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Quantum equations suggest the big bang never happened

  1. Feb 10, 2015 #1
    http://www.iflscience.com/physics/quantum-equations-dispute-big-bang

    Should we be taking this seriously or not? Thoughts?
     
  2. jcsd
  3. Feb 10, 2015 #2

    phinds

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  4. Feb 10, 2015 #3

    Chalnoth

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    I.e., no, there's no reason to take this seriously.

    It's standard knowledge within cosmology that the big bang singularity is impossible. The question remains as to what was going on in the densest times. There are two general approaches that theorists have taken in an attempt to explain the discrepancy:
    1. Come up with an alternative model which, when extrapolated forward in time, gives a universe that looks like our own. Cosmic Inflation is one example of following this paradigm.
    2. Take the currently-known components of our universe and extrapolate backward in time towards the singularity, but make use of a theory of quantum gravity to describe the universe at very early times. Loop Quantum Cosmology is one example here. This is also the approach taken by Ali and Das.

    Personally, I tend to favor the first approach, but we don't yet have evidence to show which approach is more likely to produce results, or which specific theory is likely to be accurate.
     
  5. Feb 10, 2015 #4
  6. Feb 10, 2015 #5

    Chalnoth

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  7. Feb 10, 2015 #6

    TeethWhitener

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    The actual paper was just published in Phys. Lett. B (decently reputable journal). Here's the arxiv: http://arxiv.org/abs/1404.3093v3
    The paper itself is interesting, although it's not an area I know much about. It basically takes the Raychaudhuri equation and replaces the geodesics with Bohmian trajectories (from Bohm's quantum analogue of the Hamilton-Jacobi equation). This guy Das has another paper in Phys. Rev. D explaining this procedure, but again, not my area of expertise, so I'm not sure how well I can speak to the veracity of it. But long story short, it turns out when you do a few substitutions on this quantum Raychaudhuri equation, you get the Friedmann equations with a few extra terms, one of which looks like a cosmological constant and another of which eliminates the big bang singularity. It might be speculative, but it isn't worth writing off without a second look.
     
  8. Feb 11, 2015 #7

    Chalnoth

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    Yes, just to be clear: the work itself is potentially interesting, if you like speculative theories (I haven't looked at it in detail). I was merely talking about the news article, which is sensationalist and misleading.
     
  9. Feb 11, 2015 #8

    phinds

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    Yeah, me too.
     
  10. Feb 11, 2015 #9

    bapowell

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    Except that the inflationary universe still must contend with the initial singularity.
     
  11. Feb 11, 2015 #10

    Chalnoth

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    It is true that cosmic inflation doesn't eliminate the singularity, it just pushes it further back in time (by an indeterminate amount), in that if you extrapolate the inflationary universe back in time you get a singularity eventually. But my statement was about the general paradigm of thinking of how to solve the problem of the singularity, and you can just apply the same paradigm again to cosmic inflation. Some examples of ideas based in cosmic inflation that avoid an initial singularity include considering a quantum vacuum fluctuation from an empty universe with a small but positive cosmological constant, or considering a tunneling event from a previous false vacuum state. Either of these allow an inflationary universe to begin without an initial singularity.
     
  12. Feb 11, 2015 #11
    A DeSitter zero entropy quantum vacuum ?
     
  13. Feb 12, 2015 #12

    Chalnoth

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    I do not know what you're asking, but DeSitter space does not have zero entropy: it has entropy proportional to the area of the cosmological horizon.
     
  14. Feb 12, 2015 #13
    Didn't the Cassimir Experiment suggest such a possibility ? The Universe "popped up " from nothing , and that nothing being the DeSitter model ? And that , based on Quantum Theory ?
     
  15. Feb 13, 2015 #14

    Ken G

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    It's up to scientists to change the question into the one science really deals with. Science does not deal with the question "did the Big Bang happen", because the Big Bang was not an event, it is an evolutionary story that starts from a position of significant certainty located in our present time and vicinity, and describes backward in time, involving more and more phenomena, toward more and more uncertainty, as the observations get more difficult (or impossible), and the theories get more speculative. I'm sorry if the general public cannot think in terms of that kind of nuance, but it is still our duty as those who can to make sure the question does not get turned into something pseudoscientific.
     
  16. Feb 13, 2015 #15

    PeterDonis

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    The Casimir effect shows that quantum vacuum fluctuations in a field can have real physical effects; but the field in that experiment is the electromagnetic field, which has a vacuum expectation value of zero. The de Sitter universe and the inflationary model require a field (either a cosmological constant or a scalar field) with a nonzero vacuum expectation value, which is a different thing.
     
  17. Feb 13, 2015 #16

    ftr

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    Can somebody elaborate please.So, are they saying that the matter energy in the universe equals vacuum energy.
     
  18. Feb 13, 2015 #17
    What is "un-scientific " about proposing the Big Bang never happened ? And what is this "position of significant certainty " ? In the Standard Model the only thing that can be said with certainty can only trace back to a point AFTER the initial event . As far as using the term pseudoscientific , this idea by these two scientists can not be thought of as such , after all, Hoyle 's Steady State was never termed pseudo-scientific , was it ? Yes it has been put to rest , but I'm sure Hoyle's getting a chuckle right now .
     
  19. Feb 13, 2015 #18
    Correct me if I am in error , but wasn't the results [ although debatable ] of that experiment used by quantum theorists to hypothesize a possibility of how the Universe initially started it's inflation ?
     
  20. Feb 13, 2015 #19

    PeterDonis

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    Not to my knowledge. Again, the kind of vacuum fluctuations involved in hypotheses about how inflation got started are not the same as the kind of vacuum fluctuations whose effects were detected in the Casimir effect experiment. I suppose you could view the experiment as giving support for the general idea of vacuum fluctuations, but nobody to my knowledge has cited the experiment as a contributing factor in the models about how inflation started.

    Also, why do you say the results of the Casimir effect experiment are "debatable"?
     
  21. Feb 13, 2015 #20

    Ken G

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    To answer that, you have to say what you mean by that it did happen, or that it did not happen, and make either a scientific statement. Be completely specific about what you mean by the words.
    That which we observe, like the Earth, the nearby stars, the Hubble law in near the local group of galaxies. Those are all things of significant certainty in astronomy. Going further, and back in time, the uncertainties grow, we have event horizons, dark matter, dark energy, inflation, the Planck scale, etc.
    What initial event are you talking about? What testable and objectively verifiable scientific model includes such a thing, or rules out such a thing?
    Even if you have a steady-state model, and you demonstrate that it agrees with all observations, it is pure pseudoscience to extend that model to a time of negative infinity. It simply isn't what you can use a model to do, and still be doing science.
    Yet that's just what I'm talking about-- if one does not think scientifically about what the purpose of a model is, then one takes a very black-or-white view of what a model is doing. So either the universe began in some singularity, or else it existed forever, and either of those possibilities makes perfect sense, regardless of whether or not we have any means of making any observations that could ever rule either one out. What's more, if we find evidence that some set of equations seems to resonate better with our current prejudices, this means Hoyle was right after all. The idea of universal inflation has been around for much longer than these "quantum corrections", and universal inflation has an infinitely old universe also, in something much closer to a steady-state model.
     
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