Inside the Centre: The Life of J. Robert Oppenheimer (94 page)

On the final day of the conference, 4 June, Oppenheimer led an extended discussion of the problems physicists faced in understanding mesons. In the ensuing discussion Robert Marshak made his now-famous suggestion that these puzzles might be solved by distinguishing two kinds of meson, one bigger than the other. The bigger of the two would be the Yukawa particle, responsible for the strong nuclear force, which decays into the smaller of the two – that is, the mesons found in cosmic rays – which in turn decay into electrons. In fact, though the participants at the Shelter Island Conference did not yet know this, experimental evidence confirming Marshak’s hypothesis had already been published.

In the issue of the British journal
Nature
published on 24 May 1947 (and therefore not available in the States until a few days after the Shelter Island Conference) a group of experimental physicists based at Bristol and led by Cecil Powell reported on some investigations they had conducted, which demonstrated the existence of a process whereby what they called a ‘primary’ meson could decay into a ‘secondary’ meson. The authors of this report pointed out that the existence of this process resolved many of the puzzles about mesons, including those presented by the experiments of the Italian group. These experiments by Powell and his group form the second example that Oppenheimer gave in his lecture, mentioned earlier, of important experimental discoveries coming from Europe.

In a letter he wrote to Frank Jewett, the president of the National Academy of Sciences, Oppenheimer described the Shelter Island Conference as ‘unexpectedly fruitful’. ‘The three days were a joy to us,’ he told Jewett, adding that the participants ‘came away a good deal more certain of the directions in which progress may lie.’ A few months later, when, in the aftermath of the conference, several fundamentally important papers had been published by those present, Oppenheimer was even more effusive, saying that the conference was, for most of the participants, ‘the most successful conference we had ever attended’. Out of it, he claimed, had come ‘a new understanding of the probable role of the meson in physical theory, and the beginnings of a resolution of the long outstanding paradoxes of the quantum electrodynamics’. By the end of the year, he was circulating plans for a second meeting to be held the following spring.

When the conference finished, Oppenheimer did not return to California, but went on instead to Harvard, where he was to receive an honorary degree. To avoid the usual difficulties of travelling to or from Shelter Island, he arranged for a private seaplane to fly him from Port Jefferson to Bridgeport, Connecticut, where he could catch a train to Boston. As Schwinger, who taught at Harvard, and Rossi and Weisskopf, who were both at MIT, also had to return to Boston, Oppenheimer invited them to join him. On the way they flew into a storm, so the pilot decided to land at the only available place, which happened to be a naval base, which civilian aircraft were not supposed to use. They disembarked to find an angry naval officer waiting to give them a dressing-down. ‘Don’t worry,’ Oppenheimer said to the pilot. ‘Let me handle this.’ As he stepped off the plane he offered his outstretched hand to the officer and said calmly: ‘My name is Oppenheimer.’ ‘
The
Oppenheimer?’ gasped the officer. Upon being reassured that he was indeed in the presence of the most famous physicist in the country, the officer changed his attitude completely, welcomed Oppenheimer and his companions to the officers’ club where they were served tea and biscuits, and then arranged for them to be driven to the local railway station, from where they were able to take a train to Boston.

Having at last reached Harvard, Oppenheimer was awarded his honorary degree at the graduation ceremony on 5 June. The ceremony turned out to be a historic occasion, because, in a speech that he gave to the graduates, General Marshall announced a major new policy initiative: the European Recovery Program, or Marshall Plan as it became known, which offered billions of US dollars to European countries, on the condition of closer cooperation.

Oppenheimer, as his evidence to Congress in support of the May–Johnson Bill had shown, had a deep admiration for General Marshall. Haakon Chevalier tells a revealing story that illustrates not only Oppenheimer’s
warm regard for Marshall, but also his delight at finding himself moving in the same circles as the esteemed Secretary of State, whom
Time
magazine would that year name as ‘Man of the Year’. Chevalier recalls meeting Phil Morrison in New York during this period and, in the course of catching up and reminiscing, asking him about Oppenheimer. ‘I hardly see him any more,’ Morrison replied. ‘We no longer speak the same language . . . He moves in a different circle.’ To illustrate what he meant, Morrison told Chevalier that at one of his most recent meetings with him, Oppenheimer kept saying, ‘George thinks this . . .’ and ‘George says that. . . .’ Eventually Morrison felt compelled to ask who this ‘George’ was. ‘You understand,’ he told Chevalier, ‘General Marshall to me is General Marshall, or the Secretary of State – not George.’ Oppenheimer, he remarked, had changed profoundly: ‘He thinks he’s God.’

