should be careful with the use of the terms “slow” or ‘fast” neutrons. The 300 eV neutrons mentioned are slow compared to the average energy of neutrons from ﬁssion, but they are fast compared to thermal neutrons, and as Heisenberg says rightly, their cross section is about the same as for faster neutrons. • p. 12. You still insist that Heisenberg’s belief in the stability of the reactor was absurd, and “cracked reasoning”. It is indeed very plausible because as the temperature rises the cross sections de1207 1208

Missing in carbon copy. Missing in carbon copy.

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crease. The problem is complicated because some of the resonance absorption is also in the thermal region, and will also diminish as the temperature rises, and thus counteracts the lower ﬁssion cross section. This eﬀect was understood only rather late. While Heisenberg missed it, this mistake is not as absurd or cracked, as you make it out (or as his thoughts about the bomb). • p. 16 second para. thoroughly mixes up the problem of critical size with the question of reaction stopping. “· · · providing it was assembled fast enough to minimise neutron escape” — the need for fast assembly has to do with the possibility of premature explosion, when the system is only barely above critical, and will result in an ineﬃcient explosion. The chance of a neutron escaping does not depend on the speed of the assembly. • p. 20 last few lines. You imply that isotope separation for the actual amount for the bomb was an easy task. This is by no means the case. The American isotope separation plant was a huge technological achievement. Even if Heisenberg had known the correct ﬁgures, it would have been perfectly reasonably to say that it was too big a job for Germany to do in war time. Even the Americans with their greater resources, and without disturbances by bombing, did not complete the project before the end of the war in Europe. • p. 26 line 9 from bottom. Frisch and I underestimated the problem of isotope separation; apart from the scale of the job, many hard problems had to be solved to make it possible. • Note 13 is unintelligible to me. I take it “current solutions” refers to today’s view. I cannot believe there is physicist who believed that several tons of 235 (if you ever succeeded in assembling them), would give an ineﬃcient explosion. As regards a ball of “several kilograms” one has to be speciﬁc as to how many kilograms relative to the critical size. If appreciably bigger than critical it would certainly explode, though premature initiation might make large explosions relatively ineﬃcient (though still much stronger than conventional explosives) if it was assembled too slowly.

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• Note 35, last sentence. It is not clear to me that Heisenberg was worried about the sphere being blown apart too early – but perhaps this follows from sources you do not quote. • Note 51. I have already commented that Heisenberg’s respect for the problem of large-scale isotope separation was reasonable. Certainly the terms insouciance and imbecility are inappropriate. • Appendix 2(B) and Appendix 8. The part of Fl¨ ugge’s paper which is quoted in Appendix 8 shows no indication that he is talking about a bomb, he is evidently talking about how one could make a reactor with natural uranium using fast neutrons. Finally, on a point not central to your theme: Are you sure Bothe’s famous result (p. 5, line 18) was a mismeasurement and not overestimate of the purity of the graphite he was using? My copy of your paper has a p. 4 blank. I do not believe I have missed anything essential, but I would appreciate getting a replacement page. I hope your paper will be published, but the thorough research that has gone into it deserved to be presented in a way that will be acceptable to physicists. Your sincerely, [R.E. Peierls] I shall be at this address until the end of January, then again in Oxford.

[820] Rudolf Peierls to Nevill Mott Bures-sur-Yvette, 2.1.1985 (carbon copy) Dear Nevill, Yes, I have written my memoirs, and they are being published by Princeton University Press. This did not involve a subsidy, other than advance

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on royalties on completion of the manuscript. I narrowly missed getting on the scheme of the Sloan Foundation. They approached me when I had practically ﬁnished writing, and at ﬁrst they seemed to be willing to put the book on their scheme anyway, but in the end the committee decided they could not support a book that was already written. The scheme involves an initial payment of $5,000 to enable the author to write a few specimen chapters, and if after this the committee and the author feel it is a viable scheme the oﬀer up to another $45,000 in expenses. I don’t know what can be included in “expenses”, but they mention that one purpose is to free the author from other commitments. The book will then be oﬀered to their publishers, Harper & Row, unless the author has an overriding commitment to another publisher, which will be honoured. The money paid is in principle repaid from royalties, but since repayments begin only when the royalties have reached $20,000 this would seem an academic point. I do not know how the committee chooses their prospective authors. Since their programme oﬃcer was very embarrassed at having to turn me down after ﬁrst making encouraging noises, I think he would listen if I tell him I believe you are considering writing. Would you like me to do that? My own book, called “Bird of Passage”, is written mainly for a general audience, and emphasises, as the title implies, the many places where I have lived, and the many people I have met. Of course, one has to mention the physics, which forms an essential part of one’s life, but I have tried to keep the physics bits short, and suitable to indicate to the general reader how it feels to be involved with it, while they should identify the parts of physics for the physicist reader. I intended to write ﬁrst and take to publishers afterwards, but when I was about halfway I realised it was getting very long (a total of about 160,000 words) and I was afraid no publisher would swallow that. So I sent the partial draft to Oxford Press and to Princeton, which both had suggested writing my memoirs some time ago. Both were interested, but Oxford suggested a lot of changes, and wanted to give me an editor to work with. (They had earlier suggested a “scientiﬁc autobiography” which I did not want to write, as the audience would be too small). So it went to Princeton and should be out next autumn.

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I shall be here until the end of January, then again in Oxford. Yours sincerely, Rudi

[821] Nevill Mott to Rudolf Peierls Cambridge, 12.1.1985 Dear Rudi, Thanks for yours.1209 Yes, it would be very kind, if you would write to the Sloan Foundation. I envisage — like you — a book for a general audience, or as Margaret Gowing suggests an audience of “New Scientist” readers. Though there would be some emphasis on the beginnings of Solid State — 1930– 1939; any scientiﬁc concept introduced would be fully explained. Rather like the Casimir book which Sloan did. I have suggested to Taylor & Francis that they should have ﬁrst refusal. You remember they did Born, which sold well. First reaction is that they would be interested, but would be interested in a subsidy! I am chieﬂy interest in securing a ﬁrm undertaking to publish before I set to work seriously. I wouldn’t need any personal payment — except for typing etc. I suggest you ask them if they are interested without mentioning T+F. Then I could correspond with them. I think a recurrent theme would be — why and how do scientists choose the themes they do? Sloan might like that. Best wishes to you both. I’ll hope to see you when you are back. Richard Wiggs and I got a letter in the Times about Star Wars + are urging the editor to review Bethe’s report. Nevill

1209

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[822] Rudolf Peierls to Nevill Mott Bures-sur-Yvette, 18.1.1985 (carbon copy) Dear Nevill, Thank you for your letter.1210 I have written to the man at the Sloan Foundation, Eric Wanner, telling him that you are thinking of writing, but have not yet reached a deﬁnite decision. I have not tried to describe the nature of the book you have in mind, as this had better be done in direct correspondence. Of course, I also have not mentioned Taylor and Francis. Incidentally, Sloan’s standard agreement provides that any commitment an author has with a publisher would be respected, so if, in eﬀect, you have promised the book to T[aylor] & F[rancis], they would probably agree to their publishing it, but I do not think they would be willing to pay them a subsidy. We happened to pick up here the one issue of the Times with your letter which I though was excellent. It is not the ﬁrst occasion that Air Vice-Marshall Menaul1211 has been talking nonsense. Yours sincerely Rudi

[823] Nevill Mott to Rudolf Peierls Cambridge, 26.1.1985 Dear Rudi, Many thanks for yours postmarked 19 Jan.1212 How bad the post is. I have little doubt that T[aylor] & F[rancis] will publish my thing — but I am interested in the Sloan Foundation. 1210

Letter [821]. Stewart William Blacker (1915–1987), Director General of Royal United Services Institute 1968–1976, who later became military commentator and defence consultant. 1212 Letter [822]. 1211

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Did I tell you that letters to my parents have been recovered? They contain a very vivid description of working with Bohr in 1928. My letter in the Times with Richard Wiggs (you know him? AntiConcorde project + now “project” in favour of freeze). The main purpose was to get the Times to review Bethe’s report (Union of Concerned Scientists) on Star Wars.1213 I have sent them my copy and we hope they will. When you return let us get together + see if there’s anything else we should do. I am hoping to galvanise the C.of E. diocese here to produce something on the Christian attitude — more sensible than “Christ and the Bomb”. Yours Nevill

[824] Paul Laurence Rose to Rudolf Peierls Newcastle, NSW, 21.2.1985 Dear Sir Rudolf, It was most kind of you to take the trouble to go through my Heisenberg so carefully. I have taken several of your suggestions to heart and am now making changes to the original paper which, being in a word processor, can easily be altered. As soon as it is ready I shall send you a revised version — in he meantime I enclose the missing page 4 from the version you have. It may be a little while before the new version can be forwarded, however, because I am in the throes of packing to move to Israel next month. As of 18 March my new address will be: Dept. of General History, University of Haifa, Haifa 31999, Israel. (I shall in fact be in Jerusalem until September but post will reach me via Haifa). 1213

In the mid-1980s, at the height of the Star Wars Programme, Hans Bethe wrote extensively on various aspects of the programme. See S. Lee, ‘Hans A. Bethe. Publications’, Nuclear Physics A, 762, 13–49 (2005); here pp. 37–40.

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Needless to say, I was most relieved to ﬁnd you agree with the central conclusion of the paper (and Goudsmit’s main point) that the Heisenberg bomb was essentially a slow-neutron bomb. As you say, thermal equilibrium is the basis of Heisenberg’s idea of a U235 bomb and whether or not a moderator is to be used, the end result is a slow neutron reaction. It was indeed wrong of me to use so baldly Heisenberg’s thermal neutron formula for the critical radius and insert fast neutron diﬀusion lengths so as to obtain a slow-neutron bomb of small dimensions, new factors intervene to rule out the possibility of a small slow-neutron bomb, pre-eminently the fact that a slow-neutron reaction could not occur rapidly enough to ensure that a “big” explosion would be produced. To ensure that enough U235 was exploded to yield a big bang before the expansion of the bomb caused the diminution of the cross-sections, Heisenberg had to resort to the drunkard’s walk argument mentioned by Jones. (I have avoided in the last paragraph the use of term like eﬃciency and critical mass for reasons explained below). Was Heisenberg aware that the dispersal of the uranium with temperature increase would stop the reaction? This seems to my nonphysicist’s eye to be implied throughout G39 while in the Ardenne typescript memoirs (quoted on my p. 17) the view is attributed to Heisenberg that “on account of the decline of the eﬀective cross-sections at high temperatures the chain reaction would be broken oﬀ prematurely”. Would it be right to say that the only explanation for this “decline’ would be the expansion of the uranium since in G39 Heisenberg had stated that at 300 eV the eﬀective ﬁssion cross-section has sunk around 5(barns) and will not sink lower owing to geometrical reasons” (my Appendix 3, p.2, line 9)? Moreover, in Physics and Beyond, Chapter 13, p. 158, Heisenberg attributes to Bohr the following remarks made in 1935–36: Of course things would be quite diﬀerent if we could raise a piece of matter to so high a temperature that the energy of the individual particles became great enough to overcome the repulsive forces between the atomic nuclei, and if, at the same time, we could keep the density high enough to ensure

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that collisions did not become too rare. But this calls for temperatures of something like a thousand million degrees, and long before we reached such temperatures the vessels in which we enclosed our experimental substances would have evaporated.1214 Heisenberg did not claim that the conversations in that book were given verbatim and in any case I think that the analysis of his statement after the war on his understanding of the atomic bomb raises doubts about his accuracy as a source. But this picture of his thinking in 1935-6 doesn’t seem to be at odds with the content of G39 and the Ardenne memoirs. Critical Size and Eﬃciency I suspect that your comments on my pp. 9 and 16 arise out of my handling of some of Heisenberg’s confusing deﬁnitions and concepts from an historical rather than physical point of view. Thus, from your correct point of view, an “ineﬃcient” explosion occurs when the assembly is not rapid enough as conditioned by your tau function and formula (the extent to which the chain reaction proceeds with time and the amount of mass liberated as energy). But Heisenberg was not interested (as you point out — see also my notes 12 and 33) in how the chain reaction proceeds with time; rather he is concerned with the statistical/diﬀusion problem of how to explode a minimum amount of U235 before the bomb has expanded. (Incidentally, that amount on p. 9 should read 235, not 380 grams=Avogadro’s number of U235 atoms — I don’t know how that error crept in). I wonder if it could be said that your valid concept of a critical mass has to do with the rate of internal multiplication, while Heisenberg’s looks at the problem from the other side, that is neutron escape? For Heisenberg, the speed of assembly is important because it determines the chance of neutron escape, while from your point of view the speed of assembly is crucial because it governs the rate of internal increase 1214

W. Heisenberg, Physics and Beyond. Encounters and Conversations, London: HarperCollins, 1971.

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(by the Tau expression)? Hence, Heisenberg was able, apparently to ignore, as you say, the “question of the extent to which the chain reaction proceeds”. From Jones’ description, it does seem to me that a preoccupation with neutron escape rather than internal multiplication with time is the essence of Heisenberg’s thinking on the bomb. Heisenberg’s conception of critical size and mass and “eﬃciency” in the explosion of a U235 slow-neutron bomb seem to be quite alien to the correct ideas explained in your memorandum of 1940. Isotope Separation and Self-stabilising Reactor On these issues I can understand your points and am moderating my strictures on Heisenberg. But the danger of anachronism is one which historians are more likely to worry about than physicists! (a) p. 12. You do mention that the eﬀect of the reduction of the resonance absorption as temperature rises was only understood later and that Heisenberg missed it. Can one use this to justify Heisenberg’s optimism about the reactor being self-regulating? The point perhaps is that at the time Heisenberg may have had the right conclusion but he did not have the right reasons. To impose current knowledge and justiﬁcation on his attitudes of 1940 seems to be anachronistic. (b) pp. 20, 26, and note 51. Had you and Frisch been in possession of the true facts about isotope separation and the diﬃculty of the whole undertaking in 1940, surely you might also have shelved the whole project as impractical, even for a bomb of small critical mass? The Germans in 1940 seem to have been operating with the same knowledge as you then had of the isotope separation process, yet they were deterred from pressing the project (because they were thinking in terms of tons of uranium, of course). One cannot really use hindsight knowledge of the diﬃculties subsequently encountered in the Maud and Manhattan projects to justify Heisenberg’s rather nonchalant attitude to the bomb project in 1940. He could well have argued that it was for moral reasons that he held back — though he never claimed this and the facts in any case show that morality had nothing to do with it. But I don’t think that it is convincing to maintain that Heisenberg had a clearer idea of the diﬃculties of isotope separation that did you and Frisch.

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With regard to the Fl¨ ugge paper in Appendix 8, I should perhaps have quoted the text more extensively or suppressed the last paragraph which refers to the general theme of the article (a fast-neutron reactor fuelled with natural uranium as you say). But the ﬁrst paragraph quoted is introduced by Fl¨ ugge as an excursus in which a U235 machine using slow-neutrons is discussed — and the Uran-bombe is seen as a version of this. I was a bit unhappy with “fast” and “slow” terminology for neutrons while writing the paper. But 300 eV are “slow” compared to the ﬁssion neutrons in a bomb chain reaction. I shall try to make this clearer. Once again, may I thank you for all your help with these matters. And may I also apologise for having the presumption as a non-physicist to try to argue the case with such a distinguished practitioner? Yours sincerely, Paul Laurence Rose I don’t think I will be publishing the present paper as it is something of a hybrid. But I have almost ﬁnished my general book on Heisenberg in which the theme is rehearsed. If you are interested I shall send you the text in due course.

[825] Rudolf Peierls to Paul Laurence Rose [Oxford], 8.4.1985 (carbon copy) Dear Professor Rose, I delayed replying to your letter of 21 February1215 because I saw from your subsequent note that you were going to pass through London and might telephone me. Evidently you did not have time to do so and I had better send my comments in writing. 1215

Letter [824].

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I ﬁnd the argument in the fourth para. of your letter diﬃcult to follow. It does not make sense to use the cross section for slow neutrons unless there is a moderator present. This would dilute the uranium and increase the critical size. In natural uranium that is the only way to get a chain reaction — in separated U235 it would be quite pointless. Heisenberg’s “drunken walk” argument is not meant to relate to the question of how long the chain reaction will go on, but strictly to the question of critical size. As regards your next para I do not agree that the sentence you quote can possibly relate to the dispersal of the material. He talks about a reduction of the cross section, whereas the dispersal of the uranium would involve a reduction of the density, and not the cross section. (The term “eﬀective cross section” might suggest a correction in which the density is taken into account, but I am pretty sure that the term used in German is just “Wirkungsquerschnitt” which is used as the equivalent of “cross section” though literally it is “eﬀective cross section”). In the absence of a moderator, practically all the neutrons would have energies high enough for the cross section to be practically constant. Next you quote Heisenberg’s account of a conversation between him and Bohr in about 1935. But this is a complete red herring. At the time ﬁssion had not been discovered, and the conversation was evidently about the fusion reaction. Here one is dealing with hydrogen isotopes in equilibrium with the surrounding matter, and in order to make them fast enough for the reaction (whose cross section increases with energy) one must work at an extremely high temperature, and the reaction therefore cannot take place in any vessel. Present attempts to make power from fusion therefore depend on conﬁnement by other means, e.g. by a magnetic ﬁeld. What H. quotes Bohr as saying is what any well-informed physicist would have said at the time (or today), so this conversation has no bearing on Heisenberg’s ideas about a ﬁssion chain reaction. Now about “critical size” and “eﬃciency”. These are very well deﬁned terms and there would be no diﬀerence in usage between Heisenberg and others. In particular it would not be right to distinguish “my” concept of critical size from Heisenberg’s. The critical size is deﬁned as that size of a system for which each neutron will be responsible for

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exactly one neutron in the next generation. It therefore depends on the internal properties of the materiel, i.e. the ﬁssion cross section, the number of neutrons per ﬁssion, the amount of scattering, the loss of neutrons due to absorption in uranium and in any other materials contained in the system, and also on the escape probability from the surface. In discussing the actual critical size one therefore must consider the internal multiplication and the escape together. You say that “Heisenberg · · · is concerned with how to explode a minimum amount · · · before the bomb has expanded”. But I have seen no evidence that he has considered the expansion of the bomb — only the increase in temperature which he thinks will reduce the cross section. About anachronism: If it were not for the resonance absorption, which was not known in 1940, the reactor would have been selfstabilizing, and Heisenberg would have been right. I was therefore trying to say that he could hardly be blamed or not knowing that the stability was in doubt. (But he can be blamed by planning to rely on this entirely without providing a safety shut-down in the event of unforeseen troubles). As regards the diﬃculties in isotope separation, you have shown that Heisenberg greatly overestimated the amount of U235 needed for a bomb, and to obtain that quantity might really have been impossible in wartime. Clearly, Frisch and I did not have a realistic estimate of the cost and the diﬃculties of the separation plant. I do not know whether a better guess would have led us to abandon our proposal, but the question of the technological feasibility of an untried scheme is one on which diﬀerent persons can reasonably hold diﬀerent opinions. Thank you also for the revised pages of your article. I still have a few comments on details. On p. 1 you quote my book review on the question of whether the Germans could not or would not make a bomb. But Mott and I gave a much ﬁrmer opinion in our Memoir on Heisenberg, which you also quote. On p. 5 you say Jungk made his many wrong statements because he believed everything that the Germans told him. It was however not quite so simply because Goudsmit told me that he spent half a day showing Jungk documents which showed that he was wrong, but Jungk ignored them and did not change his statements. So at least he

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wanted to believe what the Germans told him. We met Jungk at some conference, when he knew that some things he had written had been wrong, and after much argument got him to agree that it was his duty to put this right publicly. But of course he never did. On p. 9 there is something wrong even with the corrected version of the statement involving Avogadro’s number. Avogadro’s number is the number of atoms (or molecules) in one mole or gramme-molecule. One mole of U235 weighs 235 grammes. I do not know (not having Jones’ book handy) why one should consider one mole, which would not be critical, but the fact that the number of atoms in it is just Avogadro’s number seems quite irrelevant. On item (B) on p. 16A I have eﬀectively already commented above. I hope you don’t mind my many critical remarks. As I said before I believe that you have extracted from the available evidence a very important insight, and it is important that this be made available in a form intelligible and convincing to physicists among others. I was disappointed to hear that you are not proposing to publish an article on this subject, but if your ideas will be fully treated in your book that will serve the purpose. But perhaps it would be wise to enlist in the presentation of the argument, the help of a physicist knowledgeable in atomic-energy matters to forestall objections and misunderstandings. I think you have done remarkably well for a non-physicist to deal with these very technical matters; it would be surprising if some minor errors were not left in the presentation. Yours sincerely, Rudolf Peierls [826] Rudolf Peierls to Paul Laurence Rose Oxford, 28.5.1985 (carbon copy) Dear Prof. Rose, Since I last wrote to you1216 I had a conversation with Mark Walker, an American student of history whose work I believe you know. I tried to 1216

Letter [825].

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convince him that your conclusions were basically correct, but in trying to do so I got considerable doubts. Apart from the points already raised in my letter of 8 April (which I hope has reached you via Haifa) the chief doubt relates to your interpretation of Heisenberg’s papers. G39 is essentially a discussion of a power reactor, and the possibility of an explosion is mentioned only in passing as an extreme case. There is no indication (at least in the extracts you reproduce) that he thinks of this as a way of making a bomb. From the next paper, MS of a lecture on 26.2.1942, you quote only very brieﬂy, but again the subject is nuclear power, and the explosive possibility of U 235 is mentioned only in passing. The statement that the mass must be large enough for the multiplication of neutrons in the interior to exceed the loss by escape through the surface, is of course perfectly correct. In this paper, as far as your extracts go, there is no indication how we could calculate the multiplication. The quoted passages do not bear out your statement that the reactor is treated implicitly as a case of a slow-neutron reaction. The fact that fast neutrons are not mentioned explicitly does not prove anything. Now I come to G217. Here, Fig. 1, which you reproduce, clearly shows in the right-hand half, labelled “uranium 235” an arrangement without a moderator, as opposed to the left hand half. In this arrangement the neutrons are necessarily fast, i.e. they have the energy with which they are emitted in the ﬁssion process. So to any physicist, the “U235” part of the ﬁgure is a fast-neutron arrangement, and this does not need to be stated explicitly. It is true that in the relevant text he points out that neutrons which hit a uranium nucleus without causing ﬁssion are scattered, and lose energy. It is not clear whether he has in mind the energy loss by inelastic collisions or by giving kinetic energy to the U nucleus. The latter eﬀect is completely negligible since in an elastic collision the neutron loses at most 1/235 of its energy. The eﬀect of inelastic scattering would depend much on the energy levels of the U235 nucleus, about which not much was known at the time. It would however be most unlikely to change the order of magnitude of the neutron energy substantially. The fact that he mentions this energy loss at all, gives some support to the view that he has a wrong picture of the 235 reaction in mind.

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Perhaps one should not try to read too much into this remark. Are there any other similar remarks in the parts of the text which you have not reproduced? I shall be very interested in you comments. Yours sincerely, Rudolf Peierls

[827] Rudolf Peierls to Nina Byers Oxford, 12.9.1985 (carbon copy) Dear Nina, When you asked for a list of members of the Birmingham Departments I thought I had this only in a book with one or two names to a page, which it would be a major eﬀort to copy. I found, however, a list in date order, and enclose a Xerox copy. Note there are a few names at the end, which were missing from the original list. Ignore the various ticks and dashes, which served various statistical purposes. I hope you and Art have settled down again at home, which I hope has not got singed by the forest ﬁres. Here the media are preoccupied with the 40th anniversary of the atom bomb, and physicists with the Bohr centenary. I have already given a brief talk about Bohr to the European Medicine Society, and look forward to the Bohr meeting and lectures in Copenhagen, Edinburgh, Birmingham, Manchester and Cambridge Mass. After the lousiest August on record, we now have a few days of glorious summer. Yours sincerely, Rudi

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[828] Feeeman Dyson to Rudolf Peierls Princeton, 28.12.1985 Dear Rudi and Genia, Thank you for sending us a copy of “Bird of Passage” which we have been enjoying very much.1217 I had seen it before in the typescript version which was clumsy and inconvenient to hold and carry around. It is remarkable how much diﬀerence the physical shape of a book makes to the pleasure of reading it. To my delight, I found the book much better and more memorable in the printed version. It is full of good things, not only your stories, but also your political judgements and reﬂections. I did not check to see whether the text had changed between the two versions, but I assume the change was mainly in my own mind. Thank you also for the 1985 Annual Report. We are amazed to see how much you managed to do in one year, in spite of age and illness. But I suppose I should not be surprised. I remember in the Birmingham days being impressed above all by your superabundant energy and powers of endurance. We were particularly interested to hear about Jo’s disability and her operation. I remember also how Jo as a baby already showed exceptional courage and determination. We hope the operation really cured the problem. As you may know, our Katrin is still in London, very lame with a back problem which may be similar to Jo’s. We have been advising her to go back to Vancouver to have the back taken care of by an operation if necessary. But it is a tough choice for Katrin, as you can imagine. News from Mia in Africa is good. The other four daughters were all here for Christmas, in excellent health and spirits. Love from all of us, Freeman

1217

At the end of 1985, Peierls’ autobiography was published. R.E. Peierls, Bird of Passage, Princeton, Princeton University Press, 1985.

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[829] Rudolf Peierls to Arnold Kramish Oxford, 13.2.1986 (carbon copy) Dear Dr. Kramish, Thank you for your letter.1218 I sympathise with your shingles experience. My own shingles attack many years ago, mercifully aﬀected only a motonerve, and caused no pain, only partial facial paralysis. By the “Welsh incident” you presumably meant the story how he was put in charge of atomic intelligence (last complete para. on p. 168). You may certainly quote from this, or other episodes. However, my knowledge of this incident is second-hand. My analysis of the German literature was not done for Welsh. As far as I remember I sent my notes on this either to M.W. Perrin, or to J.H. Awbery, a physicist at the National Physical Laboratory who assisted the “Tube Alloys” oﬃce and probably had some connections with intelligence. I believe I got the German journals through him. Fuchs was not involved in this analysis; he had not been long enough in German academic life to know much about the background.1219 I may have shown him my ﬁndings, and possibly consulted him about speciﬁc items. I am afraid I cannot recall the date when I started this review. It certainly was done more than once, but not at regular intervals. I suspect one might be able to ﬁnd dates in my ﬁles which are still at Harwell and when declassiﬁed will be placed at the Public Record Oﬃce, but I cannot aﬀord the time to search them. I also cannot remember whether and when Fuchs met Welsh though I think it is most likely that he did. 1218

In the letter Arnold Kramish presumably asked Rudolf Peierls to comment on a draft of: A. Kramish, The Griﬃn. The Greatest Untold Espionage Story of World War II, Boston: Houghton Miﬄin Company, 1986. 1219 Fuchs did in fact assist Peierls in the analysis. See Lee, Peierls Correspondence, Vol. 1, Chapter 5, letters [327–28], [335] and [337].

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The name Alf Larssen does not mean anything to me. I am sure I did not suggest your contacting him. Perhaps it was someone else who suggested this? Or else the name got garbled but I cannot think of any name that could plausibly sound like Alf Larsen, or of anyone living above the Costa del Sol Sir Michael Clapham is a senior industrialist in I.C.I. at one time their chairman. During the war he was in I.C.I. Metals at Birmingham, which included the Kynoch Press. He had been a professional printer and therefore took a special interest in the printing side. At one time there was hope of making membranes with ﬁne pores by printing techniques. This got Clapham involved with Tube Alloys. I do not think you have missed much by not contacting him, but I am not too clear what you would be looking for. I do not know the name of the person involved in the episode with von Weizs¨acker and Bohr. I heard about this episode from Dr. Stefan Rozental at the Niels Bohr Institute in Copenhagen, and I am sure he would gladly give you all the details. On your requests for assorted copy: I enclose a Xerox of my review of Heisenberg’s book. The episode of his visit to Bohr is not dealt with in the review, but there is some discussion in the “Biographical Memoir” which Mott and I wrote for the Royal Society. I have run out of reprints, but enclose a Xerox of the relevant piece. The full text is in “Biographical Memoirs of the Fellows of the Royal Society”, Vol. 23, p. 213, 1977, which should be easy to ﬁnd in a library. We shall never know what exactly was said in the Heisenberg-Bohr conversation. You more or less accept Bohr’s recollection, but he could easily have misunderstood Heisenberg. I do not believe that Heisenberg in 1941 regarded the bomb as a realistic possibility. He did not know that one needed separated U 235, though it is not clear whether he had a good estimate of the critical size. But he thought large-scale isotope separation was prohibitively diﬃcult in wartime. He says that his advice to the authorities [w]as that the bomb not a practical possibility, and I have never heard him contradicted. A very thorough study of Heisenberg’s wartime reports and lectures is being made by a Princeton student of the history of science, Mark

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Walker who is (or at least was until a few months ago) in Germany, address: Fallmerayerstraße 28, 8000 M¨ unchen 40. A copy of the non-technical part of the Frisch-Peierls memorandum is also enclosed. Yours sincerely, Rudolf Peierls

[830] Nevill Mott to Rudolf Peierls Cambridge, 19.2.1986 Dear Rudi, I read your autobiography some weeks ago, and enormously enjoyed it, especially the early days, Russia, Genia, Peierls-Frisch. Just now I’ve written a short review for Physics Bulletin. Mine (Taylor + Francis) is promised for next month. Rather different from yours. Till my parents died, based a lot of letters to them. Perhaps less personal, but a good deal about Cambridge politics, religion, etc. Hope not too dull! Best wishes to you both Nevill

[831] Brian Pippard to Rudolf Peierls Cambridge, 13.6.1986 Dear Peierls, It occured to me that, since you were writing Dirac’s obituary for the R[oyal] S[ociety] you might enjoy a story that my father told me decades ago, concerning Andrew Robertson, one of his colleagues in the engineering department at Bristol. Finding himself, in 1926 or 1927, sitting next to Paul’s father, a French teacher in Bristol, and having to make polite conversation over dinner, he remarked: “Your son seems to be making a name for himself in Cambridge — quite a second Einstein.”

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There was a slight pause and then, somewhat distantly, from Dirac senior: “Well, actually Paul does not think much of Einstein.” Unfortunately, my father was not in Bristol at the time of Paul’s undergraduate career in engineering, but as external examiner, he heard brilliant reports of this young man who was not content with what the lecturers said, and had to work everything out in his own way. He discounted much of this eulogy as the typical response to a better-thanusual student, but realised later that the half had not been told him. With best wishes Yours ever Brian Pippard

[832] Rudolf Peierls to Manci Dirac Oxford, 28.6.1986 (carbon copy) Dear Manci, I found your letter on our return from Greece, and the Royal Society copy also went to Dalitz.1220 The “Swiftair” scheme, by which I sent the MS, is not just for special delivery but is supposed to guarantee that the letter goes by the ﬁrst available plane; so far this always meant delivery in two or three days, so this time it was very bad luck. But we can still cope with the adjustments. I am sorry we put you under such pressure of time, but the memoir will now get into this year’s volume, as we had hoped. We are very grateful to you for reading the text so carefully. Here are our reactions to your comments. First the two major issues. Paul’s father was a major inﬂuence in his life, and a very complex person; it seemed right to include a description of him. This had to include the view of other people, besides 1220

Rudolf Peierls had sent a copy of a draft of the Royal Society memoirs of Paul Dirac, which he was writing together with Dick Dalitz, to Manci Dirac for comment. See also Peierls Papers, Supp., D.17–D.35.

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Paul, and the impressions naturally diﬀer. It is very generally true that everybody’s view of their parents is inﬂuenced by emotions, and therefore is often not objective. But we have, I think, reported very fully Paul’s image of his father. His comment at the time of his father’s death, seems too private to mention in print. Your other comment is about religion. There seems no doubt that he was agnostic in his youth. What we say about his views in later life sounds a little too negative. We propose to replace the phrase “It is believed · · · ” at the beginning of the last para[graph] of the piece on “Personal Characteristics” by a more deﬁnite statement, and in a later sentence which now reads “According to Mrs. Dirac he was not anti-religious · · · ” we shall change this to “According to Mrs. Dirac he had deep religious feelings”. The original wording sounded too negative, and I hope you will ﬁnd the revised sentence more acceptable. Now about the minor points: Origin of the family from the village, and the Chateau of Dirac. Many families carry a tradition about their history, which, being transmitted by word of mouth, often becomes quite unreliable. One should not accept such folklore without conﬁrmation, and we report how close we came to documentation about the family history. About the mother’s father we correctly call him a master mariner, which is the term for a captain of a merchant vessel. You are right that Charles Dirac’s mother and family moved to Geneva after his father died at Monthey, but this was after Charles left for England, so what we say is also correct. As regards lecturing and other duties: Even if the formal appointment to the chair did not specify any lecturing duties, (it does in Oxford though far less than anybody’s actual lecturing load) it is certainly the custom that all science professors give regular lecture courses. I remember that G.I. Taylor was given a Royal Society Professorship in Cambridge (which is intended to be a pure research professorship) because he did not want to lecture. Similarly, ﬁrewatching was a duty shared by everyone in wartime, and I do not think it needs special mention. Bhabba was not Paul’s student, but Mott’s. He attended Paul’s

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lectures, of course, as did many others, but there is no indication in his papers that he received substantial advice from Paul. About Mount Elbruz, it is apparently a debatable question whether it is in Europe. I have consulted an eminent geographer, who says that opinions are divided, but the tendency is to regard the crest of the Caucasus as the border of Europe with Asia, and therefore not belonging to either. However, I am glad you queried this, because on talking with my expert, I discovered that Elbroz is not the highest mountain in the USSR, so we are reduced to calling it the highest mountain in the Caucasus! Bullard’s part as Monika’s teacher seems a little too remote to include. Paul’s illness in Vancouver: You are right that he was not treated in hospital, but in a private house and this will be corrected. Visits to Switzerland: We are grateful for the correct dates, and will include them. One textual alteration, made after we sent the draft to you, you should know about: In writing about Gabor, we changed the name to Gabriel, the name he used in his career. Genia and I had a glorious time in Greece — mostly in the North and in the mountains where it was not too hot, and the scenery was magniﬁcent. Genia managed all the walking, which was involved, except a few walks on steep paths with loose gavel. She even went up to the Meteora monasteries, of which one involves 142 steps! With many thanks again, Your sincerely [Rudi] [833] Manci Dirac to Rudolf Peierls [Cambridge], 8.7.[19]86 Dear Rudi, Your letter, dated 28th of June, arrived here this morning.1221 Thank you so much. 1221

Letter [831].

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As for your previous letter, even if it came in one day, I would not have had a chance, to reply, and for you to receive it, before you both left for Greece. I am very surprised, that you even mention the remotest possibility, of publishing my explanation, as to how Paul felt, when his father died. Noone with the slightest taste or tact, would have done so. It was written to emphasise my point, in not making a nice old man of a very domineering, almost brutal person. As I never met him, all I know is from Paul and from his mother. My motive is solely and absolutely so to act as Paul would have liked it. This too is private what comes next. “As I child I have been made to eat, until I vomited. Practically every day. Many times did I have to run out of church, to be sick. I concluded that God did not want me in his church.” Paul was pressed by Bragg to ﬁre watch with workmen in the Cavendish Laboratory. Orovan kindly arranged, Paul to have a better place to do this. These workmen apart from smell, got up early and Paul felt he could use his energy to better purpose. Bragg never ﬁre watched. Was he so greatly superior to Paul????? Very dear Rudi. I thank you from the bottom of my heart, for changing Paul’s religious convictions. I saw him pray on his knees in the Chapel of St. John’s many times. He was NO actor. It was very moving for me to be with him on those occasions. ∗ Old Mrs Bhabha should have known who was Homi’s teacher. While Homi lived in Cambridge, he very often was a guest with us. I do not think Paul would have had him that often, if he had not been his graduate student. Homi, who lived very lavishly, had Paul and me sometimes in his place. Always for tea only, but still he tried to show his appreciation. As I truly dislike that Asiatic hard hearted so and so, it does not upset me at all if you leave out things. I admired, loved Teddy Bullard. Monika is not the past in Paul’s life, but the future, and is she not more important than the man who made ∗ Mott

came to Cambridge after the war. B[habha] never returned to C[ambridge] after the war was over.

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his family deeply unhappy? To mention Bullard should be a pleasure in any case. So glad you enjoyed Greece. My darling unforgettable Judy loved Greece enormously. They spent two years there, with the 3 children. Late she went back alone, for holidays. We never visited, Paul mostly went where he was invited to. My darling Genia, I did not know that Lady Blackett had died. I hardly knew her. At our wedding, and once or twice at parties at the Royal Society. But the rumour was that she was a very indiﬀerent wife and mum. He was the best looking man I ever saw. Including actors and ﬁlmstars. My information is from Betty Waddington, whom I think you also loved. I missed her greatly after she left Cambridge. One more thing, Rudi. Anna wrote, and her letter was delivered on Sunday. I had to sign for it. She will send me Paul’s letters to Kapitza. She writes very aﬀectionately. Age changes people. It was he who was the romantic, the music lover, the peppery joke teller. Anna always left the room when we engaged in jokes. Paul also loved his stories, which were inexhaustible. Just like poor Johnny’s repertoire. Like turning on a tap. May they all rest in peace. They both gave so much of themselves to us all. I better stop. Best to the dear two of you as ever your Manci

[834] Lillian Krynen-Jacobsohn to Rudolf Peierls Brussels, 31.8.1986 Dear Sir Peierls, I am Mrs Lillian Krynen Jacobsohn; you may heard of me through my very dear father. It is very sad to inform you that Dr. F. Jacobsohn died on the 7.7.86 here in Brussels. He came to visit me after two years in America; it was to be a holiday with me and I was so happy that he came again to see me on my Birthday!

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I am sad, for the sad news, Sir I have heard about you from my father very much — in fact I have the water kettle you gave to my father when he last visit you — I do hope that I will have one day the opportunity to meet you; as I come often to London to see my friends there. I am a widow and have two sons, Robert, my eldest is here with me in Brussels and my son Paul is in Kenya, East Africa. Hope very much to hear from you + hope all is well with you! My very warm regards to you Lillian

[835] Ulrich B. Jacobsohn to Rudolf Peierls Farmingdale (Maine), 5.9.1986 Dear Sir Rudi, I’m going through my father’s letters. I came across your letter to him and realize that you may not know about his sudden death on July 8 of this year. He was travelling to visit with his brother in Berlin and stopping over with my sister Lillian in Brussels. On his ﬁrst night he fell in the dark (saving electricity, no doubt) and within another day he went into a coma with a rapid demise. He had the highest hopes for an exciting summer in Berlin but my last memory as I saw him oﬀ at the airport was one of a very tired man. He would never really express his fatigue and insisted on a rugged independence. There is not a day that passes that I do not think of him and his diﬃcult life. What makes it all somehow easier was the birth of a grandson on July 12. I think the passing of another generation and the survival of the Jacobsohn name was a strong statement for the energy he displayed in so many ways. Always a shy man, he nevertheless left a lot of strong will in all of us and future generations will be the better for this. I have heard about you all my life and feel privileged to write this letter to you even though it is with such a sad message. My father had

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ﬁnally come back to me and he had found a loving home, but it was clear that his real love was his youth in Berlin with you and all his other friends of so long ago. Some of those friends have already joined him including Heini Heldt who died just about a month earlier in Florida. I hope that someday I can meet you. Ulli

[836] I.M. Khalatnikov to Rudolf Peierls [Moscow], 11.9.1986 Dear Rudi, Three days ago my secretary, Mrs Tatiana Kachalova upon my request called you and had a talk with Zhenia. We are expecting you to come to Moscow on the 19th of October. The only thing we do not know yet is the ﬂight you are coming by. I hope you will cable us so that we could meet you both at the aeroport. In the meantime we are taking the necessary steps to make your visit not too tiring for you. In the middle of the term of your stay here you will go to Leningrad by train where our colleagues will be happy to welcome you. As for your departure to Dheli, we are also taking care of this problem. So we are all looking forward to having you here. Taking advantage of the occasion I would like to let you know how highly my colleagues and myself esteem the activities you are conducting in the Pugwash movement in support of nuclear disarmaments. I believe that one of the most important results of such activities is that the leaders of the both superpowers (at least deﬁnitely from our side) acknowledge that nuclear war was impossible and that in case it starts, the whole humankind will perish in it irrespective of the fact who started it. As you know, our Government at present attaches great importance to the support of its goodwill initiative of the moratorium of nuclear arms tests. It is no doubt that in the present situation it would be of great political signiﬁcance if the West would join the Soviet initiative.

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I hope your visit to Moscow will provide rich opportunities of our discussing these problems. With all my wishes of good health to you and Zhenia, Sincerely yours, I.M. Khalatnikov P.S. Please remember to take with you your book “The Bird of Passage”.

[837] Rudolf Peierls to I.M. Khalatnikov Oxford, 17.9.1986 (carbon copy) Dear Khalat, Thank you for your letter of 11 September.1222 Thank you also for all the careful plans for our visit. I am sorry I did not give our ﬂight number in earlier letters. We are arriving by British Airways ﬂight 710 due Moscow 15.45 on 19 October. I fully agree with your comments on nuclear disarmament. The present Soviet moratorium on testing is certainly a step in the right direction. As I mentioned in my Copenhagen paper.1223 I still cannot understand the preoccupation of all governments with parity, and the resulting arms race. I look forward to discussing these problems during our visit. I shall certainly have my book with me. Yours sincerely, Rudolf Peierls

1222

Letter [836]. R.E. Peierls, ‘Is there any logic in the nuclear arms race?’, in A. Boserup, L. Christensen and O. Nathan (eds), The Challenge of Nuclear Armaments, Copenhagen: Rhodes Intl., 1986, 265–269. 1223

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11.

1986–1995:

The Tree Needs to Grow New Rings

On the occasion of Genia Peierls’ 70th birthday, on 25th July 1978, her four children, Ronnie, Gaby, Kitty and Jo collected reminiscences from friends across the world. These were presented to Genia on her birthday in an album, and the sentiments expressed in the various contributions demonstrate Genia’s extraordinary qualities.1224 She had been the focal point of the Peierls household, but her impact had gone far beyond her own nuclear family, largely as a result of Genia opening up the family residence to colleagues, students and friends from her husband’s institute (and beyond). Colleagues who had met at Rudi’s institute and Genia’s house talked of themselves as a family and called each other cousins.1225 Freeman Dyson recalled the year he spent in the Peierls household in the early 1950s, saying ‘it was a tough year for me and it was a tough year for you. You with two babies and two opinionated teenagers on your hands, me returning from an intoxicating box-oﬃce success in America to a cold morning-after in England. During that year you taught me, partly through talking but much more by example, what it means to be a grown up.’1226 Genia was the warm-hearted centre of much of the social life around Peierls’ institute at Birmingham and to some extent also at Oxford. She made other people’s problems her own, and went about solving them. Some people may have been irritated by her occasionally unwanted concern or interference, but everybody acknowledged that her heart was in the right place. Similar sentiments were expressed in the many condolence letters which Rudi and the family received after Genia’s death in October 1224

Genia Peierls, Peierls Papers, Supp. A.119. Nina Byers’ contribution in ibid. 1226 Freeman Dyson’s contribution in ibid. 1225

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1986. Viktor Weisskopf, who had ﬁrst met Genia in Russia in 1932, remarked that she ‘represented the human side of our community of scientists,’1227 the community which Genia herself described so accurately in her letter to Raison in 1961.1228 Hans Bethe called Genia ‘one of the greatest personalities’ he had known and recalled with aﬀection how her comments and her care during his time in England prepared him for his later venture across the Atlantic, when he chose to settle in the US.1229 And while he and his wife Rose remembered her habit of organising other people’s lives as something not always entirely helpful, they were both full of admiration for her wisdom, joie de vivre, generosity, vitality, sagacity and her love of life and people.1230 Many commented on the great diﬀerence in style and character of Rudi and Genia, on the way in which they complemented each other; but Freeman Dyson, very insightfully remarked to Rudi: ‘She was like you in many ways. She understood the importance of Leo Szilard’s Tenth Command: “Lead your life with a gentle hand and be ready to leave when you are called.”’ This unsentimental approach to life was also visible in Genia’s advice about how to deal with a partner’s death: ‘In our memory there are rings like in a tree. After the death of a partner it is important to develop new rings. At ﬁrst any recollection of the past is painful, because every experience, every place is always linked to the picture of the partner. One ought to travel, ﬁnd new occupations, new impressions. Then, after a while one will have recollections which are no longer painful.’1231 Rudi Peierls took Genia’s advice, much in contrast to his old school friend Heinz Rudolph who lost his wife around the same time, and with whom he corresponded in depth about their experiences.1232 He continued leading a nomadic lifestyle and an active social life, spending time together with many old friends, but also making new ones. 1227

Letter [843]. Letter [684]. 1229 Letter [838]. 1230 Letters [838–839]. 1231 Letter [852]; editor’s translation. 1232 Letters [851–852], [875–876], [881]. 1228

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Among those new friends was Lillian Krynen-Jacobsohn, the daughter of his school friend and distant cousin, Franz Jacobsohn, who had died in the summer of 1986. After Genia’s death, Rudi and Lillian, herself a widow, corresponded with each other and eventually met. They developed a close long-distance friendship. The correspondence between them1233 sheds light not primarily on their relationship, but also on the nature of the relationship between Rudi and Genia Peierls. As indicated in much of the couple’s written exchanges after they met in 1930,1234 they were entirely honest in their approach to each other and to their friends, they were open about their need of companionship, and they were sincere in their wish for each other’s happiness, with or without each other. Throughout their married life, which spanned well over half a century, they were entirely committed to each other, but as Genia’s remark about the need to grow new rings demonstrated, this commitment to the partner ceased with his or her death. If Rudolf Peierls, not long after Genia’s death, met new female companions, he did this in the knowledge that this in no way diminished the love and aﬀection he had felt for Genia, and he did it in the knowledge that Genia would have wanted him to ‘get new impressions and grow new rings’. Rudolf Peierls found diﬀerent ways of obeying Genia’s wish to open himself to new experiences through old and new friendships and, as always, through science and travel. 1986 Peierls had received the Copley Medal, the highest award of the Royal Society, and the Rutherford Memorial Medal, which is associated with a lecture series to be delivered at selected centres in the British Commonwealth overseas. Initially, Rudolf and Genia had wanted to embark on the lecture tour together, but Genia’s illness prevented them from doing so. The trip was postponed to the following year, and in November 1987 Peierls delivered his lectures in India, visiting Moscow and Leningrad en route. In the early years of their marriage, Rudolf, when travelling long-distance by himself, would always send Genia detailed travelogues sharing his impressions and reactions to new places. Now, again traveling without a companion, 1233

Letters [845–846], [848], [853], [855], [858], [863], [867], [873–74], [888], [892], [923], [938]. 1234 See Lee, Peierls Correspondence, Vol. 1, Chapters 2 and 3.

