Random processes underlying stretched times and divergent time scales near the glass transition (Invited Paper)

A model of relaxation in glassy materials, involving anomalous slow diffusion of defects, is reviewed. The movement of the defects causes a stretched exponential relaxation. If there is an attractive force between defects then as the temperature is lowered, or the pressure increased, the number of mobile defects will decrease. This loss of mobile defects produces a Vogel type law for the singular behavior of the relaxation time scale at a critical temperature.