6 Letter from Dirac to Manci, 20 February 1937 (DDOCS).
7 Letter to Dirac from Manci, 16 February 1937 (DDOCS).
8 Letters to Dirac from Manci, 25 January and 16 February 1937 (DDOCS).
9 Letter to Dirac from Betty, 29 January 1937 (DDOCS).
10 Letter to Dirac from Manci, 29 January 1937 (DDOCS).
11 One reading of Manci’s cryptic comments in her letter to Dirac of 16 February 1937 is that his parents were sexually incompatible (DDOCS): ‘Betty told me today the reason why probably your parents did not like each other. Your father could not help it, don’t blame him dear, nor do [sic] your mother.’
12 Letter to Dirac from Manci, 18 February 1937 (DDOCS).
13 Letter to Dirac from Manci, 28 January 1937 (DDOCS). Dirac’s ‘unexpected’ marriage was noted in the Cambridge Daily News, 7 January 1937.
14 Letter from Rutherford to Kapitza, 20 January 1937, in Boag et al. (1990: 300).
15 Letter from Dirac to Kapitza, 29 January 1937, Dirac Papers 2/3/5 (FSU).
16 Letter to Manci from Anna Kapitza, 17 February 1937, Dirac Papers, 2/3/5 (FSU).
17 Dirac’s use of ‘Wigner’s sister’ became famous in his community. Both Dirac’s daughters confirm that he used this term of introduction.
18 Manci often used this expression. See, for example, Dirac (1987: 7).
19 Interview with Monica Dirac, 7 February 2003.
20 Salaman and Salaman (1996: 66–70); see p. 67.
21 Daniel (1986: 95–6).
22 Letter from Dirac to Manci, 19 February 1937 (DDOCS).
23 Dirac’s wish to have children appears obvious from his delighted reaction to the news of Manci’s later pregnancies.
24 Gamow (1967: 767).
25 Christianson (1995: 257).
26 Dingle (1937a).
27 Untitled supplement to Nature, Vol. 139, 12 June 1937, pp. 1001–2; p. 1001.
28 Dingle (1937b).
29 Report on Theoretical Physics to the Institute for Advanced Study, 23 October 1937, in the IAS Archives General Series, 52, ‘Physics’.
30 Estate of Charles Dirac, prepared by Gwynn, Onslow & Soars, who prepared the document on 7 October 1936 (DDOCS).
31 Letter to Dirac from his mother, 21 January 1937, Dirac Papers, 1/4/7 (FSU). See also the letter of 1 February 1937 in the same file of the archive.
32 Interview with Kurt Hofer, 21 February 2004.
33 Kojevnikov (2004: 119).
34 Postcard from Manci Dirac to the Veblens, 17 June 1937, LC Veblen archive.
35 Telegram from Kapitza to Dirac, 4 June 1937, KV 2/777, UKNATARCHI.
36 Service (2003: 223).
37 Fitzpatrick (1999: 194).
38 Letter from Kapitza to Rutherford, 13 September 1937, in Boag et al. (1990: 305–6).
39 Kojevnikov (2004: 116).
40 Before Landau fled Kharkov, he had worked at the Ukrainian Physico-technical Institute. He was arrested on 28 April 1938 in Moscow, and Kapitza wrote to Stalin seeking his release. His letter is quoted by David Holloway (1994: 43).
41 Letter from Dirac to Kapitza, 27 October 1937, Dirac Papers, 2/3/6 (FSU).
42 Letter to Dirac from Kapitza, 7 November 1937, Dirac Papers, 2/3/6 (FSU).
43 Letter from Fowler to Dirac, 25 January 1939, Dirac Papers, 2/3/8 (FSU).
44 This was one of Dirac’s favourite observations. See R. Dalitz, Nature, 19 Vol. 278 (April) 1979.
45 Hoyle (1992: 186).
46 Hoyle (1994: 131).
47 Hoyle (1994: 133).
48 Letter from Dirac to Bohr, 5 December 1938, NBA.
49 At least two of Flo’s poems were published in newspapers: ‘Cambridge’ appeared in the Observer on Saturday, 23 July 1938, and ‘Brandon Hill’ was published in the local Western Daily Press on Saturday, 12 March 1938.
50 On 2 February 1938, Princeton University sent Dirac a letter offering him tenure with an annual salary of $12,000, beginning 1 October 1938, Dirac Papers, 2/3/7 (FSU).
