Leó Szilárd

Leó Szilárd was born in Budapest in 1898 and studied in Berlin in the 1920s, where his teachers and colleagues included Einstein, von Laue and Planck. His 1929 paper on the entropy cost of measurement — built around what is now called the Szilard engine, a single molecule in a box — was the first work to connect information to thermodynamic entropy, decades before information theory existed.

Restlessly inventive, Szilárd conceived the idea of a nuclear chain reaction in 1933 while waiting at a London traffic light, and patented it the following year. Alarmed by the prospect of a German atomic bomb, he drafted the 1939 letter to President Roosevelt that Einstein signed, helping to launch the Manhattan Project, on which he then worked with Fermi to design the first nuclear reactor.

After the war Szilárd turned against the weapon he had helped create, campaigning for arms control and the civilian control of atomic energy. He also reinvented himself as a molecular biologist, making contributions to the understanding of enzyme regulation and bacterial growth.

Szilárd held, with Einstein, a patent on a novel refrigerator with no moving parts. A man of constant ideas and few institutional ties, he lived much of his life out of suitcases in hotels, and died in California in 1964.