The Making of the Atomic Bomb

too preoccupied to plan ahead so carefully. But Italian physics was a ruin as sere as Pompeii when he came to it. He had no choice but to push aside the debris and start fresh.

Both Fermi's biographers — his wife Laura and his protdgd and fellow Nobel laureate Emilio Segre — assign the beginning of his commitment to physics to the period of psychological trauma following the death of his older brother Giulio when Fermi was fourteen years old, in the winter of 1915. Only a year apart in age, the two boys had been inseparable; Giulio's death during minor surgery for a throat abscess left Enrico suddenly bereft.

That same winter young Enrico browsed on market day among the stalls of Rome's Campo dei Fiori, where a statue commemorates the philosopher Giordano Bruno, Copernicus' defender, who was burned at the stake there in 1600 by the Inquisition. Fermi found two used volumes in Latin, Elementorum physicae mathematicae, the work of a Jesuit physicist, published in 1840. The desolate boy used his allowance to buy the physics textbooks and carried them home. They excited him enough that he read them straight through. When he was finished he told his older sister Maria he had not even noticed they were written in Latin. “Fermi must have studied the treatise very thoroughly,” Segre would decide, looking through the old volumes many years later, “because it contains marginal notes, corrections of errors, and several scraps of paper with notes in Fermi's handwrit-ing.

From that point forward Fermi's development as a physicist proceeded, with a single significant exception, rapidly and smoothly. A friend of his father, an engineer named Adolfo Amidei, guided his adolescent mathematical and physical studies, lending him texts in algebra, trigonometry, analytical geometry, calculus and theoretical mechanics between 1914 and 1917. When Enrico graduated from the liceo early, skipping his third year, Amidei asked him if he preferred mathematics or physics as a career and made a point of writing down, with emphasis, the young man's exact reply: “I studied mathematics with passion because I considered it necessary for the study of physics, to which I want to dedicate myself exclusively… I've read all the best-known books of physics.”

Amidei then advised Fermi to enroll not at the University of Rome but at the University of Pisa, because he could compete in Pisa to be admitted as a fellow to an affiliated Scuola Normale Superiore of international reputation that would pay his room and board. Among other reasons for the advice, Amidei told Segre, he wanted to remove Fermi from his family home, where “a very depressing atmosphere prevailed… after Giulio's death.”

When the Scuola Normale examiner saw Fermi's competition essay on the assigned theme “Characteristics of sound” he was stunned. It set forth, reports Segre, “the partial differential equation of a vibrating rod, which Fermi solved by Fourier analysis, finding the eigenvalues and the eigenfre-quencies… which would have been creditable for a doctoral examination.” Calling in the seventeen-year-old liceo graduate, the examiner told him he was extraordinary and predicted he would become an important scientist. By 1920 Fermi could write a friend that he had reached the point of teaching his Pisa teachers: “In the physics department I am slowly becoming the most influential authority. In fact, one of these days I shall hold (in the presence of several magnates) a lecture on quantum theory, of which I'm always a great propagandist.” He worked out his first theory of permanent value to physics while he was still a student in Pisa, a predictive deduction in general relativity.

The exception to his rapid progress came in the winter of 1923, when Fermi won a postdoctoral fellowship to travel to Gottingen to study under Max Born. Wolfgang Pauli was there then, and Werner Heisenberg and the brilliant young theoretician Pascual Jordan, but somehow Fermi's exceptional ability went unnoticed and he found himself ignored. Since he was, in Segre's phrase, “shy, proud, and accustomed to solitude,” he may have brought the ostracism on himself. Or the Germans may have been prejudiced against him by Italy's poor reputation in physics. Or, more dynamically, Fermi's visceral aversion to philosophy may have left him tongue-tied: he “could not penetrate Heisenberg's early papers on quantum mechanics, not because of any mathematical difficulties, but because the physical concepts were alien to him and seemed somewhat nebulous” and he wrote papers in Gottingen “he could just as well have written in Rome.” Segre has concluded that “Fermi remembered Gottingen as a sort of failure. He was there for a few months. He sat aside at his table and did his work. He didn't profit. They didn't recognize him.” The following year Paul Ehrenfest sent along praise through the intermediary of a former student who looked up Fermi in Rome. A three-month fellowship then took the young Italian to Leiden for the traditional Ehrenfest tightening. After that Fermi could be sure of his worth.

