Inside the Centre: The Life of J. Robert Oppenheimer (98 page)

Dyson’s time at the institute, on the other hand, despite his acrimonious spat with Oppenheimer, was a triumph, and, in fact, Oppenheimer became one of his leading admirers and supporters. Before submitting for publication the report he gave at the Solvay Congress, Oppenheimer rewrote it, adding to it several mentions of Dyson’s paper on Feynman, Schwinger and Tomonaga (which he describes as being ‘in press’) and drawing attention to Dyson’s own original contributions to the theory that – Oppenheimer’s temporary doubts notwithstanding – had so captured the imaginations of physicists during the latter part of 1948. On 30 December, Oppenheimer wrote to Peierls in Birmingham:

In January 1949, Dyson went with Oppenheimer to New York to attend the annual meeting of the American Physical Society, of which Oppenheimer had recently been elected president. On the first day of the meeting, Dyson wrote to his parents, he received confirmation of his own celebrity when a young physicist from Columbia gave a talk during which he repeatedly referred to the ‘beautiful theory of Feynman–Dyson’. The next day, Dyson recalls, ‘Oppenheimer gave a presidential address in the biggest hall’:

It was not only Oppenheimer whose interests were moving away from Schwinger and towards Feynman and Dyson; the whole physics community was moving in the same direction. Dyson’s paper would not appear in print until shortly after the conference, and Feynman’s classic papers setting out his version of QED would not appear until September 1949, but word of mouth is a quick, efficient and powerful means of communication and, even before these papers came out, there was much talk among physicists of ‘Feynman diagrams’ or, for a while at least, ‘Dyson graphs’.

This January 1949 meeting has, in fact, gone down in history as the moment when not just the world at large, but Feynman himself realised the power of his diagrammatic methods of performing the extraordinarily intricate calculations required in quantum electrodynamics. It was this meeting, Feynman later said, ‘when I really knew I had something. That was the moment that I really knew that I had to publish – that I had gotten ahead of the world.’ The particular incident that prompted this realisation was one that involved Oppenheimer, and, more specifically, it involved Oppenheimer’s relish for publicly crushing the views and arguments of others.

Murray Slotnick, a young physicist at Cornell who had worked with
Hans Bethe, reported at the meeting on a certain extremely complicated calculation in meson theory that he had done relating to the interaction between a neutron and the electrostatic field of an electron. He had done this calculation for both ‘pseudoscalar’ and ‘pseudovector’ interactions, getting a finite result for the first and an infinite result for the second. In the discussion period after Slotnick’s presentation, Oppenheimer flummoxed Slotnick by asking ‘What about Case’s Theorem?’ When asked to explain what he meant, Oppenheimer said that Kenneth Case, an ex-student of Schwinger’s who was now at the Institute for Advanced Study, had just proven that the two kinds of interactions
had
to be the same – a proof that Case would be presenting to the conference the following day. Since Slotnick’s calculations violated Case’s Theorem, Oppenheimer insisted, they had to be wrong. As Case’s Theorem had not been published, nor was there even a pre-print of it available, Slotnick, naturally, did not know how to respond, and so allowed Oppenheimer’s point to stand and accepted that his own work had been summarily refuted.

Feynman was not there during this exchange, but when he arrived at the conference later that day he was asked for his opinion on Slotnick’s calculation and ‘Case’s Theorem’. Feynman had never studied meson theory, but his methods of calculation using ‘Feynman diagrams’ had been developed precisely to perform calculations relating to interactions between particles and electrostatic fields, so he was pretty sure that he could do this calculation. Sure enough, after a few hours that evening, he had results for both the pseudoscalar and pseudovector cases, results that confirmed his hunch that Slotnick was right. The next day, Feynman sought out Slotnick and showed him his work of the previous evening. Slotnick was absolutely dumbstruck. He had spent two years on this problem, and Feynman had solved it in an evening. Not only that, but Feynman’s calculation was more fine-grained than Slotnick’s, since he had built in a variable for the momentum transferred by the electron, a complication that Slotnick had ignored. It was Slotnick’s flabbergasted reaction that convinced Feynman that he really had something wonderful. ‘That was the moment I got my Nobel Prize,’ Feynman said, ‘when Slotnick told me that he had been working two years . . . That was an exciting moment.’

That day, after Case had given his talk, Feynman got up and asked: ‘But what about Slotnick’s calculation? Your theorem must be wrong because a simple calculation shows that it’s correct. I checked Slotnick’s calculation and I agree with it.’ ‘I had fun with that,’ Feynman later remarked. After the conference he worked out what was wrong with Case’s reasoning, a laborious task, since it involved working with Schwinger’s formalism. What made it worthwhile was the demonstration that, as Dyson had been saying for a long time, Feynman’s methods were easier and
quicker to use than Schwinger’s and, therefore, likely to give more reliable results. After the meeting Feynman worked hard to write up his version of the new theory and on 8 April 1949 the
Physical Review
received ‘The Theory of Positrons’, the first published account by Feynman of his method of calculating the energies of electrons and positrons – that is, his first statement of the new QED. Three days after delivering this paper, Feynman was in Oldstone-on-the-Hudson, Peekskill, about forty miles north of New York City, for the third and final conference in the series that had begun at Shelter Island two years earlier.

