Einstein's Genius Club (16 page)

Even Pauli's baptism was fraught with contradiction. His father Wolf remained friends with Ernst Mach, who had moved to Vienna
in 1895. A fierce positivist, dismissing all things metaphysical and spiritual, Mach nevertheless agreed to be the godfather of the newborn Pauli. (Mach seems to have haunted Einstein's living room in 1944. Not only did his positivism lay the foundations for the theory of relativity, it also underlay Russell's view of “neutral monism.”
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Gödel spent his formative years listening to and silently disagreeing with the Machian positivism of the Vienna Circle.) Later, Pauli joked that he grew up a positivist because Mach's power was stronger than that of the baptizing priest. In fact, Pauli was never a simple positivist, though he never ceased to believe that theory must be supported by experiment. His later devotion to Jung and metaphysics would have driven his godfather to distraction.

Like so many other sons and daughter of Vienna, Pauli grew up amid the strange psychic energies, ambivalences, and decadence that created Freud, Ludwig Wittgenstein, Arnold Schönberg, Gustav Klimt, Arthur Schnitzler, and, yes, the young Hitler, who dabbled in art and nursed his monstrous dreams. Perhaps it is not surprising that Pauli later became—at the same time—the disciple of Niels Bohr's crystalline rationality and of Carl Jung's mythifying depth psychology.

Young Pauli attended a “classical” Gymnasium, which emphasized not science but literature and history. He learned Greek and Latin—useful later in his life when he began a lengthy project on Kepler and the alchemists, although his language grades were less than stellar. As for mathematics and physics, Pauli needed little formal training at school to do well. He was a prodigy who had mastered calculus by fourteen and was easily advised in his reading by godfather Mach. His tutor, Hans Adolf Bauer, kept Pauli abreast of the latest theories. At eighteen, just out of high school, Pauli published his first paper, on Einstein's general relativity—a theory published only two years earlier. Whereas many senior physicists were still puzzled by its mathematical difficulties and conceptual innovations, Pauli was unfazed. Even at eighteen, his self-confidence was unshakable. The physicist Victor Weisskopf, Pauli's assistant in
the early 1930s, once pointed out to him a mistake in calculation made by another physicist. Pauli said, “Others make mistakes; but I, never.” And so it was.

Thus, when he entered the University of Munich, Pauli at eighteen was so far ahead of his peers that his mentor, the eminent theorist Arnold Sommerfeld, put him to work writing the article on the new general relativity theory for the
Encyclopädie Mathematicschen Wissenschaften
. Pauli obliged with a book-length article, 237 pages long, with almost four hundred footnotes (still in print, with supplementary notes added by Pauli just before his death). Upon reading the article, published in 1921, Einstein was all admiration:

No one studying this mature, grandly conceived work would believe that the author is a man of twenty-one. One wonders what to admire most, the psychological understanding for the development of ideas, the sureness of mathematical deduction, the profound physical insight, the capacity for lucid, systematic presentation, the knowledge of the literature, the complete treatment of the subject matter, or the sureness of critical appraisal.
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Such praise from the Master might be the capstone of a career, rather than the starting point. Yet Pauli, now under Sommerfeld's tutelage, blossomed. Munich was, as Sommerfeld wished it to be, a “nursery of theoretical physics.”
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In the early 1920s, it would produce not only Pauli, but Werner Heisenberg and Hans Bethe, each of whom was to win the Nobel Prize in Physics. Still, the city was rocked by political and economic strife as the war ended and the Central Powers disintegrated. Prince Ludwig III, the Bavarian prince regent, fled for his life in 1918 as revolution threatened. In early 1919, Kurt Eisner, a socialist who had been elected premier just a few months earlier, was assassinated. The Communist-inspired Bavarian Soviet Republic lasted only until May, when it was toppled by the Freikorps, many of whom later swelled the ranks of the National
Socialists. Munich was, for all practical purposes, the birthplace of Nazism. In 1923, Hitler and his supporters staged the failed Beer Hall Putsch in an attempt to overthrow the fragile Weimar Republic.

