Enrico Fermi, scientific collaborator

He was a master of many things, but Enrico Fermi was certainly a master of the fine art of scientific collaboration. The building of small, tightly knit teams was his specialty. His career was influenced by at least two important teams. One was the team he built in Rome in the 1930s which helped him explore the effect of neutron bombardment on atomic nuclei. The second was the team he gathered in the United States in the 1940s which helped him build the world’s first nuclear reactor at the University of Chicago. Though some of his most important work was conducted on his own, collaboration was important to him and crucial to his success.

His student and colleague from his days in Rome, Edoardo Amaldi, described it this way: “I would say that his ability to drag others into work, with great intensity, for many hours, was one of his characteristics. He did it with us in Rome, then he went to Columbia University in New York and created a new group in Columbia; he went to Chicago and created another group for the simple reason that his role was that of general counsel; back in Chicago he created yet another group. Wherever he went he had this great influence on the people around him.”

This paper will look at the teams he built, the products of those collaborations, and what made his collaborative style so special.

1 Collaboration in Rome

Fermi started collaborating early in life. As a child, he began to develop a passion for science working alongside his brother Giulio, who died unexpectedly when Enrico was just 13 years old. Together they pursued boyhood enthusiasms like making model airplanes and building electric motors. After Giulio’s tragic death, Enrico turned to his friend, Enrico Persico, and continued his exploration of the scientific world. When Fermi came under the tutelage of his father’s colleague Adolfo Amidei for a thorough grounding in the mathematics and physics of classic mechanics, he continued to meet with Persico regularly to explain what he was learning. Persico became the first of many Fermi students, and at the same time they worked together as colleagues doing all sorts of experiments, for example trying to measure the variation in the gravitational field in different parts of the city of Rome. Fermi was clearly the leader – Persico readily conceded that much in later years – but the collaboration was important because it set the model for future collaborations: Fermi would master a subject by working it through with a junior colleague.

Fermi arrived at university in Pisa knowing all there was to know about classical physics, so he set out to teach himself relativity and what was then known about quantum physics. He had to do this on his own because there was no one at Pisa who knew enough about the subjects to teach him. However, once again he found a partner in fellow-student and lifelong friend, Franco Rasetti. Fermi would learn, and would teach Rasetti, who would provide a sounding board for Fermi as he worked the two new theories through in his own, thorough mind.

Rasetti was also by Fermi’s side when Fermi began to think deeply about entropy and its quantum interpretation during the years 1925-26. The two of them held lectureship positions at the University of Florence, and Rasetti later described how Fermi came up with one of his most important breakthroughs, the so-called “statistics” which put Pauli’s exclusion principle to work in statistical mechanics, while the two of them spent idle afternoons hunting lizards on the campus of the physics institute. Rasetti served as Fermi’s sounding board for his work, continuing the pattern Fermi set with Persico and would continue into later years.

Soon after this breakthrough, Fermi was offered a permanent professorship at the University of Rome’s Institute of Physics, thanks to the energetic efforts of the Institute’s director and one of the most powerful men in Italian science at the time, Orso Mario Corbino. Corbino announced to the entire university that he was seeking students to study with the newly minted professor, and soon two students from the engineering school, Emilio Segrè and Ettore Majorana, had transferred from the engineering program to study under Fermi. Others followed, and within several years the physics department was a thriving center for training and research.

During this period Fermi was clearly the leader, developing the theoretical and experimental agenda of the team and coordinating the work assignments of each member. To read the memoirs and interviews of those who worked with him in Rome at this time, one is struck by how he towered over the others, both through his unsurpassed grasp of physics and through the force of his considerable personality. Edoardo Amaldi, one of his closest collaborators, describes working with Fermi as follows:

“The work was always carried out in a very busy atmosphere but at the same time serene, indeed pleasant, as of someone who is playing a pleasant game but which requires total commitment. Many of his [Fermi’s] theoretical works have been done in public and precisely at a table surrounded by friends and pupils, talking slowly but without interruption and writing the formulas in the pages of a notebook, one after the other without almost any correction. After a few hours of work, all the formulas of a work, even a very complex one, were written there, in logical order and ready, with the addition of an introduction, some connecting phrases and a final comment, to constitute the text of a job to be sent to the press.”

“This way of working in public was one of the methods used by Enrico Fermi to create, wherever he was, an exceptional school of modern physics, which accompanied the lessons of his courses which were always carried out with extraordinary clarity and precision.”

