ANYONE WHO DID physics before the discovery of fission could remember what that world was like. Pre-fission physics was a beautiful, intimate subject that simmered with purpose. It was attractive, awe-inspiring, and deeply satisfying. Physicists worked in an atmosphere of intellectual and emotional excitement. Things were new, there were surprises, they were turning corners. Physics had no object other than satisfying the human spirit of intellectual adventure. Through every experiment and theory coursed an aesthetic pleasure and the moral uplift of pursuing the truth. More than other scientists, physicists prided themselves that their science did not have any practical use.
Physics was a personal undertaking. A physicist enjoyed autonomy. He chose what work to do. His subject for research was his own. Physicists viewed their work as a calling, as an enlargement of their lives, not just as a career. It meant something to them personally, in the same sense that art or literature did to others. The study of physics was noble, enlightening, and constructive, a model of how life should be lived. And the scientific method was an anchor of predictability and precision in a chaotic and uncertain world. Nature was profound, yet its secrets could be unlocked. The joy of insight, physicist Victor Weisskopf once said, was “a sense of involvement and awe, the elated state of mind that you achieve when you have grasped some essential point. It [was] akin to what you feel on top of a mountain after a hard climb or when you hear a great work of music.” 1
Just as physics existed outside of political and moral concerns, physicists lived on a plane above the nation-state. They eschewed politics; they shunned chauvinism and racism (though not, in many cases, sexism); they preferred cooperation and collaboration. They were cosmopolitan. Language posed no barrier because facts and concepts were communicated by mathematics. Steeped in a common culture of rationalism and humanism, they believed there was one supreme reward for their work: the sense of sharing in the building of knowledge. From this idealism, physicists derived the belief that their true identity was not as a member of a nation or a class but as scientific searchers speaking to other searchers. They believed physics could flourish only in an atmosphere of openness and freedom.
The personal ties among physicists were extraordinarily warm and close. Indeed, they were attracted to the discipline in part because each of them enjoyed being engaged in a collective enterprise. The community was small enough, and intimate enough, that everyone knew everyone else. They all hungrily read the latest scientific journals, but they learned more from talking among themselves, and when not together they communicated constantly by mail and telegram. A physicist could do his work in any country; and when he published the results of his work, they were read all over the world.
It was a time of great opportunity and optimism for all of the sciences, but physicists sensed it was an especially fertile moment and harbored grand expectations of discoveries to come. Nuclear physics, especially, was a beehive of exuberant creativity. The powerful new theory of quantum mechanics, developed by Werner Heisenberg, Pascual Jordan, and Paul Dirac in the 1920s, had given the structure and behavior of the atom a mathematical base. Excitement grew as physicists applied the analytical force of quantum mechanics to a wide variety of physical problems. The theory was such a departure from approaches of the past and shed so much new light that it was as if explorers lost in the desert had been given a map, compass, and water.
Curious, intelligent, and ambitious, physicists journeyed from one research center to another in Europe: Berlin, Cambridge, Copenhagen, Göttingen, Hamburg, Leipzig, Leyden, Munich, Rome, Zurich. A physicist simply decided where he wanted to go and showed up there, unannounced, to witness discoveries and learn insights that excited and inspired him. In 1927 I.I. Rabi spent several weeks at the Cavendish Laboratory at Cambridge observing the work of Ernest Rutherford, then went on to Copenhagen, where Niels Bohr had his Institute for Theoretical Physics. When Rabi arrived in Copenhagen, he walked to the institute, rang the bell, and said to the secretary who answered the door, “My name is Rabi; I’ve come to work here.” 2 In this informal way, physicists learned new experimental techniques, absorbed new ideas, and made new friends.
This mixing of people and ideas brought European and American physicists into close contact with one another. The peregrinations of one physicist, Hans Bethe, illustrate how the process worked. Funded by a Rockefeller Foundation Fellowship in 1931–1932—which bestowed a generous stipend during the hard times of the Depression — Bethe traveled first to the Cavendish, then to Rome to study with Fermi. Bethe had been a graduate student at Munich in 1927 when Rabi spent the summer there. While in Europe, Rabi met Robert Oppenheimer and Edward Teller. Rabi and Oppenheimer formed a bond of friendship that grew stronger with the passing years. (Between each of them and Teller, however, existed a subtle friction that would later become the stuff of high drama.)
These transatlantic relationships were cemented through guest lectureships at American universities by distinguished European physicists such as Bohr; pilgrimages that young American physicists made to the great European centers of physics; the prestigious Solvay Conference held in Brussels, where the world’s top physicists gathered annually; meetings of the American Physical Society at the National Bureau of Standards in Washington, D.C.; and a summer symposium on theory at the University of Michigan, attended by such rising stars as Bethe and Fermi. Through such personal contacts, a powerful network formed.
As things were, no one had the time to do it all himself. But these close international links stimulated the interplay of ideas, producing one of the most creative atmospheres that had ever existed in physics. Physicists seemed to know when someone was doing interesting work, and almost every idea occurred to several scientists simultaneously. Physics attained a richness and variety of approach — and most important, an expansion of knowledge — that it never would have attained if it had been the work of isolated scientists. It was an immensely exciting time. Few noticed the shadows and thunder in the distance.
When the Nazi attacks on academics came, they initially affected the humanities more than the sciences. The exchange between a professor of physics and a professor of literature at the University of Stuttgart in 1932 captured the mood of academics in Nazism’s early days. “Well, Herr Pongs, how are you?” the physicist Paul Ewald asked. “How should I be?” the literature professor answered. “I’m not a physicist. We have to ‘relearn’ our entire field, looking upon everything ‘unter dem Evoelkischen Gesichtspunkt’ [under the racial point of view].” “I really pity you,” said Ewald. 3
Yet if physicists lived under the illusion that politics would never reach into the isolated realm of physics, it did not last for long. Shortly after Hitler came to power, the Nazis issued an edict that the greeting Guten Tag (good day) be replaced by Heil Hitler! Jewish physicists saw their academic colleagues ridicule the edict at first. Then their colleagues began making a sloppy Hitler salute, and gradually it became more formal. After a while their colleagues started crossing the street to avoid greeting them. Physicists were no longer able to keep politics at bay.
