The one-electron universe postulate, proposed by John Wheeler in a telephone call to Richard Feynman in the spring of 1940, states that all electrons and protons are quanta of a single quadridimensional field, with protons being electrons moving backwards in time:
As a by-product of this same view, I received a telephone call one day at the graduate college at Princeton from Professor Wheeler, in which he said, "Feynman, I know why all electrons have the same charge and the same mass" "Why?" "Because, they are all the same electron!" And, then he explained on the telephone, "suppose that the world lines which we were ordinarily considering before in time and space—instead of only going up in time were a tremendous knot, and then, when we cut through the knot, by the plane corresponding to a fixed time, we would see many, many world lines and that would represent many electrons, except for one thing. If in one section this is an ordinary electron world line, in the section in which it reversed itself and is coming back from the future we have the wrong sign to the proper time—to the proper four velocities—and that's equivalent to changing the sign of the charge, and, therefore, that part of a path would act like a positron." "But, Professor", I said, "there aren't as many positrons as electrons." "Well, maybe they are hidden in the protons or something", he said.
- —Feynman, Richard ♦ Nobel Lecture 11 December 1965
The postulate is the basis of modern quantum field theory:
All electrons, for example, are identical, being quanta of a single electron field filling all of spacetime. To each distinct species of particle corresponds a field, and vice versa. This, in a word, is the essence of quantum field theory: the natural framework for a description of relativistic quantum point-particles, explaining their corpuscular properties when detected in energy-momentum eigenstates and their wave behaviour when considering their spacetime propagation.
- —Govaerts, Jan ♦ On the Road Towards the Quantum Geometer's Universe: An Introduction to Four-Dimensional Supersymmetric Quantum Field Theory in "Proceedings of the Third International Workshop on Contemporary Problems in Mathematical Physics: Cotonou, Republic of Benin, 1–7 November 2003" ♦ World Scientific, 2004, p. 98