by Ray Monk
What the principle states is that no two electrons in the same atom can exist in the same quantum state, where the quantum state of an electron is characterised by four ‘quantum numbers’. One of these numbers, postulated by Pauli, is a two-valued ‘degree of freedom’, which Oppenheimer’s friends Goudsmit and Uhlenbeck identified in 1925 as the ‘spin’ of an electron. Because the spin of the electron is measured to be one half that of Planck’s constant, and the spin of the photon is an integral unit, the equations describing the behaviours of the two particles are different. Dirac’s equation provides the relatavistically correct treatment of spin ½ particles such as the electron.fn25
What Pauli and Heisenberg hoped to do was use the conceptual tools and the mathematical techniques that Dirac had provided to forge their proposed quantum-field theory. It was a huge challenge and they had very little time to rise to it, since Heisenberg was committed to a lecture tour of the United States, beginning on 1 March 1929, that would keep him away from Europe for most of the rest of the year. Nevertheless, rise to it they did, and the paper, ‘On the Quantum Dynamics of Wave Fields’, was duly delivered for publication before Heisenberg’s departure for the United States.
From the very beginning of his association with Pauli, therefore, Oppenheimer was present at the birth of important new ideas, and Pauli’s joint paper with Heisenberg was to set the agenda for Oppenheimer’s own research during his time at Zurich and for many years after that. This contributed to something that Oppenheimer’s later student and friend Robert Serber noted, namely that during his time with Pauli, Oppenheimer’s ‘interests changed and thereafter were devoted to the more fundamental questions of physics’.
Apart from allowing him to introduce himself to Pauli and gain his consent for coming to Zurich, Oppenheimer’s brief time at Leipzig in the January of 1929 was important for another reason. For it was there that he met for the first time the man who would come to know and understand him perhaps better than any other: Isidor Rabi. ‘I first met him in Leipzig,’ Rabi later recalled. ‘He had just got his degree a year or so before, and there were a lot of stories about him – as a personality: his good wit, his sarcasm and so on.’ The two got on so well not only because of the similarities in their New York Jewish background mentioned earlier, but also because of their shared sense of affronted pride when faced by the attitude towards American scientists that prevailed in Europe. After working at Hamburg under the great experimental physicist Otto Stern, Rabi had come to think that German students were no better than American students. In fact, he came to think the American system of university education was on the whole better: ‘What we needed were the leaders.’ He and Oppenheimer were united in their determination to be two of those leaders.
Like Oppenheimer, Rabi was being funded by an IEB fellowship. After spending the first few months of his fellowship in Hamburg, with Stern, Rabi had gone to Leipzig in the New Year of 1929 hoping to study under Heisenberg. When he arrived there, however, he learned of Heisenberg’s plan to leave for the US at the beginning of March and so decided, on Heisenberg’s advice, to go to Zurich to work with Pauli. It was at Zurich, from February to July 1929, that the friendship between Rabi and Oppenheimer blossomed. ‘I got to know him quite well,’ Rabi recalled, ‘because our intellectual interests about various things – science, philosophy, religion, painting – were similar and different from the interests of most young physicists at that time. We saw a good deal of one another.’
As Ehrenfest foresaw, Zurich was just the right place for Oppenheimer, and Pauli just the right man. Summing up his experiences in Europe as an IEB fellow, Oppenheimer later said:
The time with Ehrenfest had seemed terribly inadequate to what was really in Ehrenfest and the time with Kramers had seemed good but not very substantial – very good personally, very close, but not very substantial. The time with Pauli seemed just very, very good indeed.
‘I got,’ he said, ‘to be not only extremely respectful but also extremely fond of Pauli and I learned a lot from him.’
