Dirac’s other work for Peierls and his group in Birmingham consisted of theoretical investigations into the behaviour of a block of 235U if a nuclear chain reaction took place inside it. These calculations probed in detail the energy changes going on inside such a block of material and investigated whether the growth of neutrons would change if the uranium were enclosed in a container. Dirac was happy for his results to be shared with the American scientists who were working on the bomb, including Oppenheimer, who by the end of 1942 had been appointed the Scientific Director of what became known as the Manhattan Project. Oppenheimer excelled at nurturing young theoreticians in Berkeley, but most of his colleagues were surprised when General Leslie Groves – the Project Director, appointed by Roosevelt – asked him to take on responsibility for building the bomb. One of Oppenheimer’s Berkeley colleagues chortled, ‘He couldn’t run a hamburger stand.’14 Just as surprising was the authorities’ decision to appoint someone who, although a brilliant researcher and teacher, was well known to be a fellow traveller of the Communist Party.
Dirac worked mainly in his study, the one room in 7 Cavendish Avenue for which only he had the key, allowing in cleaners on the strict condition that they did not move any of his papers. If he saw any sign at all that his desk had been disturbed, he flew into a wordless rage.
The children were proving to be a handful. Dirac and Manci may well have been alarmed when Gabriel, soon after he began his mathematics degree in Cambridge, joined the Communist Party, though he kept up his membership for only six months.15 Judy was less academic and more rebellious: when she was sixteen, in 1943, Manci furiously ordered her out of the house and threw her clothes out of her bedroom window.16 Although she was allowed home a few days later, relations with her parents did not improve. Manci, always trying to enforce strict discipline, was frustrated by the feeble support she was given by Dirac – when she needed him to back her up in some altercation with one of the children, he retired sheepishly to his study or escaped to his garden. He spent hours tending his rhododendrons and gardenias, pruning his apple trees, sewing seeds and digging up asparagus, carrots and potatoes to help fill the larder. In the summer, he would shield his balding head from the sun by wearing a handkerchief knotted at each of its four corners.17 Friends noticed that he practised horticulture using the same top-down methods that he used in theoretical physics, trying to base every decision on a few fundamental principles.18 He stressed that the best way of ripening apples was to place them in linear rows, each item of fruit separated from its neighbour by precisely the same distance. In one project, he coated pea seeds with dripping and rolled them in red lead oxide powder to discourage birds from eating the newly emerged seedlings, a practice that would today induce palpitations in any self-respecting health and safety inspector.
Dirac’s heart remained in quantum mechanics. In July 1942, he took time off from war work, left his family at home and travelled with Eddington to attend a conference in Dublin organised by Schrödinger, who tried to tempt Dirac to accept a job alongside him. ‘There is plenty of food here – ham, butter, eggs, cakes, as much as one wants,’ he wrote in one of his fond letters to Manci.19 The Irish Prime Minister Éamon de Valera, a trained mathematician who had helped bring Schrödinger to Ireland, took the two guests on a joyride around the local countryside, having met them during the conference. Dirac had been amazed to see him there, attending lectures and taking detailed notes.20
On 29 September, six weeks after his return to Cambridge – still under attack from Nazi bombers – Manci gave birth to a daughter, Florence, named after Dirac’s mother, though she was always called by her second name, Monica. Two days after her birth, Dirac received a letter from Peierls gently enquiring, at the request of the project directorate, if he would be prepared to move from Cambridge to work full-time on the war effort.21 Predictably, Dirac refused.
