Inside the Centre: The Life of J. Robert Oppenheimer (22 page)

Dirac was at this time in Bristol for the summer vacation. After an initial glance at Heisenberg’s paper, he put it to one side, seeing little interest in it. When he returned to Cambridge in October, he took up the paper again and this time became fascinated with it and quickly convinced of its fundamental importance. He realised that the key to it was the non-commutative multiplications that had puzzled Heisenberg, and, unlike Heisenberg, he recognised these as being akin to a mathematical construction called a ‘Poisson bracket’, which had been introduced into mathematics in the nineteenth century. Using the method of Poisson brackets, Dirac provided Heisenberg’s theory with a new mathematical foundation, the centre of which was the equation (
p
x
q
) – (
q
x
p
) = i
h
/2π, which not only says that the multiplication of
p
and
q
is non-commutative (if it were commutative, of course, (
p
x
q
) – (
q
x
p
) would be equal to zero), but also provides an exact quantity by which
p
x
q
differs from
q
x
p
, a quantity that uses the magical ingredient
h
, Planck’s constant, together with that equally mysterious ‘imaginary’ number, i, which is the square root of –1.

By the time Heisenberg’s paper was published in November 1925, Dirac had sent his own paper – immodestly entitled ‘The Fundamental Equations of Quantum Mechanics’ – to the
Proceedings of the Royal Society
for publication in December. Astonishingly, the very same fundamental equation that Dirac had discovered had, at the same time, been discovered independently by Born and his new assistant, Pascual Jordan, who included it in a paper that they wrote together in September. Like Dirac, Born and Jordan realised that the non-commutativity in Heisenberg’s
mathematics was not unprecedented, though they saw affinities not with Poisson brackets, but with the matrix mathematics developed in the nineteenth century by the British mathematician Arthur Cayley. In October, Born, Jordan and Heisenberg worked together to produce a long and detailed paper called ‘On Quantum Mechanics II’ (often referred to as the
Drei-Männer-Arbeit
, the ‘Three-Man Paper’), which provided a rigorous mathematical foundation for Heisenberg’s new quantum mechanics, but which, because it was received by the
Zeitschrift für Physik
nine days after the
Proceedings of the Royal Society
received Dirac’s paper, cannot claim to have been the first to do so.

By the New Year of 1926, then, a revolution in physics had taken place; the basic theory of quantum mechanics had been formulated and had received two different, but essentially similar, mathematical foundations. And Oppenheimer, merely by being at Cambridge during the academic year of 1925–6 and getting to know Fowler and Dirac, was right at the centre of events. The effect on him was galvanising and he began to immerse himself in the rapid developments that followed the birth of this new subject.

Among these developments was Dirac’s second paper on the new theory, ‘Quantum Mechanics and a Preliminary Investigation of the Hydrogen Atom’, sent off for publication at the end of January 1926, which introduced a now-famous distinction between classical numbers, or ‘c-numbers’, which commute, and quantum numbers, or ‘q-numbers’, which do not. Before this article appeared in print, Dirac presented it on 2 March as a paper to the Del Squared V Club, with Oppenheimer among those present. The club minutes record that after Dirac’s paper there followed a ‘lengthy discussion’, in which, no doubt, Oppenheimer took a full part.

On 7 March, Oppenheimer wrote a letter to Fergusson, the tone of which is markedly different from his previous letter of 23 January, written shortly after, and mainly to apologise for, the bizarre attempted strangling in Paris. Whereas then he had struck a remorseful and confessional tone, now he sounds brisk, businesslike and jocular. ‘My regret at not having strangled you is now intellectual rather than emotional,’ he told Fergusson, assuring him that, if he chose to visit Oppenheimer in Cambridge before he went to Italy ‘it will be perfectly safe & I shall be very glad to see you’. Rather warily, Fergusson responded positively to this invitation and came to Cambridge some time in March. Oppenheimer, he recalls, put him up in a room next door to his own, ‘and I remember thinking that I’d better make sure that he didn’t turn up in the night, so I put a chair up against the door. But nothing happened.’ When Fergusson alluded to Oppenheimer’s behaviour during the Christmas vacation, Oppenheimer told him not to worry; he was, he insisted, ‘over that’.

