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Very Compact Early Universe

  1. Feb 16, 2010 #1
    I can't imagine an object more compact than a black hole for a certain radius and personally don't think it makes sense. Yet for earlier stages of the Universe, without a variable c , it gets far more compact than a black hole.

    Shouldn't major parts of the early universe simply collapse into black holes when such a density is present ? I mean for such a density the escape velocity would be far higher than c for major parts of the Universe, so how could it keep expanding ?
    And yes I did see explanations like, the space itself was expanding, but it doesn't sound convincing.

    Please let me know your thoughts.
    Thank you
  2. jcsd
  3. Feb 16, 2010 #2


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    Presumably you've seen this page? Anyway, the issue isn't whether verbal descriptions sound convincing to our intuitions, it's a mathematical matter of what is actually predicted by the equations of general relativity, and in this case you can find spacetimes that satisfy these equations everywhere that expand from such dense states.
  4. Feb 17, 2010 #3


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    I think what it really comes down to is the symmetry of the matter distribution. The early universe is expanding not just because we say so, but because that's what general relativity says will happen if you fill the universe with a uniform and isotropic energy density. In this case, there is no spatial curvature, but there is still a dramatic effect on spacetime by way of the time coordinate -- the universe expands!

    On the other hand, a black hole exhibits spherical symmetry. In this case general relativity gives you a static spacetime with the well known event horizon.

    I think the main point of confusion is that people often imagine the big bang as some singular point of high energy density. In fact, cosmology has nothing to say about The Big Bang itself, and most cosmologists use the term "big bang" to refer to the earliest moments in the expansion history of our observable part of the universe. These earliest moments are most accurately described by a uniformly expanding space with a homogeneous energy density.
  5. Feb 17, 2010 #4


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    The very early universe was not a black hole. It was a unique case of quantum weirdness.
  6. Feb 19, 2010 #5
    bapowell, thank you for your answer. It is very helpful.
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