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Does time dilation only affect matter that has mass?

  1. Oct 15, 2012 #1
    Does time dilation only affect matter that has mass?

    For example, A spaceship is 1 light year away from Earth at rest. It sent out a radio wave to Earth then travels at 99.99% of the speed of light. On Earth, from our perspective, we will receive that radio wave 1 year later but the spaceship arrives 70 years later. If that spaceship speed up to 99.999999% of the speed of light, it will take 7000 years from our perspective to see that spaceship.
    As a result, from our perspective, the faster that ship travels, the later it arrives, how does that makes sense?
  2. jcsd
  3. Oct 15, 2012 #2


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    You have the dilation the wrong way round. The spaceship arrives just over 1 year later by Earth's clocks, but 1/70 year later by the ship's own clocks.
  4. Oct 15, 2012 #3
    Ahh I see, I got the wrong way around all this time! Thanks for the reply!!
  5. Oct 15, 2012 #4
    So that means it only took the ship 5.21 days to arrive on Earth (from the spaceship's perspective) ? If so, that means if the spaceship can travel at 99.9999999999999% of the speed of light, it will only takes 1.41 second to arrive on Earth from the spaceship's perspective. It would be almost like... instantaneous travel...?
    In another word, From the light's perspective, all that light from the Big Bang 14 billion years ago was already spread out everywhere in the Universe since the beginning and what we're seeing are just the trails it left behind:grumpy:?
    Last edited: Oct 15, 2012
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