Irreversibility from a Reversible Equation
  After a discussion on the state of local equilibrium with temperature inhomogeneity, comparing mixture state reprsentation in statistical mechanics and pure state representation in thermo field dynamics, a simple model is solved to show that a reversible equation of motion with the initial condition having inhomogeneous temperature can lead to irreversible, viz. diffusive, behaviour. Yet, the solution is time symmetric exhibiting diffusion both towards future and past. 
Hiroshi Ezawa (Gakushuin University), Koichi Nakamura (Meiji   University) and Keiji Watanabe (Meisei University)