Wolfgang Pauli

What Would Pauli Say?

The modern version of quantum theory now known as “quantum mechanics” was born and grew to maturity in just five years, between 1925 and 1930. More was accomplished during those five years than in the preceding twenty-five years, or, for that matter, in the seventy years that have followed. Progress before 1925 was constantly hampered by conceptual doubts. Paradoxes such as the wave-particle duality the contradiction between the Einstein particle theory of light and the classical wave theory were disturbing and limiting. But by 1925 these difficulties had, perhaps from familiarity, become less inhibiting. Theorists stopped worrying about the conceptual strangeness of the quantum realm, and began to make a new physics with the strangeness incorporated in it. Once the conceptual barriers were passed, progress was astonishingly rapid. For those who had the vision, it was as if a great fog had lifted. Suddenly it was possible to see in many directions with a clarity no one could have anticipated.

Quantum physicists of the new breed began to practice in the early 1920s. They were mostly second-generation quantum physicists, having been born after Planck read his famous paper to the Berlin Physical Society in 1900. (One might fancy that the appearance of Planck's paper was a signal for the birth of a whole crop of gifted physicists: Wolfgang Pauli, Frederic Joliot, and George Uhlenbeck in 1900; Werner Heisenberg, Enrico Fermi, and Ernest Lawrence in 1901; Robert Oppenheimer, John von Neumann, and George Gamow in 1904.) One of the most brilliant and influential members of this talented group was Pauli, who not only made major contributions of his own but also, like Bohr, shaped his colleagues’ work in long, critical discussions. During the crucial years of the 1920s and 1930s, many quantum physicists felt that their work was not finished until they faced Pauli and his relentless criticism, or lacking the Pauli presence, asked the question, “What would Pauli say?”

One of Pauli’s assistants, Rudolf Peierls, tells about Pauli’s role as a critic: “To discuss some unfinished work or some new and speculative idea with Pauli was a great experience because of his understanding and his high intellectual honesty, which would never let a slipshod or artificial argument get by.” Much of Pauli s effectiveness as a critic was the result of his legendary disregard for his colleagues’ pet sensitivities. “Some people have very sensitive corns,” he once said, “and the only way to live with them is to step on these corns until they are used to it.” A typical Pauli remark, on reading a paper of little significance and less coherence, was, “It is not even wrong.” Another comment to a colleague whose papers were not of the highest quality: “I do not mind if you think slowly, but I do object when you publish more quickly than you think.”

Pauli found targets for his biting comments on all levels of competence and importance. After a long argument with the Russian theorist Lev Landau, whose work was as brilliant but not so well expressed as his, Pauli responded to Landau's protest that not everything he said was nonsense with: “Oh no. Far from it. What you said was so confused that one could not tell whether it was nonsense or not.” What may have been Pauli's debut as a belittler of authority was made during his Munich student days. In response to a comment made by Einstein at a colloquium he had this to contribute from the back of a crowded lecture hall: “You know, what Mr. Einstein said is not so stupid.”

Of Antimetaphysical Descent

From his youth, Pauli was round in face and body, and physically awkward, in contrast with his lack of intellectual awkwardness. A biographer claims that Pauli managed to pass his driver's test only after taking one hundred driving lessons. One of the most enduring contributions to the Pauli legend was the “Pauli Effect,” according to which Pauli could, by his mere presence, cause laboratory accidents and catastrophes of all kinds. Peierls informs us that there are well-documented instances of Pauli's appearance in a laboratory causing machines to break down, vacuum systems to spring leaks, and glass apparatus to shatter. Pauli's destructive spell became so powerful that he was credited with causing an explosion in a Gottingen laboratory the instant his train stopped at the Gottingen station. But none of this misfortune was visited on Pauli himself. That this was a true corollary of the Pauli Effect no one doubted after an elaborate device was contrived to bring a chandelier crashing down when Pauli arrived at a reception. Pauli appeared, a pulley jammed, and the chandelier refused to budge.

Pauli's intellectual inheritance was strong. His father, Wolfgang Joseph, was a professor at the University of Vienna and an expert on the physical chemistry of proteins. His mother, Bertha Schutz, was a newspaper correspondent and the daughter of a singer at the Imperial Opera in Vienna. The father came from a respected Prague Jewish family named Pascheles. He studied medicine at the Charles University in Prague, where one of his classmates was the son of Ernst Mach. At about the time Mach moved to the University of Vienna, Wolfgang Pascheles became a professor there, changed his name to Pauli, and joined the Catholic Church.

The Pauli's only son was born in 1900, and was baptized with the names Wolfgang Ernst Friederich; the second name was for Ernst Mach, who became the child’s godfather. At the baptism “[Mach] was a stronger personality than the Catholic priest,” Pauli liked to explain when asked about his religion, “and the result seems to be that in this way I [was] baptized ‘anti-metaphysical’ instead of Catholic. . . . [It] still remains a label which I myself carry, namely: ‘of anti-metaphysical descent.’ ”

Young Wolfgang was a prodigy at all levels of his schooling, not only in mathematics and physics but also in the history of classical antiquity. When the gymnasium classroom activities became boring, he read Einstein's papers on general relativity (only a few years after they were written), and published three papers on relativity that impressed the well-known mathematician and relativist Hermann Weyl.

