Upper and Lower Bounds on Gravitational Entropy

TL;DR

This paper discusses bounds on the universe's gravitational entropy, proposing that dark matter halos are the largest contributors, with bounds below the holographic limit but above black hole entropy.

Contribution

It introduces new upper and lower bounds on gravitational entropy and suggests dark matter halos as the primary current contributors.

Findings

Black holes provide a lower bound on gravitational entropy.

Dark matter halos likely dominate the universe's gravitational entropy.

Proposed bounds are below the holographic limit but above black hole entropy.

Abstract

The entropy in the interior of the Universe has many contributions including well understood ones from radiation and relic neutrinos. The gravitational entropy is larger and more subtle. One contribution which provides our lower bound is from supermassive black holes at the centers of galaxies. The remainder is harder to pin down. We suggest an upper bound which is many orders of magnitude below the holographic bound yet above that of the supermassive black holes. We propose that gravitational entropy in dark matter halos is the largest contributor to the present entropy of the universe.