The university community was changing, too. Studenten Verbindungen (fraternities) were increasingly nationalistic and anti-Semitic—foreshadowing the growing Nazi movement that would come to power in a few years. Members of these fraternities spent their free time roaming the streets, where they could be heard howling anti-Jewish slogans late into the night. They regularly searched out and beat up Jewish students or those who looked Jewish. Before long, Jewish physicists became one of their favorite targets because physics was so dominated by Jews. Such insults and coercion were part of the Nazis’ plan to “free” German education from the Jews’ “destructive yoke.” The Nazi Party took control of universities and appointed dozentenschaftsfuerhers (faculty leaders) who would assemble physics professors and lecture them that there was no such thing as “objective” science, that science was an outcome of “national feeling.” A vise was slowly closing.
The vituperation of Nazi academics toward Jewish physicists became increasingly aggressive and outlandish. “German physics?” asked Herr Lenard of Heidelberg University. “‘But,’ it will be replied, ‘science is and remains international.’ It is false. In reality, science, like every other human product, is racial and conditioned by blood.” Herr Tomaschek of Dresden’s Physics Institute went further. “Modern physics,” he wrote, “is an instrument of [world] Jewry for the destruction of Nordic science…. True physics is the creation of the German spirit…. In fact, all European science is the fruit of Aryan, or, better, German thought.” And then there was Herr Mueller of Aachen’s Technical College, who in a book titled Jewry and Science described a worldwide Jewish plot to pollute science and thereby destroy civilization. 4
American physicists had an inside view of the tragedy befalling Jewish physicists in Germany. The physics grapevine carried vivid accounts of Nazi persecution, dramatic stories of hasty departures, and desperate inquiries about faculty positions outside of Germany. “We have been three days in Göttingen and the rest in Berlin, and had time to see and appreciate the effects of the present German madness,” wrote one American physicist to a colleague back home. “It is simply horrible. In Göttingen, it is quite obvious that if these [Nazis] continue for only two more years (which is unfortunately very probable), they will ruin German science for a generation—at least.” Hitler didn’t care. He reportedly said: “If the dismissal of Jewish scientists means the annihilation of contemporary German science, then we shall do without science for a few years.” 5 (The irony of fate is that Hitler’s actions removed the one group of people who would have been able to provide him with the instrument for the world dominance he so eagerly sought.)
One result of all this was the exodus of the cream of European physicists, the prominent and the promising alike. Eleven Nobel laureates in physics left Germany in 1933 alone; one was Albert Einstein. They could not yet imagine the evil of the Holocaust and it was not German anti-Semitism per se that drove most of them away; they had long been used to subtle prejudice in Germany and elsewhere. Instead, it was more the fear, the expectation—almost the certainty—that the Nazis would get into a war and that the physicists caught in Germany would have to work for Hitler. That idea was too much.
These years and exile did not destroy the physicists’ intellectual and emotional bonds to the best of German culture, which was deeply ingrained in their thinking and feeling, but did profoundly, personally demonstrate to them that unfathomable evil could take hold of a civilized society. They had gone into physics to escape, and now they had to escape to do physics. And it was still not clear whether they had escaped the hangman’s noose, or whether the rope had just temporarily loosened.
Leo Szilard lived on the edge of the maelstrom as a researcher in nuclear physics at the Kaiser Wilhelm Institute in the Berlin suburb of Dahlem. A brilliant, sensitive, and intuitive genius who imagined things no one else had imagined before—and could peer into the future as few others could—Szilard was in Dahlem when Hitler took power as chancellor of Germany on January 30, 1933. With the coming to power of the Nazis, Szilard sensed a new chill more potent than Germany’s damp and biting winter air. As the situation for Jews in Europe grew darker, the streets of Dahlem seemed to him more and more like a maze, a trap.
Szilard’s ideas often appeared bizarre and remote from reality because his thinking was so far ahead of others’. Such foresight was not restricted to physics. His colleagues at the Kaiser Wilhelm Institute thought civilized Germans would not tolerate anything really rough happening under Hitler, but Szilard was not so sure. One night he saw a Nazi torchlight parade end in a square near the institute. A huge pile of books gathered there was put to the torch, and as the flames engulfed them, more books were thrown on the pyre. Among the books tossed into the flames were works of “Jewish physics” by Einstein. As Szilard watched the barbaric spectacle, he remembered that a century earlier the great German Jewish poet Heinrich Heine had written, “Wherever they burn books they will also, in the end, burn human beings.”
Szilard possessed a rare combination of concentrated thinking—often about the future—and readiness for immediate action. He reacted to the rise of Nazism by packing his suitcases and keeping them close at hand. He was used to picking up and leaving when things fell apart: he had grown up a Jew in early-twentieth-century Hungary.
Szilard was born in 1898 in the Garden District of Budapest, a neighborhood of wealthy Jewish merchant families who stood just one step below the Magyar nobility in the hierarchy of Austro-Hungarian society. Budapest was one of Europe’s most cosmopolitan cities; it had the second-largest Jewish population, after Warsaw. Horse-drawn droshkies carried silk-gowned women and their counts in red uniforms and furred hats to the grand palace of Emperor Franz Josef while coffeehouses teemed with intellectuals espousing socialist revolution. The Hapsburg Empire’s official tolerance and rich mixture of nationalities had allowed Jews such as the Szilards to find a home, but beneath the cosmopolitanism lurked a powder keg waiting to explode.
