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What existed before the big bang?

  1. May 9, 2006 #1
    i all ways wonder this. what existed before the big bang?
     
  2. jcsd
  3. May 9, 2006 #2
    i think this was supposed to go into the cosmology section.
     
  4. May 10, 2006 #3

    row

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    hi i think i read somewhere that,it is assumed that time came into existance with big bang just as the other dimensions hence the concepts like 'before' ,'after' etc.are irrevelant with bigbang.
     
  5. May 10, 2006 #4

    J77

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    From a non-cosmologists point of view...

    I agree. I always thought that everything we know, ie. space an time, came from the singularity known as the big bang.

    My question would be - in what did this singularity exist?

    What caused the singularity?

    If I'm in the place where the singularity exists, can I redo the entire universe again, both in space and time?
     
  6. May 10, 2006 #5

    EL

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    Tracing our univserse backwards in time, General Relativity predicts it started from a singularity.
    What must be kept in mind is though that GR is not compatible with quantum theory, which means that it's not meaningful to use GR to predict the earliest stages of the Big Bang. Hence wheter there was a singularity or not is an open question, and will remain so until we find a good theory of quantum gravity.
     
  7. May 10, 2006 #6
    a small silence?
     
  8. May 10, 2006 #7
    i just came up with a theory. another universe. maybe when a
    universe ends it explodes in a big bang and creates another universe. what do you guys think?
     
  9. May 11, 2006 #8

    Garth

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    Another universe - a great idea that is very popular in cosmological circles, but show me it.

    Garth
     
  10. May 11, 2006 #9

    Pengwuino

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    The big bang wasn't an explosion
     
  11. May 11, 2006 #10
    the big bang was more like the creation of "reality"
     
  12. May 11, 2006 #11

    wolram

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    The quantum gravity guys are your best bet for an ansewer, but even they do not know what topping to put on their crustless pizza.
     
    Last edited: May 11, 2006
  13. May 11, 2006 #12

    marcus

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    this fits Renate Loll's picture
    http://arxiv.org/find/grp_physics/1/au:+Loll/0/1/0/all/0/1

    Reconstructing the Universe
    http://arxiv.org/abs/hep-th/0505154

    The Universe from Scratch
    http://arxiv.org/abs/hep-th/0509010

    Loll has a quantum model of spacetime down at the fundamental (planck-scale) level from which a familiar classical large-scale spacetime emerges
    and she and her co-workers do computer model of this spacetime

    you can say that it starts (by a quantum fluctuation according to her law) with a "small silence" and then grows

    because of limitation of the computer used to model, it cannot grow indefinitely, eventually it starts to shrink and after a while *poof* disappears into a "small silence" again.

    this is not necessarily right but at least it is a quantum model that sort of works and runs by its own rules and you can put in a computer.

    Loll is at the same institute of theoretical physics as Gerard 't Hooft one of the few Nobel Laureates in theoretical physics who is still not an 'elder statesman' and 't Hooft himself is doing original work related to quantum gravity.

    I think Loll's picture of the universe is worth taking seriously, even if it seems stretching it to have everything arise from an accidental quantum hiccup. Once they get a model going they can crawl around inside it (as a virtual reality inside the computer) and measure geometrical stuff and that is pretty interesting. so in a sense who cares where it came from as long as it is fun to explore.
     
    Last edited: May 11, 2006
  14. May 11, 2006 #13

    marcus

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    Something like what you say has become a widely studied possibility. A world-class scientist who directs research in this area is Abhay Ashtekar
    He just spent the past academic term at 't Hooft's institute in Holland but now I think he may be back home at his own institute at Penn State.

    The model Ashtekar works with has a gravitational collapse prior to the big bang. there is a deterministic evolution of the wavefunction through what used to be called the "singularity".

    Strictly speaking singularities do not exist in nature so one has to find a model that will evolve through them and not get shook up by them. A lot of people are working on this.

    here are some of Ashtekar's papers

    http://arxiv.org/abs/physics/0605078
    The Issue of the Beginning in Quantum Gravity

    http://arxiv.org/abs/gr-qc/0605011
    Gravity, Geometry and the Quantum

    http://arxiv.org/abs/gr-qc/0602086
    Quantum Nature of the Big Bang

    A lot of the writing in these papers is accessible to general audience---not too technical with only occasional patches of equations.