In company with Werner Heisenberg, who in a few years would initiate the revolution that led to quantum mechanics, Pauli started his career as a research student under Arnold Sommerfeld, a professor at the University of Munich and a renowned teacher of theoretical physics. Pauli liked to joke with Heisenberg about Sommerfeld's martial mustaches and austere manner: “Doesn't he look the typical old Hussar officer?” But the student’s respect for the teacher was more lasting than the jokes. “In later years,” Peierls writes, “it was surprising when Sommerfeld visited [Pauli], to watch the respect and awe in his attitude to his former teacher, particularly striking in a man who was not normally inclined to be diffident.” And Sommerfeld admired his gifted student. He handed the nineteen-year-old Pauli the formidable task of writing an encyclopedia article on relativity. Sommerfeld found the article “simply masterful,” and Einstein agreed.

After Munich, Pauli made his brilliant and caustic presence known in Gottingen. In 1921, he became an assistant to Max Born, who had established the University of Gottingen as a center for research in theoretical physics that rivaled Bohr's Copenhagen institute. Born found Pauli “very stimulating.” But there were problems: Pauli “liked to sleep in” and did not always appear when he was needed as Born's deputy at 11:00 A.M. lectures. It finally became necessary for the Born's “to send our maid over to him at half past ten, to make sure he got up.” Like most of Pauli’s associates, Born tolerated this behavior with remarkable good humor. To Born, whose eye for scientific talent was as experienced as Bohr's, Pauli “was undoubtedly a genius of the highest order.”

After a year in Gottingen, Pauli moved to Bohr's institute, and one of the most fruitful and lasting partnerships in modern physics was formed. Although Bohr and Pauli never collaborated as authors perhaps they never agreed each in his own way had a need for critical conversation. Bohr had perfected the technique of developing his ideas by debating with anyone in sight. Sometimes with students and assistants, the “debate” was simply Bohr thinking aloud. Other times, as in discussions with Einstein and Erwin Schrodinger, the debate became deadlocked over stubborn conceptual problems. But Pauli, with his unsurpassed genius for criticism, was Bohr's favorite partner in debate. Their arguments never ended, but they always progressed, and Bohr became dependent on them. Leon Rosenfeld, one of Bohr's assistants, tells us that if Pauli was not present in person Bohr would focus on his letters: “The arrival of a letter from Pauli was quite an event; Bohr would take it with him when going about his business, and lose no occasion of looking it up again or showing it to those who would be interested in the problem at issue. On the pretext of drafting a reply, he would for days on end pursue with the absent friend an imaginary dialogue almost as vivid as if [Pauli] had been sitting there, listening with his sardonic smile.”

Pauli was one of the more itinerant of the quantum physicists. After Munich, Gottingen, and Copenhagen, he went to Hamburg, where he ascended the academic ladder. In 1928, at age twenty-eight, he was appointed to the chair of physics at the Swiss Technical University (ETH) in Zurich. There he remained, except for the five years (1940–45) he spent at the Institute for Advanced Study in Princeton.

Until about 1934, Pauli’s personal life was complicated. In 1929, he married a young dancer, Kathe Deppner, who soon left him for a chemist. That annoyed Pauli: “Had she taken a bullfighter I would have understood but an ordinary chemist. . . .” A period of crisis ensued, from which he was rescued by psychoanalysis supervised by Carl Jung, and by a stable marriage in 1934 to Francisca (Franca) Bertram.

The Critic

Pauli's grasp of physical problems was supreme among his contemporaries, probably not surpassed even by Einstein. Born recalled that “ever since the time he had been my assistant in Gottingen, I had been aware that he was a genius, comparable with Einstein himself. Indeed from the point of view of pure science, he was possibly even greater than Einstein.” Pauli's achievements, the enunciation of the exclusion principle and several major contributions in nuclear physics and particle physics, certainly rank among those of the masters of modern physics. Yet his full greatness did not equal that of Einstein, Bohr, or Heisenberg.

To some extent, Pauli was held in check by his own brilliance. At times, he understood physics too well. His critical sense became so refined and broad in scope he could not exercise his creative powers with the imagination and intuitive facility possessed by some of his contemporaries. To Heisenberg, whose reckless departures from the principles of classical physics were soon to be spectacularly successful, Pauli said, “Perhaps it's much easier to find one's way if one isn't too familiar with the magnificent unity of classical physics. You have a decided advantage there.” Then he added appreciatively, “Lack of knowledge is no guarantee of success.”

But if Pauli's fine critical sense was a personal restraint, it was an inspiration for many of his colleagues. Like a great literary critic, Pauli expressed, for all who had the intelligence to listen, a penetrating, sometimes painfully sharp, yet balanced voice of experience and insight. Much of the best theoretical work in modern physics was done with Pauli attending either in person or in spirit, “sitting there listening with his sardonic smile.”