Szilard’s mother, Tekla, was a frank and honest woman who taught her son to be candid. “I made up my mind” at an early age, he later wrote, “that if I had to choose between being tactless and being untruthful, I would prefer to be tactless.” 6 As an adult, his outstanding characteristic was not to be deterred by conventions of the time. Although Szilard’s mother was Jewish, she practiced what she called her “natural religion,” which was loosely based on the teachings of Jesus and which she conveyed through vivid parables. As a result, her son developed a strong moral and ethical sensibility, and a deep aversion to violence. He later said that his “predilection for saving the world” was traceable to the stories his mother told him. 7
Tekla and her husband, Louis, argued often in front of their son, who increasingly exhibited a trait quite likely fostered by their chronic disagreement: a tendency to worry. Playmates kidded Szilard for worrying too much, but he seemed unable to stop thinking about dangers. Intensely inquisitive, and perhaps a bit terrified about endings and abandonment, he was always jumping ahead to the next assignment in school. Most boys his age strove to fit in, but Szilard was—and would forever be—independent and irreverent. His sense of humor also helped him alleviate tension and neutralize opponents, and he cultivated an ironic wit.
Szilard’s interest in physics surfaced when he was a teenager. At about the same time, he found himself drawn to politics as well. “Ever since I was 13,” Szilard recalled later, “I was interested in physics and in public affairs but I kept these two things in water-tight compartments and it never occurred to me that these two interests of mine would ever meet.” 8
In 1916 Szilard began riding the streetcar from his home, over the ornate Franz Josef Bridge spanning the Danube River, to the Technical University just below Gellért Hill, where he attended classes and discussed with fellow students the Great War raging across Europe. Szilard was drawn into the war the next summer when he was drafted into the Austro-Hungarian army and sent to officers’ school, where he acted impertinent and nonchalant. He believed that Austria-Hungary and its ally Germany would eventually lose the war—and said so. He had little patience for what he considered mindless military discipline. His belt buckle was always tugged to one side, his boots always needed a shine.
After the war ended, Szilard returned to the Technical University, where revolutionary turmoil swirled around him. Students, artists, and intellectuals debated issues of the day in sidewalk cafés. Szilard thrived as the gadfly who asked the uncomfortable questions that others avoided. He was sympathetic to the communist regime that had come to power in Hungary at the end of the war under Béla Kun but recoiled at the brutalities that Kun inflicted in the name of the people and feared a conservative backlash. Szilard felt this backlash personally when he was confronted by angry students at the university who shouted, “You can’t study here. You’re Jews.” 9 They rushed Szilard, hitting and kicking him. The blood, bruises, and shame left Szilard with a fear of anti-Semitism that he would carry for years to come.
Realizing that, as a Jew, he was in personal danger, Szilard decided to leave Hungary for the University of Berlin. He arrived in Berlin in 1920 and took the university by storm. Berlin’s physics faculty included giants such as Einstein, Max Planck, and Max von Laue, and Szilard sensed new developments in the air. In 1932 British physicist James Chadwick discovered the neutron. The neutron had no electric charge, which meant it could pass through the electrical barrier surrounding the atom and penetrate the nucleus. Szilard saw in the neutron’s ability to easily penetrate the nucleus the possibility of eventually releasing the vast store of energy contained within the atom.
The same year as Chadwick’s discovery, Szilard moved from the University of Berlin to the Kaiser Wilhelm Institute, where he continued his experimental work in nuclear physics. As he probed the mysteries of the atom within the institute, he grew edgy as he observed what was happening outside its walls. Szilard noticed that most Germans stood passively watching the growing Nazi threat. When he asked his German friends, “Why don’t you oppose Nazism?” most of them shrugged and muttered, “What good would it do?” Szilard concluded that Hitler would gain power not because Nazism was so appealing to Germans but because so few Germans would resist it.
Unlike most physicists during these years, Szilard had no illusions that things would get better. He saw Nazism for what it was: an evil force that spelled disaster for Germany and all of Europe. Months before Hitler came to power, and years before he engulfed Europe in a bloody war, Szilard’s assessment of the problems brewing for Jews in Germany led him to grave predictions. He shared them in a letter to Rabi, whom he had met and befriended in the late 1920s. “As far as the fate of Germany is concerned,” Szilard wrote Rabi, “I always was very pessimistic, but I range now with the optimists. (You know, an optimist is a man who jumps out of the window of the 22nd floor and who says smiling when he passes the 10th floor, falling down: ‘Well, nothing happened to me up till now.’)” 10 Szilard’s sarcasm belied his deep pessimism and despair.
On the night of February 27, 1933, Nazi saboteurs set fire to the Reichstag, Germany’s parliament. Hitler blamed the arson on a Jewish-Communist plot and bullied Reichstag deputies into granting him dictatorial powers. On April first the Nazis directed a national boycott of Jewish businesses and beat Jews in the streets. On April seventh thousands of Jewish academics lost their positions in German universities. Szilard was particularly incensed by the prohibition against teaching “Jewish science”—any theory, even Einstein’s profound theory of relativity, that had been developed by a Jew. He decided the time had come to get out. He grabbed his suitcases and took the night train to Vienna. The following day Nazi border guards stopped the same train and held back everyone whose passport was stamped “non-Aryan.” This close call so traumatized Szilard that, forever after, he kept two suitcases packed and close at hand wherever he lived. 11
In Vienna Szilard called on Western embassies and warned them that the Nazi assault on Jews was just beginning. The diplomats listened politely but said, and did, nothing. So Szilard decided to leave the Continent for the greater safety of Britain. He sought a permanent academic position there, but Depression-era Britain had only a limited ability to absorb refugees—there were neither enough positions nor enough money to fund them. Unable to secure a university appointment, Szilard decided to camp out in a modest hotel in London while he contemplated his next step. For the moment, he lived on the income from his patent licenses and money he had saved from tutoring fees.
