Einstein's Genius Club (17 page)

The Zeeman effect held true for some atoms—for instance, hydrogen. In other cases, the splitting resulted not in three symmetrical lines, but in four or more lines that formed complicated patterns: thus, anomalous—and bedeviling. Pauli later recalled:

A colleague who met me strolling rather aimlessly in the beautiful streets of Copenhagen said to me in a friendly manner, “You look very unhappy”; whereupon I answered fiercely, “How can one look happy when he is thinking about the anomalous Zeeman effect?”
¹⁷⁸

Not until the concept of electron spin would the anomalies be fully explained. Pauli groped on for several years, identifying the valence electron as the culprit in an article first proposing a “classically not describable kind of two-valuedness” of the electron.
¹⁷⁹
But what was this “two-valuedness” of the electron? Pauli resisted suggestions of an electron “spin” (thus his deprecation of young Konig) until finally he was convinced, writing to Bohr that he would “capitulate completely.”
¹⁸⁰

Bohr's now obsolete 1913 atomic model had, in many ways, done its job: It failed the test of “quantization.” Indeed, its visual imprint, based on the solar system, seemed so misleading as to drive physicists away from any proposal that suggested an image. Pauli, a true believer in the quantum, benefited enormously from the swirl of conversation about electrons. In 1924, he read a paper by an English physicist named Edmund Stoner suggesting a distribution of electrons around the nucleus. Pauli was inspired. He set to work formulating the description of electron states that would eventually win him the Nobel Prize.

Known generally as the “exclusion principle,” it was dubbed “exclusion” because it describes what
cannot
happen: No two electrons can occupy a single quantum state at the same time. The exclusion
principle solved a simple but enormously important question: Why do electrons not fall into the nucleus? The answer is that electrons cannot “fall” into another, less-energized state or “orbital” if it is already occupied. More precisely, no two electrons can have the same quantum states within an atomic structure. These states are expressed as the four quantum numbers: (
n
) the size or level of the orbit, (
l
) the orbit's shape, (
ml
) the orbit's orientation, and (
ms
) the electron's spin direction. Were electrons not excluded from other states, matter would collapse into itself—as, for instance, in black holes, where the exclusion principle does not hold!

The exclusion principle and electron spin answered a number of questions beyond the anomalous Zeeman effect. Most wonderfully, especially for chemists, the exclusion principle gave the periodic table and its arrangement of elements new meaning. Working empirically, from experimental observations, Dmitry Mendeleyev, the Russian chemist who laid out the table in 1869, had arranged the elements in order of atomic mass. He also grouped them vertically by similar properties. When the exclusion principle clarified the energy value (and position) of the valence shell electron (that is, the outer shell, where bonding takes place), the hidden logic of Mendeleyev's table was revealed. His organization seemed amazingly on target. Those elements with the same valence electrons in a shell are similar—lithium and francium, for instance, each have one valence electron and are both alkali metals, though lithium is light, with an atomic number of 3, whereas francium is quite heavy, with an atomic number of 87.

Pauli's exclusion principle was one of the first in a series of interconnected discoveries that grew out of the “new quantum theory.” From 1924 through 1927, Heisenberg, Bohr, Max Born and his assistant Pascual Jordan, Enrico Fermi, Paul Dirac, Erwin Schrödinger, and Pauli, in collaboration or singly, contributed postulates, equations, and theorems to the Copenhagen interpretation. In his role as supercritic, Pauli was Heisenberg's sounding
board. Although Heisenberg is credited with creating matrix mechanics, the first complete description of quantum mechanics, Pauli provided the dialectic from which emerged both matrix mechanics and Heisenberg's uncertainty principle of 1927. Indeed, Heisenberg's great insight—that theories must be based on what can be observed—is very Paulian in temperament. While Heisenberg was pondering the “strangely beautiful interior” of atomic phenomena,
¹⁸¹
Pauli obsessed over the anomalous Zeeman effect, determined to explain rather than theorize away experimental observations.

Still, Pauli had time for Heisenberg. Pauli was “generally my severest critic,” said Heisenberg. Pauli's feelings toward Heisenberg were more complex. “When I think about his ideas,” wrote Pauli in a 1924 letter to Bohr, “then I find them dreadful, and I swear about them internally. For he is very unphilosophical, he does not pay attention to clear elaboration of the fundamental assumptions and their relation with the existing theories. However, when I talk with him he pleases me very much….”
¹⁸²
Most of Pauli's letters to Heisenberg seem to have vanished during wartime, a particularly sad loss given Pauli's careful, expansive epistolary style.
¹⁸³
Heisenberg's contribution to the dialogue consisted of thirty-four letters and more than twenty postcards.

