CHAPTER TWENTY-SEVEN

FERMI’S LEGACY

THE STORY OF ENRICO FERMI DOES NOT END WITH HIS DEATH. The Institute for Nuclear Science, though remaining an important center for physics research, changed in subtle but important ways, reflecting the loss of its most inspirational scholar. As a family man, a husband and a father, his influence has continued for generations. Fermi’s teaching had profound and lasting impact on everyone who came into contact with him and those who studied with him went on to distinguished careers shaped in important ways by their exposure to Fermi. His scientific work set the agenda for postwar physics for decades to come.

FERMI’S DEATH HAD AN IMMEDIATE IMPACT ON THE INSTITUTE. HIS spirit had infused the place. His easy collegiality, the intensity of his passion for physics, his broad range of interest across the entire field, all defined the character of the institute and the work done there. Now Fermi would no longer walk the halls, asking people what they were up to and trying to help. Now colleagues looking for advice on how to approach a problem would no longer be able to stick their heads in his doorway and ask a quick question. Inevitably, the institution began to change.

Sam Allison stayed, as did Herb Anderson and James Franck, and together they continued the work of the institute. The young Valentine Telegdi stayed on as well, eventually becoming the Enrico Fermi Professor at the university. However, important staff members drifted away—the Marshalls, Willard Libby, Harold Urey, the Mayers, and the younger ones, like Gell-Mann and Garwin. World-class physics continued to be pursued at the institute, now named for its most famous resident, but it was never the same. Indeed, no institution could have survived such a loss intact.

THOUGH SHE BRAVELY HID IT FROM THOSE WHO VISITED DURING THE final days, Laura was shattered by her husband’s unexpected, painful death. His passing in the early morning hours of November 28, 1954, brought her relief that he was no longer suffering, but it was relief laced with sorrow. They had known each other since she was an adolescent, and their marriage, though not ideal, had been a twenty-six-year adventure. She was forty-seven years old, both children were out of the house, and she was still young enough to make a new life for herself. Although she never remarried, she certainly did make a new life, in a career she had already tried out—writing.

FIGURE 27.1. Laura Fermi the writer. Courtesy of the University of Chicago Regenstein Library, Special Collections Research Center.

The book she wrote in Rome in 1936 with Ginestra Amaldi must have whetted her appetite, because in 1953 she began work on a memoir of her marriage to Enrico. In the 1954 memoir Atoms in the Family, one immediately recognizes a distinctive voice, comfortable with the English language and slightly arch in her pithy and sometimes hilarious observations about the people she met during her marriage. She could not have known that the timing of the book’s release, in the last month of Enrico’s life, would be commercially providential. His illness is mentioned nowhere in the book, but his death helped sell it. She knew that Enrico was enormously proud of the book, and its reception encouraged her to write subsequent books on a variety of subjects: the peaceful uses of atomic energy (Atoms for the World, 1957, and The Story of Atomic Energy, 1961); the rise and fall of Benito Mussolini (Mussolini, 1961); Galileo’s contribution to world science (Galileo and the Scientific Revolution, 1961, with Gilberto Bernardini); and the influx of talented and important immigrants to the United States (Illustrious Immigrants, 1968). She even drafted an unpublished novel about the women of Los Alamos and was at work on a study of women in the Italian Renaissance when she passed away. She never claimed to be a scholar, but she was proud of her efforts writing popular history and science with a clear voice and strong insights.

She eventually moved to an apartment by the lake, but she remained active in the Hyde Park community for many years, helping to establish the Cleaner Air Committee of Chicago, which fought the use of coal for heating that had led to dangerous levels of air pollution in the city. She also championed restrictions on the sale of handguns in Chicago through an organization called the Civic Disarmament Committee. Leona Libby recalls Laura’s involvement in an anti–nuclear power campaign in California, in support of her old friend Frieda Urey. Laura kept up with the circle of friends she made with Enrico and also took part in commemorations and tributes, far and wide. As a frail sixty-six-year-old, she attended the dedication of Fermilab in suburban Chicago in May 1974. It must have moved her that the largest physics lab in the country was named after her late husband.

She traveled often to Italy to see her family and old friends, particularly the Amaldis. But she never returned permanently to her native land. She missed her homeland terribly and continued to find the “immense plains” of the United States too empty for her liking. She wondered, in 1954, if she would ever be “Americanized.” Yet Chicago was her new home and there she remained. There must have been something too compelling about the United States to leave it and return home. Perhaps it was the openness of the culture, the dynamism of the society, or even the fact that she had become herself a bit of a celebrity in her new land.

