To judge from the letters Dirac received from his mother, relations between her and Charles had settled down now she was spending more time out of the house. She went to talks on Tennyson’s poetry, saw shows at the Hippodrome theatre with Charles and Betty and visited the cinema, including a trip to see one of the last great silent films, Ben Hur. But the Dirac family’s favourite novelty was the motor car, the most exciting of the new mass-produced technological innovations. One of Charles’s private tutees owned a car and treated the Dirac family to afternoon joyrides to the coast and to countryside teashops, keeping to the speed limit of 20 mph. Images of trips like these – carefree families, cutting loose from worldly concerns for a day – symbolised the prosperity of Britain in the third quarter of the 1920s. For the majority, life had never been better.
But when Dirac was not at home, his mother’s life was empty. Always in search of a plausible excuse to visit him, she invited herself to Cambridge in mid-February to see the Lent boat races, sheepishly asking if he had the time to see her when she was in town (‘I shall be dressed quite nicely & shall not be any trouble’).21 He often ignored such requests, but this time he agreed, and she arrived in a foggy Cambridge at lunchtime to spend a few hours talking with her son, who apparently gave no sign that he was living through one of the most exciting times of his life and that some of his peers were beginning to talk of him as the heir to Newton.
Dirac appeared also to resemble Newton in having no interest in forming romantic relationships with women. Many of Dirac’s colleagues had the impression that he was frightened of women of his own age and they could scarcely imagine that he would ever marry. But he did have a close friendship with one woman, the fifty-six-year-old mother of his friend Henry Whitehead, a promising mathematician at Oxford University. Isabel Whitehead, a tall, solidly-built Scot, was the wife of the Right Reverend Henry Whitehead, nineteen years her senior and formerly the Bishop of Madras in India. The couple had spent almost twenty years living there, before retiring to the UK in 1923. Among her fellow expatriates, Mrs Whitehead was notorious: according to an authoritative account of the Christian community in India, she was imperious ‘even by the domineering standards of the many British memsahibs’.22
The Whiteheads lived in a half-wood, half-brick cottage in Pincent’s Hill, near Reading, about three hours’ drive from Cambridge. Always accompanied by their dogs, they led a leisurely life, taking just an hour or two each day to run a small farm with pedigree Guernsey cattle and a few chickens. Both Isabel and Henry were Oxford-educated mathematicians, but it seems from Mrs Whitehead’s letters that the two of them talked less about science with Dirac than about other matters, especially Henry’s enthusiasm for cricket and their adventures in India, including the week they spent in their home entertaining Gandhi. In the coming years, Mrs Whitehead’s correspondence with Dirac also makes it clear that she robustly challenged his atheism and that he trusted her with his most private thoughts about his family. Pincent’s Hill became a favourite weekend retreat for him and Mrs Whitehead became his second mother, giving him not only support and affection but also something his own mother could not provide – intellectual stimulation.
During the early spring of 1928, Dirac was planning his next journey. His six-month itinerary would begin in April and take him back to Bohr’s Copenhagen and Ehrenfest’s Leiden, on to Heisenberg’s Leipzig and Born’s Göttingen, and finally his first visit to Stalin’s Union of Soviet Socialist Republics. Dirac had heard much about this country; now he would be able to judge for himself.
Note - Chapter eleven
1 Menu from College records, STJOHN.
2 Crowther (1970: 39) and Charap (1972).
3 Interviews with Dirac, AHQP, 1 April 1962, p. 15; 7 May 1963, pp. 7–8.
4 Dirac gave contradictory accounts of the goal he was pursuing at that time. In one
account, he stated that he was seeking the answer to the question ‘How could one get
a satisfactory relativistic theory of the electron?’ (Dirac 1977: 141). In another
account, he says that ‘my dominating interest was to get a satisfactory relativistic
theory of a particle, of the simplest possible kind, which was presumably a spinless
particle.’ Dirac wrote the latter words on a single sheet of paper headed ‘Sommerfeld
Atombau un Spektralinen II 539.18’ in Dirac Papers, 2/22/15 (FSU). I prefer to use
the 1977 account as it is the nearest thing we have to a carefully prepared history of
Dirac’s thinking in his own hand.
