Inside the Centre: The Life of J. Robert Oppenheimer

by Ray Monk

  Upon receiving this package from Tomonaga, Oppenheimer sent him a telegram: ‘Grateful for your letter and papers. Found most interesting and valuable mostly paralleling much work done here. Strongly suggest you write a summary account of present state and views for prompt publication in Physical Review. Glad to arrange.’ Oppenheimer also sent a copy of Tomonaga’s letter to all the participants of the Pocono Manor conference, telling them: ‘Just because we were able to hear Schwinger’s beautiful report, we may better be able to appreciate this independent development.’

  Tomonaga was only too pleased to take Oppenheimer’s advice, and on 28 May 1948, Oppenheimer received his summary of the work done in Japan, which was subsequently published in the 15 July edition of Physical Review, under the title ‘On Infinite Field Reactions in Quantum Field Theory’, together with an accompanying note from Oppenheimer, which spoke of the ‘remarkable work carried out in Japan in recent years’. On 11 April, after seeing the letter from Tomonaga that Oppenheimer had sent to all the Pocono delegates, Freeman Dyson wrote to his parents, correctly pointing out: ‘The reason that everyone is so enormously pleased with this work of Tomonaga is partly political.’

  Long-sighted scientists are worried by the growing danger of nationalism in American science, and even more in the minds of the politicians and industrialists who finance science. In the public mind, experimental science at least is a thing only Americans know how to do, and the fact that some theorists have had to be imported from Europe is rather grudgingly admitted. In this atmosphere the new Schwinger theory tended to be acclaimed as a demonstration that now even in theoretical physics America has nothing to learn, now for the first time she has produced her own Einstein. You can see that if the scientists can say that even in this chosen field of physics America was anticipated and indeed by a member of the much-despised race of Japanese, this will be a strong card to play against nationalistic politics.

  Things had come full circle since the days when Rabi, Condon and Oppenheimer had suffered from an acute awareness of the condescension with which European theoretical physicists treated their American counterparts. Now those same scientists had to check themselves and celebrate the achievements of others, so as not to appear to be basking in their own, self-evident superiority. For there is no doubt that there was at this time a sense in America that, as Oppenheimer had said in his MIT lecture, science, and particularly physics, was booming.

  One reflection of this was the launch of a new, semi-popular magazine called Physics Today, the first issue of which was published in May 1948. The magazine was published by the American Institute of Physics, the ‘whole idea’ of which was, in the words of one of its historians, to bring ‘mutually unacquainted specialists in all branches of physics together into a kind of operational unity for enhancement of physics as an important field of human endeavour’. The aim of the magazine, in the words of the same historian, was ‘to present the special fields in interesting terms that all physicists and most laymen could understand’. There were attempts by the magazine to resist the kind of nationalism that Freeman Dyson mentions in his letter to his parents – it included, for example, reports on what was happening in physics in England and the rest of Europe – but, nevertheless, the leading article of its first issue was a piece by Vannevar Bush on ‘Trends in American Science’. Moreover, its first cover was a piece of triumphalism that would have been understood only in America. What the cover showed was a hat, resting on a piece of machinery. What the editor of the magazine assumed (no doubt correctly) their readers would know was that this hat, being a pork-pie hat, was Oppenheimer’s hat, and that the machinery was a cyclotron. The editor’s intention was to symbolise the triumph of civilian over military control of atomic energy. Whether or not he was successful in that, what is indisputably symbolised by the cover is the pivotal and iconic role played by Oppenheimer during this period – so famous that he did not actually need to be pictured in order to be represented.

  In June 1948, Oppenheimer returned to California to take part in a three-day conference at Caltech on cosmic rays that had been organised to celebrate Robert Millikan’s eightieth birthday. Among those present were John Wheeler, Bruno Rossi, Carl Anderson, Frank Oppenheimer and two experimental physicists, George Rochester from Manchester and Louis Leprince-Ringuet from Paris, both of whom had collected evidence from cosmic-ray observations of yet another meson, this one (soon to be called the K-meson or kaon) much heavier than the pi-meson and the mu-meson. A brief contemporary report of the conference published in the magazine Engineering and Science Monthly states laconically: ‘Out of it all came general agreement that the symposium was an extremely successful affair; that our knowledge of these mysterious rays that bombard the earth from outer space is still fragmentary but progressing well, and that no one has yet determined from whence they come or how they originated.’