“His commitment to research was never in contrast with his didactic commitment, that he always fulfilled with an uncommon scruple both as regards the choice of the program and the time and number of lessons. On the other hand, he required, not in words but in deeds, that those who followed his teaching which for the sake of brevity I will call ‘active’, did so with the same commitment and constancy. Those who could not keep up, even at a distance, were inexorably and serenely abandoned.”

A few comments on Amaldi’s recollections are appropriate. It seems clear that Fermi enjoyed having an audience for his research – his style was a public style, and in essence he was teaching as he conducted his research. A second observation is that he was tough on those around him, tougher, in fact, than those in the US would remember him being.

The members of Fermi’s team were not simply scientific collaborators, however; Fermi drew them into weekend social activities, hiking or climbing or sunning themselves by the beach at Ostia, and within a short period of time the collaborators were good friends. Their respective wives also got to know each other and the members of the team socialized actively during the 1930s. This was an essential part of the Fermi style, and carried over to his team building in Chicago a decade later.

By the early 1930s, Rome would be the center of two collaborations: Fermi’s running discussions on quantum electrodynamics (1929-1932) and the experimental work on artificial radioactivity (1934-1938).

Fermi had read Dirac’s breakthrough work on QED when it was published in 1927, and determined to make it his own. In order to do this, he discussed his thoughts with a small group – Amaldi, Majorana, Racah, Rasetti, and Segrè – as he worked through the paper to understand it thoroughly. It is not clear to what extent this audience contributed to the final product, a paper published in The Review of Modern Physics in 1932; he is listed as the sole author of that paper. In the process Fermi invented his own interpretation of Dirac’s QED; he gave some preliminary lectures on it in Paris in 1929, and then at the Ann Arbor Summer School in 1930, but only in 1932 was he sufficiently satisfied with it that he published it. The result was one of the most influential papers on early QED. In later years, Nobel Prize-winners Hans Bethe and Eugene Wigner would each pay tribute to it as the paper that taught them QED.

It is interesting to look at the make-up of this small group. Majorana and Racah were, of course, brilliant theorists. Amaldi, Rasetti, and Segrè were capable of theoretical work but their greatest strength lay in experiment work. Fermi himself was equally strong in theory and experimental work, and so provided a bridge between the two perspectives. One is struck by how carefully Fermi chose this team to help him work through QED in order to present a new version that would be easier for the average physicist to grasp. He must have believed that if he could explain it to this group of talented physicists, he fully understood it himself. Also, by explaining it to both theorists and experimentalists, he was able to achieve a result that was useful to the widest range of readers.

These discussions, and Fermi’s own independent work, by firmly establishing quantum field theory in Fermi’s mind, allowed him to use the theory to explain beta decay, which he did in late 1933. Fermi’s theory of beta decay is indeed a quantum field theory, and owes much to Dirac, but it also shows how Fermi recast Dirac’s theory so that he and his colleagues could understand it and, more importantly, use it to solve an important physics problem.

Not long after developing the theory of beta decay he learned of the Curies’ work on creating artificial radiation by bombarding elements with alpha particles. He decided to try using neutrons to get the same effect, and immediately began a series of ground-breaking experiments, first on his own, but eventually bringing in the team that became famous as the “boys of Via Panisperna”. We have met some of these individuals before: Rasetti, Segrè, and Amaldi. Added to this group were two others, a physical chemist, Oscar D’Agostino, and a young physicist who had come to the Institute only recently, Bruno Pontecorvo. Each had a particular role to play in the experiments, which took place from March 1934 onward, but the roles were somewhat flexible and people pitched in wherever help was needed. Once again, Fermi was clearly the leader – indeed, he began the project on his own, persuaded perhaps that these experiments might also shed light on beta decay – but he put himself in the thick of the experimental work, developing suitable neutron sources, exposing targets to neutrons, and measuring the induced radiation from these experiments. In October, the two youngest members of the team – Amaldi and Pontecorvo – noticed that neutron bombardment caused significantly different levels of radioactivity on a particular target (in this case, silver) depending on the medium upon which the target rested. They called Fermi’s attention to this observation and in short order Fermi developed the theory behind “slow neutrons” – the neutrons that were hitting a bit of wood before entering the target had been slowed down, and this slowing down resulted in the neutron having a higher probability of remaining inside the target nucleus and disrupting its structure. It was a famous discovery, quite unexpected, but one which obviously was made in the context of a collaborative effort.

