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Ok so u have two twins, both have clocks set to zero.

  1. Jun 3, 2008 #1
    ok so u have two twins, both have clocks set to zero. One of them takes off at close to the speed of light. That twins clock would run slow. However If the twin were to reset both clocks and take of at the same speed in the opposite direction for the same distance. would the clocks be off by the same amount? The stationary twin can only be stationary compared to another object. So how do we know that he is not flying through spacetime making the two flights time dilate at different rates?
  2. jcsd
  3. Jun 3, 2008 #2


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    Because there is no 'absolute' preferred frame of reference in SR. That is, there is no form of 'absolute' motion. So you have nothing truly at rest to measure local motion against.
  4. Jun 3, 2008 #3
    I believe that everyone determins his/her coordinate sys stationary and time not delayed.... so most likelly 1st twin sees everything that moves (including the other twin slow motion) and just the same 2nd twin sees everything that moves also slow motion

    after all if me myself am in my oun coordinate system with my oun light clock I see the light going straight up and straight down so my light ray does travel the shortest possible path

    the questions is... is it a satisfactory answere that each twin sees the other growing old slow

    in fact is it OK that I see everything that moves growing up slower
  5. Jun 3, 2008 #4
    Make it triplets and they are all moving at 0.8c relative to you in the positvie direction. Triplet A maintains constant velocity while triplet B accelerates in the positive direction so that triplet A sees triplet B as going at +0.8c relative to him. Triplet C accelerates in the opposite direction so that triplet A sees triplet C as going at -0.8c relative to him. By your measurements using the relatavistic addition equation, triplet A is moving at 0.8c, triplet B is moving at 0.98c and trilet C has stopped! According to you all the triplets are time dilating at different rates. However, to triplet A it would appear as if both triplets B and C are time dilating at the same rate. Hope that answers your question.
  6. Jun 3, 2008 #5
    you understood me kev thx
  7. Jun 3, 2008 #6
    Yec I understand that.
    but for me it is a little confusing that B sees C getting old slow. and C sees B getting old slow. when they get back to meet each other???
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