Cosmology Group Podcasts

In this lecture, David Albert continues his introduction to thermodynamics, explaining how the entropy of a system is defined and determined in thermodynamic terms. This requires distinguishing between reversible and irreversible paths between two states of a system, and envisaging how pistons and heat baths can be used to mimic the irreversible transfer of heat between a warm body and a cool one. Tim Maudlin and David disagree on whether the entropy of a non-equilibrium system can be defined. Tim begins his discussion of statistical mechanics by considering equilibrium states- where the macroscopic description of the state no longer changes over time. (He also introduces the problem of the adiabatic piston--for some systems, it is controversial to define the equilibrium state.) We then consider how the macroscopic thermodynamic properties of the gas can be understood using a statistical mechanical model, which treat the gas as a system of monotonic moving particles. At equilibrium, such a system