At the age of seventy she succumbed to pulmonary congestion and died the day after Christmas in 1977. Buried like her husband in Chicago’s Oak Woods Cemetery, her gravestone bears the single word Writer inscribed below her name and the years of her life. She may not have chosen that epitaph herself—Nella coordinated everything relating to the burial—but it was almost certainly the way she wanted to be remembered, the role of which she was most proud.

There is, however, one aspect of her burial that is somewhat unconventional. The issue dates back to when Enrico died in 1954. At that time the family chose a plot between two existing graves, with no room for Laura. It would have been easy enough to buy a double plot, as most married couples do. When Laura passed away, the family chose to inter her in a plot some three hundred yards from Enrico’s. The urge to jump to a conclusion that it reflects something dark about their marriage is strong, but perhaps should be resisted. More likely neither Laura nor Enrico thought very much at all about where they were to be buried, nor cared. Or perhaps having lived in Enrico’s shadow during his life, in death she and her surviving family members wanted to emphasize Laura’s independent life.

Enrico’s sister Maria outlived him, but not by much. She spent most of her life in the house built by her father in Via Monginevro, having been widowed early by the death of her husband, Renato Sacchetti, who died of influenza. She had three children—Gabriella, Giorgio, and Ida—and was in regular correspondence with Laura after Enrico’s death. She died in a plane crash on June 26, 1959, on her way to a conference on contemporary Italian literature to which Laura had invited her. She is buried in the cemetery in the village of Olgiate Olona, just northwest of Milan, where the aircraft went down—apparently according to wishes she had previously expressed to be buried where she died.

When her father died, Nella was already in her early twenties, a recent graduate of the University of Chicago. She went on to marry and raise two children, Alice and Paul. She received a Master of Fine Arts degree and taught art for many years at the Lab School, which she had attended as a child. Intellectually curious, she also went on to earn a PhD in educational psychology with a thesis entitled “Baby Bust and Baby Boom: A Study of Family Size in a Group of University of Chicago Family Wives, 1900–1934.” In later years she pursued a certification in financial planning and made a new career in this field.

In an interview conducted for a CBS documentary in the early 1990s, she talked about her life with her famous parents and how it took her until the age of forty-five to come to terms with her father’s fame. Nella regretted not reverting to the family name when she divorced her husband, Milton Weiner, in 1965. For her, Los Alamos was a great adventure, but she confessed to an irrational sense of guilt for the bombings of Hiroshima and Nagasaki. She also understood the complexities of the moral dilemma faced by her father and his colleagues as they worked to design and build the terrible weapon.

Nella’s daughter Alice (who later changed her name to Olivia Fermi) remained close to her grandmother Laura. In her last years, Nella would urge Olivia to “Put your grandmother Laura first, ahead of Enrico.” The words are somewhat opaque, but we can guess at their meaning: Enrico was a star that the world would remember and it was important to foster Laura’s legacy. Nella felt Laura was important in her own right and was unjustly overshadowed by her husband.

Nella contributed to a commemorative event organized at Cornell by Jay Orear in 1991, regaling the audience with anecdotes of her childhood with her father. She died in 1995, a victim of lung cancer. By this time, she had made peace with her father’s fame and role in the history of science and was comfortable speaking publicly about him and about their relationship.

Giulio had a harder time of it. He never felt comfortable living in his father’s shadow and did what he could to distance himself from Enrico. In his adolescence he changed his name to Judd and used an American pronunciation of his last name, “FIR-mee” rather than “FAIR-mee,” rarely speaking of his famous father. He chose not to pursue physics, although he had the innate ability to do so. Instead, he pursued a rarified program in pure mathematics, leaving Oberlin early for a mathematics PhD at Princeton. His Oberlin friend Robert Fuller joined him there. After Princeton Judd did a post-doc at Berkeley, where he met and married Sarah Duncan Pietsch, an artist and a literary scholar. They moved to Washington, DC, where Judd held a position at the Institute for Defense Analysis, a distinguished defense policy think tank, for a decade. He eventually became bored in Washington and took a position working in the lab of Nobel Prize winner Max Perutz at Cambridge University, where he developed mathematical models of complex proteins. The severe depression of his adolescence never returned, but he was a quiet and shy man, who actively withdrew from the limelight, happy to contribute to the work of others, but with little interest in generating his own projects. A heavy smoker, he died of a heart attack in 1995 at the age of sixty. His health problems may have been aggravated by the stress he felt when the British government insisted that researchers at government-funded science labs present research projects of their own or else find new work.