In his younger days, Pauli had been Max Born’s assistant at Göttingen, but Oppenheimer’s relationship with Pauli could not have been more different from that with Born, nor could there be a character whose personality differed more sharply from Born’s than Pauli’s. Where Born was fragile and introverted, Pauli was blunt and unafraid to give offence. He was known as ‘the Wrath of God’ because of the ferocity of his criticisms of shoddy thinking. He was, from a young age, impossible to intimidate. As a young graduate student in Munich, Pauli had attended a talk given by Einstein and contributed to the discussion by saying: ‘You know, what Mr Einstein said is not so stupid!’ Once, in discussion with a colleague who asked him to slow down because he could not think as fast as Pauli, Pauli replied: ‘I do not mind if you think slowly, but I do object when you publish more quickly than you can think.’ Most famously, he once said of an unclear paper: ‘Das ist nicht nur nicht richtig, es ist nicht einmal falsch!’ (‘Not only is it not right, it’s not even wrong.’) His own reputation was based as much on his contributions to public discussion and on his voluminous correspondence with the top physicists of the day as it was on his publications, and he was entirely indifferent to the concern for priority that worried many scientists.
Oppenheimer did not altogether escape Pauli’s biting wit. ‘His ideas are always very interesting,’ Pauli is reported to have said about Oppenheimer, ‘but his calculations are always wrong.’ Pauli would also impersonate Oppenheimer’s habit of murmuring ‘nim-nim-nim’ while he was thinking what to say and groping for words, and took to calling him ‘the nim-nim-nim man’. Rabi recalls: ‘Pauli once remarked to me that Oppenheimer seemed to treat physics as an avocation and psychoanalysis as a vocation.’ On the whole, however, Pauli had, from the beginning, a good impression of Oppenheimer, as he reported in a letter to Ehrenfest of 15 February 1929: ‘I believe that Oppenheimer is quite comfortable in Zurich, that he can work well here, and that scientifically it will still be possible to pull many good things out of him.’
His strength is that he has many and good ideas, and has much imagination. His weakness is that he is much too quickly satisfied with poorly based statements, that he does not answer his own often quite interesting questions for lack of perseverance and thoroughness, and that he leaves his problems in a half-digested stage of conjecture, belief or disbelief.
This acute analysis contains few surprises, but Pauli then goes on to criticise Oppenheimer for something that nobody had noticed before: his respect for authority. Oppenheimer, Pauli told Ehrenfest, ‘considers all I say as final and definitive truth. I do not know the origins of this need for others’ authority.’ That Oppenheimer had such a need would certainly have been news to Born.
At Zurich, Oppenheimer seems to have come close to finding what he had claimed to (but alas failed to) find at Göttingen, namely, a community of like-minded scholars. Rudolf Peierls, who had been a student of Heisenberg’s at Leipzig, but who had received and taken the same advice as Rabi to transfer to Zurich, has described the spring and early summer of 1929 as ‘rather short for all that seems to have happened’. As well as writing a great deal, he recalls, there was ‘plenty of time for concerts and cinema, and for sailing’.
It was then easy to rent a sailboat for a few hours, and I liked to take friends out on the lake. I even persuaded Pauli to come sailing – I cherish a photo showing him, Robert Oppenheimer, and I.I. Rabi on the boat.
The photograph survives and shows a dapper-looking Oppenheimer, cigarette in hand and hat on head, talking to Rabi and another young American physicist called L.M. Mott-Smith. All three look lost in thought and deep in conversation. Meanwhile, on the right of the picture, Pauli, smiling mischievously, stares at the camera.
In a description that recalls his fellow students’ impressions of his undergraduate days at Harvard, Rabi remembers that Oppenheimer ‘worked very hard that spring but had a gift of concealing his assiduous application with an air of
easy nonchalance’.
Actually, he was engaged in a very difficult calculation of the opacity of surfaces of stars to their internal radiation, an important constant in the theoretical construction of stellar models. He spoke little of these problems and seemed to be much more interested in literature, especially the Hindu classics and the more esoteric Western writers.
Though it was an intellectually fruitful period for him, Oppenheimer published only one paper during his time at Zurich, a paper called ‘Über die Strahlung der freien Elektronen im Coulombfeld’ (‘On the Radiation of Electrons in a Coulomb Field’), which he sent to the Zeitschrift für Physik on 6 May 1929. Pauli was extremely impressed with this piece of work. ‘Using flawless methods’, he wrote to Sommerfeld in Munich, Oppenheimer ‘has calculated everything one can desire’.