His family was now complete. He never had a son of his own, a disappointment Manci later described as one of the saddest of his life.22
Dirac saw in Cambridge evidence of the prominent role the USA was now taking in the war. Every day, hundreds of uniformed American servicemen – on leave from the nearby airbases – walked the streets of Cambridge, with plenty of money to spend. They organised baseball games and, in November 1942, were visited by the stately Eleanor Roosevelt.23 At home, Dirac received intelligence reports of the American-led experiments to build a nuclear bomb and, towards the end of the year, heard that a key experiment in the programme had been completed. In a makeshift laboratory built in a disused squash court in Chicago, Enrico Fermi and his team had built a nuclear reactor, and, in the mid-afternoon of 2 December 1942, they got it working for the first time. They had arranged a self-sustaining nuclear chain reaction, releasing energy at a rate of half a watt.24 Wigner presented Fermi with a bottle of Chianti, which he shared in silence with his team, who had good cause to celebrate but also to be nervous: for all they knew, Hitler’s scientists were ahead of them. A member of Fermi’s team, Al Wattenberg, later recalled: ‘The thought that the Nazis might get the bomb before us was too terrifying to contemplate.’25
Shortly before, Peierls asked Dirac to study a sheaf of technical papers written by Oppenheimer and his Manhattan colleagues describing the explosion of a sample of uranium undergoing fission. Early in January, Dirac pointed out inconsistencies in the papers and discussed how a nuclear bomb might be constructed, including the optimal shapes of the two masses of uranium that could be propelled together to make the bomb. During the next six months of 1943, Dirac investigated theoretically the passage of neutrons in a fissioning block of uranium and presented his results in two reports, one of them in collaboration with Peierls and two of his younger Birmingham colleagues. One of them was Peierls’ lodger, Klaus Fuchs, a Bristol-educated refugee from Nazi Germany, an inept but courteous young man in his early twenties. When he and Peierls visited 7 Cavendish Avenue to talk about their secret research with Dirac, they all adjourned to the middle of the lawn in the back garden to ensure that they were out of earshot of everyone near by.26 Manci, asked to stay inside the house, resented what she knew was the implication: she was a potential eavesdropper. During some of these al fresco discussions, Dirac and Peierls noticed that Fuchs sometimes behaved oddly, complaining that he was unwell and leaving them for surprisingly long periods before returning.27 It would be another seven years before Dirac and Peierls understood Fuchs’ behaviour.
The collaboration between the scientists working on the bomb in the USA and their counterparts in Britain was tense and difficult, but the problems were apparently resolved in the late summer of 1943, after peace-making conversations between Roosevelt and Churchill. It was obvious to most of the British scientists that they should join the Manhattan Project, and about two dozen of them – including Peierls, Chadwick, Frisch and Cockcroft – joined Oppenheimer and his team in their Los Alamos headquarters in the New Mexico desert.28 Through Chadwick, Oppenheimer asked Dirac to join the Manhattan team, but he declined.29 About a year later, he stopped working on the project, but never fully explained why. Peierls later suggested, probably correctly: ‘I believe this was because he was beginning to feel that atom bombs were not a matter he wanted to be associated with, and who could blame him?’30
Dirac may have come to believe that the Nazis could be defeated without nuclear weapons. Or perhaps Dirac was influenced by Blackett, who protested that American scientists on the Manhattan Project were given access to all the research done by their British colleagues but did not reciprocate, except with Chadwick, the only Briton to be given full security clearance. Blackett felt so strongly about this that he tried to persuade his British colleagues to take no part in the Manhattan Project.31
On the night of 5 November 1943, the Luftwaffe dropped their bombs on Cambridge for what turned out to be the last time. Since the outbreak of the war, the sirens had sounded 424 times to warn of the bombings that had killed thirty people and destroyed fifty-one homes.32 As the nights closed in
, Dirac and his family were hoping that the blackout would end soon, but the authorities did not lift it until September in the following year.33 By then, he was worrying constantly about his sister Betty and her family. At Dirac’s request, Heisenberg had attested to the occupying Nazis that she was not Jewish, but Joe and their son were still in grave danger.34 When Dirac last heard from them, in early September 1943, they had recently fled their home in Amsterdam – a short tram ride from Anne Frank’s secret annex – after the Nazis told Joe that he could either be sterilised or interned in Poland. He probably knew that internment was tantamount to a death sentence, so the family headed for Budapest, hoping that it would quickly be liberated by the Allies.35
Powerless to help Betty, Dirac sat out the end of the war at home. Several of the family photographs taken around this time show him in his back garden, sitting in a deckchair, teaching Mary to read from The Wizard of Oz. One of her earliest memories was of her father spelling out the letters D-o-r-o-t-h-y.36 She and Monica were given a disciplined upbringing, following the motto of English family life, ‘Children should be seen and not heard,’ but without any exposure to religious ideas.37 Yet Dirac appears to have had at least some regard for religion as he and Manci followed the convention of having both their daughters christened.38 Probably as a result of his wife’s influence, the hard-line atheist had softened his line.
