Linearized gravity

Linearized gravity is an approach to general relativity in which the metric tensor is treated as a sum of a solution of Einstein's equations (usually the flat space) and a perturbation $h_{ab}$. The perturbation is treated using the methods of perturbation theory. The adjective "linearized" means that initially we neglect all higher-order terms in the perturbation, leading to linear different equations.

This method is useful to derive the Newtonian limit, including the first corrections, much like for a derivation of the existence of gravitational waves that lead, after quantization, to gravitons. This is why the conceptual approach of linearized gravity is the canonical one in particle physics, string theory, and more generally quantum field theory where classical fields are expressed as coherent states of particles.