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    Special Relativity question

    You know that business about how theoretically you could leap in a spaceship, travel really really fast, and the time dilation effect of special relativity would mean that your ship's clock slowed down relative to clocks on the earth, meaning effectively you travelled faster into the future? (As used in Planet of the Apes, etc.)

    Well, I used to know this, but how does that work? I've got confused. Surely time dilation happens equally relative to each frame of reference. So equally people on earth would be travelling ridiculously fast relative to the spaceship, and thus relative to the spaceship the people on earth would be speeding into the future? (And I guess thus by symmetry if you reunited the clocks (and people) into the same frame of reference, the same amount of time would've passed for each).

    So how does that 'trick' work? Is it something to do with the effects of acceleration (which isn't "symmetric" in the same way as velocity)?

    #2
    Special Relativity question

    I don't really have the answer, but I'd take a loincloth, a rifle, grow some stubble and avoid bolshie silverbacks with a vocabulary just in case.

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      #3
      Special Relativity question

      Isn't this to do with the people on earth having an essentially stationery frame of reference (relatively speaking), while the person in the spaceship doesn't?

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        #4
        Special Relativity question

        Yeah: the point being that it's only the spaceship that speeds up (to separate the clocks' frames) and slows down (to reunite them). In the frame of the spaceship when moving, it would be the stationary clock that seems to slow down, but the comparison isn't carried out in that frame.

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          #5
          Special Relativity question

          Ok, this follow-up question is probably gonna make me seem stupid, but why is acceleration not relative in the same way as velocity? Mathematically it's just rate of change of velocity, isn't it? So if my velocity is changing relative to you, surely yours is changing equally (in opposite direction) relative to me? How do you tell which party is actually the one changing the frames of reference? (Something to do with which experiences the g-force?)

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            #6
            Special Relativity question

            That's absolutely right, you've nailed it. It isn't symmetrical because one party experiences the force and the other doesn't.

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              #7
              Special Relativity question

              That's sort of begging the question, though, really. The "How do some frames get to be inertial?" question isn't answered by the theory--not even by General Relativity, I don't think. Arguably it's the wrong kind of question to ask, I suppose.

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