5 Farmelo (2002a: 133).
6See the notes for Dirac’s lectures in the 1970s and 1980s: 2/28/18–2/29/52 (FSU).
7 Huxley’s 1870 Presidential Address to the British Association for the Advancement of
Science in Huxley (1894). Dirac uses similar words: ‘The originator of a new idea is
always rather scared that some development may happen which will kill it’ (1977:
143).
8 Interview with Dirac, AHQP, 7 May 1963, p. 14; Dirac (1977: 143).
9 Letter from Darwin to Bohr, 26 December 1927 (AHQP).
10 Interview with Rosenfeld, AHQP, 1 July 1963, pp. 22–3.
11Mehra (1973: 320).
12 The talented young physicist Rudolf Peierls remarked that, even after a few days
studying the equation, ‘I have begun to have an inkling of what it deals with, but I
haven’t understood a single word.’ Letter from Peierls to Hans Bethe, 4 May 1924,
quoted in Lee (2007b: 33–4).
13 Florida State University Bulletin, 3 (3), 1 February 1978.
14 Slater (1975: 145).
15 Postcard from Darwin to Dirac, 30 October 1929, Dirac Papers, 2/1/9 (FSU).
16 Dirac gave courses on quantum mechanics in the Michaelmas and Lent terms of
1927–8 and was paid £100 for the pair: see the letter from the Secretary to the
Faculty of Mathematics, 16 June 1927, Dirac Papers, 2/1/4 (FSU).
17 Crowther later affirmed that he had left the Communist Party by 1950, but it is not
clear when he left it. I thank Allan Jones for this information.
18 Clipping, annotated by Charles Dirac, in Dirac Papers, 1/12/5 (FSU).
19 The Times, 5 October 1931, p. 21. This well-briefed article was written by a journalist
who appears to have succeeded in persuading Dirac to speak about his work.
20 ‘Mulling over the Universe with Paul Dirac’, interview by Andy Lindstrom,
Tallahassee Democrat, 15 May 1983.
21 Letter to Dirac from his mother, 26 January 1928, Dirac Papers, 1/3/8 (FSU). See also
postcard from Dirac to his parents, 1 February 1928 (DDOCS).
22 See the entry for Bishop Whitehead in Crockford’s Clerical Dictionary, 1947,
p. 1,416. See also Billington Harper (2000: 115–26, 129–33, 293–5). The quoted
description of Mrs Whitehead is on p. 145. I thank Oliver Whitehead and the late
David Whitehead, grandsons of Isabel Whitehead, for the information in the description
of Isabel Whitehead’s home.
Twelve
See how physical science, which is Reason’s trade
And high profession, booketh ever and docketeth
All things in order and pattern.
ROBERT BRIDGES, Testament of Beauty, 1929
Paul Ehrenfest could be a moody and demanding colleague, but he was a charming and generous host. In April 1928, when he realised that he would not be able to greet Dirac at Leiden railway station at the beginning of his visit, Ehrenfest arranged for a phalanx of his assistants to be waiting for him on the platform when his train steamed in shortly after 10 p.m. The problem was that none of them knew what Dirac looked like. Ehrenfest’s solution was to ensure that, outside every train door facing the platform, there was a student waving a reprint of ‘The Quantum Theory of the Electron’. The plan worked.1
On
e member of the welcoming party was Igor Tamm, a thirty-two-year-old Soviet theoretician, soon to become one of Dirac’s closest companions. Tamm was famously restless: in group photographs, while others appeared in sharp definition, he would be a blur.2 A Marxist even before he went to university, he joined the Social-Democratic Workers’ Party in 1915 and, during the subsequent years in Moscow, Kiev, Odessa and Elizavetgrad, studied science while being a part-time activist for the Bolsheviks. He tired of their fanaticism and, when they declared all other political parties illegal in the summer of 1918, was concentrating on science. He became the first Soviet theoretician to use quantum mechanics.3 In January 1927, he arrived in Leiden and, a year later, electrified by the Dirac equation, was looking forward to meeting its discoverer. Tamm wrote to his wife in Moscow that he wanted to see if there was any truth in rumours that ‘it costs a tremendous effort to get a word from [Dirac], and that he talks only to children under ten’.4
