The awful fact of excellence did not continue to elude him. As he approached a point of psychological crisis he also drove hard to extend himself, understanding deeply that his mind must pull him through. He was “doing a tremendous amount of work,” a friend said, “thinking, reading, discussing things, but obviously with a sense of great inner anxiety and alarm.”470 A crucial change that year was his first meeting with Bohr. “When Rutherford introduced me to Bohr he asked me what I was working on. I told him and he said, ‘How is it going?’ I said, ‘I’m in difficulties.’ He said, ‘Are the difficulties mathematical or physical?’ I said, ‘I don’t know.’ He said, ‘That’s bad.’ ”471 But something about Bohr—his avuncular warmth at least, what C. P. Snow calls his simple and genuine kindness, his uninsipid “sweetness”—helped release Oppenheimer to commitment: “At that point I forgot about beryllium and films and decided to try to learn the trade of being a theoretical physicist.”472, 473
Whether the decision precipitated the crisis or began to relieve it is not clear from the record. Oppenheimer visited a Cambridge psychiatrist. Someone wrote his parents about his problems and they hurried over as they had hurried to Camp Koenig years before. They pushed their son to see a new psychiatrist. He found one in London on Harley Street. After a few sessions the man diagnosed dementia praecox, the older term for what is now called schizophrenia, a condition characterized by early adult onset, faulty thought processes, bizarre actions, a tendency to live in an inner world, incapacity to maintain normal interpersonal relationships and an extremely poor prognosis. Given the vagueness of the symptomatology and Oppenheimer’s intellectual dazzle and profound distress, the psychiatrist’s mistake is easy enough to understand. Fergusson met Oppenheimer in Harley Street one day and asked him how it had gone. “He said . . . that the guy was too stupid to follow him and that he knew more about his troubles than the [doctor] did, which was probably true.”474
Resolution began before the consultations on Harley Street, in the spring, on a ten-day visit to Corsica with two American friends. What happened to bring Oppenheimer through is a mystery, but a mystery important enough to him that he deliberately emphasized it—tantalizingly and incompletely—to one of the more sensitive of his profilers, Nuel Pharr Davis. Corsica, Oppenheimer wrote his brother Frank soon after his visit, was “a great place, with every virtue from wine to glaciers, and from langouste to brigantines.”475 To Davis, late in life, he emphasized that although the United States Government had assembled hundreds of pages of information about him across the years, so that some people said his entire life was recorded there, the record in fact contained almost nothing of real importance. To prove his point, he said, he would mention Corsica. “The [Cambridge] psychiatrist was a prelude to what began for me in Corsica. You ask whether I will tell you the full story or whether you must dig it out. 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.”476 It was, he said, “a great thing in my life, a great and lasting part of it.”477
Whether a love affair or love, Oppenheimer found his vocation in Cambridge that year: that was the certain healing. Science saved him from emotional disaster as science was saving Teller from social disaster. He moved to Göttingen, the old medieval town in Lower Saxony in central Germany with the university established by George II of England, in the autumn of 1926, late Weimar years. Max Born headed the university physics department, newly installed in institute buildings on Bunsenstrasse funded by the Rockefeller Foundation. Eugene Wigner traveled to Göttingen to work with Born, as had Werner Heisenberg and Wolfgang Pauli and, less happily, the Italian Enrico Fermi, all future Nobel laureates. James Franck, having moved over from Haber’s institute at the KWI, a Nobelist as of 1925, supervised laboratory classes. The mathematicians Richard Courant, Herman Weyl and John von Neumann collaborated. Edward Teller would show up later on an assistantship.
