Measuring equilibrium properties in aging systems

We corroborate the idea of a close connection between replica-symmetry breaking and aging in the linear response function for a large class of finite-dimensional systems with short-range interactions. In these systems, which are characterized by a continuity condition with respect to weak random perturbations of the Hamiltonian, the “fluctuation dissipation ratio” in off-equilibrium dynamics should be equal to the static cumulative distribution function of the overlaps. This allows for an experimental measurement of the equilibrium order parameter function.