Hello I have not familiarised myself with the mathematics etc I merely have the conceptual idea that, for example, with the two slit experiement and electron is permitted to take "all possible paths" from the electron gun to the detector screen. The thought occurred (and as will all thoughts like this it will have obviously occurred to everyone else, I am only after an explanation, I am not claiming to have found a flaw etc)that not all paths are permitted. An electron is fired at t0 and hits the screen at t1. There is obviously a finite number of permitable paths as the time limit imposes constraints, in that it can't have gone to the andromeda galaxy and back to the screen as there is simply not enough time for the electron to propagate that distance. Can somebody point out how this is reconciled in the path integral formulation, or whether this exposes a fundamental misunderstanding on my part?