The town was pleasant, for visiting Americans at least. They could drink frisches Bier at the fifteenth-century Schwartzen Bären, the Black Bears, and sit to crisp, delicate wiener Schnitzel at the Junkernschänke, the Junkers’ Hall, under a steel engraving of former patron Otto von Bismarck. The Junkernschänke, four hundred years old, occupied three stories of stained glass and flowered half-timber at the corner of Barefoot and Jew streets, which makes it likely that Oppenheimer dined there: he would have appreciated the juxtaposition. When a student took his doctorate at Göttingen he was required by his classmates to kiss the Goose Girl, a pretty, lifesize bronze maiden within a bronze floral arbor that decorates the fountain on the square in front of the medieval town hall. To reach the lips of the Gänseliesel required wading or leaping the fountain pool, the real point of the exercise, a baptism into professional distinction Oppenheimer must have welcomed.
The townspeople still suffered from the disaster of the war and the inflation. Oppenheimer and other American students lodged at the walled mansion of a Göttingen physician who had lost everything and was forced to take in boarders. “Although this society [at the university] was extremely rich and warm and helpful to me,” Oppenheimer says, “it was parked there in a very miserable German mood . . . bitter, sullen, and, I would say, discontent and angry and with all those ingredients which were later to produce a major disaster. And this I felt very much.”478 At Göttingen he first measured the depth of German ruin. Teller generalized it later from his own experience of lost wars and their aftermaths: “Not only do wars create incredible suffering, but they engender deep hatreds that can last for generations.”479
Two of Oppenheimer’s papers, “On the quantum theory of vibrationrotation bands” and “On the quantum theory of the problem of the two bodies,” had already been accepted for publication in the Proceedings of the Cambridge Philosophical Society when he arrived at Göttingen, which helped to pave the way. As he came to his vocation the papers multiplied. His work was no longer apprenticeship but solid achievement. His special contribution, appropriate to the sweep of his mind, was to extend quantum theory beyond its narrow initial ground. His dissertation, “On the quantum theory of continuous spectra,” was published in German in the prestigious Zeitschrift für Physik. Born marked it “with distinction”—high praise indeed. Oppenheimer and Born jointly worked out the quantum theory of molecules, an important and enduring contribution. Counting the dissertation, Oppenheimer published sixteen papers between 1926 and 1929. They established for him an international reputation as a theoretical physicist.
He came home a far more confident man. Harvard offered him a job; so did the young, vigorous California Institute of Technology at Pasadena. The University of California at Berkeley especially interested him because it was, as he said later, “a desert,” meaning it taught no theoretical physics yet at all.480 He decided to take Berkeley and Caltech both, arranging to lecture on the Bay Area campus in the autumn and winter and shift to Pasadena in the spring. But first he went back to Europe on a National Research Council fellowship to tighten up his mathematics with Paul Ehrenfest at Leiden and then with Pauli, now at Zurich, a mind more analytical and critical even than Oppenheimer’s, a taste in physics more refined. After Ehrenfest Oppenheimer had wanted to work in Copenhagen with Bohr. Ehrenfest thought not: Bohr’s “largeness and vagueness,” in Oppenheimer’s words, were not the proper astringent. “I did see a copy of the letter [Ehrenfest] wrote Pauli. It was clear that he was sending me there to be fixed up.”481
Before he left the United States for Leiden Oppenheimer visited the Sangre de Cristos with Frank. The two brothers found a cabin and a piece of land they liked—“house and six acres and stream,” in Robert’s terse description—up high on a mountain meadow.482 The house was rough-hewn timber chinked with caulk; it lacked even a privy. While Robert was in Europe his father arranged a long-term lease and set aside three hundred dollars for what Oppenheimer calls “restoration.” A summer in the mountains was restoration for the celebrated young
theoretician as well.
* * *
At the end of that summer of 1927 the Fascist government of Benito Mussolini convened an International Physical Congress at Como on the southwestern end of fjord-like Lake Como in the lake district of northern Italy. The congress commemorated the centennial of the death in 1827 of Alessandro Volta, the Como-born Italian physicist who invented the electric battery and after whom the standard unit of electrical potential, the volt, is named. Everyone went to Como except Einstein, who refused to lend his prestige to Fascism.483 Everyone went because quantum theory was beleaguered and Niels Bohr was scheduled to speak in its defense.
