The Strangest Man Read online

  Age is of course a fever chill

  That every physicist must fear

  He’s better dead than living still

  When he’s past his thirtieth year3

  Göttingen students had a penchant for silly songs and for choral renditions of American tunes, which were sung with special enthusiasm at Thanksgiving. The cosmologist Howard Robertson, who introduced Dirac to ways of describing the curvature of space-time across the universe, had brought to the taverns of Göttingen one of their most popular new songs, ‘Oh My Darling Clementine’.4 Dirac probably did not join in, but he took part in the infantile games that helped to sublimate the physicists’ intense competitiveness. One of the games was ‘bobbing for apples’, when professors and students – often woozy, after a few glasses of beer – would try to sink their teeth into an apple floating on water or beer. Another activity involved running a race while trying to balance a large potato on a tiny spoon. After one of these races in Born’s home, a student saw Dirac practising surreptitiously – a sight that would have stunned his colleagues in Cambridge, including the classicist John Boys Smith, who described Dirac as being ‘childlike but never childish’.5

  Dirac’s stay in Göttingen ended in early June 1927. St John’s wanted him back and had been wooing him to apply for a fellowship, an honour well worth pursuing. If successful, he would benefit from free board and lodging in college, as well as a modest income to supplement the continuing funds from his 1851 scholarship, which would run out in 1928.6 A tenured academic post in the university’s mathematics department would almost certainly follow, and he would be set up for the rest of his working life. In his letters, Dirac was even less forthcoming about his personal life than he had been when he wrote from Copenhagen. In a letter to the college official James Wordie, Dirac wrote just a single sentence about his activities in Göttingen: ‘The surrounding country is very beautiful.’7Although he preferred Bohr’s pullulating institute to Born’s comparatively cool department, he told his mother that he preferred Göttingen, as it gave him the best opportunities for solitary walks.8

  In his research, Dirac appeared to be showing signs of running out of steam. In early May 1927, he used quantum mechanics to predict what happens when light is scattered by an atom – a problem that led to no exciting conclusions. Oppenheimer later said that he was disappointed by Dirac’s work in Göttingen and could not understand why he did not press on with the development of quantum field theory. Dirac wanted to take a long rest over the summer, he told Oppenheimer, and would then turn his attention to the spin of the electron, still not understood.

  Dirac intended to begin his break from quantum theory when he returned to England, after he had visited Ehrenfest in Leiden, a small university town in the Netherlands. Dirac stayed in the room at the top of Ehrenfest’s large Russian-style house, where he signed his name on the bedroom wall that already bore the signatures of Einstein, Blackett, Kapitza and dozens of others. The house served as a local hostel for the cream of the world’s physicists, who traded anecdotes of their lively conversations with Ehrenfest’s wife – a Russian mathematician – and their three children, two daughters and a son who had Down’s syndrome.

  Oppenheimer was planning to join Dirac in Leiden and began to learn Dutch so that he could give a seminar in the language of his host. But first he had to defend his Ph.D. thesis in an oral examination held by James Franck, the distinguished experimenter, and Max Born.9 Franck took only twenty minutes to question Oppenheimer, but that was enough. On leaving the exam room, Franck sighed, ‘I’m glad that is over. He was on the point of questioning me.’ Born was relieved that his brilliant but troublesome student was off his hands. At the end of a typewritten letter to Ehrenfest, Born wrote a postscript:

  I should like you to know what I think of [Oppenheimer]. Your judgement will not be influenced by the fact I openly admit that I have never suffered as much with anybody as him. He is doubtless very gifted but without mental discipline. He’s outwardly modest but inwardly very arrogant. […] he has paralyzed all of us for three quarters of a year. I can breathe again since he’s gone and start to find the courage to work.10

  Dirac had not been part of this departmental paralysis, nor does he appear to have been aware of it. Oppenheimer was awed by him and showed him a diffidence he granted to few of his other colleagues. Their days in Göttingen were the beginning of a forty-year friendship.