Whereas Nella resembled her father, Judd had a greater resemblance to his mother, although his eyes were Enrico’s—hazel gray and, for those who knew Enrico, very familiar. Richard Garwin recalls lecturing at Cambridge in the 1980s and noticing someone in the audience who reminded him of Fermi. The eyes, he thought, were unmistakable. It was Judd, who afterward introduced himself as Enrico’s son, much to Garwin’s astonishment and pleasure.

Of the following generation, Nella’s daughter, Olivia, and Judd’s daughter, Rachel, have been most publicly involved with their grandparents’ legacy. A psychotherapist living in Vancouver, Olivia has embraced the family history. She has two blogs—one about the Fermi family and another about nuclear policy issues. Rachel pursued a career in photography and fine arts but also embraced her grandfather’s legacy. In 1995, she produced a comprehensive photographic history of the Manhattan Project, Picturing the Bomb, with coauthor Esther Samra. She lives in the north of Scotland with her artist husband and their family.

For both Olivia and Rachel, Laura looms large in childhood memories. Neither had been born when Enrico died, so they know him only through family anecdotes passed down by their grandmother and their parents. Yet the legacy of the Manhattan Project fascinates and disturbs them. For this generation of Fermis, Fermi-Dirac statistics, beta decay, and pion-nucleon scattering all take second place to their grandfather’s work on the atomic bomb.

AFTER HIS DEATH, FERMI’S CELEBRITY PROMPTED THE USE OF HIS name to commemorate him in any number of ways. The Chicago institute now bears his name, as does the huge national laboratory built in the early 1970s fifty miles west of the city. A space telescope designed to focus on gamma-ray sources in deep space is called the Fermi Telescope. Nuclear reactors in the United States and in Italy are named after him. Countless towns in Italy have streets and plazas named after him. Train stations in Rome and Turin bear his name.

Among all these tributes he would probably be most proud of the prize bearing his name that the US AEC awards annually, first granted to Fermi on his deathbed. The US Department of Energy describes it in the following terms:

The Fermi Award is a Presidential award and is one of the oldest and most prestigious science and technology honors bestowed by the U.S. Government. The Enrico Fermi Award is given to encourage excellence in research in energy science and technology benefiting mankind; to recognize scientists, engineers, and science policymakers who have given unstintingly over their careers to advance energy science and technology; and to inspire people of all ages through the examples of Enrico Fermi, and the Fermi Award laureates who followed in his footsteps, to explore new scientific and technological horizons.

Recipients of this honor include an impressive array of men and women in science: in chronological order, von Neumann, Lawrence, Wigner, Seaborg, Bethe, and Teller were the first recipients, beginning in 1956. The award of the prize to Oppenheimer in 1963 was widely seen as an act of contrition by the US government for the way it treated him in 1954. The award of the prize to the trio of scientists who discovered fission—Hahn, Meitner, and Strassman—in 1966 was a belated recognition of Meitner’s crucial contribution to the discovery. More recently, Wheeler, Zinn, Bradbury, Agnew, Peierls, Anderson, Alvarez, Weisskopf, Garwin, and Rosenfeld have all received the prize named after their friend and mentor, as have many other luminaries. Many consider it the highest honor they have received.

Several tributes by friends and colleagues are particularly noteworthy. In addition to the warm 1955 recorded tribute, To Fermi with Love, the mid-1960s saw the production of a full-length documentary, The World of Enrico Fermi. One of the most eminent science historians, Harvard’s Gerald Holton, brought the project together with the help of the Canadian National Broadcasting Company. Dozens of colleagues and friends, as well as Laura, discuss Fermi’s life.

One of the most lasting and beautiful of the tributes to Fermi was the development and publication, in two volumes, by the University of Chicago Press in collaboration with the Accademia dei Lincei in Rome, of The Collected Papers. The organizing team of Amaldi, Anderson, Persico, Rasetti, Segrè, Cyril Smith, and Wattenberg, with Laura’s active participation, reset every journal paper and article in beautiful typeface and provided valuable introductions to many of the major papers in the volumes. In a predigital world, culling all the papers, deciding which papers were sufficiently important for inclusion, and ensuring that nothing of importance was missing was an enormous undertaking. There are some 270 papers in all, as well as a brief biography written by Segrè and several useful appendices, including a list of his many honors and a chronology of his life. It should not be considered a complete set of his work, however, because some of his important papers and lectures were only subsequently declassified, but it was as comprehensive as possible at the time.

