The Strangest Man

by Graham Farmelo

  The wary British welcome given to Manci was made no more congenial by the inclement weather. The first few months of 1937 were one of the wettest periods Cambridge had seen for years. She felt unwelcome in the university, which seemed to be a place for men; spouses were meant to be agreeable ornaments – decorative but not obtrusive. Colleges did not allow wives to attend dinners, except on special occasions, so she had to sit alone with her novels and magazines while Dirac fulfilled his duty of dining in college at least once a week. Some of his colleagues thought that his marriage had lightened his character, though he was still as uncommunicative as ever, as the archaeologist Glyn Daniel found when he sat next to him at dinner in St John’s:

  The soup came and went in silence; halfway through the Sole Véronique I decided the effort must be made – the silence must be broken. But how? Not the weather. Not politics. Not the simple approach, ‘My name is Daniel. I study megalithic monuments. Have you any views on Stonehenge?’ I turned to Dirac, who was examining the grapes on his sole. ‘Have you been to the theatre or the cinema this week?’ I asked, innocently. He paused, turned to me with what I supposed was meant to be a kindly smile and said ‘Why do you wish to know?’ The rest of the meal was eaten in silence.21

  By early September, the Diracs had moved into their grand new home, 7 Cavendish Avenue, a detached red-brick house south of the town, built sixty years before. It was in a quiet district – he had checked carefully that they would not be disturbed by the ringing of church bells – was a twenty-minute cycle ride from St John’s College and had ‘a beautiful garden’ of almost two thirds of an acre.22 In May, Dirac had written out a cheque for £1,902 10s. 0d., which paid for the property in a single transaction; unlike most newly married couples, they were unencumbered by a mortgage. The interior decor of the house reflected Hungarian tastes in the late 1920s. Manci imported much of the furniture from her Budapest apartment – heavy, dark wood sideboards and cabinets, capacious living-room chairs, gaudy side tables – though Dirac vetoed her most ornate items. Patterned, deep-pile carpeting and conventional landscape paintings helped to set the sober decorative tone.

  Manci’s children joined them in Cambridge and began to study at local schools, where they – with their uncertain, thickly accented English – had to work hard to integrate with other pupils. Although Dirac never legally adopted Judy and Gabriel, he raised them as if they were his own children and never referred to them as his stepchildren. But he also wanted biological children of his own.23

  A few days after Dirac returned from his honeymoon, he completed his first contribution to cosmology. Had physicists known that he was working on this subject, they would probably have predicted a surprising new insight into the structure of the universe, or perhaps a fresh perspective on Einstein’s theory of gravity. But he did neither. In a 650-word letter to Nature that included almost no mathematics, he set out a simple idea about the numbers that describe the universe on the largest scale. As soon as Bohr finished reading the letter for the first time, he walked into Gamow’s room in the Copenhagen Institute and said, ‘Look what happens to people when they get married.’24

  Dirac’s cosmological idea was not completely original, as it bore signs of having been strongly influenced by Eddington. Now perceived by many of his peers as a cocksure eccentric, Eddington had largely abandoned research in conventional cosmology and was spending his time trying to derive some of the most important numbers in science – such as the number of electrons in the universe – not by systematic reasoning but by pure thought. Most theoreticians, including Einstein, thought this was hokum: theoretical physics was about finding general principles, not about explaining numbers that arise in the search. In Rutherford’s scabrous words, Eddington was ‘like a religious mystic and […] not all there.’25

  In his Nature article, Dirac pointed out that the universe is characterised by several numbers that seem to be connected in a simple way. He focused on three numbers, each of them estimates:

  1. The number of protons in the observable universe. Experimentally, this number is roughly 1078 (that is, 10 multiplied by itself 77 times).

  2. The strength of the electrical force between an electron and a proton divided by the strength of the gravitational force between them. This turns out to be about 1039.

