CHAPTER THREE

GERMANY AND HOLLAND

FERMI’S FOUR YEARS IN PISA WERE SCHOLARLY AND CONTEMPLATIVE, but they were years of turmoil and chaos for the rest of the country. Though Italy was one of the victors in November 1918, the war left a power vacuum in its wake, and the following four years saw one faction after another trying to grab the political high ground. Strikes and labor unrest led to regular breakdowns in production and transportation. In the streets of the northern industrial cities of Milan, Turin, and Genoa, communists and right-wing agitators fought each other with increasing violence and lawlessness. Virulent Italian nationalists sought a voice in parliament. Italy seemed increasingly ungovernable.

In the midst of this turmoil, a brash journalist named Benito Mussolini began to promote a nationalist movement with increasing appeal to the majority of the Italian people. Bright but unsophisticated, he was drawn to socialist causes as a young man and fought briefly in World War I. Leaving service, he wrote for socialist papers opposed to Italian participation in the war, but in a turn that remains somewhat mysterious to this day, he shifted away from opposition to more of a nationalist, pro-war stance. When hostilities ended, he started a newspaper, Il Popolo d’Italia (The People of Italy), which gave voice to a new and coherent philosophy of statist nationalism that eventually became known as fascism.

As Fermi’s summer holiday of 1922 came to an end, he began to consider what to do next. Mussolini and his confederates were planning an audacious move: a national coup d’état, culminating in a fascist march on Rome to take control of the government. The march took place on October 28, 1922, the very day that Fermi and Corbino were scheduled to meet and discuss the young man’s future.

CORBINO WAS A CENTRAL FIGURE IN EARLY-TWENTIETH-CENTURY Italian physics and was to become a central figure in Fermi’s life as well. Unlike most senior scientists of his era, he played an important role in public service as well as in the development of his academic field. Born in Sicily in 1876, Corbino was just slightly younger than Fermi’s father, Alberto, a year younger than Fermi’s mentor Amidei, and he grew up in the years following Italy’s unification in 1870. He proved a promising physicist and did important work in the burgeoning field of spectroscopy that garnered him the attention of senior Italian physicists. They plucked him from his position as a teacher at a liceo in Palermo and brought him to the university in Messina on the eastern coast of Sicily. Corbino taught there from 1904 till 1908, when he survived a disastrous earthquake that destroyed much of the town. Pietro Blaserna, the director of the University of Rome’s Institute of Physics and holder of the physics chair at the university, invited Corbino to take a position at the institute. When Blaserna passed away in 1918, Corbino ascended to the directorship of the institute, a position he held until his own sudden and untimely death from pneumonia in 1937.

Corbino was even shorter than Fermi and rounder, bald with a bushy moustache and bright eyes. He was a fine teacher. Laura Fermi enjoyed a course she took with him, pronouncing him “impressive.”

Corbino’s early graduate work in Palermo was critical in shaping his internationalist view of the field. His professor had studied with the great Dutch astrophysicist Hendrik Lorentz and, unlike many of his Italian contemporaries, was eager to keep abreast of developments outside Italy. He imparted this enthusiasm to Corbino, who devoted much of his career to keeping track of external developments and, at the same time, to bringing Italian physics to the attention of the rest of the world.

Corbino was also an administrative genius. Successive Italian governments recognized this and placed him in positions of increasing importance. After the war he served as head of the committee overseeing water resources, and in 1921 he was appointed Minister of Public Instruction. In 1923, Mussolini named him Minister of National Economics, in spite of the fact that he was not, and never would be, a member of the Fascist Party. Along the way, Corbino also became a senator in the Italian parliament. He was close to Italian industry and served on the boards of several Italian electricity companies.

His academic prestige grew in tandem. He was a member of the Accademia dei Lincei, at the time the most prestigious scientific society in Italy, and president of the Società Italiana di Fisica (Italian Physical Society) from 1914 to 1919.

With each new role he further cemented his reputation as a brilliant technocrat with a sound sense of judgment and an ability to move serenely and efficiently through the bureaucratic labyrinths of Italian power. He openly regretted the various governmental responsibilities that prevented him from continuing what had been a distinguished research and teaching career. In young Fermi he saw his opportunity to put Italy where he believed it deserved to be, at the forefront of world physics. For his part, Fermi could have found no one better placed to guide his career. It was to be an historic partnership.

