by Ray Monk
News of Ehrenfest’s death seems to have reached Oppenheimer rather slowly. On 7 October 1933, nearly two weeks after the suicide, he wrote to Frank, apparently still unaware of it. What was more on his mind was what he described as the ‘work with pairs’, which he told Frank ‘has gone along nicely’. He was now more certain than ever that Dirac’s ‘theory gives the wrong answer for the production of very high energy pairs’ and seemed confident that he and his students were making progress in ‘cleaning up the formalism’.
Oppenheimer’s close attention to experimental work in this period is illustrated in the letter to Frank, as are some of the problems that it caused him. Lawrence, he writes, ‘has definitely established the instability of the H2 [deuterium] nucleus. It decomposes upon collision into neutron and proton, to the tune of about six million volts.’ This, he adds, with a discernible note of triumph, makes a ‘hopeless obstacle’ to Heisenberg’s theory of the nucleus. As it turned out, Heisenberg’s theory was a good deal more trustworthy than Lawrence’s observations.
Lawrence that autumn was given the honour of being invited to the seventh Solvay Congress in Brussels, which was held in the week of 22–9 October 1933. The theme originally chosen was the application of quantum mechanics to chemistry, but, in the light of the momentous discoveries of 1932, this was changed to the nucleus. Lawrence’s invitation was the source of great pride at Berkeley. It was, his PhD student Robert Thornton has said, ‘Lawrence’s first European recognition’. When the time came for Lawrence to leave for Belgium: ‘The whole staff went down to the train to see him off. Next morning they got together in the lab and then took off for a kind of two-day picnic climbing Mount Lassen. They were so happy you’d have thought they were all going to talk at the Solvay Congress.’
Unfortunately for Lawrence, his appearance at the Solvay Congress turned out to be something of a humiliation. Heisenberg, Bohr, Chadwick and Irène Curie all used the occasion to express scepticism about his results, unimpressed by his claim that they had been obtained (and could only be obtained) with a machine capable of 800,000 volts. No matter how many volts he had at his command, they insisted, from a theoretical point of view, his interpretation of his results did not make sense. According to Nuel Pharr Davis: ‘Lawrence left the conference feeling bad.’ A colleague at Berkeley described it as ‘one of Lawrence’s saddest experiences’. About a month later, it was shown by scientists at the Carnegie Institution in Washington that Lawrence’s results had been skewed by impurities.
From Oppenheimer’s point of view, Lawrence’s trip to Brussels had a benefit quite independent of Lawrence’s own work and reputation; namely, that it would allow Lawrence to hear, and report back to Oppenheimer on, Paul Dirac’s latest thoughts. Dirac’s paper, entitled ‘Theory of the Positron’, was on precisely the topic that consumed Oppenheimer’s thoughts and energies during this period, and he was pleased to see that, in some respects, Dirac’s thoughts were moving in his direction. However, just as Oppenheimer was immersing himself in quantum electrodynamics, Dirac was becoming disillusioned with it. In particular, he despaired of ever solving the problem that Oppenheimer had been among the first to point out and discuss: the problem that the theory gave infinite answers to questions that seemed to demand a finite answer. These infinities plagued the whole subject of quantum electrodynamics until its reformulation in the late 1940s by Richard Feynman, Freeman Dyson, Julian Schwinger and Sin-Itiro Tomonaga.
For the next two years, however, quantum electrodynamics was almost the sole topic of Oppenheimer’s thoughts, his correspondence and the papers he wrote with his students. His ambition was nothing less than a reformulation of the kind that was finally achieved in the late 1940s. As he put it in a letter to George Uhlenbeck, he and his students were hoping to develop a general formalism together with its physical interpretation. ‘The formalism,’ he told Uhlenbeck, ‘has some resemblance to Schrödinger’s earlier attempts . . . The theory seems very pretty to me, and is in every way consistent with the possibilities of measurement.’
His work continued, however, to be dogged by mathematical error. In November 1933, he and Leo Nedelsky sent a letter to the editor of the Physical Review entitled ‘The Production of Positives by Nuclear Gamma Rays’, in which they presented a method of calculating the probability that an electron/positron pair would be produced by the gamma rays emitted by a nucleus. Three months later, they were forced to publish an erratum confessing that in their final formula they had missed a factor of one third.
