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Big picture

  1. Sep 3, 2008 #1
    What are the acceptable models to eplain how the big bang is expanding the space of our visible universe? Are these the choices? 1) An expanding infinity 2) local expansion with an area of non-expansion beyond our range of observation 3) local expansion with an an area of non expansion in some higher dimension 4) finite expansion without anything outside the area of expansion. Are the other choices?
  2. jcsd
  3. Sep 3, 2008 #2


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    I don't know any other possibilities, if I understand the alternatives you present. I personally like 1) and 4). They seem to be the two possibilities you have in the standard cosmological model (LambdaCDM)

    Your option 1) would be the LCDM model with Omega=1. Which means spatially flat, and assuming no exotic complications, infinite spatial volume.
    Your option 4) would be the LCDM with Omega > 1. A finite spatial volume like the 3D analog of the 2D surface of a balloon with noting inside or outside the 2D surface. An expanding finite volume without anything else---no other space of any dimensionality.

    That doesn't cover before the big bang, where there might be a contracting region. but that is not what you were asking about. You were focusing on the expanding space directly connected with what we can see. I think your four possibilities cover all the pictures people have of that. Hope someone will correct me if I am forgetting about something.
    Last edited: Sep 3, 2008
  4. Sep 3, 2008 #3


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    They are not choices, merely nudges is the direction observational evidence steers the 'ship' of science. Theory is the term scientists prefer to predict the future course of the 'ship'.
  5. Sep 4, 2008 #4
    I wonder if this is so difficult to comphrehend due to how infinite and finite are defined. Because, to a lay person; it doesn't seem like an "actual infinity" can be increased or that something finite would not have a boundry.
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