Note 8 — VIII ON THE IDEA OF TIME IN PHYSICS

We suppose further, that, when three events , and occur in different places in such a manner that is simultaneous with , and is simultaneous with (simultaneous in the sense of the above definition), then the criterion for the simultaneity of the pair of events , is also satisfied. This assumption is a physical hypothesis about the law of propagation of light; it must certainly be fulfilled if we are to maintain the law of the constancy of the velocity of light in vacuo.