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he reverted to his habit of sending travelogues, this time to his children in the form of his ‘Dear Everybody’ circular letters. Peierls’ journey to Russia in 1987, though of course ﬁlled with meetings of colleagues at the various scientiﬁc institutes, had a more personal note than many other trips, because of the emotional ties to the place. Therefore, his assessment of the situation was particularly poignant, even more so given that it was his ﬁrst trip to Russia since Gorbachev’s ascent to power. As he told his family, ‘Talking with many people (but all intellectuals) I got a wide range of reactions to Gorbachev ... But all are unanimous that, if Gorbachev fails, there will be a terrible backlash. Perestroika proceeds in odd ways. For instance, in the Academy, decentralisation seems to consist in delegating all the awkward chores, while keeping decisions ﬁrmly at the centre. · · · Economic footnote: The price of plastic shopping bags has come down from 60 p (I believe) to 20. The price of vodka in the foreign currency shops has doubled.’1235 Before his ﬁrst extensive trip without Genia in the autumn of 1987, in June of the same year, Rudolf Peierls had celebrated his 80th birthday. The Theoretical Physics Department at Oxford marked this occasion with a symposium. The meeting was an impressive display of the breadth of physics, tackled by Peierls on his own or by his students, in collaboration with ‘Prof’, and it was an indication of the signiﬁcance of the contribution of Peierls to our understanding of the world.1236 Socially, the symposium was a welcome opportunity to meet former colleagues, friends and family many of whom came to Oxford on the occasion. The Bethes were among those who joined the Peierls family in their celebration. The jet-setting lifestyle of the two octogenarians, Hans Bethe and Rudolf Peierls, visible in their planning around the symposium is impressive. Hans Bethe travelled on immediately after the weekend to give a lecture in Switzerland,1237 and Peierls himself left Oxford for a conference in Turin on the Monday following the symposium. He returned home to England straight after the Turin confer1235

‘Dear Everybody’, 9.12.1987; Peierls Papers, Supp. A.26. R.H. Dalitz and R.B. Stinchcombe, A Breadth of Physics, Singapore: World Scientiﬁc Publishing, 1988. 1237 Letter [854]. 1236

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ence to take part in a three-hour live TV debate with Edward Teller in London!1238 Teller was the driving spirit behind the US Star Wars programme, which Rudolf Peierls alongside many other scientists, objected to on moral and rational grounds. Therefore he welcomed the opportunity to put forward his own ideas in a debate with Teller.1239 Peierls family letters ‘Dear Everybody’ with their detailed descriptions of his life in Oxford and his travels abroad as well as his annual Christmas circulars for friends and family, reveal what becomes a little less evident in his other correspondence, namely that Peierls’ life was still a remarkably busy and active one well over a decade after embarking on ‘retirement’. When Freeman Dyson commented that he and his wife were ‘stuck dumb with admiration’1240 for his breath-taking travel schedule, Peierls dryly answered that he regarded this as the ‘soft option as opposed to sitting on one’s backside and doing more serious reading or thinking, which I ﬁnd myself more and more reluctant to undertake — this kind of laziness grows with age.’1241 His busy social schedule did not stop Peierls from commenting on science and science administrative issues which still occupied him, even though he was no longer teaching actively, (but still researching and writing). For instance, after visiting the International Centre for Theoretical Physics in Trieste, he wrote a letter to its director Abdus Salam, reformulating earlier concerns about the set-up of the centre and reiterating some concerns about the low ratio of senior to junior researchers, which he believed detrimental to real progress.1242 In 1987, a doctoral thesis about the German atomic bomb project1243 which had been sent to Peierls to comment on, made him revisit the question of Heisenberg’s role in the Nazi nuclear eﬀort, as did Thomas Power’s request for an interview in connection with his own 1238

Letters [855–56]. Letter [856]. See also ‘Dear Everybody’, 6.7.1987, Peierls Papers, Supp. A.26. 1240 Letter [862]. 1241 Letter [865]. 1242 Letter [857]. See also letters [682–683]. 1243 Later published as M. Walker, German National Socialism and the Quest for Nuclear Power, 1939–1949, London: Cambridge University Press, 1990). See note 1080. 1239

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study of Heisenberg’s war-eﬀort,1244 a book which he later reviewed and took issue with.1245 It was a theme that Peierls would come back to again and again in thought and in publications as he wrote a short piece on German ethics and atomic weapons1246 as well as a review of David Cassidy’s biography of Werner Heisenberg.1247 A related issue was brought up by Andrew Brown, who was working on a biography of James Chadwick.1248 In his research he had unearthed correspondence between Chadwick and Peierls, of which the latter had been unaware. The material clariﬁed the sequence of events leading up to Peierls and Fuchs investigating German periodicals and lecture lists in 1941 in order to ascertain the likelihood of a serious German nuclear weapons programme. This, Peierls had always recalled to have been his own initiative, but he was happy to see his own recollections corrected by reliable evidence as in this case, where the sources showed that the research had been Chadwick’s idea.1249 Peierls continued to contribute to the understanding of science and science history by giving advice to scholars1250 and by reviewing important publications in the ﬁeld, although his failing eyesight made the task of reading and writing ever more diﬃcult. Despite this handicap, he still undertook to write reminiscences and recollections of friends and colleagues.1251 1244 Later published as Thoman Powers, Heisenberg’s War: The Secret History of the German Bomb, Harmondsworth: Penguin, 1994. 1245 R.E. Peierls, ‘The Bomb that Never Was’, New York Review of Books, 22.4.1993, 6–9. 1246 R.E. Peierls, ‘German Ethics and the Bomb’, The Independent, 13.6.1992 1247 R.E. Peierls, ‘The Uncertain Scientist’, N. Y. Rev. Books, 23.4.1992, 43–45. 1248 Andrew Brown, The Neutron and the Bomb, Oxford: OUP, 1997. 1249 Letters [903–905]. 1250 Letters [901], [903-905], [908], [909]. 1251 R.E. Peierls, ‘Physics and Homo Bhabha’, Nature, 323, 312 (1986), R.E. Peierls, ‘Truth and Clarity’, The lessons of quantum theory, Niels Bohr Centenary Symposium (eds. J. de Boer, E. Dal and O. Ulfbeck), 379–80 (1986); R.E. Peierls, ‘P.A.M. Dirac’, Biogr. Mem. Fell. Roy. Soc. Lond. 32, 137–85 (1987); R.E. Peierls, ‘Rutherford and Bohr’, Notes Rec. Roy. Soc. Lond. 42, 229–41 (1988); R.E. Peierls, ‘My recollections of Landau’, Landau. The Physicist and the Man, (ed. I.M. Khalatnikov), 194–97 (1989); R.E. Peierls, ‘William George Penney’, Physics Today 44(10), 138, 149, 142 (1991), R.E. Peierls, ‘Recollections of James Chadwick’, Notes Rec.

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Rudolf Peierls’ work on nuclear weapons had ceased in 1945, but his concern with the problems of nuclear armament remained with him all his life. On 9th July 1955, Bertrand Russell and Albert Einstein had issued their famous manifesto calling on scientists of all countries to save the world from nuclear war. This resulted in a series of conferences on ‘science and world aﬀairs’, the ﬁrst of which was held at Pugwash, Nova Scotia, and gave the movement its name: Pugwash Conferences. Under the ﬁrst president Cecil Powell and Secretary General Joseph Rotblat, the movement grew with increasing numbers of scientists getting involved in the annual conferences and regular meetings and workshops. Peierls played an active part in the Pugwash movement, serving on its continuing committee from 1963 to 1974 and as its chairman between 1969 and 1974. He had always given high priority to the Pugwash Conferences since attending his ﬁrst such conference in Moscow in 1960, and now in retirement, he still tried to attend and contribute whenever possible.1252 And even in the last years of his life, when his health was declining and it was becoming increasingly diﬃcult for him to engage in travel and writing, he kept up his determination to contribute to the nuclear debates with his last publication being devoted to these issues.1253 More locally, Rudolf Peierls had also become involved in the FREEZE movement, which had been publicly launched in 1985 as an

Roy. Soc. Lond. 48(1), 135–41 (1994); R.E. Peierls, ‘Yakov Il’ich Frenkel’, Physics Today 47(6), 44–49 (1994). 1252 See publications: R.E. Peierls, ‘How deep is deep enough?’ Proc. 37th Pugwash Conference, Sept. 1987, London: Taylor and Francis, 1987, pp. 414–16; R.E. Peierls, ‘Test Ban and Veriﬁcation’ ? Proc. 39th Pugwash Conference, July 1989, London: Taylor and Francis, 1989, pp. 311–12; R.E. Peierls, ‘Energy Conservation?’ Proc. 40th Pugwash Conference, Sept. 1990, London: Taylor and Francis, 1987, pp. 530– 31; R.E. Peierls, ‘Why are nuclear weapons tests claimed to be necessary?’ Proc. 41th Pugwash Conference, Sept. 1991, London: Taylor and Francis, 1991, p. 372. See also R.E. Peierls, ‘Strategic Defence Initiative’, Phys. Bull. 37, 217 (1986); R.E. Peierls, ‘Is there any logic in the Arms Race?’ The Challenge of Nuclear Armaments, (eds. A. Boserup, L. Christensen, O. Nathan), 379–80 (1986); R.E. Peierls, ‘The case for defence’, Nature, 328, 583 (1987). 1253 R.E. Peierls, C.R. Hill, R.S. Pease, J. Rotblat, Does Britain need nuclear weapons? London: British Pugwash Group, 1995.

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organisation mainly concerned with nuclear disarmament.1254 Peierls became a ‘Patron’ in 1985 and a director in 1986 until his resignation in 1989, and he chaired the local Oxford group with many of the meetings taking place in his ﬂat. In June 1989, it was decided that the local FREEZE group should not continue independent operations but instead co-operate with the Oxford Research Group (ORG), a registered charity which carried out independent research into decision-making, accountability, intergovernmental mediation and other topics with special reference to nuclear weapons. In 1989 Peierls became a ‘friend’ of the ORG. Among the friends and colleagues with whom Peierls corresponded most frequently about nuclear disarmament issues were Hans Bethe and, closer to home, Nevill Mott. The latter had been an active member of the Pugwash Movement himself, and he also participated in activities of FREEZE. The two often exchanged ideas, generally agreeing on the overall aim of arms control, but disagreeing about the best method of achieving this.1255 Although Peierls was no longer keeping up with scientiﬁc developments on a large scale, he still took an interest in science policies, followed general trends and engaged in some debates with colleagues on conceptual issues. One example of this is his concerned letter, in 1991, to Mark Richmond, the Chairman of the Science and Engineering Research Council, arguing against the planned closure of the Nuclear Structure Facility at Daresbury.1256 Peierls’ line of reasoning not only demonstrates his enthusiasm about nuclear physics, but ﬁrst and foremost insight in science teaching and training which was still applicable in the 1990s. Towards the last years of his life, Peierls thought about two scientiﬁc issues in particular — questions of measurement, which he had been in

1254 The organisation had several changes of name including Towards a Safer World (1988), safer world project (1989) and Saferworld (1991). For most of the time of Peierls’ involvement (1985–1989) it was known as FREEZE. 1255 See for instance letters [869–872]. 1256 Letter [894].

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dispute over with John Bell for some time,1257 and the discussion of symmetries and broken symmetries. Peierls had exchanged views with P.W. Anderson about this issue in an open controversy largely through the medium of academic journals,1258 and it was on this topic that Peierls delivered his last published and public lecture, the Dirac lecture in 1992.1259 As evident in correspondence about his Russian trip in 1987, Peierls took great interest in developments in East and Central Europe. This did not only concern Russia, but also his native Germany, and in particular East Berlin, where he had grown up. Shortly before the opening of the borders between East and West Germany, in June 1989, Peierls received a letter from an East German lady, Waltraud Krause, who was a close friend of one of Peierls childhood friends in Obersch¨ oneweide. This letter was the beginning of a lively exchange between the two, culminating in a visit of Rudolf Peierls to his home suburb in Berlin in 1990, when he visited the local history society, led by Frau Krause.1260 This visit was a walk down memory lane which allowed Peierls to meet some acquaintances whom he had not seen for well over half a century. During the last years of his life, Rudolf Peierls was troubled by a number of health problems, and he suﬀered a deterioration of his eyesight which restricted his reading and made correspondence more diﬃcult. Despite all this, he continued to lead an active and independent life well into his eighties. In the summer of 1994 however, after suﬀering a combination of heart, lung and kidney problems, he decided to move into a residential home close to Oxford. It was another crucial stage at the dawn of Rudolf Peierls’ life, and another step which his close friend from student days, Hans Bethe, shared in thought. On hearing of his

1257

R.E. Peierls, ‘In defence of measurement’, Physics World 4(1), 19–20 (1991); this was a reply to John Bell’s ‘Against “measurement”’, Physics World 3(8), 33–40 (1990). See above introduction to Chapter 10, notes 1060–1061. 1258 See P.W. Anderson, ‘Broken Symmetry can’t compare with ferromagnets’, Physics Today (5), 117 (1990); R.E. Peierls, ‘Spontaneously Broken Symmetries’, J. Phys. A 24, 5273–79 (1991). 1259 R.E. Peierls, ‘Broken Symmetries’, Contemporary Phys. 33, 221–26 (1992). 1260 See Peierls Papers, and Peierls’ letters in Waltraud Krause’s possession.

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friend’s illness, Bethe sent an encouraging letter of reminiscences1261 — to which Peierls, in visibly frail hand writing, replied with similar recollections.1262 Having been independent since leaving home well over sixty years earlier, Peierls nevertheless settled well into his new environment, one of the few residents at Oakenholt who would word-process circular letters to friends and family and read scientiﬁc papers in enlarged script on a computer screen! But his health deteriorated further throughout 1995. It was evident to Hans Bethe, in early September 1995, that the friend he had made almost seven decades earlier at Sommerfeld’s seminar in Munich, would be taken away from him. Bethe sent his farewell, again recalling their interconnected lives and their long-lasting friendship and he summed up their shared experiences: ‘It is good to remember all those days · · · You had a full and good life, and I thank you for letting me participate in it.’1263

1261

Letter [933]. Letter [934]. 1263 Letter [936]. 1262

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[838] Hans Bethe to Rudolf Peierls [Ithaca], 26.10.1986 Dear Rudi. We are both very sad that Genia died. She was one of the greatest personalities I have known. Genia had a great inﬂuence on me, during our year together at Manchester. Early on, she told me “Sie sind doch sehr nett”. Surely she and you have long forgotten that. But it gave me more self-conﬁdence in a personal sense, as did my whole life with the two of you. It was the best preparation for my life in America. She taught me that diﬃculties in external life are problems to be thought about and solved not to be worried about. There were so many good times afterwards: The vacation in Devon 1936 (or 1935?); I still remember Tintagel. (What did you do with Gaby and Ronnie that summer?) Many happy visits to Birmingham, without and with our children. Life together at Los Alamos, and later in Seattle where you were almost part of the department while we were just frequent visitors. One of the greatest things Genia did was the education of Jo. As soon as she knew that Jo was a dwarf, she centered all her life on Jo. She studied what one can do to strengthen the body of a person of that type, how to make her use her limbs, and generally prepare her for a normal life. She did all those things for Jo and she succeeded. Sometimes it was annoying when Genia wanted to arrange everybody’s life. I felt this on occasion when Henry had such deep psychological trouble. By then, however, I was old enough so I could ignore it. You were always marvelously tolerant. Genia lived a full life, and a good life. She helped dozens of people, in addition to her family. How could she be so wise already when she was so very young? How old was she in Manchester? 25? Rose called Betty Brown, Gerry’s wife, but Ronnie had already done so. She also called Ruth Uehling who will tell it to others in the department in Seattle. Rose and I are happy that we saw you once more, and had such a good time together, end of June last year. Genia seemed so happy at

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that time, being restored after her disabilities a year ago. I am glad she had that year. Another good year after a very full life. We will long think of her. Yours, Hans

[839] Rose Bethe to Rudolf Peierls [Ithaca], 27.10.1986 Dear Rudi. “Als w¨ar’s ein St¨ uck von mir”, the old song goes through my head as I think of Genia. Without much overt evidence of response from me she was a companion of my life since I ﬁrst met you both in Cambridge in 1939 on orders from Hans to tell you that we were after all getting married. She was very strict then — not to spoil what she had accomplished in socialising Hans and making him into a “good” husband, by which she quite speciﬁcally meant that he would help in the house. She and you — you and she, diﬀerently yet inseparably, have been Hans’ dearest friends since your common Manchester time more than half a century ago. It is as yet impossible to think of you without her, but, she would say ﬁrmly, that is a matter of time. If you are continuing your nomadic life, please come and stay with us for a while. After that very brief meeting in Cambridge, I next saw Genia in New York, in 1944. By then I had heard many stories and quotes of admonition. I was 8 months pregnant and she lived up to her reputation, as she instructed me what to do should the baby come on the train back to Los Alamos. But chieﬂy we talked about England and the war, and her happiness at having Gaby and Ronnie with her again. Later, in Los Alamos, she had other companions and I have wondered since whether she, too, dropped into that strange limbo in which purpose was centered on winning the war, and yet the war itself was a tale, a theory, a background to a daily life that was comfortable, routine, normal or did it retain for her the reality which it had been in England? In any case, her boundless energy brought variety and joy to life on the mesa.

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We certainly were the beneﬁciaries of this, especially when Hans needed a vacation from work as well as fatherhood and she took care of Henry for two weeks. He was then 7 months old and of course “completely” spoiled by his mother. I had a vivid picture of how she had projected herself into him when she came to visit the ﬁrst time after Henry was back with me, and he looked at her calmly, without fear and said in a loud decisive voice “NO”. She was delighted. It was his ﬁrst word and remained his only one for a long time. You will be inundated with stories now, of Genia’s impact on old and young, of her generosity, of her vitality, sagacity, love of life and people. I am very glad that she is part of Hans’ and my life. Isn’t it good that you were here last spring and we could visit you in June! My mother asks to tell you that she thinks of you with profound empathy and sympathy. She is basically well, but most of the time very tired so that she feels no longer up to writing. Please give my love to Jo. Yours, Rose

[840] Freeman and Imme Dyson to Rudolf Peierls Princeton, 1.11.1986 Dear Rudi. Yesterday Gaby called and told us the sad news. This did not come as a complete surprise since we had heard from Gerry Brown that Genia was back in the hospital. Still we had hoped and expected that she would bounce up again from this disaster as she had bounced up from so many disasters before. I have in front of me her wonderful letter from January of this year, bursting with her usual high spirits: “I am improving and can now walk quite respectful distances and still am thrilled to be “me” that I am bursting with delight every morning.” What a woman! Then most of the letter is an accurate diagnosis and discussion of Katrin’s problems, with a bit about Jo, nothing about herself. Finally at the end a bit about

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you: “After being married to Rudi for 55 years I was quite surprised at his performance during my troubles. He worked, washed, cleaned and nursed me with greatest skill. And even folded the clothes which I never did! Now when I am functioning again, he is peeved to see me in his kitchen.” It will be hard for you being again alone in that kitchen. But it is good to know that she was her indomitable self, full of joie de vivre and plans for the future right up to the end. She was like you in many ways. She understood the importance of Leo Szilard’s Tenth Commandment: “Lead your life with a gentle hand and be ready to leave when you are called.” We hope you will come and see us here more often now you are alone. I enjoyed very much the lunch and walk in the woods when you were here last time. Consider yourself invited whenever you feel like coming. We also had been looking forward to seeing both Genia and you at the Pugwash meeting in Austria in September ’87. Now we both look forward at least to seeing you. You and I are both supposed to be talking about international cooperation in space. I would be glad to know what you are intending to talk about. I will probably be talking mostly on the theme “Think Small”, saying that what the world needs is not grandiose spectacular projects but modest collaborative missions that do good science and are cheap and quick.1264 A large fraction of groundbased astronomy is in fact organized in this fashion, with international collaborations that work well, and this should be the model for spacescience. Does this ﬁt in with what you are planning to say? Please let me know if it doesn’t. Another request while I am writing to you. I would be grateful for a copy of your Dirac obituary for the Royal Society1265 if you have one available. I am supposed to write a much shorter obituary for the American Philosophical Society and so I would be glad to make use of 1264

Dyson further elaborated on this theme in the three Danz lectures, delivered at the University of Washington in April 1988 and reproduced in F. Dyson, From Eros to Gaia, Harmandsworth: Penguin, 1993, pp. 8–66. 1265 See letter [831], note 1220 and introduction to this chapter, note 1251.

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your facts (of course I will acknowledge your help, if you do send me a copy).1266 I have almost no independent information about Dirac and so it seems reasonable to make use of yours. Thank you very much for this, if you can do it. While Genia was dying we had a 3-day meeting in Cornell on Supernovas at Cornell to celebrate Hans Bethe’s 80th birthday. It was a small meeting, mostly supernova experts and people who worked directly with Hans. Hans was in good form, physically frail but intellectually still the old Hans. We did not know then that Genia was sick, and we were saying it was a pity you were not there. It was good to be back again at Cornell with Hans and Rose and a new bunch of bright new physicists. I don’t need to tell you how much I owe to Genia and how big a part of our life she was. All I will say is, I owe as much to you as to her, and you are a big a part of our lives as she was. Yours ever, Freeman and Imme

[841] Rudolf Peierls to I.M. Khalatnikov Oxford, 4.11.1986 (carbon copy) Dear Khalat, Thank you very much for your telegram. Genia’s death has stunned us all, but we take some comfort from the facts that the last year was for her the best year of her life, and that she suﬀered only for a few hours. You will of course understand that the plans for the visit to your Institute had to be cancelled. I know the invitation is good for the rest of this year, but I am afraid I do not think I shall within two months be in a ﬁt condition to go visiting. I am sorry to disappoint you, because I knew you wanted to be sure that the invitation would be accepted. But nobody could foresee how things would develop. 1266

F. Dyson, ‘Paul A.M. Dirac’, American Philosophical Society Yearbook for 1986, Philadelphia: Am. Phys. Soc., 1987, pp. 100–105.

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If it were possible to get a similar invitation for a visit in 1987 I would be very interested.1267 I now enclose the article on Landau, which I had hoped to write during my visit.1268 It is made up of pieces from my book, with some connecting text. I hope it is suitable. I had also a request from Okun’ for an article on Landau; I assume this was for the same volume? With best wishes, Yours sincerely, Rudolf Peierls

[842] I.M. Khalatnikov to Rudolf Peierls Moscow, November 1986 Dear Rudi, I would like to commiserate with you in your grief over Zhenia’s decease. All of us who knew her in life, will remember her. We are glad that you in principle have in mind to visit our country, and we would be happy to welcome you here any time next year you ﬁnd suitable for you to come here. Our invitation is valid for 1987 also and you could use it for getting your visa when necessary. Thank you for your recollections of Landau, they are already being translated now and will be included into our book without changes.1269 With our best wishes of good health to you, Sincerely yours, Khalat 1267

Peierls did in fact travel to Russia in 1987 and again in 1988. See ‘Chronology of the Life of Sir Rudolf Ernst Peierls’, in R.H. Dalitz and Sir Rudolf Peierls (eds), Selected Scientiﬁc Papers od Sir Rudolf Peierls, Singapore: World Scientiﬁc Publishing, 1997, p. XV. See also letter [873]. 1268 The article was later published as R.E. Peierls, ‘My recollections of Landau’, in Landau, The Physicist and the Man (ed. I.M. Khalatnikov), Oxford: Pergamon, 1989, pp. 194–97. 1269 See letter [841], note 1268.

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[843] Viktor F. Weisskopf to Rudolf Peierls Cambridge Ma., 10.11.1986 Dear Rudi, The news of Genia’s death was a terrible shock. An essential part of our world is lost. You know how fond both of us were of Genia, how much of our jest of life came from her positive human approach and her personal interest in the troubles of her friends. But it is more than that. It symbolizes the end of a world, of a way of life for us. From the moment I met her ﬁrst in 1932 in Russia, she represented the human side of our community of scientists. I remember so vividly the time we spent together in Cambridge in 1933, the Los Alamos years, and the many encounters later on and in the early days. Remember the skiing without snow in Kitzb¨ uhl (1934)? Rudi, for you, I know it must have been a loss beyond any limits. I don’t dare to think how I would feel or what I would do in a similar situation. We know you are a strong character and there are many things, not only physics, that make life worthwhile. We are with you and we hope that you will ﬁnd a form of life that is bearable. After all you have your children. Surely Johanna will be able to help you. She knows what she owed to Genia. It will take time, be patient and think of your friends all over the world. As ever, and even more so, Ellen + Viki

[844] Hanni Bretscher to Rudolf Peierls Cambridge, 14.11.1986 Dear Rudi. For all of us who knew Genia the world must seem a bleaker place without her. Thus my deepest sympathy goes to you.

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I will always remember Genia as the most generous person. In about 1941, she was visiting the Kowarskis in Cambridge. At the time, Scilla was there playing with Irene, so Genia said to Scilla, “Tell your parents that I am in Cambridge”, to which Scilla answered, “they know, Daddy has already locked the backgate.” Genia: “then tell them they don’t need to lock the back gate, I will come straight to the front door in future.” I was very grateful to Genia that she did not let this incident spoil our relationship. You probably know that I wanted to come over to Oxford to talk about your book. With visits of all my North American children to Europe this summer, I was kept busy and did not make it. I hope you will be over in Cambridge soon and able to see me; otherwise I will contact you at a suitable occasion. Meanwhile, with my best wishes, Yours sincerely, Hanni

[845] Lillian Krynen to Rudolf Peierls Nerfa, 27.1.1987 Dear Sir Rudolf, Thank you very much for your card which was forwarded to me by my son Robert from Brussels! I am so very sad that your wife died without my ever meeting her! Words come diﬃcult to me, for I do understand only too well, when you lose your partner, as I also lost my husband after 34 years of happy marriage — it is hard to replace. I would be very happy to come and see you as my father told me so much about you! Will sometime in March be alright? As I shall return to Brussels again end of Feb[ruary]. Please let me know, if you will be there; so I can make some arrangements to see you.

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Hope you are well and that you have adjusted some again. With a warm handshake in sympathy I remain Yours Lillian Jacobsohn Take care, look forward to see you.

[846] Lillian Krynen Jacobsohn to Rudolf Peierls [location unspeciﬁed], 24.2.1987 Dear Sir Peierls, Thank you very much for your letter of 19th Feb[ruary]. We both had each other in mind. In the meantime we did talk over the phone and it was nice to talk to you. My plans are now that I shall be in London on the 18th of March, will call you as soon as I am there. Thank you very much for your kind invitation, I will love to see something of Oxford and meeting you! With my warmest regards, Lillian

[847] Rudolf Peierls to Marvin Goodman Oxford, 8.3.1987 (carbon copy) Dear Dr. Goodman,1270 I am writing in reply to your letter of 22 January, addressed to Seattle.1271 I do not know the answer to your question about the meaning 1270

Marvin Goodman, Department of Mathematics, Monmouth College, West Long Branch, New Jersey 1271 Letter Marvin Goodman to Rudolf Peierls, 22.1.1987, Peierls Papers, Supp. A.9.

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of life. I do not even know whether it is a real question, in the sense that if someone claimed to have an answer there was any possibility of ﬁnding out whether it is right or wrong. This absence of an answer (or is a question) does not trouble me. Life confronts each of us with a situation not of our choosing, and faces us with the need to make choices. We try to do so as best we can, unavoidably making mistakes, errors of judgement, omissions and neglect, sometimes not noticing, and not acting upon, the need of others near us. All this is part of life, but in between there are moments [when] things go the right way, and we can contribute a little to making things better. I do not believe, as you do, that there is more injustice, more cruelty, more unhappiness in our time than in the past. Because of modern means of communication we are better informed. Also, there are many more people in the world, and tragedies that used to aﬀect a few people, now aﬀect many. But occasionally there are also opportunities of getting something constructive done on a large scale, as with “band-aid”, or the present aid to Mozambique. I do not believe that war is inevitable. Extrapolating from the cell to the human and to society is quite superﬁcial, and history does not repeat itself, “only historians repeat each other”. Of course there is danger of war, and one must work to reduce it. On the question at the end of your letter: What keeps me going is the natural desire for survival, coupled with the pleasure it gives to achieve something useful, or to give pleasure to others, or to comfort them in trouble. I have never found any use for religion. Encouragement in dark moments? Perhaps the experience accumulated in nearly 80 years of life that there will be another day. When things go wrong it helps to face the situation, and not to try to hope against hope. In the words of my late wife: “When you have hit rock bottom, the only direction is up.” Yours sincerely Rudolf Peierls

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[848] Lillian Krynen to Rudolf Peierls [location unspeciﬁed], 25.3.1987 Dear Rudi, First of all — I would like to say, how [wonderful] it was to meet you ﬁnally! You are ﬁrst as active as I am, that is our secret of being so young — you really have inspired me with your good cooking — without fuss! I likes that — came back well + did not lose my way — now I know how to go by tube. Thank you ever so very very much for showing me a little of Oxford, but there is still so much to see for next time. Hope your trip will go all well and do keep in touch, Rudi. We have something in common. Hope to see you here next time or in Spain! Love, Lillie

[849] Rudolf Peierls to Norman Moss [Oxford], 26.5.1987 (carbon copy) Dear Mr Moss, Thank you very much for the copy of your book.1272 I did not acknowledge it immediately as I was waiting for a chance to read it properly. I have now done so and found it very interesting. I think you have presented the complicated personality of Fuchs very well. I would not always follow your speculation about his inner thoughts and motivation, but in general I think you have got the picture right, very clearly presented. 1272

Norman Moss, Klaus Fuchs. The Man Who Stole the Atom Bomb, London: Grafton Books, 1987.

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It is a pity that, in areas of which I have direct knowledge, so many details are inaccurate, confused, or just plain wrong. Here is a list of those I have noticed, so you could, if you agree, correct them if the book goes in to a second printing, as I hope it will. Here is the list: p. 7, l.18 The black-red-gold ﬂag of the Weimar Republic did not have vertical bars. p. 28 l.12 When particles leave the atomic nucleus, energy is used, not released. Energy is released when particles enter light nuclei (fusion) or when a heavy nucleus splits in two (ﬁssion). p. 43 l.23 It is most unlikely that the Oxford team should have examined the possibility of electromagnetic separation, as they had no experts in the ﬁeld. p. 44 l.6 The visit in question was in the beginning of 1942, not the end (January or February). p. 46 l.11 “a few others”. The number of British scientists at Berkeley and Oak Ridge was considerable. p. 52 l.20 We were not listed as employees of the Kellex Corporation, but as employees of the British Supply Mission. p. 53 l.8 I did not tell Hunter College I did not require the girl’s services, but explained that I was not allowed to hire a black girl. p. 66 l.12 Bethe came to England in 1933 not 1934. p. 69 l.8 from below: Most scientists in Los Alamos had cars. p. 71 l.7 The purpose of the lenses is just the reverse of what you state: they are to make the detonation waves from the diﬀerent ignition points arrive simultaneously and uniformly over the surface of the sphere. Same page, l.8 Teller was not working on “Plutonium ﬁssion reactions” but on the mechanism of implosion. I then took over his group with this assignment. p. 72 l.3 I am not aware of the mathematical method for dealing with compressed plutonium devised by Fuchs, which is still in use today. Same page, third para. The weekly colloquium was attended by the whole scientiﬁc staﬀ. Fuchs was invited to the “coordinating council” which met more rarely, and which comprised mainly group leaders and a few others.

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p. 78, l.19 Frisch did not “hit on the idea of nuclear ﬁssion”. He did the ﬁrst experiment to observe ﬁssion fragments. p. 84 l.9 Frisch’s part in the pantomime was not an Indian maiden, but an Indian maid (Indian women were the standard household help in Los Alamos). p. 86 second para. My recollection is that the trip to Mexico was earlier than November, and before most of the British left. In the last but two line of the paragraph “they” should read “he”. p. 90 l.11 & 12. The name Placzek is misspelled. Diﬀerent wrong spelling appear elsewhere. Same page l.24 Queens University is in Kingston not Windsor. p. 92 l.14 A.P. French is an English scientist, although he is now in America. p. 108 l.6 from below: “Ivor Gurney” is presumably Ronald. p. 122 l.22 “terror” is presumably a misprint for error? p. 131 last few lines and over the page: It would not have been Fuchs’ assignment to analyse the samples, as he was a theoretician. He would have been asked to interpret the results of the analysis. p. 154, l. 9 from below: “Gieser” should presumably read Gisela. p. 172 p. 8-9 The sentence is not intelligible. Should “so” read “to”? You will understand that the length of the list makes me a little sceptical about details in the parts I do not know about. Yours sincerely, Rudolf Peierls

[850] Hans Bethe to Rudolf Peierls Ithaca, 27.5.1987 We are making preparations for our trip to Europe, especially our visit to Oxford. I seem to remember that you will leave immediately after the celebration on Saturday, 27 June.1273 But in case you don’t leave 1273

This refers to the planned celebrations of Rudolf Peierls’ 80th birthday.

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quite so immediately, we have decided to stay in Oxford on Sunday until 15.00, and would love to see you if you are there. We are staying at the Linton Lodge which is very close to you. It would be very nice, if you have time to do so, if you would send me a note saying whether you will be there on the 28th, c/o my sister, c/o Doris Overbeck Rebenweg 8 5450 Neuwied 23 West Germany Yours sincerely Hans

[851] Heinz Rudolph to Rudolf Peierls [Berlin], 27.5.1987 Lieber Rudi! Lange habe ich nichts von Dir erfahren. Auch eine Kopie Deines Jahresberichts f¨ ur Deine Freunde und Bekannten, u ¨ber den ich mich stets freute, vermisse ich in diesem Jahr. 1986 war f¨ ur mich ein schlechtes Jahr! Am 19. Dez[ember] starb ganz pl¨ otzlich meine Frau. Das traf mich hart, und dar¨ uber kann ich nicht hinweg kommen. Sie litt seit u ¨ber 30 Jahren hochgradig an Rheuma und hatte zeitweilig starke Schmerzen. ¨ Im vorigen Jahr kam eine Angina pectoris hinzu, die das Arzteteam in der Klinik wegen des Rheumas, des Alters (79) und des Allgemeinzustandes meiner Frau nicht zu operieren wagten, sondern eine Besserung durch Medikamente erreichen wollten. Nach zwei schmerzhaften N¨achten im Dez[ember] beschlossen meine Frau und ich, sie in die Klinik zu bringen. Bevor der Sanit¨ ater sie morgens abholte, starb sie aber v¨ ollig unerwartet in meinen Armen. Mit einem so pl¨otzlichen Tod hatten wir beide nicht gerechnet. Im Gegenteil, wir hatten noch vor, viel zu reisen.

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Weihnachten verbrachte ich mit unserer Tochter in Berlin, die dort Schauspielerin ist. Ende Januar kehrte ich nach N¨ urnberg in unser nun so leeres Haus zur¨ uck. Zur Zeit bin ich wieder vor¨ ubergehend bei meiner Tochter in B[erlin], die versucht, meine Trauer und meinen Kummer zu lindern. Man soll, lieber Rudi, die Zweisamkeit einer Ehe geniessen, so lange sie einem verg¨ onnt ist! Das Leben ist so kurz und der Tod ewig! Herzlichst Dein Heinz R[udolph] [852] Rudolf Peierls to Heinz Rudolph Oxford, 1.6.1987 (carbon copy) Lieber Heinz, Das war wirklich ein schlechtes Jahr f¨ ur Dich — und ebenso f¨ ur mich, denn meine Frau starb am 25. Oktober. Die Einzelheiten sind in dem beiliegenden Jahresbericht. Ich h¨ atte Dir das nat¨ urlich schon schicken sollen, aber ich habe das als Antwort auf die sehr zahlreichen Kondolenzbriefe ben¨ utzt, und dann die Leute u ¨bersehen, die in der Ferne leben und nichts von Genia’s Tod wußten. So sind wir jetzt beide sehr allein. Meine Frau gab immer einen guten Rat f¨ ur solche F¨ alle: “In unserem Ged¨ achtnis gibt es Ringe, wie bei einem Baum. Nach dem Tode eines Gatten ist es wichtig, bald neue Ringe zu entwickeln. Zuerst ist jede Erinnerung an die Vergangenheit schmerzhaft, weil jedes Erlebnis, jeder Ort, immer mit dem Bild des Gatten verbunden ist. Man soll versuchen zu reisen, neue Besch¨aftigungen, neue Eindr¨ ucke zu ﬁnden. Dann hat man nach einiger Zeit neue Erinnerungen, die nicht mehr weh tun.” F¨ ur mich ist das relativ leicht, denn ich reise noch immer sehr viel herum, und da sind auch immer neue Aufgaben, von denen viel zum Beispiel mit der Frage der Kernwwaﬀen und der Entr¨ ustung1274 zu tun 1274

Peierls used the word ‘Entr¨ ustung’ (indignation) instead of ‘Ab¨ ustung’ (disarmament).

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haben. Ich habe auch entdeckt, daß mir Kochen Spaß macht, und da es sehr langweilig ist f¨ ur einen zu kochen, lade ich so oft wie m¨ oglich Freunde zum Essen ein. Auf solche Weise baue ich mir schon ein neues Leben auf — es ist nat¨ urlich nicht dasselbe Leben wie vorher, aber es gen¨ ugt schon f¨ ur die paar Jahre, die noch u ¨brig sind. Ich muß Dich um Entschuldigung bitten, daß ich so lange nicht geschrieben habe — Deine Weihnachtskarte lag noch immer bei den Briefen “dringend zu beantworten”. Mit herzlichen Gr¨ ußen Dein [Rudi]

[853] Rudolf Peierls to Lillie Krynen Oxford, 21.6.1987 (carbon copy) Dear Lillie, No word from you for a long time. Did you get stuck in America, or did my two letters fail to reach you? Or have I done something to oﬀend you? That would distress me greatly — during your short visit we seemed to understand each other so well, that it would be a pity if some misunderstanding were to spoil it. I tried to phone, but the exchange ﬁrmly denied your existence — presumably you have an unlisted number. I had a lot of family around for my 80th birthday (it was the best 80th birthday I ever had!) and at the end of the week, my former department is putting on a one-day symposium to mark the occasion. Then I rushed oﬀ to a conference in Turin, only to rush back a week later for a live TV discussion involving Edward Teller, which goes on for three hours from midnight. I shall need a few days to recover, but it will be fun! I hope some time to get a sign of life from you. Love, [Rudi]

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[854] Rose and Hans Bethe to Rudolf Peierls Zurich, [date unspeciﬁed] Dear Rudi, I am so very sorry that I cocked out on Sunday! A rare opportunity missed. I am doubly glad that I was placed next to you at the banquet. I only hope this proximity did not pass the ﬂu on to you. You’ll know by Thursday. (I presumably caught it from my brother who presumably picked it up in Israel — so it’s a good Jewish ﬂu.) It was lovely of Chris to drive us.1275 I wrote him the enclosed card and then realized that I had forgotten his last name — and so has Hans. Would you be so kind as to write an address on the card and send it on? Thanks! Hans gives his lecture tonight, tomorrow and Thursday, and then we are oﬀ to Zermatt and two weeks of walking. Happiness for both of us. Thanks you for providing the occasion to come to Oxford to see you, and to share in what must be in the range of the 400.000th meal in the dining hall of New College. With warmest love, Rose 30.6.[1987] It was lovely to be in Oxford. I enjoyed seeing many people from the past, and seeing how many diﬀerent subjects you are connected with (of course I knew that). The best was the lunch on Sunday in the circle of your family. Rose has recovered from her cold, Zurich is sunny and hot, and we are enjoying it. Thank you once more and good luck for the TV debate!1276 Hans 1275

Chris Coppin, Rudolf Peierls’ son-in-law, had driven the Bethes to the airport to travel on to Switzerland, as Rose Bethe was still ill with the ﬂu. 1276 Rudolf Peierls was about to engage in a television debate with Edward Teller to be broadcast the subsequent week. See letters [853], [855–856].

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[855] Rudolf Peierls to Lillian Krynen [location unspeciﬁed], 13.7.1987 Dear Lillie, Thank you for your card and for your phone message. I would have written sooner, but your message said you would phone again last week, so I waited for your call, which never came. Since I last wrote,1277 we had the symposium to celebrate my birthday. A day of lectures, by former pupils, colleagues, and a dinner in the evening. It was very friendly and informal, and a lot of old friends came, so it was very enjoyable. It was on a Saturday and many of the visitors stayed till Sunday, and we had some to lunch and some to tea, so the Sunday was very busy. Then by Monday all my family had departed and I left myself for Turin, where the conference was interesting and instructive, but it was too hot. Then I rushed back for the TV debate, which was only 2 12 hours from 12.30 to 3 a.m. Teller is the driving spirit behind the “Star Wars” programme, which is complete nonsense, so it was fun to argue with him and with some other people. I heard from many people who actually stayed up to watch the programme; others recorded it on their video recorders. After all this excitement, life is quite peaceful again, and I am trying to make progress with a book I am writing. I ﬁnd I am waiting rather impatiently for your promised call — are you an impulsive person, given to changing your mind, and I like that, but I feel frustrated in not knowing your phone number. I even toyed with the idea of coming to Brussels for a day or two in early July, but how to arrange that? Now it is too late. I shall be in Trieste and then in Austria from 6 August to 7 September. Perhaps I could come for a short visit in September? Do disclose your secret phone number! Love [Rudi] 1277

Letter [853].

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[856] Rudolf Peierls to Hans Bethe Oxford, 24.7.1987 (carbon copy) Dear Hans, Thanks you for your letter and card from Switzerland.1278 I know you are back safely, because I have just been with the Marshaks at the Bristol Conference, who came straight from the encounter at Kennedy.1279 The TV debate went more or less as predicted. The group consisted, besides Teller and myself, of Sergei Kapitza, Enoch Powell, a woman writer (very CND) and a catholic nun. I cannot remember the name of the chairman, who did not interfere much, except when several people wanted to speak at the same time. Before we went on air, Edward started a violent quarrel with the chairman, who read out a few sentences about each of us, which he was going to use as introduction. About Teller one of these sentences was “· · · who is sometimes called the Father of the Hydrogen Bomb, although he does not like this title.” Edward blew up and said it was discourtesy to quote that title when it was known that he disliked it. After a long and violent argument, which almost delayed the programme, the chairman agreed to drop the sentence. It turned out that the title of the programme was not, as I had been told, Star Wars, but “Peace in our Time”, so the discussion was on two levels, one consisting of the two ladies saying how dreadful were nuclear weapons and (in the case of the nun) how immoral it was to use force in any circumstances. This was very eﬀectively, if kindly, dealt with by Enoch Powell, who was, for a politician, very restrained, and was very sensible and intelligent. Edward was quite predictable. When he told us how far ahead the Russians were with sophisticated defence, I said “This information could 1278

Letter [854]. Hans and Rose Bethe had attended the festivities commemorating Rudolf Peierls’ 80th birthday in Oxford on 27 and 28 June 1987. They had then travelled on to Switzerland before returning to the US. 1279

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only come from intelligence reports and I understand that people who have access to intelligence reports do not have that impression”. He did not comment. Sergei Kapitza told me afterwards he was very grateful for this, as it would have been diﬃcult for him to say this. I also raised the question how S.D.I. aﬀected Europe, was it expected to defend us as well? To which Edward said it was Reagan’s policy to be open and share information with everybody who would participate, even the Russians. So I reminded him that so far the “sharing” amounted to the European being allowed to work on some small problems whose answer would assist the S.D.I., but they were not told the overall design and there certainly was no indication of hopes to protect Europe. In view of the short ﬂight times, this seemed even harder than to protect the US. Incidentally he did not claim that a complete shield was possible, nothing could ever be perfect, but it was possible to bring down a large fraction of the missiles. The obvious answer to this came from Powell. I cannot of course remember all the details of the debate, I have a videotape, but have not yet looked at it, as I do not have a video machine. I want to look at it, because they ran some commercials during our discussion, so that some passages got lost (without telling us) and I am interested to see what got lost. I did not of course expect to convince Teller any more that I expected he would convince me, but I think some of the viewers will have seen the weakness of his position. In fact someone said it was not really necessary for me to say anything, it was enough to listen to Teller! I was very grateful for the brieﬁng you gave me, which was a great help. Nature accepted my review without any substantial change.1280 I checked the question of City College vs University College by asking 1280

R.E. Peierls, ‘The Case for the Defence’, Nature 328, 583 (1987); review of Teller’s book Better a Shield than a Sword: Perspectives on Defense and Technology, New York: Free Press, 1987.