Szilard was an idea man par excellence. Each day for months he strolled London’s busy streets and beautiful parks pondering nuclear physics and his fears for Europe’s future. One afternoon, while walking on a sidewalk in Bloomsbury, he had a fateful idea. He later recalled:
As the light changed to green and I crossed the street, it suddenly occurred to me that if we could find an element which is split by neutrons and which would emit two neutrons when it absorbed one neutron, such an element, if assembled in sufficiently large mass, could sustain a nuclear chain reaction. I didn’t see at the moment just how one would go about finding such an element or what experiments would be needed, but the idea never left me. 12
Szilard imagined that if a neutron struck a nucleus and split the atom, the breakup might release the binding energy that holds the atom together. Some of that atom’s neutrons might in turn be released, which could hit and split other atoms. If more than one neutron was released from each split atom, the process could expand exponentially. “One neutron would release two, which would each strike an atomic nucleus to release four… and so on. In millionths of a second, billions of atoms would split.” 13
Suddenly Szilard remembered the H. G. Wells novel he had read a year earlier. Published in 1914, just before the outbreak of World War I, The World Set Free prophetically described a conflict in which cities were destroyed by atomic bombs. “Of course,” Szilard wrote a friend to whom he sent a copy of the novel, “all this is moonshine, but I have reason to believe that the forecast of the writers may prove to be more accurate than the forecast of the scientists.” 14
Szilard stood alone in his belief in a chain reaction. At the time, his mentor and friend Einstein—the world’s preeminent theoretical physicist—told reporters that such an effort would be “fruitless.” 15 Attempting to unlock the energy of the atom by neutron bombardment, said Einstein, was likely to enjoy about the same chance of success as “shooting birds in the dark in a country where there are only a few birds.” 16 A doyen of the scientific establishment, the great experimentalist Lord Ernest Rutherford dismissed the prospect of a chain reaction with devastating British understatement: “The outlook for gaining useful energy from atoms by artificial processes of transformation does not look promising.” 17 With comments like these the order of the day, it is easy to appreciate Szilard’s difficulty in getting support for exploring the possibility of a nuclear chain reaction.
It was not an idle joke. Recognizing that the days of peace in Europe were numbered and that the future of Western civilization and modern science would depend on the degree of support that could be mustered in the New World, Szilard decided to emigrate to America. About Christmastime 1937 Szilard attended a dinner at Magdalen College in Oxford, where a fellow of the college told Szilard that he was leaving soon on a visit to the United States. “Buy a one-way ticket,” Szilard advised him. 18
Szilard’s reasoning was simple. As he told a fellow Jewish refugee planning to leave the Continent, Britain was “a very likeable country, but it would certainly be a lot smarter if you went to America. In America you would be a free human being and very soon would not even be a stranger.” 19 In practical terms, he also saw a much better opportunity for nuclear physics research in the United States.
In January 1938 Szilard decided the time had come to depart. He begged his parents in Budapest to join him, but they refused to budge—they were old and did not want to leave the only world they knew. Szilard could do nothing more than bid them a sad farewell. Once in New York, he found himself quickly and happily at home. Nazism was far away. He did not feel like a foreigner. When he had some difficulty adjusting, this nation of immigrants offered understanding and sympathy. He had felt much more like a refugee in Europe.
So, quickly and eagerly Szilard decided to become a U.S. citizen. Emotionally and politically, he felt that he already belonged irretrievably to America. In his thinking and action, he scarcely had any affinity with the mentality of Nazi Germany. Soon he was in touch with other refugee physicists in the United States and was visiting Columbia frequently to see Rabi. With Rabi’s help, Szilard resumed his research on the atomic nucleus and began warning anyone who would listen about the looming threat of Nazism.
Although Szilard had conceived the idea of a chain reaction, he lacked the resources—a laboratory, assistants, and financial support—to search for it. That quest fell to another refugee physicist, Enrico Fermi, who had the resources that Szilard lacked—and the brains to match. In contrast to Szilard, who moved from one temporary job to the next, lived in hotel rooms, and proposed experiments to other people, Fermi was a well-established academic who ran a famous physics institute located in a small, quiet park on a hill in central Rome. The park, landscaped with palm trees, bamboo thickets, and a garden that attracted singing sparrows at dusk, made the institute a peaceful and attractive center of study.
A short man with rounded shoulders, narrow nose, thick black hair, and hazel eyes that stood out against a dark complexion, Fermi charmed people by craning his neck forward and flashing a winning smile that exposed a gap between his front teeth. Quiet and unpretentious, he displayed an unusual combination of personal modesty and self-confidence. He wore a simple leather jacket and always drove his own car. When he encountered a roadblock in front of his institute one day, he leaned out the window and said, “I am His Excellency Enrico Fermi’s chauffeur”—which got him waved through. He had such a gift for seeing into the heart of problems and such an easy manner of solving them that other physicists nicknamed him “the Pope.”
Fermi was born in 1901 into a middle-class family of civil servants and attended Italian public schools. He showed intellectual brilliance from an early age and also a cool, reserved manner. He was more prone to deeds than to talk and carefully guarded his innermost thoughts. Though somewhat cold, he was absolutely impartial. Fermi’s most striking trait was his willingness to accept the world and people as they were. “He took people around him at their own value,” said a friend. “That’s why I was very fond of him.” 20 He understood complex theories but preferred making simple points. Likewise, though he did not spend a lot of time analyzing people, he seldom misjudged them. Fermi abhorred confrontation and avoided battles that he was not confident of winning. If faced with superior force, he invariably withdrew from a contest. Consistent with this, he rarely made promises unless he was sure he could deliver on them.
