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George Jones
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Jan22-06, 11:26 AM
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Quote Quote by Garth
Furthermore, in The Cosmological Twin Paradox the topology of a closed universe does determine a special frame of reference.
I don't think I have a problem with this. I wish I had enough time to read in detail the papers referenced in the thread!

A caution: some readers (not Garth) may be under the impression that this has been ruled out for our universe, since a Friedmann-Robertson-Walker universe is closed if and only if it will eventually start contracting, and our universe, as modeled by FRW, expands forever. Not.

The presence of a cosmological constant/dark energy can falsify this statement, and, if our universe is an FRW universe, the simplest models for universe do falsify this statement, i.e., we cannot rule out by present observational evidence that our universe is closed. Observational evidence stongly favours a universe that expands forever, but is quite neutral about whether spatial sections of our universe are closed, flat, or open.