The Arrow of Time as a Physical Realizability Constraint Why Global Time Reversal Is Mathematically Allowed but Physically Impossible

This work proposes a structural resolution to the Arrow of Time by arguing that irreversibility is not a consequence of probability or special initial conditions, but a direct result of physical feasibility. While the fundamental equations of physics are largely time-symmetric, the universe operates under finite causal speed, locality, finite energy, and mandatory dissipation. Under these constraints, global time reversal is not merely unlikely but physically unrealizable, as it would require super-causal coordination and unbounded reconstruction of dispersed correlations. The theory introduces the Physical Realizability Constraint (PRC), which restricts physical reality to processes that can be coordinately implemented within finite resources. From this single constraint, the thermodynamic, measurement, cosmological, and observer arrows of time emerge naturally. Entropy is reinterpreted as unrecoverable coordination debt rather than disorder or ignorance, and irreversible phenomena—such as material fracture, memory formation, measurement, and cosmic evolution—are shown to be enforced by structural limits rather than chance. The framework does not modify existing physical laws, but clarifies which mathematically permitted histories can and cannot be physically instantiated.