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Relative time in space

  1. Oct 17, 2015 #1
    What speed does a ship travelling through deep space need to travel at for 1 day on the ship to equal 1 day on earth?
     
  2. jcsd
  3. Oct 17, 2015 #2

    BvU

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    Any speed will do. But both will observe the other guy's clock is running slow !
     
  4. Oct 17, 2015 #3
    I think it's 11km/s in the nearby Solar system, up to some 500km/s outside the Solar system, and even bit faster outside the Milky Way.
     
  5. Oct 17, 2015 #4
    If by 1 day you mean 24 hours measured by a clock on Earth and 24 hours measured by a clock on the ship, then they represent the same amount of time regardless of the speed of the ship relative to Earth. During the 24h measured by a clock on Earth a person on Earth would have aged 1 day, during the 24h measured by a clock on the ship a person on the ship would also have aged 1 day.
     
  6. Oct 17, 2015 #5

    PeterDonis

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    If the ship and the Earth are moving relative to each other, then there is no invariant way of matching up their "rates of time flow". So this question doesn't have a well-defined answer.
     
  7. Oct 17, 2015 #6

    PeterDonis

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    How are you coming up with these numbers?
     
  8. Oct 18, 2015 #7
    What I mean is, if you travel at 87% the speed of light, then 1 day on that ship is equal to 2 days on earth. So, is there a lesser percentage of the speed of light at which time would be equal for both the ship and the people on earth?
     
  9. Oct 18, 2015 #8

    BvU

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    That's only for an observer on earth ! The guy in the ship thinks it's the other way around !

    In your line of reasoning: zero. Stay put on earth.
     
  10. Oct 18, 2015 #9
    Thanks. Much appreciated!
     
  11. Oct 18, 2015 #10

    Nugatory

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    There is - relative speed zero, meaning that the ship is not moving relative to the earth.
    You can calculate this from the time dilation formula, which google will find pretty quickly - try "relativity time dilation".
     
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