ABSTRACT
Thermodynamics is a theory dealing with energy balance, the most fundamental aspect of the universe. It puts constraints on the behavior of physical systems but has by itself virtually no predictive power. It tends to verify whether processes are commensurate with or in violation of this energy balance. Thermodynamics does not deal with time, that being the domain of kinetics, or with rheological parameters such as viscosity. It indicates direc-
tions, such as, for instance, the famous dictum of Clausius concerning the flow of heat from high to low temperature, but it does not assert anything more specific, as, for example, the amount of flow or its velocity. It is able to state that 70-million-year-old glassy rocks represent a nonequilibrium state, but it does not explain what prevents this system from relaxing to its crystalline ground state. At issue in this book is a question that has bothered and still bothers
generations of physicists: can these limitations be eliminated and can a thermodynamic theory be developed for a notorious nonequilibrium system, the glassy state, in which time and viscosity are of prime importance? We shall argue how this is, indeed, possible in certain situations, by including one extra parameter, the effective temperature, we will analyze up to which extent this description accurately encodes the main out-of-equilibrium features of the glassy state and we will consider and discuss what lies beyond the boundaries of validity of this representation. Before going into this, however, we will mention some of the classical no-
tions and observations over which mankind has pondered since the dawn of civilization up until our present time.
