Remarks on the Speed of Heat Waves

We discuss heat conductance and diffusion, two remarkable transport processes characterized by instantaneous actions. We show that the assumption of local thermal equilibrium sets a limit to the speed of change in the distribution function of a statistical system . Using Onsager’s approximation, we show that the balance equations of the extensive parameters also have solutions with finite velocities involved. At the same time the infinite speed is obtainable when second order terms are neglected. We show how the presented technique is applied in heat transfer, diffusion, and plasma physics to determine the speeds of the physical processes.