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To immigrants, then and now

ACKNOWLEDGMENTS
This book has been written with the support and encouragement of many people and we are in their debt. A word or two of heartfelt gratitude is much deserved.
First of all, thanks to Sir Christopher Llewellyn Smith, who in 1996 planted the original idea of a book about Enrico Fermi into Gino’s mind, thinking undoubtedly that Italian physicists need to stick together. Then to the family historian, Olivia Fermi, who has kept her grandparents’ legacy alive by an open cultural dialogue (see the Neutron Trail website). Her enthusiastic support of our book was also reflected in lengthy and often moving interviews with other members of the Fermi family: Sarah Fermi, the widow of Fermi’s son, Judd (Giulio); and Rachel Fermi, Enrico and Laura’s youngest granddaughter. Gino’s cousin Fausta Walsby shared some childhood memories of the Fermi family from their overlapping time in Los Alamos with her parents, Emilio and Elfriede Segrè. And more background was generously provided by Robert Fuller, who regarded Judd Fermi as his best friend. Our meeting in Ithaca with Rose Bethe and her son Henry also provided invaluable anecdotes of the Fermi history.
We particularly want to acknowledge the kindness and insights of Ugo Amaldi, himself a physicist, who spent the greater part of a day with us in

Geneva, speaking about Fermi and his family, lifelong friends of his parents, Edoardo and Ginestra Amaldi. Several follow-up communications offered an even richer rendering of this friendship and a talk with Ugo’s brother, Francesco, was helpful in filling a few blanks in the picture.
In Rome, we were delighted to have a personal tour of the Fermi museum at the university, as well as repeated help with our research from the historian Adele La Rana. Thanks also to the historian Giovanni Battimelli who offered us advice, guided us with his own writings, and provided precious access to other documents. We benefited in Pisa from the counsel of Roberto Vergara Caffarelli and the Domus Galilaeana’s welcome, where the able assistance of Maura Beghè in gaining access to its Fermi Archives was greatly valued.
Special thanks also go to the courteous and more than competent archivists Diane Harper and Barbara Gilbert at the Regenstein Library of the University of Chicago and to Savannah Gignac at the Emilio Segrè Visual Archives of the American Institute of Physics. For the American part of this book, the trip that Ellen Bradbury Reid arranged for us a few years ago to Trinity, the site of the first atom bomb explosion, lent extra poignancy to this story.
Several esteemed physicists contributed astute observations and comments regarding Fermi and his collaborators. The list includes Harold Agnew, Jeremy Bernstein, Frank Close, Freeman Dyson, Kenneth Ford, Jerry Friedman, Richard Garwin, and Murray Gell-Mann. We are especially grateful to two distinguished physicists, Kenneth Ford and Alfred Goldhaber, who have read the manuscript in galley form, giving us valuable advice and pointing out errors. Needless to say, any remaining errors are purely our own fault.
We were lucky to have an editor, Serena Jones at Henry Holt, who was a strong believer in the importance of telling this story and guided the writing of it with a gentle and deft hand. And special thanks to Molly Bloom and Emily DeHuff, whose meticulous edits improved the manuscript. We are also grateful to Katinka Matson and John Brockman, literary agents who

continue to find imaginative and creative ways of making the world of science accessible to a larger public.
And finally, many thanks to Doron Weber and to the A. P. Sloan Foundation’s program in the Public Understanding of Science, Technology and Economics for providing the means to travel and absorb the many influences on Fermi’s life. This book benefited enormously from their support.

PROLOGUE
TRINITY
July 16, 1945. Dawn broke reluctantly, the early rays of the day barely grazing the tops of nearby peaks. It was almost as if the sun sensed that its brightness would be outshone. A group of scientists, huddled together against the morning chill, set aside their worries about bad weather and concentrated on the seismic event that was about to occur.
The countdown began at 5:09:45 a.m. If all went according to plan, exactly twenty minutes later they would throw a switch triggering the detonation of the world’s first atom bomb. The tension at the site was palpable as they waited. An earthen mound above a concrete slab roof, all supported by massive oak beams, fortified the structure they were staying in. Located ten thousand yards south of the hundred-foot-high tower holding the bomb, the shelter was thought to be safe no matter how large the explosion at Ground Zero might be. The small group who manned the Trinity Project, as it was named, included George Kistiakowsky, the head of explosives, Kenneth Bainbridge, the man who had selected and built up the site, and of course J. Robert Oppenheimer.
General Leslie Groves, feeling that he and Oppenheimer should not be together in case of disaster, had gotten into his jeep a little earlier and driven five miles south to Base Camp, leaving his military deputy in charge at the bunker. Most of the physicists who had worked on Trinity were at

Campania Hill, some twenty miles northwest of Ground Zero. A few, including Enrico Fermi and Emilio Segrè, were ten miles closer, at Base Camp. Shallow trenches had been dug there to protect them, but would those trenches be enough? Everybody thought yes, but how big was the blast going to be? Might it even be a complete failure?
A few days earlier the senior physicists had started a betting pool about the blast’s magnitude; a one-dollar entrance fee built up the pot. Kistiakowsky’s wager had been one thousand tons of TNT equivalent, a low estimate, as he would discover when he climbed on top of the bunker after the blast, only to be knocked over by the shock wave that reached him a few seconds later. Hans Bethe, head of the theory division, had said eight thousand, while a worried Oppenheimer had settled for a modest three hundred.
The switch was thrown at 5:29:45. Many recorded their impressions of what happened next, an event subsequently described as brighter than a thousand suns. From base camp, Isidor Rabi’s memory was that “Suddenly there was an enormous flash of light, the brightest light I have ever seen or that I think anyone has ever seen. It blasted, it pounced: it bored its way right through you. It was a vision that was seen with more than the eye.” The flash was so overwhelmingly intense that irrational instants of fear were common. “For a moment I thought the explosion might set fire to the atmosphere and thus finish the earth, even though I knew this was not possible,” Segrè recalled.
Seconds later, as the mushroom cloud began rising in the sky, those watching it were left trying to grasp the meaning of what they were witnessing. Oppenheimer remembered the lines from the Bhagavad Gita’s scriptures coming to him: “I am become Death, the destroyer of worlds.” Bainbridge expressed himself in much more prosaic language: “Now we are all sons-of-bitches.”
Fermi was arguably the physicist most responsible for the worldchanging event that had just occurred in the New Mexico desert. There is no documentation of what he was thinking at the time. But there is a record of

what Fermi was doing. If you didn’t know him, it would seem bizarre, but everybody knew he always acted with purpose. A few seconds after the blast, Fermi stood up and began tearing a large sheet of paper into small pieces and then dropping them from his upraised hand. Forty seconds later, as the front of the shock wave hit, the midair pieces were blown a short distance away. Pacing off the distance to where they landed, some eight feet, he consulted a little chart he had prepared beforehand. Shortly afterward, Fermi told those around him that he estimated the blast’s force as roughly equivalent to ten kilotons of TNT.
A few hours later, Fermi climbed into a special lead-lined tank and headed toward Ground Zero to scoop up material for a more careful assessment of what had transpired. The detailed measurements took about a week. It was concluded that the blast’s magnitude, corresponding to twenty kilotons of TNT, was close to the estimate he had made within a minute of the explosion. None of the physicists was surprised.
The dropping of the paper pieces soon became yet another vintage Fermi story, adding to the lore of how he could, with the simplest of means, estimate the magnitude of any physical phenomenon. And, as usual, he had been right. His colleagues in Rome used to joke that Fermi was infallible, like the Pope. He had acquired the nickname “the Pope of Physics” early on. It was an appellation that persisted, deservedly, throughout Fermi’s lifetime.

PART 1
ITALY, BEGINNINGS

1
FAMILY ROOTS
Enrico Fermi’s ancestral roots can be traced to the valley of Italy’s greatest river, the Po, whose origins lie in the western Alps. It flows from west to east, neatly bisecting Northern Italy, and finally empties into the Adriatic Sea. As it travels its four-hundred-mile course, it grows steadily in volume, fed by rivers coursing down from the Alps and from ones born in the central Apennine mountain chain.
The Po Valley, defined by its river, is agriculturally fertile and culturally vibrant. It is also Italy’s economic center, thanks to large industries, but enriched by a wealth of small businesses that have adapted an older tradition of craftsmanship to the demands of the new commerce. Turin, the automotive home of Fiat, is located directly on the river. As it winds further, Milan, a center of style and fashion, is a little north, and Bologna, known for its culinary treats, a little south, of its course. Venice, an architectural wonder, is not far from the delta where the Po empties into the sea. These are the region’s dominant cities, but there are a number of midsized ones with their own history and institutions.
In most cases this diversity comes from their ancient founding during the Roman Empire and sometimes even earlier, followed by an evolution during the Renaissance into independent city-states. What we currently call Italy, a country that came together only in 1870, was until shortly before

then little more than a hodgepodge of smaller fiefdoms wavering opportunistically to and fro in their allegiances to larger European powers.
Piacenza, the ancestral home of the Fermis, lies in the midst of the Po Valley. It has a particularly impressive thirteenth-century city hall, but the town is largely neglected as a tourist attraction because it lies almost directly in the middle of a triangle formed by the better-known Parma, Cremona, and Pavia. Founded by the Romans in 218 B.C.E., the settlement was given the name Placentia, from the Latin placere, “to please.” Through the following centuries, it did indeed please, and in doing so underwent the same cyclical sacking and rebuilding that its neighbors suffered.
In 1545 the Duchy of Parma and Piacenza was established. Except for a brief interlude during Napoleon’s short-lived conquest of Northern Italy, it controlled the region surrounding those two cities until the formation of modern Italy. Shortly before that, the Fermis, a local family, made the transition away from tilling the soil. The man who would become Enrico’s grandfather, Stefano Fermi, entered the employment of the state and rose to be administrative head of a small municipality adjacent to Piacenza.
Enrico Fermi’s grandfather married Giulia Bergonzi, a woman thirteen years his junior, and began a large family; their second son, Alberto, would one day become Enrico’s father. The fluid national identities that characterized the Italian peninsula in the first years after Alberto’s birth in 1857 were such that he entered the world as a subject of the Duke of Parma and Piacenza, became a resident of the free territory of Emilia two years later and a citizen of the Kingdom of Sardinia a year after that, and finally, at age four, became an Italian. All this without ever leaving the vicinity of Piacenza.
In the 1840s, Alberto’s father, Stefano, had settled with his wife in Caorso, a small municipality that lay eight miles east of Piacenza. Their life was a simple one, centering on family, work, and church. He and his wife, Giulia, almost certainly went occasionally to Piacenza, but they probably did not venture as far as Cremona, for though it was only eight miles west

of Caorso, going there required crossing the Po and entering a different country.
Those borders vanished in 1861 with the emergence of the Kingdom of Italy. Stefano and Giulia hoped there would be opportunities for advancement in this new country, still woefully underdeveloped by comparison to those of Northern Europe. The Industrial Revolution had for all practical purposes bypassed the peninsula, and most of Italy’s workers either labored on the land as they had for centuries or engaged in minor commerce. Nor was transportation very different from what it had been since Roman times, for there was little more than fifteen hundred miles of rail lines in the whole country, almost all of it north of the Po.
Education was viewed as providing a first step to bettering oneself. More than three quarters of Italy’s population was still functionally illiterate. Many could read a little but, like Enrico’s grandmother Giulia, had not learned to write, much less how to deal with arithmetic problems beyond a simple shopping list.
The newly formed Italian government instituted a set of reforms designed to change this state of affairs. An innovative law called for universal enrollment in elementary school starting at age six. Attendance in the first four years was compulsory, though in practice the rule was often broken. The poor considered it a luxury to have their offspring removed from the workforce. The rich educated theirs at home.
Stefano and Giulia, despite their modest circumstances, insisted on having their children attend school, and Alberto, who seemed to be the most scholastically gifted of them, advanced beyond an elementary education. But given the Fermi family’s financial situation, attending university was never considered. When he reached the age of sixteen, Alberto’s schooling was finished and it was time for him to seek employment.
By then Rome was the capital of Italy. The city and its surrounding region had been an independent state under papal rule until 1870, when the Kingdom of Italy had annexed the territory. Pope Pius IX had declared the occupation violent, unjust, and invalid. Retreating into the Vatican, he

refused to recognize the existence, much less the legitimacy, of the new Italy.
Alberto Fermi, thirteen at the time, must have followed the story with keen interest. His parents, especially his mother, were devout Catholics, but he was already having the doubts that would later turn him into an agnostic, if not an atheist.
Alberto knew that he would have to leave Caorso if he was to advance in the world. Working for a company that built and managed rail lines seemed to be a particularly interesting choice in the early 1870s. At the time of his birth Italy had more than two dozen independent railway companies, each operating separate lines. Many of the lines had been founded with foreign capital, making them dependent on events outside Italy’s control. Each attempted to maximize its profits with no concern for helping to forge a national identity.
By the age of twenty-four, Alberto was employed in the service of the company that managed the northern Italian railroads, one of the four that had emerged from consolidation. Through various reorganizations, the railroads continued to employ him until his retirement. In 1905 he became a civil servant for the Italian railroads, nationalized and combined into a single company, the Ferrovie dello Stato.
During all the years of employment, Alberto’s willingness to work harder than anybody else, combined with his organizational ability, perseverance, and native intelligence, had led to his steady rise in the ranks. These personality traits would be very much imprinted on his only surviving son, Enrico.
Like his father, Alberto did not marry until he was forty-one. Ida de Gattis was fourteen years his junior. The daughter of an army officer, she was born in Bari, a city in Puglia, commonly known as the heel of Italy. Ida had been orphaned at a young age and raised by relatives in Milan. Like Alberto, she strongly advocated self-sufficiency and self-reliance. She began teaching after a three-year course for elementary school teachers, her

ambitious trajectory a relative rarity at a time when women were still discouraged from entering a profession.
Ida and Alberto were both intelligent and upwardly mobile. They were not cultured in the traditional sense of appreciating art, music, and literature, though Alberto, a rather taciturn man, was known to occasionally break into song in the privacy of his home when shaving or bathing. His choice was almost always a Verdi aria, probably because the composer was born in Busseto, a small town only a few miles from Piacenza.
When Ida and Alberto married, they settled in Rome on Via Gaeta, a street that lay a short distance from the central railroad station. Their apartment was in one of the newer buildings that had sprung up during the thirty years since Italian unification, a period during which the city’s population had roughly doubled to some four hundred thousand. Their neighbors were much like the Fermis, upwardly mobile middle-class people, the husbands typically employees of the government or of a quasigovernmental agency.
The Fermis lived on Via Gaeta for ten years, then moved to a nearby apartment in 1908. Slightly more spacious, but still far from luxurious, it had no central heating and its bathroom, as was not unusual at that time, was equipped with only a sink and a toilet. Baths were taken in two zinc tubs, a smaller one for children and a larger one on casters for the parents. By then Ida and Alberto had three children. Maria was born in 1899, Giulio in 1900, and Enrico on the twenty-ninth of September, 1901.
The closeness in age of the children and Ida’s desire to continue teaching resulted in Enrico’s being placed in a farm family. The tradition of having wet nurses for infants was centuries old in Italy, usually only adopted by the upper classes. A young woman who had recently given birth would be brought in from the countryside to nurse and care for the baby, living with the family at least until the child was weaned.
Toward the end of the nineteenth century, the reverse was becoming common for middle-class couples living in big cities: their children were sent to the countryside. With three children in less than three years, the

Fermis made such arrangements for Enrico, the youngest. At the time farms still existed close to Rome; it was not too hard to find a suitable family willing—for a fee, of course—to take on a little boy for a few years.
A child psychologist, ruminating on where such a beginning would lead, might conclude that in adulthood the person would be either very selfreliant and controlled or overly needy and dependent. Enrico was obviously an example of the former.
One can speculate that the farm family provided a loving environment and a place where he could observe, explore, and enjoy nature. The security that Fermi exuded, as well as his love of the outdoors, might be related to those farm years. Yet the pain of separation from his family of birth must have affected his development, too, and is probably related to why Fermi kept emotions to himself and never complained. This is how he learned to cope.
And those coping skills served him well in later life.

