Adaptative Spacetime Criterion

This work presents the Adaptive Spacetime Criterion (ASC), an operational and parameter-free framework to classify kinematic and structural saturation across physical media, including ordinary fluids and spacetime. The criterion does not introduce new dynamics and does not modify Special or General Relativity. Instead, it provides a unified language to compare well-known thresholds such as shock formation in fluids, the relativistic speed limit for massive systems, and gravitational horizon formation. The work is intended as a comparative and classificatory tool.