26 Letter to Dirac from his mother, 20 July 1931, Dirac Papers, 2/2/4 (FSU).
27 Postcard from Flo to Betty Dirac, 1 August 1931: ‘Having a sea voyage with Paul. The weather is fine and it is lovely. Back 6.35am Sunday. Hope you are both looking after each other’ (DDOCS).
28 The area was officially named the Glacier National Park only in the following year.
29 Robertson (1985).
30 The furniture budget was $26,000; the budget for rugs was nearly $8,000. Batterson (2007: 612). Fine Hall is now called Jones Hall.
31 Jacobson, N., ‘Recollections of Princeton’ in Robertson (1985).
32 Letter from Pauli to Peierls, 29 September 1931, in Hermann et al. (1979).
33 Enz (2002: 224–5).
34 New York Times, 17 June 1931.
35 Pais (1986: 313–17).
36 Brown (1978).
37 Enz (2002: 211).
38 ‘Lectures on Quantum Mechanics’, Princeton University, October 1931, Dirac Papers, 2/26/15 (FSU). These notes were transcribed by Banesh Hoffman and checked by Dirac.
39 ‘Dr Millikan Gets Medal’, New York Times, 5 September 1928.
40 Kevles (1971: 180); Galison (1987: Chapter 3, pp. 86–7).
41 Interview with Robert Oppenheimer, AHQP, 18 November 1963, p. 16.
42 De Maria and Russo (1985: 247, 251–6).
43 Letter from Anderson to Millikan, 3 November 1931, quoted in De Maria and Russo (1985: 243). In this letter, Anderson describes data taken over the previous ‘very few days’.
44 Interview with Carl Anderson, 11 January 1979, p. 34, available at http://oralhistories. library.caltech.edu/89 (accessed 13 May 2008), p. 34.
45 De Maria and Russo (1985: 243).
46 Letter to Dirac from Martin Charlesworth, 16 October 1931, Dirac Papers, 2/2/4 (FSU). Charlesworth was Dirac’s personal tutor during his postgraduate years and was evidently fond of him. Later, on 19 March 1935, he wrote a letter to Dirac ‘to send my [i.e. his] love’ – a remarkably forward phrase in that cultural milieu, Dirac Papers, 2/3/1 (FSU).
47 Batterson (2006: Chapter 5).
48 Brendon (2000: Chapter 4).
49 New York Times, 14 June 1931.
50 Letter from Gamow to Dirac, written in June 1965, Dirac Papers, 2/5/13 (FSU). See also Gamow (1970: 99).
51 Gorelik and Frenkel (1994: 20–2). See also Kojevnikov (2004: 76).
52 Gorelik and Frenkel (1994: 50–1). Gamow gives a partially inaccurate account of this incident in his autobiography (1970).
53 The first Soviet edition is discussed in detail in Dalitz (1995), which includes a translation of the prefaces to the book.
54 Ivanenko had ensured that the book had been translated with no changes, but the Russian edition does include an additional chapter on applying quantum mechanics to practical problems. It is not clear whether Dirac added the section as a result of ideological pressure.
55 Greenspan (2005: 161).
56 Letter from Dirac to Tamm, 21 January 1932, in Kojevnikov (1993: 60). Dirac was learning the branches of mathematics known as group theory and differential geometry.
57 Interview with Oppenheimer, AHQP, 20 November 1963, p. 1.
58 Letter to Dirac from his mother, 9 October 1931, Dirac Papers, 2/2/4 (FSU).
59 Letter to Dirac from his mother, dated 28/31 September 1931, Dirac Papers, 2/2/4 (FSU).
60 Letter to Dirac from his mother, 22 December 1931, Dirac Papers, 2/2/4 (FSU).
61 Brown (1997: Chapter 6).
62 Cathcart (2004: 210–12); Chadwick (1984: 42–5).
63 Brown (1997: 106).
Sixteen
I hope it will not shock experimental physicists too much if I say that we do not accept their observations unless they are confirmed by theory.