2
THE LITTLE MATCH
(Il Piccolo Fiammifero)
Enrico’s sister remembers him being “small, dark and frail-looking” when he rejoined the family at age two and a half. She also recalled how, probably worried by the sudden appearance of all the strangers, he immediately began crying, only to be told by his mother “to stop at once; in this home naughty boys are not tolerated.” Little Enrico did stop crying. But with bottled-up frustrations, he was known to occasionally break into flaming rages, earning him the family nickname of Piccolo Fiammifero (Little Match).
Rages were not tolerated any more than an untidy appearance. Perhaps rules had been slacker in a farm environment. In a city setting, his mother apparently would insist that his face always be clean, stopping at fountains to wash up during their excursions. Despite Alberto and Ida’s strictness in child rearing, the Fermi family appears to have been close, with a special bond developing between the two brothers, Giulio and Enrico, only a year apart in age.
Alberto and Ida had advanced in their careers despite not having university degrees; but, like many upwardly mobile parents, they wanted more for their children. All three of those children, through a combination of natural ability and the self-discipline learned from their parents, excelled in their studies, each of them consistently at the top of his or her class.

At the beginning of the twentieth century the advanced school curriculum was still oriented toward a classical education, emphasizing Latin and Italian literature with Greek added in the final five years. Mathematics, history, and science were also taught, but regarded as secondary. In particular a student preparing for the culminating graduation exam, the so-called Maturità, was expected to know practically by heart Dante’s Divina Commedia, Italy’s national literary treasure. Fermi had little interest in music or visual arts, but a love of poetry, and not only Dante, remained with him. On long hikes he could occasionally be heard reciting under his breath verses he had learned in his youth.
Maria, who eventually would become a high-school literature teacher, was drawn to the humanistic side of the studies. By contrast, Giulio and Enrico were more interested in science or at least in the technical skills they acquired by building models and little electrical motors.
The first recognition that Enrico was exceptional occurred shortly after he turned thirteen. Alberto Fermi, nearing sixty, had continued to rise in his profession and had become a chief inspector in the Ministry of Maritime and Railroads. Its offices were located in a building a little less than a mile from the Fermi apartment, and Enrico had started meeting his father at the building’s door after work and walking home with him. Adolfo Amidei, a thirty-seven-year-old engineer employed in the same office as Enrico’s father, often joined them for part of the way since his apartment was in the same direction as theirs.
When Enrico discovered that Amidei had an interest in mathematics, he asked him a few questions about geometry that his father had been unable to answer. To help his colleague’s son, Amidei lent Enrico a geometry book. The young boy quickly worked out the solutions to the problems it contained, some of which even Amidei had not been able to solve. Impressed, Amidei inquired of his senior colleague whether anybody else had commented on his son’s skill and precocity. Alberto told him that Enrico had always done well in school, but none of his teachers had noted anything out of the ordinary.

At about the same time, early January 1915, tragedy struck the family. Giulio had developed a throat abscess that was interfering with his breathing, not an uncommon consequence of a severe tonsil infection. Today, treatment is by massive doses of antibiotics, thereby usually avoiding any surgical intervention. The standard procedure in 1915 was an incision and drainage of the abscess under a local anesthetic. This surgery was performed on Giulio in a clinic, his mother and sister waiting to take him home after the anesthetic wore off. But Giulio had a dramatic adverse reaction to its administration, went into anaphylactic shock, and died on the operating table.
The family was devastated. Alberto became even more taciturn and Ida fell into a deep depression; Giulio, warmer and more outgoing than Enrico, had been her favorite. Ida’s fits of inconsolable crying lasted for hours and she was in no shape to help alleviate the pain of others. Enrico was left to grieve on his own. To prove to himself that he was not a total wreck, a week later he deliberately walked by the clinic where his brother died. It was a striking example of Fermi’s early need for emotional control.
One way for thirteen-year-old Enrico to fill the traumatic and heartbreaking void was by hard work. Amidei, recognizing both the boy’s loneliness and his eagerness to learn, tried to do what he could by continuing to lend him books; the more he did, the more impressed he was by Enrico’s intelligence and thoroughness. When Amidei once asked his young protégé if he wanted to keep a calculus book he had lent him, he was told that it wasn’t necessary because he had thoroughly assimilated the material. As people would repeatedly say over the next forty years, “When Fermi knew something, he really knew it.”
Another precious balm for Enrico was having a schoolmate of Giulio’s become his close friend. Enrico Persico shared his interests in science and in building mechanical objects. The two of them soon began taking long walks together, discussing their common dreams. Fifteen years later, the two Enricos would be Italy’s first two professors of theoretical physics. And

almost forty years later, they would still take long walks together and share dreams.
The young Fermi, insatiable in his quest to learn more about science, found his first real physics book in Rome’s Campo dei Fiori (literally Field of Flowers). This square, located between the Tiber and the ruins of Pompey’s Theatre, the site of Caesar’s assassination, remains to this day one of Rome’s liveliest areas. Now a popular outdoor food market, during Enrico’s childhood it was a horse market two days a week and once a week held stalls where one could purchase new and old books. Most of them were novels or, this being Rome, theological treatises. Occasionally one might find something else.
One day in late 1915, the two Enricos were looking through the collections in the Campo. Fermi picked up a nine-hundred-page twovolume set entitled Elementorum Physicae Mathematica. It was a text on mathematical physics written in the 1830s by a priest named Andrea Caraffa who had taught science and mathematics at the Collegio Romano, a Roman university founded in the sixteenth century by the Jesuit order. With more than four years of intense study of the language completed, Enrico had no problem with the Latin text. In any case, all the equations were in the universal language of mathematics.
Purchasing the book with his allowance, Enrico studied it carefully in the weeks that followed, making notes when he had questions. Caraffa’s subject matter was early-nineteenth-century physics, chiefly the mechanics of celestial motion and wave theory. The mathematics Caraffa employed might have provided an insurmountable obstacle had Enrico not already studied the subject on his own with books lent by Amidei. Not only was Fermi the only twentieth-century physics genius to be entirely self-taught, he surely must be the only one whose first acquaintance with the subject was through a book in Latin.
At sixteen, Enrico skipped his final year of high school. It was time for him to begin thinking about what would come next. Obviously headed toward a university, Enrico was expected to stay at home, since Italian

universities had no dormitories. But Amidei felt his young protégé would benefit greatly from being away from the oppressive atmosphere that dominated the Fermi household after Giulio’s death.
Once again Amidei’s important role in Fermi’s development surfaced. He was familiar with an elite institution in Pisa, the Scuola Normale Superiore. Admission to its small entering class, some forty students in all, was by competition. Amidei was confident that Enrico would shine. Since the school provided room and board for its matriculating students, there would be no additional financial burden on the Fermi family. The classes were mostly big lectures held at the University of Pisa, but additional supervision and instruction would be available in the Scuola. Such an opportunity would enrich Enrico both intellectually and emotionally.
Discreetly inquiring of Enrico whether he would like to attend, Amidei received an enthusiastic response. He next set out to speak to the boy’s parents. They were reluctant, particularly Ida, who felt she would be losing her other son. But Amidei was persuasive in convincing her and Alberto of the benefits to Enrico. He stressed that attending Italy’s premier institution of higher learning, a school from which many of the country’s most famous scholars, political figures, and writers had graduated, would open many doors for him. Ida and Alberto finally agreed to let him apply for admission.
Amidei had also encouraged Enrico to study German. The boy learned French, part of the usual school curriculum, but an increasing body of the scientific literature was in German, and knowledge of that language would stand Enrico in good stead. It was an interesting although unpopular suggestion, since Italy was at war with Austria and Germany.
When World War I began in August 1914, Italy initially opted to remain neutral. This probably would have been the wisest policy to continue and was generally favored by the population at large. However, in the spring of 1915, the Italian prime minister began secret negotiations with the French and British to enter the war on their side. He stoked popular opinion to this end, and in May 1915, Italy declared war on Austria. The Italian army suffered a series of defeats, climaxing in October 1917. During the closing

weeks of the war, the Italian army managed to garner a significant victory against a demoralized Austrian army.
Fortunately, Enrico Fermi had still been too young to be drafted into the army. Less than two weeks after the armistice was signed, he took the entrance examination for the Scuola Normale.

3
LEANING IN: PHYSICS AND PISA
Though a superb mathematics student, Enrico Fermi selected physics as his field of study. One of the reasons was his affinity, since childhood, for performing experiments and his fascination with the apparatus they required. His interest in science had started with models and little motors built with his brother. After Giulio’s death he continued in the same vein with Persico, the other Enrico. They gradually embarked on more sophisticated ventures: accurate measurements of gravity’s acceleration, water’s density, and the level of atmospheric pressure.
Part of their work was carried out at the Rome Meteorological Institute, a center Fermi had become familiar with because its director had been his high school science teacher, a man who helped him and Persico build barometers. At the center’s library Fermi found another influential book, denser and more up-to-date than the one he had purchased at Campo dei Fiori. This time French, not Latin, was the tome’s language.
A four-volume five-thousand-page encyclopedic treatise on physics, it was then popular throughout Europe. It was written by a Russian physicist, Orest Khvolson, and had been translated into several languages, though not into Italian. Covering physical phenomena as well as state-of-the-art instruments, it is remarkably thorough even by today’s standards. Fermi studied Khvolson at a rapid clip in the summer of 1918, laying the

foundation for his astonishing command of every aspect of classical physics. In letters to Persico, he described going through the book at more than a hundred pages a day, skipping large sections of material he was already familiar with.
At the end of August, when Fermi was seventeen years old, the announcement came for admission exams to the Scuola Normale, offered on four successive days starting October 28. Several hundred candidates were expected to apply for the few dozen openings available in all fields. No more than a handful of prospective future mathematicians and physicists would gain admission. Fermi’s acceptance by the Scuola, despite Amidei’s faith in him, was not a foregone conclusion.
The exams were extensive. The first three days consisted of eight-hour written exams, and the fourth would be an oral one. Candidates for admission in physics and mathematics would be tested on their knowledge of algebra, geometry, and physics, each day’s exam positing one problem and one essay on a theme unknown to the candidates beforehand.
The entrance examinations to the Scuola were postponed indefinitely on account of an influenza epidemic. The atmosphere in Rome that autumn, already grim because of the war, turned darker. However, by early November, the number of flu cases diminished, the war seemed to be drawing to a close, and the upcoming academic year was starting. The decision to delay was reversed and the examination rescheduled for November 12. Though the schedulers could not have known it at the time, the armistice would be signed one day earlier.
Fermi performed brilliantly in the first two days of examinations, but his work on the third day is what led to his designation as a precocious genius. The topic for the physics essay was “Distinctive Characteristics of Sound and Their Causes.” A natural starting point was to consider how a vibrating string leads to sound waves propagating in air. Fermi displayed his bravura by going well beyond this scenario. He tackled the much harder problem of how the vibrations of a rod attached to a wall generate sound waves.

Fermi derived the equation describing the motion of the rod and proceeded in masterly fashion to solve it. It was an essay that one could barely imagine a talented graduate student being able to write. It was unthinkable to see it from the pen of a self-taught high school student.
The head of the three-man committee administering the examination in Rome was Giulio Pittarelli, a distinguished geometry professor at the University of Rome. Pittarelli, an unlikely person to break academic traditions, was well aware that communication with competing students was disapproved until exams were over and the Scuola Normale had decided whom to accept. Nonetheless, he could not restrain himself. He had been so impressed by Enrico’s essay that he called him in to his office.
Quaking at the request of one of his examiners to see him privately, Fermi entered the dimly lit room. The boy, having just turned seventeen, stood before the sixty-six-year-old professor and was subjected to a round of questions. After assuring himself that Fermi had understood everything he had written, Pittarelli informed him that he definitely would be admitted. It was unimaginable that any other candidate could do as well. Pittarelli also added that in forty years of teaching he had never encountered so gifted a student.
This was a tremendous boost to Fermi’s self-confidence. Neither his parents nor his schoolteachers had thought there was anything truly exceptional about him. Amidei had, but he was a family friend and a modest man, not someone who was in a position to compare him to other would-be scientists. But Pittarelli had long been exposed to outstanding students, and was a university professor. He was going far out of his way to praise him, a fact for which Fermi would always be grateful.
The examining committee awarded Fermi the highest possible grades in all his examinations. They unanimously recommended admission to the Scuola. Fermi was thrilled to begin a new phase of life—and to do so in the birthplace of Galileo. This city was the cradle of physics, where the great master was born, studied, and began his teaching career. Galileo had deduced the laws of motion by measuring the periods of a swinging

pendulum in the Duomo and by observing objects falling from the Leaning Tower. The subject of physics had been created in his image: experiment, observe, and deduce.
When Fermi arrived in Pisa in early December of 1918, it was a rather sleepy town of 65,000 inhabitants with signs of a glorious history but little else. The university had persevered over the centuries, as had the Scuola Normale affiliated with it. Fermi had taken the four-hour train ride from Rome to Pisa, descending at the station on a cold but sunny day with his two suitcases—one with clothes, the other with a few books and things for his room. A ten-minute walk brought him to the Arno River, smaller than he had imagined it would be. Crossing it on the Ponte di Mezzo, he entered the medieval part of the city with remnants of its circuit of old walls. A short walk along the Borgo Stretto soon led him to the glorious Piazza dei Cavalieri, the square that held the sixteenth-century Palazzo della Carovana where the school was housed.
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 twoperson club for playing practical jokes, calling themselves the AntiProssimo, 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 predictably 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 detected 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.
Fermi decided to use his scholarship in Göttingen. Curiously enough, his stay there was neither especially happy nor productive. Although Fermi was not treated badly during his eight months in Göttingen, there is no indication of his having been perceived as especially promising or of his having formed any connection with Werner Heisenberg, his contemporary and a rising star there.
Fermi was surely made conscious of the low esteem in which German physicists held physics research in Italy. According to a close colleague, Fermi had felt the Germans “were very conscious of their capacity, of their preparation, of their ability. All others were coming to learn from them. And it was true. But they tried to make a point of this, to stress the point.” This bothered the proud young man.
The lonely twenty-two-year-old Fermi wrote Persico with some irony about Göttingen, including a comical sketch of the German perception of atomic scattering and a portrait of a prototypical Göttingen woman physicist. Both were uncomplimentary. He assured Persico that given the woman’s looks, there was no danger of his being summoned as best man for a wedding.
Both the foci and the ethos of Göttingen physics were unappealing to Fermi. He always pursued a physical picture rather than the mathematical formalism prevalent in Göttingen. In this respect, it’s interesting to compare Fermi to three other budding theoretical physics geniuses who were his contemporaries. Unlike Fermi’s, the talent of those three was immediately recognized in Göttingen. In addition to Heisenberg (b. 1901), there were Wolfgang Pauli (b. 1900) and Paul Dirac (b. 1902).
By 1930, all four prodigies had done Nobel Prize–caliber work, were established professors, and were attracting younger physicists from around