  Göttingen was too far away for Dirac’s family to visit. ‘Thank goodness, you are saying, I expect,’ his mother wrote in a pained aside.11 She made it clear to her son how much she envied him: ‘You are a lucky fellow to be away from home. [Here,] it is all work, work.’12 When her husband was out, she wore her new ring – seven diamonds set in platinum – which she had furtively bought with £10 of the money Dirac had sent her, considerably more than Charles allowed her to spend on herself in a year. That piece of jewellery was a private symbol of her most important relationship. She wrote to her son: ‘Don’t tell Pa […] I expect he would tell me to put the money in the housekeeping, but it is giving me such a lot of pleasure to look at it and think what a darling you are.’13 In the evenings, she would sit in the front room with photos of her son, re-reading his postcards, trying to imagine what he would be doing at every time of day.

  The twelve-year age difference between Charles and Flo had never been more plain. She still had an upright posture, smooth skin and scarcely a grey hair; he was hunch-backed, white-haired and wizened. In public, she put on the traditional show as the loyal, uncomplaining wife; in private, she was resentful of being an unpaid servant, as she often wrote to her son. At the beginning of 1927, she was surprised when her husband went on a spending spree, probably funded by his mother’s legacy. Dirac often condemned the tattiness of the family home, which had not been decorated for thirteen years, so it may well have been that Charles paid for the extensive wallpapering and the installation of a gas fire in every room, with the aim of making 6 Julius Road more attractive to his son. Charles did not entirely neglect his wife – he bought her one of the new vacuum cleaners to help with the housework: ‘Pa likes to see them at work on our carpets giving free demonstrations.’14

  Still in poor health, Charles consulted a herbalist who advised him to become vegetarian, presenting endless catering problems for his wife, who worried incessantly about his nutrition. She wrote to Dirac: ‘Pa is getting ever so many pupils he has scarcely time for meals. I am sure he is working his brain too hard and now he is a vegetarian, there are so many little things to cook which are not substantial enough for him.’15 Although she thought he was mean and ungrateful, she devoted herself to taking care of him, and her letters to Dirac betrayed no sign that the state of affairs was anything less than she should expect or deserve. But her patience was beginning to run out.

  Charles Dirac’s work ethic had been the making of one of his sons and possibly the death of the other, but it did not have much influence on his daughter. Betty had left school and was, according to her mother, ‘too shy or perhaps too lazy […] to want to do anything to earn her own living & she is not fond of housework either’.16 Without a job, she lolled around the house mourning the death of her dog and went out with her mother to evening classes in elocution and French.17 In early July, the family chased out the decorators and made sure everything in their house was spick and span, ready for the return of the itinerant son. The family had not spoken to him for nine months, but in that time had sent him weekly family bulletins, showering him with affection and pleas for news at his end. In return, he had sent his parents fewer than seven hundred words. He had not once asked after his family on his postcards, which each had the warmth of a stone.

  When Dirac arrived at the door of 6 Julius Road at lunchtime on 13 July – a dull and overcast afternoon – it is easy to imagine the tearful flutterings of his mother and sister as they hugged his unresponsive frame and the stiff handshake with his father, who was probably no less pleased to see him, even if he was unable to
show it. He was soon back in his routine, shutting out his family, working alone in his room. One of Charles’s students, D. C. Willis, left an anecdote that offers an insight into the domestic environment at the Diracs’ that summer. Willis was sent by Monsieur Dirac ‘on his errands to his home during the dinner hour […] as he was concerned about his son Paul who, rumour had it, was working in his bedroom, and would not come out, except to collect his food and use the toilet’.18

  Dirac knew he had a filial duty to be with his parents but felt wretched whenever he was with them. ‘When I go back to my home in Bristol I lose all initiative,’ he sighed in a letter to a friend, a few years later.19 He felt oppressed by both his parents – by his father’s high-handedness and by his mother’s suffocating affection. Although Dirac was twenty-five years old and internationally successful, he still felt himself to be writhing under his father’s thumb. And he saw no imminent prospect of escape.20