And then there are his scientific legacies, including discoveries related to the weak interaction, the strong interaction, Fermi-Dirac statistics, and computational physics.

THE WEAK INTERACTION HAS BEEN A RICH SOURCE OF DISCOVERIES. Neutrino physics is an enormous field in itself, and the research into the weak interaction had dominated much of particle physics, resulting in more than a dozen Nobel Prizes, including the recent discovery of the Higgs boson. Most interesting, perhaps, is the deep connection between the weak interaction and the electromagnetic interaction first posited by Sheldon Glashow, Mohammad Abdus-Salaam, and Steven Weinberg, a first step in the pursuit of one of physics’ holy grails, the unification of all forces. For this work they shared the 1979 Nobel Prize.

Since Fermi’s passing, the exploration of the strong force holding the atomic nucleus together has had an equally distinguished history. Fermi’s pion scattering experiments led the way to further discoveries about the force that holds the nucleus together. Ultimately, this has resulted in the “quark” theory of matter, first proposed by Fermi’s Chicago colleague Murray Gell-Mann. Quarks are the fundamental building blocks of neutrons, protons, pions, and many other subatomic particles. Quarks are bound to each other by bosons that physicists call “gluons.” The interaction between quarks and gluons defines the strong interaction that holds these particles, and the nucleus itself, together. Fermi’s early pion work was the first step in this direction, and the quark theory, together with our understanding of the electro-weak interaction, constitutes a synthesis called the “Standard Model” of particle physics. The Standard Model explains a lot of the observable world, but it leaves many questions unanswered, questions with which theorists and experimentalists still grapple.

What might Fermi have accomplished if he had lived longer? It is difficult to say. He understood the complexity of the results from his pion scattering experiments in 1951 and 1952, but what he made of it is a different matter altogether. Subsequent advances in organizing and understanding the elementary particle “zoo” relied on group theory. Never a fan of group theory, he learned only as much as he needed to understand the quantum theory work of von Neumann and Weil. It is hard to imagine him willingly diving into group theory in the way required to have come up with the quark theory. Yet doing so may have been more important to him than, say, the QED renormalization completed by others so successfully in the late 1940s. If he decided a problem was sufficiently important, he would invest the time required to solve it, as he did with beta decay.

He was, at heart, a conservative physicist and would have felt uncomfortable with some of the early revelations regarding the weak interaction, particularly the completely unpredicted and revolutionary discovery in 1956, by his former students Lee and Yang, that it did not obey the rules of mirror-image symmetry. In looking to solve specific problems, Fermi rarely if ever chose revolutionary approaches. Yet he certainly would have been fascinated by the theoretical work and the experimental discoveries exploring the weak interaction and would have been an active participant in neutrino physics.

A MORE STRAIGHTFORWARD LEGACY IS THAT OF THE FERMI-DIRAC statistics.

Unlike the beta decay paper (not precisely correct) and the pion experiments (suggestive, but only a stepping stone to our understanding of the strong force), Fermi-Dirac statistics are as valid today as they were when first developed in late 1925 and early 1926. Any analysis of the energy distribution within a system of particles that obey the exclusion principle—gas, liquid, solid, or plasma—involves Fermi-Dirac statistics. In the words of physicist Henry Frisch, if we did not have Fermi-Dirac statistics, physics would be “in the stone age.” The use of Fermi-Dirac statistics is so universal and pervasive across different fields of physics that it is virtually meaningless to give examples. There will always be a debate about which of Fermi’s contributions to physics is his greatest, but those who favor Fermi-Dirac statistics point to the fact that it is still used the way Fermi presented it to the world in 1926.

WHEN FERMI FIRST BEGAN USING COMPUTERS, HE WAS INTERESTED in simulating physical processes. The computers were primitive and only the simplest of problems could be represented in a program. Analysis of data generated by detectors was all done by hand and eye.

Fermi would not recognize the world of computational physics today.

