The Strangest Man

by Graham Farmelo

  He did not oppose honours on principle, but he believed that they should be awarded on merit, and not be awarded to athletes and show-business celebrities. When the jockey Gordon Richards was awarded a knighthood by the Queen, Dirac shook his head: ‘Whatever next?’10

  Fundamental physics appeared to be in a mess, just as bad as the one in the early 1920s when Bohr’s theory was the creaky framework for atomic physics. Having seen theory swept aside by quantum mechanics, he believed that nothing less than a similar revolution was needed now to replace quantum electrodynamics. Dirac wanted the initiative to come from theorists: since he was a boy, they had been setting the agenda of physics, but now experimenters were ensconced in the driving seat.

  Results from cosmic-ray projects and from the new high-energy particle accelerators had shown that the subatomic world was much more complicated than any theoretician had imagined. By the mid-1950s, it was plain that there were many more than two subatomic particles – there were dozens or even hundreds, most of them living for no longer than a billionth of a second, before they fall apart into stable particles. All these decay processes obeyed the laws of quantum mechanics and relativity, but no one knew how to apply them. Fermi had set out the first theory of the weak interaction, which acts only over very short distances, within the ambit of a nucleus, about a ten-thousandth of the distance across an atom. By then, another fundamental type of interaction had emerged, the strong interaction, which also extends only over distances on the scale of the atomic nucleus. Much stronger than the electromagnetic force, the strong force binds the protons and neutrons in the atomic nucleus and prevents the protons from repelling each other. Without this force, stable atomic nuclei could never have formed, and ordinary matter would not exist.

  Nature seemed unwilling to disclose its deepest secrets: when experimenters probed strong interaction, they found it all but incomprehensible. But, like Einstein, Dirac did not trouble himself with the complications introduced by the new interaction. In his opinion, there was no point in paying much attention to them until electrons and photons had been properly understood in the context of a mathematically defensible theory. While most others moved on, he remained – in their view – transfixed by an obsolete view of physics, hidebound.

  Oppenheimer had also retreated from the front line of research. He was a prominent adviser to the Eisenhower administration on nuclear policy, uneasy that so many aspects of the research were kept secret under the pretext of national security; he preferred Bohr’s view that superpowers should, like scientists, share their knowledge as a matter of principle. In a perceptive speech in February 1953, Oppenheimer startled a closed meeting of the Council on Foreign Relations by likening the USA and the USSR to ‘two scorpions in a bottle, each capable of killing the other, but only at the risk of his own life’.11 He believed that, despite the superpowers’ posturing and bluster, reason would prevail.

  Shortly before midnight on 14 April 1954, Dirac arrived home in Cambridge after spending a month with his stepson Gabriel in Vienna. Dirac had visited him every afternoon at the Viktor Frankl Institute, where he was being treated for psychiatric disorders, including a persecution complex and schizophrenia. Dirac had written to tell Manci of the doctors’ assessment: Gabriel had been ‘badly brought up’.12 Soon after he arrived home that night, Dirac would have told his wife of her son’s progress, and they may well have discussed the news that had broken in European newspapers that day: the American Government had withdrawn Oppenheimer’s security clearance.