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Teller, and he said “O dear, did I say City College?” So I could let the sentence stand.1281 Best wishes to Rose and her mother. Yours [Rudi]

[857] Rudolf Peierls to Abdus Salam Oxford, 17.9.1987 (carbon copy) Dear Abdus, I am writing, in the ﬁrst place, to thank you for the hospitality which I enjoyed during August. It was a most interesting and proﬁtable, as well as pleasant, time for me. I have to thank you also for the — quite unexpected — award of a medal.1282 In conferring it you very generously referred to me as a friend of the Centre, although you no doubt knew that I had opposed the plan for its foundation. Of course it is right that, once the Centre came into being, my only interest was to see it prosper and succeed, and therefore perhaps I do deserve being called a friend. As you may remember there were two grounds for my early opposition. One was a fear that the Centre would have the eﬀect of persuading many of the young theoreticians from the Third World to go into particle physics, which is one of the most diﬃcult specialities to pursue in academic isolation and without access to relevant experimentalists. It would of course be quite wrong to stop third-world scholars from choosing that subject (or any other) if they feel a passion for it, but it would 1281

In his review, Peierls refer’s to Teller’s absent-mindedness, which he illustrates by Teller’s references to a stay at City College London, whereas he had stayed at University College. 1282 Peierls had been awarded what he called a ‘minor medal’ during his visit to Trieste on the occasion of the Newton Celebrations in August 1987. See ‘Dear Everybody’, 9.9.1987, Peierls Papers, Supp. A.26.

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also be wrong to indoctrinate them in the view that this is the only part of physics that matters, or that has challenging problems. By now this danger has been averted. It may have been present in the early years, but the growth and vigour of the condensed-matter activities has provided the required balance. My other objection was that the “mix” of senior, experienced theoreticians without younger people lacking in experience (mostly from the Third World) would not be right. This is the main reason why I would have preferred a scholarship and Fellowship scheme which would have allowed third-world students and fellows to get to existing active departments, where they would be in a minority and could be exposed to the views, the advice, and the spirit of experienced colleagues. I now appreciate that, though the funds required for such a scheme might have been less than for the centre, they might have been harder to raise. In any case there is no point in arguing what might have been. But I have come to the conclusion, after my visit, that there was some substance in my worry, and that one can feel in the Centre, at present, that the ratio of senior to junior (or experienced to inexperienced) people is too low. As a result, all young participants are exposed to the lectures and seminars (although some, as you complained to me, do not even bother to attend) but they have very little personal contact with the seniors. I have, of course, seen the position only on the condensed matter side, but would guess that it is general. I was told also, of many people who got their Ph.D. somewhere by a thesis on a small piece of the subject, and who are now determined to continue for the rest of their careers working in the same narrow ﬁeld. They probably attend lectures and seminars, but do not try to get into the new ﬁelds to which they are exposed, but spend their time in the library beavering away at their own little piece. The reason could be that they just lack the necessary scientiﬁc curiosity, but no doubt close contact and discussion with people of broader views might help them. Can one do anything about this? I think I see one possibility, and that is why I am writing all this. My idea would be to arrange for every junior person to have eﬀectively a supervisor. Now one must not, of course, use the term “supervisor” which would insult some people by appearing to discredit their qualiﬁcations. The best alternative I can

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think of is to say “host”. The duties of the host would include checking that all the personal problems (housing, visas, money, etc.) of his charge are taken care of. These are well looked after by the secretaries, but they cannot be expected always to see the problems through the eyes of a stranger with a diﬀerent background, and they are very busy, so a little discussion may often be helpful. The host would also make sure that his charge knows of all the relevant meetings and lectures. He then would naturally enquire into the research plans and, where necessary, make comments and suggestions. In other words, the relationship would develop into one very similar to that between a graduate student and his supervisor, or between a post-doc and his host. The diﬃculty is of course that the number of permanent members is much too small to carry out these duties. Long-term visitors would probably be willing to help, if asked; it might be necessary to oﬀer them a small fee. Senior member of the University, and perhaps other institutions would also be able to help. I cannot judge whether allowing for all these possibilities one would be in balance; very possibly not. In that case, could one consider diverting a small part of the funds now used for bringing people from the Third World, to bringing a few more senior people to help look after them? This would be justiﬁable if it would make the visits of some of the third-world people more proﬁtable. I do not have in mind here additional permanent staﬀ, but they would have to be long-term visitors, who in return for some assistance with fares and/or housing might be glad to take on such supervisory duties. This is a very tentative suggestion, because after three weeks I cannot possibly have understood the whole structure of the Centre, but I believe it might bear looking at. Yours sincerely, Rudolf Peierls

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[858] Lillie Krynen to Rudolf Peierls [location unspeciﬁed], 28.9.1987 Dear Rudi, How are you — hope all well. I am sure you are busy preparing your long trip to Russia now. It was so very very nice that you have been here, Rudi, still feel a little bad of not having shown you more of Brussels, but then you know, my silly toe hurt so much at times. It is much better now, + I can wear my with two “beautiful” shoes again. Have I been busy with my lessons at the Club. Thank you also for calling me, it is always so nice the little contact! Keep in touch — will leave for Spain very soon. Love, Lillian P.S. Have a very good and successful trip to Russia — tell me about it next time I see you. Tschau Lillian

[859] Rudolf Peierls to Freeman Dyson Oxford, 27.11.1986 (carbon copy) Dear Freeman, Thank you for the copy of your Dirac obituary for the American Physical Society. I could not see any errors in the facts you quote.1283 I must say, however, that I profoundly disagree with your thesis that one of the chief merits of Dirac was his faith in what you call the “topdown” approach. In my opinion the statements which you quote show a 1283

See letter [840], note 1254.

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peculiar myopia in Dirac’s attitude, which probably prevented him from making even more contributions to physics than he did. Of course one must take people as they come, and Dirac was certainly great enough in what he did to disarm any dissatisfaction, but we should not regard his limitations as virtues. I do not think your account of his discoveries is right. His understanding of quantum mechanics was based on Heisenberg’s work, which leaned heavily on the experimental ﬁndings, and on the partial success of the semi-empirical Bohr-theory. His very important step in introducing a more general formulation of the theory involved no new “fundamental beliefs”, though of course a re-formulation will be inﬂuenced by the criteria of mathematical elegance. The theory of radiation was a consistent application of the principles developed in quantum mechanics to another ﬁeld, and would have been impossible without the (as I have tried to argue) largely empirical foundations. The Dirac equation originated in the remark that the Klein-Gordon equation, then the obvious relativistic generalisation of the Schr¨ odinger equation, was not a consistent one-particle wave equation, in other words it did not ﬁt the pattern to which quantum mechanics had been led. I also disagree with the claim that Einstein proceeded “from the top down”. In special relativity he was aware of the fact that the (empirically based) Maxwell equations were not invariant under Galileo transformations, but only under Lorentz transformations (one would not have expressed it that way in his time). General relativity was motivated by the empirical fact of the equality of weight and inertial mass. Another point on which I disagree is your criticism of Dirac in not accepting renormalisation theory. The beginnings of ﬁeld theory were, as you say, set up by Dirac, but he did not foresee the inﬁnities. The formalism of renormalisation is unsatisfactory mathematically, because it is deﬁned only in terms of a series expansion which is at best asymptotically convergent. But an asymptotic series does not deﬁne a function. One may like the present formalism or not, but there is nothing surprising in Dirac ﬁnding it an ugly scheme.

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Of course, all this is a matter of opinion, and does not constitute “mistakes” which was what you were asking about. I do not know whether this was the article for which you wanted a copy of our Biographical Memoir, but an almost ﬁnal copy of this was sent to you by Dick Dalitz. Yours sincerely, [Rudolf Peierls]

[860] Rose and Hans Bethe to Rudolf Peierls Ithaca, Christmas 1987 Dear Rudi, Your letter was a most welcome sign and we thank you for taking the trouble to send us — who never write — a copy.1284 What a demanding schedule of travels you keep! How can you stand it? I — who is eleven years younger — certainly could not. And Hans would not consider attempting it. However, he is going to Santa Barbara, but alas, for the month of January only. He plans to be back in Ithaca on January 28, to celebrate our friend Anne Winter’s birthday on the 29th. She is joining the octagonarians. I can report news on both ends of the age scale - my mother, while frail, is as interested in the world as ever, Monica had a little girl on November 16. I was in Kyoto for the event and stayed for another 3 weeks to help her over the tiredness of the ﬁrst weeks. Yuli, now almost 3 years old, is so far a very loving brother. Her name is Miyo. Henry had a diﬃcult year — he was transferred back to N.Y. in May, but with enough uncertainty about the direction of his stay in N.Y.C. that they decided that Kitty and Paul should remain in London at least until August 1988 when Paul will have had two years in the same school. Luckily, Henry’s work took him to London about once a month, several days each time. 1284

Refers to copy of the annual circular letter.

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My sympathy is with you on the death of your sister. One’s brothers and sisters, even when one is not close to them, are like the foundation bricks on which the house of one’s life is built. The house stands, but there is a hole in it. All the best in 1988! Yours Rose Dear Rudi: What a year! I get dizzy just reading about your travels. You must have incredible stamina, even at 80. Too bad you’ll be at Santa Barbara just after I leave. Please, if you come East after S.B., do stop here in Ithaca. We would love to see you without a big crowd. Rose wrote to you about our events. Her sister Linde is thinking of moving to Oxford, to be with her daughter Tinky (whom you know) and her non-husband and child. Also to have more intellectual company than she has in Sheﬃeld. You will enjoy her. I hope the steps toward peace in 1987 will continue and lead to further ones. The most important, I suppose, is that Gorbachev remains in power. All the best wishes for 1988! Hans [861] Heinz Rudolph to Rudolf Peierls [Nuremberg], Christmas, 1987 Lieber Rudi! Vielen Dank f¨ ur Deinen Brief vom Juni d[iesen] J[ahres] und Deinen Jahresbericht 1986, den ich wieder mit großem Interesse gelesen habe.1285 Aus diesem erfuhr ich mit aufrichtiger Trauer, daß auch Du Deine Lebensgef¨ ahrtin verloren hast, genau wie es mir auch zwei Monate sp¨ ater erging. 1285

Letter [852].

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Nun sind wir beide also Witwer geworden. Ein Schicksal, mit dem ich mich nicht abﬁnden konnte, und das mich und mein Leben ver¨ andert hat. Der Tod meiner Frau kam f¨ ur mich pl¨ otzlich und unvorhersehbar, obgleich sie seit Jahren schwer an Rheuma litt, zu dem sich 1986 noch eine Angina gesellte. Sie war ein g¨ utiger, friedfertiger und musischer Mensch, eine Frau, wie ich sie mir nicht besser w¨ unschen konnte. Was meinen Kummer und Schmerz wohl verst¨andlich macht, nachdem ich sie verloren habe. Wir wollten noch viele Reisen machen. Nun bin ich allein in unserem Haus, wo ich vorl¨ auﬁg auch bleiben werde. Meine Tochter und meine bei Bonn lebende Schwester sind mit mir in diesem Jahr gereist, um mich abzulenken. Mit wenig Erfolg. Die kommenden Feiertage verbringe ich wieder bei meiner Tochter in B[erlin], wo sie Schauspielerin ist, wie es ihre Mutter bis vor dem Kriege auch war. Mit ehrlicher Freude lese ich in Deinen Rundbrief 1986, daß Deine Schwester und Dein Bruder wohlauf sind und Du sie gelegentlich siehst. Was macht Dein Vetter Franz Jacobsohn und Karli Fulda, an die ich mich noch entsinnen kann? Mit Genugtuung wirst Du den Raketenabr¨ ustungsvertrag aufgenommen haben, obgleich das nur ein ganz bescheidener Anfang ist, mit sicherlich noch Hintert¨ urchen auf o¨stlicher Seite, wie u ¨blich.1286 Vielleicht interessiert es Dich, daß aus dem Kreis unserer ehemaligen Abiturklasse noch ein loser Kontakt besteht zwischen B¨ uttner, Eveking, Herwig, Kacken und mir. Alle in West-Deutschland, nur Herwig in West-B[erlin], den ich dort n¨ achstens wiedersehen werde. Seit 1975 sind gestorben: Kirschke, Schmidt, Amort, Konopatzki, Zimmer und Firnstein. Mit allen anderen der insgesamt 25 fand ich nach dem Krieg keinen Kontakt mehr, besonders nach der ostdeutschen Abschottung nicht mehr zu den Strausbergern. Ich hoﬀe, daß es Dir gesundheitlich gut geht, Du Deine wissenschaftlichen Interessen weiter pﬂegen, und seine Erkenntnisse weitergeben kannst. Herzlichst Dein Heinz R[udolph] 1286

In December 1987, Ronald Reagan and Mikhail Gorbachev had signed the ‘Treaty on the Elimination of Intermediate-Range and Shorter-Range Missiles’ (INF Treaty).

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[862] Freeman Dyson to Rudolf Peierls Princeton, 30.12.1987 Dear Rudi, Thank you for sending us your annual letter. It is absolutely amazing that you do so much in one year. Even if you were not 80 years old it would be amazing. Imme and I just want to say, we are stuck dumb with admiration. There is nothing more we can say. I hope when I am 80 and you are 97 you will still be inspiring us with your courage and resilience. I just ﬁnished reading Gorbachev’s book. I ﬁnd it enormously hopeful. You don’t have to agree with what he says, but you have to recognize a genuine interest in people of all kinds and an intense concern for the future of the human species. I was happy to see that he even had a meeting with Chinghiz Aitmatov,1287 a writer I happen to admire. I recently read (in English) Aitmatov’s book “A Day Lasts more than 100 Years”, a very poignant and outspoken story of the Kazakh people torn between the two cultures, the old virtues based on work and the Party. This was published in Novi Mir in 1980, long before Glasnost.1288 We look forward to seeing you here whenever you come to visit Gaby. 1987 was a good year, with the Supernova, high-T superconductors, and the INF-Treaty. Let’s hope 1988 will be better! Yours ever Freeman

1287

Chingiz Torekulovich Aitmatov (1928–), published widely in Russian and Kirghiz; he worked as correspondent for Pravda in Kirghizia from 1958 to 1966, later won the Lenin Prize and three Soviet State Prizes for Literature for various works of literature. In the 1990s, he served as an advisor to Gorbachev and in 1990 was named Soviet Ambassabor to Luxemburg. 1288 C.T. Aitmatov, The Day Lasts More Than a Hundred Years, Novyi Mir, 1980.

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[863] Rudolf Peierls to Lillian Krynen Oxford, 20.1.1988 (carbon copy) I hope your bout of bronchitis passed without leaving any after eﬀects, and by the time this reaches you, you have returned brown and refreshed from your skiing trip in snow and sunshine! I shall try to phone next week, but this letter is mainly to report my itinery in California. I shall be in Los Angeles from 31 January to 1 February, where I shall be staying at the Holiday Inn, Wilshire Boulevard, Westwood, Los Angeles. I don’t know their phone number, but one can get it from the exchange. In the daytime I shall be at the University of California, Los Angeles. There again, I don’t know my oﬃce phone, but my host there is Dr. Nina Byers. Her oﬃce phone is (213)825-3588. She or her secretary will know how to reach me. 15 Jan to 14 March I shall be at the Institute for Theoretical physics, Univ. of Cal., Santa Barbara. My host there will be J.S. Langer; his oﬃce phone is (805)961-3247. Then I shall be for a few days, probably 14–15 March, in Stanford. Contact through Dr. Sidney Drell, or his secretary, phone (415)8543300. It would be fun to meet somewhere in California! After that I go for a few days to Seattle, and then to Vancouver, to stay with my daughter Kitty. I get back here on 29 March. There is not much to report about my last few weeks. I have made some progress with my book, though I wasted a week ﬁnding a mistake I made in reproducing an old calculation. The “Pending” ﬁle on my desk, with things to read, to answer or to deal with is getting bigger all the time, and I am hoping to get the most urgent things under control before leaving! When I get back I hope we can organise something to get together, particularly if the encounter in California does not materialise. I do want to see you. Meanwhile all my love [Rudi]

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[864] Rudolf Peierls to Mark Walker [Oxford], 26.1.1988 (carbon copy) Dear Mr Walker, Thank you very much for sending me your thesis, which I found very interesting and informative.1289 You have done an impressive job in searching out and digesting information, but that was what I expected after our conversation. I had only a limited time to read the thesis, because I am going oﬀ on 31 January for about two months in the US, and wanted to reply before leaving and send you my comments. I think my strongest comment relates to the part about the preHitler days. In this you build up a picture of “German scientists” as being opposed to the Weimar republic and hankering after the past. Undoubtedly there were many scientists with that attitude, as is also shown by the examples you quote. But I do not believe this was a general as you imply. I even doubt whether this applies to the majority of serious scientists, and I do not know of any statistical evidence of this. Of course, scientists, like other people, were critical of speciﬁc actions of the government, and of speciﬁc parties which were powerful in the Weimar republic. But this does not imply they were opposed to the republic as such. By the beginning of the thirties it became clear that the republic could not survive, but many attributed this to the fact that the government could not defend itself against the extreme right, though other people’s feelings were dominated by their fear of communism. I was myself very young at that time, and my impression may have been biased by growing up in a Jewish family with a very intelligent and unusually sceptical father, but as he had a senior position in industry, the general views of industrial circles came across. While there were of course many people with reactionary views, this was even there not as 1289

The thesis was later published as M. Walker, Nazi Science: Myth, Truth and the German Atomic Bomb, Cambridge Mass.: Perseus, 1995. Mark Walker went on to teach modern German history and history of science at Union College, Schenectady.

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universal as you imply for the scientists. I asked Lady Simon, whose husband was ﬁrst in Berlin and later in Breslau, and who remembers the times very well. She says that particularly in Berlin there were very many people with liberal views among the scientists, though perhaps in Breslau your description might have been more correct. I did not have time to give attention to your footnotes, but my impression is that you quote mainly secondary sources for this period. (Even a statement by Max Born is not quoted directly from his memoirs, but from some secondary source.) On a minor point: The reluctance of German scientiﬁc organisations to join international bodies (p. 13, top) must surely have been due to some condition attached to their membership which they found unacceptable (like Planck’s reluctance to come to a Solvay Conference, as reported by Heilbron, because he felt other people had not been invited for political reasons). When I started in research about 1926 everybody I met was certainly keen to develop international contacts. On p. 257 you criticise the Farm Hall press release for following the statement of the practical impossibility of making a bomb with the statement that “therefore” the work was concentrated on the uranium machine. This seems to me to be a completely logical statement without any moral implications. This, of course, is not true of some of the later statements, but I think your strictures should be reserved until you reach them. On p. 261 you discuss the view that it was not possible for Germany to have made a weapon if they had wanted to do so, and plead an historian’s ignorance of what might have been. Here I think one can learn from the way the analogous problem appeared in Britain. There was no question that we wanted to make the weapon, and that the government realised the importance of this, There was a time when relations with the US on this problem had soured, and it was therefore a serious possibility that we should go ahead on our own. Physically this was entirely possible, and the expenditure was not excessive for what would be achieved. (But even the scientists could not be 100% sure the thing would work until is had been made). But the main objection was that the requirements for materials, production facilities and technical

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manpower could not be met without priorities which would cripple the ongoing war eﬀort. Remember also that even the American project with its bigger resources, and without the interruption by air raids etc. did not reach fruition before the end of the war in Europe. It seems to me therefore that the German scientists’ view that Germany could not produce a weapon during the war was undoubtedly correct. On pp. 269–70 you say that the estimates of the critical mass in the Maud report and in the German work were very similar 2-100 kg in Maud and 10-100 kg by the Germans. It should however be understood that while the limits given by the Maud report were conservative, we were conﬁdent that the answer would be near the lower limit. In our memorandum Frisch and I came out with an even lower ﬁgure; we mentioned 600 grams, though this was for illustration and not a ﬁrm estimate. If the answer had been near the upper limit, nobody could have produced a weapon during the war. It would either have taken ten times longer to get the ﬁssile material, or a ten times larger plant (or reactors) which would have crippled even the American war eﬀort. I suspect that the German scientists expected the critical mass to be near the upper limit. (Uranium metal is very dense) therefore a subsidiary reason for their overestimating the diﬃculties was their overestimate of the critical size, and this may also lie behind their reluctance at Farm Hall to believe that the Americans could have done it. I do not want to imply that they had got any ﬁgures about the precise cost of necessary technology, but these numbers would have inﬂuenced their intuitive reaction. On p. 388 you criticise Hahn for saying that he was only doing “pure research”. This may turn on a question of semantics. My understanding is that the normal use of this term is to indicate research that is concerned with the facts of nature, and not with the application to practical ends, regardless of whether the ﬁndings may be applicable. I am not sure whether the term would exclude research done for the purpose of the application, but in any case you accept that Hahn was not doing his research for the applications.

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In addition to the above comments on the substance of your thesis I noted a number of minor points of wording, which could confuse, or at least puzzle the reader, and I give a list below. I have made no attempts to proof read the typescript. P. 14 l.15. It sounds as if “they” refers to the scientists who stood up for the republic, which does not make sense. The trouble comes I think from the word “these” in the previous line. If this were replaced by “the” or even “the other”, there would be no problem. P. 26, beginning. Here you describe the technical means by which the number of secondary neutrons are estimated. But this description is much too simple. You describe the way neutrons are detected, but the diﬃcult part is to distinguish secondary from incident neutrons, and that is where most of the arguments and errors arose. Since it would take very long to explain the whole principle, it is probably better to omit the technical details altogether. P. 34 l.5 from below. Grammatically “him” relates to Planck, while you mean V¨ ogler. To remedy this you might say: “· · · V¨ogler who in turn had to resign for bad health, was succeeded by · · · ” P. 35, l.6. “alter K¨ ampfer” would sound better. P. 35, last l: There is nothing German about the division of labour in a major research project: it was exactly the same in the Manhattan District. The authority enjoyed by the head of the group, or the professor, may be very German. P. 49, l.5 & 6 from below: “rectiﬁcation” is necessarily from a liquid, so the diﬀerence between the two methods is not clear. One is described as being low-pressure, so perhaps the other is rectiﬁcation at normal pressure? P. 117 last two l. I see no diﬀerence between “scientiﬁc ability” and “professional competence”. Should the latter be “administrative ability”? P. 119 line 1. “responded” read “respond”.

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P. 143, l.10. “countered” makes no sense here. Perhaps “reﬂected”, or “went with”? P. 152, l.3 from below: “length” of a cube is an unusual expression. The accepted term is “side”. P. 175, footnote 23. and elsewhere: The name of Stefan Rozental is consistently misspelled. P. 196, middle: It is wrong to suggest that only in 1943 Germans had to suspect everybody of being an informer. This started long before 1943. P. 208, l.4 from below. “oven” should read “stove”. P. 233, l.4 from below and elsewhere. “Society” is a wrong translation of “Gesellschaft”. In this context it should be “company”. P. 257, l.5. Delete “were”. P. 258, second para. The word “immediate” seems to me to denote something that you are working on now, not some distant aim of your work, and I therefore see nothing wrong with its use by the Germans in the context. P. 313 and others. You talk about Jensen. There are rumours that he passed information to Allied intelligence, but I do not know any evidence. (This is not a comment on what you say!) I am sorry to quibble so much, but I would not have gone through the trouble if I did not regard your thesis as a very valuable piece of work. Yours sincerely, Rudolf Peierls

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[865] Rudolf Peierls to Freeman Dyson Oxford, 6.4.1988 (carbon copy) Dear Freeman, Your December letter has been sitting on my desk for a long time,1290 though I have not been sitting at it, spending two months making my way up the West Coast (mainly UCLA and Santa Barbara, but calling at Stanford, Seattle and Vancouver). In Vancouver Erich Vogt complained about the timing: This time my visit did not overlap with yours! I do not quite understand why you — and others — are so amazed at my travelling. To me it is the soft option as opposed to sitting on one’s backside and doing more serious reading and thinking which I ﬁnd myself more and more reluctant to undertake — this kind of laziness grows with age. The only part of my travelling which takes an eﬀort is to deal with the papers accumulated in my absence, plus those I did not manage to deal with before leaving. At the moment this syndrome is acute. I entirely agree with your impression of Gorbachev and so do most, if not all, of the people I met in Russia last November. But there were very varying opinions about his chances of succeeding. He faces much opposition, and both his insistence on eﬃciency and the restrictions on vodka made him unpopular with some. What is probably worse is that in carrying out perestroika he has to rely a great deal on the very bureaucrats who are the embodiment of the old system, as he cannot overnight change all his oﬃcials. But all are agreed that if he should fail there will be a most awful backlash. So let’s keep our ﬁngers crossed for him. All good wishes for you and Imme. Yours, Rudolf Peierls

1290

Letter [862].

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[866] Thomas Powers to Rudolf Peierls South Royalton, Vermont, 28.4.1988 Dear Dr. Peierls: I am writing to request the favor of an interview in England, if you should happen to be free, between May 18 and May 22. I am writing a history of nuclear weapons to be published by Alfred Knopf,1291 and of course have read your book, Bird of Passage. But there are a number of matters, touched on in your book, which I would very much like to discuss with you further. One of these concerns is Werner Heisenberg’s role in the German bomb program during the war, which you studied for Michael Perrin in 1941-2. In gathering information about Heisenberg I have gradually been persuaded that Heisenberg’s own description of what he did is closer to the truth than the impression received by Niels Bohr during their meeting in Copenhagen in September 1941. I certainly do not think Heisenberg did anything so unmistakable as to refuse to make a bomb, but at the same time I very much doubt he went to see Bohr to pump him for information — at that time Bohr did not believe a bomb could be built, Heisenberg knew a great deal more about how to go about it than Bohr did, and the help that Heisenberg would have needed was not the sort which might have been passed along during an hour’s evening stroll through the streets of the city. What Heisenberg really felt at the time is of course very diﬃcult to reconstruct now, nearly 45 years later. My own guess is that the best indication of what he intended is to be found in what he did — which completely lacked the passionate dedication and all-out eﬀort to engage the interest of the authorities which allowed the scientists who ran the Manhattan Project to succeed. I have discussed this question at length with Victor Weisskopf, who wrote an introduction to Elisabeth Heisenberg’s book, and ﬁnd that he has still not quite made up his mind about it. On May 13 I am going to Germany to talk to Mrs 1291

Thomas Powers, Heisenberg’s War: The Secret History of the German Bomb, New York: Knopf, 1993.

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Heisenberg and von Weizs¨acker who of course are pleased that I feel that Heisenberg’s role has been misunderstood. What Heisenberg actually did is part of my investigation. What we thought he was doing at the time is another, and it is this I would hope to discuss with you further. I am especially interested in Niels Bohr’s time spent at Los Alamos in late 1943, when he arrived with details of his meeting as well as Heisenberg’s sketch for a reactor (which I believe was thought at the time to represent Heisenberg’s sketch of the actual bomb). I know there was much discussion of Heisenberg’s role at Los Alamos at the time, and would be grateful, to hear whatever you might recollect of it. Another subject I am pursuing is that of Peter Kapitza’s role in the Soviet bomb program after the war. It is well known that Kapitza spent six or seven years under a kind of house arrest for his reluctance to work on the bomb, but I have not managed to learn in any detail what he did, or failed to do, and above all what his thinking was. It would be very helpful to me to know when you ﬁrst learned of Kapitza’s troubles at home in 1946 or 1947, and what you might have learned about the subject thereafter. I apologize for writing at such length, but I wanted to let you know the subjects of my interest and the drift of my thinking. I shall be leaving the US on Friday, May 6, and will be travelling on business for two weeks thereafter, but expect to arrive at the Charing Cross Hotel in London on the evening of Tuesday, May 17th. A letter to me there — The Strand, London WG2 N5HX — would reach me I am sure. I realize that I am writing on very short notice, and that you may have other plans, or be on the other side of the planet. In that event, perhaps we might meet on some other occasion in this country. I would of course make every eﬀort to go wherever you happened to be. Yours truly, Tom Powers

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[867] Rudolf Peierls to Lillian Krynen [Oxford], 4.5.1988 (carbon copy) Dearest Lillie, Here are two enlargements. These are the biggest size the man in the shop recommended, because they would get fuzzy if one made them bigger size. I ordered only one of each, to see how they would work out, and also to check I picked the right negatives (there are three of each). They seem right, at least they are indistinguishable from the smaller prints. Let me know if you want another one of each the same size, or to try the bigger size. I’m keeping the negatives for the moment. I also enclose the recipe for Szekely Goulash. I hope my last letter has arrived by now. How stupid of me not to remember that it would take a long time to get to you, and that this would keep you waiting for a sign of life after our weekend. Please forgive an old fool, who is thinking of you a lot although it does not look that way. Love [Rudi] [868] Rudolf Peierls to Thomas Powers [Oxford], 7.5.1988 (carbon copy) Dear Mr Powers, Thank you for your letter of 28 April, received today.1292 In principle I would be willing to see you, but I shall be abroad until 19 May and expect to be hard-pressed on my return. I suggest you phone me to try to ﬁnd out a possible time. On the 19th I should get home about 7.30–8 p.m. if my plane is not too late. On the 20th I have engagements in the afternoon, but should be home about 8.30 p.m. In case we cannot get together, here are a few comments on the points you raise: 1292

Letter [866].

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On the Heisenberg-Bohr conversation I believe we shall never know, because Heisenberg’s memory is very subject to what he would like to believe, while Bohr was better in talking than listening, and could misunderstand what people said. The Copenhagen version of the conversation did not claim that H[eisenberg] wanted to pump B[ohr] on how to make an atom bomb, which indeed would have been ridiculous, but that he was trying to ﬁnd out what the Allies were doing, which is at least credible if not proved. According to Heisenberg’s book, he had come to the conclusion that the job of making a weapon was too great an eﬀort for Germany to undertake in wartime, and this was probably right, because even the Americans with their bigger resources and less wartime dislocation, did not ﬁnish the job before the end of the war in Europe. Actually he overestimated the diﬃculties (as he admits in the book) probably because he was using a wrong estimate of the critical size. (He therefore did not believe that the Americans could succeed). The impression is therefore that he concluded, with relief, that no decision was needed whether to make a bomb or not. What his position would have been if he thought the project was feasible, is impossible to discover. These are my impressions, but I am not a historian and have not studied the documents. (Mrs Heisenberg and Weizs¨acker are also not historians and interested parties). The most thorough historical study of which I know is a Ph.D. thesis by Mark Walker, now of Union College, Schenectady, which will be published as a book. I do not remember conversations at Los Alamos about Heisenberg; I probably did not take part in any. We had more urgent things to talk about then. As regards Kapitza, the trouble was not that he refused to work on a weapon, but that he objected to the way Beria wanted to use the laboratory over his objections. He was not under house arrest but was barred from access to his laboratory (and therefore to his town house, which was in the grounds of the laboratory; he stayed in his country house. You may like to consult Prof. David Shoenberg, F.R.S., of Cambridge, who is familiar with more details. I certainly could not remember when and how I heard about Kapitza’s troubles. Yours sincerely, Rudolf Peierls

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[869] Nevill Mott to Rudolf Peierls Cambridge, 21.5.[1988] Dear Rudi, “Freeze” sent me your paper — with a nice picture. Since signing the Freeze statement some years ago, I’ve come to feel that Freeze isn’t the way forward. Isn’t the main inﬂuence that drives the arms race the fear on each side that the other may obtain a ﬁrst strike capability? Therefore, new developments that make a retaliatory capacity secure (missiles that are mobile, submarines) are good, and good for the other side to have them too. ([??] was bad!) And new missiles may even need [??] Basically one can only support second strike weapons, with a “No ﬁrst use” policy, though I know all the arguments against. My only contact with these problems now is through the Oxford Research Group (Scilla McLean) which you probably know.1293 Best wishes and I hope all goes well with you. Nevill

[870] Rudolf Peierls to Nevill Mott Oxford, 24.5.1988 (carbon copy) Dear Nevill, I do not agree at all. The idea of a First Strike is as much science ﬁction as the SDI. Even if it was possible to wipe out all the land-based missiles on the other side, there would remain submarine-launched missiles and 1293

The Oxford Research Group (ORG) was a registered charity funded by charitable trusts, which had been set up in 1982 to carry out independent research into decision making, accountability and similar themes largely with reference to nuclear weapons.

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air-launched cruise missiles. I have no inside knowledge of the techniques of submarine detection, but the experts seem to think that any eﬀective method is a long way oﬀ. But let us assume that a way can be found to knock out all these additional weapons. Even then a First Strike would be a gigantic operation, in which large numbers of missiles would have to be launched in a very short time interval (otherwise some deterrent weapons would be launched before they are destroyed, and one can allow only a limited number to fail). Of course this works ﬁne in the system analysts’ computers, but in the heat of battle, things are diﬀerent. Recall the number of occasions when American space shots which are serviced by the cream of the nation’s technical manpower, had to be postponed or cancelled. Only a completely crazy and irresponsible government could stake their nation’s survival on the success of such an operation. With all objections to present and past US presidents and past Soviet leaders, they are and were not crazy. You are right that the fear of a First Strike is real, and is important for the arms race. The remedy is to try and educate public opinion. Also the arms reduction measures which have so far been agreed and we hope will go further help to reassure each side that the other is not planning a First Strike. I don’t know how many of the politicians who talk about a First Strike believe in it, and don’t just see this as a good way to get more funds for arms. You say one should encourage “second-strike” weapons. But such weapons could also play a part in a ﬁrst strike, so in eﬀect you advocate a continuation of the present useless arms race. SDI would indeed be most dangerous if it had any chance of reaching Reagan’s goal of complete umbrella, because that would make a First Strike safe, but no serious person believes in this possibility, so it is not so dangerous, just stupid, wasteful and confusing the issues. A no-ﬁrst-use declaration would be very good in Europe, because it would force NATO to change their doctrine of using tactical nuclear weapons against overwhelming conventional attack, and thus change their deployment etc. Applied to strategic weapons it would not have

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any immediate visible consequences, and therefore nobody would believe it. So I want to stick with the Freeze, and particularly with the eﬀort to get a comprehensive test ban. With best wishes, Yours sincerely, Rudolf Peierls

[871] Nevill Mott to Rudolf Peierls Cambridge, 26.5.1988 Dear Rudi, Thanks for yours.1294 Do we disagree so much? Of course I agree that no sane gov[ernmen]t would make a ﬁrst strike! But we agree that the fear of a ﬁrst strike is real and is important in the arms race. I believe very important. So I maintain that it is good that both the Russians and the U.S. put new heavy missiles on trains etc. The important thing is that both sides should feel secure. So if — in the eﬀort to get retaliatory weapons onto railway trains or under the water, a new missile is needed, so be it. Let it be made and tested. So I am not really with you on Freeze — at least I don’t feel it is the key to the problem. The Freeze trained me a bit to do something — so I thought I’d tell you why I don’t. Shall be in Oxford on June 7 (engaged 3.30–5.30). Shall I look in on the way back — to hear your news? Best wishes, Nevill

1294

Letter [870].

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[872] Rudolf Peierls to Nevill Mott Oxford, 26.5.1988 (carbon copy) Dear Nevill, I won’t buy that argument. We are agreed that no sane government would start a First Strike. We are, I think, also agreed that there exist plenty of survivable weapons to serve as deterrent, but we have to deal with the fear of people who are worried that the deterrent will not protect them. What reason is there to think that more survivable weapons would reassure them? If it were possible just to put existing weapons on trains, I would not mind, but to pile up additional weapons will only increase further the fear of a First Strike, as will any continuation of the arms race. I believe on the other hand that a treaty reducing the number of weapons substantially would diminish the fear because a government that is considering a First Strike even as a contingency would not accept such a treaty. (A unilateral reduction, which would still be safe, would be even better in this respect, but I do not see this as practical politics). I regret I shall not be here when you come; I am leaving on 5 June for the Landau Memorial Conference in Tel-Aviv. Yours sincerely [Rudi]

[873] Rudolf Peierls to Lillian Krynen Oxford, 22.7.1988 (carbon copy) Dearest Lillie, Your card with the nice ﬂowers (I never know the name of any ﬂower (except lily!) arrived this morning. We are keeping in touch in diﬃcult circumstances. You are ahead of me in writing cards — I am ahead in phoning, but neither is really satisfactory. So perhaps I can revert

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to the old-fashioned method of writing letters, and that is what I am doing. About dates: I am leaving here for the Soviet Union (Sochi on the Black Sea) on 27 August and after a week there and another week in Moscow and Leningrad return on 12 September. But then I am oﬀ again on 19 September to Geneva (for a conference to celebrate the 80th birthday of a friend and colleague)1295 and from there to Paris, or more precisely to Bures-sur-Yvette, a suburb about 30 minutes by metro from the centre. There I shall stay in a small ﬂat for two months, i.e. until about 21 November. I was hoping we could then get in physical touch, but with your planned excursion to Africa and America, this begins to look doubtful. But there is still hope. After that I have no trips planned, surprisingly, though in March and April I shall probably again visit America (California and Washington D.C.). The timing is governed by the fact that on 24 February my brother in Manchester will have his 90th birthday, and I want to be around for that. I feel I have done too much travelling this year, and perhaps I am too inclined to accept every invitation unless there is some actual objection. I am now putting the brakes on, and I have already turned down two invitations for next year to pleasant places, but where there was no special reason why I should go. One learns even at my age. At present life is reasonably pleasant, but progress is slow. This is partly because I am now slow in reading due to my bad eyesight. Also it has taken me some time to learn the system of my new word processor, since my old one was getting old and made too many mistakes (like me). It is always fun to learn a new technique, but it takes time. But now I have mastered it. As the printer is the same, my letters will not look any diﬀerent, but will have fewer misprints, as the new system is easier to check. I am still running around to meetings. This week I am going three times to London; all concerned with arms control problems. So I have not done much entertaining, but tonight I have a dinner for six, including Nicholas Kurti, a physics professor who is also a famous cook and has 1295

On 19th September 1988, an international colloquium on Science, Culture and Peace was held at CERN in honour of Victor Weisskopf to celebrate his 80th birthday.

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appeared on TV on the subject “Physics in the Kitchen”. I feel slightly intimidated in oﬀering him dinner! Last week my eldest granddaughter was here with her boy friend. They enjoyed Oxford, but the weather was cold and wet, and she promptly caught a cold. They went on to stay with my daughter in Birmingham, who now has the cold! In early August, my oldest grandson is coming with his wife — they are getting married tomorrow, though they have already lived together for some years. Our garden is now beautiful, with masses of roses (I do know roses!) and nice vegetables. I think I already told you about my June trips: Tel Aviv, not too hot, except the last day, but very hard work, then Copenhagen with an unexpected heat wave, but a very relaxed meeting. I love Copenhagen where I have been many times. Then three days in Rome with extreme heat, punctuated by thunderstorms. And before that of course the award of the doctorate in Coimbra, with the elaborate ceremony and the clothes of which I sent you pictures, and which you can inspect if you ever come here. This brings you a little in the picture about what I am doing — before we meet and can talk I shall have forgotten half of it. I hope you will enjoy Sweden, Zermatt, and wherever else your Wanderlust takes you, and all this with a solid footing, without troublesome toes. I shall still try to phone you from time to time. I miss you. Love, [Rudi]

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[874] Lillian Krynen to Rudolf Peierls Brussels, 26.7.1988 Dear Rudi, How wonderful to receive such a long warm letter from you.1296 Yes, we do rather keep in touch in diﬃcult circumstances — well, never a dull moment with all our travelling. My sons love my photo you had made of me — could you be so very kind to have the “similar one” printed again, 2 times again?! No hurry, just when you have the time. Thank you so much, Rudi! Wish I could be there for your dinner party with Nicholas Kurti who is a famous cook (is he also a gemini?) Had also quite a few nice dinner parties at my place as the weather had not been so nice, it was nice to do cooking and my painting in the kitchen, have done quite a few again and enjoyed it! Am of[f] on the 2–8 to Sweden, have not been for a long time, hope I have luck with the weather — after that to Zermatt with my car + a young American couple who have never been to Switzerland, shall enjoy showing it, as I love Switzerland very much — Aug[ust] have the young couple staying with me + Sept[ember], a while to catch up with myself for a change + to U.S.A. no(t) date ﬁxed yet but shall be there in Oct. for sure. Just a little note — Keep well and hope all goes well with your travel — Tschau! Love, Lillie

1296

Letter [873].

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[875] Rudolf Peierls to Heinz Rudolph Oxford, 19.8.1988 (carbon copy) Dear Heinz, Ich bin wie immer ein sehr schlechter Korrespondent, und habe noch nicht auf Deine Karte aus Griechenland geantwortet und Deine Geburtstagsw¨ unsche reagiert. Ich habe mich dar¨ uber sehr gefreut, daß Du mit Mitgliedern Deiner Familie Reisen machst. Es ist sehr wichtig, neue Eindr¨ ucke zu bekommen, die nicht mit den verlorenen verkn¨ upft sind, so dass man sp¨ater Erinnerungen hat, die nicht schmerzliche Assoziationen haben. Meine Frau sagte immer, man muß wie ein Baum neue Ringe entwickeln. Jetzt hatte ich f¨ ur ein weekend Besuch von meiner ¨altesten Enkeltochter, mit ihrem Freunde, und dann f¨ ur ein anderes Weekend den ¨altesten Enkelsohn. Da alle Enkelkinder in Nordamerika leben, ist das ein grosses Ereignis. In einer Woche fahre ich wieder weg, diesmal an das schwarze Meer, zu einer Pugwashkonferenz, und dann noch f¨ ur eine Woche nach Moskau und Leningrad. Sp¨ ater dann noch zwei Monate nach Paris. Aber jetzt reise ich noch zu viel herum, und ich muß das etwas einschr¨ anken. Ich habe das Reisen schon sehr gern, aber dann bleibt nicht genug Zeit zu Hause, und man sieht seine Freunde nicht genug. Wenn ich hier bin, habe ich jetzt das Kochen sehr gern, und ich lade Freunde sehr oft zum Essen ein. Ich habe leider Deinen Geburtstag vergessen, so daß ich Deine freundlichen Gl¨ uckw¨ unsche nicht erwidern kann. Ich glaube, Du bist noch ein bisschen a¨lter als ich? Ich hoﬀe, Du wirst allm¨ ahlich noch eine zufriedenstellendere Lebensweise ﬁnden. Es ist nie dasselbe, wie es war, aber es gibt immer noch so viele interessante (und n¨ utzliche) M¨ oglichkeiten, daß es schade ist, davon keinen Gebrauch zu machen. Gibt es noch eine Fortsetzung Deiner sehr interessanten Biographie? Mit herzlichen Gr¨ ußen Dein [Rudi]

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[876] Heinz Rudolph to Rudolf Peierls [Nuremberg], Christmas, 1988 Lieber Rudi, Ich w¨ unsche Dir erholsame Weihnachtstage und ein gutes gesundes Neues Jahr. Deinen soeben erhaltenen Jahresbericht 1988 (vielen Dank!) habe ich wieder mit großem Interesse gelesen und habe festgestellt, daß Du das Jahr ausgiebig herumgereist bist und viele Erlebnisse hattest. Abgesehen von einer Reise nach und durch Griechenland, zusammen mit meiner Schwester, und Besuchen bei dieser und meiner Tochter, ist es mit weiteren Reisen nichts geworden. Der Tod meiner Frau hat meine Unternehmungslust ziemlich gel¨ahmt. Außerdem: Meine Tochter, seit 18 Jahren in B[erlin] und als Schauspielerin mittlerweile dort bekannt, beschloß endg¨ ultig in Berlin zu bleiben. Sie suchte nach einem eigenen ihren W¨ unschen entsprechenden Haus. Was in der Insel West-B[erlin] nicht so einfach und vor allen Dingen teuer ist. Dazu brauchte sie meinen Rat. Schließlich fand sie das ihr zusagende Einzelhaus in Zehlendorf und zog nach einigen Ver¨ anderungen und Verbesserungen dort ein. Bald darauf heiratete sie. Ihr Mann ist nicht vom Theaterfach, sondern, wie ich, Dipl[om] Ing[enieur], allerdings von der Baufakult¨ at. Die Festtage verbringe ich wieder in B[erlin], wo ein Zimmer f¨ ur mich bereit steht und ich kommen und bleiben kann, wie ich will. Ein großer Teil meiner Einrichtung (M¨ obel, Teppiche, Bilder, usw., vieles davon noch von den Schwiegereltern) geht n¨ achstens nach B[erlin], wo gen¨ ugend Platz daf¨ ur ist. Bei mir wird das Haus dadurch leerer. Womit ich aber zufrieden bin, weil Besitz auch eine Last sein kann. Ich bleibe vorl¨ auﬁg in N[¨ urnberg] wohnen, wo ich mich ziemlich eingelebt habe, aber kaum Bekannte oder Freunde habe. Mit 83 Jahren f¨ uhle ich mich durchaus noch r¨ ustig, mein Hausarzt meint, ich w¨ are biologisch noch 10 bis 15 Jahre j¨ unger. Ich habe noch viel vor, unter anderem auch das Reisen. Gerade weil unsere Jahre gez¨ahlt sind. Lieber Rudi, laß es Dir gut gehen und sei herzlichst gegr¨ ußt von Deinem Heinz R[udolph]

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[877] H.R. Jones to Rudolf Peierls Winchester, 23.2.1989 Dear Sir Rudolf, Two weeks hence (March 9) I am to deliver a lecture to the AngloGerman Society of Winchester on the subject ‘The History of the Atomic Bomb and what happened in Germany’ and I have been thinking for some time of seeking your comment or advice on a speciﬁc point. I have a particular reason for thinking of approaching you. I graduated in chemistry at Birmingham in 1940 and during 1940-41 worked on uranium chemistry in Professor Haworth’s team. Later in the war, having volunteered for the Instructor Branch of the Royal Navy, my ship of 1945–46, the MS Belfast, visited Japan and I spent an afternoon in Hiroshima. I gave many ‘popular lectures’ on the bomb in the Royal Navy and subsequently. In addition, my wife, (formerly Miss B.W.Cook) graduated in physics in Birmingham in 1942 and was taught by you (Applied Maths course II). We have both recently read and enjoyed your life story — particularly your thumbnail sketches of Birmingham staﬀ. I had not, until recently, sought to delve into German work on the bomb. However, in recent years, I have given an annual talk on a scientiﬁc topic of Anglo-German signiﬁcance to the (lay) members of the Winchester-Giessen society (Winchester is twinned with Giessen). So far those have been chemically based. The three topics so far have been (a) The Liebig → Hofmann (40 London) → W.H. Perkin dyestuﬀs saga (b) The work of Fritz Haber and its impact on World War I + (c) the Anglo-German origins of ICI. Having been asked yet again, I thought of the bomb and the German work. I have worked through the Virus House1297 and the ALSOS report,1298 amongst others, and those seem to contain the main ingredients for a talk. However, the matter on which I would value your 1297

David Irving, The Virus House. The History of the German Wartime Atomic Research Programme, London: William Kimber Ltd., 1967. 1298 Samuel Goudsmit, Alsos, New York: Henry Schuman, 1947.