the world to their respective centers in Leipzig, Zurich, Cambridge, and of course Rome. The four often worked on similar problems, and sometimes even on the same ones, but in markedly dissimilar ways. Each had a characteristic style, a reflection of his personal strengths and predilections. It may seem strange that style plays such an important role in theoretical physics, since science’s results are often portrayed in an impersonal manner. But human passions and special abilities shape its achievements as much as they do in other endeavors.
Pauli and Heisenberg had been Sommerfeld’s students together in Munich and in successive years were assistants of Born’s in Göttingen. Dirac had been educated at Cambridge, hardly the physics backwater that Italy was. Unlike the other three, Fermi was self-taught. In addition, Fermi considered himself an experimentalist as well as a theorist, combining action with concepts.
The three others, in contrast to Fermi, were exclusively grounded in theory. Dirac wanted mathematical elegance and beauty to be his guide. He was known for his quirkiness, often brusquely answering questions with “Yes” or “No” or “That is not a question.” Heisenberg almost failed his doctorate exam because he enraged the committee’s experimental physicist by being unable to explain how a storage battery worked. As for Pauli, he prided himself on the so-called Pauli Effect, which said that a key piece of machinery would always break when he entered the room.
One cannot imagine any of these stories being told about Fermi. He operated easily in both the theoretical and experimental spheres. Years later, when asked how he had entered the experimental field, he laughed and said, “I could never learn to stay in bed late enough in the morning to be a theoretical physicist.”
While effectively bridging experiment and theory, Fermi also had his limits. He would not make the intellectual leaps that Heisenberg became known for or formulate one of Dirac’s aesthetic mathematical marvels. Nor was he as famously critical as Pauli. But nobody could grasp all the interconnected aspects of a problem and reach a conclusion the way he

could, nobody was able to significantly probe as many areas of physics as he was, and nobody could estimate orders of magnitude of physical phenomena as surely and as quickly as he could.
All in all, Fermi did appreciate the contributions of the German community of theoretical physicists. As a pragmatist, he was cognizant that they were unlikely to follow the Italian scientific literature. Accordingly, Fermi adopted the procedure of publishing key articles in either German or English. For reasons of national pride, he usually submitted a parallel version to Italian journals.
Returning from Germany to Italy in late summer of 1923, Fermi found his interest turning increasingly to statistical mechanics, a subject that would allow him a deeper understanding of thermodynamics, the study of heat. Thermodynamics had been one of the great triumphs of nineteenthcentury science, its laws a cornerstone of physics and chemistry. But since thermodynamics is confined to macroscopic quantities, a number of individuals in the second half of the nineteenth century began to seek its underpinnings in the microscopic objects that make up the macroscopic state. They asked such questions as “What does thermal equilibrium mean, and how is it achieved? What does temperature really measure, and how does disorder come about?”
The logic behind these questions can be applied to other arenas. Knowing the size of a city, the total number of its inhabitants, and their average age tells a great deal, but it is not sufficient for planning traffic patterns. A well-oiled machine may work perfectly, but it is only by understanding its components and how it is assembled that one can truly appreciate its functioning. Asking for analogous explanations from thermodynamics led physicists to questions of probability, a topic that would continue to interest Fermi throughout his career.
Fermi’s fascination with thermodynamics and statistical mechanics was absorbing him, but he still had no job. Fortunately Corbino came to the rescue once again, arranging for him to teach a mathematics course for chemists and biologists at the University of Rome. At least he would

receive a salary, even if not a generous one. Fermi was frugal and still living at home. His material needs were met, although he felt intellectually isolated. Other than his friend Persico, who had remained in Rome as Corbino’s assistant, only mathematicians seemed to grasp the meaning of his research.
As in Pisa, there were many more mathematics chairs than physics ones in Rome. Four of the occupants had considerable international reputations. None was more distinguished than Vito Volterra, the most senior of the four, but Guido Castelnuovo, Federico Enriques, and Tullio Levi-Civita were not far behind. They welcomed Fermi enthusiastically, recognized his talents, and anticipated what he might contribute to advancing Italian physics.
Beyond being embraced in an academic circle, Fermi discovered that the mathematicians also formed a tight-knit social circle, and he was invited to be part of it. The group provided him for the first time with a community of peers. Their families and those of their close friends typically gathered together on Saturday night, usually at the Castelnuovos’, for far-ranging discussions on everything from scientific advances to local gossip.
Other than being great mathematicians, Volterra, Castelnuovo, Enriques, and Levi-Civita had another common trait, one that would come to have a significant impact on Fermi’s life. They were all Jews. This might seem a remarkable coincidence for a country that had only some forty thousand Jews, approximately a tenth of one percent of the total Italian population of forty million. It wasn’t altogether accidental.
Ghetto walls had been torn down in the middle of the nineteenth century and Jews had finally been allowed full access to university life. Education had always been valued in Jewish culture, and young Jews stood out in a country where more than half of the children over the age of ten were still illiterate. Furthermore, mathematics, if only as an aid to becoming merchants, bankers, and doctors, had been a customary subject for Jews to study. They would frequently select mathematics or related fields once universities were open to them.

The beginning of the twentieth century was a time of great pride for Italian Jews. After centuries of being shuttered away in ghettos, they were fully integrated citizens of a new nation. By and large, they became extraordinarily patriotic. Large synagogues were built in Italy’s major cities, replacing the hidden rooms in unmarked buildings where worship had previously been held. And when war was declared in 1915, Jews rushed to enlist. Volterra, then fifty-five years old, had enlisted as a lieutenant in the Army Corps of Engineers and set to work calculating artillery trajectories.
Sadly, those feelings of patriotism would erode in the 1920s and eventually turn to scorn as Jews saw their homeland reject them by aligning itself with Hitler’s racist tenets. And Fermi’s newfound colleagues in mathematics were among the first to feel the yoke of anti-Semitism.

6
THE SUMMER OF 1924
As spring approached in 1924, Fermi was worried about his mother’s health. She had suffered from a number of pulmonary ailments and recently spent time in a sanatorium. By April, all attempts to save her were failing.
In anticipation of enjoying their retirement in a peaceful setting, Fermi’s parents had purchased land a few miles northeast of Rome in a housing development intended for government employees. They were building a small dwelling there, but it wasn’t expected to be ready until the fall of 1924. It was looking as if Fermi’s mother would not live to see it completed. She died on May 8, having just turned fifty-three. Afterward Fermi seldom spoke of her, and when he did, it was mainly to praise her organizational skills. Her lingering depressions and favoritism for her deceased child had made her emotionally unavailable to him, more notable for her managerial and technical capabilities than her maternal ones.
Nevertheless Fermi felt the loss and that summer looked for consolation in the beauty of the mountains, specifically in the Dolomite peaks and valleys that lie north of Venice and south of the Austrian border. The spectacular scenery drew him to the region and he also found congenial company, since many of the distinguished Rome mathematicians vacationed there with their families. Eager to continue taking the brilliant young physicist under their wings, they were happy to have him join them. Fermi

could discuss algebraic geometry with them and also take long hikes with their children, in their twenties, closer in age to him.
The death of Fermi’s mother coincided with another death, one the whole country was focused on. It was the murder of Giacomo Matteotti, an overtly antifascist socialist deputy, which for many was a watershed in Italy’s march toward totalitarianism. On the thirtieth of May 1924, Matteotti had delivered an impassioned speech in Parliament denouncing the fraud in recent elections and the intimidation of opponents by Fascist brigades. At its conclusion he had declared, “I have finished my speech, now prepare the speech for my funeral.” Many feared his prediction would come true.
On the sixteenth of June, Matteotti’s body was discovered in a shallow grave about twenty miles from Rome. He presumably had been stabbed while trying to escape after being kidnapped. It remained murky whether his murder had been ordered directly by Mussolini, but it was a consequence of the climate Mussolini and his fellow Fascists had created during their two years of controlling the country.
Despite the unrest sparked by Matteotti’s murder, opposition to Mussolini was divided. The king was weak, ineffective, and not inclined to criticize the man he had named as his prime minister. Mussolini, emboldened, made his move on the third of January 1925. Appearing before the Chamber of Deputies, he challenged its members to impeach him, adding, “Italy wants tranquility and hardworking calmness. We will provide this with love, if possible, by force if it is necessary. You can be sure that the whole situation will be made clear within the next forty-eight hours.” Applause broke out, a clarion call for the country to turn into a totalitarian regime. Mussolini began referring to himself as Il Duce, foreshadowing a similar move by a man to the north who became known as Der Führer.
Dissent was no longer tolerated. In November 1926, a party tribunal was constituted and a special police force was formed. The Organization for Vigilance and Repression of Anti-Fascism, or OVRA, with several thousand members, began to permeate all levels of society. It would become a model

for Germany’s Gestapo and Russia’s NKVD, though fortunately for Italy it never achieved the levels of ruthlessness and efficiency of the latter two.
Fermi seemed oblivious to politics. His views were very close to those Rasetti held, described thus by the latter in a 1982 interview: “In the first few years, in 1922, Fascism didn’t seem so bad. In fact a large class of Italians welcomed it, because the Communists were very powerful and disorganized all industrial production, disorganized the railway traffic. So at that time Mussolini seemed a fairly reasonable dictator. The first act that really disgusted the more reasonable people was the Matteotti murder, which happened in 1924.” Fermi was among those “more reasonable people.”
How had Italy, a nation with a healthy democratic tradition, come to this point? The country had suffered in World War I, and not only from loss of life. Profiteering during the war had angered many returning veterans; the difficulties they were encountering in finding employment had further exacerbated the situation. The warnings of a national disaster were in place. Inflation was rising, industrial strikes were breaking out, landowners were afraid of reforms that would threaten their agrarian holdings, the army was unhappy, and the king was indecisive. Taking advantage of a government that seemed powerless, Mussolini, both cunning and ruthless, inserted himself into the mix. With a flair for propaganda and bombastic oratory, he was above all an opportunist, willing to change his position in whatever way suited his ambitions.
The Fascist Party, established in 1919, initially gained little traction, but as discontent rose, the accompanying fear of a left-wing takeover grew stronger; Mussolini exploited the desire for what he would later call “tranquility and hardworking calmness.” He organized squadrons of thugs armed with clubs, their aim supposedly that of keeping the peace. And because he was financed by the right wing, Mussolini’s hold increased.
The situation was ripe for Mussolini’s ascent. On the twenty-eighth of October 1922, he launched the famous March on Rome, directing blackshirted Fascist squadrons to advance on the capital. The army had been

mobilized and could have stopped the marchers, but that might have led to a massacre. Everyone was asking whether the king would sign the order for the army to take action.
Fermi happened to be in Corbino’s office on the morning of that march. Never having given much thought to politics, the twenty-one-year-old Fermi looked to his mentor for guidance. That evening he recounted to his family what Corbino said would happen if the king signed the order for action: “So many young men will die who were only in search of an ideal to worship and found none better than Fascism.” When Fermi had asked what one might hope for if the king avoided the confrontation, Corbino had replied, “A hope? Of what? If the king doesn’t sign, we are certainly going to have a Fascist dictatorship under Mussolini.” Both scenarios were bleak.
The king decided not to sign the order. Instead, on the thirtieth of October he asked Mussolini to form a new cabinet. Three years later the takeover was complete and Fascism firmly implanted. Opponents of the regime were jailed or went into exile. The Gregorian calendar was abandoned in favor of dating years in Roman numerals, year I coinciding with the March on Rome. Mussolini proclaimed the inauguration of a new Roman empire.
Mussolini had proved himself a master in his use of propaganda. He did so in person, in the press, and in newsreels, which were becoming an increasingly popular means of communication. The slogans he mouthed were repeated incessantly. In late 1923, after Mussolini’s utterance “Better a day as a lion than a hundred years as a sheep,” a circus owner offered him a lion cub. Mussolini adopted it as a pet-in-residence. Naming the cub Italia, he made sure newsreels filmed him in his convertible Alfa Romeo driving in the nearby Villa Borghese Park, Italia in his arms. The symbolism of a wild beast tamed by its fearless owner was not lost on the populace.
The political situation gradually entered Fermi’s consciousness, but in 1924 he ignored it. Thinking about career rather than politics, he was planning a three-month stay outside of Italy, supported by a new fellowship. In January 1923, John D. Rockefeller Jr. had founded the International

Education Board for the purpose of “promotion and advance of education throughout the world.” Part of its mission was to award fellowships to promising young scientists, allowing them to visit active research centers for periods of months to a year. Fermi was the first Italian to receive one.
He chose to use his fellowship in Leiden, the Netherlands, opting to do so because of Paul Ehrenfest, a Leiden physics professor with a lifelong interest in statistical mechanics as well as in quantum theory. In his early forties, the Viennese-born Ehrenfest, a wonderful lecturer and an astute critic, was a close friend of both Bohr and Einstein. He was also known for being personally warm and involved in the lives of his students as well as for a free-ranging intuitive style in research, one that contrasted with the more reserved approach characterizing many other senior theorists, especially those in Göttingen.
After reading a 1923 article by Fermi in the Physikalische Zeitschrift, Ehrenfest wrote him a letter telling him how impressed he was. Ehrenfest also told a young former student of his living in Rome to get in touch with Fermi. George Uhlenbeck, later a well-known theoretical physicist, arrived in Rome to serve as tutor to the Dutch ambassador’s son. He and Fermi, almost exactly the same age, contrasted dramatically in appearance, Uhlenbeck almost a foot taller. But physics, not height, is what mattered. In the course of their meaningful exchanges, the young Dutchman sang the praises of both Ehrenfest and university life in Leiden.
The stay in the Netherlands proved valuable for Fermi. Fermi never voiced why his Leiden experience had been so much happier than his Göttingen one, but always spoke fondly of the Dutch group, their openness and their acceptance of people coming from a different tradition. He was admittedly somewhat taken aback initially by how unceremonious Ehrenfest was in his manner as well as by his sloppy attire. The Jewish mathematicians in Rome were always proper and formal; Fermi described Ehrenfest to Persico as “really very nice and wouldn’t be out of place in a ghetto store for used clothing.” Ehrenfest made it known that he considered

