Nonequilibrium thermodynamics and Fisher information: sound wave propagation in a dilute gas.

As recently shown, a constrained Fisher-information extremizing (CFIE) process is able to deal with both equilibrium and nonequilibrium thermodynamic processes, thus being able to reproduce results deduced by a recourse to Boltzmann's transport equation (BTE). Here, we discuss the propagation of sound waves in a dilute gas and compare the ensuing CFIE solutions with those obtained by a recourse to Grad's approach to the BTE. The final molecular distribution function arrived at is the same following two alternative routes, either (i) the BTE via the Grad approach or (ii) the constrained Fisher treatment that does not require the use of the BTE. The way the necessary a priori information is used in these two instances, is however, quite different.