Wolfgang Pauli

Wolfgang Ernst Pauli was born in Vienna on April 25, 1900, the same year Max Planck quantized the energy of a blackbody and lit the long fuse that would burn through classical physics. His father was a professor of physical chemistry; his godfather, the man whose middle name he carried, was Ernst Mach, the physicist and philosopher whose criticism of Newton would shape Einstein’s relativity. The Pauli household subscribed to the journals where the new physics was being argued out, and the boy read them before he understood them. By the time he finished the Döblinger-Gymnasium in 1918, eighteen years old and already known in Vienna’s coffeehouse mathematics circles as a prodigy, he had absorbed general relativity well enough to publish his first paper on it two months after his graduation.

He went to Munich to study under Arnold Sommerfeld, the great teacher who had also trained Heisenberg and Debye. The doctorate came in 1921 with a thesis on the quantum theory of ionized hydrogen molecules. Sommerfeld, immediately recognizing what he had, handed his twenty-one-year-old student a commission he had agreed to write himself: a survey of relativity for the Encyclopedia of the Mathematical Sciences. Two months later Pauli delivered 237 pages. Einstein read it and wrote that whoever judged the work as mere review would not realize “that here is a mature and grandly conceived work.” It is still in print. Pauli wrote it before his twenty-second birthday.

The years from 1921 to 1928 were his most productive. He spent a year at Göttingen under Max Born, another in Copenhagen with Niels Bohr, then settled into a lectureship in Hamburg. In 1924 he proposed that the spectra of alkali atoms required electrons to carry a new “two-valued quantum degree of freedom” he could not yet interpret. Within months he sharpened the idea into the exclusion principle: no two electrons in an atom can share all four quantum numbers. The principle explained the periodic table at one stroke. It told you why lithium is reactive and neon is not, why oxygen wants two more electrons and sodium wants to lose one, why chemistry has the shape it has. Twenty-one years later, in 1945, on the strength of Einstein’s personal nomination, Pauli received the Nobel Prize for it.

Wolfgang Ernst Pauli ( ; ; 25 April 1900 – 15 December 1958) was an Austrian–Swiss theoretical physicist and a pioneer of quantum mechanics. In 1945, after having been nominated by Albert Einstein, Pauli received the Nobel Prize in Physics "for the discovery of the Exclusion Principle, also called the Pauli Principle". The discovery involved spin theory, which is the basis of a theory of the structure of matter.

The exclusion principle was only the start. In 1927, after George Uhlenbeck and Samuel Goudsmit had identified Pauli’s mysterious two-valued degree of freedom as electron spin (an identification Pauli stubbornly resisted at first because it seemed to need a faster-than-light surface velocity), Pauli wrote down the formalism the world now uses. The three 2x2 matrices that bear his name are the simplest non-trivial spin operators in physics, the building blocks of every quantum-computing qubit, the small change of quantum information theory. The Pauli equation, also from this period, was the first wave equation to include spin in a Schrödinger framework. When Dirac unified spin and relativity two years later, his larger 4x4 gamma matrices were Pauli’s 2x2 blocks stacked together.

In 1930 Pauli faced a different problem. Beta-decay electrons came out of nuclei with a continuous spectrum of energies, but the parent and daughter nuclei had sharp definite energies. Energy was apparently not conserved. Bohr was prepared to abandon conservation. Pauli refused, and on December 4, 1930, dashed off a famous letter to Lise Meitner and her colleagues meeting at Tübingen. He addressed it “Dear radioactive ladies and gentlemen” and apologized for not attending in person, explaining that he was indispensable at a ball in Zürich that night. He then proposed a “desperate remedy”: a neutral, almost massless particle emitted alongside the electron, carrying off the missing energy and momentum. Enrico Fermi gave it its Italian diminutive, neutrino, “little neutral one.” It took twenty-six years to detect. When Reines and Cowan finally caught one in 1956, they sent Pauli a telegram. He replied: “Thanks for message. Everything comes to him who knows how to wait. Pauli.”

