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Time delation by distance

  1. Feb 8, 2012 #1
    Time delation by distance!!

    Sun is so far that it take 8 minutes for its light to reach us. Let a big LED clock is placed at sun such that we can see it from earth. Now every second increment on sun's LED clock will be seen by us on earth 8 minutes later. So for us time on sun is passing very slow. Is this time delation?
     
  2. jcsd
  3. Feb 8, 2012 #2
    Re: Time delation by distance!!

    That is not time dilation, but the sun is much more massive then Earth, so that difference less the relative motion time dilation would probably equate to time on the sun is slower compared to on Earth.

    Note the Earth is not an inertial FoR :wink:
     
  4. Feb 8, 2012 #3
    Re: Time delation by distance!!

    But why that isn't time dilation. Clearly we will see the clock on sun runnning slow as compared to us!
     
  5. Feb 8, 2012 #4

    ghwellsjr

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    Re: Time delation by distance!!

    No, it will still be incrementing once per second. Clocks that are time dilated actually tick slower. In other words, we will always see the time on the clock on the sun 8 minutes earlier than clocks on earth. If there were time dilation, that 8-minute gap would get bigger the longer we observe.

    (I'm ignoring time dilation caused by gravity because I don't think you are asking about that.)
     
  6. Feb 8, 2012 #5
    Re: Time delation by distance!!

    I wonder why time will increment same as on earth once after 8 mins? Let the clock at sun changes color from red to green alternatively to show second increments. So, a red light photon as a signal from clock move toward earth, it will take 8 minutes to reach. Now one second increment occurs at sun, so another green light photon is emitted and it will take another 8 mins to reach earth.
     
  7. Feb 8, 2012 #6

    ghwellsjr

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    Re: Time delation by distance!!

    Since the distance between the sun and the earth is almost constant (at least I don't think that is your concern) and the speed of light is constant, the time it takes for the image of the clock or whatever coming from the sun will take the same amount of time, 8 minutes. It's like you are watching a live TV show on your TiVo but starting 8 minutes after it really started. Everything looks normal, just delayed by 8 minutes.
     
    Last edited: Feb 8, 2012
  8. Feb 8, 2012 #7

    Doc Al

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    Re: Time delation by distance!!

    Sun emits red light at 1:00:00
    Earth receives red light at 1:08:00
    Sun emits green light at 1:00:01
    Earth receives green light at 1:08:01
    ... and so on

    The light flashes are one second apart for both sun and earth. (Ignoring any relative motion or gravitational effects, of course.) The earth just gets them 8 minutes later.
     
  9. Feb 8, 2012 #8
    Re: Time delation by distance!!

    ok... I got it!! Thnx Doc Al
     
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