Father of the Atomic Age

by Andrew Crumey

Review of The Pope of Physics by Gino Segrè and Bettina Hoerlin. The Wall Street Journal, 21 October 2016.

In March 1939, at the Navy Department in Washington, Admiral S.C. Hooper was informed of a visitor. "There's a wop outside," the desk officer announced. The man in question, who overheard the slur, was Enrico Fermi. He had just won the Nobel Prize and had come to warn of the danger posed by his own recent discoveries in nuclear physics. Fortunately for his newly adopted homeland he had a thick skin. America, not Italy, would build the bomb.

Really it was Nazi Germany that Fermi feared more than the country he and his Jewish wife Laura had fled only a few weeks earlier. Fermi, almost single-handedly, had dragged Italian physics research into the modern age of quantum theory and relativity, and his emigration left Mussolini without the one scientist who might have given him a nuclear weapon. But if things had gone a little differently, might Fermi have done for Il Duce what Werner Heisenberg attempted for the Füaut;hrer? After reading this superb biography I am left with the nagging thought: maybe.

The book's co-authors, husband and wife, actually met Fermi, though were too young to receive any lasting impression. Gino Segrè's uncle, Emilio Segrè, was Fermi's student in Rome, choosing exile not long before Il Papa, as Fermi was half-jokingly nicknamed on account of his apparent infallibility in physics. Bettina Hoerlin's father was also an emigré physicist, and like the elder Segrè took part in the Manhattan Project. Given the authors' personal connections, their own scientific expertise, and the wealth of research they have undertaken, it is clear that they have produced a definitive study of Fermi's life and work. It is also apparent that even for the people who knew him best, Fermi was enigmatic. Urbane, genial, a team player with a generous spirit, he nevertheless kept his emotions hidden. "Not cold, but not warm either," was how one colleague described him. According to his daughter Nella, "It wasn't that he lacked emotions, but that he lacked the ability to express them."

Fermi's childhood offers some clues. For the first two and a half years of his life he was in the paid care of a "farm family" so that his parents, a civil servant and a teacher, could cope with their careers and two other children. When finally brought back, he cried with alarm, only to be chastised by his mother who told him, "In this home naughty boys are not tolerated." The repressed atmosphere worsened when Fermi was thirteen, with the sudden death of his older brother. While the parents withdrew into silent anguish, Fermi increasingly absorbed himself in mathematics, a talent noticed by a family friend who took the boy under his wing. Recognised as a prodigy, Fermi rose through Italy's most prestigious educational establishments, publishing his first paper in 1921 while still an undergraduate. In the following year Mussolini became prime minister, and much of Fermi's finest scientific work was to be carried out under the auspices of the Fascist regime.

Fermi's first major discovery came in 1926; a paper on quantum statistics that put him at the vanguard of theoretical physics. Three years later, when Mussolini created an exclusive academy of artists and scientists to promote the nation's intellectual achievements, Fermi was offered membership. It came with a substantial lifetime stipend and an expectation that the recipient would join the Fascist Party. Fermi accepted. Both in Italy and later in America he would present himself as apolitical, interested only in physics. Whether this was pragmatism, cynicism, naivety or a further manifestation of emotional withdrawal is impossible to determine.

Arguably his greatest achievement as a theorist was to predict the existence of a new fundamental force, now known as the weak interaction, in 1934. But Fermi was also a supreme experimentalist. He developed a way of producing free neutrons - particles normally trapped within atomic nuclei - and firing them into other nuclei, in the hope that they would lodge there. In this way he and his co-workers soon announced the creation of a new element, number ninety three in the periodic table. The Italian press immediately suggested calling it Mussolinium, but Fermi's team instead proposed Ausonium, from the Greek name for Italy. In fact, as later became clear, there was no new element in their samples. Instead of enlarging atoms the team had split them; the neutron bullets had provoked fission. Fermi realised that if a disintegrating atom were to eject further free neutrons then the process might continue in a chain reaction.

Fermi's apolitical stance was shaken in July 1938 when Mussolini began a campaign of persecution against Jews. Fermi's Jewish father-in-law, an admiral in the Italian navy, remained tragically loyal to his country, and would eventually die in a German concentration camp. Fermi, however, quickly began planning a research trip to America from which he and Laura would not return. His effort to secure a long-term visa was made easier by the Nobel Prize, collected en route.

A few weeks later he was at the U.S. Navy Department, having been asked by physicist Leo Szilard to alert the government to the possibility of creating a nuclear weapon. Fermi proved unpersuasive; so Szilard penned a letter that was signed by Einstein and delivered to President Rooseveldt, initiating what became the Manhattan Project. Fermi's key role was to use his neutron skills to create the world's first nuclear reactor. Segrè and Hoerlin's account of this famous episode is their book's high point, admirably conveying both the technical detail and the extraordinary tension of the operation. Fermi knew that if he could assemble enough uranium in the right shape, then the naturally released neutrons would be sufficient to initiate the desired chain reaction, producing heat. Removable absorbers could control the rate of reaction: anything from mild warmth to a potential inferno. Fermi's genius as an experimentalist enabled him to identify impurities of the components as a significant obstacle. In Germany, Heisenberg's team would fail to reach that insight, leading them down a blind alley in their effort to build a bomb.

Fermi acted as a roving consultant on the Manhattan Project, revealing nothing to Laura, even after witnessing the test detonation where he estimated the yield by calmly dropping scraps of paper and seeing how far they blew in the gust. A decade later, dying from stomach cancer, he calculated the quantities of nutrients being fed through his drip, made predictions of how many more days he might have left, and showed no trace of fear or regret. The bomb, and life itself, were for Fermi interesting problems of science, not matters for moral reflection. One can't help feeling that had he met a different, Aryan woman, and not had to leave Italy, history might have been very different.