Dutch-born U.S. physicist who, with George E. Uhlenbeck (Uhlenbeck, George Eugene) (q.v.), a fellow graduate student at the University of Leiden, Neth., formulated (1925) the concept of electron spin, leading to major changes in atomic theory and quantum mechanics. Of this work Isidor I. Rabi, a Nobelist in physics, remarked, “Physics must be forever in debt to those two men for discovering the spin.” Later it was recognized that spin is a fundamental property of neutrons, protons, and other elementary particles.

A faculty member of the University of Michigan (1927–46) and Northwestern University, Ill. (1946–48), Goudsmit worked on radar research at the Massachusetts Institute of Technology, Cambridge (1941–44), and was head of Alsos, a secret mission that followed the advancing Allied forces in Europe to determine the progress of Germany's atomic bomb project.

From 1948 to 1970 Goudsmit was a member of the staff of Brookhaven National Laboratory, Upton, N.Y., and then joined the University of Reno, Nevada. His works include The Structure of Line Spectra, with Linus Pauling (1930); Atomic Energy States, with Robert F. Bacher (1932); Alsos (1947); and Time, with Robert Claiborne (1966).