As a rule, scientists display their talents either as theorists or as experimentalists, but not both. Einstein, Maxwell, and Gibbs, for example, were great as theorists but not creative as experimentalists, while Faraday and Rutherford, great as experimentalists, were limited as theorists. Only Newton, in our company of physicists seen so far, displayed great talent as both an experimentalist and a theorist (and also as a mathematician). The subject of this chapter, Enrico Fermi, is another exception to the rule that physics is a bipartisan community. Fermi was, as his biographer and colleague, Emilio Segrè, remarks, “from the first a complete physicist for whom theory and experiment possessed equal weight.”
He began as a theorist in 1926 by showing how to count the quantum states of atoms according to Pauli's exclusion principle. In the 1930s, he built a complete theory of β decay beginning with another Pauli idea, that β particles always appear in company with tiny particles that carry no electrical charge and almost no mass. This work was a pioneering effort in what is now known as quantum field theory. Fermi could have continued in this direction and become a dedicated theorist. Instead, he chose to become an experimentalist armed with the technique of neutron bombardment. These efforts were also pioneering, and they led him finally to one of the landmark achievements of modern experimental physics: control of a nuclear chain reaction.
Enrico Fermi was born in Rome in 1901, the youngest of three children. His mother, Ida, was a schoolteacher; his father, Alberto, a railroad administrative employee. The Fermi family had few luxuries. Their apartment “had no heating of any kind,” reports Fermi's wife Laura in her charming biography and reminiscence, Atoms in the Family. While he was studying, Enrico was obliged to sit on his hands to keep them warm, and somehow contrived to “turn the pages of his book with the tip of his tongue, rather than pull his hands out of their snug warming place.”
The dominant influence in the Fermi household was Ida. “It was [Ida's] thorough and intelligent devotion that kept them together,” writes Laura Fermi. She