Fermi extraordinary even when compared to the best young theoretical physicists of the day. And Ehrenfest knew them all.
The biggest surprise for Fermi was meeting Einstein, who was spending twenty days in Leiden visiting Ehrenfest. This forty-five-year-old man took a fancy to Fermi. Einstein, himself an outsider of sorts, engaged Fermi immediately. There was a meeting of the minds, a shared interest in quantum physics and statistical mechanics. The obviously pleased Fermi tried to make light of his meetings with Einstein and the interest shown in him by the world’s greatest physicist. In the letter to Persico, he described Einstein as a “very nice person despite his wearing a wide-brimmed hat that gives him the air of a misunderstood genius. He has been taken by a great liking for me that he cannot help telling me about every time he meets me (pity that he’s not a beautiful girl).” In this case, Fermi overcame his usual embarrassment about attention paid to him. His parenthesized notation may have alluded to his lack of success in finding a girlfriend who would accord him similar admiration.
Fermi’s warm reception was not the only reason the Leiden stay was happier than the Göttingen one. Fermi had matured personally and intellectually in the two intervening years. Many papers in Fermi’s Collected Works, published in 1962, include introductions by fellow physicists who knew him at the time each paper was written. Looking back as a sixty-year-old, Persico commented on a 1924 Fermi paper, saying it had “the characteristics of the more mature style of Fermi: a fundamental idea, at the same time simple and clever, is applied to several concrete problems of physical importance with the help of mathematical methods of sufficient approximation, but not better than warranted by the underlying physical hypotheses.” No better description of Fermi’s style in theoretical physics was ever written.
In that 1924 paper, “The Theory of the Collisions between Atoms and Electrically Charged Particles,” Fermi demonstrated that if one knew the effect of electromagnetic radiation on an atom, one could also deduce the result of that atom’s collision with a charged particle. The varying electric

field the particle produced could be described analogously to how radiation was treated. The paper highlighted Fermi’s interest in all aspects of physics, the formidable arsenal of tools at his fingertips, and his ease in moving from the very practical to the very formal.
Nevertheless, in spite of the growing recognition of Fermi’s breadth, depth, and creativity, he still lacked an academic position in Italy. And he needed one.

7
FLORENCE
To obtain an academic appointment that matched his ambitions, Fermi briefly considered emigrating, but his attachment to Italy was such that he continued his attempts to advance in its university system. The milieu was not conducive since most Italian senior physics professors remained mired in nineteenth-century physics, unaware of or unwilling to accept the innovative ideas of relativity and quantum theory.
Fortunately a few Italian senior physicists were forward-looking and well positioned. Antonio Garbasso was one of them. Like Orso Corbino, he had succeeded in politics as well as in physics. He was both Florence’s mayor and a physics professor. This meant, however, that he spent most of his time in his majestic Palazzo Vecchio mayoral office and not in a physics laboratory.
Garbasso and Corbino identified Fermi, Enrico Persico, and Franco Rasetti, all three in their early twenties, as the most likely carriers of the torch toward modernity in physics. After graduation, Persico was taken on as Corbino’s assistant and Rasetti as Garbasso’s. They now had to find a position for Fermi, recognized as the most promising of the three young physicists. There was an opening as a lecturer in Florence. Although the position was neither prestigious nor well paid, Garbasso and Corbino thought it would suit Fermi until he could obtain a real professorship. Both

urged him to accept the appointment, which would also reunite him with his friend Rasetti. Fermi agreed.
At the time, Italian universities had no campuses, so departments were housed in buildings throughout the host city. This meant Florence students had to scramble, since the physics and chemistry departments were miles apart. The physics institute was located, with symbolic if not practical intent, near the villa that Galileo had returned to after his confrontation with the Inquisition and where he spent the last decade of his life under virtual house arrest. Situated amid a beautiful grove of olive trees on the Arcetri hillside, a few miles from downtown, the institute commanded a stunning view of the city. This made up for its lack of amenities, the principal one being no heating: the building’s wintertime average daily temperature was in the low forties Fahrenheit.
During his first two years in Florence as Garbasso’s assistant, Rasetti lived in a small room adjacent to the institute. With a bed, a desk, and a sink, it was sufficient for his needs. The wife of the janitor who took care of the institute would cook him simple meals. But in 1924, Rasetti’s father died, and his mother decided she wanted to be near her only child. She sold her Pisa house and bought an apartment in Florence large enough to also house her son.
The timing was propitious. On his arrival in Florence at the end of 1924, Fermi moved into Rasetti’s room in Arcetri. The facilities would be as simple as those in his Pisa dormitory and the meals no better, but he was feeling cheerful after his stay in Leiden. Physics was stimulating and Fermi was brimming with ideas. Besides, Rasetti had survived living there; he would not be more demanding than his friend.
Though Fermi and Rasetti were maturing as physicists, they still relished wicked practical jokes like the ones they had indulged in during their student days in Pisa. Rasetti described one that took place at Arcetri. Having gathered about thirty geckos in the surrounding fields, he and Fermi released them in their little dining area just before the janitor’s wife came in

with their lunches. Mayhem ensued and the two physicists roared with laughter, somewhat muted as they saw their lunches spill on the floor.
Fermi and Rasetti’s outdoor activities were also continuations of their Pisa ones: skiing, hiking, and playing tennis. Tennis remained a favored sport of Fermi’s. Other players would comment that though his style was not particularly graceful, his tenacity often made him able to wear down more accomplished opponents.
The two young physicists saw little of Garbasso. He came to Arcetri from the Palazzo Vecchio only three times a week to deliver lectures. Rasetti’s limited tasks and Fermi’s light teaching responsibilities left the two friends with time to conduct whatever research they could manage with the limited equipment at hand and the tiny budget available to them. Fermi had been working exclusively on problems in theoretical physics for the more than two years since his Pisa graduation. The possibility of conducting experimental research again intrigued him, particularly if he could do so with Rasetti and if it would serve to advance his knowledge of how quantum physics related to atomic structure.
Always an adept experimentalist, Rasetti was pursuing ideas in spectroscopy, a field once considered a backwater of physics and primarily of interest to chemists. Beginning in the 1850s, scientists had observed that an element, when heated sufficiently, emitted electromagnetic radiation. After further analysis, the radiation was seen to be different from element to element, but in all cases it consisted of distinct frequencies. This made spectroscopy an extremely valuable tool for chemical identification. Indeed, several new elements of the periodic table, most notably helium, were first detected by these means. This seemed, however, to have very little to do with atomic structure. Bohr would later say that it had been like trying to understand a butterfly by studying the colors in its wings.
That changed with Ernest Rutherford’s 1911 discovery that the atom was composed of a tiny central nucleus surrounded by electrons. Two years after that, Bohr introduced his planetary model of the atom in which electrons moved in orbits about the nucleus, much as the planets circle the sun.

Instead of a gravitational force, the negatively charged electrons were held in orbit by their electric attraction to the positively charged nucleus.
A volcano in the landscape of quantum physics had been smoldering since 1900, when Max Planck, in what he would refer to as “an act of desperation,” introduced the concept of quanta. In order to reconcile basic principles of thermodynamics with experimental data, he had concluded that the energy contained in electromagnetic radiation was both absorbed and emitted in minute packets. The energy of a single packet was proportional to the radiation’s frequency. Planck called these packets quanta.
Bohr’s model of the atom had quanta emitted when electrons jumped from an orbit with higher energy to one with lower energy. The quantum’s energy necessarily was equal to the difference between the energies of the electron in its initial and its final state.
The novel idea introduced by Bohr was to extend the notions of quantum physics to electron orbits in hydrogen by having their radii follow a numerical sequence of n squared times R, where n was any integer greater than or equal to one and R was the average radius of the smallest orbit. Since the energies of each electron depended directly on their position in the atom, those energies also followed a sequence. The integer n that characterized a given electron’s energy was referred to as its principal quantum number.
Distinct electron orbits explained why hydrogen frequencies obeyed mysterious arithmetic rules. Measuring those frequencies, the field known as spectroscopy, became the primary tool for studying atomic structure. The butterfly wings had been meaningful after all. Bohr’s model of the atom was so spectacularly successful in explaining the frequencies emitted by heated hydrogen gas that physicists immediately believed it contained some deep truth. But hydrogen, with only one electron, is the simplest of all atoms; extensions of the theory to other elements were not as convincing. Despite a subsequent series of successes over the next decade, the Bohr

model met a corresponding number of failures. It was becoming clear that some key concepts were missing.
Searching for clues in spectra became one of the central problems in physics. Elliptical rather than circular orbits were considered, corrections due to the theory of relativity were made, and changes in spectra by external electric or magnetic fields were analyzed. The hunt was on for a deeper understanding of the atom.
By the early 1920s, each electron in an atom was being assigned not one, but three quantum numbers. They were roughly thought of as corresponding respectively to the orbit’s size, its ellipticity, and its orientation with respect to an external magnetic field.
In early 1925, Fermi and Rasetti set out to examine a facet of this much larger subject. Rasetti made a specific proposal to his friend: they should carry out a set of investigations focusing on the polarization of light emitted by mercury vapor under the influence of an alternating magnetic field. He would provide the spectroscopic expertise and Fermi would be in charge of building the electric circuits.
The two obtained results notable enough to warrant being published in the prestigious foreign journals Nature and Zeitschrift für Physik, but they didn’t move the field significantly forward. However, they constituted “the first instance of an investigation of atomic spectra by means of radiofrequency fields,” a technique that was to receive numerous applications many years later, when radio frequencies became a more frequent tool in spectroscopy. The research was also distinctive because once again Fermi was showing his unique skill as both a theorist and an experimentalist.
On the whole, Fermi found the Florence position satisfactory, but he was eager to move on, win a competition for a professorship, and earn a decent salary. A professorship of theoretical physics still did not exist in Rome, so Corbino, supported by the Rome mathematicians, set out to establish one. It would be Italy’s first. Fermi knew of the backroom maneuvers, but since administrative matters were holding up the process, he decided in the fall of

1925 to enter the competition for a professorship in mathematical physics at the University of Cagliari.
He wrote to Persico in October that “given the uncertainties in Rome, I plan to compete because I think it is advisable to have a double-barreled rifle, even if I don’t find the idea of winding up on the Islands very pleasing.” “Islands” is a reference to Sardinia, where Cagliari is located. Sicily and Sardinia are often the first destination of young professors ascending the Italian academic ladder.
Volterra and Levi-Civita, two of the five professors on the Cagliari professorship selection committee, voted for him, but the other three were all physicists with little sympathy or interest in the field’s modern developments. The Cagliari position went to a man thirty years older than Fermi and undoubtedly less deserving. The committee’s three elderly members had felt obligated to reward their seasoned colleague rather than the young upstart. Their choice was even less defensible since while they were deliberating, Fermi was writing a seminal paper that would be considered a breakthrough in the world of physics.
The origins of the paper’s focus dated to 1924, when Fermi had been stymied by problems he had encountered while applying quantum ideas to notions of statistical mechanics. A year later, in 1925, after reading Wolfgang Pauli’s new Zeitschrift für Physik article on what came to be called the Exclusion Principle, Fermi was inspired.
The Exclusion Principle, for which Pauli was awarded the Nobel Prize in Physics in 1945, was an extraordinarily important advance in quantum physics. It put order into all the data accumulated in atomic spectra by answering the question of how many electrons could occupy an orbit. The principle postulated that no two electrons in an atom could have all their quantum numbers be identical. Fermi found almost immediately an innovative application for Pauli’s idea by extending it beyond the confines of the atom to the larger systems encountered in statistical mechanics. One could imagine a gas of electrons, or electrons moving freely in a metal.

They, too, would have energies obeying quantum rules and following the Pauli Principle.
The notions Fermi introduced in doing this turned out to be the key to understanding a wide variety of disparate phenomena, from the difference between electrical insulators and conductors to the stability of white dwarf stars. With this paper, first published in Italy during the spring of 1926 and almost immediately afterward in the Zeitschrift für Physik, twenty-fiveyear-old Fermi entered into the company of the world’s elite physicists—the only Italian in that select circle. It also was a way of proceeding that was characteristic of all of Fermi’s theory work: take a clear physics notion, understand it in a way others had not, and apply it to one or more important physics problems.
Fermi’s paper was quickly appreciated in Northern Europe’s great physics centers. Many noteworthy applications of it followed, among which were Pauli’s explanation of previously baffling aspects of magnetism and Sommerfeld’s study of electric current flow in metals. Now even more afraid that his protégé might be lured away from Italy, Corbino redoubled his attempt to keep him. Under his steady prodding, a competition for a professorship in theoretical physics at the University of Rome was set for November 1926. Furthermore, two other Italian universities, Florence and Milan, also determined that such a position would be desirable. Three professorships in theoretical physics had been created in a single swoop.
Bringing Fermi to Rome was not without hurdles. The city’s university had two professors of physics. Rome’s second, Antonino Lo Surdo, was not in favor of Fermi joining its faculty. He viewed the young man’s possible arrival as a challenge to his standing and did not embrace the new generation, although he would have benefited from the freshness of its ideas. In mid-1920s Rome, while Corbino was looking forward to what the young would contribute to a new Italian physics, Lo Surdo was looking backward to the physics of yesterday and attempting to maintain the old guard’s entrenchment. Like other Italian physicists of that era, he refused to accept either modern developments or their proponents.

In some ways Lo Surdo was a conservative mirror image of the progressive Corbino. Born only four years apart, both were Sicilians and had taught in Messina. However, Lo Surdo was no match for Corbino, who, while maintaining collegial civility, easily outmaneuvered him. The competition for all three chairs in theoretical physics had Corbino and Garbasso on its adjudicating committee. As expected, Fermi placed first, which gave him the position in Rome. Persico, placing second, went to Florence. And, with Persico’s position as Corbino’s assistant vacant, Rasetti transferred from Florence to Rome.
With the leverage of his new professorship, Fermi anticipated playing a major part in the overdue transformation of Italian physics research and teaching. Interest in science was slowly on the rise in Italy. Unfortunately, while there was progress on one front, Fascism was taking a toll on another.
In 1923 Italy inaugurated the Consiglio Nazionale delle Ricerche, or simply the Consiglio. It was founded largely as a result of the post–World War I realization that a flourishing economy and modern armed forces would require a country to have a solid scientific research base. Germany’s powerful umbrella organization, the Kaiser Wilhelm Gesellschaft, had been founded in 1911 and the United States’ National Research Council five years later. Italy moved to catch up by instituting its own variant. This was an auspicious start, particularly because the mathematician Vito Volterra, a man known for good judgment and impeccable honesty, was the Consiglio’s first president.
Volterra would not last long in that role. In the wake of the 1924 Matteotti murder, he had asserted his integrity and independence by joining twenty other senators in casting a vote of no confidence in Mussolini’s rule. The consequences of that vote were soon felt. With political loyalty trumping other considerations, Volterra’s influence waned. His position as head of the Consiglio was not renewed when it expired in 1926. More ominously, even Volterra’s presidency of the prestigious and supposedly independent Accademia dei Lincei was allowed to lapse when it expired, also in 1926.

