This chapter begins the final section of the book, which presents both review and new results of original research on decoherence and measurement theory. In this chapter, it is shown that normal quantum mechanics can lead to irreversible behavior in an open system, in contrast to the expectation of the Poincaré theorem that predicts repeating, cyclical behavior for all closed systems. The quantum Boltzmann equation, which implies the famous H-theorem that underlies all statistical mechanics, is derived.

Boltzmann’s equation ruling the time evolution of the one-particle distribution function is obtained by partitioning the phase space into the free-flight and collision domains in low-density gases. The expressions for the entropy production and the entropy exchange are related to the H-theorem. The transport properties and gas-surface interactions are discussed. Furthermore, the multivariate fluctuation relation for the energy and particle fluxes is deduced from the fluctuating Boltzmann equation. In addition, an integral fluctuation relation is established for the Boltzmann factorization of the multiparticle probability density into one-particle distribution functions.