To calculate the electron’s proxy wave Ψ, Feynman postulates that the wave amplitude on the screen is equal to the sum of the amplitudes of all possible ways that an electron can get there from the quon gun. Furthermore all paths are equally important, none better than any other. Feynman implements this quantum democracy of possibilities in his scheme by assigning the same amplitude to every path. Each path differs from its fellows only by its phase. A path’s phase at any location depends on its history, the route that brought it there.
