 But Galilean relativity implies that this latter projection is arbitrary. While it assumes that we can identify the same time at different spatial locations, Newtonian mechanics provides no physical way of identifying the same spatial point at different times. Thus the equivalence of inertial frames can be thought of as the arbitrariness of the projection of space-time onto space. Any such projection is, essentially, the arbitrary choice of some particular inertial frame as a rest-frame. In the relativized version of Newton’s theory, then, the class of inertial frames replaces absolute space, while absolute time remains. The structure of Newtonian space-time (also known as Galilean space-time, or neo-Newtonian space-time) expresses this fact in a direct and obvious way. (See Stein 1967 and Ehlers 1973 for further explanation.)