This small team broke up soon after, with various members leaving Rome for other assignments. In the end, Fermi and Amaldi stayed on in Rome, continuing to explore the interactions of neutrons and matter. Once again, though Fermi was clearly the senior member of the team, it was a collaboration that gave Fermi the foundational insights required for his next great work, the development of the world’s first controlled nuclear chain reaction. Amaldi’s work with Fermi during this period helped prepare the younger physicist for his significant role after World War II in helping to rebuild European physics.

2 The Manhattan Project teams

Fermi left Italy for the US in December 1938, to return only for short periods in 1949 and 1954. But once in the US, he repeated his Rome experience by gathering a small group of collaborators with whom he worked, first on what was eventually to become the Manhattan Project and then, after the war, on reactor physics, particle physics, and astrophysics. He enjoyed working with others, he liked to have people around him to serve as sounding boards for ideas and as creative partners, as well. But in the US, for the first time he found himself collaborating with people who were peers – or at least who considered themselves as such.

Within a month of arriving at Columbia University, Fermi embarked on a collaboration with Hungarian refugee Leo Szilard to develop the techniques required to create a controlled, sustained nuclear chain reaction. The two principal investigators could not have been more different. Fermi was slow, methodical, and thoroughly at ease in the lab, where he thought nothing of getting his hands dirty, and expected others to do so, too. Szilard, on the other hand, was quick, brilliant, easily distracted, and abhorred the daily grind of lab work, preferring to delegate much of the work to younger physicists like Walter Zinn. At first Fermi and Szilard were direct collaborators, but they soon realized that their styles were so very different that they decided to proceed on parallel experimental tracks. Nevertheless they continued to communicate and consult extensively. For example, over the summer of 1939 they maintained an active correspondence over the right type of moderator to slow down neutrons for the optimal reaction, concluding that water absorbed too many neutrons but that graphite, properly purified, would be ideal.

Fermi took on another, younger collaborator – a newly minted PhD physicist at Columbia named Herbert Anderson. The two men met within weeks of Fermi’s arrival at Columbia, brought together by Anderson’s curiosity about the news of the discovery of fission by German scientists. Fermi would work closely with Anderson for the rest of his life. Anderson was a perfect foil for Fermi: respectful, curious, creative, and deeply devoted to their joint work. Others soon joined Fermi. Zinn came over from Szilard’s lab. Bernard Feld and Al Wattenberg, both grad students, joined the team, as did others. Eventually the team of young, dedicated physicists Fermi gathered performed the same role in supporting him as the young men of Via Panisperna had done in Rome in the 1930s.

In the spring of 1942, the team relocated to the University of Chicago, where work began in earnest to build the first nuclear reactor. Fermi came under the supervision of Nobel Prize-winner Arthur Compton, who had been chosen by Groves and Oppenheimer to lead all research into uranium. Once at Chicago, Fermi brought several key Chicago physicists into his close-knit team: Sam Allison, John Marshall, and Marshall’s wife Leona, who was the only woman on the reactor project. Eugene Wigner from Princeton also arrived, as did John Wheeler. This was a heady time for them. They were young, working on an historic project under enormous political and military pressure, and under the guidance of the world’s most knowledgeable physicist when it came to understanding how neutrons behave. By the late 1930s Fermi had developed the knack of “thinking like a neutron”, and now he was able to put this knowledge to work for his team’s effort.

The younger members of the team had never encountered Fermi and were thrilled, not only by his formidable reputation, but also by Fermi’s delight in socializing with them. Leona Marshall described her reaction this way:

“Fermi would like to show superendurance, to swim farther, to walk farther, to climb farther with less fatigue, and he usually could. In the same way he liked to win at throwing the jackknife, pitching pennies, or playing tennis, and he usually did. These qualities of gaiety and informality of his character made it easy for the young members of the laboratory to become acquainted with him. He was an amazingly comfortable companion, rarely impatient, usually calm and mildly amused.”