Try as Dirac might to concentrate on quantum physics when he was in college, the continuing presence of the military reminded him that although victory over Hitler was in sight, it could not be taken for granted. Royal Air Force officials still occupied much of the college, and the military had taken over the Combination Room for purposes they kept secret.39 Only much later did the Fellows of St John’s find out that the room contained a huge plaster model of the stretch of the Normandy coastline on which Allied troops landed on 6 June 1944. Churchill’s leading general, Montgomery, believed the end of the war was in sight and didn’t believe the Germans could go on much longer. Yet still Dirac could not walk over the Bridge of Sighs without being challenged. When the sentry asked, ‘Who goes there?’, he was satisfied with only one reply: ‘Friend.’ Dirac knew the threat still posed by the enemy better than most. Even when victory looked inevitable, from June 1944, Dirac was aware that German scientists, including Heisenberg, might already have developed a nuclear weapon. About a year before, he had heard from the refugee Norwegian chemist Victor Goldschmidt that Heisenberg was working on the Germans’ counterpart of the Allies’ Tube Alloys project. Dirac knew that the fate of hundreds of potential victims could depend on the scientific success of his closest German friend.40
While he waited for the war to end, Dirac began work on another edition of his book. His main innovation this time was to introduce a new notation he had first invented shortly before the war broke out. This system of symbols enabled the formulae of quantum mechanics to be written with a special neatness and concision: just the sort of scheme that Dirac had learned to appreciate in Baker’s tea parties.
The centrepiece of the notation was the symbol ; together they can be combined to form mathematical constructions such as
, a bracket. With his rectilinear logic, Dirac named each part of the ‘bracket’ after its first and last three letters, bra and ket, new words that took several years to reach the dictionaries, leaving thousands of non-English-speaking physicists wondering why a mathematical symbol in quantum mechanics had been named after an item of lingerie. They were not the only ones to be flummoxed. A decade later, after an evening meal in St John’s, Dirac was listening to dons reflecting on the pleasures of coining a new word, and, during a lull in the conversation, piped up with four words: ‘I invented the bra.’ There was not a flicker of a smile on his face. The dons looked at one another anxiously, only just managing to suppress a fit of giggling, and one of them asked him to elaborate. But he shook his head and returned to his habitual silence, leaving his colleagues mystified.41
The war in Europe ended in anti-climax on 8 May 1945. The relief felt like a national exhalation. In the centre of Cambridge, thousands gathered in Market Square in the blazing heat of the afternoon, dozens of Union Jacks fluttering limply in the breeze. After the Lord Mayor’s speech, two bands marched separately round the town, each followed by hundreds of people, with dozens of couples dancing cheek-to-cheek in the streets. The authorities in St John’s College abandoned all formalities for the day: the Combination Room swelled not only with Fellows but with dozens of normally excluded undergraduates raising their glasses to the new peace.42 Dirac and his family celebrated with neighbours at an impromptu tea party in a local street, munching on scones and spam sandwiches served from trestle tables.43
If Dirac believed that science would quickly return to normal, he was mistaken. In the spring of 1945, he and seven colleagues – including Blackett and Bernal – applied for visas to enable them to attend the June celebrations of the 220th anniversary of the USSR Academy of Sciences; for Dirac, the trip would give him the opportunity to see Kapitza and other Russian friends again. But Churchill refused to allow visas to be issued on the grounds, it was later revealed, that Dirac and his colleagues might share with Stalin’s scientists some of the nuclear secrets kept from the Soviets during the war.44 During a discussion about the matter at the Admiralty in London, Blackett lost his temper and strutted magnificently out of the building, furious that the Government had dared to impugn his integrity.45 Dirac was angry, too, but showed his emotion only by withdrawing into complete silence and talking a long, solitary walk.46