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comments, since most of the German workers would have been known to you personally, is the question of their attitudes to the work they undertook since it seems likely, in several cases, that they were less sympathetic to their then regime than were UK/US scientists to our own cause. The accounts I have read are not very clear on this. This may be inevitable, if as is likely, German attitudes were mixed (as were to some extent some of our reservations on what was being created as distinct from an agreed need to be successful). Von Weizs¨acker, for instance, is quoted as saying that the physicists didn’t want to do it in principle. I do not want to put you to a great deal of trouble, but I should very much appreciate any views you have come to on this piece of history. I suppose I am interested primarily in the views of Hahn, Heisenberg + von Weizs¨acker. If you are able to send me a few lines, I should be most grateful. I should also like to know whether I may quote my reference to you on the occasion of a lecture (which is to be held in the Science School of Winchester College — a Wykeham link). I shall also quite understand if you feel unable or prefer not to comment. Yours sincerely, H.R. Jones (Mr)

[878] Rudolf Peierls to H.R. Jones Oxford, 26.2.1989 (carbon copy) Dear Mr Jones, I am happy to try to answer your questions, but your letter1299 caught me at an unfortunate moment. I have been out of town for the past two days, and tomorrow morning I leave for a two-months absence in America. You will understand that I must limit myself to a fairly short reply. 1299

Letter [877].

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One must bear in mind that Goudsmit’s book Alsos was written at an early time when there was still incomplete knowledge of the relevant documents. He later wrote an article (I do not remember in what journal) in which he toned down his criticism of Heisenberg, and he said in a letter to me that we expected a great physicist of the stature of Heisenberg also to be an outstanding person, and one should not blame him for being just a fallible human being like everybody else. The Virus House is written later and had access to more documents, but has also been criticised for a number of errors; I can’t spell out the details without going back to the sources, and there is not time for that. The most thorough account of the German atomic-energy work is a Princeton thesis by Mark Walker, which will be published as a book by the Cambridge University Press, but of course it won’t be available in time for your meeting.1300 Heisenberg was not a Nazi sympathiser, in fact he had collisions with party oﬃcials over their attack on modern physics, but he was a German patriot. He decided very early that making a nuclear weapon was too big an eﬀort to be carried out in Germany in wartime. (Even the US with their bigger industrial resources, and not being disturbed by air raids did not complete the project before the end of the war in Europe). He therefore did not ask for a crash programme, and limited himself to work on a slow chain reaction. His purpose, particularly at the end of the war, was to achieve a chain reaction, which he hoped would enhance the prestige of German science and be helpful after the war. He never suspected, of course, that Fermi had achieved this in 1942. Heisenberg therefore did not have to decide whether to work on a bomb programme, and he was probably relieved by this. I cannot say how he would have decided if he had regarded this as a realistic possibility for Germany, but I guess he would have regarded it as his duty to work on this. But this is speculation. The stories that he and other German scientists refrained from working on a weapon for ethical reasons, are complete nonsense. The 1300

See letter [864], note 1289.

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worst book on the subject which makes this his main thesis, is Jungk’s Brighter than a Thousand Suns.1301 However, it is probably true that German scientists were not emotionally involved in the war to the same extent as the scientists in the West, who took the main initiative in getting the project started. I have heard a rumour, but cannot conﬁrm it that Heisenberg regarded it an important purpose of the project to keep young scientists out of the army. I never met Hahn, and cannot comment on his attitude. One relevant fact is that after the news of Hiroshima broke, he was so depressed about what had come of his discovery that his colleagues were afraid he might commit suicide. Weizs¨acker is a more complicated problem. During the Nazi period he cooperated with the authorities more than many others, even Heisenberg. Probably this was prudence rather than conviction, but it makes it rather hard to form a picture of his attitude. That is all I have time for. If you consider giving similar talks later, I could probably suggest some further reading. Yours sincerely, Rudolf Peierls

[879] Mark Oliphant to Rudolf Peierls Griﬃth, A.C.T. Australia, 21.3.1987 Dear Rudi, Thanks you very much for your understanding and helpful letter.1302 Following Rosa’s death, I have come to live alone, in this isolated country home, while a ‘grandpa ﬂat’ is built behind our daughter’s home in Canberra. After 52 years of marriage, to be alone is my desire. 1301 1302

R. Jungk, Brighter Than a Thousand Suns, Harcourt: Brace, 1958. Letter could not be located.

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Strangely, I miss so much having to take care of Rosa!1303 She had fallen asleep after talking about her beloved garden, in an unusually rational manner. My hand was on her waist, since her back was to me, and I was suddenly aware that her breathing has ceased. In the sense that her condition was so embarrassing for her, it was a good way to go, but I miss her, selﬁshly, so very much. I remain deeply interested in the energy problem, and in the social revolution due to “high-tech”, and I hope to come to terms with a new kind of living while I am here. If I can manage it, I shall attend the Pugwash meeting in Austria in the beginning of September, and then come on to St. John’s for a farewell visit. I hope we shall meet at Pugwash or in the UK. Gratefully, Mark [880] Rudolf Peierls to Victor Frenkel [Oxford], 10.6.1989 (carbon copy) Dear Vitya, I am again late in replying to your letter of 19 March.1304 It arrived here only in May, and I was still trying to cope with the arrears that had accumulated while I was in the United States. Since then I have been travelling around again, going to meetings in Copenhagen, Brussels and Rome, so writing was diﬃcult. I am glad you and Bolotski agree with so many of my suggestions. On the points of priority with which you disagreed, I evidently had not looked at the facts suﬃciently carefully. As regards the text of Genia’s verses, I had a vague recollection of seeing a letter from Gamow with the text of some of these verses.1305 I looked in the obvious places and could not ﬁnd anything. So after a long search I started writing this letter and started to say that I could 1303

Mark Oliphant had cared for his wife Rosa during a long illness. Letter Viktor Frenkel to Rudolf Peierls, 19.3.1989 Peierls Papers, Supp. K.34. 1305 The letter with the verses survived and is in family possession. 1304

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not help. Then I suddenly remembered a folder with letters in Genia’s desk and there was Gamow’s letter. I hope this collection contains the verses you wanted. (I don’t have Gamow’s book handy). I remember that Genia said that Gamow did not remember all the verses correctly, but she never told me what the errors were. Now I want to ask you a favour: Could you get these verses copied on a typewriter? The point is that I ﬁnd Russian handwriting hard to read, and this applies particularly to poetry where there are many words with which I am not familiar. Yet, I would very much like to be able to read these verses. I would be most grateful. With best regards, Yours sincerely, Rudolf Peierls [881] Rudolf Peierls to Heinz Rudolph Oxford, 14.6.1989 (carbon copy) Lieber Großvater Heinz, Vielen Dank f¨ ur Deine Gl¨ uckw¨ unsche und Gratulation f¨ ur die Enkeltochter. Du schreibst jetzt schon immer so gewissenhaft zu meinem Geburtstag, und ich [kann] das nicht wiedergeben, denn ich weiß nicht, wann Dein Geburtstag ist. Bitte teil mir das schon mit! Ich feierte meinen Geburtstag in dem Flugzeug nach Rom, wo ich zu einer Tagung der europ¨ aischen Akademie u ¨ber Entwaﬀnung und ¨ R¨ ustungskontrolle gehen mußte. Uberhaupt habe ich schon wieder zu viele Reisen gemacht, aber jetzt habe ich f¨ ur den Rest des Jahres keine großen Reisepl¨ane mehr, außer drei Wochen im August. Es ist sehr befriedigend, daß die politische Situation in Europa schon sehr viel besser aussieht, wozu Gorbachev viel beigetragen hat. Aber was jetzt in China vor sich geht, ist ja ganz schrecklich.1306 Mit herzlichen Gr¨ ußen Dein Rudi 1306

On 4th June 1989, several hundred civilians were shot dead by the Chinese Army during a bloody military operation to crush a democratic uprising in Peking’s Tiananmen.

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[882] Rudolf Peierls to Waltraud Krause Oxford, 22.6.1989 (carbon copy) Liebe Frau Krause, Haben Sie vielen Dank f¨ ur Ihren lieben und interessanten Brief.1307 Nat¨ urlich erinnere ich mich an Lotte Augustin1308 und ich bin sehr froh zu h¨ oren, daß sie noch am Leben ist. Ich werde ihr auch gleich schreiben; es ist eine große Freude, mit ihr wieder in Verbindung zu kommen. ¨ Uber die praktischen Fragen: Meine Geschwister und ich sind nat¨ urlich an der Erhaltung des Grabes meiner Mutter sehr interessiert. Vor vielen Jahren h¨ orte ich, daß das Grab sehr u ¨berwachsen war, aber daß zwei der Friedhofsangestellten, Hans Minde und Herbert Riedel, schon freiwillig das in Ordnung gebracht haben, obwohl das nicht ihre Pﬂicht war. Ich schrieb ihnen damals, um mich zu bedanken, und schickte ihnen ein kleines Geschenk. Von Ihrem Brief habe ich den Eindruck, als ob es wieder notwendig ist, sich etwas darum zu bek¨ ummern. Ich w¨are Ihnen sehr dankbar, wenn Sie mir mitteilen, was wir am besten daf¨ ur tun k¨ onnen. Meine Schwester Annie ist vor zwei Jahren gestorben; mein 9 Jahre alterer Bruder lebt in Manchester. ¨ Antworten auf Ihre Fragen: Ich ging in Obersch¨ oneweide in die Schule. Zuerst in die Vorschule im Lyzeum (nur zwei Jahre, das erste Jahr hat meine Mutter mich zu Hause belehrt.) Dann, als ich 9 Jahre alt war, ging ich an das Gymnasium unter Herrn Strohmeyer. Im ersten Kriege wurde das “Hindenburg-Schule” getauft, aber in 1919 1307

Letter could not be located. Waltraud Krause, chair of the local history society in Berlin-Obersch¨ oneweide, the Berlin suburb where Rudolf Peierls had grown up, and chronicler of more notable graves on the local cemetery, had written to him with enquiries about his mother’s grave. Furthermore she had asked detailed questions about his family and his schooling. Letter Waltraud Krause to the editor, 18.1.2000. 1308 Lotte Augustin was the daughter of the factory gardener of the Kabelwerke Oberspree, of which Heinrich Peierls had been director. Their family had lived in the souterrain of the villa in which the Peierls family had lived.

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wurde es die “Humboldt-Schule”. Hat es jetzt noch einen Namen? Ich blieb dort bis zum Abiturium, also neun Jahre, obwohl meine Familie im letzten Jahre nach Berlin umgezogen ist, sodaß ich mit der Bahn zur Schule fuhr. Ich habe sehr viele Erinnerungen an die Zeit in Obersch¨ oneweide, aber wenn ich die aufschreiben sollte, w¨ urde dieser Brief viel zu lang werden. Daher soll das f¨ ur einen sp¨ ateren Brief bleiben. Viel davon steht in meiner Autobiographie, die aber nur auf englisch ver¨ oﬀentlicht ist. Wenn Sie, oder einer Ihrer Freunde englisch lesen k¨ onnen, w¨ urde ich Ihnen gern ein Exemplar schicken Mein bester Freund in der Schule was Heinz Rudolph, der jetzt in N¨ urnberg lebt. Ich war (und bin) nicht sehr athletisch, und hatte keine Verbindung mit dem Ruderklub. Ich lebe schon seit 1929 nicht mehr in Deutschland, da ich in Z¨ urich studierte, und dann dort als Assistent blieb. In 1933 wollte ich nach Deutschland zur¨ uckkehren, aber mit dem Hitler sah das nicht sehr gut aus, daher ging ich nach England, wo ich seither geblieben bin, außer zwei Jahre w¨ahrend des Krieges, wo ich in Amerika an der Atombombe gearbeitet habe. Meine Geschwister sind ungef¨ ahr 1935 ausgewandert, Alfred nach England, Annie nach Amerika. Mein Vater und seine zweite Frau konnten sich lange nicht entschließen, aber gingen dann in 1939 (oder sp¨ at in 1938) u ¨ber England nach Amerika. Er ist 1945 gestorben, seine Frau Else ein paar Jahre danach. Ich weiß, wieso das KWO Archiv1309 meine Adresse hatte: im Mai war eine Filmgruppe aus Berlin hier und hielten ein Interview. Sie oneweide aufgewachwußten aus meinem Briefe,1310 daß ich in Obersch¨ sen bin, und brachten mir Bilder von dem Haus in der Kunheimstraße, und auch aus dem Archiv, alte Bilder von Gruppen mit meinem Vater. Mit herzlichen Gr¨ ußen Ihr [Rudolf Peierls] 1309

KWO refers to Kabelwerke Oberspree, the AEG factory in Berlin Obersch¨ oneweide. 1310 Presumably he means Buch refering to his autobiography.

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[883] Mark Oliphant to Rudolf Peierls Griﬃth, A.C.T., 2.7.1989 Dear Rudi, You may remember that during our conversation in Cambridge last November, I mentioned that I had found much interest in a book by Nick Herbert.1311 You quite strongly stated that his own ideas were wrong. Also, you had little good to say about Paul Davies.1312 So, I have not much faith in my own judgment of what to read about the deep puzzles of modern theoretical physics. I enjoyed Hawking on Time1313 and “Three Hundred Years of Gravitation” edited by Hawking and Israel,1314 but as I read them, your warning was with me, particularly when broad and sweeping statements are made on what seems to me to be rather ﬂimsy analysis. In Nature for 1 June, 1989, J.H.Mulvey reviews favourably a book edited by Paul Davies, “The New Physics”, 1315 which I am tempted to buy, although it is expensive in Australian Dollars. Before I do so, I would welcome any comment you may care to make. I attend seminars given by local theoreticians and by visitors, but unlike you, so many are intoxicated by the mathematics of ‘strings’ and ‘fractals’, or the beautiful patterns created on their computer screens, that I found much of what they have to say about the foundations of physics quite incomprehensible. To tell the truth, when I hear Hirst talk on ‘The Theory of Everything’ I wonder whether he really understands it all. It is like listening to an echo of Abdus Salam! Old age makes me very slow in the uptake. I need time to absorb. That is why I ﬁnd the printed 1311

Probably Nick Herbert, Quantum Reality, New York: Anchor Books, 1985. Paul Davies, physicist and author of God and the New Physics, New York: Simon & Schuster, 1983; Other Worlds, Harmondsworth: Penguin, 1988; The Edge of Inﬁnity, New York: Simon & Schuster, 1982. 1313 Steven W. Hawking, A Brief History of Time, New York: Bantam Books, 1988. 1314 S.W. Hawking and W. Israel (eds). 300 Years of Gravitation, Cambridge: Cambridge University Press, 1987. 1315 Paul Davies (ed.), The New Physics, Cambridge: Cambridge University Press, 1989. 1312

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word over which I can linger, more satisfying now than lectures, unless these are given by the rare expositor who is a real teacher. Despite the phenomenon of Gorbachev, I ﬁnd the future rather terrifying. Runaway population, runaway technology resulting in the rapid decrease in productivity of soils, and hence of food production, worry me. While 20,000 children die every day in Africa from poverty and malnutrition, there is blithe talk of spending millions of dollars on developing the use of anti-protons as a source of energy for deep space exploration! We do love our toys! Best wishes, Mark

[884] Rudolf Peierls to Mark Oliphant Oxford, 6.7.1989 (carbon copy) Dear Mark, About the books by Herbert and by Paul Davies,1316 I may have sounded more negative than I intended, and if so I apologise. I have not read Herbert’s book, and therefore could not have a view of it. I do know papers he has written in which he claims that in certain circumstances observations of the Aspect type could lead to transmissions of signals with more than light velocity, and that was nonsense. I suspect that he makes similar claims in his book, but of course I do not know. I have also not read Paul Davies’s book, but I regard him as a knowledgeable and generally sound person. To my taste he is inclined too much towards philosophy, and takes people who see fundamental diﬃculties in quantum mechanics too seriously (though he does not necessarily agree with them). My only contact with him was in a radio interview, one of a series which was later published. He edited this and wrote an introduction. This contained a serious error, showing that he 1316

See letter [883], notes 1311 and 1315.

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had not understood the argument by Einstein, Podolsky and Rosen. He corrected this when I pointed it out. I may have mentioned this to you, but anyone can make a mistake, and this does not damn him completely. I have not yet read Hawking on Time. He is a very impressive person. I am little sceptical about his theories of the early stages of the universe, but they are interesting. On Paul Davies’s “New Physics” — if John Mulvey liked it I certainly have no information to put against this. I wish I could make more positive suggestions about what one should read, but I am now reading very little myself. Like you I take in information very slowly, and that goes also for the written word. Poor eyesight adds to making reading very slow, and as there is a lot I have to read I am getting more and more behind. One useful source of reasonable accounts of modern developments is the journal “Contemporary Physics” (I belong to their editorial board). This tried to bring articles which are intelligible for every physicist regardless of speciality. We don’t always succeed, but many of the articles are well written. Like you I ﬁnd the string and superstring theories very unattractive. I have not tried to follow them all, but I am put oﬀ by the fact that they are not likely to make any predictions that can be tested. Fractals are a diﬀerent matter. That is a sound concept, and there are many examples where it can be useful in practice. The new concept of “chaos” is also in principle very simple and impressive. I share your pessimism. One has to remember, though, that there always was much misery in the world. It is depressing that now that there are possibilities to improve many people’s lives, so little is done. Perhaps it may help that one is beginning to realise that our own future, because of the greenhouse eﬀect, depends very much on what happens in tropical countries, and if they are to stop cutting down the forests they must be compensated. And this may help to improve their standard of living. I am still concerned about nuclear weapons. There is no acute danger, largely thanks to Gorbachev, but the crazy stockpiles are not healthy, and many Western governments, including Mrs. Thatcher, are behaving very stupidly.

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We had Sakharov here recently when he was given an honorary degree. He is now strongly anti-Gorbachev and very pessimistic about progress with restructuring. Still, there is the old saying “An optimist is a person who says the future is uncertain”, and in that sense I am still an optimist! With best wishes, Yours, [Rudi]

[885] Waltraud Krause to Rudolf Peierls Berlin, 27.8.1989 Lieber, sehr geehrter Herr Dr. Peierls, Ach k¨ onnten Sie doch unsere Freude u ¨ber Ihre Briefe sehen! Als ich gestern — nach Empfang und Lesen Ihres lieben Briefes — gleich Frau Augustin anrief, weinte sie nur. “Ich weine vor Freude und Ergriﬀenheit dar¨ uber, daß Rudi so lieb an mich geschrieben hat! Ich kann es gar nicht fassen!” Eben komme ich von ihr, weil sie doch auch meinen Brief lesen sollte. Sie ﬁng wieder an zu weinen. “Nein, ist das lieb von Rudi! So nat¨ urlich. Daß ich in meinem Leben noch einmal mit ihm in Verbindung kommen darf!” Ob Ihnen die Ohren geklungen haben? So sagen wir doch in Deutschland, wenn man an jemanden ganz intensiv mit guten Gedanken denkt? Frau Augustin weiß nicht, daß ich schon etwas u ¨ber ihr Leben an Sie berichtet habe. Das will sie n¨ amlich nicht. Seit Tagen hat sie einen sehr schlimmen dicken Zeigeﬁnger. Heute ist er sogar verbunden. Sie will morgen versuchen, an Sie selbst zu schreiben. Noch einmal meinen herzlichen Dank f¨ ur Ihren Brief mit all den beantworteten Fragen. Wegen des Grabes Ihrer Frau Mutter sprachen Frau A[ugstin] und ich eben auch. Als G¨ artnerstochter und Blumenh¨andlerin schl¨ agt sie vor, daß man eventell Efeu oder Immergr¨ un pﬂanzen sollte. Ob das Ihnen und Ihren Geschwistern so recht w¨ are? Dann k¨ onnte ich eine Grabpﬂege anmelden (incl. Gießpﬂege). Weil ich dienstlich im Sommer nicht so oft zum Gießen auf zwei Friedh¨ ofe

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gehen kann (meine Eltern sind in Karlshost beigesetzt, weil es vor 17 Jahren auf unserem Friedhof keine Erdbegr¨ abnisse sondern nur noch Urnenbestattungen gibt), habe ich in Karlshorst und f¨ ur meine Angeh¨ origen in Obersch¨ oneweide auch diese Pﬂege schon viele Jahre bestellt und bin auch zufrieden. Daß Ihre Schwester Annie nicht mehr lebt, ist ganz sicher schmerzlich f¨ ur Sie als Br¨ uder. Ich liebe meine Schwester (5 Jahre j¨ unger) und meinen Bruder (10 Jahre j¨ unger als ich) und deren Familien sehr und w¨ urde sie sehr, sehr vermissen! Wie wird sich Frau Wilhelm freuen, wenn ich ihr erz¨ ahle, daß ich von Ihrer Familie h¨ ore. Ihr Mann Georg war doch die gesamte Schulzeit mit Ihrem Bruder Alfred (als “Primusse”). Als Georg nach dem 1. Weltkrieg nach Hause kam, sorgte Ihr Herr Vater f¨ ur seine 1. Anstellung. Herr Wilhelm ist schon seit vielen Jahren verstorben. Aber das schrieb ich schon im 1. Brief. In dem Geb¨ aude Ihres fr¨ uheres Lyzeums, Luisenstraße waren im Laufe der Jahre die verschiedensten Schulzweige etabliert: Hilfsschule, Sprachheilschule, seit einigen Jahren hat die K¨ openicker Volkshochschule das Haus gemietet. Ihr Gymnasium ist seit vielen, vielen Jahren eine 10 klassige Politechnische Oberschule, d.h. dort gehen alle Kinder bis zur 10. Klasse. Die Jungen und M¨ adchen, die f¨ ur das Abitur vorgesehen sind, gehen dann zwei Jahre zur erweiterten Oberschule. Eine ist in K¨ openick und heißt “Alex[ander]-v[on]-Humboldt-Schule”. Nat¨ urlich w¨ urde ich mich riesig freuen, Ihre Autobiogaphie besitzen zu d¨ urfen! Aus kl¨ uglichen Gr¨ unden m¨ ochte ich Sie aber herzlich bitten, eventuell bei Gelegenheit Ihr Werk zu meiner Schwester: Anita Edelmann, Bargeheider Str. 147a, Hamburg 73, D2000 zu schicken. Meine Schwester hatte Ihre Sprache studiert und w¨ urde mir dann auch beim ¨ Lesen und Ubersetzen helfen k¨ onnen. Vielen herzlichen Dank schon heute f¨ ur Ihre M¨ uhe! In der Festschrift zum 25. Bestehen Ihrer alten Schule, geschrieben von Herrn Dir. Strohmeyer, ﬁnde ich folgende Zeilen u ¨ber Ihren Vater: S. 9 “Einen nicht geringen Freund und G¨ onner hatte die Anstalt ebenfalls bis weit in die Nachkriegszeit hinein in dem langj¨ ahrigen Direktor der Kabelwerke Obersch¨ oneweide, Herrn Dr. Heinrich Peierls. In der inneren Ausstattung der Schule, bei Veranstaltungen derselben und

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bei unz¨ ahligen sonstigen Gelegenheiten hat Herr Dir[ektor] Dr. Peierls der Anstalt in der großz¨ ugigsten und hochherzigsten Weise geholfen. Auch ihm sei deshalb an dieser Stelle gleichfalls der herzlichste Dank ausgesprochen.” S. 12 Das Kuratorium, das bis zur Eingemeindung Obersch¨ oneweides in Groß-Berlin bestand, blieb in seiner Zusammensetzung die ganzen Jahre hindurch fast unver¨ andert und bestand aus folgenden Mitgliedern: Vorsitzender: B¨ urgermeister Berthold Sch¨ oﬀen: Baumeister Lehmann, Fabrikbesitzer Feldmann, Rechnungsrat Herwig Gemeindeverordnete: Dir. seigent¨ umer Nollenberg

Dr.

Peierls, Dir.

Nordquist, Hau-

dazu der Direktor der Anstalt Dr. Strohmeyer In der Festschrift beﬁndet sich auch eine Fotograﬁe Ihres Herrn Vaters. Ob Sie ihm etwas a¨hnlich sehen? Vielleicht einige S¨atze zu unserer Familie, damit Sie wissen, wer die Krause-Leute sind. Unsere Eltern waren liebe, einfache Leute (Vater Schlosser, vor 1933 sehr oft arbeitslos) immer sehr aktiv in unserer Christuskirche (Kirchenchor, Bl¨ aserchor, M¨ utterkreis, Kirchen¨ altester u.a.): w¨ ahrend der Hitlerzeit geh¨ orten meine Eltern der Bekennenden Kirche an, und unsere gesamte Familie ging in den unseligen 12 Jahren zum K¨ onigin-Elisabeth-Hospital zum Gottensdienst, weil sich dort heimlich die Bekennende Kirche traf. Diese Zugeh¨ origkeit war f¨ ur mich ausschlaggebend, daß ich sofort am 8. Juni 1945 in den Schuldienst kam. Ich war und bin’s noch: mit Leib und Seele Lehrer. Von jahrzehntelangen Schwierigkeiten, als Christ Lehrer zu sein, k¨ onnte ich nur m¨ undlich erz¨ alen!!!!! Treue F¨ urbitte meiner Eltern, viele Katholiken hatten mich immer wieder durchgebetet. Meine Geschwister durften studieren. Anita wurde Englisch-Lehrerin in Berlin und ging mit ihrem Mann Anf[ang] der 50er Jahre nach West-Ber[lin] und dann nach Westdeutschl[and]. Beide Kinder sind verh[eiratet]. Bj¨ orn ist Arzt, ebenfalls seine Frau; Kerstin ist Computer-Fachm¨ annin, Dipl.Ing. wie ihr Mann.

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Meine Bruderseele studierte mit vielen Schwierigkeiten in Leipzig Theologie und ist immer noch in seiner 1. Pfarre in Th¨ uringen im Amt. ¨ Seine Frau ist auch Arztin, seine vier S¨ ohne haben es als Pastorens¨ohne bis zum heutigen Tag nicht einfach, die Ausbildung, den Beruf zu erlernen, den sie gerne wollten. Sebastian wurde mit vielen Umwegen Solo-Pausonist im Leipz[iger] Sym[fonie] Orch[ester], Henning wurde Tischler, Tilmann studiert noch in Jena Theologie, und Melchior beginnt ab 1.9. in Jena am Technikum. O weh, nun ist das aber ein langer Brief geworden! Bitte verzeihen Sie, das war gar nicht meine eigentliche Absicht, aber ich kam dann ins Erz¨ ahlen. Inzwischen ist es 18.30. Ich merke, daß sich mein Magen nach einer Schnitte meldet. Mit dem herzlichen Wunsche, daß es Ihnen und Ihren Lieben gut gehen m¨ ochte, daß Sie ausreichende Gesundheit haben d¨ urfen, und Ihnen auch viel Freude immer wieder geschenkt werden m¨ochte, verbleibe ich mit vielen Gr¨ ußen Ihre Waltraud Krause Bitte entschuldigen Sie die vielen Tippfehler, ich bin keine Maschinenschreiberin. Meine große Hochachtung, daß Sie so ﬂießend in unserer Sprache schreiben! Ob Sie sie auch immer wieder m¨ undlich “benutzen”?

[886] Bram Pais to Rudolf Peierls Copenhagen, 28.9.1989 Dear Peierls Today I write to ask if you could help me get a certain piece of information — if it exists at all. It concerns the visit of Heisenberg to Copenhagen in 1941.1317 1317 The Bohr-Heisenberg meeting of September 1941 has occupied scientists and science historians, not least because no contemporary record of what was discussed between the two scientists during their meeting exists. See ‘The Bohr Heisenberg Meeting September 1941’, www.aip.org/history/heisenberg/bohr-heisenbergmeeting.htm.

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In 1947 Ronald Fraser, attached to the British Military Government in Germany as scientiﬁc advisor, arranged for Heisenberg and himself to visit Bohr in Copenhagen for the purpose of reconstructing what they discussed in 1941. As far as I know Bohr and Heisenberg could not agree on what was and was not said. Question: Could there exist somewhere a report by Fraser about the 1947 meeting — in which Fraser participated? I realise that this is not quite up your alley, but write in the hope that you might provide me with a lead. I need not say (to use one of Bohr’s favourite phrases) that I do not wish for you to have any inconvenience as a result of this letter. From October 1 on I shall be back at my permanent address Rockefeller University, New York NY 10021. With my thanks for your consideration, and with cordial regards,

Bram Pais

[887] Rudolf Peierls to Bram Pais Oxford, 3.10.1989 (carbon copy) Dear Pais, I am afraid I have no idea how to ﬁnd a statement by Ronald Fraser about the 1947 meeting.1318 I doubt very much that such a statement exists in the public domain, because many historians are interested in the famous conversation between Bohr and Heisenberg that someone would have picked it up before now. If it is not published, how would one ﬁnd it? Have you tried to discover the executors of Fraser’s estate to see if he left any papers and where they are? 1318

See Pais’ query in letter [886].

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If such a note exists, I doubt if it would contain anything new. Both Bohr and Heisenberg have repeatedly given their impressions of the conversation; is it likely that either of them would have changed his mind? Your sincerely, Rudolf Peierls

[888] Rudolf Peierls to Lillie Krynen [Oxford], 6.12.1989 (carbon copy) Dear Lillie, Thank you very much for your card and for your good wishes. I, too, wish you a very happy Christmas and a wonderful stay in the US. These good wishes will not reach you until after the event, as I don’t know your address in America. (Didn’t you promise to send addresses?) But I am in time to wish you a very happy and healthy 1990, at least I hope this will reach you before the end of that year! I could not remember your dates, it seems that you were in Spain, and I tried to phone you there, but always got an “engaged” signal — perhaps there was a fault. Life has been quiet here lately, with only one trip in October to a one-day meeting in Pisa to celebrate the 70th birthday of a friend and colleague.1319 Otherwise, meetings and dinner parties (I now had several parties for 8 which makes it lively) and slow progress with my book. And concerts. We had a very mild autumn with many sunny and clear days; now it has turned a little colder but still mild. I enclose a copy of my general Christmas letter — you already know most of it. I also enclose a photo of some ﬂowers on my table which I liked. I believe they are called “day lillies”, because they b[l]oom only 1319

Peierls attended an informal symposium and a banquet to celebrate Luigi Radicati’s 70th birthday.

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one day — though mine lasted much longer. You are certainly not a “day-lillie”! Hope we can get in touch again when you return. Let me know. Love, [Rudi]

[889] Etienne Bauer to Rudolf Peierls Paris, 17.12.1989 Thank you, dear Rudi, for your paper giving such good (and hectic) news from someone important for me, meaning you. I remember the “continuing committee” with you and Powell.1320 I was very impressed, but now I wonder I remember Bernal dining at home and showing us early photo from the young Chinese revolution. All those people — and there were so many, an overcrowded landscape, — building a dam and carrying the earth, a stick on one shoulder with one basket of earth at each end. Bernal was so full of admiration; we know now what ﬁerce stupid slavery the “bond en avant” has been. We simply have been blinded and fooled. We fooled ourselves. You ask me at the end of your letter if I like the developments in Eastern Europe. Not such an easy question: Russia has been ruled by enlightened tsars as Peter the Great, Catherine, followed often by good willing people who freed the serfs, who tried what they could. They have been killed. Or all their reforms thrown to the dogs: remember that Peter had decided that the tsarevich could be chosen out of the imperial family! Then came Lenin; Karenski could, may be, help Russia to become a little more democratic?? Lenin disbanded the ﬁrst Duma democratically elected. And, dear Rudi, we did not understand. We fooled ourselves 1320

Peierls had sent his annual Christmas letter at the beginning of December. Bauer’s comment refers to the British Pugwash group.

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with Marx and all that, not seeing the fact that Marx would probably have the importance of Proudhon or Ricardo if he had not been incarnated by Soviet Russia. Of course I like what happens in Eastern Europe. It is impossible not to hope. But history writes itself slowly. The germans can not not be the germans, coming back and how could they do otherwise? To the “buts de guerre” of 1915(?) which were roughly to rule over the Austro-Hungarish Empire, and, through him, over the whole Mittel Europa. They were the best before the 1st World War, so they are to day, as were the japonese when they won the war against Russia at the beginning of these century. What is going to happen, I don’t know. Nobody knows, as always. My guess would be that the blessed equilibrium of terror which gave us so many years of peace will go on. The new fact is that the weakness of Russia is obvious even to itself. And then what? Again, nobody knows. History is seldom pink or pale blue. Can Russia survive the loss of the Baltic states, the revival of religions, the explosion of micronationalisms as Georgia, Armenia, not to mention Ukrainia? What about the ultra panslavic anti-Semitic trend? The economic chaos in a country which had never a year of freedom? The Obomolov tradition? Still I am an optimist, may be because, as you know, I think you can do anything with a nuclear weapon except war. Will the unavoidable new owners of the weapon know about it? So long there is no “real” war and more freedom, what else could I do but rejoice. Except I know I have been a fool and don’t know why I would stop being one. Excuse the length of this letter and my English: Merry Xmas, New Year and all that Etienne B.

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[890] Rudolf Peierls to Etienne Bauer Oxford, [date unspeciﬁed] (carbon copy) Dear Etienne, My question was meant to be rhetorical, as I cannot imagine that any reasonable person would not be pleased by the change in Eastern Europe. But I am glad that it provoked you into writing such an interesting letter.1321 I am interested in your description of how we have all been fooled. I was never fooled by Lenin and Stalin; perhaps I had the advantage of a Russian wife and many close contacts in the Soviet Union to see the facts clearly, but even before that I never had any illusion, perhaps because as a boy I had studied Das Kapital carefully and decided it was nonsense. Yet I thought Pugwash essential, because even attributing the worst of motives to Stalin we had a common interest with him in stopping the arms race. In thinking about the phenomenon of so many reasonable people being fooled, I see the principal cause in the attitude “My enemy’s enemy is my friend”. Stalin was Hitler’s enemy, so he was our friend. Ceaucescou at one time took a stance independent from Moscow, so we developed a friendly relation with this awful man. The US in particular have been led into supporting many terrible regimes because they were anti-communist, even now San Salvador, the Contras, earlier Battista and, up to the last minute, Marcos. Perhaps your exultations of the merits of the tsars has a little of the argument enemy x enemy = friend? (I agree of course that the tsars in general were preferable to some of the modern dictators.) As a policy it is hard to say “the plague on both your houses” because taken to its logical consequence this means not cooperating with anybody, because every regime has some ﬂaws. The reasonable solution, to accept other countries or movements as they are, warts and 1321

Letter [889].

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all, without illusion, but to cooperate whenever this is to the mutual beneﬁt and does not hurt anyone else takes great maturity. As regards East Europe, of course we must rejoice at the changes — though one would have hoped for a less bloody revolution in Romania, but it much [easier] to be clear about the enemy than to work for constructive measures. The economic problems won’t go away, even democratic politicians can be stupid and even corrupt, and some injustice will emerge. Yet, I am also optimistic, at least in the sense of the old deﬁnition “an optimist is a person who thinks the future is uncertain.” A friend in Poland says at the end of a letter about physics, he was reminded of the old curse: “May you live in interesting times!” We certainly do. With best wishes Yours sincerely Rudolf Peierls [891] Rudolf Peierls to Bram Pais Oxford, 23.8.1990 (carbon copy) Dear Pais, My only comment on your story is that Kapitza may well have been unaware of Fuchs.1322 I believe he was not involved in the detailed work on the bomb. Others did know. I asked several Soviet physicists, including Artsimovich, how much time Fuchs saved them, and their estimate ranged between one and two years. I do not recall the date, but it was not many years after 1956. Of course it is also possible that Kapitza did know and was discrete. Yours sincerely Rudolf Peierls 1322

Abraham Pais was ﬁnalising his biographical work on Niels Bohr to be published the following year. In this context he had evidently approached Peierls for information. Original letter could not be located. Abraham Pais, Niels Bohr’s Times, in Physics, Philosophy and Polity, Oxford: Oxford University Press, 1991.

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[892] Lillie Krynen to Rudolf Peierls Brussels, 26.8.[1990] Dearest Rudi! Hope this reaches you well! It was so good to see you again! We spend a good and exciting time in London and could even visualize ourself to live there for a few month. Maybe — who knows, ﬁrst I have to sell my place here and in Spain! That is my main issue now, once sold I can plan ahead! Thank you also for the lovely tea you gave us — if I lived nearer to you would come more often for sure! Will keep you posted on how things will turn out — Shelly is going back to Tampa on the 22nd of September and myself 7th of October. Like to be some time with my son Robert. Do take care of yourself and drop me a card or a letter how you are getting along Rudi — yes!? Franz always called me Lady — I wish I was a real one with name — Send you much love Rudi, always Lillie

[893] Bram Pais to Rudolf Peierls Copenhagen, 3.9.1990 Dear Peierls, Thanks so much for yours of August 23.1323 Your question: was Kapitza aware of Fuchs? is of course quite legitimate. I have thought often about that — also long before I wrote my letter. I cannot swear on a stack of bibles that he did, but have concluded that he had. That was also the impression of my American lecturers who were present at that dinner. It would help a lot if our Soviet colleagues would go public with part of not all their H bomb story. If ever you come across any of that in print I’d appreciate your telling me. 1323

Letter [891].

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My Bohr MS is now in the hands of the publishers.1324 Its tentative title is Niels Bohr’s times: In physics, philosophy and polity. Among the many items I emphasize in the MS is the great importance of the Frisch-Peierls report. I have also done my best to collect all I could ﬁnd about the Heisenberg visit in 1942. With all good wishes, Sincerely yours Bram Pais

[894] Rudolf Peierls to Mark Richmond Oxford, 5.2.1991 (carbon copy) Dear Sir Mark,1325 I have been distressed by the news that it is planned to close the Nuclear Structure Facility at Daresbury, the last resource of nuclear physics in this country. I would like to remind you of the reasons — perhaps not quite obvious — why the maintenance of this country’s share in this ﬁeld is important. 1. There are many links between nuclear physics and particle physics (both called “nuclear physics” in the rather misleading language of SERC). I do not have to argue about the importance of particle physics which is implicit in your continued membership of CERN. One of the contacts is that many experiments in particle physics have to use nuclei as targets, and that therefore a good command of their properties is essential for the interpretation of the experiments. Another example is the recent evidence of the existence of a 17 keV neutrino, which, if ﬁnally conﬁrmed, would provide a surprising new piece of information for particle physics. Another 1324 1325

Ibid., note 1322. Mark Richmond, Chairman of the Science and Engineering Research Council.

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example is the observed diﬀerence between nucleon-nucleon collisions at high energy in free space and inside a nucleus, which calls for an understanding of both nuclear and particle physics. In other words, even if there were an absolute priority on particle physics as the present front line of fundamental physics, continued progress in nuclear physics would be essential. 2. Nuclear physics is an important training ground in techniques which are important for particle physics and in many other applications. Such training is also possible, in principle, in particle physics, but the necessary size of the teams in that ﬁeld results in a narrow specialisation of their members. A young person working in such a team may get experience in only a very narrow range of techniques. The educational value of nuclear physics could, I am sure, be demonstrated by a survey of the careers of people who obtained a PhD in nuclear physics. 3. The intellectual challenge of nuclear physics is perhaps of importance only to a limited number of scholars, and might not have a strong appeal to non-specialists. Yet, other countries, including Germany, France and Italy are maintaining and increasing their expenditure in nuclear physics. 4. Nuclear physics is connected with nuclear energy. The present problems of nuclear power are mostly in engineering and economics and do not add much to the case for nuclear physics. However, it would be unwise to ignore the possibility that progress in academic nuclear physics might one day bring vital progress in nuclear power or other applications. We have seen too many unforeseen surprises in this ﬁeld. It is argued that research and teaching in the subject could continue by using facilities in other countries. This will always be a second best. It is tolerable at CERN whose facilities are beyond the resources of any one of the member countries, so that our physicists there do not play the role of poor cousins. I appreciate of course that SERC has the problem of slicing up too small a cake, and the origin of the diﬃculty lies in the inadequate funding of science as a whole. I am not recommending the closing-down of,

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say, condensed matter research in order to keep nuclear physics alive, but I would plead for some place of nuclear physics in the competition for inadequate resources. I assume of course that you continue impressing on the government the impossibility of adequately supporting research within the present ﬁnancial limitations, of which this is an extreme example. Yours sincerely Rudolf Peierls [895] Mark Richmond to Rudolf Peierls Swindon, 11.2.1991 Dear Sir Rudolf, NUCLEAR STRUCTURE PHYSICS Thank you for your letter about the Nuclear Structure Facility (NSF). Unfortunately it arrived too late for me to see it before the meeting of Council on 6 February. However, I am sure you will be pleased to learn that Council did not decide irrevocably to close the NSF; rather it instructed me to look urgently for ways to run the facility, at least through 1991 and 1992, so that we can honour the ﬁrst stage of the UK-French agreement to develop and run the EUROGRAM detector array. To help Council in its further consideration of this issue, a study will be set up to assess the importance of the science being carried out at the NSF in the context of the Council’s work as a whole. I fully recognise that the NSF is a leading facility for nuclear structure research, and acts as a focus for much more of the UK nuclear structure physics programme. However, we are currently under considerable pressure as a result of recent Government decisions on funding and whilst we will be working hard to make cases to Government to increase our budget for future years, we have no guarantee that these cases will succeed.1326 Yours sincerely, Mark Richmond 1326

The Daresbury Laboratory, formed in 1962 as part of the National Institute for

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[896] Rudolf Peierls to Hans and Rose Bethe Oxford, 25.3.1991 (carbon copy) Dear Rose and Hans, I am writing to conﬁrm my conversation with Rose about my threatened appearance in Ithaca. I would arrive from Toronto on 21 May, probably in the afternoon, but I have yet to study the plane connection, and, if I may, stay until the morning of the 24th, to go to Long Island. I shall be at a conference at McMaster University on 17 May, address: c/o R.K. Badhuri, Dept. of Physics, McMaster Un. Hamilton Ont. L8S 4N1. staying at the visitors’ inn, in Hamilton. From Saturday 18 to Tuesday 21 May I shall stay with Mrs. I. Jephcott, 323 Rosemary Toard Toronto, Ont. M5P 3E4; phone (416)483-6777. If people are interested, I could give a seminar on “Spontaneously Broken Symmetries”. After my controversy with Phil Anderson, which you may have seen in Physics Today,1327 I have made some more progress, and have, I think, a new way of looking at the phenomenon. Love, [Rudi]

Research in Nuclear Science (NIRNS) did not close down. In 1994 the Daresbury and the Rutherford Appleton Laboratory merged to form the Daresbury and Rutherford Appleton Laboratories (DRAL); and in 1995, DRAL were brought under the umbrella of the Council for the Central Laboratory of the Research Councils (CCLRC). 1327 Peierls had exchanged views with P.W. Anderson about this issue in an open controversy largely through the medium of academic journals. See P.W. Anderson, ‘Broken Symmetry can’t compare with ferromagnets’, Physics Today, (5), 117 (1990); R.E. Peierls, ‘Spontaneously Broken Symmetries’, J. Phys. A 24, 5273–79 (1991).

