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What was there before Big Bang?

  1. Jun 30, 2011 #1
    What was there before Big Bang? Cosmologists suggested that there was quantum vacuum, but what was there before quantum vacuum? From where did quantum vacuum came? And why was there a quantum vacuum rather than nothing?
     
  2. jcsd
  3. Jun 30, 2011 #2

    bcrowell

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    Hi, Nernico,

    Welcome to PF!

    I think you've misunderstood something about the quantum vacuum. You seem to be visualizing it as a kind of empty space that predated the big bang. That isn't right. There is no viable cosmological model in which empty space predated the big bang. "Quantum vacuum" is just an ordinary vacuum. The "quantum" part is just a way of emphasizing that an ordinary vacuum, such as the one that exists between the atoms of air in this room, isn't really empty: it contains particles that pop in and out of existence.

    First off, we don't have a theory of quantum gravity, so there is no way that we can confidently answer questions like this using quantum mechanics. The best we can really do based on well-tested theories is to answer this kind of question using general relativity, which is classical, not quantum-mechanical.

    So in terms of GR, the picture we have is that time and space exist only for t>0. For any t>0, there is an earlier time, so we can always give cause and effect explanations. Conditions at any given time were caused by conditions at an earlier time. GR can't answer questions like why there is something rather than nothing. It can, however, say that there was something rather than nothing at time t because there was something rather than nothing at an earlier time. In GR's model, there is never any creation of matter out of nothing (in technical terms, mass-energy is locally conserved). Matter exists at all t>0, and there was never a universe full of empty space.

    GR's description of cosmology is expected to be wrong due to quantum-mechanical effects at times earlier than the Planck time, which was about t=10-43 s. There are speculative attempts to construct a quantum-mechanical theory of gravity that would fix these problems. Marcus works in that field, and he will probably chime in with a better description of that than I can give.

    Hey, Marcus, this question clearly deserves a FAQ entry -- want to write one? If so, feel free to use my material above if you find it useful.

    -Ben
     
  4. Jun 30, 2011 #3

    marcus

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    Not everybody says quantum vacuum.
    The basic game is to get a model that you can test observationally that evolves through where the older models break down, back to before the start of expansion.

    I would not even say "quantum vacuum" is the predominant theme in todays research. It was more common back in 1990s.

    The field you are asking about is called Quantum Cosmology. Here are the recent papers in QC (2009 or later).
    http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=dk+quantum+cosmology+and+date+%3E+2008&FORMAT=WWW&SEQUENCE=citecount%28d%29 [Broken]
    =======================

    Hi Ben! I just saw your post. That's a good suggestion. I will try to write something.
     
    Last edited by a moderator: May 5, 2017
  5. Jun 30, 2011 #4
    Then the whole and infinite space is infinitely occupied by something ? Beyond our universe is there something infinitely? And how can energy exist eternally without ever being brought into existence?
     
  6. Jun 30, 2011 #5

    marcus

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    You are getting philosophical Nernico.
    The typical meaning of universe is all physical existence. No beyond.

    This is cosmology forum. We discuss standard cosmo. We don't address questions like "why does existence exist?" You'd have to go to a philosophy or religion forum.

    Standard model cosmo takes physical existence for granted. The challenge is to understand it, model it, work back in time to earlier and earlier times. Predict, Test the predictions. Correct and refine our mental picture of the physical world.
     
  7. Jun 30, 2011 #6
    I am sorry english isnt my native language.
    I was asking if the whole space is infinitelly occupied by something since its impossible energy doesnt exist.
    Beyond that 'i' where all matter was compressed before the big bang, the INFINITE was occupied by energy or something? is the INFINITE occupied by something?
     
  8. Jun 30, 2011 #7

    bcrowell

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    We actually don't know whether the universe is spatially infinite: https://www.physicsforums.com/showthread.php?t=506986

    Not sure what you mean by "infinitely occupied?"

    What do you mean by "beyond our universe?" The universe doesn't have an edge.

    What makes you think that things have to be brought into existence in order to exist?
     
  9. Jul 1, 2011 #8

    Chalnoth

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    Well, it isn't necessarily wrong. There are basically two different avenues that I have seen in investigating what might have been before our universe. One is some sort of cyclic universe. This includes ideas like loop quantum cosmology and the ekpyrotic universe.

    The other is one where you're continually getting new regions of space-time produced as a result of quantum fluctuations. This includes ideas like eternal inflation and de Sitter equilibrium cosmology.

    The latter idea could, in some situations, be described as our universe being born out of a previous vacuum state.

    It's also worth mentioning that merely having a theory of quantum gravity is not sufficient to distinguish between these two scenarios. For instance, within string theory you can have either the ekpyrotic theory or eternal inflation, which are quite different ways of talking about what happened before our universe. So it isn't just about the theory of gravity, but also about about what the conditions of the early universe are.
     
  10. Jul 1, 2011 #9
    I would hihgly reccomend watching BBC's documentary "What happened Before the Big Bang?" you should find it on youtube very easily. They have a great laymans intro to manyof the current pre big bnag models such as eternal inflation, the big bounce, CCC, Ekpyrotic universe etc
     
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