The Pope of Physics

by Gino Segrè

  A porter showed Enrico to his room. It had a marvelous view of the square and, in the distance, the Leaning Tower. Like the other rooms for the forty or so students, it was small and monastic. It held only a bed, a table, a chair, a shelf, and a sink. There was no running hot water and no heating other than the hand-held ceramic brazier that could be filled with hot coals. Enrico did not regard this as hardship since it was what he was used to in Rome. As a boy he had studied in the evening sitting on his hands to keep them warm, turning pages with the tip of his tongue.

  Persico, who had taken the more conventional route of enrolling at the university in Rome, received a postcard from his friend within a few days. In it Fermi confessed to early pangs of homesickness, adding that he had quickly overcome them: “During the first days of the new life, I was slightly despondent. However everything has now passed and I have completely regained my self-control.” He could always confide in Persico in a more intimate way. Persico was almost the brother he had lost, and their closeness, intense during their teens and early twenties, would persist throughout Fermi’s life.

  Fermi was one of a handful of physics students in Pisa. At the time, the subject was not highly regarded in Italy, nor did anyone seem to notice the great advances taking place in the field elsewhere. As he would find during the next two years, Fermi was the only person in Pisa to have any real understanding—much less an appreciation—of Max Planck’s 1900 introduction of the quantum, Albert Einstein’s general theory of relativity, and Niels Bohr’s 1913 model of the atom. Physics in Italy was regarded as a purely experimental subject and taught accordingly, with emphasis on phenomena adaptable to simple classroom demonstrations.

  By contrast, mathematics was firmly established in the country. Italy’s best researchers in the field, very much up to date, had frequent and fruitful exchanges with colleagues from abroad and taught their students the latest developments. Mathematics’ primacy was reflected in the apportioning of university professorships. Pisa had five mathematics professorships while physics had only a single one. Rome was the only Italian university in which there was more than one physics professor—there were two. University courses in mathematical physics were offered, but these basically focused on using physical phenomena such as planetary motion to analyze mathematical structures.

  The lone Pisa physics professor, Luigi Puccianti, in his midforties, was a kindly, friendly man. He had made some notable investigations in his youth, sufficient to warrant his appointment in Pisa. Since then, he had given up on research, limiting his activities to teaching aided by an assistant who had graduated from the Scuola only a year earlier. There was little chance that either of them would be able to teach Fermi anything, but at least they did not perceive his clear superiority as a threat to their own position. To the contrary, in the following years, Puccianti and his assistant would often ask him to explain questions in modern physics they had difficulty understanding. They were also appreciative of the fact that Fermi had chosen physics, not mathematics, as a career path. Having someone so talented opt for their discipline would confirm the subject’s importance.

  A question naturally arises: How did Fermi learn all the consequential physics of the day? He did it the same way he had prepared for admission to the Scuola Normale: by studying relevant books. In his first two years in Pisa he read and completely absorbed contemporary texts in French, German, and English. The list includes Poincaré’s Théorie des Tourbillons, Sommerfeld’s Atombau und Spektralinien, Rutherford’s Radioactive Substances and Their Radiation, and several others. Beyond that, he began consulting recent major journals, in particular the German Zeitschrift für Physik subscribed to by the university’s library. With his background in German, Fermi was probably the only one in Pisa to read them.

  Once Fermi had absorbed the contents of what he had read, he neatly transcribed what he deemed the essential part of a complicated argument, often just a few annotated equations, into little notebooks. This lifelong habit allowed him to retrieve key notions in a way that appeared miraculous. Among the most moving are his teenage notebooks, filled with formulas and exercises, composed even before he entered the Scuola Normale and now stored in Pisa’s Domus Galileiana collection.

  While Fermi studied hard at the Scuola, he fortunately found a friend with whom he could have fun. Other than his serious-minded albeit close relationship with Persico, the element of youthful mischief and camaraderie had been missing from his life. Happily, he came to experience that in Pisa.

  4

  STUDENT DAYS

  At the beginning of the second month of required university courses at Pisa, Fermi found himself sitting next to a tall, thin first-year engineering student. The two of them began chatting about what university life was like, what they expected to learn, and what they already knew. Many years later that student, whose name was Franco Rasetti, would remember what he told his mother after the encounter, “I have met another student who is a genius, a man like I have never seen before. He must be a sort of prodigy. He knows more than all the professors put together in physics and he understands everything.” Rasetti would become Fermi’s close collaborator over the next twenty years.

  This only child was in many ways as exceptional as Fermi. Educated at home through elementary school by a father who was an avid naturalist and a mother who was a gifted painter, Rasetti had benefited greatly from both their talents. At a young age he had already collected enormous numbers of insects, animals, and plants, all of whose Latin names he knew, and he had provided extraordinarily accurate pictorial representations of the samples, even publishing articles in the Bulletin of the Italian Entomological Society. And that was not all: with an omnivorous appetite for knowledge and a phenomenal memory, he had read widely in several languages and taught himself chemistry.

