ABSTRACT
Equilibration due to the process materializing conservedness is intrinsically irreversible because of its self-constraining capability in time. Entropy, whether statistical or microscopic, basically requires an interaction-free reference for its own underpinning. Statistical entropy can be defined in terms of the distribution of quantum states even if away from thermodynamic equilibrium, with the reservation that those quantum states are a priori assumed to be almost interaction-free among themselves. Thermodynamic time's arrow in terms of statistical entropy depends upon the boundary condition to which the entropy is subject. Thermodynamic time's arrow is an outcome of pairing a strange couple, statistical entropy and microscopic irreversibility. The second law of thermodynamics formulated in terms of entropy requires a framework in which the entropy is definable, in addition to a process that generates irreversibility. Thermodynamic time's arrow in terms of statistical entropy depends upon both the definability of entropy on a macroscopic scale and the process generating irreversibility on a microscopic scale.
