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What does the theory of the big bang say about this

  1. Jul 13, 2008 #1
    I don't understand the theory as much as I would like to. Please pardon my non technical vocabulary and lack of thorough insight on the topic at hand.

    So...geez how do I put this into words...So everything imaginable in this universe was compressed, (superimposed?), into what is popularly said to be the size of an atom? Does that mean that all the energy, mass, etc was all compacted into this dense region?

    My main question here is does this include the fabric of space?? Or does the theory say that the material/energy expanded into pre-existing space that was already around the baby universe? Or was there a non existence of anything including physical dimensions beyond this compressed universe?

    Also, I read a few times where the author writes "..and after the universe was 30 seconds old" That bothers me how can you possibly have some stable experience of time when the physical universe is changing so drastically?

    AGAIN I am not a physicist so pardon my ignorance on the topic.
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  3. Jul 14, 2008 #2


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    I'm skeptical of the size estimate. Quite a lot of recent work models the big bang as a bounce----a prior collapse stage that achieves a high density, followed by re-expansion.
    I've seen estimates like the size of a grapefruit, but not an atom. But we don't know the size of the universe now! So we can't seriously estimate the size at the time of bounce.

    The models only give you a handle on the density at the moment the bounce occurs. Very roughly 1090 water.
    How big it would be would depend on how much universe there is to compress down to that density, would it not?

    There are a bunch of competing models. A book is scheduled to come out on all these approaches, written by the various proponents, in spring 2009. And the models need to be tested. It's a wait-and-see thing at the moment.

    YES, if the universe is finite then it would be a dense finite region.

    YES CERTAINLY, at least in the bounce models there is no surrounding space---so whatever the fabric of space means, it was definitely in there with the matter. I doubt that matter would be distinguishable from geometry at that density. Let's not talk about space (geometry) and matter as if they were separate things, let's just say "existence". We really don't know what it looks like at that high a degree of compression. the quantum gravity models say that gravity actually becomes repellent at that density, instead of attractive.

    I think that is a good question and you are right to be skeptical. Maybe after 30 seconds conditions could have been such that one might imagine some kind of clock, or an observer with a standardized sense of time. But if you push back closer to the bounce, or to whatever the start of expansion was, it becomes hard to define time.

    In the bounce quantum gravity models they often pick one of the physical variables to keep track of time. If you are watching, say, three variables then you sacrifice one of them and make it the clock---and study how the other two change in relation to the one that is the clock. I know :smile: it sounds unsatisfactory.

    But there is a serious question of what time means and how you can run a dynamical model---when you get into these extreme situations.

    there are also discrete models that operate stepwise. you can't say what tiny fraction of a second each step takes---time as a continuum has been lost and all that remains is sequence---stages first of contraction and then of expansion happening in order.
  4. Jul 14, 2008 #3


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    what I get from your post above all is incredulity, Mozart. You suggest that the story---especially what comes up in bad popularized accounts, is mindbogglers.

    I think that is basically right. The popularized story is pretty hard to swallow. And it is misleading. there has been a lot of change in the field since 2001, even since 2005. I don't know of any accurate up to date popularization. If you are going to be boggled, it is better to be boggled by the concepts that real scientists are currently using and investigating.

    the key field is quantum cosmology. A leading expert in QC is named Ashtekar. He often is the invited speaker on quantum cosmology at international conferences. He and his co-workers (postdocs, grad students, co-authors) are influential in current research on events around the big bang. He doesn't do popularizations, but some of his stuff is written for a wider audience than just specialists. You could sample it, read the summary at the beginning. I don't know what else to suggest.

    Here is the most introductory thing Ashtekar has written recently
    An Introduction to Loop Quantum Gravity Through Cosmology
    it is free for download, just click on PDF.

    Here are a bunch of quantum cosmology links---resulting from a keyword search

    Even though it is technical, professional journal style, it is always possible to scan introductory paragraphs, conclusion paragraphs, and see if you can get anything out.
    I don't know anything to recommend that is really ideal.

    Maybe after Rudy Vaas book "Beyond the Big Bang" comes out next spring someone will do a popularization for general audience on this.

    Here is the Amazon page on Vaas book , but it is still way too technical, and costs too much
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  5. Jul 14, 2008 #4


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