Thoughts on the cosmological principle

TL;DR

This paper discusses the limitations of the traditional cosmological principle due to cosmic structures and proposes a probabilistic reformulation, exploring how to test and justify this new approach through fundamental physics.

Contribution

It introduces a new probabilistic formulation of the cosmological principle that accounts for cosmic structures and discusses methods for testing and justifying it.

Findings

Proposes a probabilistic version of the cosmological principle.

Suggests methods to test the new formulation.

Discusses potential fundamental physics justifications.

Abstract

The cosmological principle says that the Universe is spatially homogeneous and isotropic. It predicts, among other phenomena, the cosmic redshift of light and the Hubble law. Nevertheless, the existence of structure in the Universe violates the (exact) cosmological principle. A more precise formulation of the cosmological principle must allow for the formation of structure and must therefore incorporate probability distributions. In this contribution to the Memorial Volume for Wolfgang Kummer, a great teacher and mentor to me, I discuss how we could formulate a new version of the cosmological principle, how to test it, and how to possibly justify it by fundamental physics. My contribution starts with some of my memories of Wolfgang.