ABSTRACT
Each of the two pillars of twentieth-century physics—quantum mechanics and general relativity—has enjoyed both tremendous theoretical development as well as convincing empirical confirmation. Perhaps it is all the more surprising then that general relativity and quantum mechanics are completely incompatible with each other. The reasons for the incompatibility are many and include the ways in which space, time, matter, and energy are treated by the two theories (Callender and Huggett 2001a). Furthermore, attempts to quantize the gravitational field using the same renormalization group techniques that have produced quantum field theories for the other three fundamental forces (strong, weak, electromagnetic) have been a failure. “Quantum gravity” describes any attempt, of which there are many, to provide some solution to this problem.