SIR ARTHUR EDDINGTON, 11 September 19331
The character of Paul Dirac first appeared on stage in a special version of Faust, the Hamlet of German literature. Goethe’s drama is the literary antithesis of Agatha Christie’s penny-plain narratives that Dirac wolfed down in the evenings. He had no taste for epic plays, but he will have been absorbed in this Faust, a forty-minute musical parody of the twenty-one-hour play, written as a physicists’ entertainment.2
The authors, the cast and the audience were the physicists at Bohr’s spring meeting in April 1932, and Dirac was there. In the oasis of the institute, physics had not looked more exciting for years, in hideous contrast to the world outside. Chadwick’s discovery had revitalised interest in the atomic nucleus, whose detailed structure was a mystery to theoreticians. They had a wealth of other problems to solve, too, including the status of quantum field theory and of the predicted anti-electron, monopole and neutrino – each controversial, none yet detected. As Bohr liked to point out, science often flourishes quickest when it faces problems and contradictions; the Princeton physicist John Wheeler once went so far as to spell out the central idea of the institute as ‘No progress without paradox’.3
The version of Faust performed at the Institute was in the tradition of office Christmas parties, with their licensed burlesque and private jokes that stay close to the boundaries of good taste but carefully avoid crossing them. The journalist Jim Crowther was among the audience of twenty-odd conference delegates who entered into the spirit of the occasion, happily indulging the manifold crimes against artistic taste.4 Bohr, represented in the play by the Lord Almighty, sat in the middle of the front row of the audience, convulsed with laughter as one of his colleagues mimicked his tortured oratory.
In Goethe’s original play, the sharp-tongued Mephistopheles seduces Faust, discontented with his limited wisdom, into a bargain that grants him universal insight and the love of the beguiling virgin Gretchen. The main theme of the Copenhagen version is the story of the neutrino and of Pauli’s attempts to persuade Ehrenfest of its existence. Pauli (not at the meeting) was represented by Mephistopheles, Ehrenfest by Faust, and the neutrino by Gretchen, whose songs Heisenberg accompanied at the piano. The original version of the play opens with speeches from three archangels, and the Copenhagen version began in the same way, except that the trio was represented by the English astrophysicists Eddington, Jeans and Milne, who stood on the almost room-wide desk of the main lecture theatre, declaiming in rhyming doggerel about the latest theories of the universe.
Ehrenfest’s leg was pulled unmercifully. He was played as a character who lay on the couch with his trousers in disarray, meditating on the vanity of science and life. This probably struck some participants, including Dirac, as being too close to home: Ehrenfest was morose, deeply uneasy about the state of physics and losing his spark. At the meeting, when Darwin approached him with a question, he rebuffed him, saying only, ‘I’m bored with physics.’5
In the second half of the playlet, Dirac comes under the spotlight. His monopole is a singing character, treated with respectful curiosity, in contrast to his hole theory, portrayed as bizarre and not wholly serious. In a few revealing lines, the character of Dirac describes the state of his subject:
A strange bird croaks. It croaks of what? Bad luck!
Our theories, gentlemen, have run amuck.
To 1926 we must return;
Our work since then is only fit to burn.
These few words accurately capture Dirac’s despondency about the state of quantum field theory. He had tried to produce an improved version of Heisenberg and Pauli’s relativistic version of quantum field theory but had found out during the meeting that his theory was no improvement at all: both field theories were shot through with infinities. The root of the problem appeared to lie in ‘singularities’, particular points in the theory where the mathematics become ill defined or even incomprehensible. It was a deft decision of the authors of the Copenhagen Faust, headed by Max Delbrück, to arrange for Dirac to exit the stage chased by the actor playing a bit part, Singularity.