Oppenheimer told Fergusson that he would probably have to spend
the Easter vacation at Cambridge because he had so much work to do. Almost certainly, the work in question consisted not of his laboratory experiments, but rather of a paper in theoretical physics that was to become his first publication. If he could take a break from this work, he told Fergusson, he would go for a short walking holiday in Corsica with Wyman and Edsall, in which case, he wrote, he hoped that he would be able to meet Fergusson in Italy. In the event, Oppenheimer did manage to tear himself away from his theoretical studies for the projected holiday in Corsica, though he did not, as it turned out, succeed in joining Fergusson in Italy.

Shortly before he left for Corsica, Oppenheimer, along with the rest of the theoretical physics community, received a bolt out of the blue. On 13 March, the German academic journal
Annalen der Physik
published an article by the Austrian physicist Erwin Schrödinger called ‘Quantization as a Problem of Proper Values’, which seemed to put the recent quantum-mechanics revolution in a completely new light. Or rather, it seemed to show how it would look in the
old
light, before the advent of
Knabenphysik.
In particular, what Schrödinger – who, at thirty-eight years old, was himself certainly no
Knabe
– appeared to demonstrate was that quantum mechanics could quite readily be absorbed into old, familiar physics using old familiar mathematics. All the results that had been derived by Heisenberg, Born, Jordan and Dirac using esoteric and obscure methods of mathematics could, Schrödinger demonstrated, equally be derived from a theory that used only that most well-understood and widely used of mathematical tools: the differential equation. Moreover (and this was either a great advantage or a step backwards, depending on one’s understanding of the physics of electrons), unlike the theories of Heisenberg, Born, Jordan and Dirac, Schrödinger’s theory allowed one to
visualise
what was happening inside an atom. Building on de Broglie’s work, Schrödinger’s theory called on one to imagine that an electron simply
is
a wave. In place of the term ‘quantum mechanics’, therefore, Schrödinger called his theory ‘wave mechanics’.

The reaction among physicists, particularly the older ones, to Schrödinger’s theory (which would be developed over three further landmark papers published in 1926) was almost universally and unrestrainedly enthusiastic. Max Planck wrote to Schrödinger, telling him that he had read his first paper ‘like an eager child hearing the solution to a riddle that had plagued him for a long time’. Einstein told him ‘the idea of your work springs from true genius’. Even Max Born became quickly convinced that wave mechanics provided the ‘deepest form of the quantum laws’. Heisenberg, however, hated Schrödinger’s theory, seeing in it a desperate attempt to cling on to an outdated and unsupportable visualisation of the ‘orbits’ of electrons. Dirac, too,
disliked Schrödinger’s theory, at least initially. When, however, it was proved – by Dirac, Schrödinger and many others – that, mathematically, Schrödinger’s theory was equivalent to both the matrix mechanics of Born, Jordan and Heisenberg and the ‘fundamental equations’ of Dirac himself, Dirac overcame his objections and treated Schrödinger’s version of the theory as an interesting, and sometimes useful, alternative formulation of quantum mathematics.

Once the mathematical equivalence of the three versions of quantum mechanics was realised, there remained the question – which Dirac was inclined to dismiss as ‘philosophical’, but which Born, Heisenberg, Bohr and others regarded as fundamental – namely: how does one understand the physical reality that can be modelled equally by each of these three different theories? What, exactly, is being modelled by the mathematics? What, really,
is
an electron? A particle? A wave? Could it possibly be both? Might it possibly be neither? How should one, if indeed one should at all,
picture
an electron and its movements?

With these questions hanging in the air over the entire community of theoretical physicists, Oppenheimer embarked on his holiday with Wyman and Edsall, his mind more or less completely preoccupied with the exciting developments in quantum theory. In a short autobiographical article that Edsall wrote at the end of his life, he remembers Oppenheimer during this holiday as ‘passionately eager to solve the problems of quantum physics’. Oppenheimer, Edsall writes, was, unlike their mutual friend Dirac (whom Edsall knew as a fellow graduate student at St John’s College), ‘intensely articulate’; he ‘conveyed to me the deep excitement and promise of what was going on in quantum mechanics . . . The feeling that he gave me for the central importance of the subject stayed with me.’

