Inside the Centre: The Life of J. Robert Oppenheimer (93 page)
Read Inside the Centre: The Life of J. Robert Oppenheimer Online
Authors: Ray Monk
Particularly he pointed out how much the Russian plan was designed to serve the Russian interests and no other interests, namely, to deprive us immediately of the one weapon which would stop the Russians from going into Western Europe, if they so chose, and not give us any guarantee on the other hand that there would really be a control of atomic energy, nor give us any guarantee that we would be safe from Russian atomic attack at some later time.
FBI microphones would have recorded this conversation, as they would have recorded Oppenheimer expressing similar views on very many occasions, none of which dented J. Edgar Hoover’s apparently immovable conviction that Oppenheimer was a communist sympathiser and a potential Soviet spy. His appointment to the GAC gave Hoover the opportunity to launch a renewed investigation into Oppenheimer. Indeed, it presented him with the
duty
of doing so, it being one of the measures of the McMahon Act that all AEC employees who had previously been cleared to work on the Manhattan Project had to be investigated by the FBI. So, in February 1947, FBI agents interviewed dozens of Oppenheimer’s friends and colleagues and, in the light of the information gathered (none of which gave any new grounds for suspicion), a fresh dossier on Oppenheimer was written. Before sending this to the AEC, Hoover sent it, along with another dossier on Frank Oppenheimer, to General Vaughan, Truman’s military aide. ‘You will note,’ Hoover wrote in his accompanying letter, ‘that both these individuals have a good overall knowledge of the Atom Bomb Project, and that both have been strongly alleged to be members of the Communist Party.’
About a week later, on Saturday 8 March, Hoover sent the same document to the AEC. The following Monday the commissioners met to discuss what to do about the FBI file. Conant and Bush announced themselves unconcerned; there was nothing in this new dossier, they said, that added to what they had seen, and dismissed, in 1942. When asked for his opinion, the AEC’s lawyer, Joseph Volpe, replied:
Well, if anyone were to print this stuff in this file and say it is about the top civilian advisor to the Atomic Energy Commission, there would be terrible trouble. His background is awful. But your responsibility is to determine whether this man is a security risk
now
, and except for the Chevalier incident, I don’t see anything in this file to establish that he might be.
The commissioner most shocked by the FBI’s revelations was Lewis Strauss, who, Volpe recalls, was ‘visibly shaken’ by them. Oppenheimer had told him the previous December, in connection with the offer of the Princeton job, that there was ‘derogatory information’ about him, but Strauss had not seemed worried. Now he and Lilienthal, as chair of the commissioners, were forced to take this information seriously.
On 11 March, the AEC members decided to take the issue straight to the top and went to the White House to tell the President about the FBI suspicions of Oppenheimer. Of course Truman already knew about those suspicions and was not very concerned about them. At that particular moment Truman was much more concerned about the crises in Greece
and Turkey, both of which looked in danger of falling under communist rule, becoming part of what Churchill had described as ‘the Soviet Sphere’. In response to this threat, on 12 March 1947, Truman announced to Congress what became known as the Truman Doctrine, the policy of lending support to ‘free peoples’ threatened by communism. As it happened, Oppenheimer was in Washington at this time and received from Acheson a preview of the Truman Doctrine. ‘He wanted me to be quite clear,’ Oppenheimer later said, ‘that we were entering into an adversary relationship with the Soviets, and whatever we did in the atomic talk we should bear that in mind.’ Soon after this, Baruch’s successor as US spokesman on atomic energy at the UN, Frederick Osborn, was surprised to hear Oppenheimer say that the US should simply withdraw from talks with the Soviet Union, which, he said, would never agree to a workable plan.
While Truman was busy formulating the Truman Doctrine, he told the AEC members that he was too busy to meet them and instead they met his aide, Clark Clifford, who, to their relief, did not seem very concerned about Oppenheimer’s FBI file either. By the end of March the AEC had testimonials vouching for Oppenheimer’s loyalty from an impressive array of people, including the Secretary of War, Robert Patterson, and General Groves. On 11 August, the AEC were ready to agree unanimously to approve Oppenheimer for clearance, by which time the FBI, for the time being anyway, had decided to cease their ‘technical surveillance’ of him. He was officially no longer regarded as a security risk. On the contrary, he was now the man most responsible for framing US policy on the development of atomic energy.
