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Mar1-12, 12:56 AM
You said there that "Weinberg exhibits harmonic coordinates for the FRW universe in his text book. I'm not sure whether the positive cosmological constant changes things.".
I'm talking about the Field Theory of Gravitation. Which is about Fields. What you meant above was that the FRW universe is covered by harmonic coordinates and can be modelled as spin-2 fields on flat spacetime. Now Field Theory of Gravitation is the formulism for this. Here one must separately model how space expands.