Emergence of a Cosmological Constant in Anisotropic Fluid Cosmology

TL;DR

This paper demonstrates how a cosmological constant naturally emerges from local inhomogeneities and back reaction effects in anisotropic fluid cosmology, aligning with observations without coincidence issues.

Contribution

It provides exact solutions to Einstein's equations showing the emergence of a cosmological constant from inhomogeneities, addressing the cosmological constant problem.

Findings

The cosmological constant arises from averaging back reaction terms.

Its magnitude matches astrophysical observations.

It relates naturally to baryonic matter density.

Abstract

We investigate anisotropic fluid cosmology in a situation where the spacetime metric back-reacts in a local, time-dependent way to the presence of inhomogeneities. We derive exact solutions to the Einstein field equations describing Friedmann-Lemaitre-Robertson-Walker (FLRW) large scale cosmological evolution in the presence of local inhomogeneities and time-dependent back reaction. We use our derivation to tackle the cosmological constant problem. A cosmological constant emerges by averaging the back reaction term on spatial scales of the order of $100 \ \text{Mpc}$, at which our universe begins to appear homogeneous and isotropic. We find that the order of magnitude of the "emerged" cosmological constant agrees with astrophysical observations and is related in a natural way to baryonic matter density. Thus, there is no coincidence problem in our framework.