The two men soon clicked. In Tamm, Dirac had found another intellegent and entertaining Russian extrovert; in Dirac, Tamm found a companion who was surprisingly agreeable, provided he was under no pressure to speak. The two men spent the spring afternoons strolling around the town’s cobbled streets, watching the traffic on the interlocking network of canals and occasionally walking out to the nearby tulip fields.5Tamm taught Dirac to ride a bicycle, Dirac taught Tamm physics, and they talked about matters outside science, probably including politics and Tamm’s favourite hobby of mountain climbing. Tamm was humbled by Dirac’s erudition: ‘I feel like a little child next to him,’ he wrote to his wife.6
As was customary for visitors to Leiden, Dirac gave a series of lectures. He had much improved his technique as a public speaker: when he strode towards the blackboard, he seemed to change from being a pitiful wallflower to the Demosthenes of quantum mechanics. Standing quite still, he looked into the eyes of his audience and talked plainly and articulately, with the force of an advocate, not letting a pause or hesitation break his rhythm. He did not read from a prepared text but knew exactly what he wanted to say; once he had decided on the clearest way of expressing an idea, he would not deviate from it, from one lecture to another. When Ehrenfest asked for further explanation, Dirac would respond by repeating what he said, almost word for word.7
In mid-June 1928, Dirac moved on with Tamm to Leipzig to spend a week at a conference co-organised by Heisenberg, who was agonising about the Dirac equation. Darwin and others had demonstrated that it perfectly reproduced previously successful formulae for atomic hydrogen’s energy levels, but this news cut no ice with Heisenberg. He was troubled by the equation’s absurd prediction that a free electron can have negative energy – and it had become clear that no subtle tinkering with the equation could change it. For Dirac, this was simply the next problem to be addressed. For Heisenberg, it was evidence that the equation was sick. A month after Dirac departed from Leipzig, Heisenberg wrote to Bohr: ‘I find the present situation quite absurd and on that account, almost out of despair, I have taken up another field, [trying to understand magnetism].’ 8A month later, Heisenberg was even more depressed when he wrote to Pauli: ‘The saddest chapter of modern physics is and remains the Dirac theory.’9 Dirac knew Heisenberg’s criticisms were well founded and that the onus was on him to demonstrate that the theory was more than a beautiful mirage.
Among the scientists Dirac met for the first time in Leipzig was Heisenberg’s student Rudolf Peierls, just turned twenty-one. Wiry, bespectacled and with a pronounced overbite, Peierls oozed vitality and ambition. His professors asked him to take Dirac to the opera, a challenge that his guest’s Cambridge colleagues regarded as all but impossible. They could scarcely imagine him sitting through any kind of drama: the artifice, the focus on speech or lyrics and the often contorted plotting would surely have no appeal to his literal mind. Decades later, Peierls could not remember the play or his guest’s reaction to it but squirmed at the thought of Dirac’s insistence on following the English custom of taking his hat with him to the performance, pointedly refusing to follow the German practice of leaving headwear in the theatre cloakroom. Peierls, whose formal Prussian education had given him a strong sense of politesse, found Dirac’s behaviour mortifyingly crude.10 Dirac, probably oblivious of his colleague’s discomfiture, often behaved like this: he was a stickler for English conventions of courtesy and saw no reason to deviate from them in other countries. Flexibility was not his forte.
