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Origin of the universe

  1. Oct 21, 2007 #1
    Just a general question, what are your thoughts on "where" the universe came from, or what ever other way you want to phrase that?


    Personally, I haven't the foggiest notion. I don't believe in a personal god, but I think a creator is possible. And for those that say, where did the creator come from....well if time began at the big bang, there really was no "before" the creator I guess?


    But I think the true answer is probably different. Or maybe there is no answer. maybe the universe came from absolutely nothing for no reason.....

    Or maybe its part of an infinite chain of birth of universes.....

    Or maybe, the answer is something that we have not even conceived in our wildest dreams.

    Well, what do YOU think? :smile:
     
  2. jcsd
  3. Oct 21, 2007 #2
    I'm not totally closed to the idea of a god of some sort, even if I detest religion.

    But I personally find it harder to believe that a creator has existed for all of the past and will continue to exist into eternity than anything else. That's no easier for me to swallow than saying that the universe just popped out of nowhere (literally, what I've read suggests that the universe contains not only all matter and forces we know of but also all the spacetime dimensions and therefore there was no space or time in which it existed prior to the big bang). Another possibility that I find really intriguing is that our whole universe is really just the product of a black hole in a much, much, much larger universe, since the conditions inside a black hole and at the moment of the big bang are so similar. There's no way I can think of to sidestep the "everything out of nothing" problem, but to me anything is more plausible than an eternal god, much less one that cares about us lowly humans.
     
    Last edited: Oct 21, 2007
  4. Oct 21, 2007 #3

    marcus

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    I don't know of any scientific reason to suppose that. A bunch of recent research has time going on before the big bang----a contraction phase which reaches a maximum density (which in all the models I'm thinking of turns out to be the same) and then turnaround and the beginning of expansion.

    I'm not saying you shouldn't speculate about what might have preceded the contraction phase, and what it might have looked like. I only mean that nowadays there is no good reason to suppose that time begins with the start of expansion 13.7 billion years ago. Some of the models people use now go back further.

    All these models will require testing to see which ones can be ruled out by observation and which can't be. Eventually something will win out and replace vintage 1915 classic General Relativity, with its famous singularities.:smile:

    ===========================

    I did some research for you. Here's Wikipedia about Planck density
    http://en.wikipedia.org/wiki/Planck_density
    it is 5.1 x 1096 kilograms per cubic meter

    with these models it always seems to happen that the bounce comes when the density is 82 percent of Planck.
    So that would be 4.2 x 1096 kilograms per cubic meter

    that is the density at which the quantum corrections to gravity make it overwhelmingly repel instead of attract,
    so the contraction/collapse phase bounces and turns into an expansion phase.

    If you want to look at a recent research paper, one came out day before yesterday
    http://arxiv.org/abs/0710.3565
    As a rule, you don't expect to understand everything, but they say some of it in English (instead of equations) and it is a way of getting a taste. Whatever you do, don't believe popularizations! :biggrin:
     
    Last edited: Oct 21, 2007
  5. Oct 21, 2007 #4

    marcus

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    I expect that what you mean by "a god of some sort" is an emotional relationship people have with the universe where they associate a personality with it.

    We evolved as social animals and it is natural for us to attribute personality to things and to relate emotionally to them. So that is all fine. But if you want to discuss it you have to do so in Philosophy forum. In Cosmology forum the universe is just a mechanism
    and you run your model back in time as far as it will go, as long as it still functions well and does not blow up or break down and experience singularities (i.e. glitches). And when you reach the limits of applicability of that model, you improve the model so it doesn't experience singularities at the old limit, and you run it it back even further.

    At the moment the boundary of how far back you can run models is being moved some, according to a recent piece by Carlo Rovelli in NATURE PHYSICS. We didn't need him to tell us that because it is obvious if you watch the research literature, but he says it nicely. I will get the link

    http://npg.nature.com/nphys/journal/v3/n8/full/nphys690.html
    Here's a brief exerpt:
    "Science has frontiers; sometimes these frontiers move. One of the most impressive of science's frontiers is the Big Bang, and now a quantum theory of gravity — loop quantum gravity — is providing equations with which to explore it..."

    Here's some discussion in a PF thread:
    https://www.physicsforums.com/showthread.php?t=184869
     
    Last edited: Oct 21, 2007
  6. Oct 21, 2007 #5

    cristo

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    I guess here that you're talking about Bojowald's "bounce." What I don't get, though, is how this can describe the origin of the universe. Ok, so I've not really read much about this, but from what I gather Bojowald says that a previous universe contracts down to some small size at which the quantum effects overwhelm gravity, and so the expansion begins. But how can this ever describe the "origin of the universe"? Surely, if a previous universe has contracted (and, I presume, infinitely many more before that), then the precise origin is still not known. We can say how the universe we live in today began, but we can never know how the actual process started in the first place.

    This puzzles me too. How can one "rewind" back past the bounce and the contraction phase? Does this mean that every one of these "universes" would have been identical? (I presume not, since the quantum effects will probably not be identical each time!)
     
