Abstract
The most fundamental premise to the standard model of the universe states that the large-scale properties of the universe are the same in all directions and at all comoving positions. Demonstrating this hypothesis has proven to be a formidable challenge. The cross-over scale Riso above which the galaxy distribution becomes statistically isotropic is vaguely defined and poorly (if not at all) quantified. Here we report on a formalism that allows us to provide an unambiguous operational definition and an estimate of Riso. We apply the method to galaxies in the Sloan Digital Sky Survey (SDSS) Data Release 7, finding that Riso ∼ 150h−1Mpc. Besides providing a consistency test of the Copernican principle, this result is in agreement with predictions based on numerical simulations of the spatial distribution of galaxies in cold dark matter dominated cosmological models.