The Strangest Man

by Graham Farmelo

  Everyone loved Manci: she was a real character, always full of life, always ready to chat. Dirac was more communicative than he had been in Cambridge. He was not terribly difficult to talk to. If you asked him a serious question, he would ponder it and give a reply that was always short and to-the-point.46

  However, he still had no time for strangers who tried to lure him into small talk. Louise Morse, wife of one of the institute’s mathematicians, remembers that when she asked Dirac how he was settling in at Princeton, he looked dumbfounded and leaned sharply away from her, as if she were a leak in a sewer. She remembers: ‘Without saying a word, his whole body seemed to ask “Why on earth are you talking to me?”’47

  At the Institute, Dirac worked in a modest office on the third floor of Fuld Hall, next door to Niels Bohr. One of Dirac’s main projects in his 1947–8 stay was to develop the theory of the magnetic monopole he had conceived sixteen years before. During the war, he heard reports of the particle’s discovery and, although they turned out to be false, they probably rekindled his interest in the idea.48 He produced an exquisitely crafted theory predicting how monopoles might interact with electrically charged particles, but the theory failed to make a splash. One of the few who followed it closely was Pauli, who was prompted to give one of his more polite nicknames to Dirac: ‘Monopoleon’.49

  In another project, he returned to the roots of quantum field theory. Unhappy with the new theory of electrons and photons, he looked afresh at the application of quantum theory to quantities such as electric and magnetic fields that describe physical conditions at each point in space-time. This was another piece of research that failed to strike a chord at the time but was appreciated later. The same is true of the review he wrote in 1949 about how Einstein’s special theory of relativity could be combined with Hamilton’s description of motion. Its deceptively straightforward presentation led most physicists to pay no attention to it, a mistake several of them would rue.

  Dirac still believed that modern quantum electrodynamics was wrong because it was based on a classical theory of electrons that was fundamentally flawed. So, in 1951, he produced a new theory, quite different from the one he had developed thirteen years before. This time, his classical theory described a continuous stream of electricity, flowing like a liquid – individual electrons emerged only when the classical theory was quantised.50 The theory was the dampest of squibs. No one disputed Dirac’s technical ingenuity but it seemed that he had lost his intuition for productive lines of research. He demonstrated this yet again when, as a by-product of his new theory of electrons, he reintroduced a concept that most scientists believed Einstein had slain: the ether.

  Dirac’s ether was quite different from the nineteenth-century version: in his view, all velocities of the ether are equally likely at every point in space-time.51 Because this ether does not have a definite velocity with respect to other matter, it does not contradict Einstein’s theory of relativity. Dirac’s imagination slipped through this loophole and reinvented the ether as a background quantum agitation in the vacuum; later, he went further and speculated that it might be ‘a very light and tenuous form of matter’.52 The press were more interested than scientists in the idea, which appeared to go nowhere: the logic was impeccable but it seemed to have no connection with nature.53

  By the time Dirac reached his fiftieth birthday, he seemed to be following the path Einstein had taken, towards isolation from mainstream physicists. In Princeton, Einstein was a lonely figure, uninterested in the latest research headlines and absorbed by his quixotic project to find a unified field theory without introducing quantum mechanics from the outset. He was still active in politics and annoyed J. Edgar Hoover, Director of the Federal Bureau of Investigation (FBI), by supporting several leftist and anti-racist organisations. In 1950, Hoover ordered a secret campaign to ‘get Einstein’, aiming to have him deported.54 Unaware that he was being watched, Einstein strolled to his office in the institute from his nearby home on Mercer Street, his briefcase under his arm, pausing only to pick up and sniff discarded cigarette butts. On his favourite route, he walked down the straight section of Battle Road, towering sycamores lining each side, their overarching branches entangled like the swords of a guard of honour.55

  At the Institute for Advanced Study, he was free to work and ignore the day-to-day trivia of politics. But this tranquillity was about to be disturbed by the FBI agents and journalists who were sniffing around the past of the institute’s director. Oppenheimer’s former Communist sympathies – and Dirac’s – were about to return to haunt them.

  Notes - Chapter twenty-four

  1 Osgood (1951: 149, 208–11).

  2 Interview with Feynman by Charles Weiner, 5 March 1966, 27 March 1966, AIP. Interview with Lew Kowarski by Charles Weiner, 3 May 1970, AIP.