There was a great deal of talk during this holiday. For ten days, Edsall, Wyman and Oppenheimer walked through the mountainous Corsican countryside, covering the entire length of the island, beginning in the north and ending in the impressive medieval citadel of Bonifacio, on the southernmost tip of the island, overlooking the strait that separates Corsica from Sardinia. They spent their nights in small inns, peasant huts or even occasionally out in the open. They had, it seems, very little to do with the locals, and so, spending all day and all night together, there was plenty of time and opportunity for discussion. As well as physics, Oppenheimer talked of French and Russian literature, especially Dostoyevsky. When Edsall expressed a preference for Tolstoy, Oppenheimer insisted: ‘No, no. Dostoevsky is superior. He gets to the soul and torment of man.’ Once, in a conversation about people who had achieved great things, whether in science or literature, Oppenheimer remarked: ‘The kind of person that I admire most would be one who becomes extraordinarily good at doing a lot of things but maintains a tear-stained countenance.’

Despite this remark, the Oppenheimer remembered by Edsall and Wyman during this holiday was far removed indeed from the Oppenheimer that Fergusson had encountered in France just three months previously. They even, on one occasion, saw him convulsed with mirth. What prompted this unprecedented event was a misunderstanding between Edsall and the Corsican police over some photographs that Edsall was taking of the famous fortifications at Bonifacio. Convinced that he was some kind of spy, the police took Edsall to the station for questioning. Wyman and Oppenheimer accompanied him, and, while they sat waiting in a corridor, they could hear Edsall trying to explain that he was not a spy, but a tourist. Though he himself could not stop laughing at the absurdity of the situation, Wyman was astonished when he looked up at Oppenheimer to see him slapping his thighs and chuckling.

This incident at Bonifacio, coming at the end of the trio’s ten-day hike, suggests that, from Oppenheimer’s point of view, the holiday achieved its purpose of helping him to unwind and fully regain his sanity. In fact, it seems to have done much more than that. Several times throughout his life Oppenheimer emphasised the enormous importance that these ten spring days in Corsica had for him. They had an impact similar to, but even greater than, his first trip to New Mexico in 1922. Indeed, Oppenheimer suggested on a number of occasions, this holiday was the turning point in his life.

To one of his earliest biographers, Nuel Pharr Davis, whose
Lawrence & Oppenheimer
was published the year after Oppenheimer’s death, he spoke of ‘what began for me in Corsica’ and drew attention to the significance of an undocumented episode that occurred during his time there, an episode that he described as ‘a great and lasting part’ of his life. The reason he was telling him about this, Oppenheimer told Pharr Davis, was to counteract the impression that the turning point in his life had been the security trial in 1954: ‘You see, don’t you, that I’m proving this point to you now. With something important to me not in those records.’ As for what that ‘something’ was, Oppenheimer was teasingly evasive. ‘You ask whether I will tell you the full story or whether you must dig it out,’ he wrote to Pharr Davis. ‘But it is known to few and they won’t tell. You can’t dig it out. What you need to know is that it was not a mere love affair, not a love affair at all, but love.’ ‘Geography,’ he added, ‘was henceforth the only separation I recognised, but for me it was not a real separation.’

Pharr David guessed that what Oppenheimer was alluding to here was a love for ‘a European girl who could not marry him’. This is perhaps true, but, even if it is, there is clearly more to understand about why Oppenheimer’s spring break in Corsica was such an important event in his life. His later friend Haakon Chevalier recalled
Oppenheimer once telling him, many years after the event, that ‘one of the great experiences in his life’ occurred in Corsica in 1926. The experience in question, however, had nothing to do with a ‘European girl’, or anyway not a real one. It was, rather, his reading of Proust’s
À la recherche du temps perdu
.

Once, when the topic of cruelty came into the conversation, Chevalier recalled, Oppenheimer surprised him by quoting from memory, word for word, a passage from Proust’s novel. The passage comes in the first volume of
Du côté de chez Swann
, when Mademoiselle Vinteuil goads her lesbian lover to spit on a photograph of her recently departed father. In describing this scene, Proust emphasises to his readers that there is something theatrical about Mlle Vinteuil’s ‘sadism’. She is not
really
evil; rather, she finds it erotic to pretend to be so. In fact, Proust writes, it is precisely
because
she is not really evil that she
can
derive orgasmic pleasure from the grotesque performance of her lover. In the passage Oppenheimer memorised and recited to Chevalier, Proust writes: