I continue to see references to time dilation that I don’t understand. Maybe the bluntest one is in a textbook by Resnick. Introduction to Special Relativity, p. 93: “Indeed we find that the phenomena are reciprocal. That is, just as A’s clock seems to B to run slow, so does B’s clock seem to run slow to A;” Here is Einstein’s much more plausible version from his 1905 paper, in my opinion anyway. “From this there ensues the following peculiar consequence. If at the points A and B of K there are stationary clocks which, viewed in the stationary system, are synchronous; and if the clock at A is moved with the velocity v along the line AB to B, then on its arrival at B the two clocks no longer synchronize, but the clock moved from A to B lags behind the other which has remained at B by (up to magnitudes of fourth and higher orders), t being the time occupied in the journey from A to B.” Notice that he carefully gives the initial conditions; (1) the clocks were synchronized, (2) in a common stationary reference frame; (3) which clock was set in relative motion, clock A; and finally which clock lost some time, clock A. I cannot read that paragraph and think the effects are reciprocal. I do not think that an observer riding along with clock A could claim that it was actually clock B that was running slow and losing some time. Resnick’s version does not seem logically possible, that somehow both clocks could “seem to be running slow” relative to each other. Any help understanding this would be appreciated.