Whooosh! There goes time, passing by! No Grumpy. Clocks count the cycles, and that's it. There isn't any actual time passing by. Because of the wave nature of matter. Simplify a muon to a wave in a circular path like this O. It's good for one zillion rotations. Now turn it round so it looks like this | then move it fast so it looks like this /\/\/\/\/\/\ and you should recognise the simple inference of time dilation. That was 1905. Now pay attention: "In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust. But in reality this is not the case. We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity; its results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (e.g. of light).”. RELATIVITY: THE SPECIAL AND GENERAL THEORY by A. EINSTEIN translated 1920. The word velocity is the common usage, not the vector quantity. It ought to be speed. My quote from 1920 trumps yours from 1905, so: Game, set, match.