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B Evenly expanding universe?

  1. Apr 22, 2017 #1
    I know that the universe is expanding since the beginning of time or at least the beginning of the universe it self. So I was wondering if the universe has always expanded evenly (some parts getting bigger while other grow not as fast) and if it doing so now??
    The example in my head is like dropping die in water. The die on the outer edge will dissipate faster than the die in the middle of the drops. Or even some other kind of form of the idea.
     
  2. jcsd
  3. Apr 22, 2017 #2
    Overall, the rate of expansion appears to have varied over time,
    at first slowing down then, since the last 6bn years, speeding up again.
    However the expansion is not even since gravitationaly bound objects, like galaxies, don't expand at all.
    Most of the Universe though is (almost) empty, no significant amount of matter and therefore gravity exists.
    That is what is expanding, and at a given point in time the rate of expansion is the same everywhere,
     
    Last edited: Apr 22, 2017
  4. Apr 22, 2017 #3

    Chalnoth

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    Not quite. From what we can tell, the rate of expansion has done nothing but decrease. Early-on it decreased very rapidly, and less so more recently. The rate has been slowing down slowly enough over the last few billion years that objects have started accelerating away from one another.

    If this is confusing, notice that constant expansion means a constant recession speed per distance, so as things get further, they move faster relative to one another.

    This is why I refer to it as an "accelerated expansion" rather than "the expansion is accelerating".
     
  5. Apr 22, 2017 #4
    It suggests that as time goes forward, one variable increases while another decreases.
    There is a moment when they have the same value, but there is no significance in that value.
     
  6. Apr 22, 2017 #5

    Chalnoth

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    What are you talking about?
     
  7. Apr 22, 2017 #6
    Yep, you lost me on that one as well.
     
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