= Thermodynamic arrow of time
The temporal orientation associated with the typical increase of macroscopic <entropy> away from suitable low-entropy conditions. It is a statistical claim about specified initial or boundary conditions and a macroscopic description, rather than a universal monotonicity theorem for every microscopic trajectory. <Time reversal in classical mechanics> pairs suitable increasing trajectories with decreasing ones, while <fine-grained entropy> is conserved under regular volume-preserving Hamiltonian flow.
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