137: Jung, Pauli, and the Pursuit of a Scientific Obsession Part 5

Indeed it was not. With the rise of psychoa.n.a.lysis scientists began to look into how they had come up with their discoveries. Einstein wrote, "There is no logical path to these laws; only intuition, resting on sympathetic understanding of experience, can reach them." In this way, he added, scientists could glimpse the "pre-established" harmony of the universe. Logical empiricists, however, saw this as aimless babble conjured up by scientists years after the fact.

In their view scientists constructed theories by moving logically-mathematically-from experimental data to a theory. They churned out equation after equation until they had solved the problem at hand. Einstein considered this wrongheaded. Scientists were unanimous in agreeing that their methods of research bore no resemblance to the proposals of positivists and logical empiricists. The key point for creative scientists such as Einstein was the delicate balance they had to maintain between the information obtained from experimental data and the laws of the theory as expressed in mathematics.

Pauli undoubtedly read Einstein's views as well as the famous polemic in the first decade of the twentieth century between Mach and the discoverer of quantum theory, Max Planck, whose opinions were similar to Einstein's. Planck accused Mach of degrading physics whereupon Mach simply withdrew in disgust: "I cut myself off from the physicist's mode of thinking."

Einstein believed, as did many scientists, in a world beyond perceptions in which electrons actually existed. Philosophers called this view "scientific realism." There were scores of hybrid philosophies besides scientific realism and positivism which a.s.serted that in fact there was nothing "out there." Pauli counted himself a "'heretic,' not bowing down to any G.o.d, authority or 'ism.'"

As a philosophical opportunist, Pauli saw that positivism offered a way out of the mora.s.s of 1925, when Bohr's theory of the atom had collapsed with nothing to replace it. He thus advised Heisenberg to drop the unmeasurable concept of electron orbits and focus instead on measurable concepts like energy and momentum. This meant dropping the rea.s.suring visual image of the atom as a solar system. Pauli's belief was that once the "systems of concepts are settled," that is, once the new atomic theory had been worked out, then "will visual imagery be regained," as he wrote to Bohr. At Bohr's Inst.i.tute, Heisenberg and Bohr shared all correspondence from Pauli and eagerly awaited it.

Quantum mechanics-the new atomic physics.

Heisenberg's quantum mechanics identified individual electrons within atoms by the radiation they emitted while jumping between different stationary states, that is, the condition of an electron characterized by four quantum numbers as well as its momentum and energy, measurable as spectral lines. The transitions, or jumps, of the electrons maintained the flavor of the discontinuous quantum jumps in Bohr's theory of the atom. Discontinuities were a fact of life in the world of the atom, especially in a theory based on electrons as particles.

Pauli was convinced that Heisenberg's quantum mechanics would make it possible to solve problems that he had been unable to solve with the old Bohr theory. Late in 1925, he set out to calculate the stationary states for the simplest atom-hydrogen-using quantum mechanics. It involved juggling very complex mathematics but he came up with the answer with amazing speed.

Werner Heisenberg in 1925, when he discovered quantum mechanics.

Bohr applauded Pauli's "wonderful results." Heisenberg complained he was "a bit unhappy" that he had not solved the problem himself, but was full of admiration and surprise that Pauli had done it "so quickly."

Irked that Pauli had stolen a march on him, just a month later Heisenberg, along with Pascual Jordan, another brilliant young physicist, tried applying quantum mechanics to the problem that had driven everyone to despair-the anomalous Zeeman effect. Just as Kepler's ellipses had eliminated the c.u.mbersome circles moving on circles, so Pauli's new concept of spin-part of Heisenberg's quantum mechanics-at a stroke swept away the concepts of ma.s.sive inert cores with their two-valuedness and strange forces which had cluttered up Bohr's theory. The problem had finally been put to rest, and the solution also helped set Heisenberg's quantum mechanics on a firm basis. This time they had the theory right.

Physicists applauded these calculational breakthroughs. But no one-including Bohr, Heisenberg, and Pauli-really understood the theory itself, because the properties of atomic ent.i.ties were so impossible to imagine. Not only was it unfamiliar and difficult to use, the mathematics of Heisenberg's quantum mechanics lacked any helpful visual image. Being a hybrid version of Bohr's virtual oscillators, it was like trying to visualize infinity. Its fundamental particles were also unvisualizable. But this was fine with Heisenberg, who felt the time was not ripe for a return to visual images which, in the past, had always turned out to be misleading.

Then the French physicist Louis de Broglie suggested that electrons might be waves-in other words, that material objects, such as ourselves, might be considered as waves. His inspiration was Einstein's discovery, made some two decades previously, that light-traditionally thought of as a wave-could also be a particle, dubbed a light quantum. Perhaps electrons as well as light might be both wave and particle at the same time-simply beyond imaginable.

