Please forgive if this question is not up to snuff. Indeed, I am a painter, and very much the amature physics enthusiast.(adsbygoogle = window.adsbygoogle || []).push({});

One of Einstein's classic thought problems that interested me was the idea of two astronauts passing each other at a high velocity in open space. The idea was that in this case motion was completely relative... it was equally proper to say astronaut A was zooming by astronaut B as it was to say the opposite.

If motion is completely relative in this sense, then how does this figure into the time dilation problem (i.e., the space traveler who leaves earth at a high rate of speed. For those left on earth, time passes much more quickly than for our intrepid traveler.) Sadly, if our astronaut ever returns, all of his or her loved ones are all long dead, etc.

If motion through the universe is completely relative, indeed, if it is equally proper to say that the earth left our astronaut at a high rate of speed, then does time dilation not cancel out? Or is there some objective way to measure the relative velocities and distances involved so that we know who is aging more quickly than whom?

Any feedback regarding this question would be greatly appreciated.

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# Isn't time dilation relative?

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