Structural Origin of a Universal Acceleration Scale in Causal Cosmology

This work establishes the existence of a universal acceleration scale as a structural consequence of causal cosmology. Using only relativistic causality, dimensional consistency, and the presence of a cosmological horizon, we show that an acceleration scale of order a0∼cH0a_0 \sim c H_0a0∼cH0 necessarily emerges, independent of galactic dynamics, phenomenological fitting, or modified gravity models. The result functions as a structural constraint rather than a dynamical explanation.