  We argue that entropy production in hydrodynamics can be understood via a
superspace inflow mechanism. Our arguments are based on a recently developed
formalism for constructing effective actions for Schwinger-Keldysh observables
in quantum field theories. The formalism explicitly incorporates microscopic
unitarity and the Kubo-Martin-Schwinger thermal periodicity conditions, by
recasting them in terms of topological BRST symmetries of the effective action.
