The Vacuum Energy Density and Gravitational Entropy

TL;DR

This paper proposes a new approach to the vacuum energy problem by incorporating UV/IR feedback through a quantum space-time framework, linking microscopic degeneracy with macroscopic gravitational entropy to explain the smallness of the vacuum energy.

Contribution

It introduces a reformulation of vacuum energy calculation using phase space volumes and ground state degeneracy, connecting holography and gravitational entropy to address the cosmological constant problem.

Findings

Vacuum energy can be interpreted via phase space and ground state degeneracy.

Holography links microscopic degeneracy with macroscopic gravitational entropy.

The small vacuum energy is related to the large size of the Universe.

Abstract

The failure to calculate the vacuum energy is a central problem in theoretical physics. Presumably the problem arises from the insistent use of effective field theory reasoning in a context that is well beyond its intended scope. If one follows this path, one is led inevitably to statistical or anthropic reasoning for observations. It appears that a more palatable resolution of the vacuum energy problem requires some form of UV/IR feedback. In this paper we take the point of view that such feedback can be thought of as arising by defining a notion of quantum space-time. We reformulate the regularized computation of vacuum energy in such a way that it can be interpreted in terms of a sum over elementary phase space volumes, that we identify with a ground state degeneracy. This observation yields a precise notion of UV/IR feedback, while leaving a scale unfixed. Here we argue that holography can be thought to provide a key piece of information: we show that equating this microscopic ground state degeneracy with macroscopic gravitational entropy yields a prediction for the vacuum energy that can easily be consistent with observations. Essentially, the smallness of the vacuum energy is tied to the large size of the Universe. We discuss how within this scenario notions of effective field theory can go so wrong.