Homogeneous and Isotropic Linearized Gravity as a Caldeira--Leggett System

We establish the equivalence between homogeneous and isotropic linearized gravity with minimally coupled degrees of freedom and the Caldeira--Leggett model of open systems. This connects gravitation to an established system-plus-reservoir formalism, which we use throughout. Eliminating the reservoir reduces the equations of linearized gravity to a generalized Langevin equation for the metric perturbation, with the environmental influence condensed in the spectral density. The equivalence also yields a natural setting for reduced quantization of the perturbation and stochastic gravitational dynamics. We analyze the resulting dynamics with Laplace methods, extending results presented in other open-system settings.