Just to be clear, I am not a physicist, only a interested layman. As I understand it currently, photons don't travel any path. They are emitted somewhere at some point in time and detected somewhere else at another point in time, what they did in-between is not a meaningful question, at least in the classical sense of asking for a path the photon took. When we want to calculate the probability of observing the photon at a specific place at a specific point int time, then we consider all possible paths - including the photon traveling to the edge of the universe and returning from there, including the photon going into the future and coming back - and sum them up. There is a relatively simple formula for every possible path and those possibilities interfere when we sum them up, some path amplify each other, some cancel out, in the end you have a probability distribution in space and time telling you where it is likely and where and when it is unlikely to find the photon in case you tried to observe it there. What the photon did in-between, we don't know, is a meaningless question, ... at least I can't tell.