Statistical forces from nonequilibrium media

We study the statistical force of a nonequilibrium environment on a quasi-static probe. In the linear regime the isothermal work on the probe equals the excess work for the medium to relax to its new steady condition with displaced probe. Also the relative importance of reaction paths can be measured via statistical forces, and from second order onwards the force on the probe reveals information about nonequilibrium changes in the reactivity of the medium. The presence of non-thermodynamic corrections to the forces put serious constraints on any formulation of nonequilibrium steady state thermodynamics.