An aspect of quantum theory that attempts to incorporate the gravitational field as described by the general theory of relativity; no such theory has yet been accepted, however. Unlike the quantum field theories for the other three fundamental interactions, the procedure of renormalization does not work for quantum gravity, although there is some evidence that superstring theory can provide a quantum theory of gravity free of infinities. An approximation to quantum gravity is given by quantum field theory in curved space–time, in which the gravitational interactions are treated classically, while all other interactions are treated by quantum mechanics. An important aspect of quantum field theory in curved space–time is its description of the Hawking process. It is necessary to consider quantum gravity in the very early universe, just after the big bang, and the singularities associated with black holes can also be interpreted as requiring a quantum theory of gravity. The use of loop variables in quantum gravity has led to some notable success.
Subjects: Physics — Astronomy and Astrophysics.