Thermodynamics and time-directional invariance.

Time directions are not invariant in conventional thermodynamics. We investigate impli-cations of postulating time-direction invariance in thermodynamics and requiring that ther-modynamic descriptions are not changed under time reversal accompanied by replacement of matter by antimatter (i.e. CPT-invariant thermodynamics). The matter and antimatter are defined as thermodynamic concepts without detailing their physical structure. Our analysis stays within the limits of conceptual thermodynamics and leads to effective negative temperatures, to thermodynamic restrictions on time travel and to inherent antag-onism of matter and antimatter. This antagonism is purely thermodynamic; it explains the difficulty in achieving thermodynamic equilibrium between matter and antimatter and does not postulate their mutual annihilation on contact. We believe that the conclusions of this work can be of interest not only for people researching or teaching thermodynamics but also for a wider scientific audience.