If the 19th century was the century of chemistry, the 20th was the century of physics. The burgeoning science supported such transforming applications as medical imaging, nuclear reactors, atom and hydrogen bombs, radio and television, transistors, computers and lasers. Physical knowledge increased so rapidly after 1900 that theory and experiment soon divided into separate specialties. Enrico Fermi, a supremely self-assured Italian American born in Rome in 1901, was the last great physicist to bridge the gap. His theory of beta decay introduced the last of the four basic forces known in nature (gravity, electromagnetism and, operating within the nucleus of the atom, the strong force and Fermi's "weak force"). He also co-invented and designed the first man-made nuclear reactor, starting it up in a historic secret experiment at the University of Chicago on Dec. 2, 1942. In the famous code that an administrator used to report the success of the experiment by open phone to Washington, Fermi was "the Italian navigator" who had "landed in the new world."
He had personally landed in the new world four years earlier, with a newly minted Nobel Prize gold medal in his pocket, pre-eminent among a distillation of outstanding scientists who immigrated to the U.S. in the 1930s to escape anti-Semitic persecution in Hitler's Germany and Mussolini's Italy--in Fermi's case, of his Jewish wife Laura.
A dark, compact man with mischievous gray-blue eyes, Fermi was the son of a civil servant, an administrator with the Italian national railroad. He discovered physics at 14, when he was left bereft by the death of his cherished older brother Giulio during minor throat surgery. Einstein characterized his own commitment to science as a flight from the I and the we to the it. Physics may have offered Enrico more consolatory certitudes than religion. Browsing through the bookstalls in Rome's Campo dei Fiori, the grieving boy found two antique volumes of elementary physics, carried them home and read them through, sometimes correcting the mathematics. Later, he told his older sister Maria that he had not even noticed they were written in Latin.
He progressed so quickly, guided by an engineer who was a family friend, that his competition essay for university admission was judged worthy of a doctoral examination. By 1920 he was teaching his teachers at the University of Pisa; he worked out his first theory of permanent value to physics while still an undergraduate. His only setback was a period of postdoctoral study in Germany in 1923 among such talents as Wolfgang Pauli and Werner Heisenberg, when his gifts went unrecognized. He disliked pretension, preferring simplicity and concreteness, and the philosophic German style may have repelled him. "Not a philosopher," the American theorist J. Robert Oppenheimer later sketched him. "Passion for clarity. He was simply unable to let things be foggy. Since they always are, this kept him pretty active." He won appointment as professor of theoretical physics at the University of Rome at 25 and quickly assembled a small group of first-class young talents for his self-appointed task of reviving Italian physics. Judging him infallible, they nicknamed him "the Pope."