In the summer of 1947, as he, Kitty and the children prepared to leave California to move into Olden Manor, the splendid residence reserved for the director of Princeton’s Institute for Advanced Study, Oppenheimer was at the very height of his reputation, among scientists, politicians and the general public. As the sociologist Philip Rieff has written, during these years ‘Oppenheimer became a symbol of the new status of science in American society. His thin handsome face and figure replaced Einstein’s as the public image of genius.’ Anne Wilson’s concern that he would get into ‘terrible trouble’ in the east seemed, for the moment at least, to have been misplaced.

^fn61
A Feynman diagram is a pictorial representation of the interactions of subatomic particles. A typical diagram might show, for example, an electron and a positron annihilating each other, emitting waves of electromagnetic energy.

‘
THIS IS AN
unreal place,’ Abraham Pais wrote, after he had been at Princeton’s Institute for Advanced Study for a few months. ‘Bohr comes into my office to talk, I look out at the window and see Einstein walking home with his assistant. Two offices away sits Dirac. Downstairs sits Oppenheimer.’

Apart from Einstein, the two other great physicists Pais mentions, Bohr and Dirac, were brought to the institute by Oppenheimer during his very first year there. Both were figures who had for Oppenheimer great symbolic importance: Bohr, the physicist from the previous generation for whom Oppenheimer had the greatest respect and the man whom he revered above all others; and Dirac, the greatest physicist of Oppenheimer’s own generation, whose career had been closely watched by Oppenheimer, sometimes with rivalry, but always with enormous admiration. It was no surprise that Oppenheimer wanted to attract Bohr and Dirac to the institute, but Pais himself was, in fact, more representative of Oppenheimer’s ambitions for the place. As Oppenheimer well knew, the next big steps in physics would not be taken by men of Bohr and Einstein’s generation, or even by those of Oppenheimer and Dirac’s generation; they would be taken by people the age of Pais, Schwinger, Feynman, and so on. It was those young people, above all, whom he wanted to come to Princeton to be ‘directed’ by him.

Having insisted that his contract permit him to devote some of his time to teaching graduate students, Oppenheimer abandoned the plan of depending on the trustees of the institute to identify suitable students at Princeton, and instead took the precaution of bringing his own. In a move that recalls the annual migration from Berkeley to Pasadena that students like Serber were prepared to take in the 1920s and ’30s in order to maximise their time with Oppenheimer, in the summer of 1947 no fewer than five students – Hal Lewis, Robert Finkelstein, Saul Epstein, Leslie Foldy and
Sig Wouthuysen – came with Oppenheimer when he left California for the east.

In December 1947, soon after Oppenheimer moved to Princeton,
Life
magazine ran an article about the institute under the heading ‘The Thinkers: The Institute for Advanced Study is their Haven’. The atomic bomb, the piece began by saying, was a ‘devastating projection of this century’s most abstruse thinking’. In the light of this demonstration of the power of thought, ‘the thinker has come into his own’, and therefore the institute, being ‘one of the most imposing collections of minds gathered in one place’, had become recognised as ‘one of the most important places on earth’.

The photographs accompanying the article, however, picture for the most part a distinctly unimposing collection of elderly men: the economist Walter W. Stewart reclining on his couch and looking as if he is about to fall asleep; the classics scholar Benjamin Merritt peering through a magnifying glass at an ancient Greek inscription; the mathematician Oswald Veblen leaning back in his chair and staring with apparent bewilderment at his desk; and, of course, Einstein, who is pictured twice, once in front of an audience and again sitting with Oppenheimer, telling him, according to the caption, ‘about his newest attempts to explain matter in terms of space’, and looking in both pictures like an ancient Old Testament prophet.