Computer simulations have become an essential part of any hypothesis testing in particle physics and of predicting the outcome of any given experiment. Computers also sift through petabytes of data generated by complex electronic detectors, looking for key signatures that indicate the presence or absence of a specific interaction. Computational physics has become a field of its own; most physicists are familiar with its techniques and some physicists specialize in it as a subfield. The discovery of the Higgs boson would have been impossible without advanced computational techniques. They are also central to many other physics specialties, for example astrophysics, where computational advances have enabled the modeling of complex processes involved in phenomena such as supernovae or the Big Bang.

Perhaps more interestingly, the Monte Carlo simulation techniques Fermi helped to pioneer, even prior to the invention of the electronic computer, are used wherever systematic simulations can shed light on solutions to complex problems, ranging from engineering and genetics to defense policy and nuclear strategy to finance and economics, even to law and social policy. They have been used to explore whether Joe DiMaggio’s fifty-six-game hitting streak should be considered an intrinsically rare event. Reflecting the essence of Fermi’s unique way of thinking about problems, the Monte Carlo technique is perhaps the single most important area where Fermi’s direct influence can be felt in the world outside physics.

IN ITALY, FERMI’S LEGACY WAS CHAMPIONED BY EDOARDO AMALDI. He directed the physics program in Rome and supported Bernardini’s plans to build a cyclotron in Frascatti, a Roman suburb. He fostered interest in the field by continuing to edit and update Fermi’s textbook for high schools. Edoardo also played a central role in pan-European physics, including the creation of CERN and the European Space Agency. Dismayed by the gulf that secrecy created between him and his old teacher and friend, he wrote bylaws prohibiting CERN from engaging in classified research. Fermi could not have wished for a better keeper of the flame.

The museum of physics at the University of Rome’s department of physics keeps the memory of Fermi alive among young people there, and Via Panisperna, under the auspices of the Italian Physics Society, is being converted to another museum, planned for completion in 2018. It will enable a new generation of Italians to wander the halls where Fermi launched the Rome School, where he conducted classes and seminars, and where he first bombarded uranium with slow neutrons.

The summer school in Varenna, named after Fermi, continues. The Italian Physics Society presents an annual prize, also named after him, to major figures in Italian physics and, more recently, to non-Italians as well.

The centenary of Fermi’s birth gave rise to major celebrations throughout Italy, resulting in some of the best commemorative volumes devoted to his life and work. Italian historians continue to illuminate aspects of his life and work, often providing a useful corrective to received wisdom.

After Fermi’s death, Amaldi shipped Fermi’s notebooks and other archives to the Domus Galilaeana in Pisa, convinced they belonged alongside Galileo’s archives. In so doing, he demonstrated the esteem with which Fermi’s fellow countrymen viewed him. Sixty-odd years later, it is a decision that few would second guess.

THE TWO LEGACIES STEMMING FROM FERMI’S MANHATTAN PROJECT work—the atomic bomb and the nuclear reactor—are perhaps more difficult to evaluate clearly today.

The legacy of the use of nuclear weapons is, not surprisingly, greatest in Japan, two of whose cities were obliterated by these weapons. More than two hundred thousand people perished in these attacks, and Japan has been in the forefront of the anti-nuclear movement. In 2016, President Obama became the first US leader to visit these cities, paying tribute to those who died. In response, Japanese Prime Minister Abe became the first Japanese leader to visit Pearl Harbor. Memories linger, even if enmities do not.

Over the past seventy years, at least eight other countries have learned the secret behind building nuclear weapons. Fermi understood that if it proved possible to make such a weapon, other countries would eventually do so. He had a pessimistic view of human nature and assumed that people would eventually use whatever weapons were available to prosecute warfare. Fortunately, he has been wrong, at least until now. Aside from the initial use against Japan, no nation has used nuclear weapons against another. But as Fermi would surely have agreed, there is no law of physics preventing this from ever happening again.

Aboveground nuclear testing was frequent in the 1950s and early 1960s, leading to an ever-higher level of ambient radiation around the world. As a 2009 report of the Centers for Disease Control and Prevention made clear, even the first nuclear test at Trinity site had unintended, catastrophic fallout effects on local populations, livestock, and farming. Later on, trace levels of radioactive isotopes like strontium 90 found in food and milk throughout the country led to a wave of public health concern. Though aboveground tests have ceased, we live in an environment contaminated by the radioactive residue of these tests, residue that will last for centuries.

