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Expansion of the universe

  1. Sep 10, 2015 #1
    I read in "The Theory of Everything" of Stephen Hawking that all of the galaxies are running away from ours.
    That made me think that the Milky Way is the center of universe, since each galaxy is running away from us(like waves on the surface of water centered at one point which is the Milky Way).
    Unless that the universe is infinite then it does not have center.
    I wish someone understand me and tell me whether this is right or not.
  2. jcsd
  3. Sep 10, 2015 #2


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    If you were in any other galaxy, it would appear that (most) galaxies are receding from it.
  4. Sep 10, 2015 #3
    Ok, but does not that mean that the universe is infinite?!
  5. Sep 10, 2015 #4
    It doesn't actually have a center. Or, at least, if it has, we can't prove it, I guess. Think of a cake with raisins: when you put it in the oven, it starts to rise. But each raisin would see the same scenario of every other raisin of the cake around it. Every rasin would then say "ya cool i'm the center of the cake!" but it actually has no opportunity to see the whole of it from outside. We're in the same situation, but since we are not rasins, we just say "no, there's no reason we should be at the center of the universe". This is what is called" Cosmological Principle".
  6. Sep 10, 2015 #5
    it is clear now
    thank you very much
  7. Sep 10, 2015 #6


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    I suggest the link in my signature
  8. Sep 10, 2015 #7


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    Think of the surface of an expanding sphere. Each point sees all other points receding uniformly.
  9. Sep 11, 2015 #8
    Thanks for all
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