On Horizon Molecules and Entropy in Causal Sets

TL;DR

This paper reviews various proposals for identifying horizon molecules in causal set theory to estimate black hole entropy, highlighting progress and key issues over the past two decades.

Contribution

It provides a comprehensive, accessible review of the main technical and conceptual developments in horizon molecules and entropy in causal set theory.

Findings

Multiple proposals for horizon molecules are summarized chronologically.

The review clarifies the conceptual and mathematical challenges faced.

Progress over two decades is outlined, emphasizing key insights.

Abstract

We review the different proposals and attempts to identify the ``horizon molecules" that would give a kinematical estimation for the black hole entropy in causal set theory. The proposals are presented according to their chronological appearance in scientific literature. The review is neither very technical nor merely descriptive; it is aimed to provide the reader with a lucid introduction to the necessary concepts and mathematical background, and give him or her a broad view on the subject, by focusing on the main technical and conceptual issues that summarize the progress made in the last two decades.