A Test of the Copernican Principle

TL;DR

This paper tests the Copernican Principle using the cosmic microwave background spectrum, constraining the size of potential large voids that could mimic cosmic acceleration, and discusses how future measurements could further verify this fundamental assumption.

Contribution

It introduces a novel method to test the Copernican Principle by analyzing CMB spectral distortions and limits the size of large voids that could challenge this principle.

Findings

Current spectral distortion limits exclude large voids mimicking acceleration

More sensitive CMB measurements could detect or rule out such voids

The method constrains the local gravitational potential's influence on cosmological observations

Abstract

The blackbody nature of the cosmic microwave background (CMB) radiation spectrum is used in a modern test of the Copernican Principle. The reionized universe serves as a mirror to reflect CMB photons, thereby permitting a view of ourselves and the local gravitational potential. By comparing with measurements of the CMB spectrum, a limit is placed on the possibility that we occupy a privileged location, residing at the center of a large void. The Hubble diagram inferred from lines-of-sight originating at the center of the void may be misinterpreted to indicate cosmic acceleration. Current limits on spectral distortions are shown to exclude the largest voids which mimic cosmic acceleration. More sensitive measurements of the CMB spectrum could prove the existence of such a void or confirm the validity of the Copernican Principle.