The physics behind path integrals in quantum mechanics

Abstract

We present a simple pedagogical discussion of the physics of path integrals in nonrelativistic quantum mechanics. Rather than show that the path integral gives the standard results of quantum mechanics, as is usually done in the literature, we instead discuss why it does so. Specifically, we discuss why the phase factor associated with each path is given by the classical action. We construct the path integral using Huygens’ principle. Finally, we show that the existence of many paths is a consequence of the spreading of the quantum-mechanical wave function.