John Simpson died at age 83 in Chicago on 31 August 2000 from pneumonia following successful heart surgery. He was renowned as a nuclear and cosmic-ray physicist. At the University of Chicago he was the Arthur H. Compton Distinguished Service Professor emeritus at the Enrico Fermi Institute and the Department of Physics.
Simpson was born on 3 November 1916 in Portland, Oregon. He received an AB degree in physics from Reed College in 1940. At New York University he earned an MS degree in physics in 1942 and his PhD in 1943.