Like other victims of totalitarianism, science was targeted by the regime’s heavy hand. Mussolini insisted on having a loyal party member replace Volterra as head of the Consiglio. Guglielmo Marconi, not a scientist but a distinguished inventor who had shared the 1909 Nobel Prize in Physics for his contribution to wireless telegraphy, fit the bill. This enthusiastic Fascist, who had joined the party immediately in the wake of the March on Rome, became the government face of Italian research in science. Marconi was, however, not an academic. This allowed Corbino to maintain his influence in university circles. Fermi, who continued to cocoon himself from politics, depended on him for guidance and also for protection.
While these political gyrations impacted Italian science and played out in the public domain, the greatest twentieth-century physics revolution— quantum mechanics—was on the brink of forever altering the scientific landscape.

8
QUANTUM LEAPS
The first glimpse of a decisive resolution to the ongoing quandaries of quantum physics came in June 1925. In Göttingen, twenty-three-year-old Werner Heisenberg was struck with a severe attack of hay fever. He retreated to the grassless North Sea island of Helgoland. In his words, as he was searching for a new way to attack the problems engulfing atomic structure, “There was a moment in Helgoland in which the inspiration came to me … It was rather late at night. I laboriously did the calculations and they checked. I then went out to lie on a rock looking out at the sea, saw the Sun rise and was happy.” Heisenberg had taken advantage of the white nights of Scandinavian summer and worked until greeting a new day.
Heisenberg had done away with electron orbits, replacing them with a set of abstract rules based on observable quantities in electron motion. Assisted by Göttingen’s senior theorist Max Born and his student Pascual Jordan, these ideas were soon extended into the full-blown theory that came to be known as matrix mechanics.
Its impact was not immediate, since the theory was cast in a novel mathematical formalism that almost all physicists had difficulty grasping. On the twenty-third of September, Fermi wrote to Enrico Persico, “My impression is that there hasn’t been much progress in the past few months despite Heisenberg’s formal results on the zoology of spectroscopic terms.”

Franco Rasetti remembered being told by Fermi, “Now I’m trying to see what Heisenberg is trying to say, but so far I don’t understand it.” Though Fermi was respectful of the Göttingen school’s achievements, Heisenberg’s paper seemed to confirm his earlier belief that its physicists were overly reliant on abstract mathematical techniques. Fermi wanted a clear physical picture of what they were saying.
At first young Paul Dirac did not understand Heisenberg’s theory either, but he soon recognized its essence. In early November 1925, he submitted for publication a paper entitled “The Fundamental Equations of Quantum Mechanics.” The Göttingen trio, unaware even of Dirac’s existence, was stunned reading his paper: he had reached the same conclusions they had. As Born wrote in his memoirs, “This was—I remember well—one of the greatest surprises of my scientific life. For the name Dirac was completely unknown to me, the author appeared to be a youngster, yet everything was in its way perfect, admirable.”
Youngsters were indeed leading the rise of physics. By the end of February 1926, four remarkable papers, each written by a relative unknown, had appeared in the previous twelve months. Pauli, Fermi, Heisenberg, and Dirac had all rocked the quantum world. At twenty-five, Pauli was the oldest of the four. It is no wonder that Germans began referring to theoretical physics as Knabenphysik (boys’ physics).
However, the revolution was not entirely led by youth. In early January 1926, while on a ski vacation in the Swiss resort of Arosa, thirty-eight-yearold Erwin Schrödinger was busy with something other than schussing down the slopes or charming the mysterious mistress who had accompanied him.
In a paper he wrote immediately after returning from Arosa, Schrödinger reintroduced the electron orbits that Heisenberg had done away with, but he did so with a new way to visualize them. In Schrödinger’s version of quantum mechanics, the motion of an electron within an atom was guided by a so-called wave function. That unlocked the secrets of the atom for him.
Two months later, Schrödinger brilliantly showed that his theory, to which the name wave mechanics was given, was mathematically equivalent

to matrix mechanics. In other words, every step of one had a mathematical analogue in the other. This meant there was only one underlying theory, though it apparently could be cast in two totally different forms. And Schrödinger had strong feelings about which one of the two was preferable.
He expressed them in a footnote to “On the Relation of the HeisenbergBorn-Jordan Quantum Mechanics to Mine.” In that footnote, Schrödinger wrote, “I was absolutely unaware of any genetic relationship with Heisenberg. I naturally knew about his theory, but because of the [to me] very difficult-appearing methods of transcendental algebra and because of the lack of Anschaulichkeit [clearness], I felt deterred by it, if not to say repelled.” The word “repelled” is an indication of Schrödinger’s adamant feelings.
Planck, Einstein, and most senior figures in theoretical physics agreed with Schrödinger’s assessment of the two theories, as did Fermi. Rasetti remembered his friend’s reaction to reading Schrödinger’s papers, a sharp contrast to the struggle he had seen Fermi undergo with Heisenberg’s matrix mechanics. Fermi “understood it and then he poured it into the brains of a few people around him.”
Schrödinger’s papers quickly led a number of physicists to find ways to apply the ideas and techniques he introduced. The results were startling and gratifying. The wizards worked their magic. Even the problems that had already been solved saw their answers recast and clarified by making use of Schrödinger’s wave functions. Dirac’s treatment of statistical mechanics, in another paper by this young virtuoso, was a case in point. He quickly arrived at and then extended the conclusions that Fermi had reached six months earlier.
Unaware of Fermi’s earlier work, Dirac published an article on the subject in the Proceedings of the Royal Society. Since his contribution was far from negligible, the resulting “Fermi-Dirac” statistics carries both their names. However, the identical particles it describes are known only as fermions. A large assemblage of them was called a “Fermi sea” and its

edges a “Fermi surface.” For the first time in the scientific lexicon, Fermi’s name was used.
Dirac must have felt disappointed to discover that the Göttingen trio had independently obtained his main results about quantum mechanics and that Fermi had been the first to derive the statistical mechanics that a “Fermi gas” obeyed. But Dirac’s originality was unquestioned.
Heisenberg was frustrated at seeing wave mechanics favored over his matrix mechanics. But he sensed that some key ingredients were missing. Bohr, who perhaps had a deeper understanding of the problems in quantum theory than anyone else, agreed with him. More tremors were still to come.
To decipher what might still be lacking, Heisenberg moved to Copenhagen in the fall of 1926 to work with Bohr. They were undertaking a search for quantum mechanics’ true meaning. Working intensely, they formulated two new notions in 1927. Bohr’s complementarity principle, emphasizing the complementary nature of matter as both particle and wave, and Heisenberg’s uncertainty principle, establishing a limit on the simultaneous measurement of complementary variables, formed the basis of what came to be called the Copenhagen Interpretation of Quantum Mechanics. Its formulation brought to an end the second phase of the earthshaking change to physics.
The concepts Bohr and Heisenberg proposed were presented to the physics community during a prestigious conference held in Brussels during the month of October. Solvay Conferences had been taking place approximately every three years since 1911. They were intended to be meetings in which a few dozen of the world’s leading physicists would gather for a week to address a major current scientific topic. The selection for 1927 was “Electrons and Photons,” but those present knew the real subject would be quantum mechanics, its concept revolutionizing physics’ foundations.
Significantly, no Italian was among the elite at the 1927 Solvay Conference, none deemed worthy of being invited to such an august gathering. One Italian, Enrico Fermi, would attend the next one, held in

1930. His presence there underscored Italy’s arrival on the international physics scene.
Another international physics conference was held in 1927, a month earlier than the Solvay Conference. The Volta Congress, unlike the Solvay Conference, was a one-time affair. The nominal occasion for the meeting was the hundredth anniversary of the death of Alessandro Volta, the discoverer of the electric battery. The unspoken reason was the Italian government—and Mussolini in particular—wanting to show the world that Italy belonged to science’s elite.
The meeting took place in Como, Volta’s birthplace. Located on the beautiful eponymous lake, it was a delightful setting and invitees were treated to elegant lodgings and memorable boat rides. The indefatigable Fermi even managed to take a few hikes beyond the handsomely terraced gardens and up the steep slopes surrounding the lake, reaching huts with glorious views of snowy Alps to the north and the Italian plains to the south.
To ensure that nothing was lacking in organization or trappings, Mussolini demanded that the Italian electricity companies, dependent as they were on government backing, provide massive funding for all aspects of the meeting. Corbino quietly but wisely gave an honest assessment of the proceedings, observing that “Italy should have exhibited more physics and less hospitality and that it should not deceive itself that sponsoring a conference was a substitute for scientific achievement.”
The invitation list was impressive. More than a dozen of the sixty-one individuals participating had already received Nobel Prizes, and several others would win the prize in years to come. Many hesitated before accepting the invitation. Arnold Sommerfeld, the highly respected senior professor in Munich, wrote to two eminent colleagues who had liberal views similar to his own, “I have serious reservations about attending because I assume the Italians will not forgo the opportunity of making it political and trotting out Mussolini.” After wavering, all three went to Como. However, Einstein refused, wanting no part of an occasion he sensed might be used to burnish Mussolini’s image.

The Volta Congress was notable in another respect. Though World War I had been over for almost a decade, feelings still ran high in many quarters. Since the war there had been no large international physics meeting that gathered together representatives from all the warring countries. The Volta Congress was the first. The leading physicists of Germany, France, Italy, England, Austria, the Netherlands, Belgium, Denmark, and the United States attended. In that sense it was a huge success. It was also a propaganda success for Italy. Physics was another matter.
Unlike the Solvay Conference, the Volta Congress had a broad agenda loosely tied to electrical and magnetic phenomena. This allowed for a very wide range of presentations, but the conference lacked the intense focus that made the subsequent Solvay meeting so famous. Besides Bohr’s first presentation of the Copenhagen interpretation to an international audience, none of the other more than fifty papers delivered was memorable.
Sommerfeld’s presentation, however, turned out to be influential for Italian physics because its main thrust was to emphasize the significance of Fermi’s recent work in statistical mechanics as the key to understanding the phenomenon of electric conduction in metals. The irony of Italian physicists having one of theirs achieve legitimacy through a foreigner’s approval was not lost on Rasetti: “Everybody began to realize that Fermi had achieved something very important. So that was really the revelation of Fermi in Italy. His reputation in Italy came back through Germany.”
When the week of meetings was over, the conferees were taken to Rome. On September 19, 1927, in Mussolini’s presence, they were officially welcomed from atop the Michelangelo-designed steps of the Capitoline Hill by Marconi, the current president of the Consiglio. The scene was unabashedly dramatic. Mussolini and Marconi appeared to reign from on high. Afterward, Il Duce accompanied them to a gathering at his residence, Villa Torlonia. He was delighted to have an occasion for strutting in front of an illustrious audience, bombastically proclaiming the past, present, and future greatness of the nation he led. Abhorring posturing and ostentatious displays, Fermi must have cringed.

Though Fermi could not have been pleased by the meeting’s political overtones, he was gratified to see the regard it afforded him. One souvenir of the time in Como was a photograph of him, Heisenberg, and Pauli sitting together smiling, the lake in the background. The three, an Italian, a German, and an Austrian, held the future of physics in their hands.
They knew they had already produced a revolution in physics. What they did not know was that without understanding the Pauli Principle, quantum mechanics, and Fermi-Dirac statistics, the world would not have been able to produce semiconductors, transistors, computers, MRIs, lasers, and so many of the other inventions that shape our life. In a very real sense we live in a world they created.

9
ENRICO AND LAURA
After Fermi’s appointment on November 7, 1926, as Rome’s professor of theoretical physics, he returned to the city of his birth, moving into the house on the city outskirts that had been constructed as his mother was dying. His father and sister now lived there. Maria had recently acquired a position teaching Italian literature at the same Rome high school attended by all the Fermi siblings. Sadly, Alberto Fermi was showing signs of a serious illness that would soon take his life. Maria and Enrico took turns sitting up with their father at night, but to no avail. He died on May 7, 1927, almost three years to the day since his wife had passed away.
That summer Enrico retreated to the Dolomites, just as he had done after his mother’s death. Once again he found long walks in the mountains to be restorative. And on this occasion his sorrow was mitigated by joy. Although there had been passing fancies before, this was the first time he found himself truly in love. The object of his affection was a beautiful nineteenyear-old Roman woman named Laura Capon whom he had met the summer before.
The Capons were one of Italy’s assimilated Jewish families that had risen to positions of relative prominence in the wake of Italy’s independence. Like many other such families, they were basically

nonobservant and seldom went to synagogue, though usually they married within the faith. Their closest friends tended to be other Jews.
Laura’s father, fifty-four-year-old Augusto Capon, was a career naval officer. After Italy’s unification, the military and the academy were two careers to which many Jews gravitated. Having distinguished himself both by his intellect and his valor during World War I, Capon had risen to be the head of naval intelligence and would soon be made an admiral. Like many officers, he was also a fervent monarchist. With a happy family life and four children, of whom Laura was the second oldest, he was comfortably well off.
Laura had intended to spend the month of August 1926 with her parents and three siblings in Chamonix, the resort on the French side of Mont Blanc. These plans were disrupted by the shakiness of the Italian economy. Worried that Italy might succumb to the kind of inflation plaguing other European countries, Mussolini had placed restrictions on the export of Italian currency. In effect this necessitated the Capons’ staying in Italy.
An alternative plan was quickly formulated: the Capons would vacation in the Dolomites near their friends the Castelnuovos. Guido Castelnuovo, one of the Rome mathematicians who had befriended Fermi, was only a few years older than Capon. He was a fellow Jew and, like Capon, a Venetian by birth. The two families were close, particularly with these similarities and children of the same age.
In late July the Capons arrived in Santa Cristina, a small town in the glorious east–west valley known as the Val Gardena. Located about twenty miles from the main road to the Brenner Pass, it had already become one of Italy’s most desirable summer and winter resorts, with ample opportunities for hiking, climbing, and skiing. The scenery is spectacular, with jagged peaks soaring over lush meadows and high plateaus. The church spires of small villages compete with mountain pinnacles to create a wonderland of beauty.
As soon as the Capons arrived, Laura went to see her good friend Gina, the Castelnuovo daughter closest in age to her. As Laura later recounted,

Gina greeted her by saying, “We are going to have lots of fun. Even Fermi has written my mother asking her to find a room for him.” When Laura inquired who Fermi was, Gina replied, “You must know him, I am sure. He is a brilliant physicist: the hope of Italian physics, as my father says.” And that is how Laura and Enrico got together that summer.
Laura had met Enrico two years earlier, albeit fleetingly. The occasion was apparently not filed in the annals of ardor or in the annals of memorable encounters. She described the 1924 meeting as follows:
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 too lingered on, conspicuous in its incongruity. But his eyes were cheerful and amused.
Those gray-blue eyes may have peered at her differently two years later, as did her brown warm ones toward him.
During the weeks that followed the young vacationers went on day hikes along the region’s many inviting paths, pausing from time to time to admire the glorious views. The group typically included a mix of friends and siblings. Laura discovered that though the young physicist was conscious of his rising reputation, he was not pompous; it was fun to tease him and he took the ribbings gracefully. She did not think Enrico was especially handsome, but there was something she found compelling about him. It probably was not the Tyrolean jacket and loosely fitting knickerbockers he typically wore in the mountains.
Everybody, parents included, trusted him to make the best decisions about excursions. He would pick the day’s route, make sure all the hikers had what they needed, and see to it that the youngest hikers were not too heavily burdened. Fermi’s knapsack was always by far the heaviest. Acting the role of mountain guide, he invariably took the lead and watched for trouble spots, not an infrequent circumstance on the Dolomites’ tricky scree slopes. When one came along, he helped whoever needed a hand.