Pauli's “staggering contributions” to quantum mechanics continued apace. Yet another oddity reared its head, and Pauli took up the case of the missing momentum. It was a mystery. Experimental data showed that during radioactive processes, the atomic nucleus emits an electron. This is called “beta decay.” It occurs because a neutron transforms into a proton. The atom consequently emits an electron. The energy and momentum of all the particles were measured, but the before and after did not match. A tiny amount of energy had gone missing with the beta decay and could not be accounted for. Some physicists, Bohr among them, seemed willing to give up the sacred principle of the conservation of energy. Demonstrably, they argued, energy was lost, and conservation
of energy, like much of classical physics, simply did not work for individual subatomic processes.

Not so, said Pauli. He sought the advice of Lise Meitner, a leading authority on nuclear physics. Her work helped him refute Bohr's contention that beta decay did not follow the conservation of energy except statistically—an idea that offended Pauli's austere scientific sensibility. After battling through the possibilities, he came up with a solution—what he called a “desperate remedy.” He announced his idea in a letter addressed to the Meeting of the Regional Society in Tübingen: “Dear Radioactive Ladies and Gentlemen,” he began. Pauli's wit was famous. The salutation may not have surprised the conferees, but the remedy must have done so:

[T]here might exist in the nuclei electrically neutral particles, which I shall call neutrons, which have spin 1/2, obey the exclusion principle and moreover differ from light quanta in not traveling with the velocity of light. The mass of the neutrons would have to be of the same order as the electronic mass and in any case not greater than 0.01 proton masses.
¹⁸⁴

Pauli's terminology was soon amended by Enrico Fermi to “neutrino”—in 1932, Sir James Chadwick discovered what he named the neutron, the neutral element equal in mass to the proton. Fermi, unlike the “radioactive” conferees, found the neutrino plausible, since it fit into his theory of weak force and the resulting instability in the atomic nucleus.

Not until 1956, two years before Pauli's death, was the neutrino's existence proven experimentally. It was, said Frederick Reines, its codiscoverer, “the most tiny quality of reality ever imagined by a human being.”
¹⁸⁵
Today, the neutrino is an invaluable tool in astrophysics. So small in mass and so weak in energy, it passes through the densest material as no other entity can, without collision or effect. Even supernovae, which collapse into unimaginable density, release almost all their energy in the form of neutrinos. Whatever information they carry comes from the very core of
the explosion. Pauli celebrated the confirmation of the neutrino with champagne and wrote to Reines and Clyde Cowan in Los Alamos, “Everything comes to him who knows how to wait.”

If Pauli's professional work ever suffered from his personal crises, it rarely if ever showed. But crises there were. In 1927, Pauli's father had an affair. His mother's suicide followed soon after. Pauli was stricken, but his anguish remained hidden. The following year, he settled in Zurich, where, despite his reputation as a poor lecturer (his style resembled “a soliloquy… often scarcely… intelligible” to Markus Fierz, then a student
¹⁸⁶
), ETH hired Pauli at the rank of full professor of theoretical physics. In turn, Pauli hired Ralph Kronig to be his assistant for the summer term. They spent the summer as much at play as at work. They were joined by Paul Scherrer, Pauli's nominal department head. Eating, drinking, and concert-going were the usual fare. A favorite haunt was the Kronenhalle, where the famous and infamous among artists (Thomas Mann, James Joyce, Braque, Picasso, Stravinsky) had imbibed.

By the end of 1929, Pauli was married. He had met his bride-to-be, Kate Deppner, at a friend's house in Zurich. She was not, as tradition has it, a cabaret dancer. Rather, she danced at the Max Reinhardt School of Dramatic Arts in Berlin. Pauli probably saw her in Berlin when he visited. In Zurich, Deppner danced at a school run by Trudi Schoop, who later became famous for her work in dance therapy.
¹⁸⁷
Schoop later befriended Pauli, heralding his entry into psychology and therapy.