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[897] Nevill Mott to Rudolf Peierls Cambridge, 7.5.[1991] Dear Rudi Many thanks for your paper on broken symmetry — a subject often mentioned in papers on high Tc . Your paper certainly helps me to see what this is about.1328 Best wishes, Nevill I see you don’t agree with Bell or with hidden variables. Nor do I — but I’ve never thought about it very much. High Tc is fascinating. I think the evidence is overwhelming that “tides” (in the oxygen?) form pairs strongly bound, and do not dissociate at Tc , but become a non-degenerate bose-gas. So it is just like 4 He and one has to look at the fascinating work on this; back is Feynman and the more recent work that only 10% of the He alone at T=0 have k=0. Can one have at T=0 a gas of bose (or liquid) (not a crystal) that is not a superﬂuid? I think one can. Yours Nevill [898] Rudolf Peierls to Nevill Mott Oxford, 11.5.1991 (carbon copy) Dear Nevill, Thank you for your letter.1329 I know of course, of your idea that in High-Tc substances there are pairs above Tc . When we met at Harwell, 1328 1329

See letter [896], note 1327. Letter [897].

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it occured to me that it should be possible to test this by looking at a Josephson function between a high-Tc substance above its Tc and a conventional superconductor. Do you agree that this is right? If so should one urge that this be tried? I do not know the answer to your question whether a Bose liquid could fail to be a superﬂuid at T = 0, because I do not understand, and tend to distrust, realistic theories of superﬂuidity. My guess would be that for strong purely repulsive forces this should be possible, but I have no arguments. Yours sincerely, Rudolf Peierls

[899] Nevill Mott to Rudolf Peierls Cambridge, 22.9.1991 Dear Rudi, I’ve undertaken to write to Royal Society Biographical Notice for Herbert Fr¨ ohlich.1330 I have many papers from his widow, + also Gerard Hyland at Warwick. I wonder whether you have any views on his achievements in particle physics — how important it was. It may be that Hyland is too enthusiastic — I don’t know. I think I should come over to Oxford to talk to his brother (sorry I thought he was in Oxford) — and if you could spare the time I should like to discuss this with you. Also a point in physics. Best wishes, Nevill

1330

N.F. Mott, ‘Herbert Fr¨ ohlich (1905–1991)’, Biogr. Mem. Fell. Roy. Soc. 38, 145–62 (1992).

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[900] Rudolf Peierls to Nevill Mott Oxford, 1.10.1991 (carbon copy) Dear Nevill, I was in China when your letter arrived,1331 hence my late reply. I would of course be happy to see you when you come to Oxford. Alternatively, I shall be in Cambridge on 18 October for the Chadwick celebrations,1332 arriving by a morning train from London. The meeting starts only in the afternoon, so if you happen to be in Cambridge that day, we could perhaps meet then. I cannot recall any work by Fr¨ ohlich on particle physics — perhaps I missed it or have forgotten it. If you have the references this might refresh my memory, or I could get an assessment from the particle specialists. Yours [Rudi]

[901] Rudolf Peierls to David Tabor [Oxford], 2.11.[1991] (carbon copy) Dear Dr. Tabor, Thank you for sending me your note about Orowan, which I found very interesting.1333 I did not see any errors of substance, but I am not of course familiar with all the aspects of his life. 1331

Letter [899]. In October 1991, James Chadwick’s centenary was commemorated with a meeting at which Peierls was a ‘passive participant’. See ‘Dear Everybody’, 12.10.1991, Peierls Papers, Supp. A.26. 1333 David Tabor had sent a copy of an obituary of Egon Orowan to Rudolf Peierls for comment. See Peierls Papers, Supp. K.69. 1332

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One minor point: I was not instrumental in getting him to Birmingham but of course welcomed his arrival. I think at one stage he worked in a light bulb factory, I think in Hungary. He liked to hold forth, and the strength of his experience there, about the folly of buying cheap bulbs, which cost more in power for the same amount of light. I was interested in what you say about his relations with Laurence Bragg. I had the impression that he resented not being adequately recognized and promoted in the Cavendish, but I cannot remember whether I formed this opinion from his own remarks, or at second hand. I remember one episode in Birmingham: He had an argument with experts about the mechanism of rolling metals. To demonstrate his point, he made a model of a section of a rolling mill, with the metal represented by plasticine, and when he turned the handle, the plasticine ﬂowed indeed the way he had postulated. Incidentally, the extreme formal politeness, which you call continental, is particularly Hungarian. We used to say that Hungarians generally have a polite shell over a hard core, and that in Orowan’s case the shell was particularly polite, but very transparent, and the core particularly hard. But of course I admired him for the qualities you have so well described. Yours sincerely, Rudolf Peierls [902] Freeman Dyson to Rudolf Peierls Princeton, 5.11.1991 Dear Rudi, Happy Guy Fawkes’ Day! Just two days after I came home I was surprised to see the package with “More Surprises” in my mail box.1334 Thank you very much for sending 1334

Peierls’ book More Surprises in Theoretical Physics had just appeared in print. R.E. Peierls, More Surprises in Theoretical Physics, Princeton: Princeton University Press, 1991.

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it air-mail. I have been enjoying it for the last few days. Especially I enjoy ﬁlling in the many gaps in my education, for example the Peierls transition, the Wiedemann-Franz law, the momentum of a sound-wave. Your explanations are delightfully brief and clear. I am sorry I didn’t have time to sample your cooking. With thanks. Yours ever, Freeman

[903] Andrew Brown to Rudolf Peierls Andover (Mass.), 17.11.1991 Dear Professor Peierls, Thank you very much for your letter and the copy of your Liverpool talk.1335 It was good of you to pursue the question of your wartime letters and disappointing to hear that they are still classiﬁed. Lorna Arnold’s list of ﬁles is most useful and should save me time in searching the Public Record Oﬃce — I have asked Margaret Gowing to thank her for me. There are certainly a number of your letters to Chadwick in the Churchill Archives. Some date from 1940 when you were both concerned with the ﬁssion cross section for fast neutrons. In 1941 you undertook some detective work with Fuchs at Chadwick’s behest to monitor the state of atomic research in Germany by studying the journals for evidence of signiﬁcant relocation amongst German scientists: no ﬁrm conclusions were drawn. One of my diﬃculties in writing this book is to present, as a nonphysicist, some assessment of Chadwick’s standing as an experimenter. He seems to have impressed Rutherford after a transiently shaky start 1335 Rudolf Peierls had been one of the the two key speakers at the Chadwick Centenary celebration in Liverpool in October 1991. Andrew Brown, who was preparing a biography of Chadwick, had asked him for a written version of the paper. The biography was later published as A. Brown, The Neutron and the Bomb, Oxford: OUP, 1997.

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(due to shyness) so that Rutherford recommended him for a prestigious 1851 Exhibition. This took him to Germany, where in 1914 he published what was clearly a seminal paper in which he observed that beta particles were emitted from radium in a continuous spectrum. This was a revolutionary observation made by a 23 year old scientist, working alone, which linked after a period of considerable uncertainly, to Pauli’s and Fermi’s hypothesis of the neutrino about 15 years later. The hall mark of Chadwick’s research seems to be the ability to construct simple apparatus which he employed with meticulous care in order to demonstrate previously unknown phenomena. His brilliance as an observer is epitomized by the way he unravelled the disagreements between Cambridge and Vienna over visual scintillation counting in the 1920’s. Certainly, by the Second World War, he seems to have become generally regarded as the supreme arbiter for experimental nuclear physics: the Americans initially mistrusted the results reported by Halban and Kowarski using heavy water. Chadwick was asked to scrutinize their experiment which he did, and his assurance about its validity was immediately accepted. More than this talent for experimental precision, it seems to me that Chadwick thought deeply about the underlying processes (which is probably one reason that he was so adept at demonstrating fundamentals). For example, in his 1969 interview he recalls learning of Heisenberg’s theory of nuclear forces in (?) 1932. In his joint paper with Bieler in 1921 on the collisions of alpha particles with hydrogen nuclei,1336 they had suggested that one explanation for their ﬁndings would be that the force inside the nucleus is not electrostatic. He said that with some mathematical help from Massey, he could have written the Heisenberg theory. This is not important of itself, but Chadwick always seemed very modest about his work and perhaps this led some to underestimate him. Your story about Chadwick challenging you and Bethe to calculate the cross section for the photodisintegration of the diplon seems to me another example of where he successfully completed an experiment which he sensed had some theoretical implications. 1336

J. Chadwick and E.S. Bieler, ‘The collision of alpha particles with hydrogen nuclei’, Phil. Mag. 42, 923–40 (1921).

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Please do not feel obliged to respond to any of the above, but if you did have any comments they would be gratefully received. Yours sincerely, Andrew Brown

[904] Rudolf Peierls to Andrew Brown Oxford, 2.12.1991 (carbon copy) Dear Dr. Brown, Thank you for your letter.1337 As far as I know, your assessment of Chadwick is very fair. I would add a strong sense of what is important, seeing the basic issues through a mass of details. I was interested in your ﬁnding a lot of correspondence between Chadwick and myself in the Churchill College Archives; I did not remember there was much written communication in the early forties. My recollection also was that the study of German periodicals was my own idea, whereas you say it was done on Chadwick’s initiative. Are there any letters settling this point? I do not remember whether in our conversation I mentioned the questions why after Rutherford’s death the electors did not chose Chadwick as his successor, as most of us expected. Rumour has it that he would not have been up to the social and oﬃcial duties of a Cavendish Professor, such as being host to the circuit judges. If that was indeed the reason, it would have been made ridiculous by his later record. The other puzzle is why, as master of Caius he never entered the Cavendish (except, I believe, on one occasion to examine a Ph.D. candidate). Was it because he was afraid he might get carried away into too much attention to physics, neglecting his duties to the college? Or was it perhaps lingering resentment at not being Cavendish Professor? 1337

Letter [903].

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I have a photo taken (not by me) at the 1947 Cambridge conference showing Chadwick talking with G.I. Taylor and looking unusually cheerful. If you would like to use that in your book I could send you a copy. Yours sincerely, Rudolf Peierls

[905] Andrew Brown to Rudolf Peierls Andover (Mass.), 22.12.1991 Dear Sir Rudolf, It was good of you to take the trouble to reply to my last letter.1338 I have recently written to the Nobel Foundation in Stockholm because I understand that they might release previously conﬁdential material about a Prizewinner, providing more then 50 years had elapsed. If true, this could provide a fascinating insight into Chadwick’s standing amongst his great contemporaries of the 1930s. On the question of your search of German periodicals in 1941, I have not yet copied the relevant letter verbatim. My note just said that Chadwick had suggested a literature search which Peierls and Fuchs undertook. I hope I have not misconstrued this and will write to the archivist to see whether he can provide a copy. From other correspondence, this came at a time when Chadwick was preoccupied with the possibility of a German bomb programme and he was concerned that American scientists were still publishing sensitive material in the open literature. Thank you for your observation about the Cavendish Chair. Sir Mark Oliphant made a similar comment to me in Cambridge. I doubt whether it was lingering resentment which prevented him from visiting the Cavendish during the 1950’s. Rather, I think, he would have been sensitive about intruding into somebody else’s territory and certainly 1338

Brown’s letter [903]; Peierls’ reply letter [904].

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would have required a formal invitation. As you know his Mastership ended after a period of quite intense unpleasantness. His daughters told me that he entered Caius on only two subsequent occasions. Once for lunch with a friend and the other occasion was his daughter’s wedding. Although his family were angry at the way he was treated by the College, he does not seem to have borne any grudges, but was not a gregarious man and perhaps was never at ease in the company of dons. I am sure you are right that he missed having a lab and would have wished to continue experimenting given the opportunity. I would love a photo of Chadwick looking happy for the book. With best wishes for Christmas and the New Year. Yours sincerely. Andrew Brown

[906] Hans Bethe to Rudolf Peierls Pasadena, 8.1.1992 Dear Rudi: I was terribly sorry to hear about your medical problems: ﬁrst your intestines and now phlebitis. Please take it easy! Stay in bed as much as you can, and let your friends and others help you with shopping, cleaning and everything else. I hope your troubles will soon clear up! We enjoyed your end-of-year letter, as we do always. It is amazing how much you do, travelling, going to meetings, and visiting friends and relatives. I get tired just reading your letter. And you go to such diﬃcult countries, e.g. China. I have given up travelling anywhere except the U.S. and occasionally Europe. But I hope I can go to Europe in June– July 1993: the Royal Society has invited me to give the Bakerian Lecture in June. This, I think, is a great honor, thinking of my predecessors, and I’ll have some trouble making it suﬃciently interesting. Who, by the way, was Mr. Baker? At present, I am again in Pasadena, having just arrived yesterday, Gerry Brown is here also we share an appartment, and he not only cooks

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but also provides the ideas for the physics we are doing.1339 Our oﬃce is right next to Willy Fowler’s. As usual, there are lots of interesting people around. We are trying to work on the transition from hadrons to quarks and gluons which seems to take place at a temperature of 150 MeV, as a second-order transition.1340 I am tremendously interested in the great changes in Russia. Today’s N.Y. Times had a picture of the Moscow Patriarch, in full robes, shaking the hand of Yeltsin. So Christmas has returned to Russia and Leningrad has reverted to St. Petersburg. But the hard part is yet to come, getting the economy going again Will the peasants deliver enough food? Can they get the factories which are now (or have been) to 60% on war time production, to produce civilian goods, and goods of suﬃcient quality? It is a tremendous problem. Soluble? Once more, I hope you get well soon. Gerry Brown joins me, and so does Rose. All the best! Hans

[907] Rudolf Peierls to Hans Bethe Oxford, 26.1.[1992] (carbon copy) Dear Hans, Thank you for your letter and for your injunction to take it easy.1341 I am being very sensible and spend much of my time with my legs up, with intervals of walking around, as instructed by my doctor. So far I 1339

Gerry Brown and Hans Bethe normally spent the month of January together at some university at the West Coast of America, Santa Barbara, Santa Cruz, but most often CalTech, to work together. 1340 G.E. Brown, A.D. Jackson, H.A. Bethe, and P.M. Pizzochero, ‘The Hadron to Quark-Gluon Transition in Relativistic Heavy Ion Collision’, Nucl. Phys. A 560, 1935–74 (1993). 1341 Letter [906].

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have had an army of friends doing my shopping, but next week I shall venture into town. I am glad to hear you will give the 1993 Bakerian Lecture, and I hope you will ﬁnd time to visit Oxford. You ask about Mr. Baker. He was an 18th century fellow, whose only distinction seems to have been that he left the society a sum of £100 to establish an annual lecture. As you say, the developments in Russia are very interesting. The picture is very confusing. In a week’s time two friends from St. Petersburg, distant relatives of Genia, will come for a visit, and I am looking forward to their impressions. As for the economy, I think people are terribly naive to think that as soon as you make rules for a market economy, things will immediately start to work. After all our market economies in the West (such as they are, not really text-book market rules, but much government intervention) have developed over generations, and involve many traditional mechanisms and conventions, which will not grow overnight. The fragmentation into smaller and smaller units, as in the USSR and Yugoslavia is worrying, particularly because of its eﬀect on the further proliferation of nuclear weapons. The news today is of a recruiting drive by Iran for Soviet nuclear weapons experts. Evidently, the IAEA regime is not strong enough. They would never have discovered what Iraq was doing let alone stopped them, if Iraq had not lost the war. Greeting to Gerry and other colleagues. Yours, [Rudi]

[908] Brian Cathcart to Rudolf Peierls London, 27.1.1992 Dear Sir Rudolf, You may remember me; you were kind enough to talk to me once about the Atomic Scientists’ Association. I hope this ﬁnds you well. I know you remain active in nuclear politics, as I saw recently that you were to address a Pugwash meeting in London.

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When we met, you said correctly that the ASA was not a good subject for a book. It took me longer to realise it. I did manage to put my research to use in two newspaper features, and I remain fascinated by British nuclear history. I am now well advanced in a more realistic book project, about William Penney’s atomic bomb programme from 1947–1952.1342 It is about this that I write. My principal question related to Penney at Los Alamos. He arrived there late, and new to the subject, and he left promptly at the end, yet all the British literature agrees with Gowing’s view that by the end “he knew more about the Los Alamos work as a whole than any other member of the [British] team”. How did he manage it? Your autobiography notes his ﬁrst-hand knowledge of the eﬀects of explosions in Britain. Was this really his passport around the various teams? There were many brilliant mathematicians there, could they not have done the same work? Did his knowledge at the end really extend so far beyond his original ﬁeld of blast waves? I am not sceptical about Penney’s abilities. I accept Gowing’s verdict, if only because it is clear that the Americans badly wanted to keep Penney. It is simply that I do not understand how he managed to impress so many people so thoroughly, and make himself so valuable, in so short a time. Do your memories of Los Alamos cast light on this question? I have one other question. When you left Los Alamos, I understand, you were not allowed to bring your research papers with you. Were you asked to return to Britain to write a report on your work in America? Do you remember if your colleagues were? To whom was the report given? Please go to no trouble. I would be most grateful if you could drop me a note to suggest a time when I might telephone you, or ring the number above if you have a moment, and we could discuss it. I promise that this time your thoughts will deﬁnitely be contributing to a book. Yours sincerely, Brian Cathcart 1342

The book was published in 1994. Brian Cathcart, Test of Greatness: Britain’s Struggle for the Atom Bomb, London: John Murray, 1994.

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[909] Rudolf Peierls to Brian Cathcart Oxford, [date unspeciﬁed] (carbon copy) Dear Mr Cathcart, Penney’s assignment at Los Alamos was, as you say, concerned with the eﬀect of blast waves and the measurement of their strength. But within Los Alamos there was no compartmentalisation, and all scientists were not only permitted to learn about all aspects of the work, but positively encouraged, since it was believed — rightly — that this would increase their eﬀectiveness in whatever we were doing. The only exception were purely military matters, such as the external shape of the weapons, the type of plane they were ﬁtted to etc. So Penney had the same opportunity as anyone else to learn about the design principles of the atom bomb. I do not agree with Margaret Gowing’s remark that he knew more than any other member of the British group, and I cannot imagine on what evidence it was based. I have asked her about this, but she does not remember. If it is correct, it can only mean that he made better use of the opportunities. The rule not to remove reports and other documents applied of course to everybody, including Penney, but there was no check. As far as I remember we were not supposed to be carrying classiﬁed papers; they were supposed to be handled by oﬃcial channels, and there of course only papers speciﬁcally concerned with the aﬀairs of the British team would be transmitted. However, nobody examined the papers we were carrying, except for the normal customs checks, so it would have been physically possible to “smuggle” documents, but I have no reason to believe that Penney or anyone else did so. As you know, several years passed between the time when Penney was given responsibility for weapons design and the arrival of the ﬁrst supplies of ﬁssile material. This was enough time to repeat many of the calculations that had been done at Los Alamos, and in any case, had to be calculated again, since for various practical reasons the bomb design would not be identical with the American.

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So the key information was not detailed numbers, but design principles and methods of calculation and test experiments, and that information was in the minds of all senior members of Los Alamos. On your second question: after returning from Los Alamos I never wrote a report on my work there, or on my knowledge of the work there, and I was never asked to do so. In the course of his work, Penney never asked me any questions about what I remembered, nor do I think he asked anyone else. This no doubt means that he remembered himself what he needed. Yours sincerely, Rudolf Peierls

[910] Jae Riebe to Rudolf Peierls Los Alamos, 18.3.1992 Dear Sir Rudolf, I am the liaison between the Los Alamos National Laboratory and the Los Alamos Little Theater for the 50th anniversary of the Laboratory, Los Alamos townsite, and the Little Theater. M.J. Poole gave me your name and address. We, the committee and I, were wondering if you might have a script from a 1945 or 1948 skit performed in Los Alamos. We would certainly appreciate it if you would, should you have it, send us a copy, as we are about to start work on a historical skit commemorating the anniversary. If you have any anecdotes or other information of interest from the years you lived here, we would love to have you share them with us. Sincerely, Jae Riebe

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[911] Rudolf Peierls to Jae Riebe Oxford, 10.4.1992 (carbon copy) Dear Mr./Ms. Riebe, Thank you for your letter of 18 March.1343 I believe the skit you are referring to is the one performed at the farewell party of the British members of Los Alamos in 1945. I did not myself take part in its preparation, since I was away from Los Alamos for a couple of weeks and returned only on the day of the party. I have, however, spoken to Philip Moon, who did take a prominent part. He conﬁrmed what I suspected, that there never was a script. There were some notes about changes of scenery etc. and the actors discussed the outline of the action, and then just ad-libbed. Moon promised to write down what he remembered about the play, and will send it to me, so that I can add anything that his notes bring to mind. He will send them to me in two weeks or so, and I shall pass them on to you. So you can expect some notes, but not a script, about two weeks after this letter. Also, I have in front of me a book, “British Scientists and the Manhattan Project” by F.M.Szasz of the University of New Mexico (Macmillan, 1992),1344 which has on pp. 43–44 a description of the party and the play. As the book is quite new (mine is a review copy, and it may not even be published yet) I shall try and enclose a Xerox copy of the relevant pages with this letter. The author acknowledges information from Sophie Tuck, the daughter of James Tuck. James was prominent in organising the play, and it is conceivable that his daughter might still have some notes of his. I do not know her address, but presumably you could ﬁnd it through Dr. Szasz. Yours sincerely, Rudolf Peierls 1343

Letter [910]. Ferenz M. Szasz, British Scientists and the Manhattan Project: The Los Alamos Years, London: Macmillan, 1992. 1344

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[912] Philip Moon to Rudolf Peierls [location unspeciﬁed], 12.4.1992 Dear Rudi, It was interesting to have your two phone calls about the request from Los Alamos for information about the party given by members of the British Mission.1345 I am glad that we decided that I should pass my contribution back through you, for it allows one or two minor comments that you might not wish to be made or that on the other hand, you might like to be included but would not feel you should make yourself. The account I had remembered was in fact by Bernice Brode and though you probably have one I enclose a photostat to give a framework for my own additions or (occasionally) contradictions. They will follow the order of Bernice’s text so I shall not give them numbers, nor shall I always space them line by line. Rudi, not Rudy? And not Honi Bretscher, even in pronunciation. There is a slight inference that Chadwick left for Washington because he and Aileen did not like their house. Knowing his sense of duty, I feel sure there were more important reasons, such as being able to talk face to face with General Groves. The maintenance of mutual respect between them was of utmost importance, and you will know more about that than I do. It was Sir James, and not Lady, Chadwick who authorised the party and indeed obtained oﬃcial contribution to its cost. We all contributed something material, if not ﬁnancial and the guest list was compiled by consultation; it comprised ‘ex oﬃcio’ and other distinguished names plus two chosen by each British family. Ours were two unmarried uniformed friends of whom I most clearly remember Master Sergeant Walter Breiter, the senior non-commissioned member of the Bainbridge group within which I worked. I forget how we worked out the problems of multiple invitations and ensured that both members of a married couple were asked but it was done. 1345

See letter [910].

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It is conceivable that Aileen Chadwick sent a message from Washington to buy the best available port but, beyond Chadwick’s insistence that it was not to be considered as a farewell party, rather a gesture appreciating the achievements and the friendships in which we had shared, I believe he trusted us about details. I hope I shall be able to retrieve a blank invitation card; Winifred acted as a secretary and there may be one in my mementos of her. If so, I will send a photocopy. This is the place to say that I have 13 photographs of the party and pantomime. I forget who took them but am sure they were widely circulated and expect that copies are already available to the organisers of next year’s celebration. Do you, Rudi, have a set and if so would it be useful to trace outlines of people we can identify? I would be reluctant to send my originals through the post, being sentimental about many good friends whom I shall not see again. Now back to Bernice’s text. I think you were chairman at dinner and it would be nice if that were said. I believe Jim’s claim to have checked the text of the Alamogordo’ episode with security; that would be only prudent, for we had a number of words that night be queried. Imaginary elements included dyspepsium, and silentium, which was accidentally dropped during the loading of the ‘tower’ and produced a loud bang. The thread of the pantomime was a frightened British (Philip Moon) relentlessly pursued by Security (Jim Tuck) and ﬁnally rescued by a Good Fairy (Winifred Moon, the only British wife who could display long pigtails with ribbon bows). There were various permutations of ‘security’ words such as Intelligence, Secret, Restricted, Limited, ending with Tuck’s displaying a placard LIMITED INTELLIGENCE at which stage the fairy intervened. It might be worth explaining Frisch’s sweeping; he was impersonating an Indian maid. The photos show her as a pilfering alcoholic and, though very funny, should in my view be suppressed, reducing my tally from 13 to 10. The dancing was largely to the accompaniment of Ernest Titterton, a very versatile pianist. While it went on, some of us went behind the scenes to wash dishes, etc. and after our guests left we tidied up everything so that there would be no work to be done by the staﬀ next morning.

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As he left, the very delightful Colonel commanding, whose name I cannot remember, took the trouble to go round shaking hands with a good many of us. He told me he would “never again allow it to be said that the British had no sense of humor”. Yours, Philip I hope the legs will soon improve.

[913] Rudolf Peierls to Jae Riebe Oxford, 20.4.1992 (carbon copy) Dear Mr./Ms Riebe, I now enclose a note from Professor Philip Moon about the party1346 and the pantomime, together with a copy of Bernice Brode’s account to which he refers, I regret I have nothing to add myself; Moon’s memory is evidently better than mine. As for the photos of the play which he mentions, there may be copies at Los Alamos (one is reproduced in Szasz’s book). If not, would it be useful to send them? I could explore the possibility of getting Moon’s prints copied. With best wishes, Yours sincerely, Rudolf Peierls

[914] Rudolf Peierls to Natasha, Annelya and Lev Belousov Oxford, 20.6.1992 (carbon copy) Dear Natasha, dear Annelya, dear Lev, Thank you for your letter, which arrived in a week, which is not too bad.1347 I am sorry I have not written for a long time, but time seems to pass very quickly, and I have a lot of oﬃcial correspondence. 1346 1347

Letter [912]. Letter could not be located.

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My health is now back to normal, and I can lead a normal life, including travelling. So far I have been for a week in Coimbra in Portugal, a charming old town with a beautiful old university, where I have many friends. In early July I shall go to Heidelberg for a few day’s conference, and after that brieﬂy to N¨ urnberg, to see my best friend at school, whom I have not seen since we left school in 1925!1348 Here we enjoy summer weather. Our economy is in bad shape, with high unemployment, and many business ﬁrms failing. In the university money for research is short, and the authorities try to improve eﬃciency; their idea of doing this is to make everybody ﬁll in endless forms. People in employment still have a good standard of living. I know of course that our economic troubles are much less serious than yours, and your position in turn is not as bad as in Sarajevo or in the Sudan — the world is not in good shape. All my family are well, but Kitty and her husband seem to be separating. As Gaby was divorced some time ago, that leaves two out of four marriages in tact, which I suppose is statistically normal today. Ronnie’s older son, Tim, is married, and Ben has a charming girl friend. Gaby now has a law practice in Boston. Jo is working very hard and doing well. We are watching the situation in Russia with concern. Market economy may be a good idea, but it cannot be established overnight, and in the process there is much dislocation and much opportunity for dishonesty. I hope it will come right in the long run. With best wishes, Yours sincerely, [Rudi]

1348

Rudolf Peierls visited his friend Heinz Rudolph in N¨ urnberg.

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[915] Brian Cathcart to Rudolf Peierls London, 27.7.1992 Dear Sir Rudolf, A few months ago, you were kind enough to write a most helpful reply to a letter of mine about William Penney and Los Alamos.1349 I am, you may remember, writing a book about the ﬁrst British bomb. I wonder if I could trouble you with a few further questions. First, however, let me pass on a fact I came across in my researches at the Public Record Oﬃce, which might be of interest to you. On 2nd July 1948, Penney attended, for the ﬁrst time, a meeting at the Atomic Energy Council with Cockcroft, Hinton, Portal and others. Setting out his plans for the weapon, he said at one stage that he “would be only too glad to obtain help from external sources such as Sir G.I. Taylor, Professor Peierls and others.” The Council decided that there should be a Weapons Technical Committee, involving consultants, but I have no trace of its activities. I must say that I am somewhat baﬄed as to why they made no use of your knowledge. They certainly consulted Fuchs fairly closely. The explanation that springs to mind is that they avoided you because of your considerable involvement with the Atomic Scientists’ Association. Does that seem probable to you? Another titbit I have come across at the PRO is that, just after the Japanese surrender, some or all of the British scientists at Los Alamos sent a letter to the British government urging it to support international control. I do not believe I have read of this elsewhere, and I wonder if you recall it. If you do, would you know where I could see a copy? And do you, by any chance, know whether Penney signed it? When I wrote last, I asked your views on a comment in Professor Gowing’s book that Penney knew more about the bomb than any other scientist. I have, I think, succeeded in tracing an explanation for this. First, the phrase was used by Lord Portal, who was exaggerating slightly a remark made in a memo by Michael Perrin. Second, it referred to the 1349

Letter [909].

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extent of Penney’s knowledge after the Bikini tests, when it is clear he learned a good deal about the American weapon. Finally, a general question about Penney. As chief of mission at Los Alamos, did you form any impression of him then? He was plainly a very able mathematician, but did you see in him then any of the qualities which led the government to entrust him with making the British bomb? Leslie Groves apparently came to rely on him and trust him, did you? I think I said when I wrote before that I do not wish to put you to any trouble. I can see from the footnotes of many books on my shelves that you are often pestered about Los Alamos memories. If it would be more convenient to you to answer by telephone, or if you would like me to come and see you, do let me know. Yours sincerely, Brian Cathcart

[916] Rudolf Peierls to Brian Cathcart Oxford, 6.8.1992 (carbon copy) Dear Mr Cathcart, Thank you for your letter.1350 To start with the end, I don’t mind answering questions, particularly when they are sensible questions like yours, and occasionally lead to interesting information. About Penney, I certainly did trust him. He was, in spite of his cheerful good manners, a rather private person, and I never got very close to him. I had no doubt that he was a competent theoretical physicist, and he was very knowledgeable and eﬀective in the area of his speciality, the study of blast damage. He clearly had a sense of what was important, and he preferred, and went after simple solutions rather than complicated ideas. These are positive qualities for a project leader. 1350

Letter [915].

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If I had been asked at the time whether he would become an outstanding leader of the weapons project, I would not have known. Experience has taught me not to try and predict people’s performance from general impressions. I don’t think I would have foreseen that Oppenheimer would become an outstanding leader of Los Alamos, although I had great respect for him. I am glad you cleared up the questions of Penney knowing most about the bomb. I naturally related this statement to bomb design, but if knowledge about the eﬀects of the bomb is included, it is a fair statement. Thank you for the information you unearthed in the Public Record Oﬃce. I am pleased, because I naturally assumed from the absence of an invitation that Penney somehow did not approve of me, and I am glad I was wrong. I do not know why the authorities blocked the invitation. My connection with the ASA does not look likely. A number of solid citizens, like Lord Cherwell, G.P. Thompson, and H. Skinner, were vice-presidents of the ASA. It could have been some other security trouble. From time to time there were reports from the FBI, based on garbled information, which caused me trouble. For instance, in 1951, I had diﬃculty in getting a US visa, and later I was barred, on US request, from access to US classiﬁed documents. It could also have been that they did not want too many people to know about the weapons work. I suspect G.I. Taylor also was never a member of such a committee, but perhaps he declined. I have no knowledge of a letter to the British government by members of the British mission in Los Alamos. I would be surprised if I had not heard of such a letter, but it is just possible that it was written and signed during our trip to Mexico after the end of the war, or later when I went back to London for a week or so, for meetings. It could also be that this relates to a letter which I wrote to Attlee. Returning from London, I heard that Attlee was in Washington, or was about to arrive there, and I decided to write to him. The details are hazy in my memory; I don’t know why I did not discuss this with anybody in Los Alamos, but time was pressing. Perhaps I even wrote the letter on the way in Washington. I doubt that the letter ever reached Attlee or anyone else that mattered. I kept no copy and do not remember much

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about its contents, which probably were rather naive. But it could be the basis of the rumours you heard. If a collective letter was sent, it could be that Philip Moon would remember. Yours sincerely, Rudolf Peierls

[917] Rudolf Peierls to Hans Bethe Oxford, 23.9.1992 (carbon copy) Dear Hans, I suppose you have seen the article in the September Bulletin by Goldberg and Powers, claiming that Heisenberg kept information about atom bomb design hidden from the German authorities and even from his colleagues, and thereby prevented a German bomb being built.1351 The New Scientist of 5 September refers to the article under this headline “Heisenberg principles kept bomb from Nazis”.1352 I am about to write to the New Scientist in protest,1353 but I do not think it is my job to write to the Bulletin. Do you know whether someone is picking this up, or are you?1354 I hear you are not coming to the Chicago meeting of the US and European Nuclear Societies, but you are one of the “Pioneers” and therefore no doubt have been sent the “consensus statement”. I told them I am not going to sign this, and gave my reasons — copy enclosed. I would be interested in your comments. 1351

Stanley Goldberg and Thomas Powers, ‘Declassiﬁed ﬁles reopen “Nazi Bomb” debate’, Bull. Atomic. Scientists, 48(7) 32–40 (1992). 1352 D. Charles, ‘Heisenberg principles kept bomb from Nazis’, New Scientist, (1837) September 1992, 4. 1353 R.E. Peierls, ‘Heisenberg Bomb’, New Scientist (1982) October 1992, 50 1354 See H.A. Bethe, ‘Bethe on the German Bomb Project’, Bull. Atomic Scientists, 49(1), 53–54 (1993).

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I do not remember whether I adequately congratulated you on the Einstein Prize1355 — I heard about it from Gerry so long before the news broke oﬃcially. Joe Rotblat is giving his prize money to the Pugwash Foundation and asked me whether you might be inclined to do the same. Any chance? I was twice in Germany, once in July at a meeting in Heidelberg, when I went for a weekend to Nuremberg, to see my school friend Heinz Rudolph, whom I had not seen for 65 years! Then a week at a Pugwash conference in (East) Berlin and saw a little of West Berlin where I had not been since 1934. Love to Rose, and to Linde, if she is still there. Yours, [Rudi]

[918] Rudolf Peierls to Victor Frenkel [Oxford], 13.10.1992 (carbon copy) Dear Vitya, I enclose 5 photographs, which have numbers stuck on their back. No. 1 is the one you asked for. It shows, left to right: Mrs. Simon, your brother, Pauli, your father, Tamm and F. Simon. No. 2 is taken on the same occasion. I believe the lady in the centre, in the black swimming suit is your mother, to her right Mrs. Simon, and the one to her right could be Eugenia Nikolaevna. No. 3 is Shubnikov, drinking from a drinking fountain in Batum, watched by two local boys. 4 and 5 are scenes on the “Grusia” during the post-conference excursion. 1355

In 1992, the Albert Einstein Peace Prize was awarded jointly to Joseph Rotblat and Hans Bethe.

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Please return all the photos; they are my only copies except No.1. I do not have the one with Pauli and Sack. Presumably von Meyenn would have the original or know where it is. During the conference a newspaper published a photo of Sack and me with a Polish physicist, taken at the railway station when we arrived. We were amused by the caption which I think described me as Pauli and Sack as Bloch; I kept the cutting for some time, but by now it is lost. I don’t suppose the newspaper oﬃce would keep photos that long? If they did, they might even have one of Shubnikov. Writing about Shubnikov, I hope you will not present the Shubnikow-de Haas eﬀect as a major achievement. It was a solid piece of work, but after the diamagnetic de Haas – van Alphen eﬀect no surprise. I believe de Haas, who was intrigued by the d[e] H[aas] – v[an] A[lphen] eﬀect thought the Sh[ubikov] – d[e] H[aas] eﬀect might help to ﬁnd an explanation, but in fact the theory of the ﬁrst is straight forward and can be made quantitative, whereas the other is qualitatively understood, but not easy to describe exactly. Houtermans I did know, but not closely enough to write about him. I do not know whether you have seen a long article about him in a recent issue of PHYSICS TODAY.1356 I do not remember who wrote it but it contained much detail that I did not know. If this journal is not available in your library, I shall try and send you a copy. About your other question concerning the coming centenary of your father’s birth, I hope it will be possible to get something published in the English or American journals, particularly as there was nothing at the time of his death; as you may remember we tried to get something later but did not succeed. As far as I recall, it is not unusual to have articles on the occasion of a centenary. For example, last year was the centenary of the birth of Chadwick, and there were memorial meetings in Liverpool and in Cambridge, but as far as I remember no articles. I think one could get an article published, but not collection of articles. That is never done here; we do not have the Russian custom of publishing, on the occasion of the birthday of a living scientist, or of a death, a book of 1356

Iosef B. Khriplovich, ‘The eventful life of Fritz Houtermans’, Physics Today, (7) 29–37 (1992).

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articles in which people write their recollections and assessment of the person. (I do not think it is a good custom, since the essays are usually not planned and there is a lot of repetition). You are asking about news. Life goes on much as before. After some illness in the winter, which prevented me travelling, I am now again free to get around. My last trip was to a Pugwash Conference in Berlin, and then a few days in Spain. In about ten days I go to North America for ﬁve weeks, travelling all over. But my eye sight is getting worse, and reading is very slow. For example it took me an hour to read you letter, although it was typed. (I was never a fast reader of Russian). We hear of course much of your political and economic problems, and hope they will be solved, but it looks diﬃcult. Best wishes, Yours, Rudolf Peierls [919] Hans Bethe to Rudolf Peierls Ithaca, 22.10.1992 Dear Rudy: In your recent letter you mentioned the article by Goldberg and Powers in the September Bulletin, and indicated that you do not agree with it.1357 I am now beginning to write a short article for the Bulletin on the same subject. I enclose the ﬁrst few pages of my draft, plus some pages of notes for a talk I’ll give at Cornell on November 19.1358 You will probably disagree with me also, so please let me know. It is nice to know that you are in this country. How long will you stay? It would be nice to see you some time during your visit to the U.S. All the best, Yours sincerely, [Hans] 1357

Letter [917]. Hans Bethe gave a lecture on the subject at Cornell. A videorecording of the talk is kept at Cornell. Bethe Archives, V-106, 131, 132. 1358

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[920] Bill Arrol to Rudolf Peierls Solihull, 29.11.1992 Dear Sir Rudolf, Two or three years ago, I saw you in the Athenaeum and whereas I recognized you, I didn’t think you recognized me. I ought to have reintroduced myself but didn’t and I have regretted it ever since. My reason for writing is that I have read the articles in ‘New Scientist’ about the ﬁftieth anniversary of the ﬁrst pile and William Brown’s article concerning you amongst others and the questions of the morality or otherwise of dropping the bomb.1359 I have never talked to any atomic scientist about my own wartime experience and its relevance to moral questions but it may go some distance in modifying the views of others. My ﬁrst paid job in 1938/40 was as a graduate assistant to G.M.B. Dobson at Oxford on the relation between ozone and weather. Dobson in 1940 oﬀered me a job of running a meteorological station in the Outer Hebrides, but I refused and joined the Navy as an R.D.F. (RADAR) oﬃcer. In nearly three years at sea in cruisers, I did, I suppose, well upwards of a thousand miles of convoy work, ﬁnishing up in August 1942 with the Malta Convoy of that month part of which was forced through and which prevented by only days the capitulation of Malta which was starving and with almost no air defence left. The 16-knot convoy itself was of fourteen of the fastest merchant ships we had, with the biggest escort ever assembled. Over four days, nine of the merchant ships were sunk, four got into Malta and the tanker Ohio was towed in by two destroyers. One aircraft carrier, two cruisers and two destroyers were sunk, one carrier was bombed and two cruisers — including the ‘Nigeria’ in which I was — were damaged by torpedoes. We got back to Gibraltar, were patched and sent to Charleston, South Carolina from whence, in early 1943 I was taken out of the Navy and sent to join the Montreal Laboratory. The almost instantaneous transition 1359

William Brown, ‘Forum: A breakthrough or just another bomb? William Brown considers the justiﬁcation for commemorating the science of destruction’, New Scientist (1849), November 1992.

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from war time conditions to peace time ones made me wonder why I had felt like I did over several incidents which had then recently occured. I saw three pretty gross breaches of the Geneva Conventions and had applauded all three. Again when I saw the carrier Eagle, within seconds of having been hit by four torpedoes, turn over and sink within minutes, I did not think: “My God, there are twelve hundred men aboard that ship”. I thought “Those lovely new aeroplanes sliding oﬀ the ﬂight deck, we could have used those.” Also when we were hit by one torpedo which killed ﬁfty eight men including two of my own, I felt absolutely nothing. Clearly, in peace time I would have deplored all this; in wartime I did not. After settling down in Montreal I read around a bit in books concerned with various aspects of philosophy and came across one which ﬁtted my own experience exactly. The author, whose name I have long since forgotten, came to what may be summarised as the conclusion that we are a great deal more primitive and tribal than we choose to ﬂatter ourselves that we are. In peace time a tribe is protective of its own people and reasonably decent to members of other tribes. As soon as war is declared, a tribe will be even more ﬁercely protective of its own and prepared to do extremely nasty things to the other tribe but with a perfectly clear conscience. In fact we live by two moral standards, not one, and it is therefore no good judging war time behaviour by peace time standards. Of course, this sounds counter to pretty well all religious belief, but I reckon it to be completely acceptable and a great deal more likely than the belief in a single moral code. There are two contemporary examples. The Serbs whose conduct we all deplore from a safe distance, regard themselves as being at war and therefore justiﬁed. Closer to home in Northern Ireland, I.R.A. considers itself to be at war, whereby killing and blowing things up are not only justiﬁed but desirable. We think of ourselves as at peace and regard the whole thing as just a persistent and irritating police action. My own view of the Hiroshima aﬀair at the time was that the ﬁrst bomb should have been dropped, but on a forest rather than a town on the principle that the Japanese were intelligent enough to have drawn their own conclusions. If that didn’t work, the second should have been dropped on a town. Subsequently, a cynical thought has occurred.

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Hiroshima was on ﬂat ground with very few stone buildings. Nagasaki was hilly and with lots of stone buildings. Thus the American Military could analyse at leisure the results and get the maximum information on the real eﬀects of nuclear explosions in warfare. I do hope you are well and continue to be so. Yours sincerely, Bill Arrol

[921] Rudolf Peierls to Bill Arrol Oxford, 4.1.1993 (carbon copy) Dear Bill, Apologies for this late reply to your interesting letter.1360 I was abroad when it arrived, and have been travelling a good deal since; I also wanted to think a little about what you said. I have no doubt that you are right in describing how war changes our attitudes to death, to killing, and to the “enemy”. It does not even necessarily take a declared war to produce this. There are exceptions, and one episode illustrating this sticks in my mind, though I was not actually present. In 1940 my wife was serving as a nursing auxiliary in the Queen Elisabeth Hospital. She was looking after some old women, some of whom had been bombed out. There was a daytime raid by a single German plane, which was attacked by RAF ﬁghters in full view of their window. When it was shot down in ﬂames, my wife wanted to cheer, but the old woman said: ‘The poor boy; he also had a mother!’ But this is rare. Since you mention this in the context of a discussion of the moral aspects of the atom bomb, you may be implying that there is nothing wrong with the general attitude and that it should just be accepted. If so, I would disagree. 1360

Letter [920].

