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Is our universe the unique possible outcome of the big bang

  1. Feb 28, 2012 #1
    is our universe the unique possible outcome of the big bang regardless of the original state?
    if not, what are the factors that may change the universe as we know it today?
    what they mean by (WEYL = 0) as the big bang ?
  2. jcsd
  3. Feb 29, 2012 #2


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    We could (in principle) develop a set of physical laws that constrained the universe to be exactly how it is, but Ockham's razor would say that's hogwash. Thermodynamics assumes that the universe is in one state out of an extremely large number of possibilities. Thermodynamics has proven to be wildly successful in describing our universe, so, no, our universe is not the unique possible outcome.
  4. Feb 29, 2012 #3
    thx Khashishi
    does the pahse-space of the early state of the universe has any effect?
    I don't understand what p.roger he is trying to say here:
  5. Mar 1, 2012 #4
    No because quantum mechanics comes into play and phase space no longer works in the way it does classically. Even if QM didn't come into play the chaos would be far to extreme for it to be meaningful.
  6. Jun 10, 2012 #5
    there could be millions or billions of variations because so much of our laws are based on the reality we're in (i.e., our bodies perfectly handle the gravity...) but if things were different a lifeform could evolve different.
  7. Jun 10, 2012 #6
    Yea. (At least in my view) the Universe has to be able to support life (as argued by the Anthropic Principle,) otherwise we wouldn't be here to exist in the Universe and realize it exists, but other than that, our Universe is not the one possible outcome.
  8. Jun 10, 2012 #7
    this thought right there
    kinda makes you wonder why there is a unvierse, seems a little odd to have a floating bunch of rocks expand out however far...
    maybe I should start studying philosophy to answer those whys :tongue2:
  9. Jun 10, 2012 #8


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    Short answer is no, not unique regardless of prior state. Leonard Parker is a reputable guy who has addressed this precise problem. He has a comparatively LESS TECHNICAL presentation, as an essay for nonspecialists, written with a younger guy named Ivan Agullo.

    The Gravity Research Foundation awarded it their first prize in 2011. If inflation were preceded by a period of contraction, for example, traces of the past would be expected to survive inflation---IOW could not be stretched out to featureless uniformity.
    Stimulated creation of quanta during inflation and the observable universe
    Ivan Agullo, Leonard Parker
    (Submitted on 21 Jun 2011)
    Inflation provides a natural mechanism to account for the origin of cosmic structures. The generation of primordial inhomogeneities during inflation can be understood via the spontaneous creation of quanta from the vacuum. We show that when the corresponding stimulated creation of quanta is considered, the characteristics of the state of the universe at the onset of inflation are not diluted by the inflationary expansion and can be imprinted in the spectrum of primordial inhomogeneities. The non-gaussianities (particularly in the so-called squeezed configuration) in the cosmic microwave background and galaxy distribution can then tell us about the state of the universe that existed at the time when quantum field theory in curved spacetime first emerged as a plausible effective theory.
    9 pages. Awarded with the First Prize in the Gravity Research Foundation Essay Competition 2011

    This is important. It means one can expect that whatever states preceded the start of expansion would have had an effect.

    What was there immediately prior, e.g. during a contracting phase, would have made a difference.

    So no, there are no grounds for believing that what we have now is the sole way things could be "regardless" (as you say) of what conditions and process preceded the start of expansion.
    Last edited: Jun 10, 2012
  10. Jun 11, 2012 #9
    You can study Philosophy til you're blue in the face...and you won't get that answer :-)
  11. Jun 12, 2012 #10
    Well, you'll probably get many answers--none of which will be provable, but one (or more?) of white might actually be correct, even if we don't know it. :)

    does the effect you describe (about pre-inflation conditions) allow one to make testable predictions? That would be really cool.
  12. Jun 12, 2012 #11
    a new paper just appeared on the arxiv discussing this:
  13. Jun 12, 2012 #12


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    Thanks for pointing that (and the Barrau-Grain paper) out! I hope there will be some definite testable predictions put out there. Here is a followup paper by Agullo et al that discusses the outlook for observable effects in Loop cosmology context.
    Perturbations in loop quantum cosmology
    Ivan Agullo, Abhay Ashtekar, William Nelson
    (Submitted on 5 Apr 2012)
    The era of precision cosmology has allowed us to accurately determine many important cosmological parameters, in particular via the CMB. Confronting Loop Quantum Cosmology with these observations provides us with a powerful test of the theory. For this to be possible we need a detailed understanding of the generation and evolution of inhomogeneous perturbations during the early, Quantum Gravity, phase of the universe. Here we describe how Loop Quantum Cosmology provides a completion of the inflationary paradigm, that is consistent with the observed power spectra of the CMB.
    4 pages. ICGC (2011) Goa Conference proceedings.

    (This paper refers to a longer one by the same authors which has not come out yet. It also refers to work other people presented at the December 2011 Goa conference.)

    There was also this ILQGS seminar talk by William Nelson, for which we have online audio and slides
    Last edited: Jun 12, 2012
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