If reference frame A is travelling past reference frame B could one argue that it is in fact B that is motionless as their motion is relative to each other? If this is the case then how does one measure a particular objects motion relative to light? How can it be said that one reference frames time would slow down if motion is relative to another reference frame rather than relative to light? Sorry if this doesn't make sense. As I said I am a noooooooooooooooooooooob