Since SR physics has considered motion strictly as the separation of bodies, no longer can a body move through space except with reference to another body. Consider an infinite number of frames (A, B, C, ... A1, B1, C1,...An) with common x axis. All move near the speed of light relative to their adjacent frames. If we choose as a frame of reference, say frame A, we have an infinite number of frames confirming the motion of A. If we now remove all frames except A, A is at rest. Not because of any dynamic change applied to A, but because the motion of A was always and only with respect to another frame. It is useless to argue whether A or any other frame is actually in motion with respect to space. Although this seems awkward, it is understandable in the framework of special relativity. If we now consider a mass as the origin of A, and A is the only mass in the universe, is it still useless to consider the motion of A with respect to space-time? Would it not be possible to measure the gravitational time dilation on the x axis of A to differ with significant motion along x?