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:::The flatness problem refers to the fact that, in an ''inflation-free'' universe, the FRW metric with matter and radiation equation-of-state parameters predicts that any initial nonzero curvature will increase vastly in magnitude, leaving a highly curved universe at present.  Inflation is proposed as a ''solution'' to the flatness problem; it is not the cause of it.  The process of inflation drastically flattens any initial curvature in the universe so dramatically that even after the curvature increase undergone under normal evolution, the universe still appears nearly perfectly flat. [[User:Yill|Yill]] 22:55, 5 April 2010 (EDT)
 
:::The flatness problem refers to the fact that, in an ''inflation-free'' universe, the FRW metric with matter and radiation equation-of-state parameters predicts that any initial nonzero curvature will increase vastly in magnitude, leaving a highly curved universe at present.  Inflation is proposed as a ''solution'' to the flatness problem; it is not the cause of it.  The process of inflation drastically flattens any initial curvature in the universe so dramatically that even after the curvature increase undergone under normal evolution, the universe still appears nearly perfectly flat. [[User:Yill|Yill]] 22:55, 5 April 2010 (EDT)
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:::Wait, I just realized that I think we may be talking past one another here.  I interpreted the counterexample listed on the page to be the flatness problem, but based on your response I guess that it is not.  (Obviously the flatness problem is not a counterexample to GR itself, just to the use of the FRW metric for modeling the universe.)  This counterexample seems to be more fundamental, namely the claim that space is nowhere curved, as GR says it must be by matter and energy.  Is that correct? [[User:Yill|Yill]] 23:25, 5 April 2010 (EDT)
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