In spring 1926, the flamboyant Erwin Schrodinger, at the University of Zurich, burst on the scene. At thirty-nine, Schrodinger was an outsider in age, temperament, and thought to the group of impetuous twenty-something quantum physicists who cl.u.s.tered around Bohr in Copenhagen, Sommerfeld in Munich, and Born in Gottingen.

Schrodinger had found the equation that converted de Broglie's vision of matter as waves into a coherent theory. His version of atomic physics, which he called wave mechanics, was based on treating light and electrons as waves. "My theory was inspired by L. de Broglie," he wrote. "No genetic relation whatever with Heisenberg is known to me. I knew of his theory, of course, but felt discouraged, not to say repelled, by the methods of the transcendental algebra, which appeared very difficult to me, and by the lack of visualizability."

Schrodinger's wave mechanics sprang from a preference for a mathematics that was more familiar and beautiful, as opposed to what he referred to as Heisenberg's ugly "transcendental algebra." The "Schrodinger equation" offered great advantages in calculations over Heisenberg's quantum mechanics, added to which it enabled the electron in an atom to be visualized as a wave surrounding the nucleus. It had taken Pauli twenty-odd pages to solve the hydrogen atom problem. Schrodinger did it in a page.

Schrodinger pointed out that the wave nature of matter promised a return to cla.s.sical continuity. The pa.s.sage of an electron between stationary states could be envisioned as a string pa.s.sing continuously from one mode of oscillation to another.

One year earlier there had been no viable atomic theory. Now there were two: Heisenberg's quantum mechanics and Schrodinger's wave mechanics.

Heisenberg was furious about Schrodinger's work and even more so about its rave reviews from the physics community. "The more I reflect on the physical portion of Schrodinger's theory, the more disgusting I find it," he wrote to Pauli. "What Schrodinger writes on the visualizability of his theory I consider c.r.a.p."

Heisenberg saw wave functions-that is, the solutions to Schrodinger's wave equation-as nothing more than a means to expedite calculations. To demonstrate this he applied them to the problem that had driven Born, Pauli, and himself to despair: to find a mathematical way to describe the properties of the helium atom. No one had been able to deduce stable orbits, or stationary states, for the two electrons in the helium atom using Bohr's theory of the atom. This being the case, they could not move on to deduce spectral lines for the helium atom because these resulted from its electrons dropping down from a higher to a lower orbit. Instead, the electrons' orbits remained unstable, meaning that an electron could be knocked out of the helium atom by the smallest of disturbances.

But in Heisenberg's quantum mechanics there were no orbits. The problem became one of deducing the atom's spectral lines from its stationary states expressed directly in terms of the electrons' energy and momentum in the atom. If the spectral lines turned out to be wrong, it would show that there were serious problems with the way quantum mechanics defined stationary states, that is, the energy levels of electrons in atoms. The spectral lines of the helium atom were particularly interesting to physicists because, as had been observed in the laboratory, they fell into two distinct groups. But why should this be the case?

Insight into the exclusion principle.

The helium atom has two electrons. Using his quantum mechanics Heisenberg showed how the two sets of spectra arise. To elucidate his result and speed up his calculation of numerical values for the spectral lines, he used Schrodinger's wave functions-the solutions to the Schrodinger equation-for both the spins and positions of these two electrons. The total wave function is the result of multiplying these two wave functions together. But there are many possible ways of constructing the total wave function for these two electrons.

Heisenberg found that only one sort produced the two distinct groups of spectral lines characteristic of the helium atom. This particular wave function had a unique property. It changed its sign when the spins and positions of the electrons were swapped. It was antisymmetrical, which also meant that it went to zero if the electrons had the same spins or positions.*

What was nature's selection device for choosing these two sets of wave functions for the two spectra out of the several possible ones? Heisenberg was stumped. Something strange was going on here. Perhaps it related to Pauli's exclusion principle, according to which no two electrons could have the same spin and position. If they did then one of the two wave functions that make up the total wave function-either for their positions or for their spins-would have to become zero. Perhaps that was the way nature selected the wave function suitable for a particular system of electrons. Thus Heisenberg realized that the exclusion principle was related to the symmetry property of the wave functions for a collection of electrons, in this case two electrons. It was a step forward in exploring its implications beyond making sense of the periodic table of elements.

It was a typical Heisenberg project. He chose a fundamental problem-in this case to understand the spectrum of the helium atom-and then let his intuition lead him into new terrain: the symmetry property of wave functions whether they are symmetric or antisymmetric. Thus he realized how essential the exclusion principle was for quantum mechanics: without it quantum mechanics could not be complete.

