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Universal Expansion and the Distribution of Light

  1. Dec 22, 2011 #1
    Okay to preface my question, we know the universe is expanding. We know that this is not uniform otherwise the distance between the Earth and Alpha Centauri would be increasing at the same rate as the distance between The Milky Way and M87, for example. I'm over-generalizing here for the sake of simplicity.

    Is it at all possible then, that due to the acceleration of the expansion of the universe for a galaxy that we see today to be invisible to us in the future?

    I'm thinking the answer is no. I think it is no because the reference frame. If we are traveling away from a far off galaxy at greater than c, then rate of expansion between us in our reference frame is greater than c. However in the reference frame of a photon traveling from the distant galaxy to us this would not be the case. The trip wouldn't take nearly as long and thus the photon would actually reach us.

    I could be way off track with this but any guidance would be greatly appreciated. This would answer several questions I have regarding this matter.
  2. jcsd
  3. Dec 23, 2011 #2
    Okay I was going to edit my post but it won't let me. Regardless, I just read on Wikipedia the following:

    "Since the parts of the universe cannot be seen after their speed of expansion away from us exceeds the speed of light, the size of the entire universe could be greater than the size of the observable universe."

    So to answer my own question, yes.
  4. Dec 23, 2011 #3
    Yes you have the right answer. The Universe in its entirety is larger than the portion we can see. Inflatuion allows for this without breaking any fundamental laws (rest mass travelling at or > c)
  5. Dec 23, 2011 #4

    George Jones

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    In general, I like Wikipedia, but, here, Wikipedia is wrong.
    In more detail:
  6. Dec 23, 2011 #5
    Thank you so much for posting that, I have been trying to wrap my head around this concept for a few days now and that diagram perfectly illustrates why when I point to a star in the sky and say "That star was THERE X number of years ago", I am wrong.

    It was in a different position when the light left, but by the time the light gets to us, it appears to have been in a different position.
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