Looking for a good analogy of the shape of the expanding universe

  1. I have heard people say there is no center to the expansion of the universe. I have also heard the expansion described as an ever expanding balloon with all galaxies as dots on the surface. These to statements seem contradictorily to me.

    If the expansion of the universe was like the above balloon example wouldn’t all galaxies be close to the edge or event horizon with a huge volume of empty space in the middle of which we could easily locate or at least mathematically define the center (e.g. we can determine the center of a balloon if we understand its size and dimensions).

    I get that my lack of understand likely stems from the shortfall of the metaphor but I was hoping someone could explain the expansion in terms that make sense to a non-physicist.
     
  2. jcsd
  3. A.T.

    A.T. 5,296
    Gold Member

    The 2D balloon surface represents the universe. The 2D balloon surface doesn't have an intrinsic center that lies within the surface. The universe doesn't have an intrinsic center that lies within the universe. Whether the universe is actually embedded in a higher dimensional space, like the balloon surface, is speculation and not relevant to the intrinsic geometry.
     
    Last edited: Feb 22, 2013
  4. Chronos

    Chronos 9,785
    Science Advisor
    Gold Member

    We have good observational evidence the universe either does not have a center, is unfathomably enormous, or, we ARE the center of the universe. Were this not true we would see fewer galaxies in the direction opposite the 'center'.
     
  5. The balloon analogy gives the impression of an ever expanding mass where all the bodies within that mass move further away from each other. It's a rather bleak prospect for astronomers in the future were the heavens grow increasingly dim. I like to envision a series of balloons expanding within one another. If we occupy a balloon in the middle and look to an inward expanding balloon we see a dense mass of galactic and intergalactic material expanding rapidly towards us. They however see a slightly less densely populated universe expanding at a slower velocity away from them. If we in turn look outwards we see what they see. If there is a centre to the universe, I am always perplexed as to what it,s motivative force is? Or that other old nut; " into what are we expanding?". Expansion is another concept that may be misleading, are we "the universe" being "pushed" deeper into the void? or are we being "pulled" into it?
    Sorry for the comment, but as always with concepts of universal expansion; we re left with more questions and paradoxes and little in absolute certainty.
     
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