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A few key questions about the Big bang model of the universe

  1. Mar 18, 2009 #1
    Well actually, I only have one question about the Big Bang model. According to Big bang theory, at the beginning of the universe the was a very high density region. So then the pressure on our early universe must be really really high. When there is pressure present , that means there is outward force pushing on the object with high pressure. There must have been some really large object pushing on the universe during its early stages if the early universe was extremely dense.
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  3. Mar 18, 2009 #2


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    No, at the beginning, the whole universe had a very high density, not just an artificially compressed region.
  4. Mar 18, 2009 #3
    How can the whole universe have a very had density if there must be some outside force pushing on the universe for high density to exist in the first place? High density just doesn't occur on an object without forces outwardly pushing on that object.
  5. Mar 18, 2009 #4

    Vanadium 50

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    Do you have any evidence for that statement? A chunk of tungsten has a high density, and nothing is pushing on it.
  6. Mar 18, 2009 #5
    density and pressure are not the same thing

    tungsten is dense but it doesn't have a high internal prssure does it? What about the early universe. Did it have both hight pressure and density? or just high density?
  7. Mar 18, 2009 #6
    I guess you are right. But, Tungsten doesn't exist in a vacuum. The notion that the whole universe begin as a singular point in space , with nothing but vacuum surrounding is very counterintuitive to me.

    I know , but density is proportional to pressure.

    rho= MP/RT .
  8. Mar 18, 2009 #7


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    Pentazoid, it looks to me like you are trying to think physically and understand, not just pick holes. That's good.
    Please read the essays at Einstein Online and this famous Scientific American article called "Misconceptions about the Big Bang". Then come back with possibly revised questions.
    http://www.astro.princeton.edu/~aes/AST105/Readings/misconceptionsBigBang.pdf [Broken]
    Einstein Online
    http://www.einstein-online.info/en/spotlights/cosmology/index.html [Broken]

    In the Big Bang theory there are actually several models being currently studied. Ich told you one important thing already. In all models the matter is approximately evenly distributed throughout. So above all you have to get rid of the picture of an explosion, where stuff flies out into empty space. There is no "region" of high density with some separate surrounding region of low density. That's a bad picture. Ich is making that point.

    In some of the models studied in Big Bang theory this moment of very high uniform density is the result of the collapse of a prior phase of the universe.

    The analogy people use is that of a "bounce". The very high density is achieved as in a gravitational collapse, somewhat like when a star abruptly collapses (but in the case of the star there is surrounding empty space, in our "big bounce" case it is the whole universe, the whole of space and matter, that collapses and rebounds.)

    There are a lot of technical papers about so-called non-singular cosmology, bounce models etc. The models work because of some interesting quantum effects that modify the way gravity acts at very high density. This puts a calculable limit on how high the density can get (during a collapse) before a rebound occurs---causing the kind of expansion which we currently observe.

    Please tell us again (after reading the SciAm article and the Einstein Online material) what it is you want to know.
    Last edited by a moderator: May 4, 2017
  9. Mar 18, 2009 #8

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    Good, because that's not what the big bang theory says. The universe did not explode into a pre-existing space. Space itself expanded.
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