Oppenheimer nevertheless continued to publish important work, the most ambitious of which was a paper entitled ‘On the Theory of the Electron and the Positive’,fn35 which was received by the Physical Review on 1 December 1933. This, his largest and most important paper during this period, was written jointly with Wendell Furry, who, now in his second year as an NRF, had recovered his confidence and his productivity. He was even able, on occasion at least, to stand up to Oppenheimer. During this period, it is reported, ‘it was a common sight to see them pacing the streets of Berkeley, engaged in constant harangue. Colleagues would hoist a thumb in their direction and observe that “The Fuzzy and the Furry are in conference.”’
Once they paused on a corner while Oppenheimer threw up his arms and said, ‘Wendell, you have to rationalize everything. You seem to be completely incapable of understanding anything that cannot be put into words.’ Furry smiled, gratified by the remark. Oppenheimer rocked back and roared at him, ‘I didn’t mean that as a compliment.’
Their paper aimed at nothing less than a completely new formulation of Dirac’s theory of the electron, one that sought to avoid the inconsistencies and the infinities of Dirac’s theory and to capture at a more fundamental level the physical realities of electrons and positrons.
The theory as formulated by Furry and Oppenheimer was widely recognised as a formal improvement on Dirac’s version, and Oppenheimer was very proud of it. He sent it to, among others, Bohr, Uhlenbeck, Pauli and Dirac. He also presented a version of it to the Boston meeting of the American Physical Society in December 1933. Few people, however, were persuaded that it represented a major, fundamental advance on Dirac’s work. Pauli was especially dismissive, writing to Heisenberg on 21 January 1934: ‘A short while ago, Oppenheimer sent me a manuscript . . . that completely ignored the problems treated by Dirac and ourselves.’ From Dirac himself there was no response at all. In order to elicit at least some response, Oppenheimer tried taking advantage of the fact that Frank was in Cambridge, writing to him on 7 January 1934 and telling him that he had sent the paper to Dirac. ‘I do not know how Dirac liked what we wrote,’ Oppenheimer told Frank, ‘but if you see him you might warn him that we shall send more presently.’
In a letter to the editor of the Physical Review, dated 12 February 1934, Oppenheimer and Furry pointed out some serious problems with their own theory, and then, four months later, sent another letter pointing out problems with Dirac’s new version of the theory. And still, as Oppenheimer complained in a letter to Uhlenbeck, ‘from Dirac we have not had a murmur’. The following year, Oppenheimer persuaded Dirac to come to Pasadena and further persuaded him to listen to a fifteen-minute presentation by two graduate students who worked on quantum electrodynamics, seeking to build on Dirac’s work. After the presentation was over, the students braced themselves for Dirac’s comments. The only question Dirac asked, however, was: ‘Where is the nearest post office?’
Almost as if it were cause and effect, what Dirac’s biographer calls his ‘golden creative streak’ came to an end just at the time he received the highest honour that a scientist can receive: the Nobel Prize. The telephone call telling him that he was to share the 1933 prize in physics with Erwin Schrödinger came on 9 November. Almost pathologically wary of publicity, Dirac’s first impulse was to turn it down, but Rutherford warned him: ‘A refusal will get you more publicity.’ And so the following month, accompanied by his mother, Dirac travelled to Stockholm to receive the prize. His mother di
d not share either Dirac’s taciturn nature or his dislike of publicity, so, while he avoided the press, she was only too happy to give interviews. Asked by one journalist about her son’s interest in the opposite sex, she replied: ‘He is not interested in young women.’ And so, inevitably, the next day, the newspaper headline was: ‘Thirty-One-Year-Old Professor Dirac Never Looks at Girls’.
