I'm not sure whether this question belongs in the quantum section or here, since it kind of involves both areas. I'm not even sure I can ask the question sensibly since I'm not a professional physicist, but I'll try: Suppose we look at a particle, say a photon, moving along in space time. According to Feynman's "QED, the Strange Theory of Light and Matter", I can "explain" its motion by adding up the complex numbers from various alternative "trajectories" for the particle. Now some of those alternative trajectories will have wiggled way off the striaight line - maybe they went light years away. According to the principles of relativity, no information can be transmitted faster than light. How then do those way off-path alternative histories all get combined to produce the straight line ? To be a bit more specific, if I want to send a beam of light to the moon, how does the light "know" that there isn't a shorter path via Alpha Centauri ? It can't know unless it's been there and had a look and brought the information back with it, and that's impossible. I've seen people draw pictures where they wiggle a little bit off a straight line, but that doesn't help me understand the enormously diverted alternative paths.