In a letter to Bohr of July, Pauli described Oppenheimer’s paper as ‘a continuation of the work of Heisenberg and myself on QED’ and for a while there was talk of a three-way collaboration. As it turned out, Heisenberg and Pauli published the second (and final) part of their jointly authored attempt to formulate new rules for quantum electrodynamics as a two-man paper (with an acknowledgement to Oppenheimer) in September 1929, while Oppenheimer waited until November, when he was back in the US, to deliver his own contribution to the subject: a paper for the Physical Review entitled ‘Note on the Theory of the Interaction of Field and Matter’.
A possible explanation for the abandonment of the plan to work together with Heisenberg and Pauli lies in Oppenheimer’s continued bad health. The persistent cough that had so alarmed Ehrenfest did not go away, and Dr Robbins of the Rockefeller Foundation kept (as he was asked to by Ehrenfest) a close eye on the situation. On 30 April 1929, Robbins wrote to Oppenheimer: ‘First and foremost is the question of your health.’ It would, Robbins said (apparently in response to a request from Oppenheimer), be quite appropriate to terminate his IEB fellowship a month early in order for him to prepare his teaching in Berkeley for the coming academic year. The fellowship was due to finish at the end of July, so, presumably, Robbins was now expecting it to finish at the end of June.
In a letter written on 14 May, in reply to Robbins’s letter of April, Oppenheimer said that he was ‘fairly certain that I shall be able to continue with the work until July’ and he still hoped, as he had originally stated was his intention, to visit Bohr in Copenhagen for two weeks at the end of June. Oppenheimer devoted the rest of this letter to an attempt to answer Robbins’s request for some suggestions as to how the difficulties experienced by American students in Europe might be overcome. Oppenheimer’s analysis of those difficulties, perhaps inevitably, strikes an autobiographical note. They are, he began, ‘most acute in men who combine a certain weakness, timidity, hesitancy of character with a quite robust vanity – or, perhaps, more accurately – with an urgent desire for excellence’. These students, he went on, are away from their friends, and also ‘from the pampering of an American university, and from a language which they can control’, and are ‘introduced to the more critical, more disciplined, more professional science of Europe’. This state of affairs:
induces in the victim a state of surrender, and a false metaphysical melancholy which replaces, and makes impossible, an active participation in the European scheme, and an honest attempt to learn from it. The melancholy is presumably unpleasant; it is usually dissipated by return to America, and the consequent renewal of the pampering. But it acts as a protective coating for the American against that which he was sent to Europe to learn; almost always it is a sterile melancholy. It is the melancholy of the little boy who will not play because he has been snubbed.
Oppenheimer’s suggested solution was a lot less interesting than his description of the problem. ‘I think,’ he told Robbins, ‘that the most useful preventative would be to let the men know a little better what their situation will be, and to warn them of the collapse, so that they may be on their guard against it, and may make a conscious and specific effort to avert it.’
Oppenheimer never did go to Copenhagen, nor did he stay in Zurich till his fellowship finished at the end of July. Instead he terminated his fellowship a month early and returned to the US in July. This may have been because of his cough, or it may have been, as he had earlier explained to Robbins, because he was anxious to leave himself enough time to prepare for his teaching duties in California. But the letter to Robbins suggests another reason: he simply wanted to get back home. He himself wrote in later life: ‘In the spring of 1929 I returned to the United States. I was homesick for this country, and in fact I did not leave it again for nineteen years.’
Oppenheimer’s homesickness at the end of his time in Zurich is illustrated by an episode recounted by Felix Bloch, who was then a young physicist working with Pauli. Bloch remembers visiting Oppenheimer’s apartment in Zurich and being struck by the many things he had brought with him from New Mexico: ‘I was particularly impressed by the beautiful Navajo rug he had on his sofa.’ Bloch had never been to the US and asked Oppenheimer to tell him about his country. Had he not had a genuine interest in knowing more about the US, he later told Oppenheimer’s first biographer, Denise Royal, he might easily have regretted his request, such was ‘the intensity of Oppenheimer’s affection for his country’.