  The Oppenheimer case was the climax of the anti-Communist paranoia in 1950s America. It had begun with the start of the Cold War and intensified in the late summer of 1949, when the Soviet Union tested its first nuclear weapon at least two years earlier than the Central Intelligence Agency (CIA) expected from its intelligence reports.13 The USA, terrified that its technological primacy would be eclipsed by the Soviet Union, feared that Communists held important positions in public life. An early victim was Oppenheimer’s popular brother Frank, an experimental physicist who had been fired in 1949 by the University of Minnesota when it found out that he was a card-carrying Communist (a few weeks afterwards, Dirac tried to find him a post at the University of Bristol).14 In early February 1950, there was a national outcry when Klaus Fuchs – Dirac and Peierls’ collaborator during the war, later a member of the Manhattan team – confessed to having passed critical secrets to the Soviet Union, an act of espionage that had been responsible for the unexpectedly early detonation of the Soviet nuclear weapon. J. Edgar Hoover called Fuchs’ treachery ‘the crime of the century’.15 After the revelation, Dirac and Peierls came up with an explanation of Fuchs’ peculiar behaviour during his conversations with them in the back garden of 7 Cavendish Avenue – he had been passing notes on the conversation to a Soviet intermediary. Eighteen days after Fuchs had been unmasked, the Wisconsin Republican Joseph McCarthy stoked up the febrile anti-Soviet rhetoric in the press when he claimed, in a six-hour speech on the Senate floor, that Communists infested the entire government apparatus. When Bohr complained about the apparently unending deluge of insults in the newspapers, Dirac told him not to worry as it would end in a few weeks because, by then, the reporters would have used up all the invective in the English language. Bohr shook his head, incredulous.16

  In June 1952, the Senate passed an Immigration Act that obliged applicants for US visas to list all their past and current memberships of organisations, clubs and societies. Decisions about whether to grant visas were usually left to consuls, most of them nervous of being seen as ‘soft on Commies’. No record of Dirac’s submission survives. It is most likely that he would have been open with the American authorities about his relatives behind the Iron Curtain in Hungary and his association with left-leaning organisations before the war. He may also have mentioned that he signed a petition two years before to deplore Bernal’s expulsion from the Council of the British Association for the Advancement of Science, after Bernal had made a scathingly anti-Western speech in Moscow.17 That signature had been noted by MI5.18

  Soon after Oppenheimer’s hearing began, on the rainy Monday morning of 12 April in Washington DC, he realised that he was being subjected not to an enquiry but to a kangaroo court. The FBI had illegally tapped his and his attorneys’ phones, forwarding transcripts to the prosecuting lawyers to help them prepare for the next day’s proceedings. 19 During the second weekend break in the hearing, Oppenheimer read a pessimistic note from Dirac, who was planning to visit the institute for a year, beginning in the following summer. There was, Dirac believed, little chance that the US Government would grant him a visa.20

  The enquiry closed on 5 May, and Oppenheimer returned to Princeton tired, depressed and irritable. He knew that it had gone badly: under ferocious cross-examination he had been evasive, mendacious and sometimes even disloyal to his friends. One of the most damning testimonies had been delivered by Edward Teller, who had been angry with Oppenheimer for not making him head of the Manhattan Project’s theory group and, in his opinion, for delaying his pet programme to build the first hydrogen bomb. Teller declared that, ‘if it is a question of wisdom and judgement, as demonstrated by actions since 1945, then I would say that it would be wiser not to grant [Oppenheimer] security clearance’. Immediately after Teller left the witness stand, he offered his hand to a stunned Oppenheimer, who took it. ‘I’m sorry,’ Teller said.21

  When Oppenheimer was waiting for the board’s verdict, he received a letter from Dirac: ‘I regret to have to tell you that my application for a US visa has been refused.’22 On both sides of the Atlantic, news of the refusal broke on 27 May 1955, most of the articles declaring or hinting that Dirac’s Russian connections had been the cause. Among the journalists who called at 7 Cavendish Avenue was Chapman Pincher, the well-connected Daily Express security correspondent. Manci told him, with more pith than accuracy, ‘My husband has no political interests,’ a phrase that Pincher included in a brief article in the Express (‘US-Barred Scientis
t “Not Red”’).23 A reporter from the New York Times somehow managed to interview Dirac and was told that his application had been ‘turned down flat’: the American Consul had told him he was ineligible for a visa under Regulation 212A, without specifying which of the points specified in its five pages he had transgressed.24 Dirac was uncharacteristically decisive: he asked the British Government to release him from all defence work and started to make arrangements to change the location of his sabbatical to the Soviet Union.25 He appeared to be cocking a snook at the American authorities, but he made no comment.