On that day in October 1922, when the two of them were supposed to be discussing Fermi’s future, Mussolini’s supporters marched on Rome and the prime minister petitioned the king to declare a national state of emergency, something that, under Italy’s constitutional monarchy, only the king could do. Corbino and Fermi could not help but fixate on the situation. As reported by Laura Fermi years later, they speculated as to whether the king would sign the declaration. Corbino expressed distaste over the fascists’ embrace of violence for political ends but viewed a signature as the start of a prolonged, bloody civil war. Fermi noted that the king rarely countered his cabinet’s recommendation. “Do you think he may go against his cabinet?” Fermi asked the older and wiser Corbino. “He has never been known to take the lead but has always followed his ministers.”

Corbino paused before replying. “I think there is a chance that the king may not sign the decree. He is a man of courage.”

“Then there is still a hope,” his younger colleague suggested. Fermi had clearly misunderstood Corbino.

“A hope?” he replied. “Of what? Not of salvation. If the king doesn’t sign, we are certainly going to have a Fascist dictatorship under Mussolini.”

Corbino was right. The king refused to sign, sparing Italy a long civil war, and within a week, Mussolini was prime minister of Italy, well on his way to creating the twenty-one-year-long dictatorship foreseen by Corbino.

CORBINO HAD ADVISED FERMI TO APPLY FOR A SCHOLARSHIP AT THE University of Göttingen, in the central German state of Lower Saxony. The competition for this particular scholarship, sponsored by the Italian Ministry of Education, was intense, but Fermi won it without apparent effort. On October 30, 1922, two days after the Fascist march on Rome, the fellowship committee met and awarded him the fellowship. Thus began one of the most mysterious and inexplicable periods of Fermi’s entire career.

THE UNIVERSITY OF GÖTTINGEN WAS ONE OF THE WORLD CENTERS of physics. The eminent theorist Max Born and his close colleague experimentalist James Franck had already started to build a major center, recruiting brilliant students, including young Werner Heisenberg, who would shortly become world famous. Another theorist, Pascual Jordan, had recently arrived from Hanover and would in time make his own indelible mark on quantum theory. Fermi just missed overlapping with Wolfgang Pauli, an Austrian who had already written a seminal treatment of relativity theory. The two of them would meet only five years later, at a conference at Lake Como in Italy in 1927.

Born was a slightly shy, somewhat formal gentleman in his early forties, who had studied at Göttingen early in the century with three of the world’s greatest mathematicians, David Hilbert, Felix Klein, and Hermann Minkowski. His original work on relativity won lavish praise from Einstein himself. After stints at the universities in Berlin and Frankfurt, he was recruited to Göttingen and brought Franck, an old friend and colleague, along with him. Born was at Göttingen barely two years when Fermi arrived, a newly minted graduate with some five published papers to his name. It should have been a wonderful moment for Fermi.

However, quantum theory, for which Göttingen would soon become world famous, was at a momentary impasse. Niels Bohr had developed a theory of the atom that incorporated the basic insights of quantum theory, but a number of important experimental observations remained unexplained. In early 1925, all that would begin to change, but when Fermi arrived, late in 1922, these breakthroughs were in the future.

Not only was quantum physics at a standstill but also Germany itself was an exceedingly unpleasant place. Reeling from four years of unsustainable reparation payments as a consequence of the Treaty of Versailles, the German economy entered a period of hyperinflation that destroyed the economic and financial fabric of the country and destabilized the precarious Weimar Republic. Laura Fermi writes that for the first time Enrico enjoyed a feeling of relative wealth. Because his stipend was paid in Italian lire, he was able to maintain and even improve his standard of living as the financial crisis progressed. He splurged and bought himself a bicycle. A sleepy university town with little in the way of industry, Göttingen might not have suffered from some of the more unpleasant aspects of the crisis—industrial unrest, strikes, and riots—but it could not have been a happy place.

Most importantly, Fermi felt ignored. Born was not a demonstrative man and apparently paid little attention to his new young Italian visitor. It seems that Heisenberg, Jordan, and the other scholars at Göttingen neglected him, as well. Though his letters home to his father during his stay at Göttingen show no signs of unhappiness—rather, they focus on money, family, food, vacation, his new bicycle—Laura Fermi writes that this was a moment in Fermi’s career when he needed validation and did not get it. Yet Fermi knew he was special and throughout the course of his career never needed anyone else to tell him so.

Segrè puts some of the blame on Fermi, suggesting that the young physicist was “proud, shy, and accustomed to solitude.” Years later Fermi’s future Manhattan Project colleague Leona Libby went further, observing that he had “a stored-up, never forgotten bitterness against the physicists he encountered on his first visit to Germany as a very young man. He most of all resented the fact that Marie Curie and Werner Heisenberg, in particular, had completely ignored him, to the point of exceeding rudeness,” adding, “This was the winter [1923] that made Fermi miserable because, as he told us later, he was completely unappreciated and ignored, almost ostracized from the in-group.” The intensity of the resentment is surprising at such a remove in time and place, yet it is hard to see why Libby would invent such an anecdote.