  3. The distance across the observable universe divided by the distance across an electron (according to a simple classical picture of the electron). Its value is approximately 1039.

  The first striking point about these numbers is that they are so much larger than any number that occurs anywhere else in science: 1039, for example, exceeds the number of atoms in a human body by a factor of a hundred billion. The second point is that the largest estimated number, 1078, is the square of the smaller one. This, Dirac believed, may not be a coincidence and suggested that these numbers might be related by extremely simple equations such as

  distance across the observable universe divided by the distance across an electron = linking number

  × (strength of the electrical force

  between an electron and a proton divided by the strength of the gravitational force between them)

  and

  number of protons in the observable universe = another linking number

  × (distance across the observable universe divided by the distance across an electron)2

  Having noted that in both of these cases the linking number is about one, Dirac proposed a generalisation: this is always the case – any two of the huge numbers occurring in nature are connected by very simple relationships and linking numbers close to one. This is Dirac’s large numbers hypothesis, a consequence of his faith that the laws underlying the workings of the universe are simple.

  The suggestion has an intriguing consequence: because the size of the observable universe continuously increases as it expands, it follows that the ratio of this size to the radius of an electron cannot have always had its present value, 1039, but has been increasing throughout time. If Dirac was correct to surmise that this number is connected to the ratio of the electrical force and the gravitational force between an electron and a proton, it followed that the relative strengths of these forces must have been changing as time progressed, as Milne had suggested a few years before. Dirac argued that one consequence of this is that the strength of the gravitational force withers proportionately as the universe ages: when the age doubles, the strength of gravity halves.

  Dirac’s decision to introduce his idea in such a short paper suggests that he believed he had hit on an important new principle and did not want to be beaten into print. If he was expecting the reception that greeted most of his papers, he will have been disappointed: this one was given a frosty reception. Yet none of the sceptics went public with their criticisms, with one prominent exception, the eccentric philosopher-astrophysicist Herbert Dingle. For him, the job of the theorist was to find laws based on experimental measurements, just as Dirac had done in quantum mechanics. Dingle spoke for many a more timid colleague when he wrote an article in Nature that condemned ‘the pseudo-science of invertebrate cosmythology’, and regretted that Dirac was the latest ‘victim of the great Universe mania’.26 Stung into a quick reply, Dirac repeated his earlier reasoning almost word for word, after prefacing his remarks with an uncontroversial comment about the nature of science: ‘The successful development of science requires a proper balance to be maintained between the method of building up from observations and the method of deducing by pure reasoning from speculative assumptions.’27

  In the same issue of Nature, Dingle resumed his offensive, stressing that he was not attacking Dirac personally: ‘I cited Prof. Dirac’s letter not as a source of infection but as an example of the bacteria that can flourish in a poisoned atmosphere; in a pure environment it would not have come to birth, and we should still have the old, incomparable Dirac.’28

  Dirac was not deterred. However, after he had written at length about the implications of his hypothesis in a long paper –
completed shortly after Christmas 1937 – he returned to quantum mechanics and did not revisit the hypothesis for another thirty-five years. Although his idea influenced astronomers in the late 1930s, many of Dirac’s peers regarded it as an aberration, joining Bohr in believing that Dirac had made a wrong move towards Eddington and Milne’s quasi-mystical cosmology. But his status did not suffer significantly. In October, the Institute for Advanced Study in Princeton, still seeking to recruit the world’s best theoretical physicists, put Dirac at the top of the list of the scientists they wanted to recruit, just above Pauli.29

  Back in Bristol, Charles Dirac had left a surprise for his family: solicitors found, after months of delving through his accounts, that he had been a serial tax evader.30 The authorities required Flo to pay six years of Charles’s tax debt, the maximum they were allowed to reclaim, after making her swear affidavits that she knew nothing of his deception. ‘No one knows how Pa managed to elude income tax on so many items,’ she wrote to Dirac, who heard that his father had claimed £50 a year tax relief for educating Betty at university, while his son paid the bills.31 But the nastiest revelation for Dirac was still to come, when he learned that the funds that enabled him to begin his studies at Cambridge had been provided not by his father but by the local education authority. Charles had pretended that he had stumped up the money. This petty and unpleasant deception was, for Dirac, the final straw. It negated everything that his father had done to nurture his career and revealed Charles in his true colours. This was why Paul Dirac told his closest friends, including Kurt Hofer, that he owed his father ‘absolutely nothing’.32 It was an understandable, if harsh, judgement.