On 6 May 1929, Oppenheimer wrote to Frank, thanking him for the birthday present Frank had sent of a book of Degas (Oppenheimer turned twenty-five on 22 April), and suggesting arrangements for the coming summer in New Mexico. First, he told Frank, Perro Caliente – ‘house and six acres and stream’ – was theirs for the next four years and there was an allowance of $300 for restoration. Second, Katherine Page would go out to the Pecos in May, Julius and Ella would be ready to leave New York by the middle of June, and he himself would be back in the US ‘about the middle of July’ and ‘determined not to spend more than a week or so in the East’. So, he concluded, Frank should take their parents out west in the middle of June, and he ‘and a suitable friend’ should ‘try to open up the place, get horses, learn to cook, make the hacienda as nearly habitable as you can, and see the country’. Meanwhile, he assured Frank, he himself planned to ‘come straight out to the Pecos, and have about three weeks there’.
So it was that in June 1929 Frank arrived at Los Pinos with two school friends, Ian Martin and Roger Lewis. From a Sears Roebuck catalogue Frank ordered furniture, rugs and kitchen equipment, and he and his friends stayed with Katherine Page while they waited for it to arrive. Shortly after the arrival of the mail-order goods, Oppenheimer himself arrived with a wagon loaded with bootleg whisky, mineral oil, peanut butter and Viennese sausages. For the next three weeks the four of them spent the days riding the mountains and the nights reading and drinking. ‘We’d get sort of drunk,’ Frank remembered, ‘when we were high up, and we’d act all kind of silly.’ Oppenheimer had to leave sooner than Frank. He went first to Pasadena and then to Berkeley, from where he wrote to his brother, thanking him for a letter in which he provided an account of what he and his friends had been up to since Oppenheimer’s departure. ‘It made me a little envious,’ Oppenheimer confessed, ‘and pleased me awfully to hear of gay times at Perro Caliente. And I can think how let down you will feel now that it is so nearly time to close up.’ As Oppenheimer prepared to begin his career as a teacher of physics, it was the New Mexican desert that restored his physical and spiritual health sufficiently for him to feel able to meet the challenges ahead.
* * *
fn24 Pauling was awarded the Nobel Peace Prize in 1962 for his campaigns against nuclear-weapon testing. As he had already, in 1954, been awarded the Nobel Prize for Chemistry, he thereby became, along with Marie Curie, one of only two people to have received two Nobel Prizes in different fields.
fn25 I am grateful to my friend James Dodd for explaining this to me.
8
An American School of Theoretical Physics
‘I DIDN’T START to make a school,’ Oppenheimer said towards the end of his life, re
calling his early days at Berkeley, ‘I didn’t start to look for students. I started really as a propagator of the theory which I loved, about which I continued to learn more.’ The latter part of this statement is clearly true, but the first part seems contradicted by remarks he made elsewhere in the same interview that have already been quoted: ‘I thought I’d like to go to Berkeley because it was a desert. There was no theoretical physics and I thought it would be nice to try to start something.’
In fact, he did build a school at Berkeley, one that the eminent physicist Hans Bethe has described as ‘the greatest school of theoretical physics that the United States has ever known’. And, despite his statement to the contrary, Oppenheimer went to Berkeley precisely in order to build a school. It had become important to him, as it had to Rabi, and to many American physicists who had experienced the condescension directed at them by their European counterparts, to establish a world centre for theoretical physics in the US. In some of his remarks about Berkeley, however, he indulges in a bit of condescension of his own. For example, his description of Berkeley as a ‘desert’ and his statement that there was no theoretical physics there are both a little overstated. After all, Edward Condon, whom Oppenheimer had met at Göttingen, had studied at Berkeley, both as an undergraduate and as a graduate, and had learned enough theoretical physics to get a PhD in the subject and to be accepted as a postdoctoral student by both Max Born and Arnold Sommerfeld.
