Jürg Fröhlich (ETH)

The Arrow of Time - Images of Irreversible Behavior

I sketch various examples of physical systems with time-reversal invariant dynamics exhibiting irreversible behavior. I start with deriving the Second Law of Thermodynamics in the formulation of Clausius from the existence of quantum-mechanical heat baths and then derive the Carnot bound for the degree of efficiency of heat engines. I continue with the analysis of a quantum-mechanical model with unitary time evolution describing a particle that exhibits diffusive motion when coupled to a suitably chosen (non-interacting) heat bath. A classical model with a Hamiltonian time evolution describing a particle coupled to a wave medium exhibiting friction is sketched next. I conclude with an attempt to draw the attention of the audience to the fact that the dynamics of isolated, open quantum systems featuring events is fundamentally irreversible.