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 ann
ounced 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
Pandora's Keepers Page 4