The prospect of all-out thermonuclear conflict has receded, owing largely to the end of the Cold War, but the threats of nuclear proliferation and nuclear terrorism loom larger today than in years past. North Korea increasingly rattles a nuclear saber in its fraught dealings with its neighbor to the south, as well as with the United States. Terrorism remains a serious threat. Some nuclear powers are host to active insurgent movements, and nuclear security is almost certainly not as tight as one would wish. The capture of even one nuclear weapon by an insurgent group bent on terror would be catastrophic. Policy analysts barely considered such possibilities when Fermi was alive. Today they dominate national security thinking.

Is this state of affairs truly a legacy of Enrico Fermi? If Fermi had perished somewhere in the Atlantic during the voyage on the Franconia over New Year’s 1938–1939, the Manhattan Project would have eventually moved forward, perhaps more slowly and certainly in different ways. Facing the situation they did, US political leaders decided to go ahead with the Manhattan Project, a decision neither surprising nor obviously evil. The decisions surrounding the use of the bomb in the wake of Germany’s surrender were made at the highest level, with only cursory attention paid to the views of scientists. President Truman knew that he alone bore responsibility for the decision to use these weapons against enemy cities.

This is not to let Fermi or his colleagues “off the hook” in any sense. For better or worse, they changed the future for us all. The Manhattan Project scientists have, however, assumed a greater burden of guilt than they deserve. If history is to judge Fermi and his colleagues for their wartime work, it should be with a more nuanced perspective that appreciates the situation they faced and their motivations for participating.

The other great legacy of that wartime project is the nuclear reactor. Fermi may not have invented the atomic bomb, but he and Szilard most certainly did invent the nuclear reactor. Some 450 electric power reactors operate worldwide, with 60 more under construction. About one hundred are in the United States. However, only five US reactors have come on line since 1990. The decline in the use of nuclear power in the United States and elsewhere is mainly the result of high-profile nuclear accidents around the world, including those at Three Mile Island in 1979, Chernobyl in 1986, and the 2011 accident at Fukushima. These three notorious accidents, spread out over a period of three decades, have done as much as anything to kill the prospects of nuclear energy in the United States. Yet the technology advances. Engineers at Argonne Lab, Fermi’s old stomping ground, have designed modern fast breeder reactors that produce fuel as they consume it. An initial load of fuel could, in principle, last one thousand years and produces no greenhouse gases at all. South Korea, where the nuclear allergy is less severe, is in the process of building such reactors in consultation with Argonne engineers. The future of nuclear energy in the United States is uncertain at best. Whether future generations of Americans will reconsider the option of pursuing safe nuclear energy remains to be seen.

Reactors have purposes other than providing nuclear energy. They provide the main way modern medical radioisotopes are created. Corbino was prescient. He understood the commercial value of the slow-neutron discovery for medical purposes. He never anticipated, however, that his greatest student would invent a virtual radioisotope factory. By irradiating specific elements inside research reactors, medical physicists create substances that can be used to trace the presence of cancer as well as to treat cancer once it is found. Countless lives have been saved through these techniques. More than a dozen research centers around the world produce these isotopes in reactors that can trace their lineage directly to those dusty piles of graphite and uranium that rose up from the floor in the basement of Schermerhorn Hall at Columbia and the squash court at Stagg Field at Chicago, under the watchful eye of Enrico Fermi.

FERMI’S PATH TO GREATNESS DIFFERED FROM THAT OF EINSTEIN, Bohr, Planck, or any of the others who created modern physics. It started from a profound confidence that he could solve any problem thrown his way and that nature would ultimately disclose her most precious secrets to his probing mind. That confidence was based on an incredibly solid foundation of knowledge laid down early in his life through intense and disciplined effort, under the guidance of mentors and professors who understood and cultivated his greatness. He understood that there were no shortcuts to deep understanding and was willing to make a radical commitment to gain that understanding.

The sturdy foundation of his knowledge informed his taste in the types of problems he studied. He had an unerring instinct for the “next big thing,” and the decisions he made about his own research agenda set the agenda for the field at large. This instinct led him to focus on the way in which the exclusion principle could be integrated into statistical mechanics. It then led him to focus on solving the beta decay crisis using quantum field theory. Next it led him to neutron experiments that would open up the field of nuclear physics. Finally, he understood that an accelerator that could produce beams of high-energy pions could be used to explore the nature of the strong force. That superb instinct, married to a foundation in the basics second to none, produced a wealth of lasting achievements.

