The Copernican principle in light of the latest cosmological data

TL;DR

This paper tests the Copernican principle by analyzing inhomogeneous cosmological models against the latest observational data, finding that small local inhomogeneities are consistent with the data and do not weaken standard cosmological constraints.

Contribution

It provides the first comprehensive constraints on local inhomogeneities using multiple cosmological datasets without assuming homogeneity a priori.

Findings

Local inhomogeneities are constrained to be very small, with contrast δ_L ~ 0.01.

Constraints on ΛCDM parameters remain robust when allowing for local inhomogeneities.

Data can be effectively analyzed within inhomogeneous cosmology frameworks.

Abstract

We pursue a program to confront observations with inhomogeneous extensions of the FLRW metric. The main idea is to test the Copernican principle rather than assuming it a priori. We consider the $\Lambda$CDM model endowed with a spherical $\Lambda$LTB inhomogeneity around us, that is, we assume isotropy and test the hypothesis of homogeneity. We confront the $\Lambda$LTB model with the latest available data from CMB, BAO, type Ia supernovae, local $H_0$, cosmic chronometers, Compton y-distortion and kinetic Sunyaev-Zeldovich effect. We find that these data can constrain tightly this extra inhomogeneity, almost to the cosmic variance level: on scales $\gtrsim 100$ Mpc structures can have a small non-Copernican effective contrast of just $\delta_L \sim 0.01$. Furthermore, the constraints on the standard $\Lambda$CDM parameters are not weakened after marginalizing over the parameters that model the local structure, to which we assign ignorance priors. In other words, dropping the Copernican principle assumption does not imply worse constraints on the cosmological parameters. This positive result confirms that the present and future data can be meaningfully analyzed within the framework of inhomogeneous cosmology.