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Big bang singularity

  1. Nov 16, 2012 #1
    I am a bit confused about big bang. Is the big bang referred to as the expansion of universe from singularity or not. Sorry if i have posted it in wrong section
     
  2. jcsd
  3. Nov 16, 2012 #2

    bapowell

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    The Big Bang model refers to the expansion of the universe from a young, hot, dense state. This model does not address the initial singularity -- it is understood to signal a breakdown of the physical theory. So when people refer to the Big Bang in mainstream cosmology, they aren't talking about the actual bang itself, but the model of an expanding universe emerging from a much denser initial state.
     
  4. Nov 16, 2012 #3
    Ok so why did this expansion occured
     
  5. Nov 16, 2012 #4

    bapowell

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    There is no direct cause. It might be unsatisfying, but the universe seems to be expanding simply because it can. Given the exact same distribution of energy, the universe could just as easily be contracting.

    The correct way to think of the initial expansion of the universe is as a boundary condition on the dynamics.
     
  6. Nov 16, 2012 #5
    So if i am correct than the main question arises why universe was in the hot and dense state in the first place right?
     
  7. Nov 16, 2012 #6

    bapowell

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    That, sir, is an excellent question.
     
  8. Nov 16, 2012 #7
    So are there any theories yet which suggest why
     
  9. Nov 16, 2012 #8
    There is one, but all it says is basically, if I remember correctly, something like "something called dark energy is causing this expansion and we know nothing about dark energy or why it causes the Universe to expand."

    I'm sure it's a lot more precise, but the gist of it is that, if there is a cause, then it's something we don't know anything about.

    (Please don't hold me to this, I could be quite wrong.)
     
  10. Nov 16, 2012 #9

    bapowell

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    I think the OP is asking more about the Big Bang itself, rather than theories of present-day expansion.

    The Big Bang process, more specifically, the exceptional low entropy initial conditions of the universe, remain a major unsolved problem in modern cosmology -- nobody understands why the early universe had the conditions it had (see the Boltzmann brain problem.)

    There are other ideas regarding the actual bang itself, or more correctly, what physical process was taking place at t=0. Hawking's proposal of a quantum origin for the universe -- that it was the result of a zero-energy quantum fluctuation -- is one popular example.
     
    Last edited: Nov 16, 2012
  11. Nov 17, 2012 #10
    Thank you both so we will have to wait now
     
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