Thermodynamics From Structural Selection

This paper derives thermodynamics as a structural consequence of coherent return rather than probability or dynamical assumptions. Microscopic states are defined as viable return paths, and macroscopic states as equivalence classes of such paths. Entropy is identified with the logarithmic volume of viable micro-returns, while irreversibility and the arrow of time arise from the non-invertibility of return. Introducing coherence cost and finite capacity leads naturally to the Boltzmann distribution and a structural definition of temperature as the tolerance of return to coherence cost. Interaction strength is interpreted as a statistical property of the survivor ensemble, reflecting branching between internal closure and external coupling. Thermodynamics thus emerges as a theory of structural selection and history bookkeeping, completing the selection layer of the Structural Coherence framework without invoking probability postulates, kinetic theory, or molecular assumptions.