  3 The typed manuscript of Dirac’s talk is in the Mudd Library, PRINCETON.

  4 In Feynman’s theory, the probability that a quantum such as an electron will make a transition from one point in space-time to another can be calculated from a mathematical expression related to the action involved in moving between the two points, summed over all possible routes between them.

  5 Interview by Charles Weiner of Richard Feynman, 27 June 1966 (CALTECH). See also Feynman’s Nobel Lecture and Gleick (1992: 226) and its references.

  6 Interview with Freeman Dyson, 27 June 2005. Dyson noted that Feynman made the point repeatedly.

  7 Quoted by Oppenheimer in Smith and Weiner (1980: 269). Wigner was one of the examiners of Feynman’s Ph. D. thesis; the other was Wheeler. The oral examination was held on 3 June 1942, and the examiners’ report is held in the Mudd Library, PRINCETON.

  8 See Kevles (1971: Chapter 12) and Schweber (1994: Section 3).

  9 Schweber (1994: Chapter 4); Pais (1986: 450–1); Dyson (2005).

  10 Lamb (1983: 326). ‘Radar Waves Find New Force in Atom’, New York Times, 21 September 1947.

  11 Ito (1995: 171–82).

  12 Feynman (1985: 8).

  13 Dyson (1992: 306). Interview with Dyson, 27 June 2005. Dyson’s description of himself as a ‘big shot with a vengeance’ is in Schweber (1994: 550).

  14 Dyson (2005: 48).

  15 Dirac took no pleasure in abstract art or in Schönberg’s music and found neither beautiful.

  16 ‘The Engineer and the Physicist’, 2 January 1980, Dirac Papers, 2/9/34 (FSU).

  17 Dirac Papers, 2/29/34 (FSU).

  18 Dirac Papers, 2/29/34 (FSU).

  19 Dyson (2006: 216).

  20 Letter from Manci to Wigner, 20 February 1949, PRINCETON.

  21 Interview with Richard Eden, 14 May 2003.

  22 M. Dirac (1987: 6).

  23 M. Dirac (2003: 41).

  24 I am grateful to the Salamans’ daughter Nina Wedderburn for supplying me with biographical information on her parents. Fen (1976: 375).

  25 Gamow (1966: 122); Salaman and Salaman (1986: 69).

  26 Interview with Monica Dirac, 7 February 2003.

  27 Quoted in Hennesey (2006: 5).

  28 It took centuries for women students to win equality with males at Cambridge University. The first women’s colleges in Cambridge, Girton and Newnham Colleges, were founded in 1869 and 1871 respectively. From 1881 women were allowed to sit tripos exams but they did not receive any formal qualifications from the university for passing them. From 1882, women’s results were published with the men’s, but on separate lists. In 1921, a report proposing full admission for women was defeated. Statutes allowing the admission of women to full membership of the university finally received Royal Assent in May 1948, and the first woman to graduate at Cambridge was the Queen Mother in the following October. Under this legislation, women students at Cambridge first graduated in January 1949.

  29 Reasons for Heisenberg’s post-war depression are suggested by Cassidy (1992: 528).

  30 R. Eden, unpublished memoirs, May 2003, p. 7a.

  31 Dirac first met Heisenberg after the war in 1958. ‘Hero’ quote from in
terview with Antonio Zichichi, 2 October 2005.

  32 Interview with Monica Dirac, 7 February 2003.

  33 Greenspan (2005: 253, 263–4). Dirac supported Heisenberg’s nomination, having remarked earlier that his election to a foreign membership of the Royal Society should take precedence over that of Pauli. Cockcroft writes to Dirac in his 15 February letter, ‘I agree that he [Heisenberg] is more eminent than Pauli,’ Dirac Papers, 2/4/7 (FSU).

  34 Letter to Dirac from Douglas Hartree, 22 December 1947, Dirac Papers, 2/4/2 (FSU).

  35 Letter to Dirac from Schrödinger, 18 May 1949, Dirac Papers, 2/4/4 (FSU).

  36 Soon after Blackett won the prize in 1947, Dirac sent to him ‘heartiest congratulations’, remarking, ‘You ought to have had it long ago’: letter from Dirac to Blackett, 7 November 1948, Blackett archive, ROYSOC. Yet Dirac had not nominated him.

  37 Dirac nominated Kapitza twice before 1953, on 16 January 1946 and 25 January 1950. It is clear from Dirac’s records that he later nominated Kapitza several times (RSAS).