Finally, and not inconsistent with the other explanations, this was Fermi’s first time living and working outside of Italy for any substantial length of time. In spite of his comfort with the language, he may have felt alien and lonely simply by virtue of his being so far away from home.

If Fermi was deliberately shunned by the Göttingen “in-group,” this may also have reflected snobbery among German physicists toward their Italian colleague. Fermi never carried himself as a particularly cultivated or cultured individual. He was obsessed with physics and aside from his outdoor activities had little interest in anything else. His regular habits involved getting up early, working all day long, with a lunchtime break for several hours in the early afternoon. When he came back from lunch, he would work until late afternoon, have dinner, and go to sleep. Each day was very much like the last. He had little time for nightlife, café life, or cultural life. Though Born was no night owl, the younger students loved to hang out in cafés and talk about culture and philosophy well into the night.

Furthermore, the group that Born and Franck recruited was certainly more inclined toward philosophy than Fermi was. Heisenberg was obsessed by what quantum theory really meant about the nature of reality. Pauli, although not quite so obsessed, thought deeply about these issues, as well. In Fermi they did not find a fellow traveler. Fermi preferred to stick with questions that had definite answers, answers that he could find through careful, systematic work. As quantum theory developed, the philosophical issues became more complex, and yet throughout his life Fermi resisted any speculation of a philosophical nature. His aversion to the deeper questions could well have influenced his German colleagues to ignore him.

One wonders why Curie would have, in Libby’s words, “ignored him, to the point of exceeding rudeness.” She may have been a bit prickly, but by the time she visited Göttingen in 1923, she had nothing to gain from being rude to a young Italian physicist. On the other hand, she was known to be strongly skeptical of theory and theorists. To the extent that Fermi presented as a theorist—which is quite likely, given that he did no experimental work while he was in Göttingen—it is possible that she lumped him together with other theorists and thus had no time for him.

The work he did was indicative of the problems that interested him at the time and in many ways throughout the rest of his career. His Scuola Normale dissertation focused on probability theory, and continuing the theme, the papers he published while he was at Göttingen focused on various aspects of the field in which probability and statistics are central—statistical mechanics. Fermi loved the mathematics of probability and statistics and enjoyed statistical mechanics for exactly this reason.

One of his Göttingen papers involved a probabilistic concept called the “ergodic theorem.” The ergodic theorem is central to the study of statistical mechanics. In statistical mechanics, a system is said to be ergodic if, in principle, it can start in a given state and, over time, pass through every possible state, eventually returning arbitrarily close to its original state. Fermi became interested in ergodic processes during this period. In particular he wondered whether certain well-specified systems were actually ergodic in their behavior or only seemed to be so. He developed a proof of the ergodic theorem that, though not mathematically rigorous, was sufficiently useful and penetrating to attract the attention of physicists outside Italy.

Fermi returned to statistical mechanics in late 1925 and early 1926 with historic results. Indeed, probability and statistics remained a central preoccupation thereafter. Why did Fermi find probability and statistics so compelling? Not all physicists do. Whereas knowledge of probability is essential to an understanding of most of modern physics, in and of itself it is not a field on which many physicists focus. Fermi loved to gamble, particularly on the outcome of his own athletic competitions. He also loved to pose riddles that required an understanding of probability. His way of solving problems, now known as Fermi problems, often consisted of evaluating the probabilities of particular events, to at least an order of magnitude, and linking those probabilities together to arrive at a solution that seemed reasonable. The so-called Fermi paradox—Fermi’s back-of-the-envelope observation that if intelligent life exists elsewhere in the universe we should have been visited by it long ago, given the size and age of the universe—is in itself a study in probability.

One possible reason probability and statistics captivated him may stem from the trauma of Giulio’s death. Here was something unexpected, totally improbable, and yet it occurred, with devastating results. Perhaps the experience awoke within Fermi a desire to understand, delimit, and prepare to the extent possible for events that were out of one’s control. The odds were low that Giulio would die when he did and yet it happened. Fermi may have taken away from this trauma the need to understand the likelihood of any particular event and a feeling that in understanding that probability he was in a better position to anticipate it, prepare for it, and perhaps even shape its outcome. We will, of course, never know. What we do know is that the study of probability ran like a thread through his career and was at the root of many of his most important contributions.