Yet Pauli seems to have been oblivious to the turmoil. At nineteen, he was the resident expert on general relativity. He lectured on it in Sommerfeld's class, wrote his second paper on it in June 1919, and tended to sleep late, enjoying the nightlife and clearly untroubled by missing a few morning lectures. He later recalled the “cheerful mood” of those on their way to and from physics and mathematics conferences. Only rarely did the real world intrude on Sommerfeld's institute, as when extremist students threatened to disrupt a lecture by Einstein, scheduled in late 1921. Einstein wisely decided not to attend.

Pauli had already met Einstein at a 1920 conference in Nauheim. It must have been a heady moment for the young student, at work on the relativity article. The conference was one of several during 1920 at which Einstein was expected to defend general relativity. His name recognition not only among physicists, but among the general populace had increased exponentially when in 1919 Arthur Stanley Eddington was able to measure the bending of light during a solar eclipse, thus confirming Einstein's postulate on gravitational magnetism. Still, with fame came controversy, some of it stirred not by science but by blatant anti-Semitism. The Nauheim conference witnessed a “dramatic… duel between Einstein and Philipp Lenard,” in the words of the mathematician Hermann Weyl. Lenard's anti-Semitism was so virulent that it colored his view of relativity and embittered him against “Jewish physics.” Ironically, it was Einstein, the “Jewish fraud” of relativity, who had been able in 1905 to explain anomalies Lenard observed in his own work on cathode rays.

In Sommerfeld's institute, consisting of not much more than a library, a laboratory, a seminar room, the director's own office, and, of course, a lecture hall, Pauli and his fellow students (Werner
Heisenberg among them) learned how to theorize not only on relativity, but on quantum theory as well. It was, of course, the “old” quantum theory first postulated by Bohr in 1913. Bohr's now obsolete atomic model resembled a solar system; its electrons, however, did not follow the rules of classical physics. Sommerfeld was active in the attempt to “manage” Bohr's unwieldy model, suggesting, for instance, elliptical orbits. In the years to follow, Sommerfeld's students, Pauli and Werner Heisenberg among them, rode the wave of quantum theory thoroughly grounded in the rudiments of research. Throughout both of their lives, the very mention of Sommerfeld transformed the usually sardonic Pauli into a deferential and respectful pupil.

In only six semesters, Pauli finished all required coursework. He began his thesis on ionized molecular hydrogen—a little-remembered excursion into quantum theory (Enz remarks that Pauli's ego might have led him to tackle a too-difficult problem). Pauli had distinguished himself sufficiently to be offered an assistantship with Max Born, the physicist whose “probability interpretation” reconciled wave and particle, introduced the notion of probability as a state of knowledge rather than a state of ignorance, and won Born a Nobel Prize in 1954. During the winter of 1921, while completing the thesis, Pauli assisted Born at the University of Göttingen. Until 1933, the university, founded in 1737 by the Hanoverian King George II of England, boasted first-rate mathematics and physics departments: Among other illustrious former faculty was Bernhard Riemann, the nineteenth-century mathematician, whose geometry made Einstein's general relativity theory possible, as we shall see.

Born was fond of Pauli, despite the latter's tendency to sleep late and miss lectures. Much later, Born wrote,

[E]ver since the time he had been my assistant in Göttingen, I had been aware that he was a genius comparable only to Einstein himself. Indeed, from the point of view of pure science
he was possibly even greater than Einstein even if as an entirely different type of person he never, in my opinion, attained Einstein's greatness.
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Genius Pauli may have been; still, his somewhat erratic comportment hinted at a psychological imbalance, which surfaced in the early 1930s.

In Göttingen, Pauli and Born collaborated on an important series of calculations that would, in theory, test Niels Bohr's idea of the harmony of atomic motions. The “Göttingen calculations,” based on the celestial mechanics of perturbation (i.e., the effect planets have on each other as opposed to the much greater effect of the sun's gravitation), seemed to contradict Bohr's description of the helium atom. This was one of an increasing number of difficulties facing the Bohr atomic model and his early formulation of quantum theory.

In 1922, Niels Bohr was invited to lecture at Göttingen University. Bohr was at the pinnacle of his career. He had just founded an institute for theoretical physics in Copenhagen, where he taught. He was six months away from being awarded the Nobel Prize for his atomic model. Everyone who was anyone came to the lectures, dubbed the “Bohr Festspiele.” Among those attending were Werner Heisenberg and, of course, Wolfgang Pauli. Bohr was to become the greatest mentor of young physicists in the century. Pauli was thereafter a disciple, colleague, and friend of the Danish scientist. The young Heisenberg and Paul Dirac were also drawn into Bohr's orbit.