What makes the doubts about Oppenheimer’s loyalty seem so perverse is that, from this distance anyway, one of his most striking characteristics is his deep, and sometimes fierce, devotion to his country. It is one of the very few things that remained constant throughout his life and is clearly evident in almost everything he did. It was behind both the extraordinary energy and effort that he put into directing Los Alamos and his determination to play a leading role in the formation and execution of America’s atomic policies. It is also evident – and had been from the very beginning of his academic career – in his concern to establish the US as the world’s centre of theoretical physics.
In the post-war period Oppenheimer was to see that dream he had had in the 1920s – of America replacing Germany as the country where the most fundamental developments in physics took place – become a reality. Moreover, he himself was able to play a leading part in making it a reality, not (as he had done before the war) through his publications and his teaching, but rather through the influence that he wielded at a series of important conferences.
The first, and most important, of these was the Shelter Island Conference, which took place in June 1947 and has gone down in history as one of the most important conferences in the development of physics in the twentieth century. Rabi said it ‘would be remembered as the 1911 Solvay Congress is remembered, for having been the starting-point of remarkable new developments’, while Richard Feynman has said: ‘There have been many conferences in the world since, but I’ve never felt any to be as important as this.’
Shelter Island was the conference at which Willis Lamb introduced the discoveries about hydrogen spectra – the so-called ‘Lamb shift’ – for which he won the Nobel Prize. It was at Shelter Island, too, that Rabi reported on experiments conducted in his laboratory at Columbia, which measured, with an unprecedented degree of accuracy, the magnetic interactions between the protons and electrons in hydrogen and found that the measurements obtained disagreed, slightly but significantly (by about 0.22 per cent), with those derived from the then-accepted theory. The conference was also the occasion at which Robert Marshak first proposed that the puzzles about the meson, to which Oppenheimer himself had devoted so much thought over the previous decade, could be solved by what became known as the ‘two-meson hypothesis’. Moreover, it was at this conference that Richard Feynman gave the first public presentation of what became known as ‘Feynman diagrams’
fn61
and, in the attempt to understand the startling series of experimental observations that had been made in 1947, the seeds were sown for the major advances in quantum electrodynamics that Feynman and Schwinger were to make in the coming years.
Not only were all these young physicists American, but, unlike Oppenheimer and most of his generation, all of them had been graduate students at American universities: Lamb at Berkeley, Marshak at Cornell, Feynman at Princeton and Schwinger at Columbia. For a long time the US had been the country in which the best physics was being done (much of it by refugees, emigrants and people trained overseas), but now it was also the country producing the best physicists.
In terms of the number of participants, the Shelter Island Conference was not large. Just twenty-three people took part, but every one of them was either a world-renowned scientist (like Bethe, Fermi, Rabi, Teller, Uhlenbeck and Wheeler) or widely identified as an up-and-coming star (for example, Feynman, Pais and Schwinger). Together with Kramers and Weisskopf, Oppenheimer was asked to act as a ‘discussion leader’, each of whom was asked to draw up an outline of what they thought ought to
be discussed under the general heading ‘Foundations of Quantum Mechanics’. Weisskopf’s outline was divided into three: 1. problems in quantum electrodynamics; 2. problems in understanding nuclear and meson phenomena; and 3. proposed experiments using high-energy particles. Kramers concentrated entirely on issues in quantum electrodynamics, while Oppenheimer’s outline was focused solely on the problems of understanding mesons and, in particular, the discrepancy between the currently accepted theory and experimental results.
One such result (mentioned by name in Weisskopf’s outline and alluded to in Oppenheimer’s) was an experiment carried out in Italy during the war, of which Oppenheimer, in a non-technical lecture he gave later in the year, gave an excited and colourful account. Now confident of America’s unquestioned position at the forefront of physics, he could afford to be generous in his assessment of work in Europe, and told his audience that ‘of the two or three important experimental discoveries of the last two years, two at least come from Europe’:
One was carried out long before its publication in the cellar of an old house in Rome by three Italians who were under sentence of death from the Germans because they belonged to the Italian Resistance. They were rescued by an uncle of one of the men from a labor squad at Cassino, and smuggled into a cellar in Rome. They got bored there, and they started to do experiments. These experiments were published last spring; and in the field of fundamental physics they created a real revolution in our thinking.