After that summer, Laura was delighted to learn that Fermi had been appointed to a professorship in Rome. The two could continue to see each other in the environs of the busy city. When summer again came in 1927, Laura returned with her family to the Dolomites, the scene of her budding courtship with Enrico. He returned as well.
Fermi fit nicely into the Capon family mix. The Capons were upperclass, but their standing was based on achievement, not inherited wealth or rank. Fermi felt at ease with them and they, in turn, were not skeptical of Laura’s choice of a suitor, although he was not Jewish and not raised in their socioeconomic bracket.
Though both Fermi and Laura had grown up in Rome, their circumstances differed considerably. The Capons lived in a house located not far from the Fermis’, but their beautiful garden-enclosed villa had little in common with the apartments Enrico had inhabited. The Capons had servants to take care of household affairs, slept on ironed linen sheets, went on expensive vacations, and always spent a few weeks in the fall at Laura’s aunt and uncle’s imposing country residence in the hills above Florence.
At the end of the summer, Laura began her customary stay with her Florence relatives. It afforded her on this occasion a chance to quietly study for university exams later that fall, a time when many Italian university examinations were given. Laura had just finished her second year in Rome’s university, having chosen general science as a major. Though the major did not involve an intensive study of physics, it did require attending Orso Corbino’s introductory course and gave her at least some feeling for Fermi’s vocation.
In early September, Fermi had departed for the Como conference that became so pivotal to his international recognition. Both of them sensed that their separation would not be for long. After more than a year of knowing each other, their romance had blossomed. Later that month, Laura remembered, she was disappointed upon learning that Fermi had purchased an automobile, since he had laughingly told friends he intended to do

something crazy, either get married or buy a car. But just as with his decision to be either a theorist or an experimentalist, he soon did both.
The car, an egg-yolk-colored Bébé Peugeot two-seater convertible with a rumble seat, added a certain zest to Laura and Enrico’s courtship as well as a degree of uncertainty, because the Bébé was unreliable. Fermi always kept the hand crank by his seat to start the car and hesitated to take it for long trips. For Sunday excursions in the countryside, Franco Rasetti, who had a similar car, provided backup for automotive mishaps. It was fun for everyone.
Laura appreciated the closeness of the bond between Fermi and Rasetti though she could not help but notice their dissimilarities. While Fermi delighted in female company, Rasetti seemed not to care much about girls even though they were attracted to him. Laura commented that he examined girls with “dispassionate detachment, bending his head to one side for a better view, with narrowed eyes behind his glasses. He examined them, dissected them with his piercing look, as if they were rare butterflies or strange plants.” Fermi’s musings on the female species were more forthright. He had told Laura that he sought a wife who was blond, tall and strong, and from “country stock.” Laura met no part of that profile.
Although close, Fermi and Rasetti diverged in other ways as well. Fermi was rapidly moving toward bourgeois values; Rasetti continued to be something of a loner, still living with his mother. For Fermi, the days of throwing cats in the air during a lecture or of setting geckos free to scare a cook were over. His penchant for pranks had changed into a kind of goodnatured humor.
Undoubtedly Laura affected Fermi’s demeanor and contributed to his general happiness. He much admired her wit, intelligence, and casual elegance. Nor was he insensitive to her beauty. Leona Marshall, a coworker of Fermi’s fifteen years later, remembered her own reaction to meeting Laura: “When I first met her in 1942, I thought her the most beautiful lady I had ever met.” When Marshall commented to Fermi on his

wife’s beauty, she writes: “Enrico caught his breath and told me I could have no idea how beautiful the teen-age Laura was.”
Laura had been seventeen years old when she and Enrico first briefly met. He was obviously smitten. Those feelings began to be reciprocated two years later, in the summer of 1926. Admittedly Fermi did not come from a prestigious background, but that was more than made up for by the brilliant future toward which he was obviously heading. As Gina Castelnuovo had first said to Laura, everybody knew he was “the hope of Italian physics.” When Enrico proposed marriage, Laura accepted.
Although enamored of him, Laura found one trait of his annoying. It was her husband-to-be’s insistence on repairing everything he thought needed repairing without asking for help from anybody else. Fermi ascribed the attribute to his mother. He told Laura about how his mother had contrived to fix a pressure cooker, creating her own version in the process. As he explained to Laura, “If she wanted something, she would make it for herself.” Having observed this at an early age, the son followed in his mother’s footsteps.
This trait emerged inconveniently on Enrico and Laura’s wedding day. Fermi was late for their departure for City Hall, located on top of the Capitoline steps. When Laura nervously asked about what had delayed him, the groom told her that when he unpacked a new shirt, he discovered the sleeves were too long. Instead of quickly pinning them up, he had painstakingly sewn a fold in them.
A photo of the wedding party includes friends and family: Corbino and Rasetti were among the twenty-five stylishly attired witnesses attending the ceremony. On an oppressively hot day, women wore fashionable hats and flapper-style dresses. Laura, in a scalloped dress, stood elegantly next to her beloved, their arms locked, revealing Fermi’s long white shirt covering his wrist. His efforts at shortening his sleeves had not been altogether successful. But the dominant figure in the photo is Laura’s father, the admiral, whose height and dashing uniform set him apart from the others.

He is clad from head to toe in white, from a jaunty officer’s hat to spotless white shoes.
Fermi could not help thinking of when, less than a year earlier, he had been atop the Capitoline steps. At that time, he was among those greeted by Mussolini after the Como Congress, where he had been in effect anointed as a physics genius. His marriage to Laura was an anointing of another kind. The only cloud in the sky on that July day in 1928 was the dark cloud of Il Duce on those same Capitoline steps in September 1927. Little did the wedding party realize how the Fascist dictator would soon change their lives.
The ceremony had gone smoothly. There was only a civil wedding, since the Capons were secular Jews and Fermi a nonbeliever like his parents. Only Fermi’s sister, Maria, a deeply pious Catholic, minded the lack of a religious rite. As soon as Laura and Enrico were declared man and wife, Fermi’s best man, Corbino, came over to Laura, kissed her hand, and said, “Congratulations, Mrs. Fermi.”
That afternoon Laura and Enrico boarded a two-engine seaplane that flew to Genoa. Commercial aviation had started in Italy only two years earlier, so this was an adventure. From there they boarded a train and were off for their honeymoon in an Alpine valley lying between the Matterhorn and Monte Rosa. Not quite twenty-seven, Fermi now had a wonderful wife, a professorship in Rome, a thriving career, and even a semifunctional car. It was remarkable to think that only six years earlier he had been an impoverished Pisa student with an indeterminate future.

PART 2
PASSAGES

10
THE BOYS OF VIA PANISPERNA
The Colle Viminale (Viminal Hill), one of ancient Rome’s proverbial seven hills, rises gently from the flat expanse linking the Forum to the Colosseum. Via Panisperna, one of the many streets that wind their way up the hill, housed the Rome physics department when Fermi became a professor there in 1927. The department, its address at number 89A, lay in the midst of the rapidly growing capital. Rome had almost quadrupled in population since 1870, the year of Italy’s unification, a time when the city had only two hundred thousand inhabitants. The university had expanded accordingly, with most of the students locally based.
The villa at 89A Via Panisperna, with three floors and a basement, was spacious enough to accommodate the physics department. Orso Corbino and his family lived on the third floor. The second floor held a well-stocked library and the research laboratories of the department’s three professors and their students. Classrooms and the shop occupied the first floor. The building had a serene atmosphere, in large part due to the palm trees and the bamboo thickets in the extensive garden surrounding it. A high wall shielded the plantings and villa from the noisy and dusty street and added to the semblance of an oasis of tranquility. As Emilio Segrè wrote, “I believe that everybody who ever worked there kept an affectionate regard for the old place and had poetic feelings about it.”

Segrè, not a sentimental man, was clearly taken by this setting and all that it encompassed. At age twenty-two, he became part of an ambitious endeavor, nothing less than establishing Italian physics for the future. Fermi and Rasetti, both only twenty-six, had set the stage; they were building a unique research institute that would attract a top cadre of students. Segrè, a fourth-year engineering major at the university, would be the first to join them.
The recruitment of Segrè was not sheer happenstance; it came about because of mountain climbing. This was an avocation he shared, it turned out, with Rasetti. When Segrè heard that Rasetti had come to Rome, he contacted him immediately. The man quickly came to fascinate the younger climber. Aside from being a first-rate mountaineer, Rasetti spoke many languages, was widely read, knew everything about insects and plants, was doing serious research in a burgeoning field, and was the best friend and coworker of the reportedly extraordinary Enrico Fermi. Listening to Rasetti talk made physics seem much more enticing than engineering. But Segrè was cautious. Was there really a future in Italy for physics?
An event in the summer of 1927 convinced him that there was. After having done a number of climbs together, Rasetti and Segrè set off in August for the Matterhorn, or the Cervino, as Italians call it. They ascended a ridge on the Italian side, known as a difficult route, and descended down the easier Hornli Ridge on the Swiss side. While on this expedition, Rasetti told Segrè he was planning to go afterward to a physics conference nearby at Lake Como. The conference, with many of the world’s eminent physicists present, promised to be a festive occasion, one honoring the hundredth anniversary of the death of Alessandro Volta. Rasetti, still a youngster, had not been invited but he didn’t anticipate problems in attending, at least the plenary sessions.
The thought of seeing all the great men of physics excited Segrè and he decided that “by tailing Rasetti, who in turn was tailing Fermi, I might be able to go to some of the lectures and see what was going on.” For Segrè, “what was going on” became a turning point. He made up his mind to

become a physicist, in no small part because of the prospect of an apprenticeship under Fermi and Rasetti.
Fermi was hoping to draw other promising researchers to Via Panisperna, but didn’t quite know how to proceed. The indefatigable Orso Corbino helped him. During the previous spring he had paused in one of his lectures to second-year engineering students and a few general science students, including the future Mrs. Fermi. He announced that he was recruiting a brilliant young man named Enrico Fermi to the physics faculty in a few months. If any of them felt up to the challenge, Corbino was inviting them to participate in a field that was in the midst of a revolution. Great things were happening.
One of the students who felt ready to accept the challenge was Edoardo Amaldi, age eighteen. Two years earlier Amaldi’s father, a well-regarded Rome mathematician, had taken the family for summer vacation to the Dolomites. There they joined the Castelnuovo circle of university mathematicians, including the Capons and Fermi. During that summer young Amaldi had gone on a number of hikes with Fermi and even on a long bicycle tour with him. Amaldi had been enormously attracted by the energy and joie de vivre of the new physics professor. Now, a little older and encouraged by Corbino, he was eager to shift from engineering to physics. The pattern of switching to physics that had begun with Rasetti after meeting Fermi was repeating itself.
These four, Fermi, Rasetti, Segrè, and Amaldi, formed the nucleus of what came to be known as the Boys of Via Panisperna. The Boys stuck to the same basic Italian schedule: working five days a week from early in the morning until one, taking a two-hour break for lunch at home, returning to work at three, and then staying until seven or eight in the evening.
There was one point of the workday that was sacrosanct. It occurred in the late afternoon, when the Boys would gather for an informal discourse by Fermi on a topic he chose or one that was perplexing the group. In his methodical way, Fermi would proceed, without consulting texts, to obtain all the formulas that might apply, solve the problem, and consider further

questions. Fermi enjoyed this informal method of teaching and would continue to employ it throughout his life. His delivery was so smooth and seemingly effortless that students frequently did not realize how impromptu the session really was.
On Saturday mornings, plans were made for the next week’s activities. Sunday was reserved for play: sometimes excursions into the Roman countryside, other times longer hikes in the nearby hills or trips to the beach at Ostia once the weather turned warm. Sunday outings were always group affairs for Fermi, but the members of the group varied according to who was in Rome and available for a daylong jaunt. In the early days, before he became a professor, the group might be his sister, Maria, Enrico Persico, and a few mutual friends. Later Laura, one or more of the Boys, and new friends might join. Arrangements were always flexible.
The many photographs of the changing group have a common look: smiling men dressed in casual clothes and similarly smiling young women in skirts and fashionable 1920s cloche hats, wearing hiking boots instead of elegant shoes. Conversations during the outings often had a cheerful teasing tone as they urged one another on as to who could be sillier. Occasionally the subject turned to physics, though never related directly to the research the Boys were engaged in. That was reserved for the rest of the week.
Playtime was not limited to Sunday day trips. During summer vacations, the Boys and their friends hiked in the Dolomites, and in the winter they skied in the Alps or the Dolomites, despite the scarcity of ski tows or lifts. Fermi, who loved all these activities, was an easy and sought-after companion. His piercing eyes shone with the intensity of his intellect, but his easy smile invited close friendships.
A merry mood and close camaraderie prevailed in Via Panisperna. One aspect of this was the bestowing of nicknames. This being Rome, several of them received ecclesiastical monikers. Fermi, regarded as infallible, was Il Papa (the Pope), and Rasetti was addressed as Cardinal Vicario (Cardinal Vicar), a nod to his position as Fermi’s right-hand man. Segrè’s judgmental disposition led to his being known as Basilisco (Basilisk), the legendary

reptile capable of causing death with a single glance. Amaldi, with his youthful, cherubic, rosy face, was Fanciulletto (Young Boy). And then there was Corbino, whose ability to perform miracles, chiefly the raising of funds and the creation of assistantships for his young protégés, earned him the title of Padreterno (God Almighty).
The Boys of Via Panisperna, originally a four-member group, soon grew to include an unusual fifth, Ettore Majorana. Majorana’s brilliance had become obvious to his fellow students while he was studying for an engineering degree at the university. Segrè befriended the shy and selfdeprecating young man and encouraged him to switch to physics. A short interview with Fermi convinced Majorana. A relative loner among the Boys, Majorana became known as Il Gran Inquisitore (the Grand Inquisitor) for his terse and critical manner, applied to the research of others, but particularly to his own work.
Il Gran Inquisitore rivaled Il Papa in the rapidity of his calculations. One day, at Fermi’s request, Majorana had examined a complicated equation to determine how much energy it would take to ionize an atom, that is, to remove its electrons. Fermi was trying to approximate it numerically. Over the next few days Majorana retreated and then returned to Via Panisperna to compare his answers to Fermi’s. To the astonishment of the Boys, Majorana had solved the equation analytically, his answer agreeing with Fermi’s numerical conclusions. Until then, they had thought nobody could rival Enrico.
The paper Fermi wrote on this topic, applying statistical mechanics to atomic physics, was greeted with considerable approval. However, its acclaim was not as high as Fermi had expected. He soon learned that that was because almost identical results had been derived a year earlier by an Englishman named Llewellyn Thomas. Since Thomas’s paper had been published in the Proceedings of the Cambridge Philosophical Society, a journal unavailable in Italy, Fermi had not seen it. And so, just as he had previously scooped Dirac, Fermi was now the one to be scooped.