Fermi began his career as a physicist in 1922, the year he received his doctorate from the University of Pisa. That same year, Benito Mussolini marched on Rome at the head of his armed Black Shirts and seized control of the Italian government in the name of Fascism. Preoccupied as he was with physics, the menace of Fascism seemed remote to Fermi. In 1923 he won a fellowship to study in Germany with the renowned Max Born, who had gathered a group of brilliant young physicists around him at Göttingen, including Werner Heisenberg and Wolfgang Pauli. Heisenberg and Pauli did not bring Fermi into their circle of conversation; most of the time the young Italian worked alone in silence. As a result, Fermi, who had succeeded almost effortlessly until then, felt ignored and unappreciated at Göttingen, an unwelcome foreigner in Germany. The experience embittered Fermi, who would remember it for a long time to come.
Fermi returned to Italy and took up a professorship of theoretical physics at the University of Rome. Over the next decade Fermi turned his physics institute into a leading center for the study of the nucleus. Fermi preferred tackling concrete problems. His method was never to waste time and to keep things as simple as possible—a no-nonsense, matter-of-fact, commonsense perspective. In this way, he kept going forward until he reached his goal, carefully and relentlessly. He was a master at achieving important results with a minimum of effort. Like Szilard, Fermi saw the significance of the neutron and designed experiments around it. He decided to bombard nuclei of atoms with neutrons and see what happened. Fermi’s insight was to slow neutrons down by sending them through paraffin (a particularly dense substance); the slower the neutrons moved, he thought, the more likely they were to stick in the nucleus they were hitting.
Fermi began his neutron experiments in the mid-1930s in typically methodical fashion: by systematically bombarding all the elements in the periodic table. He started with water—testing hydrogen and oxygen at the same time—and finally came to uranium, one of the heaviest elements.
The results were puzzling. Fermi observed that the uranium nucleus captured the bombarding neutron, emitted an unusually large amount of radiation, temporarily became a heavier isotope (with the same chemical characteristics but a different atomic weight), then decayed to an element heavier by one atomic number. The simplest explanation consistent with the known facts—the yardstick typically applied by scientists to interpret experimental results—was that the uranium was mutating up the periodic table. These man-made, very heavy “transuranic” elements should be unstable: their radioactive breakdown could explain the copious radiation being emitted.
During these years Fermi grew increasingly alarmed by Mussolini’s policies, first the invasion of Ethiopia, then the intervention alongside Nazi Germany in the Spanish civil war. And there was something else: although anti-Semitism was not yet an issue in Italy, Fermi’s beloved wife, Laura, was Jewish. In 1936 Fermi traveled to the United States to lecture at the University of Michigan summer school, where he came into contact with a large number of American and visiting European physicists. Fermi liked what he saw at Ann Arbor: well-equipped labs, eager students, and plenty of praise for his scientific talent. He returned the next two summers as well. Each visit made him like America’s people, culture, and institutions more and more. At the same time, he gained perspective on Fascist Italy. America increasingly looked like the future to him, a land of freedom and opportunity far from the troubles of Europe.
Back in Italy, Fermi remained outwardly friendly, but now he kept his own counsel with all but his closest friends. As long as Fermi felt he could work unhindered in physics, he tried to ignore the nature of the Fascist regime and the trend of events. Like many of his countrymen, he tried not to see the unfolding truth, because it was too unpleasant to contemplate. But the atmosphere in Italy took a sharp turn for the worse in July 1938. That month Mussolini published the Manifesto della Razza, which announced that “Jews do not belong to the Italian race.” The manifesto was soon followed by edicts copied from Nazi racial laws. Not long after, the Fascist press began attacking Fermi for “having transformed the physics institute into a synagogue.” 21
Fermi realized that it was time to get his family out of Italy. He wrote to four American universities that had expressed an interest in hiring him. To avoid suspicion, he mailed each letter from a different location in Rome. When all four responded favorably, Fermi chose Columbia University and awaited an opportunity to make his escape. Listening to the radio on the night of November 10, 1938, Fermi and his wife heard that he had won the Nobel Prize during the same broadcast that reported the horrors of Kristallnacht, the murderous anti-Jewish pogrom that had swept Germany the night before, and the institution of a new set of racial laws excluding Italian Jewish children such as their own son and daughter from public schools.
Fermi decided to use the Nobel ceremony in Sweden to spirit his family out of Italy. In early December he, Laura, and their two children left by train for Stockholm. There were tense moments along the way. When they crossed the frontier from Switzerland into Germany, a Nazi border guard slowly and deliberately flipped through their passports. Fermi watched anxiously until the guard moved on to the next compartment. He and his family reached Stockholm safely, where he received the Nobel Prize on December tenth. Two weeks later, on Christmas Eve, the Fermis left for New York. A short time later, Laura Fermi’s Jewish father, who had been an admiral in the Italian navy, disappeared into a concentration camp and was never heard from again.
Upon arriving in New York, the Fermis put up at the King’s Crown Hotel, on West 116th Street just east of the Columbia University campus, where Szilard had also settled. Szilard had exchanged experimental data about neutrons with Fermi since 1936, so the two men had much to discuss when they inadvertently bumped into each other in the hotel lobby one morning. 22 Fermi was a scientific celebrity because of his recent Nobel Prize. Szilard, by contrast, had kept his pioneering nuclear research secret out of fear that the Nazis would somehow learn about it and use it to make an atomic bomb. “You didn’t know what he was up to” was the complaint around Columbia’s new Pupin Laboratory. “He was always a bit mysterious.” 23 As a result, most Columbia physicists looked upon Szilard as an inconvenient interloper who nosed around faculty offices and showed up uninvited in the lab to pester and offer unwanted advice.
One physicist at Columbia knew both men well: Rabi. Rabi bridged the world of transatlantic physics, counting both native-born and refugee physicists as personal friends. He had first met Fermi and Szilard in Germany during the 1920s and had remained in touch with both ever since. He shared with Fermi a passion for physics, but with Szilard he shared even more: similar roots. Although their temperaments were very different—Rabi was affable, politic, and of a sunny disposition, while Szilard was eccentric, impolitic, and moody—they were both Jews who hailed from Central Europe, and thus shared certain shadows.