The Italian scientists in question were Marcello Conversi, Ettore Pancini and Oreste Piccioni (when Fermi gave a seminar explaining the importance of their experiment, he remarked jokingly that he ‘would not dare to pronounce those names’). In February 1947, the
Physical Review
published a letter of theirs, ‘On the Disintegration of Negative Mesons’, reporting on experiments they had conducted in 1945, which showed conclusively that something was fundamentally wrong with meson theory as it then stood. According to that theory, the mesons found in cosmic rays were also the particles that Yukawa had suggested as carriers for the nuclear force that binds protons and neutrons together in a nucleus. Mesons are found with both negative and positive charges, and, if that theory is correct, then negative mesons should always be absorbed by surrounding nuclei, whereas positive mesons should not. Because every nucleus is positively charged, positively charged mesons should be repelled, and instead of being absorbed will decay very quickly (mesons have a life of only a few microseconds) into electrons and neutrinos. What Conversi, Pancini and Piccioni found was that, contrary to the theory,
negatively charged mesons – though absorbed by the nucleus of the relatively heavy element of iron – decayed in carbon, which is a much lighter element. What Weisskopf and Oppenheimer wanted the illustrious scientists gathering at Shelter Island to discuss was: what is going on? Why do the carbon nuclei not absorb the negatively charged mesons?
The conference started on Monday 2 June at the Ram’s Head Inn, Shelter Island, right on the tip of Long Island. Reflecting the post-war celebrity of nuclear physicists, the event was reported in gushing terms by the
New York Herald Tribune
:
Twenty-three of the country’s best known theoretical physicists – the men who made the atom bomb – gathered today in a rural inn to begin three days of discussion and study, during which they hope to straighten out a few of the difficulties that beset modern physics.
It is doubtful there has ever been a conference quite like this one. The physicists, backed by the National Academy of Science, have taken over the Ram’s Head Inn . . . The conference is taking place with almost complete informality, aided by the fact that the scientists have the inn all to themselves and feel that there is no one to mind if they take off their coats and get to work.
The organiser of the conference, Duncan MacInnes, recorded in his diary that ‘it was immediately evident that Oppenheimer was the moving spirit of the affair’, while the chairman of the conference, Karl Darrow, has recorded:
As the conference went on the ascendancy of Oppenheimer became more evident – the analysis (often caustic) of nearly every argument, that magnificent English never marred by hesitation or groping for words (I never heard ‘catharsis’ used in a discourse on [physics], or the clever word ‘mesoniferous’, which is probably O’s invention), the dry humour, the perpetually-recurring comment that one idea or another was certainly wrong, and the respect with which he was heard.
Abraham Pais says his recollections confirm these impressions:
I had heard Oppenheimer speak before but had never yet seen him in action directing a group of physicists during their scientific deliberations. At that he was simply masterful, interrupting with leading questions (at physics gatherings interruptions are standard procedure), summarizing the main points just discussed, and suggesting how to proceed from there.
The first day was dominated by the reports of Lamb and Rabi of the startling experimental results mentioned above. Lamb’s experiments, conducted like Rabi’s at Columbia, and, again like Rabi’s experiments, using radar technology developed during the war, measured the energy of electrons far more precisely than had previously been possible and established that electrons in hydrogen atoms do not behave as Paul Dirac’s theory would predict. Electrons at one level, Lamb discovered, have a higher energy than those at another, rather than (as Dirac’s theory would suggest) all of them having the same energy. An explanation of this ‘shift’ would, as Oppenheimer suggested in the discussion that followed Lamb’s presentation, require a new understanding of quantum electrodynamics (QED). The results reported by Rabi of experiments conducted by two students of his, John Nafe and Edward Nelson, also seemed to call for adjustments to QED, since they gave accurate and reliable measures of the ‘magnetic moments’ of the electrons in hydrogen that contradicted what the Dirac theory would predict. During the second day papers by Kramers and Weisskopf addressed the theoretical issues raised by what became known respectively as the Lamb shift and the ‘anomalous magnetic moment’, and Schwinger indicated during the discussion of Kramers’ paper what shape might be taken by the new understanding of QED that these observational results seemed to demand.
