Planck evidence for a closed Universe and a possible crisis for cosmology

TL;DR

Recent Planck data suggests the universe may be closed, which could resolve anomalies in lensing amplitude and parameter tensions, but raises questions about potential inconsistencies in cosmological observations.

Contribution

The paper provides evidence that a closed universe model explains Planck lensing anomalies and resolves internal tensions, challenging the standard flat universe assumption.

Findings

Planck data prefers a closed universe with positive curvature.

A closed universe explains the enhanced lensing amplitude.

Assuming flatness may conceal a cosmological crisis.

Abstract

The recent Planck Legacy 2018 release has confirmed the presence of an enhanced lensing amplitude in CMB power spectra compared to that predicted in the standard $\Lambda$CDM model. A closed universe can provide a physical explanation for this effect, with the Planck CMB spectra now preferring a positive curvature at more than $99 \%$ C.L. Here we further investigate the evidence for a closed universe from Planck, showing that positive curvature naturally explains the anomalous lensing amplitude and demonstrating that it also removes a well-known tension within the Planck data set concerning the values of cosmological parameters derived at different angular scales. We show that since the Planck power spectra prefer a closed universe, discordances higher than generally estimated arise for most of the local cosmological observables, including BAO. The assumption of a flat universe could, therefore, mask a cosmological crisis where disparate observed properties of the Universe appear to be mutually inconsistent. Future measurements are needed to clarify whether the observed discordances are due to undetected systematics, or to new physics, or simply are a statistical fluctuation.