The central concept of the theory of relativity is the relativity of velocity. Thevelocity of a material body is not an intrinsic property of the body; it depends on a free choiceof reference system. Relative velocity is thus reference-dependent, it is not an absolute concept.We stress that even zero-velocity must be relative. Every reference system possesses its ownzero-velocity relative only to that particular reference system. Does the theory of relativityformulated in terms of relative velocities, with many zero-velocities, imply the Lorentz isometrygroup? We discuss the many relative spaces of Galileo and Poincar′e, as quotient spaces.
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