There was also the problem that had been Pauli's original bete noir from his PhD thesis, in which he showed that Bohr's theory of the atom failed to produce a stable hydrogen-molecule ion, H+2, even though it existed in nature. This problem vexed Born and Heisenberg as well. Pauli wrote to his friend Wentzel, "In Copenhagen sits a gentleman who is calculating H+2 according to Schrodinger." The "gentleman" was the Danish physicist vind Burrau who, as Pauli pointed out, started directly with Schrodinger's wave mechanics as opposed to starting from the quantum mechanics as Heisenberg had done and used Schrodinger's wave mechanics only for calculations. As a result he was able to solve the problem simply. Heisenberg wrote to Pauli that, in his opinion, Burrau had straightened out the situation and mentioned the symmetry properties of the wave functions that Burrau had deduced. Perhaps Heisenberg had hoped to find a solution starting from his quantum mechanics. But these once-key problems had become mere calculations now that the correct atomic physics had been worked out.

Although problem after problem that had resisted solution using the old Bohr theory was now being solved by atomic physics, the meaning of the theories used-Heisenberg's quantum mechanics and Schrodinger's wave mechanics-was still not understood. And the tension between the two factions was growing.

To the Schrodinger faction Burrau's successful result, as well as Heisenberg's for the helium atom (despite his a.s.sertion that he had used Schrodinger's theory merely to facilitate calculations) was proof that Schrodinger's theory offered a solution to every problem of atomic structure, whereas Heisenberg's was daunting to use and ugly. This of course greatly pleased Schrodinger.

Heisenberg's uncertainty principle.

In fall 1926, Bohr summoned Heisenberg to his inst.i.tute in Copenhagen to hammer out a resolution to the dispute with Schrodinger. They struggled for days over numerous cups of tea and bottles of Carlsberg beer. Heisenberg wrote to Pauli: "What the words 'wave' or 'particle' mean we know not any more; [we are in a] state of almost complete despair."

The crux of the problem was this: how could ordinary language, with its visual connotations, be used to describe a realm of nature that defied the imagination?

While Bohr and Heisenberg were deliberating in Copenhagen, Pauli had an idea. He immediately wrote it up and mailed it to Heisenberg. It was based on an insight Born had had, looking into Schrodinger's wave equation.

Born had suggested that the wave function was a wave of probability for an electron moving between stationary states. Pauli pushed the idea further. He realized that the wave function gave the probability of an electron being detected in a certain region of s.p.a.ce. In his usual way, he didn't bother to write a paper to publish this idea and in the end Born took the credit.

But as he was working out the mathematics for Heisenberg, he came up with another extraordinary discovery: if he could determine a particle's position accurately, he could not determine its momentum with the same accuracy. Pauli was puzzled as to why this should be so. Why couldn't he determine both with the same degree of accuracy? Heisenberg was struck by the insight. He was, he wrote to Pauli, "more and more inspired by the content of your last letter every time I reflect on it."

By February 1927 Bohr and Heisenberg had hit an impa.s.se in their discussions on the deep meaning of the quantum theory, which seemed to be riddled with ambiguities. Bohr took a skiing break. Left to his own devices, Heisenberg set to work. The result was a paper that he called "On the Intuitive Content of the Quantum-Theoretical Kinematics and Mechanics." Hidden behind this daunting t.i.tle was one of the most earth-shattering discoveries of modern physics: the uncertainty principle.

Heisenberg realized that the supposed ambiguities of the quantum theory were essentially a problem of language. The issue was how to define words such as "position" and "velocity" in the ambiguous realm of the atom, a world in which "things" can be both wave and particle at the same time. He used the term "intuitive" in the t.i.tle of his paper, for his goal was to redefine the word in the world of the atom.

Certain concepts in quantum physics, Heisenberg claimed, such as "position" and "momentum" (ma.s.s times velocity), were "derivable neither from our laws of thought nor from experiment." Instead we would have to look into the peculiar mathematics of quantum mechanics, which should have alerted us all along that in the realm of the atom we would have to apply such words with great care.

In his paper Heisenberg made the amazing a.s.sertion that the more accurately we measure an electron's momentum in a certain experiment, the less accurately we can measure its position in that experiment. This quickly became known as the uncertainty principle. It was earth-shattering in that it questioned our understanding of the inherent nature of the physical world as completely as Einstein's relativity theory.

In the cla.s.sical physics of Newton we can measure the position and momentum of an object with the same degree of accuracy by observing how it moves. Using a telescope and a clock we can measure both the location of a falling stone and how fast it is moving with an accuracy limited only by the width of the telescope's crosshairs and the clock's mechanism. If we make these errors as small as possible we can deduce very precisely the stone's position and momentum. In principle, the product of the errors in measurements of position and momentum can both be zero. In quantum mechanics this is not possible.

