- #26

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Yes.sn't the simple fact that a(t) is used in cosmology calculations regarding things like the age of the universe and the size of the observable universe

No. ##a(t)## is a coordinate-dependent quantity. One of the most basic rules of GR is that coordinate-dependent quantities are not "reality"; the "reality" is invariants, quantities that are the same in all coordinate systems and which represent actual physical measurements.intrinsically imply the expansion of vacuum is a reality?