  A month later, Oppenheimer heard the outcome of his ‘hearing’: the Board voted two to one that he was a loyal American, though nevertheless a security risk. To ram home their victory, his enemies in the Atomic Energy Commission withdrew his security clearance a day before it was due to expire. Oppenheimer was shattered, and he considered emigrating to England to take up a professorship in physics at Cambridge University, an offer that he discussed with Dirac.26 His fiercely loyal wife, who had given one of the powerfully supportive testimonies during the hearing, became an alcoholic and remained one for the rest of her life. After a family vacation in the Caribbean, where he was watched by FBI agents suspicious that a Soviet submarine might whisk him back to Russia, he returned to the institute. His eloquence and appetite for his work were undiminished, though many of his colleagues thought his spirit was broken. He looked less like the blazingly confident scientist, an American hero after the Manhattan Project’s success, than a scientific martyr, the Galileo of the McCarthy era.

  Three days after the New York Times announced the Oppenheimer verdict as the lead story on its front page, it printed a short report on Dirac’s case, featuring quotes from an interview with Dirac, printed below a photograph that made him look like a criminal. Embarrassed and angry, senior American physicists seized on this latest of many rejected visa applications from top scientists, and it became a cause célèbre. Two days after the report was published, John Wheeler and two Princeton colleagues fired off a letter to the newspaper, deploring the Government’s action: ‘[we] believe this action is exceedingly unfortunate for science and this country’, adding that the Act that led to the refusal of Dirac’s visa ‘seems to us a form of organized cultural suicide’.27 Dozens of other physicists turned the screws on the State Department and the American Consulate in London, who blamed each other for the outcome of the decision, which had been ‘close’, they told journalists. Within two weeks, the New York Times reported that the State Department was reviewing the ban; a humiliating climb-down looked certain and was duly announced on 10 August. But it was too late: Dirac had made other arrangements.

  Dirac’s plans for a sabbatical in Russia fell through, so he accepted a long-standing invitation to visit India. At the end of September 1954, Dirac and his wife set sail for Bombay, the first stage of their round-the-world trip, scheduled to last almost a year. The Diracs arranged for their friends Sol and Dorothy Adler to stay in 7 Cavendish Avenue to look after Mary and Monica, both anxious and dreading their parents’ long absence. Monica, then twelve years old, cannily observed one important reason why her parents were going far away: Manci believed that Dirac had a female admirer who was showing him rather too much affection, so she wanted him away from Cambridge for as long as possible.28 Dirac may well have wanted to see something of the country described to him in the fireside reminiscences of his confidante Isabel Whitehead, who had died in the previous year, six years after her husband.

  The Diracs’ four-month stay in India was organised by the physicist Homi Bhabha, Dirac’s former colleague in Cambridge and founding director of the Tata Institute in Bombay.29 He was exceptionally cultured, an exhibited artist and a connoisseur of poetry in several languages. Bhabha made sure that the Diracs were treated like royalty from the moment they arrived on 13 October, though he could do nothing about Bombay’s unbearable heat and humidity, which quickly drove them to depart for the comparative cool of the Mahabaleshwar Hills nearby.30 Manci disliked much more than the climate: she hated the spicy food and the chauffeur-driven rides through vast, stinking vistas of destitution and squalor; nor did she appreciate being treated as a second-class celebrity, her husband’s consort. The experience did, however, give her a glimpse of the respect and reverence that she would later expect, and a little of this taste for glamour later appeared to have rubbed off on Dirac.31 For the first time in his life, he felt the adulation of a mass crowd when he gave a public lecture during the evening of 5 January 1955 as part of the Indian Science Congress in Baroda, near Calcutta. In a special enclosure at Baroda cricket ground, he delivered his talk to thousands of wide-eyed spectators, many of them watching the presentation on a cinema screen outside the ground.32

  Perhaps having learned from the debacle at Le Palais in Paris, Dirac had found a way of talking to people who wanted to learn about quantum physics but who knew nothing about it. Shedding his dislike of metaphor and visual imagery in descriptions of the subatomic domain, he spoke in simple, equation-free language and introduced a simile, later given wide currency, to link subatomic particles with his favourite game:

  When you ask what are electrons and protons I ought to answer that this question is not a profitable one to ask and does not really have a meaning. The important thing about electrons and protons is not what they are but how they behave – how they move. I can describe the situation by comparing it to the game of chess. In chess, we have various chessmen, kings, knights, pawns and so on. If you ask what a chessman is, the answer would be [that] it is a piece of wood, or a piece of ivory, or perhaps just a sign written on paper, [or anything whatever]. It does not matter. Each chessman has a characteristic way of moving and this is all that matters about it. The whole game of chess follows from this way of moving the various chessmen […]33

  The physicists in the front row as well as the non-experts in the audience gave a warm reception to Dirac’s forty-minute summary of the fundamentals of quantum mechanics. Though he had none of Eddington’s verve as a populariser, it was clear that he had somehow acquired the skill vital to scientists who detest administration and who are well past their peak as researchers: the ability to share his work with the public.

  Most eminent among the politicians Dirac met in India was its charismatic Prime Minister, Jawaharlal Nehru, who had led India since its independence from Britain in 1947. Although he had the politician’s talent for casting broad-brush thinking in colourful, populist language, Nehru was also a cultured thinker who would lighten a quarrel by quoting the poetry of Robert Frost. During the meeting in Delhi with Dirac on 12 January 1955, Nehru asked him if he had any recommendations for the future of the new republic of India. After his usual reflective pause, Dirac replied: ‘A common language, preferably English. Peace with Pakistan. The metric system.’34 The men apparently did not discuss nuclear weapons, though the subject was on their minds. Eleven days before, at the Science Congress in Baroda, Dirac heard Nehru lecture scientists about the imperative to help with the reality of the new weapons, commenting that ‘We are not playing with atomic bombs at present.’35 With Nehru’s support, Bhabha would later spearhead plans for India’s programme and become his country’s Oppenheimer.36

  Two weeks after the Diracs sailed from Bombay on 21 February 1955, the trip turned unpleasant. After contracting jaundice, Dirac spent eight days in hospital in Hong Kong, where his doctor agreed to allow him to sail on to Vancouver, though with a litany of health warnings and dietary instructions.37 Manci thought he should not travel, but he insisted and paid dearly for his obstinacy by spending most of the voyage in bed, sick with jaundice, vomiting every few hours, plagued by itches, sometimes unable to sleep through the night.38 When the Diracs sailed into Vancouver in mid-April, he was exhausted and dispirited, his skin a pale shade of yellow.39 The University of British Columbia accommodated them on one storey of a finely appointed mansion, where he immediately took to his bed.

  Two days later, he heard the news from Prin
ceton that broke his heart: Einstein had died. For the first time, Manci saw him weep – a sight she had never seen before and would never see again.40 It was for a hero, not a friend, that Dirac shed those tears. During those first hours of grief, he may have recalled his student days in Bristol when he first became acquainted with relativity theory, which inspired him to be a theoretician. What mattered most to Dirac were Einstein’s science, his individualism, his indifference to orthodoxy and the ability he demonstrated later in life to ignore his critics’ catcalls, muted only by timidity and cowardice. After Einstein’s ashes had been scattered into the New Jersey winds, Dirac succeeded him as the most famous loner in theoretical physics, an elderly rebel with a cause that no one else could quite understand.

  Sick, depressed and believing he was dying, Dirac told Manci that he had just one request: to see Oppenheimer. She quickly succeeded in bringing together the two friends in the Vancouver apartment, each of them broken, each at their nadirs, each looking fifteen years older than when they last met. No record of their conversation remains, but it is likely that Dirac’s main wish was to commiserate with Oppenheimer over the outcome of the trial and, perhaps, over the conduct of Teller and the prosecutors. Teller, a pariah to many of his former friends, had become one of the few physicists Dirac disliked and would criticise, if only to those close to him.41 Oppenheimer was at his considerate best: he advised Dirac to get treated in the USA and to recuperate for a few weeks in one of the apartments at the Institute for Advanced Study.