  A similar impression is given in the concluding remarks to the symposium that Caltech’s president, Lee DuBridge, had asked Oppenheimer to give. Indeed, in these remarks Oppenheimer appears far more interested in the recent developments in theoretical physics made by Schwinger than he does in anything that was actually discussed during the symposium. After remarking that he found it ‘hard to disbelieve Leprince-Ringuet’s evidence for a very heavy meson’, he quickly turned his summary into an exposition of ‘the developments in electrodynamics that are so much associated with Schwinger’s name’, speculating that in those developments may lie a solution to the unsolved problems in cosmic-ray studies and particle physics.

  Still more obsessed with the new QED than Oppenheimer was Freeman Dyson, who developed during the summer of 1948 a fervent ambition to understand fully all three versions of the new theory – Schwinger’s, Tomonaga’s and Feynman’s – and demonstrate the equivalence of all three. Dyson was disappointed not to have been invited to the Pocono conference in March, but delighted when Bethe showed him Tomonaga’s papers, particularly as one of the things Tomonaga demonstrated was something that Feynman had been saying for a long time: that Schwinger’s results could be obtained without the formidably difficult mathematics that Schwinger himself had used to derive them. ‘To me that was very important,’ Dyson later said. ‘It gave me the idea that this was after all simple.’

  In order to improve his understanding of Schwinger’s theory, Dyson signed up for the Ann Arbor summer school in Michigan, where Schwinger would be delivering a series of lectures. Up to that point the main source for Schwinger’s ideas were the notes taken of his mammoth Pocono talk. This would change over the next two years, as Schwinger wrote up his ideas in a series of important articles that were published in the Physical Review, but, for a young physicist like Dyson, impatient to master the new theory, the Ann Arbor lectures were a golden opportunity to learn it straight from its originator.

  The summer school was due to start on 19 July, two weeks after the end of term at Cornell. During his year at Cornell, Dyson had seen much of Feynman and had come not only to admire him, but to like him a great deal. To fill those two weeks, then, Dyson accepted an offer he received from Feynman to accompany him on a trip to Albuquerque, ‘where love had drawn him’. Being with Feynman twenty-four hours a day as they travelled across the United States provided Dyson with the perfect chance to understand Feynman’s own version of the new theory, which, like Schwinger’s, was as yet unpublished. ‘I knew,’ Dyson writes in his autobiographical book, Disturbing the Universe, ‘that somewhere hidden in Dick’s ideas was the key to a theory of quantum electrodynamics simpler and more physical than Julian Schwinger’s elaborate construction.’ By the time he left Feynman to go to Ann Arbor, Dyson had a pretty firm grasp of that key.

  From Ann Arbor, Dyson wrote to his parents:

  Yesterday the great Schwinger arrived, and for the first time I spoke to him; with him arrived a lot of new people who came to hear him especially. His talks have been from the first minute excellent; there is no doubt he has taken a lot of trouble to polish up his the
ory for presentation at this meeting. I think in a few months we shall have forgotten what pre-Schwinger physics was like.

  The lectures that Schwinger gave during the five weeks of the summer school were, in fact, identical to the series of articles that would soon start appearing in print. In Disturbing the Universe Dyson says he learned less from the lectures – which he describes as ‘a marvel of polished elegance, like a difficult violin sonata played by a virtuoso, more technique than music’ – than from personal conversations with Schwinger. In the lectures, Dyson says, Schwinger’s theory ‘was a cut diamond, brilliant and dazzling’, but in conversation, ‘I saw it in the rough, the way he saw it himself before he started the cutting and polishing. In this way I was able to grasp much better his way of thinking.’ After spending five weeks working through ‘every step of Schwinger’s lectures and every word of our conversations’, Dyson felt that he ‘understood Schwinger’s theory as well as anybody could understand it, with the possible exception of Schwinger’.