Since the phenomenon of independent findings was common before the age of rapid communication, the discovery was credited to both men and hence goes by the name “Thomas-Fermi equation.” Having been scooped on this one occasion had a relatively small impact on Fermi, whose international reputation was growing. His career beginnings in Rome had been off to a strong start. Soon there would be other reasons to recognize the Pope.

11
THE ROYAL ACADEMY
Though Fermi’s main emphasis was on research and teaching, he knew that he should reach out beyond the confines of Via Panisperna if he hoped to promote the growth of physics in Italy. He became active in the government’s National Research Council and served as an editorial consultant to the Enciclopedia Treccani, the Italian rival to the Britannica.
He also began writing for the Periodico di Matematiche, a journal aimed at keeping secondary school teachers abreast of recent developments in physics and mathematics. Fermi’s early articles in the Periodico demonstrated his dazzling ability to explain what had been achieved and what still needed to be answered.
Because of Fermi’s rising prominence, he felt responsible for keeping the Italian general public informed. Physicists, chemists, and other scientists were aware that new developments were taking place in atomic physics, but what bearing did they have on everyday life? In a long piece entitled La Fisica Moderna (Modern Physics) that Fermi wrote in 1930, he tried to provide an answer. He began with the rhetorical question “What practical consequences have been or might be derived from such a great increase in our knowledge of matter’s intimate structure?”
His reply, still valid, is that it usually takes years, if not decades, for applications of fundamental new insights to be developed. But Fermi

reassured readers “that the work of scientists is not distancing itself from life, losing itself in the pursuit of abstruse and purely abstract ideas.” And he was right in that as well.
Fermi had an ulterior motive in accepting many of these writing commitments. They allowed him to earn money to supplement his relatively modest professor’s salary, about ninety dollars a month. Though a man of simple tastes, he was aiming to have the kind of upper-middle-class way of life many of his colleagues enjoyed. A few years earlier, as a young bachelor, he had slept in a freezing room adjacent to the Florence Physics Institute; that was no longer acceptable for a married man with a growing professional reputation. Fermi now strove for a lifestyle that included a comfortable residence, interesting vacations, a housemaid, and occasional entertaining.
This was the mode of living that Laura had grown up with and expected to continue. Her dowry allowed them to purchase an apartment but they had no savings. Conservative by nature, they both also hoped to have a little nest egg if something unexpected and untoward were to occur. As Laura wrote, “Enrico felt that we needed more, not to lead an extravagant existence, but to acquire a sense of security and to be prepared for emergencies.”
Fermi thought of a strategy for achieving greater security. He would, with Laura’s help, write a physics textbook for Italian high schools. In 1928 he had published a book, Introduzione alla Fisica Atomica (Introduction to Atomic Physics), but it didn’t make any money. A high school textbook might be different. There was no such text in Italian that Fermi thought adequate. With this book, students would learn physics in a new way, not having to consult obscure texts as he had been forced to do.
Laura and Enrico set to work on the textbook after their honeymoon, a trip that mixed romance and physics. The passionate husband could not stop sharing his infatuation with his trade; as Laura correctly deduced, “I was to learn physics, all there is to know about physics.” By and large, Fermi dictated the book’s contents to Laura. If she didn’t understand what her

husband was saying, she would interrupt. This would often evoke the response “It’s obvious,” which would then lead Laura to reply that it wasn’t obvious at all. Cooperation had its limits.
Working on the book mostly during vacations, Laura and Enrico adopted a program of writing six pages a day. This meant that the five-hundred-page text took almost two years to complete. Laura opined that it “was mediocre prose [but] it still served its purpose of bringing economic returns for many years.” That income would not be needed after all. By the time the book was published, the Fermis had acquired a far more lucrative funding stream. Unexpectedly, it was thanks to Mussolini.
Since the mid-1920s, Il Duce had wanted to establish a prestigious Italian academy that would bring together prominent scholars and artists. Such an institution already existed: the Accademia dei Lincei. Originally founded in 1603, the Lincei had not taken its modern form until 1870, when Rome became the capital of Italy. The new Italian government had then provided the Accademia with a distinguished residence by purchasing the beautiful Palazzo Corsini on the banks of the Tiber. But the Lincei was too independent for Mussolini’s taste. It took stands that were not always pleasing to Il Duce.
Mussolini wanted an academy whose actions on the cultural front would be in line with Fascist doctrines, one in which Italy’s very recent past would be glorified. He also wanted to personally select its members. Accordingly, in January 1926, he announced the formation of the Royal Italian Academy. It would take him three years to assemble the funding for its support and for the annual awarding of four Mussolini Prizes.
Mussolini’s choice for the Academy’s location was pointed: Villa Farnesina was directly across the street from the Lincei’s Palazzo Corsini. The villa, a grand early-sixteenth-century building, was a jewel with ground-floor frescoes by Raphael. Mussolini made sure the message to Italy was not lost: his Academy was superior to the Accademia. He provided generous financial support for its members: a university professor would more than double his salary. Artists were similarly compensated. To

underscore the Academy’s political connection to the regime, Mussolini scheduled its first meeting on the anniversary of the 1922 March on Rome, the event that marked his ascent to power.
In March 1929, Mussolini announced the Academy’s first thirty members. The list included composers, artists, and playwrights. It had also appeared likely that a physicist would be appointed. Corbino was the natural choice, but the Academy’s by-laws stipulated that if one was a senator, as Corbino was, he was not eligible for membership. Lo Surdo, the second Rome physics professor, thought he might be named, particularly because he was an ardent Fascist. But much to everyone’s amazement, Fermi was chosen. Given the stipend that came with the nomination and the fact that it was a lifetime position, Fermi’s financial worries were over.
Corbino had certainly been the force behind Fermi’s selection, but Mussolini must have been pleased to see that Fermi did not hold any expressed antifascist views and was not even a member of the Accademia dei Lincei. Ironically, Fermi would have been a member except for a supposedly accidental lapse by Lo Surdo. Corbino, away on a trip to the United States, had asked him, in his absence, to nominate Fermi. Upon Corbino’s return, Lo Surdo claimed to have forgotten. The truth was almost certainly that he, jealous of Fermi’s success, had tried to keep him out of the Accademia. When Fermi was appointed to the Royal Academy, Corbino must have felt avenged.
In keeping with Fascism’s bombastic style, the appointed Academicians were required to purchase an elaborate uniform to wear at official gatherings. Complete with cape, silver sword, and plumed hat, this outfit was Mussolini’s creation, an image designed by Il Duce to impress onlookers and ensure that Academicians were conscious of the honor they had been granted. Unpretentious, Fermi found wearing the uniform embarrassing and went to some lengths to avoid being seen in it.
Though certain occasions could not be avoided, Fermi was probably the only Academician to arrive in a yellow Bébé Peugeot rather than a chauffeured limousine. An oft-told story revolves around his driving the

Bébé to a high-powered government meeting. As Fermi—in his undistinguished car—approached guards blocking the access road, he asserted, “I am the driver to His Excellency Fermi. And His Excellency would be very annoyed if you didn’t let me in.” When Fermi recounted the story, he underscored that in both comments he had told the truth.
More disturbing to Fermi than the Academy’s ostentatious trappings was the obtrusive hand of Fascism in the selection of its members. The rumor spread that Federigo Enriques had been in the initial group of thirty Academy members, but a lesser mathematician had been chosen at the last minute. Was Enriques’s being Jewish the reason, or was it because the mathematician chosen was a Fascist? Government interference was also blatant in the conferring of the Mussolini Prize. In 1931, when Fermi nominated three distinguished mathematicians to choose from, all of whom happened to be Jewish, Il Duce summarily rejected each.
It is commonly said that there were no serious problems with antiSemitism under Fascism until Mussolini came under Hitler’s influence in the late 1930s. Mussolini was open about his longtime affair with Margherita Sarfatti, who was Jewish and an ardent promoter of artistic modernism. It does seem more than coincidental, however, that the Royal Academy never had a Jewish member.
Probably the insidious exclusion of Jews was partially due to a rapprochement between the regime and the Catholic Church. The schism dated back to 1870 when, in the final event of Italian unification, the Papal State was defeated and Rome captured. The Pope refused diplomatic recognition of the nascent Kingdom of Italy and, in turn, Italy did not recognize the Vatican State. The so-called Concordato or Lateran Pacts of February 1929 put an end to that almost-sixty-year hostile stalemate. The Pacts negotiated around this issue with a series of trade-offs. The Vatican was given a large sum of money and gained control over Italian marriage and divorce laws. The government, under Mussolini, recognized Catholicism as the official state religion and mandated religious education in public schools. Considerable benefits had accrued to the Catholic

Church. But when Il Duce refused to kneel before the pontiff or kiss his hand, Pius XI began to see the high cost at which they had come. Once Italy was officially made into a Catholic country, Jews—by definition—were marginalized.
Two years later, Mussolini further tightened his control over Italy. In the fall of 1931, the government announced that all of Italy’s university professors would be required to sign a loyalty oath professing allegiance and devotion to king, country, and the Fascist regime. Again, this disproportionately affected Jews. Although Jews made up 0.1 percent of Italy’s population, approximately 10 percent of university professors were Jewish. If one counted only those academics in the fields of science, mathematics, and medicine, the percentage of Jewish professors was much higher.
Of the more than twelve hundred and fifty professors at the time, only a dozen refused to sign the oath, among them the mathematician Vito Volterra. Some who took the oath justified their actions by reasoning that their places would just be filled by Fascist loyalists. Others maintained that it would be better to oppose the system from within. Many claimed the oath was a simple formality that meant nothing.
Fermi was not asked to take the oath, since he had already joined the Fascist Party a few days after his nomination to the Royal Academy. Although it was not a requirement for his appointment, it was an expectation. Fermi had been happy to oblige, since politics meant little to him. Physics is what mattered, and as long as he could pursue his research without undue interference, the rest did not concern him—an attitude shared by the other Boys as well.
Fermi’s apolitical stance and desire to avoid clashes with the Fascist regime were well known. Enrico Persico, by now a professor of physics in Turin and nicknamed Prefetto di Propaganda Fede (Prefect of Propaganda for the Faith) by the Boys because of his success in spreading the quantum gospel, was aware of this. In a letter to Fermi recommending that he hire as his assistant Giancarlo Wick, a bright twenty-two-year-old Turin theorist,

Persico alerted him to Wick’s professed antifascism. Fermi’s response was that he had no prejudices about political views but preferred having no public expressions of antifascism.
Wick, not a radical, was willing to curtail his political activities. He even took the oath of loyalty to the regime in 1937, when he became a professor. But in 1951, when the University of California regents asked all faculty members to swear they were not and had never been Communists, Wick resigned his Berkeley professorship rather than do so. Although he had in fact never been a Communist, Wick remarked to a friend, “I had once to take such an oath in Italy for mere survival reasons and I always regretted it.” He never wanted to be in that position again.

12
CROSSING THE ATLANTIC
Ignoring the increasingly repressive political atmosphere in Rome, the Boys of Via Panisperna concentrated their energies on physics and were successfully making their mark. Edoardo Amaldi, Emilio Segrè, and Ettore Majorana had published—with a boost from Fermi—their respective first articles by 1928. They, as well as Rasetti, began to think of expanding their horizons. The prized Rockefeller Foundation fellowships, instituted in 1923, were becoming more widely available, and the Boys thought obtaining one might be a good vehicle for advancement.
Fermi had been the first Italian physicist to win a Rockefeller fellowship and had subsequently studied in Leiden. A few years later, Rasetti was awarded one. It would have been natural for Rasetti to go to one of the Northern European physics centers. Instead, always the most adventurous of the Boys, Rasetti was determined to see America, in particular the Wild West. He opted to spend the fellowship year at Pasadena’s California Institute of Technology, familiarly known as Caltech.
The United States was not yet the physics powerhouse it would soon become thanks in large part to the efforts of a dynamic mix of individuals, some fully American-trained, such as Arthur Compton and Ernest Lawrence, and others who had studied in Europe, such as J. Robert Oppenheimer, Linus Pauling, and Isidor Rabi. That mix was further

enriched by a number of European scientists who had emigrated. To them, America was a land of promise and a refuge from totalitarian regimes. It was to become home.
When Rasetti arrived at Caltech in 1928, he was impressed by the variety and vitality of American science. With his wide range of interests, he became friends with a broad spectrum of its biologists, geologists, and astronomers as well as with the physicists. On his return to Rome he regaled the other Boys with tales of his adventures and of strange customs, such as prohibitions against alcohol and the institution of faculty clubs where one mingled with other professors. He regarded America as a new world, one he urged them to see. Highlighting his affection for the United States, Rasetti imported a Ford Model A, undoubtedly one of the few Model A’s in Rome and certainly the only one on Via Panisperna.
Rasetti’s research work in California had been noteworthy and served as leverage for his obtaining an Italian professorship. Corbino once again held sway. To ensure that Rasetti was not separated from the other Boys, he managed to have a new physics professorship created in Rome. Rasetti filled it. Fermi began working immediately with him, as they had five years earlier in Florence. Again, Fermi was largely responsible for theory and Rasetti for experiment. This two-year collaboration was the springboard for a book Fermi published in 1934, Molecole e Cristalli (Molecules and Crystals). Translated into several languages, it became a standard text for both physicists and chemists seeking to understand the workings of the still new quantum mechanics.
As in Florence, Fermi also undertook independent research of deep theoretical significance while he was collaborating with Rasetti, who was focusing on more straightforward experimental projects. Quantum mechanics had shown how an electron interacts with an electric or magnetic field but not how it was able to either emit or absorb electromagnetic radiation. This was the question foremost in Fermi’s mind. A new subject, given the name quantum field theory, was in the process of being invented. Perhaps his own approach would help solve its mysteries.

