What is the entropy of the universe?

New paper! You can find some additional discussion on Cosmic Variance.

What is the entropy of the universe?

Paul Frampton, Stephen D.H. Hsu, Thomas W. Kephart, David Reeb


Abstract: Standard calculations suggest that the entropy of the universe is dominated by black holes, although they comprise only a tiny fraction of its total energy. We give a physical interpretation of this result. Statistical entropy is the logarithm of the number of microstates consistent with the observed macroscopic properties of a system, hence a measure of uncertainty about its precise state. The largest uncertainty in the present and future state of the universe is due to the (unknown) internal microstates of its black holes. We also discuss the qualitative gap between the entropies of black holes and ordinary matter.