When Heisenberg and his colleagues heard about the dropping of the first nuclear bomb, soon after the news was broadcast on BBC radio, they were both perplexed and incredulous. One detainee, Otto Hahn, observed sourly: ‘If the Americans have a uranium bomb then you’re all second raters. Poor old Heisenberg.’58 Not knowing that the British were recording their conversations – it was unthinkable, Heisenberg chuckled – the Germans talked freely about their feelings. The British authorities declassified their conversations only in 1992; ever since, historians have pored over the transcripts and have come to a variety of conclusions. Some experts believe that Heisenberg never came close to an understanding of how to make a nuclear bomb; others that he could have made one but slow-pedalled his research in order to prevent the Nazis from acquiring the device. It is, however, indisputable that, during the conversations recorded at Farm Hall, neither Heisenberg nor any of his colleagues expressed any serious qualms about working for the Nazi regime.
*
By October 1945, Dirac’s life in Cambridge had almost returned to normal. A few weeks before, he had been surprised by the high number of students attending his quantum-mechanics course, several of them still in uniform. At the beginning of the first lecture he announced to the audience, ‘This is a lecture on quantum mechanics,’ evidently believing that many of the students were in the wrong room. When none of them got up to leave, he repeated his announcement, this time more loudly. But still no student left.59
A few weeks later, Betty and her son Roger – both hungry, traumatised and anxious – returned to stay in 7 Cavendish Avenue before they were reunited with Joe. Betty and her son had almost starved to death in Budapest, and she had seen that the liberation was not as joyous as many journalists reported; in her opinion, the Russian troops who liberated the city were far more brutal than the Nazi army they had ousted. In Betty’s later years, her memories of the conflict were too painful to share, though she often remarked that she regarded the survival of her family as a miracle: ‘Everything afterwards was a bonus.’60 Best of all was the birth of her daughter, Christine, just over nine months after Betty and Joe were reunited.
For the sake of tact, Betty may not have mentioned during her stay in Cambridge that she despised most of the Hungarian acquaintances she had met. Her memories of the double-dealing and inhospitable citizens of Budapest were to become a running sore in her relationship with Manci, with Dirac the embarrassed and ineffectual peacemaker.61
The university and St John’s College were settling back into their clockwork routine. Dirac preferred this way of life, free of distractions, but he had a few other duties to discharge: during the war, Crowther had persuaded him to support their French colleagues behind Nazi lines by taking on the undemanding role of the British presidency of the Anglo-French Society of Sciences, working with an informal committee whose members included Blackett, Cockcroft and Bernal.62 After the war, Crowther decided to relaunch the Society with a prestigious series of talks about scientific developments during the conflict, and he persuaded Dirac to give the first presentation, on ‘Developments in Atomic Theory’.63 The venue for the occasion – a red-letter day in French science – was Le Palais de la Découverte, a public science centre that stands like a Greek temple on a dark side road in the seventh arrondissement. Soon after sundown on Tuesday 6 December, hundreds of the city’s leading scientists made their way to Le Palais to hear Dirac talk. Two thousand people clamoured for a seat in the lecture theatre, expecting to hear the secrets of the atomic bomb.64
Minutes after Dirac began to speak, the audience realised that it was not going to hear about the latest in nuclear technology but a presentation on the state of quantum mechanics. Dozens tried to leave, but there was no escape: the exit was jammed with the overflow crowd of hundreds, listening to the lecture via loudspeakers. For the physicists who were interested, a treat was in store: they heard Dirac coin two of the best-known technical terms that he introduced: ‘fermions’, quantum particles that obey the laws that he and Fermi had set out in 1926, and ‘bosons’, the other type of quantum particles, which obey laws set out by Einstein and the Indian theoretician Satyendra Bose. For most of the audience, this was not much consolation for a wasted evening: at the end of the lecture, several of them bolted for the door.
At the dinner party afterwards, embarrassment was no doubt still in the air, but Dirac was probably oblivious to it. During six bleak years for science, in which he had contributed more to engineering than to quantum physics, he was relieved that life was returning to normal. But he was now well past thirty, the age he once believed marked the end of the theoretician’s productive career: was he now too old to have radically new ideas?
Notes - Chapter twenty-three
1 Article by Lannutti in Taylor (1987: 45).
2 Interview with Monica Dirac, 1 May 2006.
3 The committee was called MAUD, possibly short for Ministry of Aircraft production Uranium Development committee: Gowing (1964: Chapter 2).
