The one-electron universe postulate, proposed by theoretical physicist John Wheeler in a telephone call to Richard Feynman in the spring of 1940, is the hypothesis that all electrons and positrons are actually manifestations of a single entity moving backwards and forwards in time.
"[1]A similar "zigzag world line description of pair annihilation" was independently devised by E. C. G. Stueckelberg at the same time.
Wheeler suggested that these backwards sections appeared as the antiparticle to the electron, the positron.
According to Feynman he raised this issue with Wheeler, who speculated that the missing positrons might be hidden within protons.
[1] Feynman was struck by Wheeler's insight that antiparticles could be represented by reversed world lines, and credits this to Wheeler, saying in his Nobel speech: I did not take the idea that all the electrons were the same one from [Wheeler] as seriously as I took the observation that positrons could simply be represented as electrons going from the future to the past in a back section of their world lines.