51 Letter from Anna Kapitza to Manci Dirac, 9 March 1938, Dirac Papers, 1/8/18 (FSU).
52 Nature, 21 May 1938, No. 3577, p. 929. Schrödinger’s well-publicised letter was published in Graz Tagepost, 30 March 1938. See Moore (1989: 337–8).
53 Letters from Dirac to Manci in August 1938 (DDOCS). Wigner married Amelia Frank on 23 December 1936 in Madison, and she died on 16 August 1937. See ‘The Einhorn Family’, compiled by Margaret Upton (private communication).
54 Bell wrote to Dirac on 15 March 1938: ‘I had already and for a year or two reached the conclusion the Soviet trials were probably of the frame-up type. After all, that is not new. The Tom Mooney case in California in 1918 was such and the victim has been in prison ever since […] also the Sacco & Vanzetti case. Moreover, we seem to do it ourselves to a great extent in India. However, the “confession technique” is peculiarly Russian, on its present scale at least.’ Letter to Dirac from J. H. Bell, Dirac Papers, 2/3/7 (FSU).
55 Moore (1989: 347); letter from Schrödinger to Dirac, 27 November 1938, Dirac Papers, 2/3/7 (FSU).
56 Dirac gives these reasons in his obituary of Schrödinger in Nature, 4 February 1961, 189, p. 355–6.
57 Letter from Dirac to Kapitza, 22 March 1938, Dirac Papers, 2/3/7 (FSU).
58 Howarth (1978: 234–5).
59 The Times, 6 October 1938.
60 ‘Eddington Predicts Science Will Free Vast Energy from Atom’, New York Times, 24 June 1930. He was speaking at the World Power Conference. He suggested that such energy could be released by arranging for particles to annihilate or to make hydrogen nuclei fuse to form a helium nucleus.
61 Rhodes (1986: 28).
62 Weart and Weiss Szilard (1978: 53).
63 Weart and Weiss Szilard (1978: Chapter II).
64 Weart and Weiss Szilard (1978: 71–2).
65 The event took place in the Society’s house, 24 George Street, beginning at 4.30 p.m. Max Born was present.
66 Mill (1892: Book 2, Chapter 12).
67 This quote is from the text of the lecture, Proceedings of the Royal Society (Edinburgh), 59 (1938–9: 122–9); p. 123.
68 Granta, 48 (1): 100, 19 April 1939.
Twenty-two
As I write, highly civilized human beings are flying overhead, trying to kill me. They do not feel any enmity against me as an individual, nor I against them. They are only ‘doing their duty’ […].
GEORGE ORWELL, The Lion and the Unicorn, 1941
Advances in aviation technology had made the aerial bombing of Britain inevitable, though some people in Cambridge could not believe the Germans would ever bomb a town of such beauty.1 Nuclear weapons were being discussed, too, in newspapers and popular magazines, but most of the public and national leaders seem not to have noticed. Dirac, aware of the potential of nuclear fission, had an inkling of what might be in store: like many scientists, he would soon have to decide whether to drop his research and participate in the largest military programme the world had ever seen.
Soon the conflict would disperse Dirac’s extended family across two continents. He waited every day for news of Betty in the Netherlands. Manci was worried about her Jewish relatives, especially her parents and sister, who had left Budapest and settled in New York State, assisted by Wigner and his new wife Mary. Although she strongly supported the war, Manci knew the pain of being suspected as an alien and smarted at the subtle signs of disapproval from strangers when she revealed her thick accent, which many took to be German. In her adopted country, she felt like a ‘bloody foreigner’.2
When the Diracs ventured into the centre of Cambridge on the freezing nights of January 1940, they saw that much of the town looked just as it did in Newton’s day. Under the moonlight, the architecture of the city – the College buildings, King’s Parade, Senate House – had never looked more sublime.3 The mood of the town was, however, becoming more apprehensive: thousands were bracing themselves for an attack, ready to flee to the new bomb shelters. Dirac and his family stayed indoors,
carefully observing the ‘blackout’, preventing every shard of light from escaping into the night by covering their windows with black paper. By six o’clock each night, the town was as quiet as a village on a Sunday morning; by ten, it was almost deserted.4 The church bells had been silenced, the street-lamps switched off.