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In war it becomes necessary to kill, or inﬂict injuries on people, to avoid damage to ourselves, our friends, our country, and in doing so one cannot always aﬀord to feel pity. But unnecessary violence, i.e. violence that does not serve the aims of the ﬁghting, is immoral. Thus it is generally accepted that it is wrong to kill defenceless prisoners. It also used to be thought that it was wrong to attack unarmed civilians, but in this respect there has been a change in our attitude. Of course, none of us are omniscient, and it is not easy to predict the consequences of any particular action, and whether it will, or will not, promote one’s aims. The bombardment of cities was explained by the belief that this would undermine the morale of the enemy, and weaken its determination. In World War II this was probably not true, but it was based on a genuine belief it must be accepted. However it seems to me that there was no serious attempt to analyse how the population was likely to react, and the decision was in part taken because it seemed the easy thing to do. I believe the main danger of nuclear weapons, when the enemy has no deterrent, is that it is so easy, that a single plane or missile can do what otherwise requires a whole air ﬂeet, so that in a situation of stalemate there is a great temptation to use nuclear weapons when one cannot think of anything else to do. I may well have misunderstood the implications of your letter, and if so I apologise. Please let me have your comments. Yours sincerely, Rudolf Peierls

[922] Bill Arrol to Rudolf Peierls Solihull, 18.1.1993 Dear Sir Rudolf, I was very interested indeed to receive your letter1361 and in particular the exception you mentioned over the war time experience of your wife 1361

Letter [921].

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in the Q.E.Hospital. I would regard her reaction as entirely normal in the circumstances and that of the old woman as exceptional. Leaving aside for the moment two issues; the bomb and, as I hope to mention later, satellite T.V., I think the present moral tribe position is not at all desirable but it is a global fact of life. If one is living at a given time under a moral code dictated by one’s tribe, things one sees or does are accepted with a clear conscience. There will always be a comparatively small proportion of exceptions; criminals in peace time and paciﬁsts in war. The question of conscience needs stressing. I remember an occasion during the Malta relief convoy when one of our destroyers had forced a U-boat to surface and its crew were surrendering lined up along the foredeck. The destroyer came in still ﬁring its forward four inch gun. As it happened it did not do any more damage as it could not depress the elevation enough, but I didn’t think: “Oops, he ought to check ﬁre,” I actually said: “Good, that’ll teach the bastards”; an attitude I would never have taken in peace time. I never met anybody in three years in the Navy who had the slightest doubts about the rightness of all we were doing; this included incidents considerably more dubious than the above one. I hope I do not misinterpret your view as accepting, once a war has started, that there may be a continuum of increasing violence with occasional large bumps like the introduction of mass bombings of civilians. This, I am sure, would be the view of the vast majority of people and is perfectly reasonable. The alternative, which I accepted at the end of WW2, was the existence of two almost opposite moral codes acting as a bistable system. The moment a country were to ﬁnd itself in a war situation whether declared or not, the population would ﬂip into the wartime code and at the end of hostilities, ﬂip back to the peacetime one just as in the case of the primitive tribes. This would have been so up to the end of WW2. What then about the bomb and satellite T.V.? Looking at the former in 1945 from the point of view of General Groves and his colleagues, they would have been operating in the wartime moral code where anything goes. Their country had suﬀered the humiliation of Pearl Harbour. They had realised both on land and sea the ﬁghting qualities of the Japanese and they had a fair idea that in the event of nuclear

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war they could nip into a deeper shelter when things ﬁnished, could emerge and go on governing their countries. This idea has long since gone. The next phase was the nuclear arms race in which the USSR and the USA each built warhead stock of over 10,000 a country in hours. Why each of these countries should build up such excessive stockpiles may be explained by J.K. Galbraith in his latest book (with a title like “The Politics of Contentment”)1362 something to the eﬀect that the American defence industry has become so large and powerful that it is eﬀectively a political entity out of control of the government. The collapse of communism in the USSR makes the situation dangerous not merely because a nuclear warhead is so easy to deliver, but because there are several countries such as Iran and Iraq both rich and totally irresponsible and are keen to buy Russian military surplus stores including bombs. The impact of TV on warfare is not to be ignored. A good case can be made that America lost the Vietnam war not only because they couldn’t beat the Vietnamese on the ground but that the constant, night after night TV broadcasts eventually disgusted the home viewers who wanted to return to normal. The Gulf War was a brilliantly-fought halfwar which stopped dead in its tracks when the so-called Turkey shoot of smashed Iraqi trucks and bodies on the road to Basra was shown on American CNN. The funniest latest example was the landing of the gallant 20,000 US troops on the beaches of Mogadishu to tackle the wicked Somali Clan Chiefs. All the cameras were lined up behind the beach as the landing craft ﬁnally turned up. The ramps were lowered and out came the troops including one who fell ﬂat on his face in the sand. The home viewers expected drama and got farce. To sum up: because of the inﬂuence of my own wartime experience I am prepared to accept the view that we are more primitive and tribal than we care to think and that this involves us in a bistable system of morals; the two codes of this system applying respectively in peace and war being very diﬀerent indeed. 1362

John Kenneth Galbraith, The Culture of Contentment, Boston: Houghton Mifﬂin, 1992.

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In the case of all countries, this principle still applies and did so among large powers until 1945. From this stage, the build up of nuclear weapons has up till now precluded their further use through good old fashioned fear. Instant satellite television is beginning to have an eﬀect on war. The insatiable public demand for entertainment in the States and the almost impossibility of maintaining military secrecy means that some future wars may be brought to an end by TV audience disapproval rather than military exhaustion. I hope all this helps to explain the view of wartime morals which I and perhaps others feel to be more in accordance with the military history than the usual one. Yours sincerely, Bill Arrol

[923] Lillie Krynen to Rudolf Peierls Tampa, 27.1.[1993] Dearest Rudi, Hope the new year has started well for you and that you are back your old self with your good health! You had quite something to go through last year — hopefully it will be a better one this time! As always, I enjoy so much your letters — I truly do Rudi — they are part of my life even when so far away, for you were also part of my “father” when you were in Heidelberg — I loved it whenever I visited Mama and Franz — seems so long ago — and I miss them very much · · · Did I tell you that my uncle Robert from Berlin passed away last year, age 91, now I have no one left in Germany (he was Franz’s brother) as you may have known. You always have such exciting trips Rudi — I envy you very much! From Berlin to Spain you went — how wonderful — I loved Spain, enjoyed for 10 years, but alone it became a hassle for me + I have put it on the market for sale. Have some Spanish people interested — hope they can pay.

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Then you went all the way to North Amerika to see all your familie — wonderful! When you were there — I was in Kenya visiting my son Paul + wife Liliane + my granddaughter Evelyn — it was so good to see them again after 2 years, they are too far away for me, but love it there — Paul was running a Restaurant there with “Swahili food’ very special + novelty to the tourist — he also does Bushtours to show the tourist how the African live and eat + this culture, he does it real nice — but not much money in it, Paul is a giver and enjoys what he does, he does go through a lot of Malawi, my worry all the time — but he says Mom I have to live with it. — Am back here since Oct. Xmas spent in California, Fremont with Peter and Nina + their family, it was a good change from Tampa — my life here is too qu[iet] for me really Brussels is more my cup of tea — also I have more connection there! To call Europe is expensive + I have to restrict myself — but have regular contact with Robert and Paul. This summer will be in London around Aug[ust] maybe we could see you it would be so nice Rudi — Cannot give you any speciﬁc dates yet, but know it will be August. Will of course let you know in time, when I am back in Brussels some time in May. My time is spent on painting and going to some classes to improve myself + I think I did a lot already. Maybe one of your trips will bring you to Brussels again — that would be so nice — the last time we had such a good Rabbit Lunch. Do you still cook? I do a lot here for eating out is not always to one’s expectation, specially in Tampa. But then once in a while it’s a nice change. Shelly is working on tax returns for three months now — it’s quite complicated here the tax! Dear Rudi — hope this reaches you well + that you can enjoy “home a little”! Have you ﬁnished your 2nd book? The Inaugural was quite interesting to see — hope Clinton can really do something better for all of us — we shall have to see — Keep well + do keep in touch — as I say I love your mail — and you, Rudi — send you sunshine and love Lillie

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[924] Rudolf Peierls to Hans Bethe Oxford, 7.2.1993 (carbon copy) Dear Hans, I do not know how long you are staying in Pasadena, so I am sending this letter in two copies.1363 You ask about the level of the Bakerian lecture. As far as I know, the audience will be scientists, predominantly physicists, but only a minority of theoreticians, and few experts on astrophysics or whatever your subject will be. So I would say it should be a serious lecture, with substantial content, intelligible as far as possible to the non-expert, but not excluding some passages of recent results that would be best appreciated by the experts. Is that a reasonable picture? Talking of the Bakerian lecture, I would be interested to know about plans for your visit. The point is that this year’s Pugwash Conference in Sweden is from 10 to 15 June. I am certainly going to be at your lecture (in fact I am supposed to take the chair as Atiyah has to be somewhere else). I hope you will come to Oxford during your visit, and I would not like to miss that. So if you plan to come here after the Bakerian lecture, I would skip the Pugwash Conference completely. If you plan to come here before the lecture, I might attend the second half. I expect you will stay with Linde, but if for any reason this will not work, you (and Rose, if she is with you) would be welcome to stay here. I have another question: I am reviewing Power’s book for the New York Review of Books. I have read about 3/4 of the book in proof.1364 I ﬁnd it has many interesting bits of information I did not know. I also ﬁnd that he is very sloppy, and practically every item I can check from my own knowledge is somehow garbled. So I am suspicious of what I cannot check. Where he quotes from documents I assume he quotes correctly, but I do not necessarily accept when he quotes from such secondary sources such as Robert Jungk or David Irving. 1363

See letter [906], note 1339. Thomas Powers, Heisenberg’s War: The Secret History of the German Bomb, New York: Knopf, 1993. 1364

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One episode which I found surprising is when Bohr arrived at Los Alamos with the famous sketch by Heisenberg and claimed that the Germans might have a weapon using slow neutrons, and that you and others had to argue to convince him that this made no sense. I ﬁnd this surprising since Bohr was the ﬁrst to point out that you could not get a powerful explosion with thermal neutrons. But Powers cites documents which seem to leave no doubt. No doubt you remember the episode: is it right that Bohr was temporarily so misguided? Greetings to Gerry Brown and/or Rose, Yours [Rudi]

[925] Hans Bethe to Rudolf Peierls [Ithaca], 19.2.1993 Dear Rudi: Thanks a lot for your prompt letter,1365 and thanks for your advice about the Bakerian Lecture. It turns out that the public lecture which I gave last week at Berkeley, as a rehearsal ﬁts your description quite well. It was a success. Our plans are to go to Oxford after the lecture. We probably want to look at a museum in London on Friday (11 June) in the morning and then take a train to Oxford some time in the afternoon. We expect to stay until Tuesday (15 June) afternoon, then go to Manchester where I’ll repeat the lecture — just about 60 years after we both came there. Of course we expect to stay with Linde, but thanks very much for the oﬀer to put us up. We very much want to see you of course. Sorry the time coincides with the Pugwash, and thank you for giving that up. On the story of Bohr bringing Heisenberg’s sketch to Los Alamos, this is quite wrong. Bohr gave it to Oppy and said: “the Germans talk about an atomic bomb, and this is what Heisenberg gave me.” 1365

Letter [924].

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Bohr said nothing about slow neutrons (which is in accord with your remark that Bohr had pointed out that you could not get a powerful explosion with slow neutrons). Instead, Edward Teller and I, looking at the picture, said “this is obviously a reactor”, and others concurred. We wondered what the Germans could possibly want to do with it? drop it on London? I was interested in your reaction to the Powers book.1366 I also found it had many interesting bits of information that I did not know. But I did not ﬁnd contradictions to my own knowledge — probably I did not read it as attentively as you. I did correct some (unimportant) scientiﬁc inaccuracies, which I wrote him about. When he quotes Robert Jungk, this is of course totally unreliable, but David Irving, I thought, was pretty good — even if in later years, D.I. became much too pro-German. There will be lots to talk about. See you again in London and Oxford. Yours Hans

[926] Rudolf Peierls to Bill Arrol Oxford, 10.4.1993 (carbon copy) Dear Bill, It is over two months since I received your letter of 18 January.1367 The delay in my reply was partly due to my being under pressure of other problems, but I also found it diﬃcult to formulate my reaction. I agree with much of what you say, but I believe your picture is too black-and-white. In theory the morality of war is that violence is necessary to ﬁght a war, but that any violence which clearly does not contribute to winning is amoral. The obvious example is killing 1366 1367

Ibid., note 1364. Letter [922].

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prisoners or soldiers who are surrendering. This is accepted by most of the civilian population in wartime and there are many examples of simple people being friendly and helpful towards prisoners of war. Once people are involved in actual combat, their attitude may be diﬀerent, as you say. I have never been in that situation, and cannot claim to know how I would behave if I was. But surely there were many reports of sailors rescuing survivors of enemy ships. The fact that, as you say, this attitude is not general, should not be taken as showing that it does not exist, or is very exceptional. Of course these moral principles are sophisticated and go against the grain of the simple “friend-or-foe” attitude, and they can easily go by the board in moments of excitement, and under the inﬂuence of mass movements. I do not therefore believe that there is an absolute distinction between peace and war. Take the case of popular indignation against vicious criminals, such as the recent case of the murder of a toddler by youths.1368 Here people started attacking a house because a boy there had been interrogated by the police (who found him innocent). Here the police are able to prevent the violence, and in doing so they are supported by the bulk of the population. But that is not always so; remember the lynch law in the southern US during the last century. This was not war, but there was mindless violence all the same. Or consider Northern Ireland. There is no declared war, but the IRA and their supporters feel justiﬁed in using indiscriminate violence, as do the loyalist activists. Yet the majority of people with strong feelings on either side, deplore the violence. How does this ﬁt into your picture? As you say the media can inﬂuence the civilian population against violence, but they are also capable of building up hatred that leads to violence. Life is too complicated to believe in simple regularities. Yours sincerely, Rudolf Peierls 1368

In February 1993, a two-year old toddler was abducted and murdered by two ten-year-old boys, and incident which had widely reported and had caused public outrage and much debate.

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[927] Bill Arrol to Rudolf Peierls Solihull, 27.5.1993 Dear Rudi, I have been holding back on answering your letter1369 as I have been watching developments in the former Yugoslavia. I ought at this junction to state that I do not for a moment want to persuade anybody of my views on morality in war and peace any more than I would argue with a man on his religious views when I haven’t any. It would be fun, though, to put the proposition to a professional moral philosopher, but I don’t know any such person. Recently I have thought of two scientists who were in their respective services in the war. One was Peter Schoeck who was director of Research of Bosch when I was President of EIRMA — the European Industrial Research Management Association; an organisation of 160 of the biggest ﬁrms in Europe from Finland to Portugal, as represented by their research or technical directors — Peter Schoeck had served as a midshipman in the German Navy and was very proud of that fact. The other is Dr. Phil Raesbeck, whom I recruited from the staﬀ of Birmingham Chemistry Department and who was my successor at Lucas. Philip was giving me a lift in his car the other day and was able to discuss things. I knew that he had volunteered for the RAF when at the minimum age and had ﬂown three years with Coastal Command piloting ﬂying boats, followed by a year in Bomber Command. He had never felt the slightest compunction about bombing cities. The Germans had to be beaten and that was that. I am quite prepared to concede that a theory based on primitive tribalism in modern times is black and white rather than gradualist and would further allow that the tribes may be somewhat frayed at the edges. Nevertheless the general principle could be sound. Lynch Law in the U.S. in the last century was indeed tribal; the white tribe dominant but frightened of the fecundity of the numerous but suppressed black tribe. In 1943 I was for several months in Charleston, 1369

Letter [926].

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South Carolina where the equivalent of apartheid was just as strong as the conditions I had seen in South Africa. Lynch Law earlier was, I am sure, a deliberate policy of suppression rather than just a mindless violence. In Northern Ireland the situation is such that the IRA do regard themselves at war. Their organisation is military and there is not the slightest compunction visible in their actions. The main reason why the government must treat the situation as a civil police action may well have a lot to do with the forty million Americans who regard themselves of direct Irish descent. The tribal aspect is exacerbated because of the mass movement of Scottish protestants to Northern Ireland some three or four hundred years ago. Ex-Yugoslavia represents a situation of even greater complexity with its roots, like those of Northern Ireland, going back centuries. The three tribes — Croats, Moslems and Serbs are frayed a bit at the edges through local intermarriage and trade but once a tripartite civil war has been in operation, separation has again taken place. We can regard the French, British, Canadians and odds and ends as fourth tribe which regards itself as at peace and just trying to help. This lot are supposedly being checked and paciﬁed by the United Nations — and there’s a multitribal organisation for you — which has shown itself to be completely powerless to intervene militarily and powerless (fortunately) to persuade anybody else to do so. The ultimate outcome is still not foreseeable, but probably after much futile hand wringing, the Serbs will keep all they’ve got and ﬂop back to respectability again. A naughty thought occurs to me, that in ten or twelve years time — although I shall not live to see it — the then President of the United States, Ms Hillary Clinton, will invite President Karadzic to address a Joint Session of Congress on “Peace in the Balkans”. After all it was only seventeen or eighteen years after the exposure of the Holocaust that Kennedy said “Ich bin ein Berliner”. Truly, politics is a wonderful thing. In Europe I feel that tribalism should be encouraged to stop the French and Germans from turning a free trade area into a federal republic. You may have heard the updated description of the ideal European.

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He should have the sense of humour of the Swede, the incorruptibility of the Italian, the modesty of the Spaniard, the respect for law of the Frenchman and, of course, the complete lack of hypocrisy of the British. With kind regards. Yours sincerely, Bill

[928] Rudolf Peierls to Bill Arrol Oxford, 4.7.1993 (carbon copy) Dear Bill, I am again late in answering your letter1370 — I was travelling and was unwell part of the time. Your description of the “tribal” reaction is evidently correct. The question is whether we should approve of it. If I understand you correctly, you see no objection to any manifestation of tribalism, and regard even lynch-law as a reasonable reaction, like our reaction to the Nazis. I must say I ﬁnd that hard to believe. I suspect that if you were watching a lynch mob, you would feel as disgusted as most people. Now that there is more or less peace between black and white in the US, has the white tribe been defeated? What you call tribalism is not far from “herd instinct”, and I believe that we are in a morally better position if we try to rise above the herd and make our own judgements about right and wrong. You say it would be interesting to put these problems to a moral philosopher. I do know a moral philosopher in New College,1371 though I do not meet him very often. If you have no objection, I might, when I next meet him, show him our correspondence and get his comments. 1370

Letter [927]. Jonathan Glover, New College Oxford. Rudolf Peierls passed the correspondence to J. Glover, who replied in a detailed letter of 30.5.1995. Letter in family possession. 1371

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But of course if one consulted ten moral philosophers one would get ten diﬀerent answers. About Yugoslavia I agree with you, and by now it is evident that the Serbs are going to keep all they have. An interesting phenomenon is that people who have lived peacefully and on friendly terms with their neighbours see them as enemies as soon as ﬁghting starts in the area. It seems that the mainstream mechanism for this is fear — they expect these people to turn against them. Best regards, Yours sincerely, Rudolf Peierls

[929] Rudolf Peierls to Victor Frenkel [Oxford], 7.10.1993 (carbon copy) Dear Vitya, First let me thank you again very much indeed for looking after me so well, and thank you and Olga for the hospitality.1372 This is my ﬁrst opportunity of doing so, because in Rome I was taken ill with pneumonia and other troubles, and after a day in hospital there I was taken to hospital in Oxford, from which I was discharged yesterday. I am sending on your letter to Mott, with some delay, and will now approach the Oxford Press.1373 In this I have some queries. Firstly I 1372

Rudolf Peierls had visited Russia in September 1993 to attend the celebrations for the 75th anniversary of the Ioﬀe Institute. (See ‘Dear Everybody’, 5.10.1993, Peierls Papers, Supp. A.26.) From there he went to Italy to deliver a paper on ‘Technology Transfer through research training’ at the Accademia Lioncei Workshop, but was taken ill while in Italy. 1373 Viktor Frenkel was hoping to get a biography of Fritz Houtermans published in English, and Peierls tried to help him make contacts with Oxford University Press. He approached OUP, and engaged in an exchange of letters with Donald Degenhardt who disagreed with Peierls on the intellectual and economic viability of the project. See letters to and from Donald Degenhardt, 10.10.1993, 26.10.1993, 19.10.1993 and 1.1.1993, Peierls Papers, Supp. E.58.

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must confess that I did not write down, and cannot remember, the subjects of the two biographies, other than Gamow’s, that you are planning. Then, it seems to me that it would not be a good idea to propose to the Press three alternative subjects, for them to select. To me this would give an impression of lacking seriousness. It would be preferable to start with a deﬁnite proposal, perhaps of Gamow, of whom the Press will know enough to judge the importance. But one can add that, if for some reason they regard the subject as untimely, you have the material for the other two studies, and could write them up. But of course all this is subject to your approval. We should also make it clear whether you would send the text in English, or in Russian, with their ﬁnding a translator. Presumably you would be willing to send a specimen chapter if asked. I have not yet been able to look into the question of the E-mail, and therefore will try to phone you at your home on Sunday (10.10.) to get the answers to my questions. I hope the number I have, 552-69-85, is still correct. Yours sincerely, Rudi

[930] Etienne Bauer to Rudolf Peierls Paris, 6.1.1994 Dear Rudy, It’s lovely receiving your yearly bulletins, but I miss you. I mean you, the smiling gentleman, full of genuine opinions of your own. I know you have so many ﬁends the world over that you have to use a general way of saying “I have not forgotten you”. What else could you do? It brings back so many things. Thank you, dear Rudy. I have decided not to go any more to the Pugwash meetings: I am too puzzled by the world as if I — or any body except you — had ever understood the known or unknown parameters that shape history. When I read about past events (incidentally, what is an event?) for instance the French Revolution or the 14/18 war, no historian for as

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much as I know ever told me how or why it all began: causality links don’t seem to have been seriously established because, seem’s to me, they cannot be. Economic science has the advantage to express itself by ﬁgures. Economists never predicted the end of the prosperity, no Kremlin expert announced the fall of the Russian Empire. I am lost, Rudy, Hitler was so convenient and nice to oﬀer us a world in which good and evil were patent. Don’t think I am sad: lot of friends, Lyda included, bad painting but it thrills me to do it. It’s simply that I have lost the illusion that my brain, any brain, is able to understand. Maybe you if you understand my English. Rudy, I remember dancing with Lady Peierls and that laugh, Bernie, slowly gone, Pierre Auger, Francis Perrin, brothers in law and ﬁrst among the pugwashites. But there is the Nouveau Louvre, “A thing of beauty is a joy for ever”. How true! But who said it? Love from Etienne B.

[931] Rudolf Peierls to Etienne Bauer Oxford, 8.1.1994 (carbon copy) Dear Etienne, Thank you for saying so politely that my annual letter was too impersonal — it was. Like you, I am depressed about the state of the world, with a few exceptions — improvement in South Africa, though still possible trouble ahead, and perhaps, perhaps, peace in the Middle East. But how can you expect historians, or anybody else, to explain why things are happening? Any historian who claims to do that must be na¨ive or dishonest. The progress of history is like Brownian motion, and no physicist is able to predict the course of that, I am exaggerating a little. Brownian motion is governed by a large number of collisions, comparable in magnitude and each extremely small

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compared to the resulting change of momentum. The factors governing historical events are not quite as numerous, and diﬀer greatly in magnitude. Occasionally there is a jolt that makes a noticeable diﬀerence and may be regarded as one of the causes of world events. But never as the single cause. For World War I there were also many reasons. The assassination in Sarajevo was one of many. I lived in Germany at the time, and heard an interesting one: The German Government at ﬁrst did not take the situation as very serious. During the critical weekend nobody was on duty in the German Foreign Ministry, when an urgent message arrived, I think from London, asking that the government was evasive, and that aﬀected the British and French reaction. This had some inﬂuence on the course of events, but of course also not a decisive one. Pugwash is one of the factors that can sometimes inﬂuence things, but not usually in a decisive way. At the moment it is not clear to me what openings we have to get any eﬀect, and perhaps the only argument for continuing is to keep the organisation going to be ready to act when the chance arises. With best wishes, Yours sincerely, Rudolf Peierls

[932] Andrew Brown to Rudolf Peierls Andover, Mass., 23.1.1994 Dear Sir Rudolf, I was sorry to learn about the deterioration in your eyesight, and appreciate all the more your careful reading of the chapter.1374 I will make some minor revisions in the light of your comments. Your remarks about Nunn May were interesting and now I look at my notes, Chadwick had similar reservations. He wrote to Massey in 1374

Rudolf Peierls had read a draft chapter of Andrew Brown’s biography of James Chadwick. See letter [903], note 1335.

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1946, when Massey had just become Chairman of the Association of Atomic Scientists and was proposing to give evidence in Nunn May’s defense. “I am not suggesting that you should not act as an advisor to his counsel, if you were asked to do so, but I think it would not be wise to espouse his cause too warmly or jump spontaneously to his defense without some knowledge of the circumstances. He is entitled to the best defense that can be provided for him, but I am afraid that some of our friends and colleagues may take up May’s cause without reﬂection and from political prejudice. I have already heard the words “scientiﬁc witchhunt” and similar phrases. This is pure nonsense. I am quite certain that proceedings would not have been taken against May only after very thorough investigation and out of a deep conviction that he had committed a serious oﬀence.” With best wishes, Yours sincerely Andrew Brown

[933] Hans Bethe to Rudolf Peierls [Ithaca], 7.6.1994 Dear Rudi, I hear from Linde that you are not at all well, that you have trouble both with your heart and with your kidneys. I hope both of them will clear up soon and that you can go home and enjoy life. Thank you for your statement about Fuchs coming to Los Alamos. It was helpful. I think the matter of that miserable book is fairly well under control; you may be interested in the enclosed Op. Ed. in the Washington Post. But I suppose the book has good sales nevertheless. The book reminded me of the past, as did a story which (for some reason forgotten) I had to tell several times: how we visited Chadwick in 1933–34, when he was disintegrating the deuteron together with Goldhaber. He bet that we could not make a theory of that process and on

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the way back to Manchester, on the long train ride, we did of course solve it. Do you remember? During that year, 1933–1934, you introduced me to nuclear physics. Yes, I think you did — I was too much stuck in my old work, like order in alloys (Kellnerinnen, you remember),1375 while you were always open to new problems. So we worked together on the deuteron, neutron-proton scattering, and then we wondered about Wigner or Majorana forces. It was the basis of my work for several years at Cornell, including my three articles in Reviews of Modern Physics. Altogether my year with you in Manchester was one of my most productive years, and maybe yours, too. Manchester was dirty and foggy, but I remember it as a happy time. I am amazed we could do so much work with Gaby just in her ﬁrst year, She must have been an exemplary baby. Later came Los Alamos, again a very productive time for both of us. And then 1948 when Rose and I visited you in Birmingham, and just at the time Dyson wrote me a letter that he had shown that QED converges in every order. We had an interesting time in physics, and often together. Including just a year ago at the Royal Society, which you described to well. I could not hear the questions and you could not see the questioner. With all our disabilities, I hope we’ll see each other soon again. Always yours, Hans [934] Rudolf Peierls to Hans Bethe Oxford, 9.7.1994 Dear Hans, As you will understand I was not in a position to respond immediately to your wonderful letter, but by now I can try. No doubt we both learnt 1375

Genia Peierls had coined the phrase ‘Kellnerinnen’ (waitresses) for Bethe’s method of working out order/disorder transitions in binary alloys. See S. Lee, Peierls Correspondence, Vol. 1, letters [33] and [34].

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[things ??]1376 from each other, but I am sure I learnt more from you than vice versa, but let us not argue. What I never learnt was persistence. I remember Genia’s [face] when she found one evening that because of a small error you had scrapped several days’ work and started again. You ask if I remember our bet with Chadwick. I certainly do, and it is written up in my memoirs. Do you remember [???] Some recollections intrude, which are not related to physics such as your habit of numbering letters and pages in letters. (What totals did you ﬁnally reach?) [???] Your habit of consulting two watches at once to eliminate [systemic] errors and [???]. Now after two weeks in hospital, (heart, kidneys and lungs) and two weeks of convalescent homes I am starting a new life. It is clear that in the foreseeable future I shall not be able to look after myself. So the only options are: Get someone else to live with me in the ﬂat or to live in a retirement home. The ﬂat’s not really suitable for joint occupation, so I am trying the alternative for a few weeks. This is a beautiful estate in the middle of the country, roughly 5 miles from Oxford. I have a room with bathroom and meals, very good meals, are provided. [???] of course means a [???] restricted lifestyle. All this time Jo had been great, as have the others, but not to the same degree. Love to Rose, Rudi

[935] Bruno W. Augenstein to Rudolf Peierls Santa Monica, 7.3.1995 Dear Professor Peierls, Chandrasekhar and I have corresponded over a draft of the enclosed paper, which deals with one of his enthusiasms — namely the role of 1376

The letter was hand-written at a time when Rudolf Peierls was physically frail. Some passages are illegible.

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beauty and simplicity in physical theories. A point of that correspondence prompts me to write to you. The primary theme of my paper is that Iwanenko and Landau in 1928 published a paper detailing a theory of the relativistic spin 1/2 electron, with a treatment comparable to that of Dirac in spirit and tested outcome; I argue that the Russian paper was eﬀectively independent of Dirac’s conception. The main point of my paper is that the comparative simplicity of Dirac’s theory made it the lasting clear winner of the competition for a proper spin 1/2 theory. The Russian paper asserts that the theory it treats is, however, indeed equivalent to that of Dirac, a conclusion I ﬁnd plausible in my paper, although Iwanenko and Landau gave no formal proof. Following the correspondence with Chandrasekhar, it struck me that you might have some deﬁnite historical and participant insights into these issues. As well as being a preeminent world physicist, you were most active in that era, and I believe you knew among other things, as to whether and how these theories and their origins were discussed in their day (since published discussions seem essentially absent), and whether Landau himself (or others) pursued the Russian theory far enough to test the formal equivalence to the Dirac/Iwanenko and Landau theories. There are some nice points in the Russian arguments. I would be very appreciative of any comments you might have on these issues, which seem to me to be of potential interest and historical relevance. Cordially, Bruno W. Augenstein Enclosure: Dirac, Frenkel, Iwanenko and Landau in 1928 — An Instance of Parallel Evolution and the Role of Simplicity? B.W. Augenstein, 1994.

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[936] Hans Bethe to Rudolf Peierls [Ithaca], 8.9.1995 Dear Rudy: I am very sorry you have so much trouble with various parts of our body. It must be very trying, and you have been very brave living with all this. It reminds me how much our lives were connected, beginning with Sommerfeld’s reading room where all the graduate students sat, and we giggled together so much. The Americans, Rabi and Condon, thought we were laughing at them. Perhaps the most productive year in my life was the year I spent in your house in Didsbury. You introduced me to Nuclear Physics — I believe I had not realized that it was the coming subject. Our trip to Cambridge has become famous, when we saw the Chadwick-Goldhaber experiment. Chadwick challenged us: I bet you cannot ﬁnd a theory for this photo-disintegration of the deuteron, and then we worked it out on the train back to Manchester. Physics was then · · · easy. Then there was our paper saying that the free neutrino would never be observed because the cross section was so small. Our cross section was correct but we never dreamed of powerful neutrino sources, reactors and supernovae. And the work for Bragg on order in alloys. I did it laboriously by counting conﬁgurations — Genia called it “Kellnerinnen” later you did it professionally. After the war was a most important period. We sent each other Ph.D’s, good ones. In 1948 I may have visited you twice, early and late in the summer. I picked up Salpeter, the Austro-Australian, and he became a great astrophysicist. We were both intrigued by renormalisation theory in every order. You oﬀered Dyson a job, when he came back to England. Gerry Brown stayed with you for many years. He has now become my closest collaborator on supernovas. It is good to remember all those days. We travelled together a great deal in physics. You did a lot in physics and you educated countless

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good physicists, mostly in Birmingham. I was greatly impressed at your 80th birthday when they all came to celebrate. You had a full and good life, and I thank you for letting me participate in it. Yours, Hans

[937] Gillian Gehring to Jo Hookway Sheﬃeld, 21.9.1995 Dear Jo, Yesterday I had an email from Oxford to tell me that your father died on Tuesday. I was so sorry because it must have come as such a shock to you and the rest of the family. Did you get to go down to Eynsham or was it too sudden? I only knew him towards the end of his active life. His major scientiﬁc breakthroughs had come earlier in the 1930’s and others, particularly with the nuclear bomb in the 1940’s. Several times when I was in Europe, French, German and other scientists commented how unjust it was that he had never received the Nobel Prize for physics. Maybe it was his breadth which was not helpful — nuclear and solid state physicists were surprised to hear that he had been active in other ﬁelds — each had thought he had done plenty in one ﬁeld. Others thought that his involvement with nuclear ﬁssion had been too controversial. Whatever the verdict — he should have received it as one of the main important thinkers in 20th century physics. Only on Monday I was talking to a Hungarian physicist (based in Bristol for many years) who commented that Landau had not had many pupils. What a contrast to your father! The list of those who passed through Birmingham was breathtaking. He taught people how to think. All my teachers, Sam Edwards, Brian Flowers, Walter Marshall were Peierls’ pupils. I guess I am an intellectual granddaughter!

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But for you there is overwhelmingly the private grief. He was such a caring man for all and especially as a father. I send to you and Chris as well as your brothers and sisters (I only ever met Kitty) all my sympathy for the loss of your father. However much you feel that life is drawing to its natural close, one feels appalled by the ﬁnality that comes with death. There will be a time, I guess, for funeral obituaries and a memorial service — but now I wanted to express my concern with your personal grief. All my family joins in sending their condolences — the children never knew him but they heard us talk about him on Sunday. With all our sympathy, Gillian

[938] Lillie Krynen to Ronald Peierls [Tampa], 5.9.19951377 Dear Dr. Ronald Peierls, With great sadness I read in the New York Times of the Death of your father. I am Lillie and was for some time very close to Rudi and we contacted each other much. It is truly a great loss and I will miss his long letters — I still have them — he liked my father, Dr. Franz Jacobsohn and I am sure you must have heard of Dr. Jacobsohn who is also mentioned in his book “Bird of Passage”. I am so glad that I saw Rudi in Oxford last. I hope he did not suﬀer — I do miss him, we had lovely times in Brussels · · · My feelings go out to all of your familie and may I one day have the honor of meeting you all; for he told me much about the familie. In sadness I will always remember Rudi — Sincerely with my warm regards, Lillie

1377

Misdated, probably 22.9.1995

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[939] Lorna Arnold to Joanna Peierls Oxford, 27.9.1995 Dear Jo, Though we’ve talked together in the last week, I do want to write to give you and your family my deepest sympathy and also to try and tell you something of what your father meant to me. He was very kind to me and I was greatly privileged to be one of his friends. Of course in my early UKAEA days I knew of his scientiﬁc reputation and his importance in history, but I never expected to meet him. Then some time in the late 1960s, he wanted some information from the archives and I went to Boar’s Hill to see him. I was very nervous because he was so famous and so awesomely clever but I need not have been frightened! He was courteous and friendly. After that I saw him occasionally but, later, met him quite frequently through Pugwash and then the Freeze Movement, which he got organised in the Oxford area. I remember many meetings in Northmoor Road and in the Nuclear Physics Lab. One special memory is on manning a Freeze display one wet day outside Selfridge’s. We were collecting signatures from passers-by on a big sheet like a table cloth (I had to go and get a large plastic covering to keep the rain oﬀ between signings!) Rudi stood at the table all the morning in his raincoat and barret, politely explaining about Freeze and nuclear weapons to the people — mostly young — who stopped to ask. He’d brought a thermos of coﬀee to share, and he wouldn’t take any time oﬀ to go into Selfridge’s to get warm and have a rest and a coﬀee break. (I have a snap that I think Jack Paton took.) I have some happy memories of other visits to the ﬂat, sometimes for lunch and dinner. (Rosalind Tureck was there on one occasion). We missed two Royal Society conversazione that Rudi invited me to (he apologized that he “stood me up!”). Both times were because he was suddenly taken ill and had to go to hospital. I went to see him there when he was well enough, and then at the nursing home in Eynsham. Later I used to go to Oakenholt, and it was a joy to see him though it was sad to see him so physically frail. It was an

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inspiration to see how in spite of such diﬃculties he went on reading big books — like Powers’ book on Heisenberg and Holloway’s ‘Stalin and the Bomb’ — and writing brilliant reviews for the New York Times; and then doing a report for Pugwash.1378 His mind and his spirit seemed unquenchable. I loved hearing him talk about the other great scientists he knew, like Igor Tamm and Hans Bethe, and Robert Oppenheimer — and was sorry not to be a scientist so that I could appreciate his talking about physics. He was always interesting, often witty, never unkind about anybody (or almost anybody). I shall miss him greatly — he was a dear and very special friend and I was incredibly lucky to have known him a little. I’m glad I have some good photographs, and can reread ‘Bird of Passage’. Please excuse this long rambling letter; I could go on and on, but I must not. With my warmest good wishes and much sympathy. Lorna Arnold

[940] Heinz Rudolph to Joanna Peierls Nuremberg, 7.11.1995 Dear madam, Yesterday when I arrived at home from a long journey to my daughter in Berlin there was your letter and my heart misgave me. The mail in Nuremberg had forgotten to send all letter for me during October to my address in Berlin. I opened your letter and I could read: my friend Rudi is dead · · · I am very, very sad and I am sorry. I take an interest in your grief. 1378

Peierls’ last publication was a report, jointly with some other members of the British Pugwash group, on the necessity for Britain to build nuclear weapons. Tom C. R. Hill, R. S. Pease, R. E. Peierls, J. Rotblat, Does Britain Need Nuclear Weapons? A Report from the British Pugwash Group, London: Pugwash, 1995.

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Rudi and I were school friends. In his book “Bird of Passage” which he gave me in 1992 he writes on page 12 about me, namely Heinz (Henry) Rudolph, “he was then my closest friend”. We studied in Berlin, he after in Leipzig and Z¨ urich. But when he was in England (1932) the connection to me was interrupted. I do not know why. After the 2nd World War I did not live in Berlin but in Bavaria. In 1978 I wrote a letter to him to the University of Oxford. Rudi answered me immediately and now we had a good communication again by many letters. In Juli 1992 when he was for some days in Heidelberg (University) I invited him to come from there to Nuremberg to see me. He did so. It was a great pleasure to see each other. But he could stay only two days. Then he had to ﬂy to Madrid, the bird of passage. In September 1992 he was in Berlin for a conference at the Humboldt University. I came also to Berlin. Only one evening for a supper your father came in the house of my daughter and my son-in-law, then he had to leave Berlin. In his annual letter for his friends on November 1994 he announced to live in a retirement home because his problems of health. He wrote to me how much you had taken care of his needs and problems. I wrote him to his birthday in June 95 and got an answer. My next letter was in August. No answer. On 22 September when I was in Berlin I wrote him a long letter to his retirement home. But your father could neither receive it nor read it; he was already dead.. . . I am deeply sad. But that is the way of the world and we can’t help it. My compliments to you, dear madam, to your brother and to your sisters. Heinz Rudolph [941] Lord Flowers — Funeral Address Oxford, 29.9.1995 We have come here to express our gratitude to someone who meant so much to each of us, and to bid him one last quiet, unostentatious farewell.

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Rudi Peierls was a dearly loved father and a caring family man. He was a physicist of great distinction, acclaimed in many lands. He was a gifted and percipient teacher. He was an inspiration, and a truly good friend. He was one of the great ﬁgures of the nuclear age. He was the ﬁrst to show that nuclear weapons were feasible. Later, he tried to show us how to live more safely in a world which possesses them. But this is not the time to elaborate on Rudi’s scientiﬁc and humanitarian achievements, despite their great signiﬁcance. We here are all aware of them, and there will be other occasions for that. Rather we should take a little time to reﬂect together on his qualities as a human being, and privately, perhaps to wonder how best we can attempt to follow his example. We shall remember always his honesty and integrity, his quickness of mind, and his gentle but persuasive sense of humour. We shall remember his penetrating appraisal of our work — ruefully sometimes, no doubt — but also the encouragement that always followed it. We shall remember with joy the warmth of the welcome we got in the home he created with Genia, where hospitality and fun were of the highest order. His graduate students became members of an extended family, a relationship to which many have remained faithful to this day. We shall remember that there was a special quality about him, rare perhaps for someone of such undisputed scientiﬁc brilliance. He was unfailingly modest, gently courteous, and acutely sensitive to the feelings of others. We shall remember his courage in adversity. How it was business as usual after Genia’s sudden death. How he enjoyed what I can only call her memorial party, with food she might have prepared herself. The speeches of their family and friends. His own tribute to her — grateful, humorous, moving, but always perfectly controlled. We remember latterly how he fought oﬀ growing blindness with gadgets and gumption, and the remorseless deterioration of his bodily functions with good humour. “It is sometimes a bit diﬃcult”, he would say, mentally perfectly alert, “but I can manage, thank you.” Only the other day, when he must have known the end was near, he asked a visitor to buy him a pound of coﬀee with which to entertain his guests.

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We shall all miss him dreadfully. But despite the love of family and friends, and the great esteem in which he was so widely held, his death came not a day too soon. He had lived what Genia might have called “ach, marvelous life”, but his body had grown burdensome, and it was time he was relieved. We must be grateful for that. In a few seconds I shall ask that we keep silence for just one minute while we each remember him in our own fashion. But now the time has come to say: “Good-bye Rudi, and thank you.”

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Bibliography

A complete bibliography of Rudolf Peierls’ works can be found in R.H. Dalitz and Rudolf Peierls (eds.), Selected Scientific Papers of Sir Rudolf Peierls, with Commentary, Singapore: World Scientiﬁc, 1997, pp. 787–805 or in R.H. Dalitz, “Complete bibliography for Prof. Sir Rudolf Peierls”, Nuclear Physics A, vol. 604, pp. 7–23 (1996).

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Archival Sources

The documents reproduced in this volume are taken from several archives in the UK and the US as well as from a collection of material held by the Peierls family. The archival collections used are: Papers and correspondence of Sir Rudolf Ernst Peierls, 1907–1995; held at: Department of Western Manuscripts, Bodleian Library, University of Oxford; cited as Peierls Papers. Papers of P. A. M. Dirac, 1902–1984, held at Florida State University. Paul A. M. Dirac Science Library. Tallahassee, FL 32306. USA; photocopies held at Churchill College Archives, Cambridge, England, CB3 0DS; cited as Dirac Papers. Papers of Hans A. Bethe, 1906–2005, Owning Repository: Cornell University. Carl A. Kroch Library. Division of Rare and Manuscript Collections. University Archives. 2B Carl A. Kroch Library, Ithaca, NY 14853; cited as Bethe Papers. Papers of Sir James Chadwick, 1891–1974. Owning Repository: Churchill College. Archives Centre. Cambridge CB3 0DS, England, UK; cited as Chadwick papers. Papers of J. Robert Oppenheimer, Owning Repository: Manuscript Division, Library of Congress, Washington, D.C.; cited as Oppenheimer Papers. The following list summarizes information about the provenance of the material reproduced in this volume. This includes information about when and where the letters were written, sender and addressee, whether the copy reproduced is the original or a carbon copy as well as where the reproduced copies are located.

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1066

peierlsroot2

rudolf peierls

Where no source is given, the letters are taken from the Peierls Papers in the Bodleian. Key: pc cc RP loc. unsp. date unsp.

