Theodore "Ted" Allen Welton (July 4, 1918 – November 14, 2010) was an American theoretical physicist best known as the co-author of the fluctuation dissipation theorem.

He worked at Los Alamos National Laboratory on diffusion problems during the Manhattan Project and was present at the Trinity Test.

In 1948, he gave a simple qualitative description of the quantum electrodynamic corrections in atomic physics such as the Lamb shift as the interaction of non-relativistic treated electrons with stochastic quantum mechanical fluctuations of the electrodynamic field in the vacuum state, the mean value of which vanishes, but the standard deviation does not.

[5] In 1950 he worked at Oak Ridge National Laboratory in the Theoretical Physics Division; and in the following year, with Herbert Callen, he published the landmark fluctuation-dissipation theorem, showing that the explanations of Brownian motion and Johnson noise are specific examples of the more general theorem.

[2] Over the course of his career, Welton contributed to the development of nuclear reactors, and worked on particle physics and electron microscopy.