Like the one at Pocono, this conference was organised by Oppenheimer, who, a month before it bgean, had sent to the invitees a rather brisk, businesslike letter, informing them that the Oldstone Inn had been reserved for the nights of 10–14 April. ‘We will start work on Monday morning and should have four full days together.’ Twenty-four scientists attended the conference. Among those who had not been at the other two were Yukawa, now a visiting fellow at the institute, and Freeman Dyson, whose invitation was recognition of his new-found status as a member of the elite group of leading physicists.

‘We had lovely weather for the conference,’ Dyson wrote to his parents soon after it had finished, ‘and could sit outside whenever we were not conferring. However, since the conference was run by Oppenheimer, that was not often.’

Everyone agreed that this Oldstone conference was, as Pais puts it, ‘Feynman’s show’. Having worked out his methods systematically, Feynman was now able to demonstrate them persuasively, and at Oldstone, Pais writes, Feynman’s version of QED ‘began its rapid and never-waning rise in popularity’. At the end of the meeting Oppenheimer wrote to the National Academy of Sciences, the sponsors of all three conferences in the series, expressing, on behalf of the people who had taken part, ‘a real sense of satisfaction for the fruitfulness and value of the conference’. He added:

Remarkably, he was not exaggerating. During the two years of these conferences, QED went from being a set of unsolved problems to what Feynman insisted was a part of physics that ‘is
known
, rather than a part that is unknown’. ‘At the present time,’ Feynman declared in 1983, more than thirty years after the theory was developed, ‘I can proudly say that there is
no significant difference
between experiment and theory!’

In 1965, Feynman, Schwinger and Tomonaga were awarded the Nobel Prize in Physics for their respective contributions to constructing this ‘jewel’. Dyson has been called the greatest physicist not to have won the prize, his main rival for that title being Oppenheimer himself.

DURING THE TWO
years that American physicists excitedly solved the problems of quantum electrodynamics – or excitedly watched them being solved – the world outside became a much darker place. The Berlin Blockade of 1948–9 and the Communist Party victories in Czechoslovakia (1948) and Hungary (1949) had persuaded public opinion in the West that the Soviet Union was indeed, as Churchill had predicted, attempting to expand its sphere of influence and that democracy therefore had to be defended from the communist threat. The post-war world that many scientists had dreamed of in 1945 – a world of international cooperation, based on the mutual recognition of the folly of a nuclear arms race – never looked like materialising. Instead what transpired was exactly what the scientists had warned against: growing tensions between the world’s superpowers brought about and fostered by the mutual suspicion, paranoia and fear that inevitably accompanied the forlorn attempt to keep scientific facts secret from scientists.

In December 1948, Oppenheimer gave a lecture at Rochester entitled ‘The Open Mind’, in which, while accepting the failure of past attempts to cooperate with the Soviet Union and agreeing that the blame for that failure lay chiefly with the Soviets, he emphasised, against the prevailing cultural current, the advantages of openness and magnanimity in international relations. ‘We need to remember that we are a powerful nation,’ he urged. The United States did not have to conduct its affairs in an atmosphere of fearful suspicion. The policies developed and pursued in such an atmosphere ‘appear to commit us to a future of secrecy and to an imminent threat of war’. As a model of an alternative attitude, Oppenheimer cited the example of Ulysses Grant, who, at the end of the Civil War, spoke to the defeated Confederate General Lee and allowed Lee’s troops to keep their horses, since ‘they would need them for the spring plowing’. Even in recognition of the evils committed by the Soviets
in the past, Oppenheimer urged, Americans should keep an open mind about the future and act from a position of magnanimous strength rather than fearful weakness.

When he gave this lecture Oppenheimer possibly imagined himself to be, as he believed the United States to be, in a position of unassailable strength. It was just a month earlier that he had been on the cover of
Time
magazine, which began its long article on him with an impressive list of his achievements and titles:

In the years that followed, however, it would be shown that none of those titles and achievements could save him from the very fear and suspicion against which he had campaigned. For five years, starting in the summer of 1949, his standing – among his fellow scientists, among politicians and among military men – would be systematically attacked in a concerted and successful attempt to ruin him. What made the attack all the more pitiable to watch was the fact that his enemies were able to use against him his own personal and moral weaknesses, which were often cruelly exposed during these years.

The first serious blow to Oppenheimer’s reputation, and the moment when those personal and moral frailties were first held up for all to see, was his appearance before HUAC on 7 June 1949. As Oppenheimer had correctly remarked in his letter to Frank the previous October, the revelations about Alger Hiss that had come out of the HUAC hearings were a ‘menacing portent’ of things to come. Having investigated communist ‘subversion’ among actors in Hollywood and politicians in Washington, in April 1949 the committee, under its new chairman, John Wood, turned its attentions to scientists, and, in particular, to the group of young radicals at Berkeley that had so concerned the FBI and military security during the war.