Structure and statistical properties of the semiclassical Einstein equations

Abstract

We treat the semiclassical Einstein equation as a quantum-classical hybrid and demonstrate the formal equivalence of its two derivation methods. This approach identifies the left-hand side of the equation as the expectation value of the Einstein tensor given the state of matter, and not its actual value in each realization of the set-up. As a result, standard criticisms of semiclassical gravity do not apply, and stochastic gravity emerges as a necessary extension