Hello! I am new in Relativity theory and i met somewhere that they say that the spatial distance between two events in two different inertia frames of reference is not the same. Did any one meet this before. So how can one show that inequality. I am thinking about the contraction of length when the observer is in a moving frame with a certain speed relative to a frame at rest. But as i think this can be used when both of the events are in one frame and the observer in the other. please help!