Heisenberg wrote all this down in a detailed fourteen-page letter to Pauli. He asked for "severe criticism" after all, it was Pauli who had given him the key idea. Pauli was elated. "It becomes day in the quantum theory," he declared.

Bohr's complementarity and beyond.

Bohr, however, was furious. He refused to let Heisenberg publish his paper on the subject, saying that Heisenberg had not provided any firm foundation for his argument. Furthermore, Heisenberg had based the argument entirely on the a.s.sumption that light and electrons behaved like particles.

Bohr insisted that electrons and light be understood as both wave and particle, even though this could not be imagined. One could visualize electrons and light as either a wave or a particle so long as one remembered the restrictions required by quantum mechanics, among them Heisenberg's uncertainty principle understood within the larger context of waves and particles.

This meant that electrons in experiments could exhibit one aspect or the other, but not both at once. If one experimented on an electron as if it were a wave, that was what it would be for the duration of the experiment, and similarly if one treated it as a particle. Bohr called this "complementarity."

Bohr was convinced that complementarity was relevant not only to physics but also to psychology and to life itself. Its basic idea, he wrote, "bears a deep-going a.n.a.logy to the general difficulty in the formation of human ideas, inherent in the distinction between subject and object." As in the Chinese concept of yin and yang, complementary pairs of concepts defined reality. There is nothing paradoxical about an electron having the characteristics of both a wave and a particle until an experiment is performed on it. It dawned on Bohr that in the weird quantum world there need not be only yes and no, an electron need not actually be either particle or wave. There could be in-betweens as well as ambiguities. An electron's wave and particle aspects complement each other, and their totality makes up what the electron is. Thus the electron is made up of complementary pairs-wave and particle, and position and momentum. Similarly it is the tension between complementary pairs-love and hate, life and death, light and darkness-that shapes our everyday existence.

Bohr sent the ma.n.u.script of his article on complementarity to Pauli for corrections and critical remarks. Pauli replied immediately. Apart from certain comments on details, he entirely agreed with Bohr's thesis.

Only the more philosophically inclined scientists took complementarity seriously. Pauli was one. He began to look to complementarity as another way to study consciousness as in the various ways of "knowing" practiced in the East and West. He was growing more and more interested in the conscious and the unconscious, the rational and the irrational, and in how physics could be used to understand these complementarities. He was beginning to suspect that this was to be his life's work. The only problem was how to approach it.

Paul Dirac and quantum electrodynamics.

The previous autumn the eccentric twenty-five-year-old English physicist Paul Dirac had visited the Bohr Inst.i.tute. Dirac had already made important contributions to atomic physics and was eager to rub shoulders with other physicists of his generation whose papers he had studied in detail, Heisenberg and Pauli among them.

Dirac had been privy to the intense conversations between Bohr and Heisenberg on the issue of whether light and matter could be both wave and particle. In 1927 he was able to provide the vital clarification through a mathematical method he had developed for moving between the two and thus brought about "complete harmony between the wave and light quantum descriptions." Dirac's mathematical method ultimately concerned the way in which electrons and light interact. It formed the basis for a whole new subject, which scientists dubbed quantum electrodynamics. Pauli and Heisenberg worked enthusiastically to develop this new field.

Dirac's equation.

The following year Dirac came up with a crucial equation-the Dirac equation. It described how electrons interacted with light and also agreed with relativity theory. The equations in Heisenberg's and Schrodinger's theories did not agree with relativity, and while the spin of the electron had to be inserted into these theories, it popped right out of Dirac's, thus underscoring the relationship of spin to relativity.

But Pauli and his colleagues were dissatisfied. Among other problems, Dirac's equation for the electron predicted that objects with negative energy should actually exist. Physicists believed particles of negative energy to be like negative time: they simply could not exist. Heisenberg commented to Pauli that Dirac's equation was the "saddest chapter in modern physics." Furthermore, it did nothing to elucidate Pauli's exclusion principle.

Pauli's anti-Dirac equation.

In 1934 Pauli set out to find an equation to supplant Dirac's. His colleague in this was his a.s.sistant Victor Weisskopf. Weisskopf had been a student of Born's and Bohr's. Like Pauli, he was Viennese. The two shared a deep appreciation for literature and music, in particular Mozart's operas. Weisskopf was also a concert-level pianist. Well over six feet tall, athletically built, and with a cultured air, he stands out in group photographs.

