= Cosmological principle
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The <cosmological principle> assumes that the universe is statistically homogeneous and isotropic on sufficiently large spatial scales. It applies to a coarse-grained description, not to each <galaxy> or local void. Combined with the <Copernican principle>, <cosmological isotropy> around us supports a homogeneous description rather than a specially centred model. It motivates an <FRW metric>, whose expansion is governed by a few time-dependent quantities. Observations sample only a finite <past light cone>, so they support this hypothesis without proving global <spatial homogeneity> beyond the observed region.
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