In the starkest contrast to these pictures are two of Oppenheimer. In the first – captioned ‘talking shop’ – he is shown engaged in obviously earnest and intense discussion with Dirac and Pais, all three of them looking quite sure that what they are discussing is of great importance. In the second – captioned ‘Oppenheimer’s students’ – Oppenheimer is shown perched on a desk, with five young men evidently hanging on to his every word. By accident or design, the contrast between the two sets of photographs sends a very clear message: under Oppenheimer, the institute would no longer be the resting place for eminent old men whose best work was behind them; it was to be a place where up-and-coming young men who meant business would make new and fundamental contributions to scientific knowledge.

These were exciting years for physics, as Oppenheimer, after the Shelter Island Conference, knew they would be, and he was determined to be, as far as possible, at the centre of developments. Indeed, though Oppenheimer was at this time chairman of the Atomic Energy Commission’s General Advisory Committee, and as such perhaps the most influential person in the country in the development of America’s atomic policies, and though he had moved east partly so that his regular trips to Washington would not be so difficult or time-consuming, it was actually physics, rather than politics, that dominated his first two years at Princeton. As he had done in the 1930s, he published jointly with his students. In October 1947 he
submitted the paper he had given at Shelter Island, ‘The Multiple Production of Mesons’, to the
Physical Review
as a joint publication, co-written with Hal Lewis and Sig Wouthuysen. A few months later he submitted another paper, ‘Note on the Stimulated Decay of Negative Mesons’, this time co-written with Saul Epstein and Robert Finkelstein. But, more importantly, he directed his students to the area where, in the wake of Shelter Island, the fundamentally important new steps would be taken: that is, to quantum electrodynamics, in which, as Oppenheimer knew, the solution to the puzzles posed by the recent experiments conducted at Columbia would be found.

Oppenheimer encouraged the young physicists at the institute to attend the many important seminars and conferences being given at that time, not just in America, but also in Europe. For example, he encouraged Pais to travel to a small conference in Copenhagen in September 1947, where Cecil Powell reported on his recent experiments at Bristol, which demonstrated the truth of Marshak’s ‘two-meson’ hypothesis. It was there that Pais first heard the names that would soon become accepted for the two particles: the pi-meson and the mu-meson. When he returned, Oppenheimer asked Pais to give a seminar reporting on what he had learned at Copenhagen. To Pais’s surprise, Einstein turned up to hear his account of Powell’s work. ‘It was,’ says Pais, ‘the only occasion in all my institute years that I saw Einstein present at a physics seminar given by someone other than himself.’

Oppenheimer was so excited by the developments in physics during this time that he could not resist mentioning them, or at least alluding to them, even in his public, non-technical lectures. One example of this – his mention of the experiments conducted by the three Italian scientists, Conversi, Pancini and Piccioni, in his lecture ‘Atomic Energy as a Contemporary Problem’, given in September 1947 – has already been mentioned. Another example occurred a couple of months later. On 13–15 November 1947, Oppenheimer was in Washington to attend the tenth Washington Conference on Theoretical Physics. Also there was Schwinger, who gave a report on a series of calculations that he had made relating to the quantum-mechanical interactions between electrons and photons, particles and radiation, in a relativistic field. These calculations were so subtle, so intricate and so complicated that Schwinger was possibly the only man then alive who could have performed them, but they also pointed to the fundamental change in QED that was needed to account for the Lamb shift and the anomalous magnetic moment of the electron. Feynman, who was at the conference, reports that he himself ‘did not have time to understand what exactly Schwinger had done’, but he knew that, whatever it was, it had to be interesting, because ‘it got Oppy so excited’. What excited Oppenheimer was the possibility that
both
the energy shift of
electrons observed by Lamb
and
the anomalous increase in the magnetic charge of electrons reported by Rabi, Nafe and Nelson could be accounted for by the
same
set of calculations. This strongly suggested that something new and important had been discovered about the way electrons react to their own magnetic fields.

‘The importance of Schwinger’s calculation cannot be underestimated,’ writes the physicist and historian of physics Silvan Schweber: