Euclidean quantum gravity

Summary

Euclidean quantum gravity is an approach to quantum gravity that writes the gravitational path integral as a sum over Riemannian metrics. These metrics come from Lorentzian ones by a Wick rotation. Each metric is weighted by $e^{-I/\hbar}$, where $I$ is the Euclidean Einstein–Hilbert action. It was developed mainly by Stephen Hawking and Gary Gibbons in the late 1970s. It gives a quick derivation of the temperature and entropy of black holes and underlies the Hartle–Hawking state.