At the beginning of the war, the population of the town had swelled by almost a tenth, to about eighty thousand. At the beginning of September 1939, trainloads of children had arrived from London and other towns that were expected to be the targets of enemy bombers. The evacuees, many with their home addresses written on luggage labels tied around their necks, were billeted with local families, many of which received them less warmly than sentiment now recalls.5 The Diracs did not take in any of these children, though in the coming months they saw them virtually overrun the town.6
Everyone, including the dons, carried around a foul-smelling rubber gas mask. For the time being at least, academics in their gowns had lost their special status and were no more important than the thousands of volunteers and part-time workers who were preparing for war. The texture of day-to-day conversations changed: people talked more loudly, endlessly repeating catchphrases such as ‘I’m doing my bit’ and ‘Don’t you know there’s a war on?’ All over the town, posters warned that ‘Careless talk costs lives’, words that looked comically alarmist, as there were no signs of an imminent conflict: by March 1940, nothing much had happened since the collapse of Poland, and the restless public called it the Phoney War or, sometimes, the Bore War. Most of the evacuated children drifted home.
The university ticked over, though there were fewer dons as many of them had left to take up posts in government, the armed forces and war research establishments.7 There were fewer students, too, but a skeleton programme of teaching continued, and Dirac gave his lectures on quantum mechanics as usual. A regular visitor to the college, he saw how much its atmosphere had changed: it now accommodated not only its staff and students but also uniformed members of the Army, Navy and Royal Air Force, who worked in the new buildings completed shortly after the outbreak of war. The college was one of the national centres of the Air Force, and hundreds of its cadets were trained there, mixing uneasily with the undergraduates, who had different catering facilities. The menus for college members were now much more modest: at High Table, about all the Fellows could expect was a ladleful of mutton stew and vegetables grown on college land. Gardeners had dug up the lawns to grow onions and potatoes.
At home, the Diracs lived like most others in Britain. They queued for their ration books and food coupons and took pots and pans to local collecting points to be melted down and turned into weapons.8 Dirac had chopped down a tree in the garden for firewood, cultivated potatoes and carrots in a nearby allotment, and grew giant mushrooms in his cellar. But Manci, well into her pregnancy, wanted support. She would not dispense with her servants, and she fretted at the thought of losing even one of them. Dirac’s mother in Bristol was counting the days to the birth of her second grandchild, hoping that the child would be a boy and that his parents would name him Paul.9 But she was to be disappointed: the child was a girl, Mary, born on 9 February 1940, at London’s Great Ormond Street Hospital.10 As Manci wrote in her notebook, Mary was a ‘daddy’s girl’, as she would remain. Dirac was a doting father, in his reserved way, dandling her on his knees, trying to entice her to play with a new doll sent by her godmother, Schrödinger’s wife Anny.
Desperate to see her first granddaughter, Flo made a flying visit to see the baby and her mother. Flo’s manner with the baby did not impress Manci, who complained to Dirac the next day:
It is awful of me to write about her, you never criticize my parents. But I never felt as much that she has neither heart nor feelings … She has no notion of how to handle a tiny thing as a baby but she picked her up. It was quite terrible to me.11
Dirac may have sensed that this would not be the last clash between the two women closest to him, each jealous of the other’s place in his affections. But their disputes appear not to have spoiled his first few months of paternity. He now had the domesticity he craved, but it was soon disrupted by an urgent request to do something he had hoped to avoid: to join the scientists’ war effort.
Rudolf Peierls was now in Birmingham, a professor of physics by day and volunteer fireman by night, equipped with a uniform, a helmet and an axe. Peierls had settled in England after fleeing Nazi Germany in 1933 with his Russian wife Genia, a former member of the Jazz Band of Soviet physicists. Like most scientists who had lived under Hitler, Peierls wanted him crushed, but the British authorities were slow to accept his offers of assistance: in early February 1940, Peierls and his wife were officially classified as ‘enemy aliens’.12 The couple’s naturalisation papers came through later that month so he was eligible to work on secret projects, though the authorities still looked at him with suspicion and denied his request to work on the new radar technology.