4 Gowing (1964: 53n.).
5 Nye (2004: 73–4).
6 Nye (2004: 75–85).
7 The quote is from Churchill (1965: epilogue).
8 Letter to Dirac from F. E. Adcock, 24 May 1942, Dirac Papers, 2/3/12 (FSU).
9 Letter to Dirac from Nigel de Grey of the Foreign Office in London, 1 June 1940, Dirac Papers, 2/3/10 (FSU).
10 Copeland (2006: Chapter 14).
11 Letter from Sir Denys Wilkinson, who was one of Dyson’s fellow students in Dirac’s lecture course, 15 January 2004; also phone call, 16 January 2004. ‘I went to Dirac’s lectures in Cambridge in 1942/3. Freeman Dyson, a year junior to us but very precocious, was also in the class. He was very disruptive because he asked questions. Dirac always took a long time to answer them and on one occasion ended a class early so that he could prepare a proper response’ (interview, 15 January 2004).
12 Sir Denys Wilkinson, letter, 15 January 2004; phone call, 16 January 2004.
13 Letter from Dirac to Peierls, 11 May 1942, UKNATARCHI.
14 See Thorp and Shapin (2000: 564).
15 Letter from Wigner to the US Office of International Affairs, 1 September 1965, Wigner archive, PRINCETON.
16 Anecdotes from interview with Monica Dirac, 7 February 2003 and 1 May 2006; and with Mary Dirac, 21 February 2003.
17 Hoyle (1987: 187).
18 Dirac, M. (2003: 41).
19 Letter from Dirac to Manci, 13 July 1942 (DDOCS).
20 With his usual understatement, Dirac wrote to Manci, ‘It seems a little strange to have a prime minister at these very specialized lectures. I wonder how he can spare the time.’ Letter from Dirac to Manci, 17 July 1942, DDOCS.
21 Letter from Peierls to Dirac, 30 September 1942, AB1/631/257889.
22 Letter from Manci to Dirac to ‘Anna’, 15 October 1986, Wigner archive in PRINCETON.
23 ‘Mrs Roosevelt’s Village Hall Lunch’, Cambridge Daily News, 5 November 1942.
24 Wattenberg (1984).
25 Interview with Al Wattenburg, 30 October 1992.
26 One of their meetings probably occurred on 31 July 1943, as Dirac proposes this date for a meeting in his letter to Fuchs of 19 August 1943 (BOD). Dirac wrote another letter to Fuchs on 1 September 1943 (BOD).
27 Peierls (1985: 163–4).
28 Szasz (1992: xix and 148–51).
29 Gowing (1964: 261).
30 Peierls, ‘Address to Dirac Memorial Meeting, Cambridge’, in Taylor (1987: 37).
31 Brown (1997: 250).
32 A further seventy people in Cambridge had been injured and 1,271 homes in the town had been damaged (Barham 1977: 53).
33 ‘Cambridge Streets Light-Up at Last!’, Cambridge Daily News, 26 September 1944.
34 Joe wrote of his family’s ‘threatening situation’ to Heisenberg on 25 March 1943 and sought his assistance. Four months later, Heisenberg replied to say that he was not able to offer specific help but hoped to make contact with Joe during a later visit to Holland (this meet
ing does not seem to have taken place). Joe wrote again to Heisenberg on 2 February 1944 from Budapest urgently requesting confirmation of Betty’s Aryan descent. See Brown and Rechenberg (1987: 156).
35 Letter from Betty to Dirac, 20 July 1946, Dirac Papers, 1/7/2A (FSU).
36 Interview with Mary Dirac, 21 February 2003.
37 Gabriel later recalled that Dirac declared that there ‘was no God and no Heaven or Hell’. Letter from Gabriel Dirac to the Diracs, 18 January 1972, Dirac Papers, 1/8/14 (FSU).
38 E-mail from Mary Dirac, 17 February 2006. Monica confirms that both daughters were christened.
39 Boys Smith (1983: 44).
40 Letter from Lew Kowarski to James Chadwick, 12 April 1943 (CHURCHILL).
41 Interview with the late John Crook, 1 May 2003. Professor Crook was present when Dirac made this remark.
42 ‘Happy Crowds Celebrate VE-Day’, Cambridge Daily News, 9 May 1945.
