Enrico Fermi
The Italian-American physicist, a rare master of both theory and experiment, who built the first nuclear reactor and achieved the first controlled chain reaction.
Physics almost always splits its talent in two. There are theorists who work with chalk and paper, and experimenters who work with wires and machines, and the greatest of each are rarely the other. Enrico Fermi was both, at the highest level, which makes him nearly unique in the history of the field. He worked out the statistics that govern electrons in metals and neutrons in a reactor, and then he built the machine that proved it. He is the reason physicists can name the day the atomic age began.
Exile from Fascist Italy
Fermi grew up in Rome and became Italy's leading physicist under Mussolini. In 1938 the regime passed anti-Jewish racial laws that threatened his wife, Laura, who was Jewish. That December Fermi traveled to Stockholm to collect the Nobel Prize for his work on neutron bombardment, and instead of going home he sailed on to New York. He never returned to Italy. Fascism had handed the United States one of the century's essential minds.
The squash court
Under his direction at the University of Chicago, in a doubles squash court beneath the stands of an old football stadium, Fermi's team stacked graphite blocks laced with uranium into a lattice they called an atomic pile. On December 2, 1942, they slowly withdrew the control rods and the pile went critical: the first controlled, self-sustaining nuclear chain reaction in history, humming for about 28 minutes before Fermi shut it down. The pile had no shielding and no cooling; the safety plan was a physicist standing ready with an axe to cut a rope and drop an emergency rod, plus a squad poised to douse the reaction with cadmium solution. It never came to that. A colleague phoned the news in code: 'The Italian navigator has landed in the New World.' The reaction proved that fission could be tamed for a reactor or unleashed in a bomb.
The Fermi estimate
Fermi had a signature trick: a fast, rough calculation from almost no data, close enough to be useful. It is still taught as the 'Fermi estimate.' He gave the most famous demonstration at the first bomb test. Standing about ten miles from the Trinity blast on July 16, 1945, he tore a sheet of paper into scraps and let them fall as the shock wave arrived, then paced off how far it blew them. From that alone he pegged the explosion's power at roughly ten kilotons, an answer the instruments later confirmed as the right order of magnitude while the analysts were still doing their sums.
He died young, of stomach cancer, in 1954, at 53, with element 100 (fermium) and a national laboratory, Fermilab, named for him. The Italian navigator who landed in the New World had, in a dozen years, helped invent both the reactor that lights cities and the weapon that could erase them.