hi can inertial reference frame be in different sizes at least in theory? i mean that can there be two different frames of reference in same place at same time, where the observer in both frames observes physical laws to be normal in their own frame of reference, but the other frame appears to be smaller than the other and both agree with this? is there some fact that deny this? special relativity could give at least one restriction for such inertial obs. reference frames: -if the frame is L times larger, its time must run L times slower- otherwise it would emit light at superluminal speed. right? there is at least two open questions what comes into mind: 1 would change in size of reference frame cause some internal forces (inertia or tidal) in the inertial reference frame or not? 2 would larger reference frame have more energy than smaller? yes -i know that in astronomy there aren't any known phenomena where the size of inertial reference frame would change into another or be another.