  38 Letter from Dirac to Kapitza, 4 November 1945, Dirac Papers, 2/4/12 (FSU); See also letter from Kapitza to Stalin, 13 October 1944, reproduced in Boag et al. (1990: 361–3).

  39 Boag et al. (1990: 378).

  40 Letter from Kapitza to Stalin, 10 March 1945, cited in Kojevnikov, A. (1991) Historical Studies in the Physical Sciences, 22, 1, pp. 131–64.

  41 Letters from Kapitza to Stalin, 3 October 1945 and 25 November 1945, reprinted in Boag et al. (1990: 368–70, 372–8).

  42 Letter to Dirac from Manci, 12 July 1949 (DDOCS).

  43 Tallahassee Democrat, 29 November 1970.

  44 Bird and Sherwin (2005: 332).

  45 Sources of anecdotes: ‘young daughters scurrying’, interview with Freeman Dyson, 27 June 2005; ‘welcoming Einstein for Sunday tea’, interview with Monica Dirac, 7 February 2003, interview with Mary Dirac, 21 February 2003; the ‘early evening drinks parties’, one of the social rituals at the institute during Oppenheimer’s tenure as Director; ‘amateur lumberjacks’, interview with Morton White, 24 July 2004.

  46 Interview with Freeman Dyson, 27 June 2005. E-mail from Dyson, 23 October 2006.

  47 Interview with Louise Morse, 19 July 2006.

  48 Dirac received several importunate letters from the maverick Austro-Hungarian experimenter Felix Ehrenhaft, who asserted that he had evidence for the existence of the magnetic monopole, Dirac Papers, 2/13/1 and 2/13/2 (FSU).

  49 Letter from Pauli to Hans Bethe, 8 March 1949, Hermann et al. (1979).

  50 The new theory made little impact, though it did interest scientists – including Dennis Gabor at Imperial College in London – who were studying electron beams in television sets. The correspondence between Dirac and Gabor (1951) is in the Gabor archive at Imperial College, London.

  51 Dirac (1954).

  52 Dirac (1954).

  53 ‘The Ghost of the Ether’ was published in the Manchester Guardian article on 19 January 1952; the New York Times published ‘Briton Says Space Is Full of Ether’, 4 February 1952. In Dirac’s talk to the 1971 Lindau meeting (for former Nobel Prize winners), he said that the ether appeared not to be useful to quantum mechanics, though he did not rule out that the concept might one day be useful.

  54 Jerome (2002: Chapter 12, 278–82).

  55 Interview with Einstein’s acquaintance Gillett Griffen on 20 November 2005, and with Louise Morse on 19 July 2006. The anecdote about Einstein picking up cigarette butts and sniffing them is from Kahler, A. (1985), My Years of Friendship with Albert Einstein, IX, 4, p. 7.

  Twenty-five

  The former Communist was guilty because he had in fact believed the Soviets were developing the system of the future, without human exploitation and irrational waste. Even his naiveté […] was now a source of guilt and shame.

  ARTHUR MILLER, Time Bends, 1987

  ‘What happened to daddy’s brother?’ Dirac’s daughters would ask their mother. ‘Shhh! Don’t talk about it,’ was Manci’s stock reply. Dirac spoke about Felix’s suicide only with her and even then he could not bring himself to go into any details. She knew that he still had not come to terms with it. On one occasion, when Mary and Monica persisted, Dirac took out from a drawer a small tin and prised it open to reveal some photographs of his late brother, before hurriedly snapping the tin closed and putting it back. More than twenty-five years after his brother’s death, a brief look at Felix’s face was all he could bear.1

  From Dirac’s behaviour at home, it appears that he tried to avoid what he regarded as the worst mistakes his father had made in bringing up his children. Unlike Charles, Paul encouraged his daughters to bring their friends home; he did not lean on them to study science or any other subject, nor did he offer them any career advice. They knew that there is more to life than work. The family always ate together, but the mealtimes were not what most people would regard as normal: Dirac would sit at the head of the table, eating slowly, sipping regularly from his glass of water and making it clear that he preferred to eat in silence. If one of his daughters pressed him to speak, he would point to his mouth and mutter irritably, ‘I’m eating.’ He was quite fussy about food – for example, refusing to eat pickles on the grounds that they were always bad for digestion – and would not allow Manci to use a drop of alcohol in any food, especially if it might be eaten by the girls. There was trouble in the kitchen if he sniffed or tasted in the Christmas pudding so much as a drop of brandy.