Viki, as Weisskopf became known to his friends, loved to tell the story of his first meeting with Pauli in the fall of 1933: The first time I came to see him, I knocked at the door-no answer. He was in a very bad mood at that time, the whole period was a difficult one for him for personal reasons. When he didn't answer, after a few minutes I opened the door. 'You are Weisskopf; yes, you will be my a.s.sistant. I will tell you that I wanted to take [Hans] Bethe but he works on solid state [physics]. I don't like this kind of physics although I started it.' He gave me some problem...and after a few weeks I showed him what I had done; he was very dissatisfied with it and he said, 'I should have taken Bethe.'

This was Pauli's idea of humor, but it also shows what a difficult, sharp-tongued man he could be. Many people could not handle his sardonic sense of humor and this led, no doubt, to some physicists thinking twice before taking on the job of his a.s.sistant. But despite the inauspicious start Pauli's collaboration with Weisskopf was to be both fruitful and memorable.

The two came up with an equation that had many of the same properties as Dirac's and agreed with relativity theory. But while Dirac's was for any particle with half a unit of spin, theirs was for particles with no spin. None had been detected at the time. However, when they included spin in their equation it no longer agreed with relativity.

But why? As he was fiddling about with his equations Pauli realized something entirely new: that particles with no spin differ fundamentally from particles with half a unit of spin. Particles with half a unit of spin-1/2, 3/2 and so on (known as Fermions after the Italian physicist Enrico Fermi)-obeyed Fermi-Dirac statistics (discovered by Fermi and Dirac in 1926), meaning that the overall wave function (that is, the solution of the Schrodinger equation) for a collection of Fermions exhibited antisymmetry.*

The only known such particles at the time were the electron, neutron, neutrino, and proton. Particles with whole-number spin-zero, one, and so on (called Bosons after the Indian physicist Satyendra Nath Bose)-obey Bose-Einstein statistics (discovered by Bose and Einstein in 1924), meaning that they have an overall wave function that remained the same when their positions and spins are exchanged; it was symmetrical. In other words, the two sets of particles have different symmetry properties. From this Pauli deduced that the exclusion principle applies to particles with half a unit of spin and not to particles with a whole unit of spin.

There was no obvious reason for this. The only conclusion was that nature had spoken. Something more than mathematics was involved in wave equations. Physicists now began investigating the properties of wave equations for particles of any sort of spin. The difficult mathematics involved was very much to Pauli's taste.

Six years later, in 1940, he summarized and extended this work. Instead of using any particular wave equation such as Dirac's, his own, or any other, he used the mathematical properties of wave functions to explore how they behaved when relativity theory, spin, statistics, and the exclusion principle were applied to them. He cut through all the mathematics to deduce a conclusion that was highly significant. The exclusion principle, he discovered, cannot be applied to any theory that includes relativity and applies to particles with whole-number spin; but it is essential to theories dealing with particles with half-units of spin.

The "connection between spin and statistics is one of the most important applications of special relativity theory," he wrote. He had been trying for a long time to find a connection between spin, statistics, and relativity and at last he had done it. Compact yet rigorous in its mathematical presentation, the paper he wrote on the subject was Pauli at his best. Many physicists regard it as his most brilliant.

Finally, some sixteen years after Pauli had first come up with the exclusion principle and with the concept of spin-and had first realized that there were four, not three quantum numbers-he had managed to discover some of the key implications of his first great discovery. From the start everyone had realized that the exclusion principle explained the periodic table of elements. Now it was known that it could be used as a tool to explore the behavior of every particle with half a unit of spin and that it had no connection with any other sort of particle.

Mephistopheles.

G.o.d's whip.

PAULI never failed to give full rein to his sardonic humor and caustic wit. He ruthlessly criticized people who he thought did not think clearly. In 1926 he was at a lecture given by the Dutch physicist Paul Ehrenfest. Ehrenfest, a senior figure whose circle included Einstein and Bohr, was famous for his profound understanding of physics and his excellence at explaining difficult concepts. A charismatic teacher, he had motivated a succession of brilliant young students, but he seemed never to make great discoveries to match those of his famous colleagues, and the comparison tortured him. To him Pauli was one of those young "smart alecks.... Always so clever they were! And n.o.body understood anything."

After his lecture Pauli offered a string of critical comments. Finally Ehrenfest retorted, "I like your publications better than I like you." "Strange. My feeling about you is just the opposite," Pauli countered. The two later became good friends and Ehrenfest came to admire Pauli's critical ac.u.men. "There is in rebus physicus only ONE G.o.d's whip (Thank G.o.d!!!)," Ehrenfest wrote to Pauli a couple of years later. Pauli was delighted with the t.i.tle Ehrenfest had bestowed on him and there after often signed himself "G.o.d's whip."