  After her marriage, Betty left England to live with her husband Joe, who owned and ran a flourishing camera shop in Amsterdam. Within a year they had a son, but their happiness was soon blighted by the news from Berlin, where Hitler was seeking ‘living space’ outside Germany and was thirsty for Jewish blood. It would not be long before the Teszlers would feel the full force of Hitler’s ambitions.

  At the High Table in St John’s, everyone was talking about the German Chancellor and the pell-mell rush towards another global conflict. The only European country then openly at war was Spain, where Hitler supported Franco’s fascist army; the British Government refused to take sides, outraging socialist opinion, particularly in Cambridge, from where many idealists journeyed to support Franco’s opponents. Dirac’s eyes were, as usual, focused on the Soviet Union. That the country was suffering from an unconscionably bloody purge was clear to newspaper readers in Britain, but it appears that Dirac – like many others on the left – thought the reports were exaggerated. In Moscow, Kapitza was not aware of the extent of Stalin’s murderous rampage; even so, he knew that several of his colleagues were being harassed and that he risked deportation to a labour camp if he complained, though the censors did not allow him to mention this in his letters.33

  In the early summer of 1937, when the Diracs were in Budapest to see her family, Manci wrote to Oswald Veblen and his wife. ‘Paul would like very much to go to Russia, but everybody advises him not to.’34 Dirac insisted on making the visit and wanted to take his family, but Hungarian regulations allowed only Manci to accompany him. Kapitza confirmed the arrangements in a telegram intercepted by MI5, still checking mail he was sending to Cambridge.35

  At the end of July, during an oppressively hot summer, the Diracs arrived at the Kapitzas’ summer home days before Stalin authorised the torture of suspected enemies of the people. Only a short drive away, his henchmen were gouging out the eyes of their victims, kicking their testicles and forcing them to eat excrement. On the roads around Bolshevo, some of the trucks marked ‘Meat’ and ‘Vegetables’ hid prisoners on their way to be shot and buried in the forests to the north of the city which Dirac admired through his binoculars.36 For many years, Soviet people would refer darkly to ‘the year 1937’, the height of the Great Purge, Stalin’s chaotic and brutal campaign of mass intimidation, imprisonment and murder.37 By the end of the year, the purge had claimed about four million lives. As Kapitza knew, one of the victims was Boris Hessen, a member of the delegation that had visited London and Trinity College six years before. Five of his fellow visitors would also soon be executed. Now confined to the Soviet Union at Stalin’s behest, Kapitza had received all his equipment from the Cavendish Laboratory and had resumed his research.

  The Diracs spent three idyllic weeks in Bolshevo with the Kapitzas in their modest summer house in the heart of a pine forest, with wild strawberries ripe for gathering and a fast-flowing river close by. They spent one languorous day after another lounging around on the covered veranda, telling off-colour jokes, the Diracs bringing the latest news on the Crocodile and his departing ‘boys’, the Kapitzas gossiping about life under Stalin. The two men took advantage of the cool mornings to do some manual labour – chopping down trees and clearing shrubs close to the house – and messing around with the boys. Manci, always as soignée as a duchess, wanted nothing to do with physical exercise and avoiding cooking anything more complicated than a boiled egg. Dismayed by the dacha’s lack of creature comforts, including toilet paper, she could scarcely believe that, for the first time in her life, she had to sleep outside, in a tent. But she was too polite to gripe: she shone in conversation and won over Kapitza, who saw that she had opened Dirac up. He wrote to Rutherford: ‘It is great fun to see Dirac married, it makes him much more human.’38

