If one makes a interferometer with a "arm" giant enough or moves it fast enough.. Forget that, basically you could have just a laser and detector floating in space, not connected, at huge distance, with the same speed and direction relative to a, say, planet in background. If the distance is large enough and/ or the system is moving fast enough, shouldn't the photon miss the detector by the time it gets there (as the detector has moved away from the position the laser was aimed at ) ? If we take away the planet in the background and there is only the laser and the detector in whole of space, then they are basically standing still. There is no way to measure their speed because there is nothing to measure it against (unless there is Eather .. which we still cannot really measure). If they are standing still, laser would surely hit the detector. I understand the system where the photon is replaced with .. something. A particle. System where the particle would simply have kinetic energy in another direction.. but can the same be for a photon? It would kinda have to move faster than c in order to cover that increased distance when summing the two vectors.. Any help clarifying this in my mind would be appreciated.