    If anyone wants a more thorough treatment there is this 100-page treatise with computer animations and much technical detail, by Martin Bojowald
    http://arxiv.org/abs/gr-qc/0601085
    Loop Quantum Cosmology
     
    Last edited: May 12, 2006
  15. May 12, 2006 #14

    Chronos

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    Still dodging the issue, in my mind. At some point [e.g., the 'original' big bang] we must confront a breakdown in causality. The cyclical universe model merely pushes responsibility for explaining the existence of our universe to an earlier 'cycle'. I fail to see how this is superior to arguments favoring a universe from nothing.
     
    Last edited: May 12, 2006
  16. May 12, 2006 #15

    EL

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    If the Universe is "cyclic", why do we need a moment of creation (i.e. an "original" big bang)?
    However, I agree in that I do not find an eternal (cyclic) universe more satisfactory than a "universe from nothing".
     
  17. May 12, 2006 #16

    marcus

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    Hi EL, you and Chronos are referring, I think, to some interesting questions like where does the overall cosmic process come from, however you picture it. I am not entirely sure how you would phrase it.

    Chronos referred to the "original" big bang, which has something of that flavor.

    I am not sure that a question like "how did existence come into existence?" is a scientific question. I am not sure that it can be be answered by science.

    what I am concerned with is a rather different business. I am concerned with questions that one can clearly ask and attempt to answer in the context of science.

    It is more like asking simply "what was the situation one hour or one year before what used to be called the singularity?"
    What was there one hour or one year before the start of expansion? Or better let me say one second.
    what immediately preceded the expansion stage that we see around us?

    Asking this conforms to the traditional way that scientists work back in time. You construct a model that fits observations made in the present and that you can run backwards in time. If it breaks down somewhere along the line, you fix it and check to see that it still fits observations. And as with any model, you try to devise more tests, new observations that will provide more stringent tests that the model will or will not be able to pass. One can never fully believe. One always continues to test. (well, within reason:smile:)

    All (scientific) inferences about the past are based on some model and their relative credibility depends on how well the model has been tested.

    At this point in scientific history we are just beginning to develop and test models that inch back a little bit before the start of expansion, through a brief period called a "bounce"

    If you have read the Ashtekar article "the issue of the beginning" you will realize he is not talking about a cyclic process and he does not consider the broad philosophical or metaphysical question (as per Chronos "original" big bang) of how the whole process whether cyclic or not might have come into existence.

    the only "beginning" Ashtekar is talking about is the matter of fact beginning of expansion. According to his model it was preceded by a contraction. And he is very careful not to say what kind of contraction. It could be a black hole collapse, or it could be somebody else's big crunch. Ashtekar's model does not, at this point, say details like that. So he avoids putting a name on it. All the model says is that immediately before the start of expansion there was some kind of gravitational collapse, which could be of an entire spacetime or it could be of a small portion or region of a larger tract. he says it is a classical region---that is all. And that is all the model tells us, at least for now.

    he also says that the wavefunction undergoes a deterministic evolution through the bounce. (at least in this particular quantumgravity model)
    it is significant, I think, that he says deterministic.

    that evolution through the bounce is what Ashtekar and the others have been following through repeatedly with their computer models---and what you see plotted out graphically in several of the more technical papers.

    I think it is important to stress that nobody is ducking some important scientific question. The philo or meta question of how or why did existence come into existence is not being addressed because that is not what this model of the bounce, or ex-singularity, is about.
    Asking the philosophical question makes as much sense, or as little sense, as it did 10 years ago or 20 years ago before this work was done.

    Also it is important to stress that the new model has not been tested. some papers have been written about the phenomenology of LQC, with some ideas of tests being presented. but that is pretty rudimentary.
    Some names in connection with this are Roy Maartens and Parampreet Singh---there may be others too.

