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Why no 'Big Crunch' a femtosecond after Big Bang ?

  1. Mar 8, 2005 #1
    Why no 'Big Crunch' a femtosecond after "Big Bang"?

    When the Universe was the size of a grapefruit, with the mass of 100 billion galaxies (actually, 20 times that mass, I suppose, given dark matter and dark energy), why did it not instantly suffer gravitational collapse into a megamega black hole?

    After all, nothing (except Hawking radiation?) escapes from a puny black hole with the mass of only 100 million Suns or so.
  2. jcsd
  3. Mar 8, 2005 #2
    The most honest answer is that is just not what the equations of cosmology predict will happen.

    If you want to rationalize it, perhaps say that in the beginning the universe was expandind faster than gravity could catch up ( expansion has unlimited "velocity", gravity goes the speed of light).
  4. Mar 8, 2005 #3


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    You can think of the Big Bang as a "kick" of sorts. In the classical approximation, the answer is that the universe had enough kinetic energy to keep expanding, despite the force of gravity. That's not entirely correct in the general relativistic way of looking at things, but the idea is the same.

    As to how it got that initial kick, nobody knows. If the big bang theory is true, then we may never know.
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