Isador Isaac Rabi was born in 1898 in a village in what is now Poland but was then the northeasternmost province of the Austro-Hungarian Empire. His parents emigrated to America before he was a year old. “Had we stayed in Europe,” he later said, “I probably would have become a tailor.” 24 Like millions of other turn-of-the-century immigrants, the Rabis settled in the crowded Lower East Side of New York. It was a tough neighborhood where youngsters grew up fast. A contemporary of Rabi’s described the neighborhood’s “wisdom of the streets”:
We would roam through the city tasting the delights of freedom, discovering possibilities far beyond the reach of our parents. The streets taught us the deceits of commerce, introduced us to the excitement of sex, schooled us in strategies of survival, and gave us our first clear idea of what life in America was really going to be like.
We might continue to love our parents and grind away at school and college, but it was the streets that prepared the future. In the streets we were roughened by actuality, and even those of us who later became intellectuals or professionals kept something of our bruising gutter-worldliness, our hard and abrasive skepticism. You could see it in cab drivers and garment manufacturers, but also in writers and professors who had grown up as children of immigrant Jews. 25
Synagogues and saloons coexisted on nearly every Lower East Side street, and these contradictory symbols of life in the Jewish ghetto seemed vivid symbols to the young Rabi of the ways of people and the world. The streets made him impish, quick-witted, buoyant, and brash. He always said exactly what he thought, whether or not he believed it would meet with approval. He was cynical, yet compassionate toward others.
Against the worldliness of the streets stood the piety of his parents, David and Sheindel Rabi, devout Jews who raised their son according to strict Orthodox tradition. Hardly a sentence went by in their conversation without a reference to God. Rabi’s earliest reading was Yiddish Bible stories. When he was nine years old, his family moved to Brownsville, the Jewish enclave of Brooklyn. One day as he browsed in the local branch of the Carnegie public library near his parents’ small grocery store, he stumbled on a book about astronomy. The explanatory power of the Copernican system impressed him deeply. “It was so beautiful, so marvelous,” said Rabi years later. “Instead of the idea that there is some special intervention every day for the sun to come up, I came home with this great revelation.” Pleased with himself, Rabi announced to his parents: “It’s all very simple, who needs God?” 26
Rabi began testing other assumptions as well. Orthodox law forbade riding streetcars on the Sabbath. One Saturday he rode a streetcar, expecting God to strike it (or at least him) with lightning, but nothing happened. In synagogue, rabbis held out their tallis-covered hands; the congregation averted its eyes at the risk of blindness. One day Rabi did not, and again nothing happened. As Judaism began to look more and more like superstition to him, his life outside home became increasingly secular as he abandoned the religious practices and rituals of his immigrant parents. But the moral perspective of his Orthodox upbringing—the struggle between good and evil in the world—continued to shape his outlook. “My early upbringing, so struck by God, the maker of the world, this stayed with me,” Rabi later said. “There’s no question that basically, somewhere way down, I’m an Orthodox Jew.” 27
Rabi’s testing of Jewish ritual and his growing exhilaration with science reflected a search for some all-encompassing system to explain both the universe and, more personally, the hard life of his family and friends. As an adolescent, he began to read books about Marxism and to attend neighborhood meetings of the Socialist Club. After a while, though, Rabi began to feel that Marxists were either kidding themselves or trying to kid him. “Part of the Socialist thing was ‘equality’—anybody can do this or that,” he recalled later. “But after I went to high school and looked at my classmates, I said, ‘Those people can’t run a government or a world,’ and dropped the whole thing.” 28
When Rabi finished high school in 1916, his parents forcefully suggested that he go into Hebrew studies at a yeshiva. Instead, he decided to break away by going “way out west” to Cornell University in upstate New York. Ithaca, with its spectacular waterfalls and nearby Finger Lakes, certainly seemed like romantic country to a New York City boy who had devoured the novels of James Fenimore Cooper. Rabi scraped together enough money to attend college by summering as a sales clerk at Macy’s department store and winning two state scholarships. Once at Cornell, he enthusiastically immersed himself in Ivy League culture—but it was not a total immersion: Rabi reaped its rewards, but he also refused to change his personality or diminish his independence.
When Rabi graduated with a degree in chemistry in 1919, he couldn’t find a good job because of anti-Semitism and a postwar recession, so he returned to Cornell for graduate study. He soon realized that he should change his focus. His Orthodox upbringing had given him a feeling for the mystery of physics, a taste for generalization, and a belief in the profundity and underlying unity of nature. “When you’re doing physics, you’re wrestling with a champ,” he liked to say. “You’re trying to find out how God made the world, just like Jacob wrestling with the angel.” 29 Physics brought Rabi nearer to God because the world was his creation. And like God, physics was infinite and certainly not trivial; it had class and drama. Doing good physics was “walking the path of God.” 30
A decade later Rabi was a full professor at Columbia University and an accomplished physicist. He liked the atmosphere of the laboratory, but he was completely uninterested in details—decidedly hands-off. He studiously avoided nuts-and-bolts issues. “When things were going well and you were getting interesting data,” said one of his graduate students, “he was right there on top of the experiment helping with the interpretation. But when there were leaks in the apparatus, he just disappeared.” 31 His way of training theoretical physicists was to tell a young man when he arrived that if he was bright enough to be a theoretical physicist, then he was bright enough to find his own problem, solve it, and, when he was finished, come back and tell him all about it.
In 1931 Rabi spent a year at the University of Hamburg, where he watched brown-shirted Nazi hooligans march past the university in an eerie torchlight parade. His Hamburg professors at first dismissed Nazism because the brownshirts were so few in number and so coarse. But his wife, Helen, attending a nearby art school whose students included several Nazis, had a very different and more troubling view. She did not look Jewish, and Nazi students therefore talked openly to her. They told her about the “next war,” and there was no doubt whatsoever about their vicious anti-Semitism. Rabi grew more alarmed when Hitler became chancellor in 1933. By then he was back in the United States at Columbia, but he had extensive contacts in Germany, including Szilard, who relayed what was happening there in frightening detail.