Other acid quips have since become part of Pauli's lore. When students or colleagues tried out a new theory on him, he would sometimes shout, "Why, that's not even wrong," meaning that it was so far from correct it wasn't even possible to judge it by the normal standards of right and wrong. Other favorite one-liners of his included, "You're no more interesting drunk than sober," and "So young and already so unknown." Colleagues remember that Pauli liked to dream up a cutting remark, keep it in mind, and then, at the appropriate time, use it.

Pauli even criticized Bohr, who sometimes took offense. To Einstein, "I will not provoke you to contradict me, in order not to delay the natural death of [your present] theory," he wrote, about one of Einstein's attempts at a unified theory of gravitation and electromagnetism. Einstein, conversely, was quick to compliment the younger man on pointing out an error in another attempt at a unified theory. "So you were right, you rascal."

The one person Pauli never criticized was his mentor Sommerfeld. Pauli once wrote of the "awe you instilled in me...not even accorded Bohr." In his presence Pauli was a completely different person. Whenever Sommerfeld visited the Swiss Polytechnic Inst.i.tute, later referred to as the ETH, in Zurich, where Pauli was working, Weisskopf recalled Pauli would always be saying, "Yes, Herr Geheimrat [Honored Teacher], yes, this is most interesting, but perhaps you would prefer a slightly different formulation, may I formulate it this way."

At base, Pauli's razor-edged criticism arose from his dislike of shoddy thinking. As a child he had been raised in a house in which everything from science to politics was pulled apart and criticized. "Obedience to authority was not sung to me in the cradle," he once wrote. But he simply said what was on his mind. He did not mean his criticisms to be taken personally and he was hardest of all on himself. In a letter to Pauli asking his advice, Heisenberg referred to him as the "master of criticism," and later recalled that "I have never published a work without having Pauli read it first." He was often called the "conscience of physics."

Fresh start.

In professional terms, 1927 was a year of immense achievement for Pauli. He had been instrumental in helping Bohr and Heisenberg straighten out quantum theory and was engaged in working with Heisenberg in developing the field that Paul Dirac had initiated, quantum electrodynamics. Then came a shock.

Pauli's father had always been a womanizer. It was a situation that his mother, the brilliant intellectual journalist, Bertha, had had no choice but to resign herself to. Late that autumn, Wolfgang Sr. finally left her. He had fallen in love with a woman Pauli's age, a sculptor named Maria Rottler whom Pauli referred to caustically as his "wicked stepmother." No doubt the younger woman with her artistic ambitions offered Pauli's father a new lease on life, but to Pauli the desertion of his mother was an unforgivable act of treachery and betrayal.

It was more than Pauli's poor mother could bear. Not long after her husband left, on November 15, 1927, she took poison and died. Clearly for Pauli it was an unbearable trauma. He closed up and said not a word about it to his friends or colleagues. The extent to which it affected his mental well-being only became clear much later, when he began a.n.a.lysis with Jung.

The same month that Pauli received news of his mother's death, he also received another, more welcome, communication: the offer of a position at the prestigious ETH. The new job would mean leaving Hamburg for Zurich.

It happened that both the ETH and the University of Zurich were about to lose their most formidable theoretical physicists. Peter Debye, at the ETH, had accepted a position at the University of Leipzig while Schrodinger, at the university, had agreed to succeed Max Planck at the University of Berlin. Debye had been a student of Sommerfeld's. His main interest was investigating the structure of molecules by studying how they behaved when struck by x-rays, work that was later to earn him a n.o.bel Prize. The ETH decided to offer the vacant post to one of the two rising stars of theoretical physics-Pauli and Heisenberg. First Heisenberg was offered a position at the ETH, one of several offers he had that year. In the end, however, Debye lured him to Leipzig where he became a professor.

Next the ETH turned to Pauli. The eccentricities of his teaching style were well known. Valentine Telegdi remembered them as "pedagogically maladroit, but full of gems of wisdom which one had to find (and polish) oneself." Only the most brilliant students could understand anything-though for them it was a lesson not only in physics, but also in how to think critically about the subject. As Markus Fierz, later Pauli's a.s.sistant and then close friend, described it: His presentation was more like a soliloquy than a lecture. He spoke with an unclear tw.a.n.gy voice, and he wrote with small untidy letters on the blackboard. Sometimes he would lose the thread or, doubting the correctness of a derivation or a statement, shake his head or gaze noddingly into the air. He then continued, mumbling unintelligible words or saying "yes, yes, yes," though n.o.body knew what had disturbed him in the first place. This seemed to me extremely mysterious, and it contributed to intensifying the demonic aura surrounding this queer man.

The president of the ETH went personally to Hamburg to a.s.sess Pauli's performance. He decided that Pauli was young enough to improve and immediately offered him a position, starting on April 1, 1928, with a contract for ten years.

Zurich.