    So at present one has models where time stops at beginning of expansion and one also has at least one model where time does NOT stop there.
    One cannot, at present, claim that time stops at beginning of expansion because this has not been proven.
    Nor can one claim that time does NOT stop. Because the model that continues on back through the bounce has not been adequately tested.

    Personally it does not bother me to be in a situation where this question has not been resolved----lack of resolution in science is a routine circumstance.

    Also the grand question of cosmic existence has still the same status as before---this little extension back in time past where the 1915 General Relativity model broke down is just that: a little extension. It lets us peer back just a wee bit further, test a little bit more, extrapolate a little further etc.
     
    Last edited: May 12, 2006
  18. May 12, 2006 #17
    I think the cyclic model seems to make sense. And I don't want to limit it to the big bang-big crunch scenario. Our universe probably did exist forever and the current universe we live in is a phaze that happened 13.7 billion years ago (age of our current universe). Perhaps when our universe dies, whether it be the Big Crunch, Big Freeze, or Big Rip, the universe will just finish its current cycle and begin as a new universe. Each phaze of the universe maybe radically different than the next or previous universe. Perhaps our next universe will be nothing but energy with no matter. New laws of Nature will probably arise.

    Now what I really would like to know is whether the laws of the universe were a result of randomness or an intelligent force beyond our reasoning. What do you think? I know this sort of leaves the realm of science, but this topic pretty much does that already.
     
  19. May 12, 2006 #18

    marcus

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    I just want to make clear that we are talking at cross purposes. Not about the same thing.

    I think the question "what existed before the big bang?" is a definite concrete physics question that one can hope will be answered near-to-mid-term.

    One can hope to have a model that is roughly similar to the present one that cosmologists use, but quantized, and which is testable in various ways by observations of some sort.

    But talking about "cyclic" universes strikes me as going off into the realm of speculation. At the moment I cannot very well see how one could verify such a notion---so it remains rather in fantasy land. Or myth. People can believe in cycles (or "branes" bumping again and again into each other) if their personality and tastes are such that they LIKE to believe in such things. And it does not harm that I can see.
    Lots of scientists like to speculatate about such notions.

    But I think there is a qualitative difference between that---fantasizing "cycles" of tens and hundred of billions of years, as if one could at present know----and simply asking about ONE SECOND BEFORE the start of expansion. (it is like asking about the derivative of a function, instead of wanting the whole plot)

    there may be things we can extrapolate, using a quantum cosmo model that we can test. it is possible. there is a research program at Penn State currently pursuing that knowledge.

    maybe you do not see a qualitative difference between one second and tens of billions of years, which is fine. they both are periods of time. I cant say one view is wrong and the other right. But just want to say that I do make a distinction.
     
    Last edited: May 12, 2006
  20. May 12, 2006 #19
    I don't think there is evidence that creation exist. So why should one assume that it should and believe that there was nothing before the big bang and that our existance needed to be created. Creation to me is an old belief that stuck around from before science started explaining things like the proccess of life, the formation of planets and stars, our weather and many other things that would make one believe that creation exist.
     
  21. May 12, 2006 #20

    marcus

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    I agree with you Enos. You might like to learn what Laplace said to Napoleon.

    "Sir, that is an assumption which I don't need!"

    Laplace was a mathematician who made a very good model of celestial motion (planets stars etc.). This model explained a lot of things. Napoleon had been a student in Laplace mathematics class in school and when he was a great man he recieved a visit from his old teacher. Laplace gave him a copy of his book of Celestial Mechanics. Napoleon said thankyou Laplace and what is the role of God in your model of the universe? Laplace replied that God was an extra assumption that he didn't need in the model.
    Maybe the same could be said of the notion of creation. If you just focus on the model then you may not see any need to elaborate the story and put in that detail---it might simply be irrelevant.

    Je n'avais pas besoin de cette hypothèse-là

    more authoritative version of story, in Wiki encyclopedia:
    http://en.wikipedia.org/wiki/Laplace
     
    Last edited: May 12, 2006
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