For several weeks after the end of the war in Europe, news had been seeping out about the Nazi concentration camps. Manci was outraged not only with the Germans but also with ‘these dirty Poles’ – she was sure they had connived in the atrocities. She wrote to Crowther that she had one of her rare rows with Dirac, apparently because his reaction to the revelations of unconscionable cruelty was too restrained for her taste.47 The Diracs knew that several of Manci’s relatives had probably been murdered in the camps and that Betty’s husband Joe might also be dead. News of him arrived in a telegram delivered to the Diracs’ home at the beginning of July, when they were preparing to visit the Schrödingers in Dublin.48 Joe was alive. In Budapest, he had fallen into the hands of the Nazis, who dispatched him to the Mauthausen-Gusen concentration camp in Austria, where he was one of thousands forced to work in the Wiener Graben quarry, mining granite with a pickaxe and carrying the slabs up the hundred and eighty-six steps to the top.49 Many of his fellow prisoners perished from the freezing cold, were worked to death or were summarily shot through the neck by SS guards after being injured or collapsing from exhaustion. After the camp was liberated in the summer of 1945, he emerged looking close to death – desperate for a morsel of food and with a broken wrist, a seriously infected kidney and missing a finger.50 While recuperating in an American military hostel in France, desperate for news of Betty and their son Roger, he wrote to Manci to suggest that Kapitza might help to find her, as the Russians had taken over Hungary. He did not have to wait long to hear the denouement: in early September, he heard from Manci that Betty and Roger were safe.
On 6 August, Dirac heard the news he had been dreading: with the tacit agreement of the British Government, the Americans had dropped a nuclear bomb on Hiroshima, killing about forty thousand Japanese civilians. At nine o’clock that evening, Dirac was in his front room listening to the radio news bulletin: ‘Here is the news: it’s dominated by the tremendous achievement of Allied scientists – the production of the atomic bomb. One has already been dropped on a Japanese army base. It alone contained as much explosive power as two thousand of our great ten-tonners.’51
After reading official statements, including one from Churchill and President Truman, the BBC announcer ended with almost comic bathos: ‘At home, it’s been a Bank Holiday of sunshine and thunderstorms; a record crowd at Lords has seen Australia make 273 for five wickets.’52 All was
well again – cricket had resumed. The national press rushed to praise the achievement of the leading British scientists, including Cockcroft and Darwin, who had helped to design the bomb. None mentioned Dirac, probably to his relief. One of the few civilians who were not shocked by the destructiveness of ‘the atomic bomb’ was the seventy-nine-year-old H. G. Wells, who first coined the term in 1914. On 9 August, just as President Truman ordered the dropping of another nuclear bomb on Nagasaki, the Daily Express published a weary personal perspective on the age he had foreseen.53 He died a year later.
On 14 August, when news reached Britain of Japan’s surrender, public euphoria resurged, and, in Cambridge, Market Hill swelled with an encore of the VE Day celebrations.54 In the USA, the press showered Oppenheimer with praise and likened him to Zeus. He was the triumph of physics personified.55
Dirac had no idea that, only fifteen miles from Cambridge, Heisenberg had been interned by the British Secret Service with nine other German scientists in Farm Hall, a red-brick Georgian House on the outskirts of the village of Godmanchester.56 They were treated well – given the run of the house, provided with daily newspapers and allowed to walk freely around the grounds, though they were warned that their liberties would be curtailed if any of them tried to escape. A few days after their arrival, Heisenberg wondered why the authorities were keeping him and his colleagues interned without making it public: ‘It may be that the British Government is frightened of the communist professors, Dirac and so on. They say “If we tell Dirac or Blackett where they are, they will report it immediately to their Russian friends, [like] Kapitza”.’57
The Strangest Man Page 47