  On entering university, Rasetti chose engineering as a field, having decided that this would allow him to have a comfortable and stable career. He set aside his other passions, avocations to be indulged in periodically. Meeting Fermi changed Rasetti’s life. Soon the young Pisan became convinced by his new friend that physics was a field of tremendous interest, where his extraordinary experimental dexterity would be valued. The two became inseparable, Fermi often eating dinner at Rasetti’s home, where he lived with his parents. The family meal provided welcome relief from the dull fare Fermi encountered at the Scuola.

  In turn, Rasetti had a great influence on Fermi. In addition to providing collegial company, Rasetti introduced his urban peer to the beauties of the Apuanian Alps, a nearby chain of six-thousand-foot peaks. Located along the coast some twenty miles north of Pisa, these scenic mountains are famous for the views of the sea and for the many quarries located near the central town of Carrara. These quarries are the source for marble used in the construction of some of the world’s most striking buildings, particularly Italy’s splendid churches.

  The mountain peaks also allow for technical climbing. Rasetti had been initiated into the sport as a teenager, had loved it, and had made some noteworthy Alpine ascents. Fermi did not share Rasetti’s desire to summit steep mountains on treacherous and challenging routes, but hiking was much to his liking. He did not have any trouble keeping up with Rasetti. Like all the male Fermis, Enrico was somewhat on the short side, with broad shoulders and a torso that was a little long in comparison to his legs. But those sturdy legs never seemed to tire, and Fermi would not hesitate to start out on a fifteen-mile excursion with a heavy pack on his back.

  For Fermi, Rasetti also provided a release from his gloomy home atmosphere in Rome. Belatedly, Enrico was able to indulge in the adventures and harmless pranks of youth. He and Rasetti formed a two-person club for playing practical jokes, calling themselves the Anti-Prossimo, or Anti-Neighbor Society. One of their simplest tricks was to walk by one of the outdoor urinals common in Italy at that time and inconspicuously throw a small piece of sodium between the feet of the unsuspecting man using the facility. The resulting geyser of foam would predictabl
y alarm the user, much to the amusement of the pranksters.

  Occasionally Fermi and Rasetti brought their mischievous ways to the classroom. Once, when a lecturer was scheduled to explain how cats manage to turn themselves around during a fall to land on their feet, the Anti-Prossimo decided to sneak a live cat into the lecture hall and throw it into the air as an illustration. The live demonstration and its noisy aftermath were not appreciated.

  Although several such pranks dotted their student days, Fermi and Rasetti were viewed with trust by the faculty. They obviously were talented students, and in the third year of their studies, they, along with their contemporary Nello Carrara, were given the keys to the university physics laboratories. The trio had free range to explore and to see what could be accomplished with the equipment at hand. Excited at the prospect of doing research, they set to work bringing the equipment in the laboratory up to date and building what was needed.

  Each of the three selected a different thesis topic. The thesis was to be divided into three parts: a general introduction to the subject, a description of the underlying conceptual questions, and finally, the results with an interpretation of a performed experiment. It would have been easy for Fermi to write a thesis based purely on investigations in theoretical physics, but a thesis had to conform to those dictates. Fortunately he enjoyed experimental work and the format posed no problem for him.

  For his thesis Fermi chose an ambitious topic, the study of X-rays, or as they were often still called, Roentgen rays, the name honoring their discoverer. Efforts were made in Pisa years later to find the original copy of his thesis, presumably available in the university’s library. The efforts proved futile until 1990, when the thesis was in fact discovered in the library. Fermi’s had been filed erroneously under the name Terni.

  Fermi was self-deprecating about his thesis. He wrote to Persico in the frank and intimate style the two adopted with one another, “I have a lot to do for my thesis, which I might add has turned out to be a solemn piece of filth.” Nevertheless Fermi did publish two articles based on its results in Il Nuovo Cimento, the journal of the Italian Physical Society. But these were not his debut publications.

  Fermi’s first original work was on the subject of relativity, a topic very much in the news following the 1919 observation of a solar eclipse. During that event, in accordance with Einstein’s theory of general relativity, the path of distant starlight was seen to bend as it passed close to the solar surface. It was rumored that only a half dozen people in the world could understand how this observation related to Einstein’s theory. That was an exaggeration, but Fermi was almost certainly the only Italian physicist able to comprehend the details.

  In contrast, a number of Italian mathematicians were current on the fine points of general relativity. Foremost among them was Tullio Levi-Civita, a recently appointed professor in Rome. He had done much of the early work in the Riemannian geometry that provided Einstein with the tools for formulating his theory, leading Einstein to quip that the two best things in Italy were “Spaghetti and Levi-Civita.”

  During the summer after his first year in Pisa, Fermi began to apply notions of general relativity to the effects of gravity on the motion of electrically charged particles. To do so he needed a new and better system of coordinates than the usual x and y axes. Location on a sphere such as Earth is specified by longitude and latitude. But what is the optimal coordinate system for specifying the paths through the curved space of general relativity? Fermi’s solution, which now goes by the name of the Fermi coordinates, was a significant advance.