FERMI ARRIVED BACK IN ROME FOR THE SUMMER OF 1923, HAPPY TO be home, and Corbino soon found him a one-year appointment teaching physics to engineering students at the University of Rome, alongside his old friend Persico, who had stayed in Rome and received a physics degree at the university under Corbino’s watchful eye. During the academic year, one spring weekend Fermi met another young person, someone destined to have perhaps the greatest impact on his life.

Her name was Laura Capon.

Laura Capon was a bright, vivacious young woman, just shy of seventeen years old, the daughter of a prominent Roman Jewish family. She grew up in relative splendor, in a home in the elegant district just north of Viale Policlinico, at Via dei Villini 33. Her father, Augusto Capon, was an officer in the Italian navy. By the time Laura met Enrico, her father was an admiral.

The admiral valued intellectual ability and achievement, which explains in part why he decided that, unlike most young women of her socioeconomic status, Laura should eventually earn a degree in general science from the University of Rome. There, she would take a course in physics taught by a young man named Enrico Persico.

The admiral’s intellectual and social ambitions brought him into contact with major Roman intellectuals, and he entered the circle of the two great mathematicians of Rome, Tullia Levi-Civita and Guido Castelnuovo, both of whom also happened to be Jewish. The two mathematicians were friends, and the latter held a Saturday evening salon at his home to which Levi-Civita and a variety of other prominent mathematicians were invited. Augusto Capon was also a regular at the salon. The adults often brought their children along, and the children became close friends. Laura became particularly fond of Castelnuovo’s daughter Gina. It was with this group of friends that Fermi found himself one Sunday in the spring of 1924. He was older than the rest of them but had gotten to know them because he, too, was a regular visitor to these salons and enjoyed the company of the younger group as much as he enjoyed being with the older intellectuals.

FIGURE 3.1. Young Laura Capon with friend, date uncertain. Courtesy of AIP Emilio Segrè Visual Archives, Uhlenbeck and Crane-Randall Collections.

Early photos of Laura reveal a slim woman with a round, cherubic, happy face. It is easy to see why Fermi found her appealing. Years later, when a colleague complimented him on how attractive his daughter Nella was, he replied, “You should have seen Laura when she was young.” Their first meeting was hardly auspicious. Laura was unimpressed with this man, introduced as a brilliant young scientist who was already teaching at the university at the age of twenty-two:

He shook hands and gave me a friendly grin. You could call it nothing but a grin, for his lips were exceedingly thin and fleshless and among his upper teeth a baby tooth lingered on, conspicuous in its incongruity. But his eyes were cheerful and amused: very close together, they left room only for a narrow nose, and were gray-blue, despite his dark complexion.

The group of friends went to play in a park on the northern outskirts of the city just on the other side of what is now the Via Salaria, near a bend in the Tiber River. Fermi, who was a bit older than the others, took the role of leader and decided the group should play soccer. Laura explained she had never played the game before. Fermi assured her it would be fun and made her the goal keeper for his team. Laura describes what happened next:

There was an easy self-reliance in him, spontaneous and without conceit. Luck, however, was against him: at the height of the game the sole of one of his shoes came loose and dangled from the heel. It hampered his running, made him stumble and fall on the grass. The ball zoomed above his fallen body and sped toward the goal. It was up to me to save the day: while I was observing our leader’s predicament with more amusement than pity, the ball hit me in the chest. Stunned, I wavered, almost fell, recovered my balance. The ball bounced back into the field and victory was ours.

Our leader pulled out of his pocket a large handkerchief, wiped off the perspiration that streamed down profusely from the roots of his hair over his face, then sat down and tied his loose sole with a piece of string.

It was, she concluded, “the first afternoon I spent with Enrico Fermi, and the only instance in which I did better than he.” She would not see him again for some two years.

THE YEAR WENT BY QUICKLY, BUT FOR FERMI THE ACADEMIC YEAR was cut short by the death of his mother on May 8, 1924.

The family had been caring for her through a series of respiratory illnesses, so her passing was no surprise. Yet we can be sure it had an effect, though he would never speak directly about it. Giulio may have been her early favorite, but there is no reason to think that Ida and Enrico were not also close. Ida found some pride and a bit of respite from her grief in Enrico’s increasing and gratifying success. Segrè notes that Fermi in later years expressed admiration for his mother’s ability to make things for herself when she had to—a makeshift pressure cooker being an example. Fermi’s ability with his hands may have been inherited from this fragile, disciplined former schoolteacher. Her death was a blow, but it was a blow that he dealt with in typical fashion, that is, privately.