When Szilard arrived at Columbia in 1938, he shared with Rabi his idea of a chain reaction and his concern about what it meant for Europe. When Fermi arrived early the following year, the three physicists began a close collaboration. To work on the problems of fission and a chain reaction attended to all of their concerns at once: it was at the center of their scientific interests, the practical consequences might be enormous, and nothing could be more important politically than to guard against the danger that Nazi Germany might get an atomic bomb first. Like Szilard and Fermi, Rabi had become increasingly alarmed by Hitler and feared that the United States might stand by and allow him to take over Europe. Rabi began thinking about what he could do as a physicist to help in the war that he saw coming and that he felt sure would eventually involve America.
Niels Bohr also saw war coming. As a theoretical physicist, Bohr was thrilled and excited by the discovery of fission; but as a Danish Jew, he feared that Nazi Germany might use the discovery to make an atomic bomb. This fear was written on Bohr’s face when he arrived in New York in January 1939 to spend a semester at the Institute for Advanced Study in Princeton, New Jersey. “He stooped like a man carrying a heavy burden,” said a friend who saw Bohr standing on the deck of his ship as it pulled alongside the Hudson River pier. “His gaze, troubled and insecure, shifted but stopped on no one.” 32
A tall Scandinavian with a large head and hands, bushy eyebrows, big jowls, and unruly combed-back hair, Bohr had a quiet, unassuming demeanor that masked a lively and profound mind of great creativity, subtlety, and humanity. He looked rather ponderous, but when people drew near him his blue eyes sparkled, exuding the warmth and charm of his personality. His great kindness and reluctance to hurt anyone’s feelings, coupled with his insistence on not letting any inexact or wrong statement pass, led to his frequent comment: “I am not saying this in order to criticize, but this is sheer nonsense!” 33
As a talker, Bohr found it very hard to get to the point. He thought of the implications of everything he said so much that he was unwilling to make any statement without qualifying it. It didn’t help that he spoke in a mumbling voice not much above a whisper. An equally laborious writer, he preferred talking to writing. He also could be absentminded. But if he sometimes seemed scatterbrained about what was right before him, Bohr was stunningly acute when it came to what could not be seen. He possessed a powerful mind and formidable theoretical insight into physical processes.
Bohr was as much a philosopher as a physicist. He loved paradoxes. When faced with an apparently insoluble problem, he always said, “Every great and deep difficulty bears in itself its own solution. It forces us to change our thinking in order to find it.” 34 Unlike most physicists of his day, who kept science and moral concerns quite separate, Bohr generalized this concept of “complementarity” to fields outside of physics, including politics, believing that rational inquiry, conducted in an open society and led by an informed elite, could harmonize technological progress with humanistic values and smooth out conflicts between nations. He was also deeply aware of the dangers that scientific innovation could pose to society. This concern, which Bohr felt with great intensity, was called der Kopenhagener Geist (“the Spirit of Copenhagen”) by other physicists. Bohr was widely admired both for his scientific accomplishments and for his humanity; it was on account of both that he enjoyed immense prestige among physicists. 35
Outside the walls of his Copenhagen institute, Bohr fought his anxiety by working tirelessly on behalf of scientists fleeing Nazi persecution: finding out who was in need, raising funds to assist them, circulating lists of names to institutions that might find jobs for them. As the head of the Danish Committee for the Support of Fugitive Intellectuals and Scientists, which he helped organize in 1933, Bohr had become the head dispatcher of an “underground railroad” that delivered many of Europe’s most brilliant scientists to Britain and America. Every year, he traveled to both countries to sell “his refugees,” including a trip to Princeton in the spring of 1939.
Bohr spent his time at Princeton that last spring before World War II analyzing the theoretical implications of fission. The big question of the moment was whether additional neutrons—what physicists called “secondary neutrons”—were also released by fission. If they were (and there were enough of them), these secondary neutrons could split still other uranium atoms in a multiplying chain reaction—proving true the idea that had come to Leo Szilard while walking on a London street back in September 1933.
Bohr hoped a chain reaction was impossible. He began studying the problem with a young Princeton physicist named John Wheeler in February 1939. He and Wheeler worked in Fine Hall, a Georgian brick pile on Princeton’s campus housing the physics and mathematics departments. Bohr’s office had bookshelves on one wall, a blackboard on another, and large windows looking out onto a green lawn on another. Bohr began each day standing at the blackboard. Soon he began drawing and writing equations, erasing figures with the sleeve of his coat. He probed and stabbed at the bowl of his pipe as he paced his office for hours, littering the floor with matchsticks. Sometimes he paced the hallway that circled the second floor of Fine Hall, thinking as he walked. Back in the office, Bohr broke one piece of chalk after another in bouts of furious writing at the board. At the end of the day, he would lift the edge of the rug on the hardwood floor and kick broken bits of chalk under it. Otherwise, he would be scolded for messiness by the cleaning lady.
There was a large radio in the common room, and each afternoon at four Bohr would have tea with other faculty members and all of them would listen intently to news of the intensifying crisis in Europe. War seemed inevitable. Bohr took it all in with remarkable equanimity. The Western democracies were making the mistakes now, he remarked, but the Nazis would be making the mistakes in the end. 36
Amid this tension-filled atmosphere, Bohr and Wheeler pondered the secrets of fission, formulating a hypothesis that fit the known facts. They knew that natural uranium consisted of two isotopes. More than 99 percent of uranium atoms consisted of an isotope of atomic weight 238, and less than 1 percent were of atomic weight 235. They also knew that elements of odd atomic weight tended to be less stable than those of even atomic weight. They reasoned then that only the rare isotope U-235 was fissioning when its nucleus was penetrated by a neutron while secondary neutrons would mostly be absorbed by U-238, which would not fission. The two isotopes were chemically identical and could be separated only by mechanisms that depended on the difference in their weight. Since the weights were so close—differing by only three parts in 238—it seemed an impossible task to separate the two in any meaningful quantities. Bohr was relieved to conclude that a fission bomb could not be constructed without separation and that the world was safe from destruction after all.
