Theodore Welton

Theodore Allen Welton (4 July 1918 to 14 November 2010) was an American theoretical physicist best known as the co-author, with Herbert Callen, of the fluctuation dissipation theorem. Born in Saratoga Springs, New York, he took a B.S. at the Massachusetts Institute of Technology in 1939 and his Ph.D. at the University of Illinois in 1944. In 1944 and 1945 he worked at Project Y in Los Alamos in Richard Feynman's T-4 Group on diffusion problems during the Manhattan Project and was present at the Trinity Test. He later taught at MIT and the University of Pennsylvania. In 1948 he gave a simple qualitative description of quantum electrodynamic corrections such as the Lamb shift as the interaction of electrons with fluctuations of the vacuum electromagnetic field, and in 1951 he and Callen published the fluctuation dissipation theorem, which shows that Brownian motion and Johnson noise are specific examples of a more general result. He also worked at Oak Ridge National Laboratory, on nuclear reactors, particle physics and electron microscopy.