Temporal Decay Theory formalizes the progressive drift of adaptive organizational systems from alignment with underlying reality constraints. The model describes this drift as a differential relationship between epistemic distance and accumulated obsolescence under bounded corrective capacity. The paper integrates systems modeling, governance architecture analysis, and path-dependent calibration dynamics to explain how rigid constraint regimes, while locally stabilizing, may generate long-horizon instability through repeated state interruption and re-normalization. The framework introduces Harper’s Law as a structural principle governing alignment persistence and proposes continuity-aware corrective mechanisms to mitigate drift accumulation in complex adaptive systems. This work is presented as a formal theoretical preprint.