Why should photons obey the rules of causality? This may have a quick answer, but it has been on my mind so here it goes: why, if according to special relativity, do photons obey the rules of causality, if they are inherently timeless. According to special relativity, wouldn't a particle travelling at light speed experience no time, and therefore, why would it be expected to obey the rules of causality as experienced by those not going the speed of light?
 A: Consider a photon that is emitted and then absorbed. For any "timely" observer (that is, anyone that sees the time flowing) will see the emission of the photon to happen before the absorption, and everyone will agree on which one comes first. So, whatever happens when and where the photon was emitted, cannot affect the place it will be absorbed before it arrives.
The ordering of light-like separated events is an invariant of Special Relativity. They have to follow causality because everyone else does, and they will all agree on it.  
A: In order to help the answer to this question, I would recommend the distinction between two things: You are referring to photons, that is lightlike movements. If you "remove" this lightlike movement (and the photons) from your consideration, there will remain two events: one event of emission and one event of absorption. Both events should have a timely dimension. And the first event seems to happen before the second event so that there is no causality issue.
