A simple question, but maybe not so simple to answer. If the speed of light is relative, to what it is it relative? If it is absolute, against what is it absolute? It occurs to me that the speed of light could be considered to be absolute, in and of itself, and that every other speed (or rather velocity) can be considered relative to: 1. the rest frame against which the velocity is measured, and 2. the "absolute" speed of light (in the direction of the velocity being considered). The velocity of another inertial frame, when compared to our inertial frame, could be seen to "compress" the range of velocities from 0 -> c, relative to and in terms of the other inertial frame, into the range v (inertial frame) -> c, relative to and in terms of our inertial frame. Mathematically it works, does it have any physical validity?