While he had worked with junior people since his time in Rome, this was the first time in his career that Fermi actually felt that he “reported” to a senior physicist. Of course in Rome Fermi technically reported to Corbino, and the two of them spoke all the time, but Corbino was basically content to allow Fermi to run his group as he saw fit. Compton, on the other hand, had grave wartime responsibilities and ran the Chicago team with a much firmer grip. Nevertheless, early on he came to have complete confidence in Fermi’s scientific judgment, in part because he saw Fermi at work and almost immediately understood just how much better a physicist Fermi was than anyone else on the Chicago team. When it became clear that the facility in the nearby Argonne Forest area outside Chicago would not be ready in time to meet the deadline for creating a working reactor, known as CP-1 (Chicago Pile-1) Compton wondered whether it would be safe to build the reactor on the Chicago campus. With Fermi’s assurances that it would be safe, Compton took the (in retrospect) almost unbelievable decision to authorize work underneath the stands of the disused football stadium in the exact middle of the campus. Fermi was right, of course, and December 2, 1942 is now remembered as the date on which the energy within the atomic nucleus was first harnessed.

Fermi’s Chicago team included theorists and experimentalists, several “peers” and more young people who were exposed to a truly world class mind for the first time in their careers. While the youngsters in the group had never been exposed to someone of Fermi’s stature, even those who might consider themselves Fermi’s peers could not help but be impressed. On a train ride with Fermi, Compton, a very fine physicist, explained that he had been skiing at high altitude and his watch had become unreliable. He told Fermi he had pondered on the problem for several days and had come up with physics behind this problem. He wondered if Fermi cared to solve the puzzle. With a scrap of paper and a pencil, Fermi took less than five minutes to do so, much to the amazement of the older physicist. A bit later, Luis Alvarez, a younger member of the team and a future Nobel Prize-winner, recounts that a small group was working on a problem and asked Fermi if the equations governing X-ray diffraction in solid media could be applied to neutrons. Alvarez offered to get a book from the next room that contained the X-ray diffraction equation. Fermi told him to stay put, that he would derive it from Maxwell’s Equations, which he proceeded to do in six steps. Alvarez was astonished at this performance, as were the others in the group. These seasoned professionals had never seen the level of expertise and insight that Fermi brought to bear on any given problem.

Fermi’s colleagues and collaborators enjoyed working with him not only because he was so good at what he did, and inspired people with his way of thinking, but because of his insistence on doing so much himself. He built equipment, lugged graphite bricks, climbed on detectors, and generally behaved as an equal – first among equals, perhaps, but he never pulled rank and never made younger or less distinguished colleagues feel disrespected. People collaborated with him because they enjoyed doing so, and they knew that working with him would bring out the best in them.

This is part of the reason Oppenheimer asked Fermi to join the team at Los Alamos in the summer of 1944. At that point it had become clear, owing in part to the fine work by Fermi’s student and former Rome colleague Emilio Segrè, that working with plutonium posed some difficult technical challenges. Momentum had slowed considerably, and morale on the mesa was not good. Fermi had been working with Dupont to perfect the gigantic plutonium production reactors at Hanford, Washington, not without incident – xenon-135 poisoning had shut down Reactor B – but Fermi agreed to join the Los Alamos team when Oppenheimer explained that his presence was needed to help sort out the formidable obstacles facing the project. His arrival would also boost lab morale. Fermi was brought in as a sort of physicist without- portfolio. He was to serve as a universal resource for the other scientists, the go-to person when other scientists at the top secret facility had problems they couldn’t solve. By all accounts his presence made a difference and he played an important part of overcoming many of the technical obstacles that beset the project during this last year and morale began to improve. At Los Alamos, Fermi reconnected with old friends, not only Edward Teller but also Niels Bohr and Hans Bethe, who was now the chief of the Theoretical Physics Division at Los Alamos. He also got to meet another group of younger physicists who cherished their work with him – people like Richard Feynman, who was instantly impressed, perhaps even intimidated, by Fermi’s powers of calculation and physical insight.

One specific project he took over when he arrived was the socalled “water boiler” experiments. Working with him were Herb Anderson, L. D. Percival King, and Joan Hinton. Under Fermi’s leadership they built and conducted experiments with a small, spherical nuclear reactor to measure the reactivity of increasingly concentrated solutions of uranium and water. The purpose was to help estimate the critical mass of U-235, an essential piece of information for the development of the uranium device.

Fermi’s contributions were numerous, and when the first fission test, on July 16, 1945, was successful, many felt that his work – not only at Los Alamos but at Columbia and Chicago over the prior five years – had been instrumental in the success of the project. Science historian C. P. Snow’s verdict was that Fermi was “the key man” on the project, and while the success of the Manhattan Project was truly a team effort, few made contributions as significant as did Fermi.

