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
Manifold properties from causal sets using chains