  Fermi realized that mathematicians would be interested in this research but also that they were unlikely to read about it if were published in the Nuovo Cimento. It would be better to have his work in the Rendiconti dell’Accademia dei Lincei (Proceedings of the Academy of Lynxes). The Accademia accepted only articles presented by a member. Fortunately for Fermi, a recent Pisan member of the Accademia was happy to oblige. He brought Fermi’s work to the attention of Levi-Civita and his colleagues at a January 1922 meeting. Shortly after, Fermi’s paper was published. At the age of nineteen, Fermi was beginning to be known in Italian academic circles beyond Pisa’s ancient walls.

  5

  THE YOUNG PROTÉGÉ

  After four years at the Scuola Normale, Fermi received a magna cum laude doctorate in physics in July 1922. The oral defense of his thesis was anticlimactic; some of the eleven examiners in black academic robes and square hats were repressing yawns. None of them shook hands with him or offered congratulations, as was the custom. For them, his presentation was too erudite.

  Afterward, Fermi returned to Rome. In spite of his brilliance, he had no obvious prospect for employment. Lacking a mentor, he found himself stymied. A very real danger loomed that university-based Italian physicists would not recognize his contributions to the nascent field of theoretical physics, and that mathematicians would not regard him as one of their own. Who, then, would be his advocate?

  The prescribed path for entering academic life in Italy was first a position as assistant to a professor and then a libera docenza, the qualifying title for being a teacher. After sufficient time passed, one entered a competition for a professorship. This meant presenting your publications to a panel of five professors chosen by the Ministry of Education, since universities were state institutions. The professors would make the appointment after scrutinizing the merits of all candidates.

  Given the system, appointments often involved favoritism. In addition, even if lucky enough to become a professor, one initially was almost always assigned to a minor university. After a few years, one might be able to transfer to a major center such as Turin, Bologna, or Padua and eventually maybe even to Rome.

  Fermi was lucky; an influential patron recognized his astonishing talent. Moreover, this man, Orso Mario Corbino, was connected politically as well as being extraordinarily astute. Born in 1876 in a small town on the eastern shore of Sicily, Corbino—in his own way—was almost as remarkable as Fermi. Corbino’s father had a small spaghetti-making enterprise. His mother, though from a relatively well-to-do local family, had never learned to read or write, the norm for Sicilian women at the time.

  Young Orso was sent to the nearby town of Catania for high school, entered university there, and then continued on to Palermo, the island’s largest city. There he developed a passion for physics. Graduating at twenty, he taught high school for several years while continuing to conduct experiments. At twenty-eight he won a competition for a physics professorship at the University of Messina, Sicily’s third largest city. Four years later, he was offered a professorship in Rome.

  At the onset of World War I, Corbino shifted his research to topics benefiting the war effort. In doing so, he came into contact with economic, industrial, political, and military leaders. They all realized Corbino’s organizational and administrative acumen as well as his technical proficiency. As he moved into their spheres, a broad recognition for Corbino’s overall excellence followed. In 1920 he became a Senator of the Kingdom, a lifetime selection made by the king, and in 1921 he was named minister of public education.

  These notable appointments, political and administrative, coexisted with the retention of his physics professorship. Though conscious of the honors, Corbino was nevertheless saddened to venture forth from the cloistered world of academia. Expressing this feeling in a 1922 speech delivered to the Senate, he lamented, “I became a Senator, I became a Minister … but I miss the world of science; above all, in the midst of the bitterness of politics, I regret having left behind the peaceful days spent performing experiments while surrounded by apparatus.”

  More than any other senior physicist in Italy, Corbino was aware of the extraordinary advances taking place in quantum physics and was distressed to see that nobody in Italy participated in them. Serendipitously, Fermi appeared in Corbino’s office, unsure of how much time the illustrious senator would have for a new university graduate. This shrewd judge of talent detect
ed the young man’s promise and saw him as the answer to his dream of Italy as a serious contributor to modern physics.

  Thus began a close relationship that would last until Corbino’s early death from a heart attack in 1937. During these fifteen years, the older man would advise Fermi on both professional and personal matters while constantly smoothing the way for the growing and increasingly successful research group Fermi led. Though not a participant, Corbino took pride in the group’s achievements and made sure he was aware of their progress on almost a daily basis.

  But the first thing Corbino did for Fermi was to ensure for him a stay in a great research center in northern Europe. Sensing that his young protégé needed to be challenged, Corbino wanted Fermi to meet others who might be his equals. The Ministry of Public Education offered a yearly scholarship for study outside Italy to a recent university graduate in the sciences. Not surprisingly, the selection committee that included Corbino unanimously chose Fermi as its 1923 recipient.

  Germany, then the world leader in science, was Fermi’s destination in January of that year. Language difficulties were not a problem, for his grasp of German was excellent—though still more at a reading rather than conversational level. He even had written his childhood friend Persico an occasional letter in German, signing off as Heinrich Fermi.

  Two schools of theoretical physics had emerged in Germany as training grounds for young physicists during the early 1920s, both concentrating on atomic physics. They were where Fermi was most likely to find his peers. One was in Göttingen. Its university had been a world center of mathematics for over a century, and now, with Max Born at the helm, it was also a world center of theoretical physics. Arnold Sommerfeld, whose Atombau und Spektralinien was the bible for atomic phenomena, had made Munich the second mecca.