🇮🇹Enrico
Fermi

On December 2, 1942, in a squash court beneath the west stands of Stagg Field at the University of Chicago, Enrico Fermi supervised the first self-sustaining nuclear chain reaction in history. Chicago Pile-1 — a stack of graphite blocks and uranium bricks assembled by a team of scientists over several weeks — went critical at 3:25 in the afternoon. Fermi monitored it from an instrument panel, calling out readings in a calm voice, drinking tea from a thermos. When the experiment was complete and the control rods were reinserted to shut down the reactor, someone opened a bottle of Chianti that had been hidden in a paper bag. They drank from paper cups. A few of the scientists signed the label of the bottle. No announcement was made to the press. Arthur Compton telephoned James Conant with the coded message: "The Italian navigator has just landed in the new world." The nuclear age had begun.

Enrico Fermi was born on September 29, 1901, in Rome, Italy, the youngest of three children of Alberto Fermi, a railroad administrator, and Ida de Gattis, a schoolteacher. He was self-taught to an unusual degree: at thirteen, he bought two second-hand books on mathematical physics at a market in Rome and read them cover to cover, working every problem, filling in every gap in the proofs. He did not know, as he worked through them, that the books were written in Latin — or rather, he did not mind. He studied physics at the Scuola Normale Superiore in Pisa, effectively teaching himself, and submitted a doctoral thesis on X-ray diffraction at the age of twenty. His examiners were embarrassed: the thesis was far more sophisticated than anything they could adequately evaluate. He received his doctorate in 1922.

His first great theoretical achievement came in 1926 with the development of Fermi-Dirac statistics — a quantum statistical framework for particles that obey the Pauli exclusion principle (now called fermions), complementary to the Bose-Einstein statistics that govern bosons. The Fermi-Dirac distribution describes how fermions — electrons, protons, neutrons — distribute themselves among available energy states, and it underlies all of solid-state physics and the behavior of metals, semiconductors, and white dwarf stars. In 1933 he produced a theory of beta decay — the process by which a neutron decays into a proton, an electron, and a neutrino — that was the first successful quantum field theory of the weak nuclear force. His paper was rejected by Nature as "too speculative." It is now recognized as one of the most important theoretical papers in nuclear physics.

The experimental work that won him the Nobel Prize came in 1934 in Rome, when he discovered that bombarding atomic nuclei with slow neutrons produced new radioactive isotopes far more efficiently than fast neutrons. This was, as he realized, because slow neutrons spent more time near a nucleus and were therefore more likely to be captured. He and his group in Rome systematically bombarded every element in the periodic table with slow neutrons, producing new radioactive isotopes in almost every case and apparently producing — though they did not realize it at the time — fission fragments from uranium. It was left to Hahn, Meitner, and Strassmann to identify nuclear fission four years later; Fermi's group had been producing it without recognizing what they had seen. He received the Nobel Prize in 1938, traveled to Stockholm to collect it, and did not return to Italy — he and his wife Laura, who was Jewish, had already decided to flee Mussolini's racial laws. They went directly from Stockholm to New York.

At Columbia and then at Chicago, Fermi worked on the Manhattan Project with a mastery of both theory and experiment that was unique among his contemporaries. He was, in the assessment of his colleagues, the last physicist who could do everything — derive a theoretical result in the morning and set up the apparatus to test it in the afternoon. He is remembered for Fermi estimation: the technique of arriving at accurate order-of-magnitude answers to apparently intractable questions through a chain of simple, well-chosen approximations. The question "How many piano tuners are in Chicago?" is a classic Fermi problem. The technique was Fermi's characteristic way of thinking — not solving exactly, but placing bounds intelligently, narrowing the range until the answer emerged.

His most famous offhand remark came during a lunch conversation at Los Alamos in 1950. The conversation turned to the apparent lack of contact from extraterrestrial civilizations. Fermi paused and asked, simply, "But where is everybody?" — a question that has generated a vast literature under the name the Fermi Paradox. If the universe contains billions of stars older than the sun, and if even a small fraction have planets that develop intelligence, the galaxy should be full of detectable civilizations. That we see none is one of the most disturbing puzzles in science. Fermi died on November 28, 1954, of stomach cancer, at the age of fifty-three. He had been working at the University of Chicago until weeks before his death. Element 100, discovered the year he died, was named fermium in his honor.