Just two months later, Oppenheimer was himself the subject of a somewhat similar headline. ‘Forgetful Prof Parks Girl, Takes Self Home’ announced the San Francisco Chronicle on 14 February 1934, underneath which it told the story of how, at four o’clock in the morning, a policeman on patrol in the hills overlooking Berkeley had found Melba Phillips in a panic, sitting alone in a parked car that belonged to Oppenheimer. She and Oppenheimer had been sitting in the car together, she told police, when he had excused himself to go for a walk. Now, two hours later, he had still not returned. The police searched the area for him and then phoned the Berkeley faculty club, where he was staying at the time. The staff of the faculty club found him in bed, asleep. The newspaper report says that Oppenheimer told police that, after leaving the car, he had forgotten about Melba and gone home. Raymond Birge, in telling this story, comments: ‘Like all geniuses, Oppenheimer was very absent-minded.’ But, in fact, he wasn’t. ‘I never saw the slightest evidence of any absentmindedness in Oppie,’ one of his students recalls, ‘quite the contrary in fact.’
If one resists the temptation to think that this ‘absent-mindedness’ was merely an affectation, then one seems forced to conclude two things: first, that the problems of quantum electrodynamics had a really extraordinary hold on Oppenheimer’s thoughts at this time; and second, that his interest in Melba Phillips was, by comparison, slight. In any case, though Melba stayed at Berkeley for another year, and would join in with the intellectual and social life centred on Oppenheimer’s graduate students, she never again agreed to go on a date with her erstwhile PhD supervisor (she had received her PhD in May 1933).
On 4 June 1934, Oppenheimer wrote to Frank, who was still in Cambridge, telling him that, though he was continuing to work on ‘disentangling the still existing miseries of positron theory’, he hoped his latest ‘manifesto’, written jointly with Furry, would be his last word on the subject. Theoretical physics, he told Frank, ‘is in hell of a way’, largely due to ‘the utter impossibility of making a rigorous calculation of anything at all’. He mentioned that he had been asked to go to Princeton for a year and permanently to Harvard: ‘But I turned down these seductions, thinking more highly of my present jobs, where it is a little less difficult for me to believe in my usefulness, and where the good Californian wine consoles for the hardness of physics and the poor powers of the human mind.’ That summer he would be at Perro Caliente without Frank, but with the Uhlenbecks: ‘We are going to miss you terribly, and it is with very mixed feelings that I shall return to the mountains without you.’
Oppenheimer drove to New Mexico from Ann Arbor, where he attended the summer school, with the Uhlenbecks as his passengers. He had boasted to Frank that ‘Garuda does ninety-five with an unopened throttle’, but in demonstrating his car’s speed to the Uhlenbecks by racing trains across the open prairie, he got something in his eye that scratched his eyeball so badly that, for a while, he had to wear an eye-patch and George Uhlenbeck had to take over the driving. After a six-week holiday in Perro Caliente, the Uhlenbecks returned to Berkeley with Oppenheimer. When they finally got back to Ann Arbor, George Uhlenbeck learned that Hendrik Kramers had been invited to succeed Ehrenfest at Leiden and that he, George, had been invited in turn to succeed Kramers at Utrecht. Much as he loved America and Ann Arbor, there was never any doubt that he would accept. Oppenheimer wrote to him acknowledging the inevitability that he would accept, but expressing his sadness ‘that the American part of you, which has grown so big, will gradually disappear’. ‘I have such a feeling about America,’ Oppenheimer wrote. ‘And let us think, if you must leave us now, that you will come back some time to America; that by accepting in full the responsibilities of being a Dutchman, you will have earned for yourself the right to be a little of an American too.’
That summer, Oppenheimer’s burgeoning school of theoretical physics – what Wolfgang Pauli described as the ‘nim-nim-nim boys’ – was strengthened by the arrival of no fewer than three new NRC fellows: Robert Serber, Edwin Uehling and Frederick W. Brown. This represented nearly half the total number of awards for theoretical physics in the whole United States (three out of seven), showing that, by now, after just five years, Oppenheimer had succeeded in his aim of transforming Berkeley into the leading school of theoretical physics in the country.
Robert Serber, who had taken his PhD at the University of Wisconsin, had originally planned to spend his National Research Fellowship at Princeton working with the Hungarian-American physicist Eugene Wigner, but, just like Wendell Furry before him, he decided after attending the Ann Arbor summer school and seeing Oppenheimer in action that Berkeley was the place to be. ‘When I arrived,’ he remembers, ‘I discovered that most of the National Research Fellows in theoretical physics were already there.’ ‘The word had gotten around,’ he said in an interview many years later; ‘Oppenheimer had the most lively school in theoretical physics in the country then.’
