Enrico Fermi. Jack of Both Trades

In physics research, there is a stark divide between theorists and experimentalists. Very occasionally, a person appears who bridges that divide. One such was Enrico Fermi. Born in 1901, at age 22, he made his first breakthrough in theory. He realized that Einstein's E = mc2 predicted that a small decrease in mass from an atomic nucleus could release an enormous amount of energy. Three years later, he made his next. Wolfgang Pauli had propounded his exclusion principle. Fermi had become an expert in the statistical mechanics of Ludwig Boltzmann. He applied this to the analysis of the energy distribution of particles in a gas, with the constraint that they obey the exclusion principle, another theoretical achievement. Over the next decade, he made two more breakthroughs. The first, theoretical, was his analysis of beta decay, the ejection of an electron from a nucleus. The second, the one destined to have a worldwide impact, was experimental: the production of a sustained nuclear reaction. This was the crucial step toward building the atom bomb and peaceful uses of nuclear energy.