# Time and the principle of relativity

We know that every moving clock with respect to some clock A, is running slower than A. My question is simple - why it does not contradict the principle of relativity? Why can't we say that the clock which runs faster than any other clock is at absolute rest?

I remember that I've read in some book that its because the process of measuring time (in a moving train for example) is done in unequal conditions, but I didn't quite understand that.

• I recently watched [Escaping Contradiction: Simultaneity is relative ](youtube.com/watch?v=PuHKTpVvH_U). I think that this might explains things nicely. Commented Jun 11, 2014 at 18:43
• because 1) the contraction (Lorentz) factor depends on square of relative velocity and 2) by relativity principle each frame/observer can assume itself as stationary (zero velocity) and only other frames as moving, this provides the relativity of simultaneity Commented Aug 13, 2014 at 2:42

The clock A is running faster than any other clock - from its relative point of view only! Any clock B in (non accelerated) movement with regard to clock A would say the contrary: that clock A (and any other clock) is moving slower than clock B.

By the way, this contradiction is settled, if clock A starts at clock B and returns to clock B after a travel (including obligatorily acceleration processes) for time control. The travelling clock turns out to have run slower than the other one (but only due to the existence of acceleration processes!)

The missing ingredient is that simultaneity is also relative. For "rest" frame A, fill the universe with clocks synchronized with clock A that are also resting. For "moving" frame B (say, moving to the right), fill the universe with clocks synchronized with clock B that are moving along.

Let clock A encounter clock B when t = 0 on both. Thereafter, clock A receive a stream of B-synched clocks, and when comparing readings (only meaningful when two clocks are at the same location), find these B-clocks slow. Meanwhile, clock B will encounter a stream of "head-wind" A-synched clocks, and on comparison also find these clocks run slow.

For two observer A and B ,B moving with respect to A with velocity $$v$$. After time $$t$$ has elapsed in absolute rest frame(reference frame) Person A will say $$t$$ time has elapsed but person B will say time less than $$t$$ has elapsed ,from that A will conclude that his clock is moving faster than the clock of B . And similarly B will think the opposite way that his clock is running slower than than the clock of A.

• Your logic is somewhat unclear and sloppy Commented Jan 3, 2019 at 8:27