  7. Oct 21, 2007 #6

    marcus

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    If I gave the impression you can rewind back past the contraction phase, then I spoke wrong. All they do now AFAIK is just go back a little bit before. And the models are fairly simple (homegeneous isotropic, or small perturbative variations around that).

    they don't try to say where the prior contracting phase "came from". It is just that when it is quantized the bang seems to have a mechanism which you can work back with. It doesnt experience the usual glitch that the classic model runs into.

    I think you are right about not assuming the prior region of spacetime was identical with ours! It is early days to try to say much of anything about it.

    All I can do is offer papers and say "read", and you know the papers as well as I do. They are all cited in the current one.

    Ashtekar and his group seem to be taking a leadership role. We may soon be calling it the "Ashtekar bounce" instead of the "Bojowald bounce" (although the latter sounds better :smile: )


    I don't think it CAN describe the origin of the universe. I think the Big Bang, or the Bounce, is a fascinating process to try to understand. But I don't equate it with the origin of the universe.
    The Bang, or Bounce, is too dense and hot for matter as we know it to exist. So what did exist? how did matter as we know it come about from conditions at the bounce? Was there an inflation first? and if so what caused it? and then after inflation where did ordinary matter come from? I think you have read a lot about that already---people have been trying to answer these questions and getting rid of the singularity only makes the questions sharper. We can ask the same questions only now we don't have the stupid singularity.

    But none of this necessarily has to do with the "Origin of the Universe"----unless by "universe" we explicitly mean just our current expanding phase of it. IMHO it probably doesn't have anything to do with the Origin of the Universe. That Origin business is a slippery issue to try to tackle. I have more hope that the Big Bang, or bounce, will be understood in my lifetime, and maybe a little ways back before that. I'd be very happy if just that step of understanding could be taken.
     
    Last edited: Oct 21, 2007
  8. Oct 21, 2007 #7
    I know that what I'm about to say is more philosophical than scientific. But, the easiest way to explain the universe and where it came from etc is simply to say that the universe doesn't exist, and we don't exist at least materially. That would solve the whole problem. But why do we think etc. You don't have to be in material existence to think. But then you run into the problem of where thoughts come from. Thought is- to employ one's mind rationally and objectively in evaluating or dealing with a given situation. Mind is- the element, part, substance, or process that reasons, thinks, feels, wills, perceives, judges, etc. Process is- a systematic series of actions directed to some end. Action is- an act that one consciously wills and that may be characterized by physical or mental activity. Mental is- of or pertaining to the mind. Conscious is- known to oneself. This brings us all back to thoughts and thinking, in which case material existence is not required. Thought did not need to evolve from anything it is a state which is, was, will be, nothing more.
     
  9. Oct 21, 2007 #8

    cristo

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    Ahh, ok, no I must just have read what you said incorrectly. It makes more sense that you cannot rewind back the contraction phase; but still, going back any distance past the bounce is going further than we have before!

    Yes, sorry, I was just being lazy I guess. That, and the fact that my university does not subscribe to Nature Physics, and so I still have not been able to read the Bojowald paper!

    I agree; alliterative terms are always nicer on the ear!



    This is what I suspected. At least we're taking steps to trying to understand the process, but I'm not sure we'll ever be able to answer the question of the origin of the universe. We end up being drawn further into the realms of philosophy, though, if we muse on this fact for too long!

    Yes, well these are the standard questions (along with the many others) that still have no real answer. It's good to have a theory that's got rid of the singularity, though. However, it's early days, so I forsee that there will be a lot more work to do on it!
    That would be very pleasing, and a huge breakthrough for the field. Anyway, thanks for your reply! :smile:
     
  10. Oct 21, 2007 #9

    cristo

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    Yes, it is, and therefore your comments should be taken to the philosophy forum. Please refrain from attempting to discuss topics other than cosmology in the cosmology forum.
     
  11. Oct 21, 2007 #10
    Sorry Cristo. I thought that cosmology was the branch of philosophy dealing with the origin and general structure of the universe(mixed science and philosophy) , and that Astronomy was the rigid science of the universe.

    Honest mistake, I won't post anymore philosophy in the cosmology forums. Sorry :blushing:
     
  12. Oct 21, 2007 #11

    marcus

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    Nature Physics seems to be making stuff free after it is a month or two old.
    http://npg.nature.com/nphys/journal/v3/n8/full/nphys654.html

    This is the Bojo article. But I may have been too excited about that article when the press releases were coming out. I may have over-reacted. It seems to me now that the latest Ashtekar challenges some of Bojowald findings and may also push ahead in a few areas.

    I agree with what you said of general overview in your post.
     
  13. Oct 22, 2007 #12

    cristo

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    Ahh, thanks for the link, marcus!
    Such is the nature of the press! Still, it's an interesting article, and at least written in a language I can understand!
     
  14. Nov 5, 2007 #13

    Nice post :smile:
     
  15. Nov 7, 2007 #14

    Chronos

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    Rewinding reaches a logical and scientific end in BBT at T=1 planck time. This 'Planck Wall' still appears to be invulnerable to the scientific method [observation]. Limits of mathematical approaches remain unclear, but, I do not trust math that cannot be observationally confirmed. I recall having mathematically 'proven' 1=2 in high school, but was rebuked for the sin of multiplying by zero [a singularity thing]. Forced to choose, I would favor the 'creator' version.
     
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