The glass transition phenomena of liquid are hereunder discussed in terms of the non-equilibrium statistical mechanics. The hitherto accepted theories such as free volume theory and entropy theory are criticized from the standpoint of molecular dynamics of shear viscosity.
The molecular expression of the shear viscosity is given in terms of time-correlation function of the pair configuration distribution function. It is clarified that the elementary molecular process of viscosity is fluctuation of the pair distribution function whose dynamical aspects are discussed by using Langevin-type stochastic equation. It is suggested that the generalized random force of the stochastic equation is related to mobility of a molecule which was discussed in the free volume theory, and that the concept of the cooperative molecular rearrangement used in the entropy theory is substantially equivalent to the one of the fluctuation of the pair configuration distribution function of the present theory.