The jibes about hole theory were not confined to the entertainment; throughout the meeting, Dirac had to put up with Bohr
’s hostile questioning and the taunts of other colleagues. Dirac appeared to take it all on the chin; according to one colleague, during the meetings that week he did not utter a word.6 In the final session of the meeting, Bohr lost patience and put him on the spot: ‘Tell us, Dirac, do you really believe in that stuff?’ The room went silent, and Dirac stood briefly to intone his twelve-word reply: ‘I don’t think anybody has put forward any conclusive argument against it.’ Although outwardly loyal to his interpretation of hole theory and to his proposal of the anti-electron, the absence of the particle was sapping his morale. Soon, even he stopped believing in his hole theory, he later told Heisenberg.7
Just less than three weeks after the Copenhagen meeting, news broke from the Cavendish of another experimental sensation: the atom had been split. It was the work of John Cockcroft and the dishevelled Irishman Ernest Walton, an expert in engineering hardware. Together, the two men had built the largest machine ever constructed in the Cavendish, capable of accelerating protons through 125,000 volts and smashing them into a metal target.8 Quantum mechanics predicted that the accelerated protons should have enough energy to break up the nuclei at the heart of the lithium atoms, but it was a challenge to prove it. Cockcroft and Walton increased the intensity of their beam until it was high enough to stand a chance of splitting some of the atoms in their lithium target. After eight months of work, when the beam was delivering a hundred trillion protons per second, telltale flashes on the detector in Cockcroft and Walton’s darkened laboratory told them that they had split lithium nuclei into two nuclei of a different element, helium. Here, on the nuclear scale, Cockcroft and Walton realised the dream of alchemists by transforming one type of element into another. For the second time in three months, Rutherford was overseeing the announcement of a great experiment. He was not best pleased when Crowther’s news-management skills faltered and the story leaked to the press and broke in the popular Sunday newspaper Reynolds’s llustrated News, which trumpeted the latest Cavendish finding as ‘Science’s Greatest Discovery’.9 Other newspapers soon followed, including a nervous Daily Mirror: ‘Let it be split, so long as it does not explode.’10
When the discovery was announced, Einstein happened to be in Cambridge to give a lecture. On 4 May, at the height of public interest in the experiment, an intrigued Einstein paid a private visit to the Cavendish Laboratory for a demonstration.11 He must have been gratified to see that Cockcroft and Walton’s results were consistent with his most famous equation: the total energy of the particles involved in the nuclear reaction is conserved only if energy and mass are related by E = mc2. Cockcroft and Walton had been the first to verify the equation.
Eddington – ready, as ever, with a down-to-earth analogy – linked Cockcroft and Walton’s fragmentation of the nucleus to what appeared to be the fissuring of society. He observed that splitting the once-indivisible atom had become the ordinary occupation of the physicist since 1932 and that the social unsettlement of the age seemed to have extended to atoms.12 By 1932, Cambridge University’s political centre of gravity had moved sharply to the left. Only six years before, the great majority of students worked to break the General Strike; by May 1932, the Cambridge Union – bellwether of student opinion – supported the motion that they saw more hope in Moscow than in Detroit.13 The students were fearful of another war, angry that the spirit of the Locarno Treaty was being mocked by events. Another war was beginning to look all but inevitable.
The Cavendish triumphs demonstrated the quality of Rutherford’s leadership of experimental physicists in Cambridge. By comparison, the university’s theoreticians were embarrassingly unproductive – their titular head was the Lucasian Professor Sir Joseph Larmor, then seventy-five and about to retire, not before time. To no one’s surprise, the authorities announced in July that his successor was Dirac, who was not quite thirty and just a few months older than Newton’s age in 1669 when he took the Chair. As soon as the authorities announced his appointment, he left Cambridge for a while to escape the clamour of congratulations.14
Dirac knew that the Chair was more than an accolade: it was a vote of confidence but also a challenge. He was expected to continue to be a leader, to set the pace in his field, to leave a legacy that scientists would talk about for centuries. By no means all the holders of the Lucasian Chair had justified their promise: William Whiston, John Colson and Isaac Milner are in no one’s list of great mathematicians or scientists. Dirac still had more to prove. He was confident in the durability of his early work on quantum mechanics, though he had good reason to fear that his later ideas – field theory, hole theory, the monopole – might one day be regarded as honourable failures. Worse, he worried that he was becoming too old to come up with original theoretical ideas: earlier in the year, soon after Heisenberg’s thirtieth birthday, Dirac told him: ‘You are now past 30 and you are no longer a physicist.’15
Rutherford wrote to congratulate Dirac, hoping that he ‘will still continue to be a frequent visitor to the Cavendish’, probably an allusion to Larmor, who rarely set foot in the Laboratory. One of Dirac’s colleagues summed up the mood when he told the new professor: ‘I don’t think any recent election to a professorship can have been more popular.’16 Only Larmor was sniffy about his successor’s appointment, later cattishly remarking that Dirac was ‘an ornament of the German school […] though a minor one.’17
Dirac did not look the part of the distinguished Cambridge professor. Shy as a mouse, he had so little gravitas outside the lecture theatre that in the streets of Cambridge he passed for a tyro graduate student. He was nervous in the company of women of his own age, so many of his colleagues assumed he was gay, that he would die a bachelor and had no interest in having children. Yet Kapitza knew better. He came to know Dirac well during their relaxed conversations in the Kapitzas’ house, a noisy den that always seemed to be teetering on the edge of familial anarchy. Dirac was at ease there, talking with Kapitza and Rat over a Russian-style meal, playing chess and larking about with their two rumbustious sons. The contrast between the dysfunctional household of 6 Julius Road and the happiness he saw in the Kapitzas’ home could scarcely have been plainer. Perhaps Dirac was already longing for the vibrant family life that Kapitza and Bohr had shown him, an environment in which sourness and unkindness were rare, not the norm.
