Physics of Nonequilibrium Systems

Most phenomena in nature take place under non-equilibrium conditions which, for instance, can be associated to temperature, electrical field, or concentration gradients. They are driven by thermodynamic forces and fluxes, and they dissipate energy and produce entropy. Many processes in biology can serve as examples, but also open systems that deal with climate and tipping points. Further examples are thermal osmosis, the thermoelectric effect, and oscillating chemical reactions. Nonequilibrium theory also determines relaxation behavior and fluctuation lifetimes, i.e., the timescales of physical processes. Even reversible oscillatory processes like an oscillating spring or belong to systems that can be described by nonequilibrium theory.

This course introduces into the thermodynamics of irreversible processes and into the application of these concepts to elementary biological reactions and to systems of general physical importance. We derive Onsager's phenomenological equations and the reciprocal relations. We derive important fluctuation theorems, e.g., the Jarzynski equality. As an important example, this course also introduces into the physics of nerve pulses. We contrast classical dissipative theory of nerves with an adiabatic hydrodynamic treatment of nerves leading to the possibility of solitons in membranes. Both are examples for nonequilibrium processes.