A particle travelling through space will (at least according to Newton's first law) continue at the same velocity etc. etc. My question is this: how does this particle "know" that this is how it must behave and that it is behaving correctly? Either the rules of the universe are contained within the particle (unlikely) or they are imposed upon it by the fabric of the universe (more likely). If the latter, then how can a "straight path" or constant "speed" be discerned/defined/imposed at the quantum field level?