  After the summer school, Dyson took a two-week holiday in California, during which he did not think about physics, and then, in September, on a Greyhound bus heading back east, he experienced some kind of epiphany. ‘As we were droning across Nebraska,’ Dyson recalls, ideas ‘came bursting into my consciousness like an explosion’.

  Feynman’s pictures and Schwinger’s equations began sorting themselves out in my head with a clarity they had never had before. For the first time I was able to put them all together. For an hour or two I arranged and rearranged the pieces. Then I knew that they all fitted. I had no pencil or paper, but everything was so clear I did not need to write it down. Feynman and Schwinger were just looking at the same set of ideas from two different sides. Putting their methods together, you would have a theory of quantum electrodynamics that combined the mathematical precision of Schwinger with the practical flexibility of Feynman.

  By the time he reached Princeton to take up the one-year fellowship that Oppenheimer had offered him at the institute, Dyson had already mapped out the paper he would write, the title of which would be ‘The Radiation Theories of Tomonaga, Schwinger and Feynman’. Walking to the institute for the first time, he reflected that he – a twenty-four-year-old at the start of his career and with no major publications to his name – felt himself in a position ‘to teach the great Oppenheimer how to do physics’.

  According to a letter he wrote his parents, Dyson, after spending ‘five days stuck in my rooms, writing and thinking with a concentration which nearly killed me’, finished writing his article on the seventh day of being in Princeton. As it happened, Oppenheimer was not at that time in Princeton, but in Europe, where he would remain for the next six weeks, attending conferences in France, England, Denmark and Belgium and revisiting old haunts and old friends. Dyson, together with seven other young physicists who had been invited to spend the year at the institute (most of them students of Schwinger’s), was using Oppenheimer’s office while a new building that would contain their individual offices was hurriedly being completed.

  Actually, though Dyson did not know it, Oppenheimer already knew the general outline of the paper, since, before completing it, Dyson had written to Bethe ‘announcing the triumph’. In his letter, he told Bethe: ‘I have succeeded in re-formulating the Schwinger method, without any changes of substance, so that it gives immediately all the advantages of Feynman theory’, adding: ‘Incidentally, the complete equivalence of Schwinger and Feynman is now demonstrated.’ Like Oppenheimer, Bethe was then in Europe, and a few days after he received Dyson’s letter, he and Oppenheimer were both in Birmingham attending a four-day conference on ‘Problems of Nuclear Physics’, which was held on 14–18 September. The organiser of the conference was Rudolf Peierls, who remembers:

  In the middle of the conference somebody had a letter from Dyson . . . summarizing the results he had just obtained in linking the Feynman and Schwinger approaches and showing connections and also in proving that the infinities could be thrown out not merely in the first order in which they appeared but to all orders, which was an important formal result.

  There had been very few international conferences since the war ended, and at these European meetings the tendency was for the Europeans to learn what was happening in America. Everywhere he went, Oppenheimer wrote home to Frank, ‘there is the phrase “you see, we are somewhat out of things”’. His return to Europe had, he told his brother, confirmed him in the knowledge ‘that it is in America largely that it will be decided what manner of world we are to live in’.

  At the eighth Solvay Congress, held in Brussels from 27 September to 2 October 1948, Oppenheimer was asked to report on progress in quantum electrodynamics. His report, of course, emphasised the importance of Schwinger’s work. After a historical account of the development of the ‘old’ QED by Dirac, Pauli and Heisenberg, Oppenheimer’s report stressed the infinity problems that theory gave rise to, citing his own 1930 paper on the subject. To solve these problems, he told his audience, ‘more powerful methods are required’, the development of which ‘occurred in two steps, the first largely, the second almost wholly, due to Schwinger’. Oppenheimer’s account of Schwinger’s breakthroughs, however, was markedly free of the excitement with which he had discussed them earlier in the year. Indeed, the tone of the report was strikingly downbeat, especially towards the end, where Oppenheimer drew attention to some perceived weaknesses in the theory, such as the fact that it could not deal with the forces acting between mesons inside nucleons. These weaknesses, he concluded, suggested that the new quantum electrodynamics was not a ‘closed’ – that is, a completed – system. Schwinger had made an important step forward, but his was not the last word on the subject.