"In April 1928 I arrived in Zurich as a new professor, dressed like a tourist with a rucksack on my back." Pauli went straight to his office in the imposing physics building at number 35 Gloriastra.s.se, a broad street off the main avenue, Ramistra.s.se, on which sits the princ.i.p.al building of the ETH. There he met his new colleague Paul Scherrer, who had had the office spruced up for the new professor's first day.

At twenty-eight, Scherrer, a debonair experimental physicist, was Pauli's exact contemporary. He had carried out important research on the x-ray a.n.a.lysis of crystals with Debye before joining the ETH in 1920 and, by 1927, had been promoted to head of the physics department. Besides his brilliance in research Scherrer was a charismatic lecturer. Twice a week he gave lectures to explain difficult concepts in physics to both scientists and laypeople, backed up by an array of spectacular demonstrations. The auditorium was always packed for what became known as the "Scherrer circus." On one occasion Scherrer tried out one of his simplified explanations on Pauli, who replied in his caustic way, "Ja, simple it is all right, but also wrong."

Pauli rented a flat on Schmelzbergstra.s.se, 34, a steep, narrow, tree-lined road, in a pleasant three-story house set back amidst trees, a few minutes walk from the physics department.

He immediately hired Kronig, who had been the first to realize that Pauli's fourth quantum number was the spin of the electron, as his a.s.sistant. "Every time I say something, contradict me with detailed arguments," Pauli told him. Next Pauli convinced his closest friend, the physicist Gregor Wentzel, to take the position vacated by Schrodinger at the University of Zurich. Like Pauli, Wentzel had been a student of Sommerfeld's in Munich. When Pauli was a student Wentzel had been Sommerfeld's a.s.sistant and joined in their cafe conversations. Two years Pauli's senior, he had already made important contributions to the new atomic physics. He had an easy-going manner, enhanced by his ever-present cigar and readiness for a good time. In letters Pauli addressed him as "Dear Gregor" and signed himself "Wolfgang"-in those days an extraordinary degree of informality.

Pauli had barely settled into the ETH when he was back at work with Heisenberg. But as the two resumed their research on quantum electrodynamics, they encountered such difficulties that Pauli began to lose heart. He lapsed into the state of mind he had had when previous problems proved intransigent-like in 1924, when his frustration over the anomalous Zeeman effect drove him to seek solace in the bars and wh.o.r.ehouses of the Sankt Pauli district, and again in 1925, when the Bohr theory of the atom collapsed and he daydreamed about giving it all up and becoming a film comedian. This time he played with the idea of dropping out to write a utopian novel. In reality he just needed a rest from physics.

He wrote to Bohr that he was having trouble concentrating. He wished he could say that he had no time for research or that he was tired, he added, but neither was true. "I am only stupid and lazy. I think that somebody ought to give me a daily thrashing! But since unfortunately there is no one around to do it, I must seek other means to reinvigorate my interest in physics." On the weekends he often went to Leipzig, where regional meetings of the German Physical Society were held. Heisenberg, too, was there and he and Pauli had endless discussions about issues holding up their progress in quantum electrodynamics.

One problem was that Pauli was distracted by the entertainment Zurich offered. He also had just the right mix of colleagues to share it with-Kronig and Scherrer. On warm Sundays the three friends swam at the Strandbad, a beach on Lake Zurich, a ten-minute drive from the city. To cap off the afternoon they would then go back to the city and walk along the elegant Bahnhofstra.s.se to Paradeplatz where they went to Sprungli's cafe for ice cream and coffee. The rotund Pauli a.s.signed Kronig the task of monitoring his ice cream intake.

In the evenings, after work, they walked down Ramistra.s.se to Bellevue Square, at the intersection of the Limmatquai, which runs alongside the river Limmat, and the Utoquai, to their favorite restaurants. The most elegant was the Kronenhalle, usually reserved for after-concert dinners. The dining room still retains its old-world flavor with its high ceiling, tables covered with white tablecloths, and waiters gliding around in black trousers, white shirts, black ties, and long white ap.r.o.ns tied at the back. Across the street and around the corner on Limmatquai is the Cafe Odeon. A masterpiece of art deco design, it was the meeting place for artists, poets, and intellectuals of every persuasion, even the occasional anarchist such as Lenin, who brooded and plotted there until the Allies returned him to Russia in a sealed train in 1917, as if he were a plague bacillus.

Across the Limmatquai is the Cafe Terra.s.se where the physics department took its colloquium speakers for dinner. It had a more intellectual atmosphere than the Kronenhalle and the discussion often continued there. In those days the now-enclosed dining room was an outdoor garden. Another spot Pauli and his friends frequented with some regularity was the Bauschanzl beer garden, just across the river Limmat from the Cafe Terra.s.se, today a rather garish and pricey restaurant. Other bars and cafes where they spent time, such as the Cafe Voltaire, the headquarters for dadaism, are gone.

