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Hawking's Position on Repeating Big Bang

  1. Aug 2, 2013 #1
    What is the evidence for Hawking's statement here:

    "After giving a brief historical background on relativistic physics and cosmology, Hawking discussed the idea of a repeating Big Bang. He noted that in the 1980s, he and physicist Roger Penrose proved the universe could not “bounce” when it contracted, as had been theorized.

    Therefore, time began at the moment of singularity, and this has likely occurred only once, Hawking said. The age of the universe — now believed to be about 13.8 billion years — fits that model, as the number and maturity of observed galaxies seem to fit in the general scheme."


    http://www.space.com/20710-stephen-hawking-god-big-bang.html
     
  2. jcsd
  3. Aug 2, 2013 #2

    Simon Bridge

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    He tells you the evidence: "The age of the universe ... the number and maturity of observed galaxies ...".

    To get the details you've have to hunt through Hawking and Penrose published papers from the 80's.
    He's basically asserting that the Universe has physics consistent with being bounded at "the start".
    The model he was addressing appears to be the Lynds or Poplawski style one where the Universe never reaches the singualrity.
    Hawking has his own ideas about the start of time.
    There are other models.
     
    Last edited: Aug 2, 2013
  4. Aug 3, 2013 #3
    Hawking and Penrose have two assumptions 1 , gravity is described by GR and 2 matter/energy satisfies certain energy conditions.
    Assumption 2 is violated by inflation, although Borde Guth and Vilenkin argue that you will still get a singularity despite this.
    But assumption 1 is challenged by quantum theories of gravity that do predict a bounce.
    Intersentingly Penrose now thinks the universe is cyclic but via neither assumptions being violated , rather its through a novel affect he calls rescaling.
     
  5. Aug 3, 2013 #4
    How does the age of the universe of the number and maturity of observed galaxies prove that the big bang only occurs once?

    Telling me to hunt through his papers isn't very helpful :-)

    So what your saying is that he assumes that the universal constants are the same from t=0 to now? Why would that mean that the big bang is a singular occurrence?

    I appreciate that there are other models but that doesn't help me with my question :-) nor does it discredit his view
     
  6. Aug 3, 2013 #5
    How does a nonrecurring big bang assume gravity = GR? I haven't heard of g=GR to be honest, that is new to me. 2 Which certain conditions?

    How is assumption 1 challenged by quantum theories and how do quantum theories predict a bounce?
     
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