Discrete quantum gravity and causal sets

Abstract

This paper provides a thorough introduction to the physical and conceptual need for a theory of quantum gravity; some knowledge of general relativity and nonrelativistic quantum mechanics is assumed. A theory of quantum gravity would have wide-ranging implications for high-energy physics, astrophysics, and cosmology. The paper goes on to describe an important approach to quantum gravity that is not well known outside of the quantum gravity research community — causal sets. The causal-set approach falls within the framework of discrete quantum gravity, which considers the possibility that the small-scale structure of spacetime might be discrete rather than continuous. Herein, I elucidate the arguments for why a discrete causal structure might be appropriate for a theory of quantum gravity. The logical and formal development of a causal-set theory as well as a few illuminating examples are also provided. PACS Nos.: 04.60-m, 04.60Nc