3 Post-war collaborations

Returning to Chicago after the war and settling into his post war roles as physicist, government advisor, and minor celebrity, Fermi kept the small group of CP-1 collaborators around him. Herb Anderson never returned to Columbia. He stayed with Fermi at Chicago and when the university’s new cyclotron, the largest yet to be built, went on line in the late 1940s the two of them, along with younger colleagues Ronald L. Martin and Darragh E. Nagle, began to explore the atomic nucleus at high energies. Their results suggested that the proton and neutron might have an internal structure, although it would take more than 20 years, and much higher energies, for that hint to bear full fruit in the discovery of quarks and gluons.

While the cyclotron was being built, Fermi kept himself busy in other collaborative efforts. He continued to do experiments with the Argonne reactor, alongside his Manhattan Project colleagues Leona Marshall and Walter Zinn, to explore how neutrons interact with matter. That was experimental work, of course, but on the theory side there were at least two significant collaborations. One was with the brilliant astrophysicist and future Nobel Laureate Subrahmanyan Chandrasekhar. The two of them spent considerable time discussing cosmic rays and came up with a theory about how these rays develop such astonishing energies as they travel through space. Fermi and Chandrasekhar believed the best explanation was that interstellar and intergalactic space was filled with large, hugely powerful magnetic fields that served to accelerate charged particle to extraordinary speeds. These particles would hit the Earth’s atmosphere with energies far greater than cyclotrons could impart to protons, potentially striking the atmosphere with far greater energy than even the biggest accelerators today can match. The universe as we know it today is far bigger, and far more complex, than we understood it to be in the early 1950s, but the Fermi-Chandrasekhar hypothesis remains one of the possible explanations for such high energy cosmic rays.

The other was with a brilliant graduate student of Edward Teller’s, Chen-Ning Yang, with whom Fermi thought about whether pi-mesons were “fundamental” particles; they considered the possibility that these particles were composed of a nucleon and an anti-nucleon. The paper arising from these discussions was prescient: we now know that a pion is a combination of a quark and an anti-quark.

The collaborations with Anderson, Leona Marshall, Chandrasekhar, and Yang were formal, resulting in published papers that were read by scholars around the world. However, Fermi found time for more informal collaborations, none more important than the collaboration with his old friend Maria Goeppert Mayer. Maria and her husband Joseph Mayer were social friends with the Fermis at Columbia in the early 1940s, and they came to Chicago after the war, becoming fixtures in the physics department. In late 1950, Fermi had become interested in the phenomenon of spin-orbit coupling and had tried to persuade his young student and colleague Richard Garwin to explore the phenomenon, but Garwin showed no interest. One day, Fermi was sitting in Maria Mayer’s office listening to her describe her struggles to make sense of the shell model of the nucleus. It occurred to him that consideration of spin-orbit coupling might be the solution to the particular problem with which she was grappling and he suggested it to her. The suggestion hit her like a bolt of lightning and she immediately understood it would solve the puzzle. A week or so later she had a fully formed theory of the nuclear shell structure, and asked Fermi to put his name on the paper as a co-author. Fermi refused, observing that she had done all the work herself and furthermore, if he put his name on the paper everyone would assume that he had really done the work and that Mayer was just along for the ride. Reluctantly she published it under her name alone. In 1963, she won the Nobel Prize in physics for that paper.

He also collaborated outside the University of Chicago, particularly at Los Alamos, where he spent summers after the war working with a small team on the possibility of a fusion weapon. When President Truman, against the advice of Oppenheimer, Fermi, and others, gave a green light to development of a fusion weapon, Fermi worked intensively on the project from 1949 to 1951. The scientists involved included his old friends Edward Teller and Hans Bethe, as well as Hungarian mathematical genius John Von Neumann and Polish mathematician Stan Ulam, with whom he developed a particularly close professional and personal relationship. Much of Fermi’s effort consisted of trying to poke holes in Teller’s various proposals for a fusion device. Fermi was joined by Ulam on this, working very closely with him during the summer of 1950. By early 1951, however, Ulam and Teller had achieved a breakthrough concept that made a fusion weapon feasible, and Fermi decided to spend his time on other matters.

Perhaps one of Fermi’s most important final collaborations, in 1953, involved Ulam and two other staff members at Los Alamos, John Pasta and Mary Tsingou. In one of the first examples of computational physics, they programmed the lab’s computer to simulate a vibrating string, introducing a non-linear equation into the mix. The result was surprising, to Fermi at least: instead of tending toward greater randomness over time, the vibrations demonstrated a complex quasi-periodicity. The paper is considered one of the first systematic explorations of chaos theory.

