# Observer problem in Relativity [closed]

Which clock or observer conclude that time dilation has occurred? Is it the stationary clock/observer or the moving one? (Please bear in mind that each observer/clock independently concludes that one second has lasped according to their lightclock)

The stationary observer concludes that Event A and B occured simultaneously. The moving observer concludes that Event B occured first. Who then concludes that Simultaneity is Relative?

## closed as unclear what you're asking by John Rennie, Jon Custer, sammy gerbil, Prahar, Daniel GriscomMar 28 '18 at 0:50

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• It is still (as of v2) unclear what you are asking. However each observer concludes that the other observer's clock is running slowly, and there are probably thousands of other physics SE questions on this subject. – tfb Mar 19 '18 at 12:51
• Thank you for your response which I respectfully quote "...However each observer concludes that the other observer's clock is running slowly...". What you have just kindly stated is itself a conclusion. My question is therefore: which observer concludes that ''each observer concludes that the other observer's clock is running slowly''? – Jerry Gopaul Mar 19 '18 at 13:02
• They both do. Each observer makes a conclusion about the other one. The whole point of special relativity is that there is no "objective" reference frame, one can only make claims about someone else's reference frame with respect to their own. – Billy Kalfus Mar 19 '18 at 13:13
• Well, if they communicate with each other (or can make deductions based on special relativity) then both of them do, obviously. – tfb Mar 19 '18 at 13:15
• I'm tempted to think that you'll soon edit your post to ask "which observer concludes that (uniform) motion is relative?" – Alfred Centauri Mar 19 '18 at 13:42

My question is therefore: which observer concludes that ''each observer concludes that the other observer's clock is running slowly''?

Alice observes that Bob's light clock runs slower than hers and Bob observes that Alice's light clock runs slower than his.

Alice will explain to Bob that the fact that Bob observes her clock to run slow is because Bob's clocks are not synchronized.

Bob will explain to Alice that the fact that Alice observes his clock to run slow is because Alice's clocks are not synchronized.

That relatively moving observers don't agree on whether two events are simultaneous is known as the relativity of simultaneity.

See this answer for a spacetime diagram complete with arguing observers.