Bohr's lectures were exciting but not particularly accessible (one student described Bohr's style as “neither acoustically nor otherwise completely understandable”
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). Still, most of the attendees knew Bohr's theories. The lectures were an occasion to discuss, argue, and augment. Pauli must have been active at the conference, since he wrote Bohr immediately after its close, thanking him for answering “the most diverse questions.”
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Those questions, together with Pauli's reputation, led Bohr to
invite the twenty-two-year-old prodigy to his new Copenhagen institute for a year. Pauli quickly accepted. In addition to his own work, Pauli spent the year translating Bohr's papers and lectures (including Bohr's Nobel Prize lecture) into German. During his year in Copenhagen, Pauli gained lifelong friends, colleagues, and collaborators. Above all, he became one-third of the trio who would forge a new, more successful quantum theory. Though Pauli and Heisenberg left Copenhagen—Heisenberg went to Leipzig in 1927, Pauli to Hamburg in 1923 and then to Zurich in 1928—the three men met regularly at conferences and corresponded prolifically.

Through it all, Pauli was a “nuclear” force, as it were—not only an incisive theorist, but a critical sounding board, a mediator, an adviser. As a collaborator, he supported and inspired, argued fearlessly, worried the details, and spared no weak postulate his sarcasm and scorn. Silvan Schweber, reviewing a comprehensive history of quantum theory, remarks on

Pauli's staggering contributions to the technical developments (Pauli exclusion principle, solution of the hydrogen atom in matrix mechanics, spin, paramagnetism, quantum electrodynamics,…) and to the resolution of the philosophical problems engendered by the new mechanics of the micro domain. Pauli was the critic par excellence who was at the center of the vast network of correspondents and became the ultimate arbiter of the
Kopenhagener Geist der Quantentheorie.
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Little wonder, then, that Pauli was chosen to write the two volumes on quantum theory for the
Handbuch der Physik
. The first volume, published in 1926, summarized old quantum theory—the state of quantum physics from Bohr's 1913 atomic model up to 1925. The second volume, published in 1933, summarized the new quantum mechanics and laying out what became known as the “Copenhagen interpretation.” These volumes are bookends to the heady years during which quantum theory revolutionized physics.

As with all scientific theory, the Copenhagen interpretation was the product of many hands and minds—among them, Erwin Schrödinger, who postulated wave mechanics, Paul Dirac, who devised quantum algebra, and Max Born, who “measured” quantum probability. Still, when the Copenhagen interpretation was explained at the Fifth Solvay Conference of 1927, it was primarily the work of Bohr, the “father” of the new quantum theory, and his two “offspring,” Heisenberg and Pauli. Each played his typecast role—Bohr the quixotic and intuitive muse, Heisenberg, the excitable boy wonder, Pauli the indefatigable critic.

It was Heisenberg who devised the linchpins of modern quantum mechanics: matrix mechanics and the uncertainty principle. We will revisit these notions in a subsequent chapter; here, we will simplify dramatically. Matrix mechanics involves measurements of quantum states with a twist: They are not observational measurements. Heisenberg fretted over a simple, undeniable fact: We cannot see into an atom to measure it. If we cannot see the atom, he reasoned, efforts to model it were fruitless (rebuking, as sons do, the father—Bohr was an inveterate visualizer). Instead, Heisenberg set out to quantify the only evidence we can observe: the frequencies and intensities of light spectra. To predict the numerical values of atomic energy, he created a system of equations that, with help from Pauli and Max Born, were extended into a “matrix” language. The pretty atomic model of a nucleus and orbiting electrons had been erased and converted into a numerical table.

While Heisenberg was thinking up matrix mechanics, Pauli was in the grip of the “anomalous Zeeman effect.” Named after Pieter Zeeman, a Dutch physicist, the Zeeman effect (as distinguished from its anomalous counterpart) is the splitting of a spectral frequency into three symmetrical lines of very slightly differing energy when placed near a magnetic field. This effect can be explained by classical physics, as it was by Zeeman's teacher,
Hendrik Lorentz. Zeeman and Lorentz shared the 1902 Nobel Prize for their work.