By the standards of British academics, Dirac was wealthy. When he took up the Lucasian Chair, his annual salary rose sharply, from £150 to £1,200, supplemented by his annual college ‘dividend’ of £300. The modern value of his salary at the end of 1932 is £256,000. He had seen the last of penury, though for him frugality was too ingrained to be anything other than a way of life.18 So far as he was concerned, a suit and a tie were all he needed, and he wore them indoors and outdoors, rain or shine, until most men would regard them as being fit only for the bin. His mother, perpetually chivvying him to smarten up, thought it was high time she bought some new clothes for herself and asked him to pay for them: ‘If you have a really substantial salary in the autumn you may be able to treat your mother to a winter coat.’19
Charles and Flo were the toast of the city for producing its most famous scientist, but the old quarrels continued. Worried that Charles was planning to convert their daughter into a nun, Dirac’s mother suggested that he pay for Betty to take a degree in French at the university. There was not much chance that Charles would pay for it as he believed that higher education should be a male preserve. Betty sensed this, as she told her brother in a letter: ‘I haven’t actually asked Pa for financial assistance, but he takes no interest in it and doesn’t seem willing to help in any way.’20 But Betty was not resentful: she accepted it as part of her father’s character and, besides, most other men felt the same way.
In Betty’s letters to Paul around this time, she seems conventionally affectionate to him, but nothing of substance is known about their relationship. It seems safe to conclude that he thought well of her, however, because in July 1932 he generously offered to pay for his s
ister’s fees and expenses for the next four years.21 Although she struggled before successfully crossing the first hurdle of gaining a mandatory pass in Latin, she was a contented student. In a touching letter to her brother she assured him, ‘I will do my best to give you value for your money, and I am honestly working, for the first time in my life, I believe.’22 Her educational liberation seems to have disheartened Charles, now a stooped and tottering invalid. He was slowly losing his grip on his family, Flo reported to her son: during a routine domestic stand-off about the use of their car, he huffily agreed to give in to her and Betty, but only after an hour’s sullen reflection. It was a momentous moment, the first time in thirty-two years of marriage that she could remember him backing down.23 He may well have wondered how his life had come to such a pass. Perhaps he would have sympathised with Fatty Bowling, the narrator of Coming Up for Air, George Orwell’s satire on 1930s suburbia. Like Charles, Bowling was a hostage to his ungrateful family, tied by convention and financial convenience to a slattern he despised. Unlike Bowling, however, Charles took pleasure from his friends and his work: language students still traipsed up to 6 Julius Road for his tutorials, and he was still active in the local Esperanto Society.
By early August, Charles was planning to visit his family in Geneva. As usual, he did not tell his wife about his travel plans but disclosed them to his son, in a letter written almost entirely in French (only the final line was in English). He trod carefully:
7 August 1932
My dear Paul
I suppose that you are very busy so I will only take a few minutes of your time to tell you how happy and proud I am of your great success. All the newspapers have given us the details. Several friends and acquaintances have asked me to congratulate you on their behalf.
Will this new position change your plans to go to Russia? I would like to know the date when you have decided because as soon as I am strong enough to undertake the journey I should go to Switzerland to sort out some family matters and I do not want to be away from Bristol when you are here.
The Strangest Man Page 30