At issue was an old problem that had emerged in a new and more challenging form. Einstein’s 1905 work on the photoelectric effect had demonstrated that light sometimes behaves as if it consists not of waves but of particles. Turning the tables, early in 1926 an articulate, cultured Viennese theoretical physicist named Erwin Schrödinger published a wave theory of matter demonstrating that matter at the atomic level behaves as if it consists of waves. Schrödinger’s theory was elegant, accessible and completely consistent. Its equations produced the quantized energy levels of the Bohr atom, but as harmonics of vibrating matter “waves” rather than as jumping electrons. Schrödinger soon thereafter proved that his “wave mechanics” was mathematically equivalent to quantum mechanics. “In other words,” says Heisenberg, “ . . . the two were but different mathematical formulations of the same structure.”484 That pleased the quantum mechanicists because it strengthened their case and because Schrödinger’s more straightforward mathematics simplified calculation.
But Schrödinger, whose sympathies lay with the older classical physics, made more far-reaching claims for his wave mechanics. In effect, he claimed that it represented the reality of the interior of the atom, that not particles but standing matter waves resided there, that the atom was thereby recovered for the classical physics of continuous process and absolute determinism. In Bohr’s atom electrons navigated stationary states in quantum jumps that resulted in the emission of photons of light. Schrödinger offered, instead, multiple waves of matter that produced light by the process known as constructive interference, the waves adding their peaks of amplitude together. “This hypothesis,” says Heisenberg dryly, “seemed to be too good to be true.”485 For one thing, Planck’s quantized radiation formula of 1900, by now exhaustively proven experimentally, opposed it. But many traditional physicists, who had never liked quantum theory, greeted Schrödinger’s work, in Heisenberg’s words, “with a sense of liberation.”486 Late in the summer, hoping to talk over the problem, Heisenberg turned up at a seminar in Munich where Schrödinger was speaking. He raised his objections. “Wilhelm Wien, [a Nobel laureate] who held the chair of experimental physics at the University of Munich, answered rather sharply that one must really put an end to quantum jumps and the whole atomic mysticism, and the difficulties I had mentioned would certainly soon be solved by Schrödinger.”487
Bohr invited Schrödinger to Copenhagen. The debate began at the railroad station and continued morning and night, says Heisenberg:
For though Bohr was an unusually considerate and obliging person, he was able in such a discussion, which concerned epistemological problems which he considered to be of vital importance, to insist fanatically and with almost terrifying relentlessness on complete clarity in all arguments. He would not give up, even after hours of struggling, [until] Schrödinger had admitted that [his] interpretation was insufficient, and could not even explain Planck’s law. Every attempt from Schrödinger’s side to get round this bitter result was slowly refuted point by point in infinitely laborious discussions.488
Schrödinger came down with a cold and took to his bed. Unfortunately he was staying at the Bohrs’. “While Mrs. Bohr nursed him and brought in tea and cake, Niels Bohr kept sitting on the edge of the bed talking at [him]: ‘But you must surely admit that . . .’ ”489 Schrödinger approached desperation. “If one has to go on with these damned quantum jumps,” he exploded, “then I’m sorry that I ever started to work on atomic theory.” Bohr, always glad for conflicts that sharpened understanding, calmed his exhausted guest with praise: “But the rest of us are so grateful that you did, for you have thus brought atomic physics a decisive step forward.”490 Schrödinger returned home discouraged but unconvinced.
Bohr and Heisenberg then went to work on the problem of reconciling the dualisms of atomic theory. Bohr hoped to formulate an approach that would allow matter and light to exist both as particle and as wave; Heisenberg argued consistently for abandoning models entirely and sticking to mathematics. In late February 1927, says Heisenberg, both of them “utterly exhausted and rather tense,” Bohr went off to Norway to ski.491 The young Bavarian tried, using quantum-mechanical equations, to calculate something so seemingly simple as the trajectory of an electron in a cloud chamber and realized it was hopeless. Facing that corner, he turned around. “I began to wonder whether we might not have been asking the wrong sort of question all along.”
