quantum gravity curvature curved spacetime quantum field theory
The theory of quantum field theory in curved spacetime may be considered as an intermediate step towards quantum gravity. QFT in curved spacetime is expected to be a viable approximation to the theory of quantum gravity when spacetime curvature is not significant on the Planck scale. However, the fact that the true theory of quantum gravity remains unknown means that the precise criteria for when QFT on curved spacetime is a good approximation are also unknown.