Fermi was not the only one trying to advance the new subject. All the young theoretical physics geniuses, Dirac, Heisenberg, Pauli, and Jordan, were attacking the same problems. Fermi was less troubled than the others about conceptual difficulties. Instead, he laid out procedures to follow in an easily accessible fashion and then applied them to solving a number of relevant problems, with particular emphasis on explaining previously puzzling results.
Fermi’s conclusions on quantum field theory were published in a number of shorter papers and finally summarized in a long pedagogical article. In addition to its methodology, it was notable in being Fermi’s first publication in an American journal, Reviews of Modern Physics. The article’s appearance in 1932 strongly influenced a whole generation of theoretical physicists, including Hans Bethe and Richard Feynman. Both future Nobel laureates considered the article pivotal in their own careers and in understanding field theory, commenting on its “enlightening simplicity.” Feynman later wrote, “Almost my entire knowledge of QED (quantum electrodynamics) came from a simple paper by Fermi.”
Fermi’s decision to publish in an American journal was influenced by the very favorable impression of the country from his first visit. The trip came about because of an invitation by George Uhlenbeck, Fermi’s friend from Rome and Leiden days. Uhlenbeck and his fellow student in Leiden, Sam Goudsmit, had just accepted faculty positions in physics at the University of Michigan.
Happily ensconced in Ann Arbor, they started a summer school for theoretical physics to bring American students together for a period of two months to hear lectures delivered by a few prominent physicists. Paul Ehrenfest, their Leiden mentor, had already agreed to come. Spurred by happy memories of his time in Leiden and encouraged by Rasetti’s tales of America, Fermi accepted the offer. Laura joined him.
Neither Enrico nor Laura knew much about the United States. Laura admits she had never heard of the American Civil War and assumed Abraham Lincoln was Jewish, Abraham being a common name given to

Jews in Italy. Neither of the Fermis knew English beyond basic communications: Fermi could read physics articles but little else. Their reactions to America diverged sharply. The country had little appeal to Laura, who counted the summer of 1930 as a failure in terms of any potential Americanization. In contrast, Fermi found he liked the United States very much. Within the university’s ivory tower, Fermi was relatively impervious to societal changes and the effects of America’s deepening economic depression. The spontaneity and lack of pretension of Americans is what spoke to him.
Laura, suffering from what she later admitted was snobbery, was less convinced. She, like many of her European friends, considered Americans uncultured and unrefined. While her husband had a busy life with other physicists, she had few friends and little to do. It is also likely that Laura was afflicted with morning sickness. The Fermis’ first child, their daughter, Nella, was born on January 31, 1931, less than six months after their return to Italy.
Fermi returned to Ann Arbor in the summers of 1933 and 1935, catching on to spoken English, although his Italian accent would never disappear entirely. Laura remained in Italy both times. The new mother was reluctant to travel with her little one across the Atlantic, where she would sit in a strange house in Ann Arbor and not have the help of their tried and true nursemaid.
Returning to Rome, Fermi found that his rising fame as a theoretical physicist was beginning to attract visitors, most of them Rockefeller fellows from northern Europe, who spent appreciable amounts of time at Via Panisperna. Bethe was one of the first, arriving in February 1931. He was soon writing his Munich friend Rudolf Peierls, later Sir Rudolf, about the wonders of Fermi’s approach to physics: “His ability to summarize any problem is amazing; he can immediately tell whether or not a paper makes sense … and his judgment of the theoretical and experimental (!) literature is infallible.” Even after a short time in Rome, Bethe had recognized why Fermi was called the Pope.

Peierls, obviously intrigued, followed Bethe to Rome with his own Rockefeller fellowship a year later. Managing to extend his fellowship, Bethe joined Fermi again a year after that in the spring of 1932.
Via Panisperna had become a magnet for creativity and innovation in the field, much like Copenhagen under Bohr’s tutelage, Munich under Sommerfeld’s, Zurich under Pauli’s, and Leipzig under Heisenberg’s. Felix Bloch from Switzerland, George Placzek from Czechoslovakia, Edward Teller from Hungary, and numerous others came to Rome. They had all studied in more than one of those Northern European centers and sought to learn the less formal problem-oriented style advocated by Fermi. An added bonus was to spend time amid Rome’s wonders.
Foreigners were not the only physicists coming to Via Panisperna. Word spread in Italy, and young Italian aspiring theoretical physicists such as Giulio Racah, Giancarlo Wick, and Ugo Fano also came to Rome. Largely thanks to Fermi they had become intrigued by the prospect of physics as a career path.
Pilgrimages to the Eternal City had been taking place for centuries. This was a new kind of pilgrimage, one whose endpoint was an encounter with a new kind of Pope.

13
BOMBARDING THE NUCLEUS
By 1930, Enrico Fermi was internationally recognized and Rome was becoming a world center of physics. To establish further prominence, it was timely to focus on the most exciting field in physics: the atom’s nucleus. What transpired within the minuscule nucleus had largely been set aside, at least until the motion of the atom’s electrons around its central core was understood. The problems raised were now coming to the fore.
In a talk Orso Corbino gave in September 1929, the Padreterno had said, “The study of the atomic nucleus is the true field for the physics of tomorrow,” and he continued by asserting that to study physics “without an up-to-date knowledge of the results of theoretical physics and without huge laboratory facilities is the same as trying to win a modern battle without airplanes and without artillery.”
Fermi followed up Corbino’s envoi with a 1930 article in the Periodico, declaring that he, too, believed that studying the atomic nucleus was the foremost problem in the future of physics. He expanded Corbino’s assessment by asserting that more than “up-to-date knowledge” would be asked of theoretical physics and that “we should expect that it will be necessary to modify the laws valid for the atom before obtaining a satisfactory theory of nuclear phenomena.” The challenge was formidable.

The unexpected picture of the atom that Ernest Rutherford discovered in 1911 and Niels Bohr extended two years later did not attempt to explain the atom’s nucleus. It did, however, seem plausible to interpret it as saying that the simplest of all nuclei, hydrogen, was nothing but a single particle with positive electric charge. The particle’s mass, almost two thousand times as great as the electron’s, accounted for why most of hydrogen’s mass was concentrated in the nucleus. That positively charged particle was eventually given a simple name: proton.
But puzzles began right away. The next element in the periodic table of elements, helium, had a nucleus with two protons. But the helium nucleus’s mass was approximately four times the size of a proton’s. Something else had to be contained in it, but it was far from obvious what that might be. The same puzzle persisted all along the periodic table, with the imbalance between the number of protons and nuclear masses only growing.
Aside from the question of mass there was a glaring problem. What kept a nucleus together? The gravitational force was far too weak to make any difference. The only other known force, the electric one, explained how atoms were constituted: positively charged nuclei attracted negatively charged electrons. But rather than attracting protons to one another, electric forces caused repulsion.
Some other forces, unknown and powerful, had to be at work. As Fermi had written in one of his first publications, “These numbers show that the energy of the nuclear bonds is a few million times greater than those of the most energetic chemical bonds.” But neither Fermi nor anybody else in the next ten years had been able to obtain a clue as to why those bonds were so strong.
That wasn’t all. Even before he discovered the atomic nucleus, Rutherford had observed two kinds of decay in radioactive elements in which electrically charged particles were emitted, one negative and the other positive. In beta decay, an electron was emitted. In alpha decay, a positively charged particle was emitted. The alpha particle, far more massive than an electron, was ultimately identified as a helium nucleus.

After the decay, the final nucleus differed from the initial one by having a different electric charge, plus one unit for beta decay and minus two units for alpha decay.
Since the existence of protons within the nucleus was well established, it was likely that two protons could unite inside a helium nucleus. But the presence of electrons in a nucleus’s interior was dubious. The main attempt to circumvent this puzzle was to conjecture that a proton inside a nucleus had found an electron and bonded tightly to it.
This possibility had its pros and cons. It would explain how it was that electrons were observed to be exiting from a nucleus: they were contained in it to begin with. It would also explain the extra mass seen in nuclei other than hydrogen. Since the electron’s and the proton’s electric charges were opposite in sign but equal in magnitude, a bound-together electron-proton pair would have mass but no electric charge.
On the other hand, the conjecture had more than its share of problems, including one based on Heisenberg’s uncertainty principle. But even putting that aside, how could an electron and a proton bind tightly together? And if they did, how could the electron free itself to form a beta ray? As if that wasn’t enough, there was another problem: energy was apparently not conserved during beta decay. As expected, the difference in a nucleus’s energy before and after it emitted an alpha particle matched the energy carried away by the exiting helium nucleus. The same was not true for beta decay.
All these interesting problems led Fermi in 1931 to organize an international weeklong meeting in Rome on nuclear physics to debate the issues. He was also hoping it would be an aid for him and the Boys to stay abreast of both experimental and theoretical developments in the field. Held at the Italian Royal Academy, it brought together leading experts from around the world. Underlining its importance and coincidentally the Academy’s, Mussolini attended the inaugural meeting, held on October 11. The Italian press gave ample coverage to the event, not failing to note that

the proceedings demonstrated “the depth and universality of Italian thought.”
The gathering showed the Boys once again where the big challenges in nuclear physics lay, but it didn’t provide them with a road map for how they could enter the field. Rome didn’t even have equipment that was crucial for studying nuclear decays. That didn’t deter Fermi. He and Amaldi enjoyed constructing experimental apparatus, so late in 1931 they set about building at least one of the needed items: a cloud chamber. This table-sized instrument contains vapor that records, via the formation of drops, the passage through it of electrically charged particles, alpha particles being prime examples.
Since the Via Panisperna Institute lacked what Amaldi and Fermi needed for building the chamber, they shopped in Rome in order to find just the right items, confounding clerks at the hardware stores with their strange assemblage of purchases. Fermi, a devotee of the do-it-yourself method, felt in his element by starting from scratch.
A cloud chamber is a delicate instrument. The one Amaldi and Fermi built could not compete with those built in more sophisticated laboratories. Their valiant attempt was, however, a useful lesson for them. It drove home to them the need for better experimental facilities and for further training in top foreign laboratories. Amaldi had already spent ten months in Leipzig and Segrè had left for Hamburg. Rasetti, the group’s senior experimentalist, now traveled to the Berlin-Dahlem Institute, where Lise Meitner and Otto Hahn were doing state-of-the-art nuclear physics research.
As 1931 came to an end, a giant jump in the field of nuclear physics was beginning to occur. The key was to make use of an intense source of radioactivity to produce a beam of alpha particles and then use that beam to bombard an appropriate target. The technique was first developed by the German physicist Walter Bothe and then perfected by the French chemist Irène Curie and her physicist husband, Frédéric Joliot, in their Paris laboratory. They employed a target made out of beryllium, element number

4 of the periodic table, and searched for what sort of radiation was induced in the beryllium after it had been bombarded.
Exposing a layer of paraffin wax to the radiation that had been produced in the target, Curie and Joliot observed a copious production of protons. They concluded that quanta of electromagnetic radiation, particles known as photons, were causing protons to be expelled from the paraffin.
In Cambridge, Rutherford’s right-hand man, James Chadwick, saw the note detailing the Paris experiment and reported its results to Rutherford. He was flabbergasted by his mentor’s immediate response, “I don’t believe it,” a reaction Chadwick described as “entirely out of character.” Rutherford and Chadwick had their own views on what caused those protons to be emitted: a particle whose existence they had been contemplating for years. It was massive and neutral: they had called it a neutron. When Chadwick now saw an opportunity to catch the evasive prey, he dropped all his ongoing research in order to do so. After two weeks of almost nonstop work, Chadwick proved that neutrons, not electromagnetic quanta, were responsible for knocking the protons out of the wax.
Curie and Joliot had misidentified what they had seen. In considering who should get the Nobel Prize for the discovery, Rutherford is reported to have said, “For the neutron to Chadwick alone; the Joliots are so clever that they soon will deserve it for something else.” Three years later, in 1935, Chadwick was awarded the Nobel Prize in Physics for his discovery.
Although the neutron’s discovery would eventually come to be seen as a watershed moment in nuclear physics and the true dawn of the subject, it took a while for it to become clear that was the case. Neutrons could account for the missing mass in nuclei, but there was a great deal of confusion about whether they should or should not be treated on a footing similar to protons. Were they elementary or were they composites? There was also no understanding of what kind of force could hold neutrons and protons together within the nucleus.
The first glimmers of hope in addressing this all-important issue came with three papers Heisenberg produced in late 1932 attempting to describe

what such a force might be like. They provided a promising beginning on a subject that continues to this day. And Heisenberg was not the only one making such efforts; Majorana and others were as well. Chadwick and Rutherford had not been the only ones to have doubts about the Curie-Joliot report. In Italy, Majorana had shaken his head after reading it and had said to the other Boys, “They haven’t understood anything. The effect is probably due to protons recoiling after being struck by a heavy neutral particle.” None of them thought much about the remark, but a few weeks later they looked at Majorana with new respect.
Unfortunately, as was almost always the case with the hypercritical Majorana, he thought his own results were of no consequence. When Fermi asked Majorana if he might give at least a preliminary report on his work at a Paris meeting Fermi was planning to attend, the Gran Inquisitore had reportedly been furious, telling Fermi, “I forbid you to mention these things that are so stupid. I don’t want you to go around discrediting me.” Majorana was sadly showing signs of the paranoia and isolation that increasingly plagued him.
Fermi and the Boys tried to persuade Majorana to visit a few of the great European nuclear physics centers to gain some exposure to other theorists working in the field of nuclear physics and hopefully be convinced that his thoughts were not “so stupid.” In particular, Fermi suggested a stay in Leipzig where Heisenberg was a professor. With a grant, Majorana left for Leipzig in January 1933. There, as Fermi had hoped, he found his work appreciated by Heisenberg, who even managed to persuade Majorana that his contribution to the theory of nuclear forces needed to be published.
Majorana’s findings subsequently appeared in Zeitschrift für Physik, one of the last papers that foreigners sought to publish in this prestigious German science journal. The respect accorded to German science was being eroded by the diaspora of German scientists, many of whom were Jewish, fleeing Nazism’s far-reaching tentacles. The research that was useful to National Socialism’s racism was the distorted pseudoscience of eugenics.

Basic science research continued, but soon that became reoriented toward weaponry and war.

14
DECAY
The Germany that Majorana found was very different from what it had been only a few months earlier. Adolf Hitler had become Chancellor on January 30, 1933. In an all-too-frequent scenario, political events were impacting the world of science. Laws were passed within two months giving Hitler total legislative and executive control; his dictatorship was firmly established. Another law was soon enacted that excluded Jews from civil service and restricted the number of Jewish students allowed in schools and universities. Göttingen’s twin pillars of physics, the experimentalist James Franck and the theorist Max Born, went into exile.
Einstein didn’t wait for the law that discriminated against Jews to be promulgated. After a prolonged visit to the United States, he had sailed back to Europe in March. When the ship docked in Antwerp, he went straight to the German embassy, renounced his German citizenship, and a few months later returned to the United States. He never went back to Europe.
Fermi, like most Italians, did not believe that the overt anti-Semitism sweeping Germany was a harbinger of what would soon be coming to his own country. Italy’s Jews were a far smaller proportion of the population than Germany’s and had risen to prominence in many positions of the government and the military after Italy’s unification. By and large they