Working late one evening in his room under the eaves of Bohr’s institute Heisenberg remembered a paradox Einstein had thrown at him in a conversation about the value of theory in scientific work. “It is the theory which decides what we can observe,” Einstein had said.492 The memory made Heisenberg restless; he went downstairs and let himself out—it was after midnight—and walked past the great beech trees behind the institute into the open soccer fields of the Faelledpark. It was early March and it would have been cold, but Heisenberg was a vigorous walker who did his best thinking outdoors. “On this walk under the stars, the obvious idea occurred to me that one should postulate that nature allowed only experimental situations to occur which could be described within the framework of the [mathematical] formalism of quantum mechanics.”493 The bald statement sounds wondrously arbitrary; its test would be its consistent mathematical formulation and, ultimately, its predictive power for experiment. But it led Heisenberg immediately to a stunning conclusion: that on the extremely small scale of the atom, there must be inherent limits to how precisely events could be known. If you identified the position of a particle—by allowing it to impact on a zinc-sulfide screen, for example, as Rutherford did—you changed its velocity and so lost that information. If you measured its velocity—by scattering gamma rays from it, perhaps—your energetic gamma-ray photons battered it into a different path and you could not then locate precisely where it was. One measurement always made the other measurement uncertain.
Heisenberg climbed back to his room and began formulating his idea mathematically: the product of the uncertainties in the measured values of the position and momentum cannot be smaller than Planck’s constant. So h appeared again at the heart of physics to define the basic, unresolvable granularity of the universe. What Heisenberg conceived that night came to be called the uncertainty principle, and it meant the end of strict determinism in physics: because if atomic events are inherently blurred, if it is impossible to assemble complete information about the location of individual particles in time and space, then predictions of their future behavior can only be statistical. The dream or bad joke of the Marquis de Laplace, the eighteenth-century French mathematician and astronomer, that if he knew at one moment the precise location in time and space of every particle in the universe he could predict the future forever, was thus answered late at night in a Copenhagen park: nature blurs that divine prerogative away.
Bohr ought to have liked Heisenberg’s democratization of the atomic interior.494 Instead it bothered him: he had returned from his ski trip with a grander conception of his own, one that reached back for its force to his earliest understanding of doubleness and ambiguity, to Poul Martin Møller and Søren Kierkegaard. He was particularly unhappy that his Bavarian protégé had not founded his uncertainty principle on the dualism between particles and waves. He trained on him the “terrifying relentlessness” he had previously directed at Schrödinger. Oskar Klein, Bohr’s amanuensis of the period, f
ortunately mediated. But Heisenberg was only twenty-six, however brilliant. He gave ground. The uncertainty principle, he agreed, was just a special case of the more general conception Bohr had devised. With that concession Bohr allowed the paper Heisenberg had written to go to the printer. And set to work composing his Como address.
At Como in pleasant September Bohr began with a polite reference to Volta, “the great genius whom we are here assembled to commemorate,” then plunged in. He proposed to try to develop “a certain general point of view” which might help “to harmonize the apparently conflicting views taken by different scientists.”495 The problem, Bohr said, was that quantum conditions ruled on the atomic scale but our instruments for measuring those conditions—our senses, ultimately—worked in classical ways. That inadequacy imposed necessary limitations on what we could know. An experiment that demonstrates that light travels in photons is valid within the limits of its terms. An experiment that demonstrates that light travels in waves is equally valid within its limits. The same is true of particles and waves of matter. The reason both could be accepted as valid is that “particles” and “waves” are words, are abstractions. What we know is not particles and waves but the equipment of our experiments and how that equipment changes in experimental use. The equipment is large, the interiors of atoms small, and between the two must be interposed a necessary and limiting translation.