Large Scale Inhomogeneity Versus Source Evolution -- Can We Distinguish Them Observationally?

TL;DR

This paper examines whether large-scale homogeneity of the universe can be observationally distinguished from source evolution effects, emphasizing the need for independent distance measures or a theory of source evolution.

Contribution

It presents two theorems clarifying the limitations in proving cosmic homogeneity without independent distance measures or source evolution models.

Findings

Homogeneity cannot be proven without independent distance measures.

Source evolution can mimic inhomogeneity in observations.

Theorems define the conditions needed for observationally distinguishing homogeneity.

Abstract

We reconsider the issue of proving large scale spatial homogeneity of the universe, given isotropic observations about us and the possibility of source evolution both in numbers and luminosities. Two theorems make precise the freedom available in constructing cosmological models that will fit the observations. They make quite clear that homogeneity cannot be proven without either a fully determinate theory of source evolution, or availability of distance measures that are independent of source evolution. We contrast this goal with the standard approach that assumes spatial homogeneity a priori, and determines source evolution functions on the basis of this assumption.