43 Interview with Monica Dirac, 1 May 2006.
44 Pincher (1948: 111). The account of this event by Chapman Pincher implied that Dirac lied. Pincher remarks, ‘Dr PAM Dirac, one of the scientists involved, told me at the time that he was not then engaged on vital war research. But, as the British White Paper on atomic energy states, he had been helping the British atom-bomb project by theoretical investigations on chain reactions.’ Pincher had not allowed for Dirac’s literal-mindedness.
45 Brown (2005: 266).
46 Interview with Leopold Halpern, 26 February 2006. Dirac told Halpern that he was disappointed with the actions of the British Government and that he went on long solitary walks in order to cool his anger. Dirac heard of the refusal of his application for an exit visa from the Home Office official C. D. C. Robinson (letter to Dirac, 13 June 1945, Dirac Papers, 2/3/15 [FSU]). Two days later, Nevill Mott wrote to Dirac to inform him of the protests that would be made by the disappointed scientists. Mott makes it plain that he does not expect Dirac to be an active member of the protesting group (letter to Dirac from Mott, Dirac Papers, 2/3/15 [FSU]).
47 Letter from Manci Dirac to Crowther, 18 May 1945, SUSSEX.
48 Telegram from Joe Teszler to the Diracs, 1 July 1945, Dirac Papers, 1/7/5 (FSU).
49 Interview with Christine Teszler, 22 January 2004.
50 Letters from Joe Teszler to Manci, 19 July, 2 August, 23 August, 31 August, 6 September and 27 September 1945, Dirac Papers, 1/7/5 (FSU).
51 Cornwell (2003: 396).
52 The team playing at Lord’s was not an official Australian side, but was called ‘The Australian Services’ team.
53 Smith (1986: 478).
54 ‘How Cambridge Heard the Great Victory News’, Cambridge Daily News, 15 August 1945.
55 See, for example, Time, 20 August 1945, p. 35.
56 Cornwell (2003: 394–400).
57 Anon. (1993: 36).
58 Anon. (1993: 71).
59 Dalitz (1987a: 69–70). Also, interview with Dalitz, 9 April 2003.
60 Interview with Christine Teszler, 22 January 2004.
61 Letter from Betty to Dirac, 20 July 1946, Dirac Papers, 1/7/2A (FSU).
62 Brown (2005: 173).
63 Crowther (1970: 264).
64 The official report on the lecture is in the UKNATARCHI (Dirac Papers. BW83/2/257889).
Twenty-four
In America, the young are always ready to give those who are older than themselves the full benefits of their inexperience.
OSCAR WILDE, The American Invasion, 1887
In September 1946, Dirac was scratched again by the next generation’s talons. He was at a conference on ‘The Future of Nuclear Science’ at Princeton’s Graduate College, half a mile from the campus. Nestled among trees at the top of a grassy hill, the college looked like a Gothic abbey, its majestic tower dominating the surrounding countryside – a picture of English arcadia. Many visitors thought the college had been a landmark in Princeton for centuries, but it had stood there for only thirty-three years.
The conference was the first of a series of international events during the university’s bicentennial celebrations – months of ceremonial glad-handing, sybaritic dinners and colourful parades.1 The conference organiser Eugene Wigner, fresh from the Manhattan Project, had put together an impressive guest list, including Blackett, Fermi, Oppenheimer, Van Vleck and the Joliot-Curies, all ready to put the war behind them and begin the next chapter of physics.
At 9.30 a.m., at the beginning of the conference’s second day, Dirac was introduced by one of the most exciting scientific talents in America, Dick Feynman (he called himself Dick rather than Richard). Brought up in the New York suburb of Far Rockaway, he was a clean-cut twenty-eight-year-old, brimming over with ideas and sophomoric humour but still grieving after the death of his first wife fourteen months before, from tuberculosis. He was afraid he was already burnt out, he later admitted. When he introduced Dirac, Feynman seemed unburdened by self-doubt but felt ‘like a ward-heeler [machine politician] in the 53rd district introducing the President of the United States’.2 Feynman was not expecting to be impressed: a few weeks before, he had been disappointed by his hero’s handwritten script, which Feynman thought was backward looking, stale and ‘unimportant’.
Dirac discussed how elementary particles could be described using his favourite mathematical device, the Hamiltonian: for Dirac, this was the only way to proceed, and he did not spare his audience – many of them non-specialists – the technical details. As Feynman feared, the talk fell flat. Worse, Dirac was bereft of new ideas.3 After the applause, Feynman tried to give lay members of the audience a sense of what Dirac was saying, not hiding his disappointment and remarking that Dirac was ‘on the wrong track’. He cracked even more than his usual quota of jokes, prompting Bohr to stand up and ask Feynman to take the proceedings more seriously.