In early February 1940, when Dirac was cradling his newborn daughter in his arms, Peierls was thinking about nuclear weapons. Like most scientists who were following the debate, he believed that such a weapon would not be possible after all. Niels Bohr and John Wheeler had apparently provided the clinching argument by proving that the fission of uranium by slow neutrons was due entirely to the rare isotope of uranium 235U, containing a total of 235 nuclear particles, not to the much more common uranium isotope 238U, which contains 238 particles. A little less than one part in a hundred of a typical sample of natural uranium is 235U, and the rest is almost entirely 238U. It followed that if a nuclear bomb were made using naturally occurring uranium, very few nuclei would undergo fission, so any chain reaction that started would soon fizzle out. But a loophole was spotted by one of Peierls’ Birmingham colleagues, Otto Frisch, the scientist who had given fission its name and been the first to explain it, in collaboration with his aunt, Lise Meitner. Frisch was one of an almost unbroken string of bachelors who lodged with Rudolf and Genia Peierls and became part of the household, helping with the washing up and keeping their children amused during the blackouts.
The crucial question Frisch asked was: ‘Suppose someone gave you a quantity of the pure 235 isotope of uranium – what would happen?’ When Frisch and Peierls did the calculations, they found the amount of 235U needed was about a pound, about the volume of a golf ball. Although it would be difficult and expensive to produce much of this rare isotope, the resources required, compared with the costs of running the war, would be chickenfeed. Frisch later recalled that when he and Peierls tumbled that the purification process could, in principle, be completed in weeks, ‘we stared at each other and realized that an atomic bomb might after all be possible’.13 Even more terrifying was the thought that the Germans might already have done their calculation and Hitler might be the first to have the bomb.
Frisch and Peierls secretly typed up two memos on the properties of a ‘Super-Bomb’ and the implications of building one, setting out their conclusions in a total of six foolscap pages, which they sent to the British Government, keeping just one carbon copy.14 The authorities were grateful but asked them to understand that, as Peierls later recalled, ‘henceforth the work would be continued by others; as actual or former “enemy aliens”, we would not be told any more about it’.15 If the Government wanted scientists to build a nuclear weapon, they would need to find a way to distil pure 235U from mined uranium ore, which contains the mixture of 238U and 235U. Several groups were set up in the UK to investigate ways of separating the uranium isotopes, including ones at the universities of Liverpool and Oxford. Scientists in these groups knew that Dirac had invented one method of doing it: the centrifugal jet stream method of isotope separation, which he had investigated in the spring of 1934 but abandoned after the Soviets had detained his collaborator, Kapitza. By the late autumn of 1940, Dirac had heard that his long-discarded experiment might, after all, have important applications in developing material to make a nuclear bomb.16 Soon he would be under pressu
re to resume his studies of the technique.
In the United States, Leó Szilárd – a close friend of Manci’s brother Eugene Wigner – was trying frantically to persuade the Government to develop a nuclear bomb before the Germans. He was working at Columbia University in New York with his fellow refugee Enrico Fermi, the experimentalist best qualified to build a nuclear weapon if it were feasible. Progress was slow and funds were short, partly because few government officials took Szilárd’s hectoring seriously. In the summer of 1939, Wigner, Szilárd and Teller persuaded Einstein to write to President Roosevelt, drawing his attention to the possibility of nuclear weapons and the danger that the Germans might produce one first.17 After a long delay, Roosevelt invited Einstein to join a committee of government advisers but he brusquely declined and sat out the war at the Institute for Advanced Study in Princeton, where word spread that the Nazis were indeed working on a bomb. In the spring of 1940, Dirac’s friends Oswald Veblen and John von Neumann wrote to the director Frank Aydelotte, urgently seeking his assistance to fund investigations into the chain reaction. In their letter, they mentioned a recent conversation with the Dutch physical chemist Peter Debye, who had led one of Berlin’s largest research institutes until the German authorities sent him abroad in order to free his laboratories for secret war work.
[H]e made no secret of the fact that this work is essentially a study of the fission of uranium. This is an explosive nuclear process which is theoretically capable of generating 10,000 to 20,000 times more energy than the same weight of any known fuel or explosive […] It is clear that the Nazi authorities hope to produce either a terrible explosive or a very compact and efficient source of power. We gather from Debye’s remarks that they have brought together in this Institute the best German nuclear and theoretical physicists, including Heisenberg, for this research – this in spite of the fact that nuclear and theoretical physics in general and Heisenberg in particular were under a cloud, nuclear physics being considered to be ‘Jewish physics’ and Heisenberg a ‘White Jew’.
The Strangest Man Page 44