— — — — —

postcard carbon copy Rudolf Peierls location unspeciﬁed date unspeciﬁed

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380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406

10.8.1945 13.9.1945 14.9.1945 13.12.1945 13.12.1945 14.12.1945 14.12.1945 18.12.1945 4.1.1946 21.2.1945 26.2.1945 6.3.1946 7.3.1946 8.3.1946 12.3.1946 12.3.1946 14.3.1946 26.3.1946 29.3.1946 1.4.1946 2.4.1946 8.4.1946 3.5.1946 19.5.1946 12.6.1946 13.6.1946 14.6.1946

L.R. Groves Raymond Priestley G.C. Wick RP RP RP RP RP RP RP RP James Chadwick Niels Bohr G.P. Thomson RP RP RP RP RP William Penney G.P. Thomson Hans Bethe James Chadwick Ed Salpeter RP Max Born RP

James Chadwick RP RP John Cockroft Raymond Priestley G.C. Wick James Chadwick G.C. Wick James Chadwick Niels Bohr James Chadwick RP RP RP G.P. Thomson James Chadwick Hans Bethe G.P. Thomson William Penney RP RP RP RP RP Max Born RP Max Born

Washington [loc. unsp.] Rome Washington [loc. unsp.] [loc. unsp.] Washington [loc. unsp.] Washington Birmingham Birmingham [US, Washington] Copenhagen London Birmingham Birmingham [Birmingham] [Birmingham] [Birmingham] Fort Halsted London Ithaca [loc. unsp.] Santa Fe [Birmingham] [Edinburgh] [Birmingham]

o cc o cc cc cc cc cc o cc o cc o o cc o cc cc cc o o o cc o cc o cc

e e e e e e e e e e e e e e e e e e e e e e e e e e e

Chadwick Papers

Chadwick Papers Chadwick Papers

Chadwick Papers

PRO:AB 3

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Key: g – German; e – English; RP – Rudolf Peierls; loc. unsp. – location unspeciﬁed; date unsp. – date unspeciﬁed

Chadwick Papers

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407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434

20.6.1946 21.6.1946 21.7.1946 29.7.1946 26.8.1946 24.1.1947 7.3.1947 10.3.1947 10.3.1937 13.3.1947 24.4.1947 May-47 2.6.1947 5.6.1947 26.6.1947 1.7.1947 18.7.1947 28.7.1947 6.8.1947 14.8.1947 27.8.1947 3.9.1947 23.9.1947 27.9.1947 7.10.1947 8.10.1947 26.10.1947 1.11.1947

RP Y.I. Frenkel Y.I. Frenkel Tony Skyrme RP RP G. Placzek RP Otto Frisch James Chadwick RP RP Niels Bohr RP Niels Bohr RP RP RP RP RP RP Hans Bethe Hans Bethe RP Y.I. Frenkel RP RP RP

Y.I. Frenkel RP RP RP Robert Oppenheimer Hans Bethe RP James Chadwick RP RP George Placzek Robert Oppenheimer RP Niels Bohr RP Niels Bohr Niels Bohr Hans Bethe Robert Oppenheimer Hans Bethe Klaus Fuchs RP RP Hans Bethe RP Hans Bethe John Cockroft Robert Oppenheimer

[Birmingham] Leningrad Leningrad Santa Fe Birmingham Birmingham Schenactady [loc. unsp.] [loc. unsp.] New York [Birmingham] Birmingham Copenhagen [Birmingham] Copenhagen [Birmingham] [Birmingham] [Birmingham] Birmingham Birmingham [Birmingham] Ithaca Ithaca [Birmingham] Leningrad [Birmingham] [Birmingham] Birmingham

cc o o o o o o o o cc cc o o cc o cc cc cc o cc cc o o cc o cc cc o

e e e e e e e e e e e e e e e e e e e e e e e e e e e e

source

Oppenheimer Papers Bethe Papers Chadwick Papers Chadwick Papers Oppenheimer Papers

Oppenheimer Papers

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cc cc cc o cc

e e e e e

Bristol Bristol [Birmingham] Birmingham [Birmingham] [Ithaca] Cambridge [Birmingham] Berkeley Cambridge Ithaca [Birmingham] Ithaca [Princeton]

o o cc cc cc o o cc o o o cc o o

e e e e g e e e e g e e e e

Birmingham [Birmingham] [Birmingham] Edinburgh [Birmingham] [Birmingham] Manchester

o cc cc o cc cc o

e e e e e e e

to

location

435 436 437 438 439 440

RP RP RP Hans Bethe RP RP

Niels Bohr Hans Bethe Abram Pais RP Nevill Mott cc

441 442 443 444 445 446 447 448 449 450 451 452 453 454

2.11.1947 24.11.1947 27.11.1947 4.12.1947 17.12.1947 [date unsp.], early 1948 [date unsp.] 2.2.1948 6.2.1948 6.2.1948 11.2.1948 12.2.1948 17.2.1948 3.3.1948 4.3.1948 4.3.1948 18.3.1948 23.3.1948 7.4.1948 8.4.1948

Nevill Mott Nevill Mott RP RP RP Hans Bethe Werner Heisenberg RP Robert Serber Werner Heisenberg Hans Bethe RP Hans Bethe Robert Oppenheimer

455 456 457 458 459 460 461

15.4.1948 17.4.1948 6.5.1948 22.5.1948 24.5.1948 29.5.1948 4.6.1948

RP RP RP Max Born RP RP Leon Rosenfeld

RP RP Nevill Mott Niels Bohr Werner Heisenberg RP RP Hans Bethe RP RP RP Hans Bethe RP RP and Mark Oliphant Robert Oppenheimer Robert Serber Hans Bethe RP Max Born Max Born RP

source

World Scientiﬁc Book - 9in x 6in

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original/ carbon copy

language

source

462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489

16.8.1948 8.10.1948 4.11.1948 10.12.1948 16.12.1948 30.12.1948 16.1.1949 21.1.1949 25.1.1949 31.1.1949 2.2.1949 2.2.1949 14.2.1949 17.2.1949 23.2.1949 7.3.1949 16.3.1949 31.3.1949 13.4.1949 22.4.1949 10.6.1949 10.7.1949 27.7.1949 22.8.1949 26.8.1949 16.10.1949 9.11.1949 4.12.1949

Robert Oppenheimer RP Robert Serber Hans Bethe RP Robert Oppenheimer Freeman Dyson RP RP N. Kemmer RP Hans Bethe Wolfgang Pauli RP Wolfgang Pauli RP Robert Oppenheimer Freeman Dyson RP RP RP Wolfgang Pauli RP Niels Bohr RP RP RP Ed Salpeter

RP Robert Serber RP RP Robert Oppenheimer RP RP Freeman Dyson Hans Bethe RP N. Kemmer RP RP Wolfgang Pauli RP Robert Oppenheimer RP RP Robert Oppenheimer Freeman Dyson Wolfgang Pauli RP Hans Bethe RP Niels Bohr Robert Oppenheimer Raymond Priestley RP

Princeton Birmingham Berkeley New York [Birmingham] Princeton Princeton Birmingham [Birmingham] Cambridge [Birmingham] Ithaca Zurich [Birmingham] Zurich Birmingham [Princeton] Princeton [Birmingham] [Birmingham] [Birmingham] Zurich [Birmingham] Copenhagen Birmingham Birmingham [Birmingham] Ithaca

cc cc o o cc o o cc cc o cc o o cc o o o o cc cc cc o cc o cc o cc o

e e e e e e e e e e e e g e g e e e e e e g e e e e e e

Oppenheimer Papers

Oppenheimer Papers

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490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517

7.12.1949 8.12.1949 26.1.1950 [date unsp.] 5.2.1950 5.2.1950 7.2.1950 14.2.1950 15.4.1950 20.4.1950 Mar-50 12.5.1950 15.5.1950 18.5.1950 25.5.1950 13.6.1950 17.6.1950 19.6.1950 24.6.1950 27.7.1950 3.8.1950 6.9.1950 19.9.1950 23.9.1950 25.9.1950 16.10.1950 26.10.1950 1.11.1950

RP RP RP Genia Peierls G.I. Taylor Klaus Fuchs RP RP RP Egon Orowan RP D.H. Wilkinson RP RP Niels Bohr RP RP RP Freeman Dyson RP Freeman Dyson Robert Oppenheimer RP Freeman Dyson RP RP Claude Bloch RP

Niels Bohr James Chadwick Ed Salpeter Klaus Fuchs RP Genia Peierls G.I. Taylor Niels Bohr E.C. Bullard RP [Birmingham] RP John Cockroft D.H. Wilkinson RP VC Manchester Guardian Freeman Dyson RP Robert Oppenheimer RP RP Philip Moon RP Freeman Dyson John Cockroft RP Claude Bloch

[Birmingham] [Birmingham] [Birmingham] Birmingham London Cambridge Birmingham [Birmingham] [Birmingham] Cam/Mass cc Cambridge [Birmingham] [Birmingham] Copenhagen [Birmingham] [Birmingham] [Birmingham] Princeton Birmingham Ann Arbor [Princeton] [Birmingham] Princeton [Birmingham] [Birmingham] Copenhagen [Birmingham]

cc cc cc cc o o cc cc cc o e o cc cc o cc cc cc o o o cc cc o cc cc o cc

language

source

e e e e e e e e e e e e e e e e e e e e e e e e e e e

Oppenheimer Papers

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518 519 520 521 522 523 524 525

8.11.1950 8.11.1950 8.12.1950 12.2.1951 19.2.1951 28.2.1951 10.3.1951 9.4.1951

Freeman Dyson Verena Dyson RP Robert Oppenheimer Hans Bethe RP RP RP

Princeton Princeton [Birmingham] Princeton Ithaca Birmingham Birmingham [Birmingham]

o o cc o cc cc cc cc

e e e e e e e e

526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544

26.4.1951 1.5.1951 22.5.1951 27.8.1951 13.12.1951 14.1.1952 14.1.1952 18.1.1952 21.1.1952 23.1.1952 25.1.1952 [date unsp.] 3.2.1952 4.2.1952 6.2.1952 7.2.1952 7.2.1952 [date unsp.] 14.2.1952

RP H. Froehlich RP Robert Oppenheimer RP RP RP Claude Bloch RP RP Gerry Brown RP RP RP RP RP RP Gerry Brown RP

RP RP J. Rzewuski RP RP Hans Bethe Robert Oppenheimer Viscount Portal of Hungerford H. Froehlich RP Raymond Priestley RP Claude Bloch R.H. Dalitz Gerry Brown RP Claude Boch Gerry Brown RP M. Chretien Gerry Brown R.H. Dalitz Gerry Brown R.H. Dalitz M. Chr´etien RP M. Chr´etien

[Birmingham] Liverpool [Birmingham] Princeton [Birmingham] [Princeton] [Princeton] Pasadena [Princeton] [Princeton] [Birmingham] [Princeton] [Princeton] [Princeton] [Princeton] [Princeton] [Princeton] [Birmingham] [Princeton]

cc o cc cc cc cc cc o cc cc o cc cc cc cc cc cc o cc

e e e e e e e e e e e e e e e e e e e

source

Bethe Papers

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545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572

18.2.1952 19.2.1952 23.2.1952 24.2.1952 27.2.1952 28.2.1952 1.3.1952 3.3.1952 3.3.1952 10.3.1952 12.3.1952 14.3.1952 18.3.1952 25.3.1952 26.3.1952 2.4.1952 13.4.1952 2.5.1952 14.8.1952 14.8.1952 14.8.1952 16.8.1952 20.8.1952 29.8.1952 30.8.1952 1.9.1952 15.9.1952 20.10.1952

Gerry Brown RP RP M. Chr´etien Gerry Brown RP RP RP RP Gerry Brown RP Claude Bloch Gerry Brown Gerry Brown Freeman Dyson RP RP RP Wolfgang Pauli Wolfgang Pauli RP Wolfgang Pauli RP Wolfgang Pauli Wolfgang Pauli RP Ed Salpeter RP

RP Gerry Brown Gerry Brown RP RP Gerry Brown M. Chr´etien P.A.M. Dirac Gerry Brown RP P.A.M. Dirac RP RP RP RP R.H. Dalitz Claude Bloch Robert Oppenheimer RP RP John Cockroft RP Wolfgang Pauli RP RP Wolfgang Pauli RP Ed Salpeter

[Birmingham] [Princeton] [Princeton] Birmingham [Birmingham] [Princeton] [Princeton] [Princeton] [Princeton] [Birmingham] [Princeton] Pasadena [Birmingham] [Birmingham] [Ithaca] [Princeton] [Princeton] Birmingham Zurich Zurich [Birmingham] Zurich [Birmingham] Zurich Zurich Les Houches Ithaca [Birmingham]

o cc cc o o cc cc cc cc o cc o o o o cc cc cc o o cc o cc o o cc o cc

e e e e e e e e e e e e e e e e e e g g e g e g e g e e

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original/ carbon copy

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573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600

30.10.1952 26.11.1952 10.12.1952 12.12.1952 15.12.1952 15.12.1952 16.12.1952 18.12.1952 26.12.1952 5.1.1953 5.1.1953 20.1.1953 23.1.1953 24.1.1953 24.1.1953 13.2.1953 17.2.1953 23.2.1953 17.3.1953 23.3.1953 9.12.1953 1.1.1954 11.1.1954 9.2.1954 16.4.1954 29.4.1954 28.5.1954 12.8.1954

Wolfgang Pauli RP Ed Salpeter RP Hans Bethe Hans Bethe RP RP Freeman Dyson RP RP RP Wolfgang Pauli Wolfgang Pauli Wolfgang Pauli RP Wolfgang Pauli Ed Salpeter Wolfgang Pauli RP RP R.H. Dalitz RP R.H. Dalitz RP RP R.H. Dalitz RP

RP Robert Aitken RP John Cockroft RP RP Hans Bethe Ed Salpeter RP Hans Bethe Hans Bethe Wolfgang Pauli RP RP RP Wolfgang Pauli RP RP RP Wolfgang Pauli Nevill Mott RP R.H. Dalitz RP R. Oppenheimer R.H. Dalitz RP Robert S. Aitken

Zurich [Birmingham] Ithaca [Birmingham] Ithaca Ithaca [Birmingham] Birmingham Ithaca Birmingham Birmingham Birmingham Zurich Zurich Zurich Birmingham Zurich Ithaca Zurich Birmingham Birmingham Ithaca [Birmingham] Ithaca [loc. unsp.] [Birmingham] Ithaca [Birmingham]

o cc o cc o o cc cc o cc cc cc o o o cc o o o cc cc o cc o cc cc o cc

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1074

No.

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601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628

8.10.1954 12.10.1954 22.10.1954 30.10.1954 13.1.1955 17.2.1955 28.2.1955 17.3.1955 31.3.1955 4.4.1955 7.4.1955 18.4.1955 18.4.1955 6.5.1955 9.5.1955 3.6.1955 4.8.1955 9.9.1955 11.9.1955 14.9.1955 16.9.1955 20.9.1955 21.10.1955 8.11.1955 25.11.1955 30.11.1955 1.12.1955 6.3.1956

RP RP Felix Bloch RP Nicholas Kemmer RP RP R.H. Dalitz Freeman Dyson RP RP RP R.H. Dalitz Wolfgang Pauli RP Wolfgang Pauli R.H. Dalitz RP Freeman Dyson RP RP RP RP RP Wolfgang Pauli RP RP RP

R. Oppenheimer R.H. Dalitz RP Felix Bloch RP Freeman Dyson R.H. Dalitz RP RP Dalitz Freeman Dyson Nevill Mott RP RP Wolfgang Pauli RP RP John Cockroft RP Freeman Dyson Wolfgang Pauli Robert S. Aitken Robert S. Aitken Lev Landau RP S.C. Redshaw Wolfgang Pauli William Penney

[Birmingham] [Birmingham] Geneva [Birmingham Edinburgh [Birmingham [Birmingham] Princeton Princeton [Birmingham] [Birmingham] [Birmingham] Princeton Zurich [Birmingham] Zurich Brookhaven [Birmingham] Berkeley [loc. unsp.] [Birmingham [loc. unsp.] [Birmingham] [Birmingham] Zurich [Birmingham] [Birmingham] [loc. unsp.]

cc cc o cc o cc cc o o cc cc cc o o cc o o cc o cc cc cc cc cc o cc cc cc

e e e e e e e e e e e e e e e e e e e e e e e e e e e e

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original/ carbon copy

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629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656

22.3.1956 25.4.1956 24.5.1956 6.6.1956 6.6.1956 10.6.1956 17.6.1956 21.6.1956 12.7.1956 7.9.1956 25.9.1956 26.9.1956 22.10.1956 6.12.1956 15.2.1957 5.4.1957 30.11.1957 12.12.1957 6.1.1958 8.1.1958 10.1.1058 13.1.1958 3.3.1958 13.3.1958 14.3.1958 20.3.1958 25.3.1958 25.3.1958

RP Nevill Mott Nina Byers RP RP RP Nina Byers RP Freeman Dyson RP Freeman Dyson RP RP RP Hans Bethe Gerry Brown Stanley Mandelstam RP RP RP Robert S. Aitken RP RP Gerry Brown RP Hans Bethe RP Gerry Brown

John Cockroft RP RP Lev Landau O. Hood Phillips Nina Byers RP Nina Byers RP Freeman Dyson RP Lev Landau N. Kemmer R. Serber RP RP RP Felix Bloch F.R. Shotton H.A. Bethe RP Robert S. Aitken Gerry Brown RP Lev Landau RP Gerry Brown RP

[Birmingham] Cambridge Chicago [Birmingham] [loc. unsp.] [Birmingham] Chicago Birmingham La Jolla [Birmingham] Princeton [Birmingham] [Birmingham] [Birmingham] Ithaca Copenhagen Columbia [Birmingham] [Birmingham] [Birmingham] Birmingham Birmingham [Birmingham] Copenhagen [Birmingham] Ithaca Pisa Copenhagen

cc o o cc cc cc o cc o cc o cc cc cc o o o cc cc cc o cc cc o cc o cc o

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No.

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657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672

27.3.1958 4.6.1958 13.6.1958 25.6.1958 25.6.1958 14.7.1958 22.7.1958 6.8.1958 14.8.1958 19.11.1958 1.12.1958 26.2.1959 8.3.1959 31.3.1959 15.5.1959 [date unsp., May 1929] 15.6.1959 22.7.1959 6.8.1959 10.8.1959 11.8.1959 8.9.1959 13.3.1960 19.12.1960 6.1.1961 14.4.1961 27.4.1961

Gerry Brown Gerry Brown RP Gerry Brown Gerry Brown Nina Byers Gerry Brown Gerry Brown Gerry Brown P.R. Kabir RP Nina Byers RP Nina Byers Sam Edwards RP

RP RP F.W. Shotton RP RP RP RP RP RP RP P.R. Kabir RP Nina Byers RP RP Sam Edwards

Copenhagen Copenhagen [Birmingham] Copenhagen Copenhagen Birmingham Copenhagen Copenhagen Copenhagen Calcutta [Birmingham] Stanford [New York] Stanford Manchester [Birmingham]

o o cc o o o o o o o cc o cc o o cc

e e e e e e e e e e e e e e e e

RP Gerry Brown RP RP RP Gerry Brown Lev Landau RP RP RP Robert Oppenheimer

Klaus Fuchs RP Nina Byers John Cockroft Nevill Mott RP RP Niels Bohr Hans Bethe Robert Oppenheimer RP

[Birmingham Minneapolis [New York] [Birmingham] Birmingham Minneapolis Moscow [Birmingham] Birmingham Birmingham [Princeton]

cc o cc cc cc o o cc cc o cc

e e e e e e e e e e e

673 674 675 676 677 678 679 680 681 682 683

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original/ carbon copy

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684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711

16.7.1961 30.7.1961 2.8.1961 30.10.1961 17.12.1961 8.1.1962 21.1.1962 24.2.1962 2.4.1962 2.5.1962 16.5.1962 24.5.1962 3.8.1962 5.12.1962 21.12.1962 19.4.1963 8.5.1963 6.6.1963 27.6.1963 23.8.1963 29.8.1963 20.9.1963 1.11.1963 9.11.1963 23.11.1963 7.2.1965 9.10.1965 5.11.1965

Genia Peierls Egon Orowan RP RP RP D. Thouless RP RP RP RP Hans Bethe RP Sam Edwards RP Freeman Dyson P.R. Kabir RP RP Margaret Gowing RP Margaret Gowing RP RP Maud Juliusberg RP RP RP Hans Bethe

Mr. Raison RP Egon Orowan Margaret Gowing D. Thouless RP D. Thouless Hans Bethe Selwyn Lloyd Hans Bethe RP Lev Landau RP Freeman Dyson RP RP P.K. Kabir Tony Skyrme RP Margaret Gowing RP Margaret Gowing Nevill Mott RP Maud Juliusberg A. Dorozynski Robert Oppenheimer RP

Birmingham Ivanhoe [Birmingham] [Birmingham] [Birmingham] Cambridge [Birmingham] [Birmingham] [Birmingham] [Birmingham] Ithaca [Birmingham] Manchester [Birmingham] Princeton Pittsburgh [Birmingham] [Birmingham] London [Oxford] London [Oxford] [Oxford] Berlin [Oxford] Oxford Oxford Ithaca

cc o cc cc cc o cc cc cc cc o cc o cc o o cc cc o cc o cc cc o cc cc cc o

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712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739

26.11.1965 6.12.1965 14.12.1965 25.7.1966 26.7.1966 27.7.1966 20.1.1967 24.1.1967 23.10.1967 30.10.1967 23.10.1968 12.2.1969 30.6.1969 14.2.1970 22.2.1970 28.2.1970 19.3.1970 13.6.1970 1.7.1970 25.9.1970 20.5.1971 [date unsp.] 18.1.1972 8.2.1972 15.2.1972 2.3.1973 2.3.1973 6.6.1973

RP Harold Urey RP Nevill Mott RP Nevill Mott Hans Bethe RP Nevill Mott RP RP RP C.H. Paterson RP Hans Bethe RP RP RP RP C. Moller RP Kitty Oppenheimer RP RP Hans Bethe Nevill Mott RP Nevill Mott

Harold Urey RP Hans Bethe RP Nevill Mott RP RP Hans Bethe RP Nevill Mott Folliot Sandford Unwin RP R.J. Eden RP Hans Bethe C. Moller Sam Edwards C. Moller RP Hans Bethe RP Kitty Oppenheimer Hans Bethe RP RP Nevill Mott RP

[Oxford] San Diego [Oxford] Cambridge [Oxford] Cambridge Ithaca [Oxford] Cambridge [Oxford] [Oxford] [Oxford] Oxford [Oxford] Rehovoth [Oxford] [Oxford] [Oxford] [Oxford] Copenhagen [Oxford] Princeton [Oxford] [Oxford] Ithaca [Cambridge] [Oxford] Cambridge

cc o cc o cc o o cc o cc cc cc o cc o cc cc cc cc o cc o cc cc o o cc o

e e e e e e e e e e e e e e e e e e e e e e e e e e e e

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740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767

[date unspec.] 9.11.1973 21.11.1973 28.9.1974 12.4.1975 1.1.1976 2.10.1976 28.10.1977 13.1.1978 8.4.1978 18.4.1978 24.5.1978 23.10.1978 24.2.1979 30.5.1979 23.7.1979 26.8.1979 8.12.1979 2.1.1980 15.1.1980 13.4.1980 1.7.1980 20.8.1980 22.9.1980 9.10.1980 13.11.1980 28.1.1981 5.3.1981

RP Freeman Dyson RP Franz Jacobsohn W. Eveking RP RP Nina Byers RP E. Heisenberg Heinz Rudolph RP Nevill Mott Heinz Rudolph RP Nina Byers RP RP Hans Bethe RP RP Hans Bethe John Bell Jo Rotblat RP RP John Bell RP

Nevill Mott RP Freeman Dyson RP RP Nina Byers V. Ginzburg RP Margaret Gowing RP RP E. Heisenberg RP RP E. M. Lifshitz RP Nina Byers Jo Rotblat RP Hans Bethe Nina Byers RP RP RP Nina Byers John Bell RP H. Montgomery Hyde

[Oxford] Princeton [Oxford] Heidelberg Darmstadt [Leiden] [Oxford] Los Angeles [Oxford] Munich [loc. unsp.] [Oxford] Cambridge N¨ urnberg US Los Angeles [Oxford] [Copenhagen] Ithaca [Copenhagen] Sao Paulo Ithaca Geneva London [Oxford] [Oxford] Geneva [Oxford]

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1080

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768 769 770 771 772 773 774

28.7.1981 19.12.1981 Dec. 1981 31.12.1981 3.1.1982 19.1.1982 23.1.1982

cc cc o cc cc o o

e e e e e e e

14.2.1982 10.4.1982 27.4.1982 10.5.1982 29.6.1982 2.10.1982 4.10.1982 7.10.1982 8.10.1982 14.10.1982 11.12.1982 5.2.1983 16.2.1983 13.2.1983 24.2.1983 4.5.1983 11.5.1983 20.6.1983 6.7.1983 4.8.1983

Nina Byers Nevill Mott RP Nevill Mott Abdus Salam RP Genia and Peierls Rudolf RP RP John Bell RP Freeman Dyson RP Abraham Pais Nina Byers RP J.M. Sanchez Ron RP Baym Channel 4 John Bell RP Franz Jacobsohn RP RP David Shoenberg Franz Jacobsohn

[Oxford] [Oxford] Cambridge [Oxford] [Oxford] Trieste London

775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794

RP RP Nevill Mott RP RP Abdus Salam Ilse and Hans Thorner Nevill Mott Franz Jacobsohn RP Freeman Dyson RP Franz Jacobsohn RP Genia and RP J.M. Sanchez-Ron RP Nevill Mott RP RP RP John Bell RP Franz Jacobsohn David Shoenberg RP RP

Cambridge Heidelberg [Oxford] Oxford Oxford Heidelberg Oxford Oxford Madrid Oxford Cambridge Oxford [Oxford] Oxford Geneva Oxford Heidelberg Cambridge Varenna Oxford

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795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822

17.11.1983 27.11.1983 6.12.1983 11.1.1984 13.1.1984 2.2.1984 8.3.1984 12.3.1984 20.3.1984 6.4.1984 9.4.1984 6.6.1984 17.6.1984 26.6.1984 5.7.1984 18.7.1984 22.7.1984 13.8.1984 15.8.1984 28.8.1984 9.9.1984 17.9.1984 30.11.1984 24.12.1984 27.12.1984 2.1.1985 12.1.1985 18.1.1985

John Hendry RP John Hendry E. Orowan Hans Bethe RP RP E. Orowan P.L. Rose P.L. Rose RP RP RP P.L. Rose R.H. Stuewer RP RP A. Humphreys RP Nina Byers RP RP P.L. Rose Nevill Mott RP RP Nevill Mott RP

RP John Hendry RP RP RP Hans Bethe E. Orowan RP RP RP P.L. Rose David Shoenberg V. Frenkel RP RP R.H. Stuewer P.L. Rose RP A. Humphreys RP Nina Byers Kearton RP RP P.L. Rose Nevill Mott RP Nevill Mott

London Oxford London Belmont Ithaca Santa Barbara Santa Barbara Belmont Jerusalem Jerusalem [Oxford] Oxford [Oxford] Jerusalem Minneapolis Oxford Oxford Oxford Oxford Santa Monica Oxford Oxford Newcastle Cambridge Bures-sur-Yvette Bures-sur-Yvette Cambridge Bures-sur-Yvette

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823 824 825 826 827 828 829 830 831 832 833 836 837 834

26.1.1985 21.2.1985 8.4.1985 28.5.1985 12.9.1985 28.12.1985 13.2.1986 19.2.1986 28.6.1986 8.7.1986 13.6.1986 18.8.1986 17.8.1986 31.8.1986

RP RP P.L .Rose P.L. Rose Nina Byers RP Arnold Kramish RP Manci Dirac RP RP RP Moss RP

Cambridge Newcastle [Oxford] Oxford Oxford Princeton Oxford Cambridge Oxford [Cambridge] Cambridge Cambridge Cambridge Brussels

o o cc cc cc o cc o cc o o o o o

e e e e e e e e e e e e e e

835 836 837 838 839 840

5.9.1986 11.9.1986 17.9.1986 26.10.1986 27.10.1986 1.11.1986

RP RP I.M. Khalatnikov RP RP RP

Farmingdale Moscow Oxford Ithaca [Ithaca] Princeton

o o cc o o o

e e e e e e

841 842 843 844 845 846 847

4.11.1986 Nov-86 10.11.1986 14.11.1986 27.1.1987 24.2.1987 8.3.1987

Nevill Mott P.L. Rose RP RP RP Freeman Dyson RP Nevill Mott RP Manci Dirac Brian Pippard Elaine Wheatley Elaine Wheatley Lillian Krynen-Jacobsohn Ulrich Jacobsohn I.M. Khalatnikov RP Hans Bethe Rose Bethe Freeman and Imme Dyson RP I.M. Khalat Viktor Weisskopf Hanni Bretscher Lillian Krynen Lillian Krynen RP

I.M. Khalat RP RP RP RP RP Marvin Goodman

Oxford Moscow Cambridge Cambridge Nerfa [loc. unsp.] Oxford

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language

848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875

25.3.1987 26.5.1987 27.5.1987 27.5.1987 1.6.1987 21.6.1987 [date unsp.] 13.7.1987 24.7.1987 17.9.1987 28.9.1987 27.11.1987 Christmas 1987 Christmas 1987 30.12.1987 20.1.1988 26.1.1988 6.4.1988 28.4.1988 4.5.1988 7.5.1988 21.5.1988 24.5.1988 26.5.1988 26.5.1988 22.7.1988 26.7.1988 19.8.1988

Lillian Krynen RP Hans Bethe Heinz Rudolph RP RP Rose and Hans Bethe Lillian Krynen RP RP Lillian Krynen RP Rose and Hans Bethe Heinz Rudolph Freeman Dyson RP RP RP Thomas Powers RP RP Nevill Mott RP Nevill Mott RP RP Lillian Krynen RP

RP Norman Moss RP RP Heinz Rudolph Lillian Krynen RP RP Hans Bethe Abdus Salam RP Freeman Dyson RP RP RP Lillian Krynen Martin Walker Freeman Dyson RP Lillian Krynen Thomas Powers RP Nevill Mott RP Nevill Mott Lillian Krynen RP Heinz Rudolph

[loc. unsp.] [Oxford] Ithaca [Berlin] Oxford Oxford Zurich [loc. unsp.] Oxford Oxford [loc. unsp.] Oxford Ithaca [Nrnberg] Princeton Oxford [Oxford] Oxford South Royalton [Oxford] [Oxford] Cambridge Oxford Cambridge Oxford Oxford Brussels Oxford

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1084

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876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903

Dec-88 23.2.1989 26.2.1989 21.3.1989 10.6.1989 14.6.1989 22.6.1989 2.7.1989 6.7.1989 27.8.1989 28.9.1989 3.10.1989 6.12.1989 17.12.1989 [date unsp.] 23.8.1990 26.8.1990 3.9.1990 5.2.1991 11.2.1991 25.3.1991 7.5.1991 11.5.1991 22.9.1991 1.10.1991 2.11.1991 5.11.1991 17.11.1991

Heinz Rudolph HR Jones RP Mark Oliphant RP RP RP Mark Oliphant RP Waltraud Krause Abraham Pais RP RP Etienne Bauer RP RP Lillian Krynen Abraham Pais RP Mark Richmond RP Nevill Mott RP Nevill Mott RP RP Freeman Dyson Andrew Brown

RP RP HR Jones RP Victor Frenkel Heinz Rudolph Waltraud Krause RP Mark Oliphant RP RP Abraham Pais Lillian Krynen RP Etienne Bauer Abraham Pais RP RP Mark Richmond RP Hans and Rose Bethe RP Nevill Mott RP Nevill Mott David Tabor RP RP

Nurnberg Winchester Oxford Griﬃth [Oxford] Oxford Oxford Griﬃth Oxford Berlin Copenhagen Oxford [Oxford] Paris Oxford Oxford Brussels Copenhagen Oxford Swindon Oxford Cambridge Oxford Cambridge Oxford [Oxford] Princeton Andover

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904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 932 933 934

2.12.1991 22.12.1991 8.1.1992 26.1.1992 27.1.1992 [date unsp.] 18.3.1992 10.4.1992 12.4.1992 20.4.1992 20.6.1992 27.7.1992 6.8.1992 23.9.1992 13.10.1992 22.10.1992 29.11.1992 4.1.1993 18.1.1993 27.1.1990 7.2.1993 19.2.1993 10.4.1993 27.5.1993 4.7.1993 7.10.1993 10.10.1993 26.10.1993 29.10.1993

RP Andrew Brown Hans Bethe RP Brian Cathcart RP Jae Riebe RP Philip Moon RP RP Brian Cathcart RP RP RP Hans Bethe Bill Arrol RP Bill Arrol Lillian Krynen RP Hans Bethe RP Bill Arrol RP RP RP Donald Degenhardt RP

Andrew Brown RP RP Hans Bethe RP Brian Cathcart RP Jae Riebe RP Jae Riebe N., A. and L. Belousov RP Brian Cathcart Hans Bethe V. Frenkel RP RP Bill Arrol RP RP Hans Bethe RP Bill Arrol RP Bill Arrol Victor Frenkel Donald Degenhardt RP Donald Degenhardt

Oxford Andover Pasadena Oxford London Oxford Los Alamos Oxford [loc. unsp.] Oxford Oxford London Oxford Oxford [Oxford] Ithaca Solihull Oxford Solihull Tampa Oxford [Ithaca] Oxford Solihull Oxford [Oxford] Oxford Oxford Oxford

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1086

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935 930 931 932 933 934 935 936 937 938 939 940 941

1.11.1993 6.1.1994 8.1.1994 23.1.1994 7.6.1994 9.7.1994 7.3.1995 8.9.1995 21.9.1995 [22].9.1995 27.9.1995 7.11.1995 29.9.1995

Donald Degenhardt Etienne Bauer RP Andrew Brown Hans Bethe RP Bruno Augenstein Hans Bethe Gillian Gehring Lillian Krynen Lorna Arnold Heinz Rudolph Lord Flowers

RP RP Etienne Bauer RP RP Hans Bethe RP RP Jo Hookway Ronald Peierls Joanna Hookway Joanna Hookway Oxford

Oxford Paris Oxford Andover [Ithaca] Oxford Santa Monica [Ithaca] Sheﬃeld [Tampa] Oxford N¨ urnberg o

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Bethe Papers

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Name Index

Abers 769 Abragam, A. 476 Abraham, M. 685, 685∗ , 734, 734∗ , 735, 750–52 Abrikosov, A.A. 445∗ , 499, 499∗ Adams, Ruth 824 Adler, Felix, T. 166, 166∗ , 168–69, 497, 497∗ Ahfors, Erna 829–30 Ahfors, Lars 829–30 Aitken, Robert S. ix, 469, 469∗ , 528–29, 259∗ , 575–76 Akers, Wallace Alan 30, 30∗ , 34, 49, 51 Aleksandrov, A.D. 849 Alford, William L. 293∗ Allock, G.R. 537, 537∗ Alvarez, Louis, W. 514, 516 Amaldi, E. 17 Anderson, H.L. 291, 292∗ Anderson, John 35, 84, 678, 689–90 Anderson, Phil, W. 930, 930∗ , 1006, 1006∗ Andropov, Yuri 849–50 Appleton, Edward Victor 582 Ardenne, Manfred von 890, 901–902 Arfken, G.B. 186∗ , 317, 345, 345∗ Arrol, Bill 1033, 1035–36, 1039, 1043, 1045, 1047 Ashmore, A. 588, 588∗ , 590–91 Aston, Francis 582 Atiyah, Michael, F. 849, 849∗ , 1041 Attlee, Clement 3, 3∗ , 689, 1028 Auger, Pierre 1050 Augustin, Lotte 987, 987∗ , 992 Awbery, J.H. 911 Bagge, Erich 864, 866 Baier, Monika ix Baranger, M. 337, 337∗ Bardeen, John 277–78, 776∗ Barker, F.C. 138, 138∗ , 153∗ , 207, 207∗ , 230 Barnes 623

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Barnes, C.A. 796∗ Baruch, Bernard Mannes 76, 76∗ Barwich, Heinz 885, 890 Bauer, Etienne 998, 998∗ , 1000, 1049–1050 Baxendall, K.D. ix Baym, Gordon 771, 771∗ , 842, 842∗ Beasley 371 Beck, Guido 798 Becker, Richard 55 Bell, John 439, 682, 758, 758∗ , 800–803, 809–10, 825, 827, 838, 843–44, 846, 846∗ , 930, 930∗ , 1007 Belyaev, S.T. 603, 603∗ Bethe, Hans Albrecht viii, xi, 11–12, 39, 39∗ , 47, 47∗ , 66, 69, 69∗ , 81, 88, 88∗ , 90∗ ,91, 91∗ , 93, 96, 96∗ , 97, 101, 105, 108, 109∗ , 113, 114, 127, 127∗ , 129, 133, 133∗ , 134, 138, 139, 140∗ , 153, 154∗ , 163, 165∗ , 169, 170∗ , 171, 171∗ , 191, 191∗ , 201, 218, 226, 226∗ , 245, 262, 262∗ , 267–68, 285, 287, 291, 295∗ , 296, 307, 315–16, 318–19, 330, 356, 406, 408, 408∗ , 410, 415–17, 451–52, 454, 457–59, 464, 466–67, 467∗ , 468, 468∗ , 474, 497, 525–26, 547–49, 561, 561∗ , 562, 263∗ , 573–74, 582, 584, 586–87, 587∗ , 593, 601, 633–34, 640, 660, 660∗ , 665–66, 682, 686–87, 701, 706, 710, 710∗ , 711, 727, 727∗ , 728, 731, 736, 743–44, 759, 761, 776, 795, 795∗ 96∗ , 797, 799, 833, 842, 842∗ , 858–59, 877, 879, 898, 900, 900∗ , 923, 925, 929–33, 943–44, 948, 948∗ , 950∗ , 957, 1006, 1012, 1015–16, 1016∗ , 1029, 1029∗ 1030∗ , 1032, 1032∗ , 1041–42, 1052–53, 1053∗ , 1056, 1060, 1065 Bethe, Rose (n´ee Ewald) ix, 48, 95, 98, 154, 164, 267, 268, 727, 727∗ , 796–97, 923, 932–34, 936, 948, 948∗ , 950∗ , 952, 957–58, 1006, 1016, 1030, 1041–42, 1053–54 Bevin, Ernest 142 Bhabba, Homi Jehangir 682, 915–16, 965 Bjorklund, F.E. 593 Blackburn, Raymond 65 Blacker, Stewart William 899∗ Blackett, Patrick Maynard Stuart 127–28, 135∗ , 148, 216∗ , 248 Blackett, Constanza 918 Blackman, M. 34, 34∗ , 46 Blair, J. Morris 317 Blatt, John M. 154, 154∗ , 455–56, 461 Bleaney, Brebis 718 Bleuler, Konrad 71, 71∗ Blin-Stoyle, R.J. 461, 472 Bloch, Claude 13, 258, 258∗ , 260, 281, 287, 290, 297–99, 308, 310, 361, 361∗ , 363, 371, 374, 374∗ , 375, 375∗ , 388, 388∗ , 390, 394–96, 431–32, 439 Bloch, Felix 238, 238∗ , 467–77, 511, 569, 640, 745–47, 877, 1031 Blokhintsev, D.I. 801 Blunt, Anthony 882–85 Bohm, David 800, 822, 847 Bohr, Aage 33, 563, 580, 586, 590, 597, 604, 879

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Name Index

peierlsroot2

1091

Bohr, Margarete 633 Bohr, Niels viii, viii∗ , 11–12, 12∗ , 13, 17, 28, 28∗ , 33, 33∗ , 36, 82–84, 84∗ , 85–86, 97∗ , 105, 105∗ 106∗ , 112, 115, 124, 124∗ , 135∗ , 150, 182–83, 188, 193, 193∗ , 194, 194∗ , 196, 202, 202∗ , 207, 215, 230, 230∗ , 233, 233∗ , 234, 236, 243, 247, 444–45, 506, 506∗ , 539, 582, 632, 640, 648, 681–82, 703, 724, 729, 729∗ , 759, 771∗ , 776∗ , 794–95, 795∗ , 796, 803, 806, 821, 854, 864–66, 869–70, 872, 876, 876∗ , 877–79, 900–901, 905, 909, 912, 927∗ , 956, 968–69, 971, 995∗ , 996–97, 1001∗ , 1003, 1042–43 Boltzmann, Ludwig 617, 620 Bolsterli, Margarete 623 Bolsterli, Mark 623, 623∗ Bopp, Friedrich 590 Born, Gritli 57 Born, Gustav ix Born, Irene 57 Born, Max 11, 55–57, 57∗ , 58, 80, 131, 138, 141–42, 143∗ , 145, 152, 164, 194, 235, 254, 254∗ , 255, 319, 380, 415, 465, 474, 480–81, 512, 584, 681, 839–40, 844, 864, 893, 898, 963 Bothe, Walther 881, 896 Bowcock, J.E. 473, 473∗ Bradbury, Noris 22, 22∗ Bragg, William Lawrence 29, 31, 36, 113, 127, 133, 133∗ , 582, 917, 1010, 1056 Breit, Gregory 13, 106, 106∗ , 125, 131, 154, 154∗ , 161, 161∗ , 192, 192∗ , 207, 233, 265, 286, 286∗ , 293, 317–18, 331, 336, 339–40, 345, 345∗ , 366∗ , 740 Brenner, Sheila 288, 297, 297∗ , 303, 317, 322, 340, 371, 404, 412, 430, 465, 473 Bretscher, Egon 22, 22∗ , 23–24, 48 Bretscher, Hanni 938, 1022 Brevik, Iver 735, 735∗ , 736 Brillouin, L´eon 746 Brink, David 679, 685, 685∗ , 728 Broglie, Louis de 800, 828, 847 Brooke, B.N. 643, 645 Brown, Andrew 927, 927∗ , 1011, 1011∗ , 1013–15, 1051, 1051∗ , 1052 Brown, Betty 932 Brown, Gerald E. ix, 13, 13∗ , 161∗ , 198, 198∗ , 234∗ , 235, 253∗ , 284–88, 285∗ 88∗ , 295, 295∗ 96∗ , 301, 302∗ 303∗ , 308, 309∗ , 315, 320, 324, 326, 329, 335, 337, 337∗ , 339∗ , 340, 340∗ , 344–46, 355, 359∗ , 363, 363∗ , 365–66, 366∗ , 412, 418, 439–41, 465, 495, 496∗ , 516, 563, 563∗ , 571–74, 574∗ , 575–79, 579∗ , 580∗ , 581, 581∗ , 585, 587∗ , 588, 588∗ , 589, 592, 592∗ 93∗ , 595–97, 600, 600∗ 601∗ , 602, 602∗ , 605, 606∗ , 623, 623∗ 24∗ , 630, 634, 640–641, 686, 796–97, 934, 1015–16, 1016∗ , 1042, 1056 Brown, Traudl 566, 589–90, 592, 594, 596, 604, 631 Brown, William 1033, 1033∗ Browser 141 Brueckner, Keith 293, 317, 320∗ , 325, 373, 373∗ , 450, 450∗ , 525, 564∗ , 584,

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584∗ , 595–87, 602–604, 710, 710∗ , 712 Bukharin, Nikolai 872 Bullard, Edward Crisp 216, 216∗ , 916–918 Buneman, Oscar 53 Burkhard, G.H. 584 Burkill, Mrs 167 Burt, Michael G. 685, 685∗ , 733∗ 34∗ Butler, S.T. 208, 253, 253∗ , 370, 411, 613 Byers, Nina 13, 437, 439, 441, 544, 544∗ , 545, 549, 551–52, 569, 569∗ , 570, 587, 599, 610, 610∗ 11∗ , 612, 614, 625, 754–55, 764, 768, 791, 791∗ , 792, 798, 802, 812, 836, 886, 889, 909, 922∗ , 961 Camerini, U. 97 Candlin, D.J. 495, 495∗ Carlson, Bengt 75, 75∗ Carroll, Lewis 862 Case, K.M. 177, 177∗ Casimir, Hendrik Brugt 29, 29∗ , 31, 36, 36∗ , 648, 893, 898 Cassels, J.M. 611, 611∗ Castillejo, Leonardo 620, 679 Cathcart, Brian 757∗ , 1017–18, 1018∗ , 1019, 1026–27 Chadwick, James viii, xi, 1, 4, 14, 18, 22, 26, 29, 31–32, 35–36, 36∗ , 39, 48, 76, 78–79, 196∗ , 204, 248, 382∗ , 582, 678, 682, 866, 870, 870∗ , 877, 927, 927∗ , 1009, 1009∗ , 1011, 1011∗ , 1012, 1012∗ , 1013–15, 1022–23, 1031, 1051, 1051∗ , 1052, 1054, 1056, 1065 Chandrasekhar, Subrahmanyan 244, 244∗ , 1054–55 Chang, W.Y. 68, 68∗ Chapman, Sydney 679 Chau, P.Y. 273 Cherneva, Olga ix Cherwell, Lord 741, 842, 1028 Chew, Geoﬀrey F. 338, 338∗ , 449, 449∗ , 492, 492∗ , 493, 546, 546∗ , 567, 567∗ , 599, 628, 631 Chr´etien, Max 287, 287∗ , 296, 296∗ , 300, 308–10, 325, 333, 342–43, 349, 372, 432, 434∗ , 567∗ Chuvilo, I. 887–88 Clapham, Michael 912 Clayton, D.D. 796∗ Clayton, Henry H. 75, 75∗ Clementel, E. 456 Cocconi, G. 460 Cockroft, John Douglas 5, 17, 27∗ , 39, 51–52, 77, 103, 204, 211, 227, 231–32, 236, 244, 248, 255, 382, 405, 517, 542–43, 582, 627, 872 Cohen, Karl 652 Cohen, Morrell 749

