Source: U.S. National Archives
Published: July 1945
Why Are They Called Fermi Questions?
Circulated: May 12, 2020
A Fermi question is named after Enrico Fermi, a Nobel-prize winning Italian-American nuclear physicist. In 1945 he worked on the Manhattan Project during World War II.
During the Trinity test, which was the first detonation of a nuclear device, Fermi estimated the energy released by the blast.
“About 40 seconds after the explosion the air blast reached me. I tried to estimate its strength by dropping pieces of paper before, during, and after the passage of the blast wave. The papers during the shock wave fell about 2 1/2 meters… estimated to correspond to 10 kilotons of TNT.”
Fermi’s incredibly simple and fast calculation was within the right order of magnitude; the actual yield was 18.6 kilotons.