The marriage proved to be a disaster. Kate had been in love with a chemist from Berlin before the marriage, and their relationship did not seem to end with the wedding. As soon as she left Pauli, in 1930, she married her old lover. Pauli's letters during the scant year of their marriage were rueful and self-deprecating. “My wife presumably doesn't join me; even if I am married it is at least in a loose way!” he wrote Oskar Klein.
¹⁸⁸
Within two months of the wedding, he promised his friends a printed notice if his wife should run away. Later, according to Enz, Pauli proclaimed himself
more distraught at Kate's choice of a “mediocre chemist” as his rival than with the dissolution itself.

With the end of his marriage, Pauli became irritable and subject to mood swings. He drank heavily, spent time in cabarets, picked fights, and was once beaten. During a trip to the United States, in the summer of 1931, he broke his shoulder, having fallen “in a slightly tipsy state,”
¹⁸⁹
and had to lecture in Ann Arbor with his left arm uncomfortably elevated in a cast. When depression overcame Pauli in the winter of 1931, his father suggested a visit to the eminent psychologist Carl Gustav Jung. Pauli dived into Jung's works, attended conferences, and made an appointment to see the great man. In February 1932, as Jung proposed, Pauli began therapy with Erna Rosenbaum, a young, inexperienced student whom Jung trusted not to “tamper” with Pauli. Indeed, Jung seems immediately to have recognized in Pauli the makings not only of an interesting patient, but of an inspired collaborator as well. In addition, Jung recommended Pauli to a female analyst—significantly, given Pauli's failed marriage and his mother's suicide.

During Pauli's analysis with Rosenbaum, which lasted about five months, he recounted hundreds of vivid dreams. Some of these dreams he noted in letters to her. In October 1932, Jung took over Pauli's case. For two years, often in letters, Pauli described his dreams to Jung and provided sophisticated analyses of them. “I did not have to explain much of the symbolism to him,” said Jung.
¹⁹⁰
So rich were the dreams that Jung incorporated many of them into a chapter of
Psychology and Alchemy
(1944).

Pauli and Jung corresponded for decades. Their letters, from 1932 to 1958, are now collected in a book entitled
Atom and Archetype
. Their complex intertwining of ideas and theories is laid out in their joint publication,
The Interpretation of Nature and the Psyche,
published in 1952. Their relationship seems to have grown not so much from Pauli's need for analysis as from their shared intellectual eclecticism.
¹⁹¹
Eventually, the Jungian ideas of synchronicity let Pauli to speculate on a “unified theory” that would not only
join the physical forces, but bridge the dualism of physical and psychic that was the hallmark of the modern era. Still, outwardly, Pauli's life ran in separate paths—his colleagues in physics did not know about his immersion in Jungian symbols and archetypes, and his Jungian associates had little contact with ongoing physics.

Analysis seems to have given Pauli a measure of psychological peace and social ease. In 1933, he proposed to Franca Bertram, the woman with whom he would live the rest of his life. “Proposal” might be to grand a word for what Pauli said: “[N]ow we marry.”
¹⁹²
Before their wedding, the couple visited family and friends in Vienna and Hamburg and stayed with Bohr and his family in Copenhagen. Evidently, Franca Pauli enjoyed socializing as much as her husband. Throughout their life together, they entertained and visited friends, many of them Pauli's academic colleagues, throughout the world.

Pauli's professional life in Zurich was happy, but as Hitler's power increased, the Paulis became increasingly vulnerable. Pauli held an Austrian passport. When Austria was annexed to Germany in 1938, Austrian passports were nullified, and Pauli was forced to take a German passport. Given his Jewish heritage, he was subject to Nazi persecution. Switzerland, neutral but geographically vulnerable, began mobilizing its tiny army in 1939. In 1940, however, Germany turned its armies to the west, and Pauli, rather belatedly, began to act. He had applied for Swiss citizenship in 1939. Prudently, in 1940, he also applied for a visa to the United States, on the strength of an invitation to the Institute for Advanced Study. When he was turned down for Swiss citizenship, he arranged for leave for the winter semester from ETH (Eidgenössiche Technische Hochschule). On June 11, with visas to America, Spain, and Portugal in hand, the Paulis tried to board a plane to Barcelona, via Rome. But Italy had just declared war. The plane was cancelled, and the Paulis were forced to wait in Zurich. Finally, on July 31, the couple left by train through France to Barcelona and then Lisbon.
It was a harrowing journey, recapitulated later in the summer by Pauli's sister, Hertha, who wrote about the experience in her fictionalized autobiography,
Break of Time
. Once in Lisbon, the Paulis boarded a ship to New York, where they were met by John von Neumann.