Time symmetry and thermodynamics

Abstract

It is commonly thought that time asymmetry and process irreversibility find their best illustrations in thermodynamics. We argue that neither Fourier's law of heat transfer nor the second law of thermodynamics can indicate such an irreversible arrow of time. Irreversible processes of nonequilibrium systems are out of the scope of thermodynamics and belong in the research field of dynamics. The solution of any differential equation will automatically define the time symmetry or time asymmetry. Reversible processes and extreme irreversible processes are the only two types of process that can be treated in thermodynamics. There is no tight connection between time symmetry and reversibility, nor between time asymmetry and irreversibility. Temporal irreversibility is characterized by dynamic properties such as velocities. An electronic circuit is devised to illustrate that wave form process can be irreversible. The techniques of Fourier spectra and decay frequency spectra may be used to characterized dynamic properties.