Vacuum Particle Creation under Action of a Strong External Field: an Example of Irreversible Behavior of a System with Time Reversal Symmetry ∗

On the basis of a kinetic equation (KE) of the Vlasov type, which is a strong non-perturbative consequence of the QED equations of motion in the quasiparticle representation, we investigate the irreversible behavior of the electron-positron plasma (EPP) created from vacuum under action of a pulsed external quasiclassical field. The basic KE is upon time reversal. Nevertheless the EPP reveals some features characteristic for irreversible processes. The nondecreasing entropy principle is introduced for the asymptotic in- and out-states: S out ≥ S in . Some features of the entropy evolution are investigated for different excitation levels of the EPP.