Hugh Everett's work has been described by many people in terms of many worlds, the idea being that every one of the various alternative histories, branching histories, is assigned some sort of reality.

Gell-Mann is responsible together with Pierre Ramond and Richard Slansky and independently of Peter Minkowski Rabindra Mohapatra Goran Senjanovic Sheldon Lee Glashow and Tsutomu Yanagida for the see-saw theory of neutrino masses that produces masses at the large scale in any theory with a right-handed neutrino. He is also known to have played a large role in keeping string theory alive through the 1970s and early 1980s supporting that line of research at a time when it was unpopular.