One of the PhD students to arrive that year was Willis E. Lamb, the future Nobel laureate and Oxford professor, who, after graduating in chemistry from Berkeley, had decided to pursue doctorate work in physics, and, as he later put it, ‘naturally I wanted to work with Oppenheimer’. ‘Oppenheimer’s office,’ Lamb remembers, ‘was room 219 LeConte Hall.’
As were many of his students, I was given a small table in the room. Oppenheimer had no desk, but only a table in the middle of the room, heavily strewn with papers. One wall was entirely covered by a blackboard and hardly ever erased. One set of open shelves had reprints of Oppenheimer’s publications. I was allowed to have a copy of most of these.
More details of the way Oppenheimer worked with his students have been given by Serber:
His group would consist of eight or ten graduate students and about a half dozen postdoctoral fellows. He would meet the group once a day in his office. A little before the appointed time its members would straggle in and dispose themselves on the tables and about the walls. Oppie would come in and discuss with one after another the status of the student’s research problem, while the others listened and offered comments. All were exposed to a broad range of topics. Oppenheimer was interested in everything, and one subject after another was introduced and coexisted with all the others. In an afternoon we might discuss electrodynamics, cosmic rays, astrophysics and nuclear physics.
Undeterred by the criticisms of colleagues – one of whom likened him to a mother hen fussing over her chickens – Oppenheimer quite deliberately set out to mould his group of graduate students (PhD students as well as NRC fellows) into a social as well as an intellectual unit.
The first evening that Edwin Uehling spent with this group very nearly gave him a criminal record. It started at Oppenheimer’s apartment, where Uehling and his wife were invited to meet Oppenheimer’s other graduate students, including Melba Phillips. Then they had dinner at a Mexican restaurant, where they drank wine and listened to music until after midnight, after which, on the way back to Berkeley, they were chased by the police because they – Oppenheimer in ‘Garuda’ and Uehling in his Buick – were speeding. After a police car collided with Uehling’s Buick, Uehling was charged with dangerous driving (later reduced to not observing due caution) and Oppenheimer with speeding, but, much to everyone’s relief, the incident was not reported in the press.
Oppenheimer (at that time thirty years old), Serber emphasises, ‘was a bachelor then, and a part of his social life intertwined with ours’.
Often we worked late and continued the discussion through dinner and then later at his apartment on Shasta Road. When we tired of our problems, or cleaned up the point at issue, the talk would turn
to art, music, literature and politics. If the work was going badly we might give up and go to a movie. Sometimes we took a night off and had a Mexican dinner in Oakland or went to a good restaurant in San Francisco. In the early days this meant taking the Berkeley ferry and a ride across the bay. The ferries back to Berkeley didn’t run very often late at night, and this required passing the time waiting for them at the bars and night clubs near the ferry dock. Frequently we missed several ferries.
After the Berkeley spring semester ended in April, and it was time for Oppenheimer to leave for Pasadena, Serber recalls: ‘Many of his students made the annual trek with him.’
Some things were easier in those days. We thought nothing of giving up our houses or apartments in Berkeley, confident that we could find a garden cottage in Pasadena for twenty-five dollars a month. We didn’t own more than could be packed in the back of a car. In Pasadena, in addition to being exposed to the new information on physics, we led an active social life. The Tolmans were good friends, and we had very warm relations with Charlie Lauritsen and his group . . . We spent many evenings at the Mexican restaurants on Olivera Street and many nights partying in Charlie Lauritsen’s garden.
Danish by birth, Lauritsen had been in the United States since 1916, when he emigrated with his wife and small baby, and in Pasadena since 1926. Before he came to Caltech and started an academic career, he had been a radio engineer – a background he put to good use in his work in experimental physics. At Caltech’s high-voltage laboratory Lauritsen worked on developing ‘super-voltage’ X-rays for use in medicine. Then, after Cockcroft and Walton succeeded in splitting the atom, Lauritsen, now working at the new Kellogg Radiation Laboratory, converted one of the X-ray tubes into a particle accelerator, and began work on the artificial production of neutrons and the bombardment of deuterium.