He also believed that anyone could learn what he knew. He believed this quite literally and lived his life devoted to that belief. In the process of digesting physics in his own way so that those around him could grasp it, he developed a technique of stripping problems to their bare essentials and leading his students through step-by-step solutions, ignoring complexities that would obscure the essence of the problems. This conviction ensured that the way he thought about physics influenced future generations of physicists.

A constant theme throughout his career was the central role of probability and chance in his analytic framework. He became a deep student of probability early on, driven perhaps by the loss of his brother, a low-probability event with profound personal consequences. In the world of quantum theory all physicists must understand probability, but Fermi placed it front and center in his research, returning to it time and again—in the Fermi-Dirac statistics, in the Thomas-Fermi model of the atom, in his pen-and-paper analysis of neutron diffusion, and in his pioneering use of Monte Carlo methods to simulate physics problems. The Fermi Paradox—the conclusion that if life existed elsewhere in the universe, they should have visited us by now—is a classic example of how he could break down almost any problem into a series of probabilistic assumptions.

He sacrificed much for physics. He was willing to compromise his political beliefs in exchange for the freedom to pursue physics without interference. He was willing to put his family life second to his career, with unhappy consequences. He may even have sacrificed his life, if we believe that his exposure to radiation had any relationship to his ultimate demise.

Confidence born of innate ability and a strong foundation, a firm belief in his ability to solve any problem, an instinct for important research, an unshakeable faith in his ability to make others understand, a fascination with the role of probability and chance at the core of how the world works, the willingness to make enormous sacrifices for science—all these made Fermi who he was and contributed to his ability to make a lasting impact. Like all of us, however, scientists are prisoners of the era into which they are born. To have had the impact of Einstein, it helped to be born during a period when some of the deepest problems of physics had come to the fore. If Einstein had been born a century earlier, he may have achieved much, but certainly nothing of the magnitude of general relativity. It was Fermi’s great good fortune to have been born during a period in which the quantum revolution was unfolding.

And yet that great good fortune had a darker side. As Fermi realized when he was young, one implication of the twentieth-century revolutions in physics was the enormous energy locked inside matter, energy that could blow to smithereens the first physicist to unleash it. He could hardly have realized that it would be his fate to be that first physicist. If every great gift has a price to be paid for it, this was certainly a major one: the field he loved, and pursued with such passion for his entire adult life, uncovered a secret of nature that gave man the ability to destroy the world. Another price was one with which other driven professionals are familiar: the neglect of family relationships in pursuit of compelling career objectives. In many ways Fermi paid for his great gift, but this was an inevitable cost of that gift and the time in which he lived.

GEOFFREY CHEW AND UGO AMALDI HAVE BOTH DESCRIBED Fermi AS “the last man who knew everything.” Obviously, he did not know everything. His knowledge of science beyond physics was superficial, and his knowledge of history, literature, art, music, and much else besides was limited, to say the least. He was not a universal genius.

He did, however, know everything about physics. In his day that was rare enough. Chandrasekhar marveled that Fermi, with no prior background in astrophysics, could jump into the field relatively late in life and make significant contributions. He should not have been surprised. Fermi loved all aspects of physics and he lived at a time—perhaps the last time—when it was possible for someone with the proper background and innate ability to master all of physics. Fermi did so, not only across all subdisciplines of the field—astrophysics, nuclear physics, particle physics, condensed matter physics, even geophysics—but across theory and experiment. In this, he was truly unique. He saw physics as an integrated whole, comprehensible through a handful of powerful analytical tools he worked hard to master. Today physicists rarely talk across subdisciplines, and when they do they have increasing difficulty understanding each other. Even in Fermi’s day, theorists and experimentalists had trouble seeing the world from each other’s perspective. Today the problem is compounded by the magnitude and complexity of experiments and the increasingly sophisticated mathematics involved in cutting-edge theory. To be a world-class researcher in any subdiscipline today requires enormous commitment. A particle physics experiment might take a decade or more to conduct and involve many thousands of physicists, none of whom would have the time to explore other areas of physics, however motivated they might be. This problem is true for every subdiscipline of the field.

Fermi was certainly the last man who knew everything about physics, the study of matter, energy, time, and their relationships—the way the physical world works. He knew everything about how the physical world worked across subdisciplines and across theory and experiment as far as physicists were able to know these things during his lifetime. Our knowledge has evolved since he died, shaped by theory and experiment in ways that would have delighted Fermi had he lived. Even so, for one person to master all the physics of his day was a unique achievement. We may never see another like him.