A few hours later, Feynman looked out of the window of the lecture room and saw that Dirac had excused himself from the conference programme and was ‘paying no attention to anybody’, lying on a patch of grass, leaning on an elbow, gazing lackadaisically at the early-autumn sky. Here was Feynman’s opportunity to talk informally with Dirac about a matter that had intrigued him for the past four years. When Feynman was a graduate student, he had studied Dirac’s ‘little paper’ on how the classical least-action principle can be applied in quantum mechanics, demonstrating that it could be used to build another version of quantum mechanics, different from Heisenberg’s and Schrödinger’s but giving the same results.4 In his paper, Dirac had cryptically remarked that a critical quantum quantity is ‘analogous’ to its classical counterpart, but Feynman believed that the correct phrase was ‘proportional to’ (that is, if the quantum quantity changes, the classical one always changes proportionately). Here, at last, was Feynman’s chance to find out what Dirac meant.
Feynman described his problem to Dirac and came to the crunch:
FEYNMAN: Did you know that they were proportional?
DIRAC: Are they?
FEYNMAN: Yes they are.
DIRAC: That’s interesting.5
Dirac then got up and walked away. Feynman subsequently became famous for his new version of quantum mechanics but thought the credit was undeserved. The more closely he looked at the ‘little paper’, the more he realised that he had done nothing new. He later said, repeatedly, ‘I don’t know what all the fuss is about – Dirac did it all before me.’6
Feynman knew he had much to do if he was to prove himself a great physicist. When the conference photograph was taken, he appeared to hint at the extent of his ambition by standing behind Dirac, just as Dirac had done in the 1927 Solvay Conference photograph, when he stood directly behind Einstein. Within a few years, Feynman’s power as an analyst and intuitionist made him, in the eyes of many, the finest theoretician in America. Wigner agreed with that judgement: ‘Feynman is a second Dirac, only this time human.’7
The next five years saw the emergence of a new theory of electrons and photons, in some ways the climax of fifty years of theoretical
physics. This was largely an American success, the accomplishment of hungry young scientists who had suspended their academic careers during the war to work on nuclear weapons, radar and other projects.8 Physicists had worked in lavishly funded, goal-driven international teams, having set aside the elitist traditions of European academia and collaborated in the less formal, can-do social environment of the United States. Now it was time for payback.
On Capitol Hill, the physicists argued that they deserved the support of the government’s tax dollars to pursue curiosity-driven research. It is a fair bet Willy Loman and the other struggling breadwinners of middle America would have baulked at the physicists’ case if they had been aware of it, but the politicians were persuaded and gave unheard-of levels of federal support for basic physics research and training. The US Government and private institutions funded theoretical physics. At much greater expense, Uncle Sam equipped experimenters with machines that could probe the structure of matter even more finely, using beams of subatomic particles accelerated to within a whisker of the speed of light in a vacuum. The pursuit of ‘high-energy physics’ had flourished in Europe in similar ways, though there was no doubt that in this branch of science – and many others – America led the world.
The first conference of leading subatomic physicists to take place in the USA after the war, at the beginning of June 1947, set their subject’s agenda for the next thirty years.9 Twenty-three carefully selected scientists – all of them men – gathered at an inn on Shelter Island, a small and secluded spot near the eastern tip of Long Island, to review their subject. The gathering could scarcely have had a more spectacular opening: in the first two presentations, experimenters announced that the Dirac equation made predictions that disagreed with new experimental results. The first speaker, Willis Lamb, had the air of a cowboy who had strayed into a physics laboratory. But his appearance was deceptive: he was a deep thinker, an accomplished experimentalist who could hold his own with the best theorists. He got the meeting off to a flying start by announcing a serious flaw in Dirac’s theory: two energy levels of atomic hydrogen that, according to the theory, should have the same energy turn out to be slightly different. Photons emitted by hydrogen atoms when they jump between the two energy levels had been detected by Lamb and his student Robert Retherford, at the Columbia Radiation Laboratory. In a masterly experiment using microwave technology developed during the war, they studied these photons and showed that each of them has only about a millionth of the energy of a quantum of visible light.
The Strangest Man Page 48