Explaining Cosmological Anisotropy: Evidence for Causal Horizons from CMB data

TL;DR

This paper provides strong evidence for large-scale anisotropy in the CMB data, suggesting the existence of causal horizons that challenge the assumption of isotropy in the universe, and supports a model linking horizon size to dark energy density.

Contribution

It demonstrates the violation of isotropy in CMB data with high statistical significance and connects these anisotropies to causal horizons and a model explaining cosmic acceleration.

Findings

Detected anisotropy with probability ~10^-9

Identified three large-scale patches with 40-70 degree radii

Found correlation between horizon size and dark energy density

Abstract

The origin of power asymmetry and other measures of statistical anisotropy on the largest scales of the universe, as manifested in Cosmic Microwave Background (CMB) and large-scale structure data, is a long-standing open question in cosmology. In this paper we analyze the Planck Legacy temperature anisotropy data and find strong evidence for a violation of the Cosmological principle of isotropy, with a probability of being a statistical fluctuation of order ~ 10^-9. The detected anisotropy is related to large-scale directional LCDM cosmological parameter variations across the CMB sky, that are sourced by three distinct patches in the maps with circularly-averaged sizes between 40 to 70 degrees in radius. We discuss the robustness of our findings to different foreground separation methods and analysis choices, and find consistent results from WMAP data when limiting the analysis to the same scales. We argue that these well-defined regions within the cosmological parameter maps may reflect finite and casually disjoint horizons across the observable universe. In particular we show that the observed relation between horizon size and mean dark energy density within a given horizon is in good agreement with expectations from a recently proposed model of the universe that explains cosmic acceleration and cosmological parameter tensions between the high and low redshift universe from the existence of casual horizons within our universe.