A Larger Estimate of the Entropy of the Universe

TL;DR

This paper revises the estimate of the universe's entropy, highlighting supermassive black holes as the dominant contributor and providing new calculations for cosmic horizon and dark matter entropy.

Contribution

It presents the first updated and larger estimate of the universe's entropy, emphasizing the role of SMBHs and including dark matter entropy estimates.

Findings

SMBHs contribute at least ten times more entropy than previously thought.

The total observable universe entropy is approximately 3.1x10^104 k.

Cosmic event horizon entropy vastly exceeds interior entropy.

Abstract

Using recent measurements of the supermassive black hole (SMBH) mass function, we find that SMBHs are the largest contributor to the entropy of the observable universe, contributing at least an order of magnitude more entropy than previously estimated. The total entropy of the observable universe is correspondingly higher, and is S_obs = 3.1+3.0-1.7x10^104 k. We calculate the entropy of the current cosmic event horizon to be S_CEH = 2.6+-0.3x10^122 k, dwarfing the entropy of its interior, S_CEHint = 1.2+1.1-0.7x10^103 k. We make the first tentative estimate of the entropy of weakly interacting massive particle dark matter within the observable universe, S_dm = 10^87-10^89 k. We highlight several caveats pertaining to these estimates and make recommendations for future work.