His father, Alberto, had been planning to move the family out of the city and to a modern but modest suburban area, Città Giardino Aniene, about five miles north of central Rome. He had bought a plot at what became Via Monginevra 17 and was in the process of having the home built when Ida passed away. The family moved there in 1925. It was an improvement over Via Principe Umberto 133, but by no means grand. Alberto and his surviving children, Enrico and Maria, called it home for the next few years. Alberto died in 1927 and Fermi married the following year, moving to his own apartment and leaving Maria installed at the family home.

TOGETHER CORBINO AND FERMI PLOTTED FERMI’S NEXT STEP. Corbino was aware of an International Rockefeller Foundation fellowship that might be available to Fermi for another overseas scholarship. In the interim, Fermi had made the acquaintance of a young Dutchman, less than a year his senior. The two events came together in a happy coincidence.

The Dutchman was named George Uhlenbeck. A graduate student in physics at the University of Leiden, in southern Holland about five miles outside of The Hague, Uhlenbeck had taken a year off and was working with the household of the Dutch ambassador to Rome, serving as a tutor in math and science to the ambassador’s two sons. Shortly after he arrived, Uhlenbeck received a note from his thesis adviser, Paul Ehrenfest, that a young physicist in Rome named Fermi had written an insightful paper on the ergodic theorem. This was exactly the kind of paper that would have appealed to Ehrenfest, a keen student of statistical mechanics who had been looking for ways to integrate it with the emerging quantum theory. Ehrenfest had an instinct that Fermi was a potential intellectual soul mate and urged Uhlenbeck to make Fermi’s acquaintance and report back.

The two young men got on famously. In 1962, Uhlenbeck recalled those first meetings with Fermi: “He was younger than I was, but he was in a sense a wonder child, like Pauli. Anyway, we had then a little seminar, with Pontremoli, Persico, and me, in this old building.… He was so much ahead of all three of us, that he was the one who talked all the time.”

The Dutchman and the Italian became lifelong friends.

Enthused at the prospect of working with Uhlenbeck’s colleagues in Holland, Fermi spent the rest of 1924 in Leiden on his Rockefeller fellowship and enjoyed his time immensely. Ehrenfest had enormous respect for his new young colleague. After the disappointment of Göttingen, Fermi was delighted to find his abilities appreciated. No doubt this had to do with the outgoing character of Ehrenfest and the team he had around him, including Uhlenbeck and another graduate student, Samuel Goudsmit. Uhlenbeck and Goudsmit were the Dutch equivalent of Fermi and Rasetti—extremely close friends who shared an impish sense of humor and a passion for their chosen profession. They even physically resembled their Italian counterparts: Uhlenbeck, tall and gaunt, towered over the shorter, sturdier Goudsmit. The two Dutch physicists were inseparable. Fermi found them engaging companions.

Much of Fermi’s success in Leiden was certainly due to Ehrenfest, and Fermi wrote to his sister Maria of his delight in getting to know the Dutch physicist, describing him as a “persona molto simpatica”—a very kind person. Ehrenfest, a close friend of Einstein and one of the participants in the philosophical dialogue between Bohr and Einstein over the meaning of quantum physics, was, in Einstein’s eyes, the best teacher of his generation. Indeed, Einstein visited Ehrenfest while Fermi was there, and Fermi met the great physicist for the first and only time. Fermi kept a group photo of Einstein, Ehrenfest, and a gathering of other colleagues; Fermi is not pictured, leading at least one scholar to presume that Fermi took the photo himself. Einstein clearly impressed the young man, who wrote an enthusiastic letter to Maria describing his encounter with the great scientist, in which the two spoke German since Fermi’s Dutch was not up to par. However, in later years, Fermi expressed annoyance at the level of adulation given Einstein by an adoring world. The creator of the theory of relativity was the only physicist about whom Fermi ever overtly expressed a sense of envy.

Ehrenfest shared Fermi’s deep interest in matters relating to statistical mechanics and probability. This shared intellectual passion formed the basis of a productive and influential relationship for both men. Ehrenfest also clearly appreciated just how special Fermi was, how much the young man had mastered, and how clearly he thought about complex physics problems. He was impressed and let Fermi know it.

Fermi got to work quickly and by November he presented a theoretical paper analyzing problems associated with the intensity of multiple spectral lines that had arisen during experiments at the University of Utrecht. In it he expressed his appreciation for an idea suggested by Ehrenfest. In contrast, none of his earlier Göttingen papers made any reference to ideas suggested by his German colleagues. The rest of his time at Leiden went quickly and by the beginning of January 1925, Corbino’s efforts resulted in a lectureship in Italy for his gifted protégé. This time, it was Florence. Fermi took on a teaching position at the university and rejoined his old friend Franco Rasetti, who had himself found a position teaching experimental physics.

He may not have known it, but in Florence Fermi was destined to make scientific history.