  Mary and Monica were growing into sharply contrasting personalities that, as Dirac noticed, resembled those of their parents. Mary was rather like him – quiet, trusting and literal-minded – while Monica bore a resemblance to her mother – confident, questioning and assertive. The girls did not get on well: Mary was intimidated by Monica and their mother, while Monica felt psychologically manipulated by Mary. Dirac and Manci, perhaps trying to atone for Mary’s vulnerability, treated her as their favourite and often left Monica feeling angry and resentful. Monica still recalls that her parents organised only two birthday parties for her when she was a child, while they gave one to Mary every year.

  Worried that these tensions were getting out of hand, Dirac and Manci separated their daughters using the classic English institution of boarding school, sending Mary to a strict and devoutly religious school near Cromer, in East Anglia.2 On the first weekend she was away, Dirac went on a Sunday morning cycle ride with Monica, who was hoping to begin a new stage in her relationship with her father. But this time he did not stop and chat as he had always done when Mary was with them: during the three-hour ride, he said not a word to her. She was devastated.

  No one in Cambridge counted Dirac and Manci as among the most attentive parents: as soon as the Cambridge term was over, they usually headed off on a foreign trip, leaving their children with friends. But the family did take vacations together. In the summer, Dirac would take two days to motor to their favourite destination, Cornwall, driving like a caricature vicar. During the Christmas vacation, shortly after the New Year, the family would stay for a few days in the pea soup of London fog.3 While Manci lunched with friends or went shopping, Dirac took the girls to South Kensington and walked them round the Science Museum, where they pushed the buttons on the interactive displays and filed past the relics of the Industrial Revolution. In the evening, the family headed to the West End for entertainment – Mary recalled that her father’s favourites included the musical The Pajama Game and Tchaikovsky’s ballet The Sleeping Beauty.4

  Dirac’s taste in the arts defies conventional classification, ranging from high culture to catchpenny trivia. On Saturday mornings, he raced his daughters to the front door to pick up the latest edition of their favourite comics, the Dandy and the Beano, which he would study as if they were works of literature. Mostly, he pursued his leisure interests alone, reading a Sherlock Holmes story, listening to a classical concert at full blast on the radio or sitting impassively watching the television he had first rented so that the family could watch the Queen’s
coronation. But pageantry was not for him: he preferred the new variety shows and, with millions of other male viewers, sat agog as lines of feathered young women high-kicked their way through their risqué dance routines. This was rather unbecoming, Manci thought, though she happily accompanied him on at least one discreet trip to a London production of the Folies Bergère.5

  Like Einstein, Dirac was a modernist in science but not in art. His favourite music was the classical canon of Mozart, Beethoven and Schubert, and he had no time for the experiments of contemporary composers. He also had no taste for the extremes of abstract art: the nearest he came to liking a modern artist was a fondness for the surrealism of Salvador Dalí. When he visited his sister Betty and her family in Amsterdam, two minutes’ walk from where Ehrenfest shot himself and his son, Dirac would set off in the morning with a compass – but not a map – on the six-mile walk to the Rembrandts of the Rijksmuseum.

  If Cambridge colleagues knew anything of these interests, Dirac would have been more engaging than the desiccated figure he cut in the early 1950s, rather like a prototype for Bertrand Russell’s fictional don, Professor Driuzdustades.6 Dirac no longer seemed at home in the mathematics department, though he remained a loyal Fellow of St John’s, observing all its rituals without complaint. Every Tuesday night during term, he would don his gown and eat at High Table, while Manci – not allowed to eat with him – ate at a cheap Indian restaurant with Monica on St John’s Street, Manci grumbling over her curry and samosas that the college made her feel like an impostor.7

  Sensing that the university no longer held her husband in the highest regard, she blamed him for not insisting on the respect that was due to him. But he was too self-effacing to assert himself: he had no interest in status for its own sake and was indifferent to the baubles handed down by the establishment. In the early 1930s, he declined an honorary degree from Bristol University because he believed degrees should be qualifications, not gifts, and later declined honorary degrees, replying to offers with ‘regretfully, no’.8 In 1953, he refused a knighthood, infuriating Manci, mainly because his decision deprived her of the chance to become Lady Dirac.9 He did not want people outside the university to call him Sir Paul but to address him by the name he used on the rare occasions he answered the telephone at home: ‘Mr Dirac’.