After the conference, Dirac travelled with Tamm to Göttingen. Its theoretical physics department was losing its edge as its leader, Max Born, struggled to maintain his momentum. Overworked, worried that younger and fresher minds were leaving him behind, depressed by marital problems and the Nazis’ ‘blood and soil’ anti-Semitism, he slid into a nervous breakdown.11 His colleague Jordan was openly a conservative nationalist but in private was writing reactionary articles in the journal Deutsches Volkstrum (‘German Heritage’), under the cover of a pseudonym.12
Göttingen was, however, still on the itinerary of every young theoretician. During this visit, Dirac began his long friendship with two other visitors, who embodied his taste for the company of both introverts and extroverts and who were to lead him to his first close relationships with women of his own age. At the flamboyant extreme was George Gamow, a Russian theoretician two years Dirac’s junior, destined to be the court jester of quantum physics. Variously nicknamed Johnny, Gee-Gee and (by Bohr) Joe, he was a six-foot three-inch, 220-pound giant and close to being Dirac’s polar opposite: loquacious, a passionate smoker and drinker, relentlessly jocular.13 Shortly before his visit to Göttingen, he had made his name by being one of the first to use quantum mechanics to explain the type of radioactive decay in which an alpha particle can be ejected from types of atomic nuclei (impossible, according to classical mechanics). Dirac, probably to Rutherford’s frustration, had attended many Cavendish seminars about new findings in nuclear physics but showed no interest in trying to understand them.14 As theoreticians, Gamow and Dirac were entirely different: Gee-Gee did not try to come up with fundamental new ideas but preferred to apply ones discovered by others. Yet the two men got along well and often dined together, Dirac listening expressionlessly as his new friend told of how he had learned Euclidean geometry under artillery bombardment and other such stories, most of them more impressive for their colour than their accuracy.15
At the other end of the personality spectrum was Eugene Wigner, who had recently arrived in Göttingen after spending years with Einstein in Berlin, having switched to physics after being trained as an engineer. The scion of a wealthy Jewish family, Wigner and his two sisters had been raised by a governess in a grand apartment in one of the most exclusive residential areas of Budapest, overlooking the Danube. He loved to reminisce about his boyhood home: the formal family dinners, the scurryings of the two uniformed servant girls, the scent of freshly cut roses.16 Unlike Dirac, the young Wigner was politically alert and acutely aware of the instability of his country. Since the break-up of the Austro-Hungarian Empire in 1918, Hungary had been through a bloody Bolshevik revolution led by Béla Kun and the White Terror organised by nationalist and anti-Semitic forces. Wigner was fearful of the future of the country, then under Admiral Horthy’s authoritarian regime.
Despite all the political upheavals, Wigner had an exceptionally fine school education in mathematics and science, even more thorough than Dirac’s. Historians still debate why Budapest in the early twentieth century produced so many intellectual innovators, including John von Neumann, whom Dirac would later rate as the world’s finest mathematician, and Wigner’s friends Leó Szilárd and Edward Teller, both to do important research into the first nuclear weapons.17 The success of this cohort of Hungarians is partly due to their education, shortly after the war, in Budapest’s excellent high schools and partly to the vibrancy and ambition of the city’s Western-focused culture.18
Wigner was one of the shyest and most uncommunicative of the quantum physicists but, compared wi
th Dirac, he was gregariousness itself, so conversation during their evening meals together was probably strained. They had to find a common language – Dirac did not know Hungarian, hated to speak French and spoke fractured German with a bitumen-thick accent, while Wigner’s English was weak, and he liked to converse in German or French. They probably settled on German. No record remains of the details of their early conversations, but it is likely that Wigner mentioned his politics and youthful experiences of anti-Semitism: since he was sixteen, he had followed his father in ideologically opposing Communism, and his views had hardened a year later during Kun’s regime, in which his father was thrown out of his job as director of a tannery.19 For a few months, the Wigners had fled to Austria but returned after the Communists were overthrown.
Dirac would have been content to listen to as much of Wigner’s life story as he was willing to tell. But when Wigner turned his attention to physics, he quickly saw that Dirac had no interest in sharing his thoughts and ideas. The moment Wigner began to probe, Dirac withdrew into himself like a frightened hedgehog.20 Igor Tamm knew how to avoid this kind of defensiveness: keep conversation to a functional minimum, avoid personal questions and never risk wasting breath on trivialities. Tamm and Dirac’s relationship flourished partly because they had complementary talents: intellectual leadership was provided by Dirac, while the social impetus came from Tamm. It was he who introduced Dirac to what would be one of the greatest pleasures of his young life: mountain climbing. In one long trip east, the two journeyed out to the wooded Harz – ablaze with fireflies in the evenings – and they climbed the challenging peak of Mount Brocken (1,142 metres).21 Dirac was smitten: apart from equations, nothing did more to stir his sense of beauty than mountains.22
The Strangest Man Page 22