  Kapitza will almost certainly have enthused about the new institute being built for him. He was dealing adroitly with the authorities, bombarding them with complaints but always avoiding confrontation and keeping on the right side of the power brokers. In return, he was given unusual leeway to employ the staff he wanted and to allocate funds as he saw fit, with a minimum of bureaucracy.39 In the following year, he was even able to hire Lev Landau as the institute’s resident theoretician after he had been arrested in Moscow, having fled the Kharkov police, in fear of his life.40 Kapitza had resumed the experiments he had begun in the Mond Laboratory and had successfully liquefied helium the previous February. Exciting new results were afoot.

  Kapitza persuaded Dirac to demonstrate his support of the Russian experiment by sending his next paper to the Bulletin of the Soviet Academy of Sciences, in commemoration of the twentieth anniversary of the Bolshevik revolution. In the article, he investigated the symmetries underlying classical and quantum descriptions of matter, following the lead given by his brother-in-law Wigner. It was another elegant piece of work, though it produced no useful results and appeared to be more evidence that Dirac was losing his touch.

  The Diracs and Kapitzas knew they were in uncertain times but could scarcely have guessed that they would not sit around the same dinner table again for another twenty-nine years.

  At noon on 25 October 1937, Dirac stood among two thousand mourners in Westminster Abbey, probably wondering whether to join in the prayers and hymns or stay silent. He was at the memorial service for Rutherford. Nine days before, two weeks after the beginning of the autumn term, he had died after complications arising from surgery on his umbilical hernia: Cambridge was rife with rumours of a botched operation. Within days, government officials agreed that he was eligible to be commemorated in the ‘science corner’ of Westminster Abbey, alongside Newton, Darwin and Faraday. The funeral service was a national event, attended by a representative of the King, members of the cabinet, the former prime minister Ramsay MacDonald, eighty Cambridge scientists, and several foreign guests.41 Bohr stayed with the Diracs and joined the Rutherford family party for the event, which ended when an official placed a small urn of the great experimenter’s ashes a few inches from Newton’s grave.

  Two days after the service, Dirac wrote a consoling note to Kapitza, also grieving from the recent death of his mother. In his reply, Kapitza did not mention that the Crocodile’s death occurred just as he was making his most exciting discovery – at sufficiently low temperatures, liquid helium could flow entirely without re
sistance to its motion. Such ‘superfluid’ helium could climb spontaneously up the walls of its container and behave in other strange ways that were beyond classical mechanics but which later were explained by applying quantum mechanics to the constituents of the fluid. Nature published Kapitza’s results in a December issue, alongside a paper by two Mond experimenters who also announced the discovery of superfluidity: although Kapitza had spent two years without laboratory equipment, he had already caught up with the leaders in his field. It was no longer so easy for his detractors to sneer that he was really just a self-promoting lightweight.

  Worried that the future of the Cavendish was in danger, Kapitza wrote to Dirac to enjoin him to take an active interest in securing the laboratory’s future: ‘I think that you who are now the leading personality in physics in Cambridge, you must take some serious interest in upkeeping the great traditions of the Cavendish Laboratory, so important for all the world.’42

  But such a role was beyond Dirac – and, besides, he had no interest in it. The directorship of the Cavendish passed to the crystallographer Sir Lawrence Bragg, who steered the laboratory away from studies of the innermost structure of matter, partly because it could no longer keep up with the competition from the United States. With Rutherford’s passing, the Cavendish had seen the last of its glory days as a place where experimenters probed atoms with the finest possible probes, though Bragg steered the laboratory’s agenda into productive territory, culminating in Watson and Crick’s discovery of the double-helix structure of DNA in 1953.