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 system, 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 probability function of the overlaps $x(q)$. This allows for an experimental measurement of the equilibrium order parameter function.