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Name Index

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1093

Cohen, Stanley 404, 406, 417, 430, 565, 597–98, 601 Com`es, R. 747–48 Compton, Arthur 319, 740 Condon, Edward U. 1056 Corson, Dale, R. 236∗ Cottingham, W.N. 599, 610, 610∗ , 613, 615, 626 Cramer, Gabriel 862 Crampin, A.F. ix Creisen, Kenneth I. 460 Cripps 141 Curie, Marie Sklodowska 582 Cutkovski, R.E. 466, 466∗ 67∗ Czyz, Wieslaw 594, 594∗ Dabrowski, J. 584, 587, 594 Dale, Henry 683, 683∗ , 689–90 Dalitz, Richard Henry 13, 206, 206∗ , 235, 241, 254, 254∗ , 255, 262, 278–79, 288, 291, 297, 309, 318, 323, 336, 370, 370∗ , 410–11, 411∗ , 416–17, 438, 438∗ , 439–40, 448, 452–53, 457, 460∗ , 461, 463, 465, 465∗ , 468∗ , 469, 472, 485, 487, 491, 494, 502, 505, 513, 516, 534–36, 561–62, 572, 616, 679, 686, 743, 765∗ , 818, 914, 914∗ , 925∗ , 937∗ , 957, 1064 Dalitz, Valda 461, 516 Dancoﬀ, S.M. 69, 69∗ , 130, 130∗ , 407, 407∗ , 414, 414∗ 15∗ , 438, 460, 460∗ , 468, 468∗ , 483∗ , 424, 526 Davies, Paul 989–90 Davison, Boris 257, 453, 453∗ , 469–70 Deacon, Richard (McCormick, Donald) 757, 794∗ Debye, Peter 644 Dedijer, Stevan 480 De Dominicis, Cyrano 574, 574∗ , 580–581, 580∗ 581∗ , 601∗ Dee, Anne 496, 580, 586 Dee, Philip 77, 89, 204 De Haas, Wander Johannes 513, 1031 De Konig, R. 724 Delbr¨ uck, Max 877 Deppner, Margarete K¨ athe 75∗ Deutsch, Martin 229, 229∗ , 316, 316∗ , 357 Devons, Samuel 204, 204∗ , 206, 618 De Witt, Bryce 284∗ , 800, 808 Diebner, Kurt 864 Dirac, Gabriel 916 Dirac, Margit (n´ee Wigner) 914, 914∗ , 915–17 Dirac, Paul Adrien Maurice viii, xi, 55–59, 71, 100, 111, 141–42, 156, 173–74, 174∗ , 175, 182, 285–86, 286∗ , 289, 289∗ , 295, 303, 322, 331, 338, 345, 347, 353, 360, 389, 394, 445, 639, 682, 682∗ , 683, 683∗ , 721, 721∗ , 722–26, 725∗ , 759, 825–26, 853–55, 872, 915–18, 927∗ , 930, 935–36, 936∗ , 955–56, 1055

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Dorozynski, Alexander 699, 699∗ Drell, Sidney 961 Dumond, Jesse W.M. 614, 614∗ Dwyer, Peter 883 Dyson, Freeman 12–13, 153, 153∗ , 154, 158, 158∗ , 159, 159∗ , 160, 160∗ , 162–63, 168–69, 171, 174, 174∗ , 175–78, 179∗ , 180–81, 191–92, 197, 206, 234, 237, 242, 244–45, 246∗ , 247, 247∗ , 248, 251, 260, 262, 265, 268, 284–85, 291, 291∗ , 295∗ , 307, 319, 323–24, 341, 348, 358, 367∗ , 369, 404, 408, 408∗ , 409, 414, 414∗ , 415, 430, 437, 438∗ , 439, 441–42, 451, 455, 464, 468, 468∗ , 482–83, 491, 493, 499, 508, 519, 522–24, 553, 553∗ , 554–55, 577, 587, 597, 640, 670–71, 672∗ , 749–50, 802, 828, 828∗ 29∗ , 831, 831∗ , 910, 922, 922∗ , 923, 926, 934, 935∗ 36∗ , 955, 960, 967, 1010, 1053, 1056 Dyson, Imme 750, 829–31, 934, 936, 960, 967 Dyson, Verena (n´ee Huber) 245, 245∗ , 250, 262, 264, 368, 522, 829, 829∗ Eberhard, P.H. 846, 846∗ Eden, Anthony 583 Eden, R.J. 564, 564∗ , 682, 721, 721∗ Edgworth, Francis Ysidro 862 Edwards, Sam 437, 439, 453, 453∗ , 463, 463∗ , 473–74, 479, 483–84, 484∗ , 492, 492∗ , 495, 498–99, 509, 509∗ , 510, 512–13, 574, 594–95, 617, 619, 668, 708, 710, 730, 1057 Eggington, Anne 765, 765∗ Einstein, Albert viii∗ , 135∗ , 142, 144, 151∗ , 156, 462, 795, 839, 844–45, 844∗ , 872, 918, 928, 956, 991, 1030, 1030∗ Eisberg, Robert Martin 631, 631∗ Eisenbud, L. 81∗ , 154∗ Elliot, Roger 679 Ellis, C.D. 877 Eveking, Wilhelm 764, 959 Everett, Hugh 800, 802, 808–809 Ewald, Peter Paul 90∗ Eyges, Leonard 170, 170∗ Fatehally, R.A. 71∗ , 73∗ Feather, Norman 480–81 Feenberg, Eugene 164, 164∗ , 169, 169∗ , 170, 170∗ , 192 Feinberg, G. 599, 611, 767 Feldman, D. 258, 258∗ , 308, 308∗ , 352, 352∗ , 387, 387∗ , 439, 463, 511, 511∗ , 512 Feldman, Gordon 463∗ , 474, 478, 479∗ , 489, 495, 495∗ , 497, 524–25, 525∗ Feller, David 284 Fermi, Enrico 16, 185, 192, 238, 238∗ , 239, 249, 269, 277, 286, 289, 292∗ , 295∗ , 331, 407, 443, 450, 458, 461∗ , 490–91∗ , 493∗ , 526, 567∗ , 585, 612, 683, 683∗ , 685∗ , 694, 710, 710∗ , 712, 740, 748–49, 820, 858, 879, 881, 890, 983, 1012 Fernbach, S. 131, 131∗ , 151∗

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World Scientiﬁc Book - 9in x 6in

Name Index

peierlsroot2

1095

Ferrell, Richard 316∗ , 336, 345 Ferretti, Bruno 86, 86∗ , 87, 87∗ , 88, 88∗ , 135∗ , 138, 138∗ , 139, 253 Feshbach, Herman 81∗ , 254, 254∗ , 888 Feynman, Richard 13, 109, 112–13, 114∗ , 140, 140∗ , 154, 159∗ , 161, 161∗ , 165, 168, 174, 192, 200, 206, 235, 239, 241, 249, 254, 284–85, 295∗ , 297, 301, 304, 334–36, 346, 369, 410, 453, 453∗ , 459, 463, 483, 483∗ , 484, 499–500, 511, 633, 669, 1007, Finkelstein, R. 155, 155∗ , 156–57, 176, 674 Fisher, Ronald 863 Flowers, Brian Hilton 405, 411, 439, 487, 617, 817, 824, 1057, 1060 Fl¨ ugge, Siegfried 890 Fock, Vladimir 710, 712∗ , 713 Foot, Philippa 769, 769∗ Foster, E.M. 725 Fowler, Ralph Howard 25, 28, 722 Fowler, Willy 796, 1016 Fox, Evelyn 616, 621 Frampton, Paul 769, 769∗ Frank, Charles 868, 875, 892 Frenkel, Natasha 101 Frenkel, Viktor 761, 873, 985, 985∗ , 1030, 1048, 1048∗ Frenkel, Yakov Ilich 59–63, 63∗ , 64, 64∗ , 99, 101, 682, 790, 928∗ , 1055 Friedel 747 Frisch, Otto Robert 11, 16∗ , 24, 24∗ , 77, 95, 95∗ , 211, 214, 465, 582, 640, 648–49, 682, 692–93, 759, 797, 864, 875, 877–79, 893, 895, 903, 906, 913, 944, 964, 1003, 1023 Frisch, Ursula ix Fr¨ ohlich, Herbert 99∗ , 275, 275∗ , 276, 278, 640, 873, 1008, 1008∗ , 1009 Fubini, Sergio 450, 450∗ Fuchs, Klaus 6, 6∗ , 7, 23, 23∗ , 53, 56–57, 78, 92, 113, 209, 209∗ , 211–12, 214–15, 219–25, 227∗ , 232, 234, 271∗ , 443–44, 622, 640, 681, 682∗ , 756–57, 759, 811, 882–86, 911, 911∗ , 927, 942, 942∗ , 943–44, 1001–1002, 1011, 1014, 1026, 1052 Fulda, Karli 959 Gammel, J.L. 584, 584∗ , 585, 624, 710, 710∗ Gamow, George 68, 68∗ , 548–49, 640, 874, 878–79, 985–86, 1049 Gardner, Eugene 131∗ , 208 Gardner, Frederic Horace 278, 278∗ , 280 Gardner, J.W. 230∗ Garlick, G.F.J. 73, 73∗ Gattrell, Jane ix Gavoret, J. 603, 603∗ Gehring, Gillian 1057 Gell Mann, Murray 284∗ , 307, 307∗ , 318∗ , 450∗ , 451, 453, 453∗ , 459, 504, 524, 701, 703

April 7, 2009

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1096

World Scientiﬁc Book - 9in x 6in

peierlsroot2

rudolf peierls

Gerlach, Walther 804, 810 Ginzburg, Vitaly L. 750–51, 761, 766–67, 767∗ Goeppert-Mayer, Maria 202, 202∗ 207, 207∗ , 699 Goldberg, Stanley 1029, 1029∗ , 1032 Goldberger, Marvin L. 248, 450, 450∗ , 451, 458, 458∗ , 492, 544, 568 Goldhaber, Maurice 1052, 1056 Goldstein, Rose 142, 467, 561 Goldstone, Jeﬀrey 587, 587∗ , 634 Gorbachev, Mikhail 762, 925, 958, 959∗ , 960, 960∗ , 967, 986, 990–92 Goudsmit, Samuel, Abraham 482, 482∗ , 483, 499, 863, 868–69, 875, 881, 901, 906, 981, 983 Gowing, Margaret 446, 446∗ , 647, 647∗ , 677, 677∗ , 678, 689, 692–93, 773, 776, 776∗ , 835, 841, 853, 855, 864, 866, 869, 892, 898, 1011, 1018, 1026 Grechkov, Andrei 832 Greene, Hugh Careton 682, 702∗ Greenglass, David 7 Greenglass, Ethel 7 Gromyko, Andrei 74, 74∗ , 76, 78–79 Groves, Leslie Richard 1–3, 14, 32, 39, 80, 462, 863, 863∗ , 875, 892, 1022, 1026, 1036 Guggenheim, E.A. 53 Gunn, John Currie 413, 465 G¨ unther, M. 207, 235, 235∗ , 636, 638 Gustafson, Torsten 109 Haefeli, Hans 829 Haefeli, Verena 829 Hager, Margret 883, 885 Hahn, Otto 55, 57, 866, 964, 982, 984 Hamburger, Hilde 824 Hammack, K.C. 170∗ Halban, Hans 256∗ , 324, 692–94, 1012 Harris, Colin viii Harteck, Paul 868 Hartree, Douglas Rayner 418, 652, 710, 712∗ , 713 Hawking, Stephen 989, 989∗ , 991 Haworth, Walter, Norman 19, 981 Haxel, Otto 202∗ , 867, 867∗ , 871 Heidegger, Martin 760, 762 Heine, Volker 709 Heisenberg, Elisabeth 772–73, 773∗ , 774–75, 968, 971 Heisenberg, Jochen ix Heisenberg, Werner viii, ix, 11, 55–57, 57∗ , 58, 67∗ , 128, 128∗ , 132, 135∗ , 144, 146, 193, 200, 200∗ , 239, 258∗ , 288, 288∗ , 308, 387, 444, 444∗ , 511, 682, 759–60, 760∗ , 761, 772, 772∗ , 773, 775, 852, 854–55, 863, 863∗ , 864–67, 867∗ , 868–70,

April 7, 2009

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World Scientiﬁc Book - 9in x 6in

Name Index

peierlsroot2

1097

875, 880–81, 892–96, 900–906, 908, 912, 926–27, 928∗ , 956, 968, 968∗ , 969, 971, 982–84, 995, 995∗ , 996–97, 1003, 1012, 1029, 1029∗ , 1041∗ , 1042, 1060 Heitler, Walter 57∗ , 88, 88∗ , 90, 93, 109, 141, 171∗ , 194, 840, 841∗ Hendry, John 759, 852–53, 853∗ , 854, 856 Herbert, N. 844, 844∗ , 989, 989∗ , 990 Herman, Armin 867, 867∗ , 868 Hertz, Gustav 890 Higginbotham, C.W. 243, 247 Higgs, Peter W. 480–81 Hilbert, David 240 Hinton, Christopher 5, 1026 Hitler, Alfred 57, 142, 549, 696, 772–73, 870∗ , 962, 988, 994, 1000, 1050 Hochhut, Rolf 884 Hoddeson, Lillian 771∗ , 776∗ Hodge 694 Hofstadter, R. 465 Holloway, David 890, 1060 Hood-Phillips, Owen 547, 547∗ Hookway, Jo (n´ee Peierls) vii, ix, 765, 860, 910, 922, 932, 934, 938, 1025, 1054, 1057, 1059–60 Horowitz, J. 473, 473∗ Houghton, R.A. 613 Houtermanns, Fritz Georg 1031, 1031∗ , 1048∗ Huber, Katrin 251, 829–30, 910, 934 Huby, R. 195, 195∗ Hughes, Donald J. 24, 24∗ Hulme, Henry R. 726, 726∗ Humphreys, Andy 882, 882∗ , 883–84 Humphreys, W.J. 470 Hyamns, Bernard 514, 514∗ Hylleraas, Egil A. 366 Infeld, Leopold 67 Ioﬀe, Abram F. 62∗ , 275∗ , 557, 790, 1048∗ Irving, D.J.C. 864, 864∗ , 868, 981, 1041, 1043 Irving, John 206, 206∗ , 399, 401, 404, 509, 509∗ Israel, W. 989∗ Iwanenko, Dimitri 1055 Jacobsen, J.C. 84, 86 Jacobsohn, Franz 688, 752, 755–56, 824, 834, 848, 851, 852∗ , 918, 924, 959, 1002, 1039, 1058 Jacobsohn, Robert 919, 939, 1002, 1039–40 Jacobsohn, Ulrich 919 Jauch, Josef Maria 603, 603∗

April 7, 2009

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1098

World Scientiﬁc Book - 9in x 6in

peierlsroot2

rudolf peierls

Jeﬀreys, Harold 365∗ Jenkins, A.L. 584, 587 Jensen, Johannes 28, 202, 202∗ , 966 Jephcott, Mrs 1006 Johnson, Mikkel B. 744, 744∗ Joliot, Fr´ederic 493∗ , 497 Joliot, Ir`ene 493∗ , 497 Joos, Hans 887 Joos, Inge 887 Jordan, Pascual 721, 721∗ Jost, R. 187, 187∗ , 188, 201, 238, 508, 673, 673∗ Juliusberg, Heinz 696, 698 Juliusberg, Maud 687, 696, 696∗ , 697 Jungk, Robert 872, 881, 906–907, 978, 984∗ , 1041, 1043 Justi, Eduard 122, 122∗ Kabir, Praban R. 606–608, 609∗ , 673–74, 684, 705 Kachalova, Tatiana 920 Kalckar, Fritz 106, 106∗ K¨ allen, Gunnar 258, 258∗ , 394, 394∗ , 444, 444∗ , 448, 453, 459, 500, 512, 540, 540∗ , 597 Kalos, Malvin, H. 438∗ , 457, 457∗ , 460∗ , 468 Kannegiser, Nina 803 Kapitza, Pjotr Leonidivich 629, 724, 760, 871, 871∗ , 872, 917, 969, 971, 1001–1002 Kapitza, Sergei 950–51 Kapur, P.L. 69, 69∗ , 80, 107–108, 108∗ , 613 Karplus, Robert 239, 239∗ , 240–41, 284–85, 323, 329, 329∗ , 337–38, 346–47, 355–56, 358, 364, 366, 626, 626∗ Kearton, C.F. 891 Kemble, Edwin C. 801 Kemmer, Nicholas 151, 151∗ , 166–67, 480–82, 558 Kernan, Anna 888 Keynes, John Maynard 861 Khalatnikov, I.M. 445∗ , 499, 499∗ , 920–21, 927∗ , 936–37, 937∗ Khrushchev, Nikita 444, 540∗ Kim, Young Sun 672, 672∗ , 673 Kistiakozsky, G.B. 650 Klein, Abraham 135∗ , 329∗ , 483, 483∗ Klein, Oskar 444∗ Klein, Felix 135∗ , 394 Klein, Oskar Benjamin 444∗ Knudsen, A.W. 41, 465∗ Kobayashi, Minoru 168 Kohn, Walter 319, 319∗ , 613 Kolsrud, Marius 235, 235∗ , 255

April 7, 2009

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World Scientiﬁc Book - 9in x 6in

Name Index

peierlsroot2

1099

Kowarski, Leo 692, 939, 1012 Kramers, Hendrik Anthony 111, 135, 135∗ , 175, 521, 521∗ Krause, Waltraud 930, 930∗ , 987, 987∗ , 992, 994–95 Krebs, Anni (n´ee Peierls) 987–88, 993 Kristensen, P. 374, 374∗ , 387, 390, 394–95, 431, 431∗ , 375–76, 378–79, 434, 511, 511∗ Kroll, Norman M. 239, 241, 285, 304, 304∗ , 337, 337∗ , 346, 358, 450, 450∗ , 626, 626∗ Krook, Max 72, 72∗ , 86∗ , 138, 138∗ , 139, 318, 318∗ Krynch, Georg J. 73∗ , 288, 340, 359 Krynen, Lillie (n´ee Jacobsohn) 918, 924, 939–40, 942, 955, 961, 970, 975, 978, 997, 1002, 1039, 1058, Kuper, C.G. 537, 537∗ Kurchatov, Igor 889 Kurti, Nicholas 121, 811, 976, 978 Lamb, Willis 109∗ , 158, 160–61, 207, 241, 286, 329∗ , 336, 337∗ , 358, 360, 365, 404, 412, 430, 446, 496∗ , 565, 579, 592, 597, 603, 603∗ , 606, 606∗ , 665, 679, 732, 732∗ Landau, I.L. ix Landau, K.T. 700 Landau, Lev Davidovich 63, 72, 72∗ , 182, 182∗ , 277, 444–45, 445∗ , 505–506, 505∗ 506∗ , 507–513, 524, 526, 531–32, 545–46, 556, 556∗ , 568, 582, 632–33, 640, 666, 666∗ , 682, 683∗ , 699–700, 734, 734∗ , 762, 790, 801, 874, 889, 927, 937, 937∗ , 975, 1055, 1057 Landsberg, P.T. 733, 733∗ , 735 Lange, Herbert 778 Lapere, Robert 883 Larmor, Joseph 582 Larssen, Alf 912 Lassen, N.O. 231, 231∗ Lattes, C.M.G. 91∗ , 97∗ , 131, 131∗ Laue Max von 55, 57 Lawrence, Ernst Orlando 75, 81 Lederman, Leon 625, 625∗ Leighton, R.B. 293, 293∗ Lehman, H. 485, 485∗ , 533 Lennox, Edwin 96, 96∗ , 100, 114 Leprince-Ringuet, Louis 97∗ Levinger, Joseph 287, 316, 338 Levy 616 Lewis, H.W. 200, 200∗ Lewis, Robert 1 Lewis, Vaughan 644 Lifshitz, E.M. 445, 445*, 545, 545∗ 546∗ , 557, 557∗ , 629, 734, 734∗ , 762, 801

April 7, 2009

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1100

World Scientiﬁc Book - 9in x 6in

peierlsroot2

rudolf peierls

Lilienthal, David E. 65, 74, 74∗ Lindhard, Jens 193, 193∗ , 194, 208, 231 Lindenbaum, S.J. 449, 449∗ Lloyd, Selwyn, B. 442, 661, 661∗ Longmire, Conrad 50, 226, 226∗ Lorentz, Hendrik Antoon 59, 63, 71, 88, 100, 110–11, 186, 277, 289, 289∗ , 290, 301, 350, 379, 387–88, 396, 432, 506–507, 565, 582, 956 Love, A.E.H. 679 Low, Frances 284∗ , 285, 301, 304, 307, 307∗ , 316, 318, 320–23, 325, 327, 327∗ , 328, 332–33, 338–39, 359, 459, 546, 546∗ , 567, 567∗ , 604, 621 Luﬀman, W.F. 255 Luttinger, J.M. 238, 238∗ , 508, 508∗ Lyttleton, R.A. 481 Ma, Shih-Tsun 171, 171∗ MacDowell, Sam 791, 793 Mack, Julian Ellis 430, 430∗ , 598 Mackenzie, Kenneth Ross 764, 764∗ Madsen, Børge 85–86 Mandelstam, Stanley 13, 437, 439, 496, 560–61, 566, 568, 568∗ , 619, 621, 626, 628, 631, 667, 667∗ , 672, 675, 675∗ , 676 Maris, Theodor A.J. 590, 590∗ Markov, M.A. 526 Marshak, Robert E. 70∗ , 91∗ , 165∗ , 593, 597, 600, 600∗ , 950 Marshall, Walter 24, 49, 371, 473, 522, 522∗ , 1057 Martin, P.C. 460 Martin, Susan K. ix, 857 Massey, A. Stewart Wilson 413, 573, 1012, 1051–52 Matthews, Paul T. 241, 247, 247∗ , 291, 291∗ , 439–40, 464, 473–74, 475∗ , 483, 495, 499, 512, 524, 525∗ , 571, 573–74, 599, 618 Maximon, Leonard 587, 587∗ , 590 Mayers, D.F. 592, 592∗ , 603∗ , 606∗ McMillan 39, 131, 246 McCarthy, Joseph Raymond 7, 13, 280, 541 McCauley, Graham 592∗ 93∗ , 635, 660, 660∗ McKinlay, William A. 254, 254∗ McManus, Hugh 20, 40∗ , 71, 71∗ , 109, 111, 113, 140, 173, 206, 206∗ , 261, 264–65, 278–79, 312, 314–15, 326, 342, 352–53, 374, 374∗ , 433, 510, 512 McNamara, Paul 833 Mehta, Madan Lal 672, 672∗ Meiman, Naum 762, 925, 958, 959∗ , 960, 960∗ , 961, 986, 990–92 Meitner, Lise 11, 78, 435, 811, 869, 878–79 Metzger, Kurt 509, 509∗ Messel, Harry 452, 452∗ , 456 Messiah, A.M.L. 291, 291∗ , 473, 473∗

April 7, 2009

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World Scientiﬁc Book - 9in x 6in

Name Index

peierlsroot2

1101

Michel, L. 736–37 Milne, A.E.H. 679 Minde, Hans 987 Minkowski, H. 685, 685∗ , 734, 734∗ , 735–36, 750–51 Møller, Christian 28, 58, 73, 73∗ , 83, 169, 265, 290, 374, 374∗ , 381, 387, 390, 394–96, 415, 431, 431∗ , 432–34, 476, 511, 511∗ , 685, 685∗ , 729, 729∗ , 733, 734∗ , 735–36, Molotov, V.M. 79 Mondragon, Alfonso 586, 598 Montgomery-Hyde, H. 759, 811, 811∗ Moon, Philip 21, 28, 33, 78, 86, 204–205, 242, 247, 285–86, 325, 456, 543, 549, 603, 1021–24, 1029 Moorehead, Alan 883, 883∗ , 885 Moorhouse, Gordon 207, 465, 465∗ Motchane, Leon 736∗ Mott, Nevill 11, 29, 95, 95∗ , 98, 114, 121–23, 254, 254∗ , 256–57, 257∗ , 275, 434, 465, 497, 501, 543–44, 597, 629, 629∗ , 680, 694, 707–709, 714–15, 745, 746∗ , 747–48, 760∗ , 762, 762∗ , 776, 776∗ , 790, 790∗ , 814–16, 823, 840, 841∗ , 863∗ , 892, 898–99, 906, 912–13, 915–917, 929, 972, 974–75, 1007–1008, 1008∗ , 1009, 1048 Mottelsohn, Ben Roy 597 Mountbatten, Louis 815 Muirhead, H. 91∗ , 97∗ Muscott, Mrs 580 Mydral, Alva 815, 815∗ Nabarro, Frank 868, 868∗ , 776∗ Nabir, Pasha 813 Nambu, Y. 262, 262∗ Nataf, R. 480 Nath 702, 706 Negele, John 796 Nemeth, Judith 710, 710∗ Neumann, John von 682 Neumann, Maurice 239, 239∗ Ney, E.P. 199, 199∗ Nicholson, Angus F. 496, 600, 600∗ , 605–606 Nicolaisen, Ida ix Nisbet, A. 480 Nordheim, Lothar 169, 169∗ 70∗ Noyes, H.P. 267, 291 Nunn-May, Alan 123, 222, 222∗ , 882, 1051–1052 Occhiliani, G.P.S. 91∗ , 97∗ 98∗ Ohnuma, Shoruku 593, 593∗

April 7, 2009

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1102

World Scientiﬁc Book - 9in x 6in

peierlsroot2

rudolf peierls

Oliphant, Marcus L.E. 18, 21, 28, 33, 49, 60, 65, 85–86, 114, 136, 204, 204∗ , 205, 242, 400, 408, 429, 582, 649, 692–93, 984, 985∗ , 989–90, 1014 Onnes, Heike Kammerlingh 351, 515∗ Opechowski, W. 521, 521∗ Oppenheimer, J. Robert viii, xi, 1–2, 7, 11–12, 22, 48, 65, 82, 82∗ , 88, 88∗ , 90, 104, 105∗ 106∗ , 110∗ , 135–37, 150, 155, 156∗ , 157, 159–60, 176–78, 180, 196, 199–200, 200∗ , 242, 246–47, 250, 266, 269, 280–81, 284, 294, 356, 372, 408, 442–43, 461, 461∗ , 466, 471, 541, 636–38, 681–82, 683*, 687, 691, 700, 737, 738∗ , 739, 759, 835, 842, 1028, 1042, 1060, 1065 Ore, Aadene 366, 366∗ Orear, Jay 567, 567∗ Orowan, Egon 218–19, 642, 644–45, 686, 856, 860–61, 1009, 1009∗ , 1010 Orowan, Jolan (n´ee Schonfeld) 644, 857, 861 Ovenhauser, A.W. 748–49 Overbeck, Doris 945 Owen, David 841 Pais, Abram 110, 110∗ , 114, 135∗ , 187, 200, 200∗ , 205, 205∗ , 206, 238, 238∗ , 253, 284, 294, 294∗ , 323, 323∗ , 375, 460, 835, 995–96, 996∗ , 997, 1001, 1001∗ , 1002–1003 Pais, Josh ix Pandharipande, Vijay R. 796 Paneth, Friedrich A. 256∗ Paneth, Heinz Rudolph 256, 256∗ Panofski, W.K.H. 242–43, 246, 248 Pauli, Wolfgang Ernst viii, viii∗ , xi, 11, 135∗ , 141, 170–71, 171∗ , 172–73, 174∗ , 175–76, 179, 179∗ , 182, 185, 185∗ , 187, 190, 201, 249, 267∗ , 275, 287–89, 289∗ , 290, 290∗ , 347, 373, 373∗ , 375∗ , 379, 382, 384, 385∗ , 386, 393, 396, 398, 401, 402∗ , 418, 418∗ , 423–24, 426–29, 431, 431∗ , 432, 434, 441, 444, 444∗ 445∗ , 505, 505∗ , 507∗ , 509, 509∗ , 512–13, 524, 527, 532, 532∗ , 533, 537, 570, 585, 640, 682, 723, 739, 755, 759, 820, 844–45, 854–55, 859, 1012, 1030–31 Pauling, Linus 141 Pegram, G.B. 652 Peierls, Alfred 697–98, 976, 987–88, 993 Peierls, Else (n´ee Hermann) 699, 988 Peierls, Gaby 568, 686∗ , 792, 852, 857, 922, 932–34, 960, 1025, 1053 Peierls, Genia (n´ee Kannegieser) viii, 6, 10, 11∗ , 54, 64, 76, 78, 101, 114, 178, 209, 211–12, 247, 251, 266, 268, 270, 414, 445–46, 462–63, 597, 638, 642, 644, 673, 686, 702, 727–28, 738, 741, 750, 754–55, 757, 762–64, 768, 770, 779, 791, 795–800, 803, 812–13, 821, 823, 825, 828, 828∗ , 834, 836, 838, 840∗ , 852, 852∗ , 856, 858, 861, 873, 889, 910, 913, 914–17, 922, 922∗ , 923–26, 932–36, 938–39, 946, 985–86, 1017, 1030, 1953∗ , 1054, 1056, 1062–63 Peierls, Heinrich 696∗ , 987∗ , 993 Peierls, Julie 657, 803 Peierls, Ronnie 563, 563∗ , 568, 686∗ , 803, 857, 922, 933–34, 960, 1025, 1053

April 7, 2009

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World Scientiﬁc Book - 9in x 6in

Name Index

peierlsroot2

1103

Peng, Huan-Wu 57, 57∗ , 58, 58∗ , 59, 70, 70∗ Penney, William 5, 43, 43∗ , 45, 443, 538, 682, 927∗ , 1018–20, 1026–28 Perkins, D.H. 414 Perrin, Francis 51, 648, 1050 Perrin, M.W. 911, 968, 1026 Philby, H.A.A. 883, 883∗ Piccioni, O. 458 Pilkington, Lawrence 644 Pippard, Brian ix, 715, 715*, 918 Placzek, A. ix Placzek, George 12, 17, 22, 24, 24∗ , 33, 33∗ , 69, 69∗ , 74, 76, 79, 84, 97, 105, 105∗ 106∗ , 124∗ , 125, 135, 165, 193, 230, 239, 247, 249, 284, 877–78 Planck, Max 55, 142, 963, 965 Pohl, Robert Wichard 790 Polanyi, Michael 142, 861 Pollard, E.C. 196, 196∗ , 317 Pollock, F. 337∗ Pomeranchuk, Issak Yakovlevich 445∗ , 531, 531∗ , 532, 762 Pontecorvo, Bruno 205, 493, 493∗ , 812 Portal, Charles Frederick Algernon 5, 49, 49∗ , 271, 1026 Powell, Cecil, F. 91∗ , 97, 97∗ , 98, 98∗ , 114, 130, 135, 177, 205, 273, 517–18, 683, 928, 950–51, 998 Powers, Thomas 927∗ , 968, 968∗ , 970, 1029, 1029∗ , 1032, 1041–43, 1060 Pratts 624 Preston, Melvin A. 67, 67∗ , 68, 69∗ , 150 Priestley, Raymond 10, 14, 18, 197, 231, 278 Pryce, Maurice 53, 157, 227, 227∗ , 232, 289∗ , 307 Pursey, D.L. 480 Rabi, Isidor Isaac 246, 1056 Radcliﬀe, John 288, 316, 319, 324, 336, 338, 360, 365 Radicati, Luigi 453, 456, 472, 997∗ Raesbeck, Phil 1045 Raman, Chandrasekhara 244∗ , 267, 607 Ramsay, W.H. 148 Rarita, W. 73, 73∗ Ravenhall, D.G. 138∗ , 206, 207∗ , 234, 234∗ , 235, 253, 253∗ , 262, 265, 302, 302∗ , 316, 329–30, 345, 366, 479 Rayleigh, John William Strutt 582 Rayski, Jerzy 173, 173∗ , 185, 185∗ , 208, 264, 273 Redmond, P.J. 325, 456–57, 472, 472∗ , 562, 612, 612∗ Redshaw, S.C. 534, 534∗ , 573 Regge, T. 667, 667∗ Reid, Robert 682, 683∗ , 701, 701∗ , 702 Rennie, A.R. 257

April 7, 2009

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1104

World Scientiﬁc Book - 9in x 6in

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rudolf peierls

Richmond, Mark 1003, 1003∗ Riebe, Jae ix, 1020–21, 1024 Riedel, Herbert 987 Roberts, Adam 823 Robertson, Andrew 918 Rohrlich, Fritz 201, 201∗ , 603, 603∗ Rotblat, Josef 794, 802, 841, 928, 928∗ , 1030, 1036∗ , 1060∗ Rose, Morris Edgar 164 Rose, R.L. 760–61, 863, 865, 867, 875–76, 880, 892–93, 900, 904, 907 Rosenberg, Ethel 7 Rosenberg, Julius 7 Rosenfeld, A. ix Rosenfeld, J.L.J. ix Rosenfeld, L´eon ix, 56, 59, 73, 73∗ , 135∗ , 148, 148∗ , 172, 172∗ , 193, 193∗ , 373, 573, 586, 591, 640, 776∗ , 805, 877, 879 Rossi, Bruno B. 135∗ Rudermann, Malvin, A. 450, 450∗ Rudolph, Heinz 755–56, 756∗ , 774, 777, 789, 923, 945–46, 958, 979–80, 986, 988, 1025∗ , 1030, 1060–61 Ruelle, D. 736–37 Russell, Bertrand 928 Rutherford, Ernest 97∗ , 582, 640, 701, 844, 872, 924, 927∗ , 1011–13 Rzewuski, Jan 173, 173∗ , 185, 185∗ , 208, 264, 273 Sachs, R.G. 292∗ , 297, 297∗ , 299, 605, 605∗ Sachs, Werner 727 Sack, Heinrich 1031 Sakharov, Andrei 849, 851, 992 Salam, Abdus 241, 247∗ , 291, 291∗ , 473–74, 474∗ , 475, 481, 483, 483∗ , 498, 501, 543, 613, 636, 636∗ , 637–38, 683, 761, 817, 819–20, 926, 952, 989 Salant, E.O. 400, 402 Salpeter, Ed ix, 13, 54, 70, 70∗ , 140, 140∗ , 153, 153∗ , 172–73, 199, 201, 205, 285, 291, 295, 295∗ , 301, 307–308, 308∗ , 309, 309∗ , 315, 317–22, 327, 327∗ , 330, 332, 335–37, 344, 344∗ , 345, 356, 359, 363–64, 399–400, 404, 408, 408∗ , 412, 418, 429, 438, 454, 457, 459, 467, 467∗ , 561, 561∗ , 640, 759, 759∗ , 1056 Salpeter, Mika 404, 429 Salzman, G. 567, 567∗ 68∗ Sanchez-Ron, J.M. 839–40, 840∗ Sanford, Folliot 718, 718∗ Sawicki, J. 594 Schaefer, Glen 495, 495∗ , 496, 603, 606∗ , 634 Schafroth, M.R. 522, 522∗ , 523 Schein, Marcel 170, 170∗ , 323, 323∗ Scherrer, Paul 869 Schiﬀ, L.I. 616, 627, 702

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Name Index

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1105

Schiﬀer, Max 284 Schlapp, Robert 480–81 Schonland, D.S. 236, 253, 509∗ , 517 Schr¨ odinger, Erwin 16, 16∗ , 74–75, 141–43, 145–46, 260, 302, 618, 621, 807, 828, 854, 872, 856 Schultz, P.F. 587, 616 Schwartz, Laurent 250, 250∗ Schweber, Silvan, S. 91∗ , 284, 285∗ , 408∗ , 468∗ Schwinger, Julian Seymor 13, 73, 73∗ , 109, 109∗ , 113, 136–38, 148, 154, 154∗ , 159, 159∗ , 160–61, 161∗ , 166, 166∗ , 167–168, 171, 171∗ , 172, 172∗ , 173–74, 174∗ , 175, 175∗ , 176, 184–87, 190–93, 207, 207∗ , 239–40, 240∗ , 248–49, 262, 284–85, 289, 289∗ , 295∗ , 316, 319∗ , 321, 329, 329∗ , 347, 356, 356∗ , 369, 437, 463–64, 479, 483, 513, 569, 612, 615, 626 Scott, W.T. 236, 236∗ , 244, 254, 434–35 Segr`e, Emilio, G. 130, 170, 170∗ Seitz, Frederic 464, 776 Serber, Robert 106∗ , 130, 130∗ 31∗ , 132, 137, 150, 151∗ , 152–53, 246, 459, 459∗ , 560, 687, 738, 738∗ Shakespeare, William 884 Shaw, G.B. 884 Shaw, Gordon, L. 584, 584∗ Shilpp, P.A. 846 Shoenberg, D. 257∗ , 761, 776, 849–50, 871, 871∗ , 971 Shotton, F.W. 571, 571∗ , 575, 588, 594 Shubin, Semyon 762, 762∗ Shubnikov, Lev 762, 762∗ , 1031 Shutt, Ralph 450, 450∗ Silverman, A. 460 Simon, Francis 58, 122, 649–51, 869 Simon, Lady 869, 963, 1030 Singwi, K.S. 208∗ , 317 Sirlin, Alberto 568, 568∗ Skinner, H. 49–50, 121, 588, 682, 1028 Skyrme, Tony H.R. 23, 23∗ , 64–65, 69, 75, 80, 128, 128∗ , 201, 208, 239, 257, 320, 447, 464, 676 Slater, John, C. 67, 624 Slotnick, Murray 170, 170∗ , 192, 192∗ , 238 Smith, Adam 861 Smith, Alice 842 Smith, Chris Llewellyn 765 Smith, Cyril 776 Smith, Jack 164, 164∗ , 165, 170 Smyth, Henry Wolf de 80, 222, 222∗ Snyder, H.S. 236, 236∗ , 244, 254 Sommerfeld, Arnold 174∗ , 275∗ , 366, 547, 721, 854, 858–59, 931, 1056

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Sondheimer, E.H. 257, 257∗ Sondheimer, F. 676∗ Sood, P.C. 604, 604∗ Sparkes, Miss 336 Stalin, Joseph 444, 540∗ , 681, 683, 889 Standing, Kenneth, G. 604, 604∗ Steinberger, J. 291, 292∗ , 490, 567, 567∗ Stern, M.O. 316, 804, 810 Stern, Otto 135∗ Stimson, Henry 4∗ Stuewer, Roger ix, 759, 876–77, 879 Stuttart, James 591, 591∗ , 624 Suter, Christian ix Svartholm, N.V. 74, 401, 401∗ Swiatecki, Wladek, J. 163, 163*, 192, 208, 208∗ , 439, 478 Swirles, Bertha 365, 365∗ Szilard, Leo 135, 923, 935 Tamm, Igor 63, 407, 407∗ 408∗ , 414∗ 15∗ , 438∗ , 454, 460∗ , 468, 468∗ , 483∗ , 506, 524∗ , 526, 682, 761, 766, 766∗ , 767, 767∗ , 1030, 1060 Taylor, G.I. 131, 138, 140, 155∗ , 211, 211∗ , 212–13, 582, 650, 1014, 1026, 1028 Taylor, Hugh, S. 218 Taylor, J.C. 524, 524∗ , 532∗ Taylor, T.B. 131∗ , 151∗ Teller, Edward 23∗ , 72, 72∗ , 207, 207∗ , 461∗ , 640, 741, 842–44, 926, 943, 947, 948∗ , 949–51, 951∗ 52∗ , 1043 Ter Haar, Dirk 169, 169∗ , 679, 686 Thellung, A. 533, 533∗ , 537, 577, 841 Thirring, Walter 450∗ , 458∗ , 508, 508∗ Thomas 371 Thomas, L.H. 29, 29∗ Thomas, R.G. 581, 581∗ Thomson, G.P. 5, 35, 41, 46–47, 258, 450, 881 Thonemann, Peter Clive 258 Thorner, Hans 755, 755∗ , 821, 823 Thorner, Ilse ix, 756, 821, 823 Thouless, David, J. 585, 585∗ , 653, 656, 656∗ , 657 Titeica, Serban 620 Titterton, Ernest, W. 23, 23∗ , 1023 Tizsa, Laszlo 858 Tomonaga, Sin-Itiro 13, 136–37, 158–59, 159∗ , 161∗ , 165, 168, 174, 174∗ , 186–87, 207∗ , 237, 238∗ , 285, 289, 289∗ , 295 Treiman, Sam 672, 672∗ Truman, Harry, S. 3, 3∗ 4∗ Tuve, M.A. 866, 870, 870∗

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Name Index Tyabji, S.F.B.

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725, 725∗

¨ Uberall, H. 524∗ Uhlenbeck, George Eugene 187, 200, 200∗ , 201, 375 Uhlmann, A. 887 Unwin, K. 719 Uretzky, Jack, L. 612, 612∗ Urey, Harold Clayton 32, 32∗ , 66, 66∗ , 582, 652, 684, 702, 705–706 Ustinov, Peter 642 Vachaspati 190 Valatin, J.G. 287, 439, 474, 477, 495, 512 Van Alphen, P.M. 513, 1031 Van Hiew, Nguyen 971, 972∗ Van Hove, L´eon 239∗ , 240, 240∗ , 241, 284 Van Wieringen 208 Van Wyk, C.B. 177, 177∗ , 180–81 Verlet, L. 603, 603∗ Villars, Felix 172, 172∗ , 175, 179∗ Vogt, Erich 496, 496∗ , 967 Waddington, Betty 273, 917 Wade 371 Waerden, Bartel Leendert van der 67 Walker, Darcy 201, 489 Walker, Mark 761, 761∗ , 907, 913, 926∗ , 962, 962∗ , 971, 983 Walker (Miss) 55 Waller, Ivar 70, 478 Walton, Ernest 353 Wanlass, S. Dean 293∗ Ward, John, C. 316 Wataghin, Gleb 428, 428∗ , 429, 434 Weiner, Charles 771, 842, 877 Weisskopf, Victor, F. 70, 70∗ , 75, 81, 81∗ , 96–97, 109∗ , 114, 135, 135∗ , 168, 179, 182, 218, 444, 444∗ , 482, 525, 597, 621–22, 640, 679, 830, 859, 877, 923, 938, 968, 976 Weitzner, H. 710, 710∗ Weizs¨ acker, C.-F. 144, 146, 912, 969, 971, 982, 984 Wentzel, Gregor 48, 71, 71∗ , 167, 277, 293, 441, 544–45, 569 Wheeler, J.A. 72, 72∗ , 110∗ , 135∗ , 206, 230, 230∗ , 231, 299, 797, 870, 876–79 Whittaker, Edmund Taylor 376, 376∗ , 377, 582 Wick, Gian Carlo 8∗ , 16, 16∗ , 17, 20, 25, 86∗ , 337–38, 338∗ , 466, 466∗ 67∗ , 490, 503–504, 587 Wiggs, Richard 841, 898, 900 Wigner, Eugene, P. 67, 67∗ , 69, 69∗ , 75, 81, 81∗ , 105–106, 106∗ , 125, 218, 284, 293, 326, 496, 587, 693∗ , 709, 725, 858, 1053

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Wilkinson, Denys ix, 225, 228, 439, 850 Williams, E.J. 236, 244, 253–54 Wilson, A.H. 745–46, 746∗ , 747, 776 Wilson, Bob 26, 97∗ , 153, 201, 287, 287∗ , 367, 367∗ , 409, 457 Wilson, R.N. 489, 489∗ Womersley, John, R. 216, 216∗ , 217 Wong, Chun Wa 710, 710∗ , 712, 712∗ Woodward, John 286–87, 287∗ , 296, 296∗ , 309, 316–17, 337–38, 360, 366, 468, 495 Wooster, Nora 273∗ Wooster, Peter 273, 273∗ Wouthuysen, S.A. 200, 200∗ Writhman, Arthur S. 284, 316, 737, 737∗ Wroe, D. 207–208, 208∗ Yahuda, Abraham Shalom 839, 839∗ Yamada, E. 187 Yamanouch, C. 876 Yang, C.N. 239, 258, 284, 308, 308∗ , 387, 387∗ , 455, 458, 511, 511∗ , 674 Yang, Frank 284∗ , 636 Yeshida, S. 472, 496, 498 Yoccoz, Jean 613∗ , 616, 626, 656∗ Yukawa, Hideki 131, 152, 166∗ , 187, 260, 294, 399, 621 Zachariasen, F. 611, 611∗ , 615 Zienau, S. 579, 579∗ Ziman, John Michael 502, 502∗ , 709, 709∗ Zilsel, P.R. 366, 366∗ Zuckerman, Solly 815, 824

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With William Penney, Otto Frisch, and John Cockroft (1946).

Mark Oliphant, John Cockroft and Robert Oppenheimer at the Nuclear Physics Conference in Birmingham (1948).

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With Gaby, Genia, Jo, Kitty and Ronnie (1949).

With Annie Krebs, Hermann Krebs, Genia and Ilse Krebs.

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Kyoto, 1953.

With John H. Van Vleck, Ilya Mikhailovich Frank, Nevill F. Mott and John C. Slater.

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With Shin-Ichiro Tomonaga and Alexander Proca.

Jo, Kitty, Gaby and Nina Byers.

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Kitty, Nina Byers, Jean Lascoux, Genia, K.S. Singwi, Gaby, Jo (1955).

The extended Peierls family with among others: Gerry and Lilo Field, Genia, Gerry and Traudl Brown, Paul and Margit Matthews.

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Jo, Ronnie, Kitty and Gaby, photo taken at the time of Genia and Rudi’s Silver Wedding Anniversary.

Moscow, 1956.

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With Landau, Moscow 1956.

With Aage Bohr, Lloyd Elliott, Erich Vogt and Harry Gove.

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With Kitty, Jo, Genia, Nina Kannegiser, Gaby and Charlie Gross (Cambridge, 1961).

Outside Buckingham Palace with Jo, Kitty, and Genia.

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With C.N. Yang.

Pugwash Conference with M.D. Millionshikov and Jo Rotblat.

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With E.L. Andronikashvili.

With G. Wentzel.

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In New Dehli.

Birmingham, outside the Arts building.

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Powell Memorial Meeting, with Viki Weisskopf and D.H. Perkins.

With Gerry Brown and Viki Weisskopf.

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At Boar’s Hill House.

With Jo, Genia and Hans Bethe.

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With Genia.

With Genia at Pokljuka, Slovenia.

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Oxford Symposium.

With Pope John Paul II.

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Coimbra: Award of honorary doctorate.

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