Despite Bohr’s conclusion, Szilard labored to keep the possibility of a chain reaction secret. He felt so strongly about the need for secrecy that he decided to withhold his own groundbreaking research from publication. Such self-denial was one way, he thought, of preventing the Nazis from realizing fission’s military potential. Another way was to urge other scientists to do the same. This was a major departure from the scientific ethos of the day. Science was open; no scientist hid results; there was no progress without publication. It was quite unaffected by national boundaries.
Szilard learned that neutron experiments were being done by Frédéric Joliot in Paris, so he wrote Joliot, imploring him not to publish his results. “If more than one neutron were liberated, a sort of chain reaction would be possible,” he confided to Joliot. “In certain circumstances this might then lead to the construction of bombs which would be extremely dangerous in general and particularly in the hands of certain governments,” he broadly hinted. Szilard closed the letter, “In the hope that there will not be sufficient neutrons emitted by uranium, I am…,” but then crossed out this closing, simply signed the letter, and mailed it. 37 Joliot refused his request, publishing his results in a European scientific journal later that spring.
Undeterred, Szilard approached Fermi, who was working separately on his own neutron experiments. Although the two had started out together in the Columbia laboratory, it had not worked out—their temperamental differences made collaboration impossible. Szilard preferred brainstorming to manual labor, whereas Fermi expected everyone to roll up his sleeves. Szilard’s research assistant at Columbia, Bernard Feld, noted that Szilard made intuitive leaps from Point A to Point D, whereas Fermi moved methodically from Point A to Point B. 38 Szilard believed neutron research might be applicable to military purposes, whereas Fermi doubted anything militarily useful would result from it. Szilard was disposed to constantly reevaluate premises; Fermi was by nature cautious and careful. 39
Fermi considered Szilard a brilliant but very peculiar man who enjoyed startling people. He was certainly startled when Szilard walked into his Pupin Hall office one afternoon and told him that it was his duty to withhold results of his neutron experiments until it was clear whether they were potentially dangerous. This was especially important, Szilard argued, because astute reporters had gotten on the trail after Bohr had announced Hahn’s fission results at the Washington conference in early February. With fission, “hope is revived that we may yet be able to harness the energy of the atom,” the New York Times reported on February fifth. The February sixth issue of Newsweek also reported on fission. The Times’ science correspondent, William Laurence, buttonholed Fermi after a meeting of the American Physical Society at Columbia on February twenty-fourth, and inquired whether uranium could be used to make an atomic bomb. The unusually long silence that followed made Laurence feel that he had asked something important.
“We must not jump to hasty conclusions,” Fermi said carefully. “This is all so new. We will have to learn a lot more before we know the answer. It will take many years.”
How many? Laurence replied.
“At least twenty-five, possibly fifty years,” answered Fermi.
“Supposing Hitler decides that this may be the very weapon he needs to conquer the world,” Laurence persisted. “How long then?”
Fermi was guarded, but to Laurence the implications were clear. Fission meant a chain reaction, and a chain reaction meant an atomic bomb. 40
When Szilard learned from Rabi the next day that Fermi had publicly discussed the possibility of a chain reaction, he was horrified. He rushed to Fermi’s office; he wasn’t there. Szilard went back to Rabi and asked him to tell Fermi that “these things ought to be kept secret.”
Szilard sought out Rabi again the following day:
I said to him: “Did you talk to Fermi?” Rabi said, “Yes, I did.” I said, “What did Fermi say?” Rabi said, “Fermi said ‘Nuts!’” So I said, “Why did he say ‘Nuts!’?” and Rabi said, “Well, I don’t know, but he is in and we can ask him.” So we went over to Fermi’s office, and Rabi said to Fermi, “Look, Fermi, I told you what Szilard thought and you said ‘Nuts!’ and Szilard wants to know why you said ‘Nuts!’” So Fermi said, “Well… there is the remote possibility that neutrons may be emitted in the fission of uranium and then of course perhaps a chain reaction can be made.” Rabi said, “What do you mean by ‘remote possibility’?” and Fermi said, “Well, ten percent.” Rabi said, “Ten percent is not a remote possibility if it means that we may die of it. If I have pneumonia and the doctor tells me that there is a remote possibility that I might die, and it’s ten percent, I get excited about it.” 41
“We both wanted to be conservative,” Szilard noted, “but Fermi thought that the conservative thing was to play down the possibility that this may happen, and I thought the conservative thing was to assume that it would happen and take the necessary precautions.” 42
Szilard grew increasingly frantic that spring the more he thought about fission. For weeks he rushed about the Columbia University labs and faculty offices, bearing witness to the great and dreadful events he foresaw. He was anxious—almost desperate—to prove or disprove a chain reaction. Half in hope and half in fear, he set up an experiment on the night of March third. The setting was the vaultlike laboratory on the seventh floor of Pupin. The experiment was designed to reveal pulses on an oscilloscope that could be expected from the neutrons of split uranium atoms. All Szilard had to do was flip a switch and watch the oscilloscope screen. If pulses appeared on the screen, it would mean that secondary neutrons were emitted in the fission of uranium—and that would confirm a chain reaction.
Szilard flipped the switch, saw the dreaded pulses, and watched them for several minutes with mounting horror. Then he flipped off the switch and walked back in silence to his hotel. “That night,” Szilard later recalled, “there was very little doubt in my mind that the world was headed for grief.” 43