  In October 1927, Dirac returned to Cambridge to reacquaint himself with his friends in St John’s and Trinity. He now had even fewer social distractions, as Kapitza had recently married. His new wife was the émigré Russian artist Anna Krylova, a dark-haired beauty whom Kapitza unaccountably called ‘Rat’, a nickname that nonplussed audiences in Cambridge theatres for years, whenever they heard him holler it across the stalls. She and Kapitza contributed to the design of the detached house that was being built for them on Huntingdon Road, near the city centre, complete with a huge back garden and a studio for her in the loft.21 Later, this house would become almost Dirac’s second home in Cambridge but, in the early autumn of 1927, he was working hard on his project, first mooted to Oppenheimer, aiming to combine quantum theory and Einstein’s special theory of relativity in the simplest practical case: to describe the behaviour of a single, isolated electron. The quantum theories of Heisenberg and Schrödinger were deficient because they did not conform to the special theory of relativity: observers moving at different speeds relative to one another would disagree on the theories’ equations. At stake here was the prestige of being the first to find the theory; would he be the sole winner of a scientific prize or would he, yet again, have to share it?

  Dirac worked on the problem for the first six weeks of the term but without success. He took a break in late October to sit, for the first time, at the top table of international physicists at the Solvay Conference in Brussels.22 The aim of these invitation-only conferences, funded by the Belgian industrialist Ernest Solvay, was to bring together about twenty of the world’s finest physicists every few years to ponder the problems of quantum theory. The youngest star of the first conference in 1911 had been Albert Einstein, then emerging from obscurity and quick to point out the prejudices of older, more conservative minds. In 1927, Einstein was the uncrowned king of physics and entering middle age, still a popular and unassuming figure but showing signs of crustiness and disillusion. He was ploughing his own furrow, seeking a unified theory of gravity and electromagnetism without assuming that quantum mechanics was correct. Now it was Einstein who seemed inflexible and backward-looking.

  The conference was to become a landmark in physics – the place where Einstein first publicly articulated his unease with quantum mechanics but failed to dent the confidence of Bohr and his younger colleagues. There is no sign of the lively conference atmosphere in the famous photograph taken outside the building where the sessions took place: the twenty-nine conference delegates all look expressionless, as though they are posing for a communal passport photograph. Einstein sits at the centre of the front row, with Dirac standing behind his right shoulder. Dirac was so proud of this photograph that, for once succumbing to vanity, he prompted the University of Bristol’s physics department to have it framed and mounted on one of their walls.23 This portrait, a dismal memento, was for decades the best visual evidence available of the meeting, but in 2005 more clues about the atmosphere of the meeting appeared, with the release of a home movie of the delegates during a break between the lectures.24 What is most striking about this two-minute clip is the delegates’ cheerfulness. Marie Curie, the only woman in the group, does a fetching pirouette; the beaming Paul Ehrenfest waggishly pokes out his tongue at the camera. Dirac, the youngest delegate, looks relaxed and happy as he talks with Max Born.

  Heisenberg later remembered that the most intense discussions took place not during the conference sessions but over meals at the delegates’ nearby Hotel Britannique, near the site of today’s European Parliament.25 At the epicentre of the debates about quantum theory were Bohr and Einstein’s disagreements about Heisenberg’s uncertainty principle, which Bohr defended successfully against Einstein’s repeated onslaughts. Most of their colleagues were fascinated to hear the two men lock horns, but Dirac was an indifferent bystander:

  I listened to their arguments, but I did not join in them, essentially because I was not very much interested […] It seemed to me that the foundation of the work of a mathematical physicist is to get the correct equations, that the interpretation of those equations was only of secondary importance.26

  Dirac and Einstein were poles apart, and neither was comfortable speaking the other’s language. Dirac was twenty-three years younger, and his awe rendered him even more shy than usual. But probably the main reason why they did not engage was that their approaches to science contrasted so sharply, partly because they responded so differently to philosophical matters. They agreed that science was fundamentally about explaining more and more phenomena in terms of fewer and fewer theories, a view they had read in Mill’s A System of Logic. Yet, whereas Einstein remained interested in philosophy, for Dirac it was a waste of time. What Dirac had retained from his reading of Mill, bolstered by his studies of engineering, was a utilitarian approach to science: the salient question to ask about a theory is not ‘Does it appeal to my beliefs about how the world behaves?’ but ‘Does it work?’

