Symmetry and the order of events in time. The asymmetrical order of events in time in a reversible energy converter

The positive increase of entropy that occurs in irreversible processes has always served as a criterion for distinguishing the past from the future. The unerring ability of the Second Law of Thermodynamics to predict the order of events in time based on a change of entropy in macroscopic systems has led to the concept of the thermodynamical arrow of time. In this paper we analyze a cyclical reversible energy converter, in which thermal energy is converted into useful work without any net change of entropy. While it is usually assumed that time is an outsider in the equations of reversible thermodynamics[1,2,3], if not an illusion itself[4], it has been clear to many theoretical physicists from Laplace to Einstein that even in theory, all events must be considered to take place in time[5,6,7,8,9]. Our analysis of a reversible thermodynamic system shows that there is, in theory, an asymmetry in the events occurring in time. This leads us to the hypothesis that there may be another determinant, more fundamental than the increase of entropy in irreversible processes, for establishing an alternative thermodynamic arrow of time. This alternative is embedded in the Second Law of Thermodynamics. This determinant, which becomes clear once the thermodynamics of antimatter is considered theoretically[10,11], relates the flow of entropy to the order of events in time.