He moved to ETH Zürich as professor in 1928. He stayed in Switzerland through the worst years in Europe, slipped to Princeton in 1940 ahead of the Wehrmacht, became an American citizen in 1946, then turned around and went back to Zürich, where he died of pancreatic cancer in December 1958. He had been admitted to a room numbered 137, and the coincidence chilled him: the fine-structure constant of nature, which Pauli had spent his life trying to understand, is roughly 1 over 137. He told his assistant he would not leave that room alive, and he did not.

Pauli was Vienna-bred, sarcastic, and absolutely without mercy when confronted with sloppy thinking. His seminar interjections were legendary. Ganz falsch, completely wrong, was the routine verdict. But the dismissal he reserved for the worst offenders was sharper still. Of a paper so muddled it could not be checked he is said to have remarked that it was nicht einmal falsch, “not even wrong,” meaning that to be wrong was at least to make a definite claim, and this paper had not managed even that. The phrase has outlived its origin and entered the working vocabulary of every scientist who has ever had to read a manuscript whose author confused obscurity with depth. The first time he met Paul Ehrenfest, Ehrenfest told him that he liked Pauli’s Encyclopedia article better than he liked Pauli. “Strange,” Pauli answered. “With me, regarding you, it is just the opposite.” They became close friends.

Around him gathered the legend of the “Pauli effect,” the apocryphal claim that experimental apparatus broke when he walked into the room. The Hamburg physicist Otto Stern, on whose Stern-Gerlach magnets some of the early spin work had been done, was said to have banned Pauli from his laboratory on these grounds. A famous incident at Göttingen recorded a complicated vacuum-tube device collapsing for no reason; investigation revealed that Pauli’s train, en route from Zürich to Copenhagen, had been stopped on the platform at Göttingen station at precisely that moment. Pauli, a serious man who took the borderlands between physics and the psyche seriously, was delighted by the legend and did nothing to dispel it.

That openness to the borderlands led him to Carl Jung. In 1932, after his mother’s suicide and the collapse of a short and ruinous first marriage, Pauli began analysis with Jung in Zürich. He stayed in contact with Jung for the rest of his life. Pauli, who had ranked among the sharpest critics of pseudoscience in his discipline, was simultaneously serving Jung as a scientific sounding board, sharpening Jung’s notion of synchronicity (meaningful coincidence) into something they hoped could mesh with the acausality of quantum measurement. Their correspondence, published as Atom and Archetype, is one of the more peculiar documents in the history of twentieth-century thought: the conscience of physics on one side, the founder of analytical psychology on the other, both convinced that the deep structure of reality had a side that neither matter nor mind alone could explain. He kept the Jung work private during his lifetime, knowing how his colleagues would react.

The Pauli effect was named after his anecdotal bizarre ability to break experimental equipment simply by being in its vicinity. Pauli was aware of his reputation and was delighted whenever the Pauli effect manifested. These strange occurrences were in line with his controversial investigations into the legitimacy of parapsychology, particularly his collaboration with C. G. Jung on synchronicity. Max Born considered Pauli "only comparable to Einstein himself... perhaps even greater". Einstein…

Pauli’s published output was small compared to Heisenberg’s or Born’s. He wrote sparingly, preferring letters to papers, and many of his most consequential ideas circulated only as photocopies passed hand to hand between Copenhagen, Göttingen, and Cambridge. The neutrino letter was never published in a journal at all. Einstein, who had nominated him for the Nobel, declared Pauli his “spiritual heir.” Max Born said he was “only comparable to Einstein himself, perhaps even greater.” George Gamow wrote that it would be as hard to find a branch of modern physics where the Pauli principle was not used as it would be to find a man as gifted, amiable, and amusing as Pauli was.

In the quantum story he stands at a particular junction. From Bohr and Sommerfeld he inherited an old quantum theory of orbits and angular momenta, full of integer rules whose origin nobody could explain. From Heisenberg, Born, and Schrödinger he received the new mechanics in matrix and wave forms but without spin, the missing two-valuedness that made atoms add up. Pauli closed that gap. The exclusion principle, the spin matrices, the neutrino, the spin-statistics theorem he proved formally in 1940: each of them is a load-bearing beam in the building that runs from Planck’s blackbody curve to today’s quantum computers and Standard Model. He was the conscience of physics because he understood, better than almost anyone, what the new theory could and could not say. And he never let his friends forget it.