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Big Bang Question

  1. Jul 7, 2007 #1

    BJL

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    I'm not a physicist, in any way. But I've had this idea about the universe for a while, and I would like to get some feed back on it.

    I have this idea that the Big Bang wasn't necessarily all of the matter in the universe. That just like matter accumulates and will eventually reach a sufficient mass to turn into a star or turn into a black hole, matter will accumulate into a sufficient mass to trigger a Big Bang. But this isn't all the matter in the universe. The accumulation of matter only has to be enough to trigger a Big Bang explosion.

    I understand that light can't escape a black hole. So it makes sense to me that, perhaps, this accumulation of matter had sucked in all the matter from such a wide area that we are now flying through the vacancy that its gravity created before it exploded. And light from outside this vacancy hasn't had enough time to reach us.

    And I also understand that part of the necessity for dark matter is that we seem to be expanding quicker than we could otherwise explain. Perhaps it is because there is actually gravity out there from matter outside our Big Bang that is pulling us towards it.

    Again, I'm not a physicist. The idea, though, where our Big Bang represents all the matter there is has always struck me as unnecessarily extreme, given the way we know matter otherwise tends to accumulate to the point that it triggers events (stars, black holes). We could have a Big Bang without it necessarily being all the matter in a much larger universe.
     
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  3. Jul 7, 2007 #2

    SF

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    Sorry to bother the first poster, but I got another question too, unrelated to the first but very ontopic.
    Please answer each one separately :)

    Let's say we're right after the Big Bang and the Universe just started expanding.
    What would we see if we were there? (Let's assume the original matter doesn't bother us).
    1) There would be no "edge".
    2) If the universe is positively curved, would we "see our back of the head" ?
    2b) If the universe is positively curved and we tried to move, would we be in the same situation Neo was in Matrix Revolutions when he was held captive in the subway station?
    2c) If the universe is positively curved and really really small, how would our own gravity affect us?

    *For those who don't know what I'm talking about when I say "positively curved", check out:
    http://www.astronomynotes.com/cosmolgy/s3.htm
     
  4. Jul 7, 2007 #3

    marcus

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    those seem like intelligent questions to me. you are picturing what it would be like to live in a universe that is spatially S3
    "ess-three" is also called the "three-sphere"
    it is the analog of a 2D spherical surface (without necessarily having any 3D space surrounding it or inside it)
    but instead of being 2D it is 3D

    it has no boundary or edge, it is positive curved
    (if you do sophomore-level pointset topology, it is a "compact" topological space, which is a way of saying finite)

    EVERYTHING YOU IMAGINE ABOUT LIVING IN S3 is right except maybe the Matrix imagery and EXCEPT FOR ONE LITTLE THING
    which is that if the S3 is expanding very rapidly, with typical distances growing much faster than the speed of light, then you might not be able to see the back of your head because light wouldn't be able to make the trip around the "world" and get back to you.

    finally you ask the question 2c and the answer depends on expansion
    in a non-expanding case, even if you were the only matter in the universe your own mass could be enough to collapse to blackhole.
    you just have to be smaller than your Schwarzschild radius (in the simple electrically neutral, non-rotating case)

    but in an expanding universe the density can be higher than Schw. density and it won't collapse. (one way to think is that expansion can outrun the influence of gravity just like it can outrun light)
    ==========

    It is quite possible that our universe is spatially S3
    so what you are imagining is plausible realistic diagrams of early times
     
    Last edited: Jul 7, 2007
  5. Jul 7, 2007 #4

    marcus

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    The idea you seem to be driving at is what you say at the end:

    That is certainly right. We could indeed. It is very possible and also it is becoming an acceptable idea among professional cosmologists.

    But they don't necessarily picture it the same way you do.

    Also, another idea that is gaining ground is that the Big Bang is actually a Big BOUNCE---that it resulted from a previous contracting phase----some region of a prior spacetime that for some reason collapsed.

    There is an article in the current issue of a journal called NATURE PHYSICS that is getting a lot of attention right now, and raising quite a lot of controversy too :smile: , that is about one of the mathematical models that show this. there are a bunch of mathematical models and also computer simulations that show this happening (while matching observed reality in other ways). For some reason this tends to get some people worked up---the whole thing is fun to watch.

    Here's the Nature Physics website, but it only has a summary---takes a subscription to access the full article.
    http://www.nature.com/nphys/index.html
    If you want to know more about it I will get some links to stuff that is free to download instead of restricted access.
     
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