4 Observations on Fermi’s collaborative impulse

Much of Fermi’s most productive work involved collaborations with colleagues rather than working on his own. In Rome, he brought together a group of young physicists who learned from him, who served as his audience as he reformulated Dirac’s QED in a way to enable him to develop the theory of beta decay, and who helped him with his first experimental explorations of the atomic nucleus. In Rome, he was clearly the leader, but encouraged his youthful collaborators to participate fully in every project he undertook. He could be very demanding, but demanded no more of those young colleagues than he demanded of himself. He was careful to balance the team’s skill set, mixing theorists like Majorana with experimentalists like Segrè. He would learn by teaching and in turn they taught him by learning. It was a symbiotic set of relationships, which he cultivated and valued highly. But at no time during his Rome years did he collaborate as a peer. He would sometimes add his collaborators’ names to his publications, but there was no doubt in anyone’s mind that he was the leader of this group. Indeed the only peers he had during this period in all of Europe were a handful of theorists and experimentalists in Britain, France, and Germany. No one in Italy came close to his universal mastery of physics.

In the US, the situation was a bit different. While people like Anderson, Marshall, Feld, and others were clearly junior partners in relation to Fermi, Fermi and Szilard were on more of an equal footing. Szilard was not as revered among physicists as was Fermi, but he was three years older than Fermi, possessed a brilliant mind and had independent access to enormous resources and networks of his own. Einstein was a close personal friend of Szilard’s and the Hungarian polymath was often able to call upon high level contacts in the business community to help fund his various projects.

Other Manhattan Project collaborations were similar. His relationships with Oppenheimer and Compton were as peers. Neither was as respected as Fermi within the physics community, although Compton like Fermi was a Nobel Laureate. But in each case Fermi was respectful of the authority granted to these colleagues by the US government, authority that meant a lot to a man who was acutely aware of his alien status during the war. More of a peer in the world of physics was Wigner, who would one day win a Nobel Prize but who had already established himself as a dominant figure in the field. And after the war, his collaborations were with notable peers such as Chandrasekhar, Ulam, and Bethe.

What becomes apparent in this review is Fermi’s comfort with collaborations at all levels, and all circumstances. He loved collaborating with younger physicists because it enabled him to play the role of teacher as the collaborations progressed. He loved collaborating with older, more mature physicists because he enjoyed the interactions with minds who had thought about deep problems of physics for a long time. Striking also is the generosity with which he approached collaboration. He could have easily insisted on deference as one of the greatest physicists of all time, but he never did. Instead, he was careful to treat his colleagues with respect and generosity. The example of Maria Mayer is but one of many that could be cited. As he matured he rarely published papers under his name alone, but preferred to list co-authors in alphabetical order, a practice which sometimes left his name buried in the middle of other, less experienced names.

Why was he such an energetic collaborator, a seeker of colleagues with whom he could discover the secrets of the physical world? Two reasons come to mind. First, he genuinely enjoyed having others around him with whom he could discuss his ideas, probe their implications, and ensure that he himself understood them. He always believed – like all great teachers – that the best way to understand something is to teach it to someone else. But there is a second, equally important reason. Fermi was essentially a social person, highly gregarious, at ease in groups of friends, eager to mix socially with his work colleagues in the evenings and on weekends. The combination of a mind trained to think aloud in the presence of others, and a temperament that was fundamentally social by nature, ensured that he would work in teams for much of his professional life. His willingness to do so was no doubt bolstered by a supreme confidence in his own abilities, which led to a certain generosity of spirit, particularly in his time in the US. Once he had made a name for himself he never particularly cared about who got credit for the work of his teams. In fact, as the experience with Maria Mayer shows, he could be concerned that he might unjustly get credit for certain achievements if he lent his name to them.

We must be thankful that he worked this way. He was also extremely private in terms of his personal life, and wrote almost nothing about his life beyond physics, so it is to the writings of his collaborators, those who worked closely with him throughout his career, as well as the memoir of his wife Laura, that we turn when we try to get a three-dimensional picture of Fermi the physicist and Fermi the man. Had those who knew him well not committed their memories to paper, we would really know very little about one of the 20th century’s greatest scientists.

Acknowledgments

The author wishes to thank Francesco Guerra, Adele La Rana, and Nadia Robotti for their helpful comments on previous drafts of this paper. The author remains solely responsible for the content and for any errors herein.