One warm summer's night after a day of swimming in the lake, ice cream at Sprungli's, and dinner at Cafe Terra.s.se, the three friends sat in the Cafe Odeon, penning a postcard to Pauli's friend and successor in Hamburg, Pascual Jordan, who had worked with Heisenberg to crack the puzzle of the anomalous Zeeman effect. In the three years between his appointment as Born's a.s.sistant at Gottingen in 1924 and his arrival at Hamburg, Jordan had carried out ground-breaking work on the new quantum mechanics. Pauli addressed his postcard to "PQQP Jordan," a joking reference to an important equation Jordan had helped establish. "We are about to study the Zurich night life and try to improve it following the new method due to Pauli: by comparison," the three wrote exuberantly. "Many Greetings, Kronig," wrote Kronig. "This method, however, may also be used to worsen matters!-Greetings, Pauli," added Pauli. "I, too, have heard so many bad things about you that I would like to meet you. Scherrer."

Shortly afterward Kronig left for a position at Utrecht in the Netherlands and was replaced by Felix Bloch who had been Heisenberg's first PhD student. Tall, handsome, and urbane, Bloch fit in well with the crowd. Other soon-to-be-famous young physicists pa.s.sed through the ETH, among them Rudolf Peierls, a student of Sommerfeld's and Heisenberg's, who succeeded Bloch as Pauli's a.s.sistant. A young man with immaculately parted hair and round-rimmed gla.s.ses, he had to suffer the sting of Pauli's famous biting remarks. One was particularly memorable: "[Peierls] talks so fast that by the time you understand what he is saying, he is already a.s.serting the opposite."

J. Robert Oppenheimer worked with Pauli during the first half of 1929. Pauli wrote of Oppenheimer that he treated "physics as an avocation and psychoa.n.a.lysis as a vocation." Perhaps Pauli sensed in Oppenheimer's complex and tortured personality a reflection of himself.

Motivated by his new colleagues, brilliant a.s.sistants, and a coterie of exceptional postdoctoral students, Pauli re-entered the stalled collaboration with Heisenberg. By September 1929 they had completed their opus, which they published in two parts. Its eighty-four pages firmly established quantum electrodynamics as a field of research and combined Heisenberg's intuitive approach and Pauli's penchant for rigorous calculations to dazzling effect. Covered with lengthy equations, the papers contained a wealth of new mathematical techniques that have since become part of every physicist's repertoire for exploring how elementary particles interact. "Not for the curious," quipped Pauli.

As well as its scientific importance, Zurich was a center of German culture and Pauli became a habitue of its intellectual salons. There he met, among others, the philosopher Bernard von Brentano; the writers James Joyce and Thomas Mann; Waldimir Rosenbaum, a wealthy political activist and lawyer; and the artists Max Ernst and Hermann Haller, the son of Einstein's stern but beloved former boss at the Swiss Federal Patent Office, Kurt Haller. Haller made a bust of Pauli that stands in the La Salle Pauli at CERN. He looks as if he is in deep contemplation, pondering weighty problems. "The sculptor Haller in Zurich has made a bust which makes me look rather introspective-i.e., Buddha-like," Pauli wrote to Kronig rather proudly.

Pauli in love.

Amid this whirl of nightlife and salons Pauli was also building up the prestige of his department and conducting intense physics research. But no matter how much he filled his days and nights, he still anguished over his mother's death. It was only in 1929 that he hinted at his feelings, signing the papers on quantum electrodynamics that he had written with Heisenberg simply "Wolfgang Pauli," omitting the suffix "Jr." He no longer cared whether he was confused with his famous father whom he now loathed.

Then in May 1929 he made a rather strange decision that may or may not have had something to do with his mother's death: he left the Catholic church and unofficially adopted his father's original religion, Judaism. Perhaps it was his response to the harsh judgment of Catholicism, which condemns suicide as a mortal sin, that led him to take this step. He later described himself as a "Jew from the waist up." This may seem odd, in light of his ill feelings toward his father. But he had little regard for either Catholicism or Protestantism, to which his parents had converted in 1911, and he was well aware of how Jewish he looked, with his swarthy complexion, dark wavy hair, and dark eyes.

For all its pleasures Zurich had no Sankt Pauli red-light district where Pauli could seek consolation for his sorrows. He took to making frequent trips back to Hamburg and Berlin. Then, in December 1929, he suddenly announced, to the amazement of his colleagues, that he was going to marry-and, not only that, but that his intended was a cabaret dancer. He had always dismissed marriage as a bourgeois inst.i.tution.