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Infinite Universe

  1. Oct 23, 2015 #1
    Could an infinite Universe ever end?
  2. jcsd
  3. Oct 23, 2015 #2


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    Gold Member

    No. By definition.
  4. Oct 23, 2015 #3


    Staff: Mentor

    If by "end" you mean "end in space", then obviously not, as DaveC426913 pointed out.

    If by "end" you mean "end in time", i.e., "come to an end", then according to GR, no; any spatially infinite universe must keep expanding forever.
  5. Oct 24, 2015 #4
    I didn't know that. Care to elucidate?
  6. Oct 24, 2015 #5


    Staff: Mentor

    There are no solutions in the FRW family of spacetimes that are spatially infinite and recollapse; all of the spatially infinite solutions expand forever. The only solutions that recollapse are spatially finite (closed universes--but not even all of those recollapse, some, with positive cosmological constant, expand forever).
  7. Oct 24, 2015 #6


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    Science Advisor

    I'm not sure that's true. You could have universe with a negative cosmological constant and open curvature that recollapses. However, it might not "end" in the sense that quantum gravity might demonstrate that something happens after the recollapse.
  8. Oct 24, 2015 #7


    Staff: Mentor

    Hm, yes, you're right. (I think a flat universe could also recollapse with a negative cosmological constant.) AFIAK, nobody has proposed that such a model might describe our actual universe, so it would not be relevant in a practical sense, but as a matter of theory, yes, such a model could be spatially infinite and recollapse.

    Yes, agreed; this would be true of closed models that recollapse as well.
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