The UD Origin of the Second Law of Thermodynamics: From Field Equations to Entropy Increase

This paper demonstrates that the second law of thermodynamics is not an independent fundamental law but a necessary consequence of the UD field equations. From the UD action, we derive the conservation law U + D = C via Noether’s theorem. We then construct the energy functional for D-type fields and prove rigorously that in an isolated system, the total condensation D = ∫ D² dV strictly decreases: dD/dt 0 strictly. Unlike statistical mechanics, where entropy increase is probabilistic, UD theory establishes it as an ontological necessity. The arrow of time emerges from the intrinsic unidirectionality of the U-D competition. All four laws of thermodynamics are unified within the UD framework.