  At the conference, Dirac made his first recorded outburst on topics outside physics – religion and politics. Some four decades later, Heisenberg described the event, which took place one evening in the hotel’s smoky lounge, where some of the younger physicists were lying around on the chairs and sofas. Dirac’s youthful outspokenness needed to be indulged, the elderly Heisenberg said: ‘Dirac was a very young man and in some way was interested in Communistic ideas, which of course was perfectly all right at that time.’27 Most vivid in Heisenberg’s memory was a rant from Dirac about religion, triggered by a comment about Einstein’s habit of referring to God during discussions about fundamental physics. Like many of Heisenberg’s accounts of incidents in the 1920s, this one is implausibly detailed – it consists of two speeches of several hundred words, quoted as if his memory were word perfect – but it is consistent with other accounts of Dirac’s views. According to Heisenberg, Dirac thought religion was just ‘a jumble of false assertions, with no basis in reality. The very idea of God is a product of the human imagination.’ For Dirac, ‘the postulate of an Almighty God’ is unhelpful and unnecessary, taught only ‘because some of us want to keep the lower classes quiet’. Heisenberg wrote that he objected to Dirac’s judgement of religion because ‘most things in this world can be abused – even the Communist ideology which you recently propounded’. Dirac was not to be deflected. He disliked ‘religious myths on principle’ and believed that the way to decide what was right was ‘to deduce it by reason alone from the situation in which I find myself: I live in a society with others, to whom, on principle, I must grant the same rights I claim for myself. I must simply try to strike a fair balance.’28 Mill would have approved.

  During Dirac’s assault on religion, Pauli had been uncharacteristically silent. When asked what he thought, he replied, ‘Well our friend Dirac, too, has a religion, and its guiding principle is “There is no God and Dirac is his prophet”.’ It was an old joke, but everyone laughed, including Dirac.29 The opinions he expressed here, with uncharacteristic forwardness, were entirely in keeping with Kapitza’s views and would not have drawn comment
from any of the intellectuals who were flirting with Bolshevism. Although Dirac never put any of his political views on paper, it was clear from his actions in the coming decade where his sympathies lay.

  During the Solvay Conference, Dirac gave a talk on his new field theory of light. He annotated his draft script with rewordings and other changes in every paragraph – more than any other talk he gave in his entire life – indicating that he was on edge.30 Afterwards, he heard that his idea had been taken up and extended in a way he could have easily foreseen. Pascual Jordan, working with Eugene Wigner, had produced a field theory of the electron to complement Dirac’s theory of the photon. Although Jordan and Wigner’s mathematics was similar to Dirac’s, their theory did not appeal to Dirac, who could not see how their symbols corresponded to things going on in nature. Their work looked to him like an exercise in algebra, though later he realised he was wrong; his mistake stemmed from his approach to theoretical physics, which was ‘essentially a geometrical one and not an algebraic one’ – if he could not visualise a theory, he tended to ignore it.31

  That was not the only surprise Dirac received in the lecture hall. Shortly before the beginning of a lecture, Bohr asked Dirac what he was working on. He replied that he was trying to find a relativistic quantum theory of the electron. Bohr was baffled: ‘But Klein has already solved this problem,’ he said, referring to the Swedish theoretician Oskar Klein.32 The lecture began before Dirac could reply, so the question hung in the air, where it remained: Bohr and Dirac did not have the chance to talk further about it before the conference dispersed. Another three months would elapse before Bohr appreciated his error when he read Dirac’s wondrous solution to the problem.