Relaxation in glassforming liquids and amorphous solids

The field of viscous liquid and glassy solid dynamics is reviewed by a proc ess of posing the key questions that need to be answered, and then providin g the best answers available to the authors and their advisors at this time . The subject is divided into four parts, three of them dealing with behavi or in different domains of temperature with respect to the glass transition temperature, T-g, and a fourth dealing with "short time processes." The fi rst part tackles the high temperature regime T > T-g, in which the system i s ergodic and the evolution of the viscous liquid toward the condition at T -g is in focus. The second part deals with the regime T similar to T-g, whe re the system is nonergodic except for very long annealing times, hence has time-dependent properties (aging and annealing). The third part discusses behavior when the system is completely frozen with respect to the primary r elaxation process but in which secondary processes, particularly those resp onsible for "superionic" conductivity, and dopart mobility in amorphous sil icon, remain active. In the fourth part we focus on the behavior of the sys tem at the crossover between the low frequency vibrational components of th e molecular motion and its high frequency relaxational components, paying p articular attention to very recent developments in the short time dielectri c response and the high Q mechanical response. (C) 2000 American Institute of Physics. [S0021-8979(00)02213-1].