Noise in driven systems

It is known that a direct relation exists between the noise in a system in equilibrium and transient drift toward equilibrium. It seems that a similar relation should exist for a system in a nonequilibrium stationary state. It is now necessary to distinguish between two types of transients; those produced by selecting those systems satisfying certain initial and those produced by actual physical perturbation. It is shown that a simple relation exists between noise and the transients produced by selection and that no relation exists in the case of transients produced by perturbation. In the equilibrium case it is shown that the two types of transients, though still logically and operationally distinct, can be described by the same impedance operator.