  Back in Princeton, Dyson, having sent his paper on Feynman, Schwinger and Tomonaga off to the Physical Review (it was received on 6 October 1948), was awaiting Oppenheimer’s return from Europe with some trepidation. On 10 October, he wrote to his parents: ‘The atmosphere at the Institute during these last days has been rather like the first scene in “Murder in the Cathedral” with the women of Canterbury awaiting the return of their archbishop.’ A few days later, when Oppenheimer finally arrived back, Dyson was astonished to discover that he seemed not only to have lost his enthusiasm for the new QED, but to have become actively hostile towards it. Oppenheimer was, Dyson wrote home, ‘unreceptive to new ideas in general, and Feynman in particular’.

  In Disturbing the Universe Dyson writes that he had known that Oppenheimer did not appreciate Feynman:

  but it came as a shock to hear him now violently opposing Schwinger, his own student, whose work he had acclaimed so enthusiastically six months earlier. He had somehow become convinced during his stay in Europe that physics was in need of radically new ideas, that this quantum electrodynamics of Schwinger and Feynman was just another misguided attempt to patch up old ideas with fancy mathematics.

  Why Oppenheimer’s attitude to the new theory changed so drastically after his trip to Europe in the autumn of 1948 is something of a mystery. He never explained it to Dyson or to anyone else, and no documents or recorded conversations exist that can shed much light on it. It is possible that he was influenced by spending several weeks in an atmosphere very different from the triumphant, optimistic mood that prevailed among American scientists during this time. It seems possible, too, that he was influenced by specific views of individual European scientists, many of whom were much more sceptical towards, and less impressed with, Schwinger’s theory than their American counterparts. As the historian of science Jagdish Mehra puts it: ‘The old guard in Europe was not altogether satisfied with Schwinger’s breakthroughs.’ Particularly resistant was Paul Dirac, who remained unconvinced by the new theory till his dying day. When Dyson once asked Dirac what he thought of the new developments, Dirac replied: ‘I might have thought the new ideas were correct if they had not been so ugly.’ It was a view that Dirac was to state in print in many places, including a paper he published in 1951,
which provided a new theory of the electron. In it he wrote:

  Recent work by Lamb, Schwinger, Feynman and others has been very successful in setting up rules for handling the infinities and subtracting them away, so as to leave finite residues which can be compared with experiments, but the resulting theory is an ugly and incomplete one and cannot be considered as a satisfactory solution of the problem of the electron.

  Dirac’s use of the word ‘incomplete’ here echoes so strongly the sentiments expressed by Oppenheimer that one is very tempted to imagine that, more than anything else, it was the influence of discussions with Dirac that prompted Oppenheimer’s change of attitude towards Schwinger’s theory. Dirac was, after all, at the eighth Solvay Congress and is on record as having responded to Oppenheimer’s report with an attack on the new theory.

  Whatever its cause, Oppenheimer’s change of heart put a great strain on his relations with Dyson. Within a few days of his return to Princeton, Oppenheimer gave Dyson a copy of the report he had delivered at the Solvay Congress. Dyson, already upset at Oppenheimer’s attitude towards his paper on Feynman, Schwinger and Tomonaga, was sufficiently horrified by Oppenheimer’s report to write a memo on the subject. On 17 October, Dyson sent the memo to Oppenheimer, together with a note that explained that he had written it because ‘I disagree rather strongly with the point of view expressed in your Solvay Report.’ The memo consisted of six numbered points, almost all of which centred on a defence of Feynman’s version of the new theory. ‘As a result of using both the old-fashioned quantum-electrodynamics (Heisenberg–Pauli) and Feynman electrodynamics,’ Dyson wrote, ‘I am convinced that the Feynman theory is considerably easier to use, understand, and teach.’