He was always averse to philosophical physics; a rigorous simplicity, an insistence on concreteness, became the hallmark of his style. Segre thought him inclined “toward concrete questions verifiable by direct experiment.” Wigner noticed that Fermi “disliked complicated theories and avoided them as much as possible.” Bethe remarked Fermi's “enlightening simplicity.” Less generously, the sharp-tongued Pauli called him a “quantum engineer”; Victor Weisskopf, though an admirer, saw some truth in Pauli's canard, a difference in style from more philosophical originals like Bohr. “Not a philosopher,” Robert Oppenheimer once sketched him. “Passion for clarity. He was simply unable to let things be foggy. Since they always are, this kept him pretty active.” An American physicist who worked with the middle-aged Fermi thought him “cold and clear… Maybe a little ruthless in the way he would go directly to the facts in deciding any question, tending to disdain or ignore the vague laws of human nature.”

Fermi's passion for clarity was also a passion to quantify. He seems to have attempted to quantify everything within reach, as if he was only comfortable when phenomena and relationships could be classified or numbered. “Fermi's thumb was his always ready yardstick,” Laura Fermi writes. “By placing it near his left eye and closing his right, he would measure the distance of a range of mountains, the height of a tree, even the speed at which a bird was flying.” His love of classification “was inborn,” Laura Fermi concludes, “and I have heard him ‘arrange people’ according to their height, looks, wealth, or even sex appeal.”

Fermi was born in Rome on September 29, 1901, into a family that had successfully made the transition during the nineteenth century from peasant agriculture in the Po Valley to career civil service with the Italian national railroad. His father was a capo divisione in the railroad's administration, a civil rank that corresponded to the military rank of brigadier general. In accord with a common Italian practice of the day, the infant Enrico was sent to live in the country with a wet nurse. So was his brother Giulio, but because Enrico's health was delicate he did not return to his mother and father until he was two and a half years old. Confronted then with a roomful of strangers purporting to be his family, and “perhaps,” writes Laura Fermi, “missing the rough effusiveness of his nurse,” he began to cry:

His mother talked to him in a firm voice and asked him to stop at once; in this home naughty boys were not tolerated. Immediately the child complied, dried his tears, and fussed no longer. Then, as in later childhood, he assumed the attitude that there is no point in fighting authority. If they wanted him to behave that way, all right, he would; it was easier to go along with them than against.

In 1926, when he was twenty-five years old, Fermi was chosen under the Italian system of concorsos, national competitions, to become professor of theoretical physics at the University of Rome. An influential patron had seen to the creation of the new post, a Sicilian named Orso Mario Corbino, a short, dark, volatile man, forty-six when Fermi sought him out in 1921, the director of the university physics institute, an exceptional physicist and a Senator of the Kingdom. Since the old guard of Italian physicists resented Fermi's rapid promotion, he especially welcomed the protection of Corbino's patronage. Corbino found support for his efforts to improve Italian physics from the Fascist government of the bulletheaded former journalist Benito Mussolini, although the senator was not himself a party member.

In the later 1920s Corbino and his young professor agreed that the time was ripe for the small group they were assembling in Rome to colonize new territory on the frontier of physics. They chose as their territory the atomic nucleus, then finding description in quantum mechanics but not yet experimentally disassembled. Fermi's tall, erudite Pisa classmate Franco Rasetti signed on as Corbino's first assistant early in 1927. Rasetti and Fermi together recruited Segre, who had been studying engineering, by taking him along to the Como conference and explaining the achievements of the assembled luminaries to him — by then, Segre saw, Pauli and Hei-senberg recognized Fermi's talents and included him among their friends. The son of the prosperous owner of a paper mill, Segre contributed elegance to the group as well as brains.

Corbino added Edoardo Amaldi, the son of a mathematics professor at the University of Padua, by frankly raiding the engineering school. The group quickly nicknamed Fermi “the Pope” for his quantum infallibility; Corbino, like Rutherford at the Cavendish, called them all his “boys.” Rasetti departed to Caltech, Segre to Amsterdam, for seasoning. Fermi sent them out again in the early 1930s, after the decision to go into nuclear physics: Segre to