The Scale of Cosmic Isotropy

TL;DR

This paper introduces a formalism to quantify the scale at which the universe's galaxy distribution becomes statistically isotropic, providing an estimate consistent with cosmological models.

Contribution

It presents a new operational method to determine the crossover scale of cosmic isotropy using SDSS data, addressing a longstanding challenge.

Findings

Estimated isotropy scale R_{iso} ~ 150h^{-1} Mpc

Method applied to SDSS DR7 galaxies

Results align with cold dark matter model predictions

Abstract

The most fundamental premise to the standard model of the universe, the Cosmological Principle (CP), states that the large-scale properties of the universe are the same in all directions and at all comoving positions. Demonstrating this theoretical hypothesis has proven to be a formidable challenge. The cross-over scale R_{iso} 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 R_{iso}. We apply the method to galaxies in the Sloan Digital Sky Survey (SDSS) Data Release 7, finding that R_{iso}\sim 150h^{-1} Mpc. 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.