Description
Effective field theories in particle physics are usually designed for experiments where the initial state — the vacuum before a scattering event — is as clean and isolated as possible. Yet many physical systems, from condensed matter to cosmology, evolve in noisy and dissipative environments. Over the past decade, this recognition has driven progress at the interface between high-energy physics and condensed-matter. Motivated by these insights, I will present a framework for gravitational dynamics that combines General Relativity with the Schwinger–Keldysh formalism. I will show how symmetries, locality, and unitarity constrain dissipation and noise, and illustrate the approach by deriving the most general conservative and dissipative dynamics of scalar and tensor perturbations during single-clock inflation. I will conclude by discussing future prospects for dissipative dark sectors in the late universe.
