Causal Foundations of Relativistic Spacetime: Structural Constraints on the Emergence of Physical Geometry

This work examines why relativistic spacetime, rather than alternative causal organizations, is realized at large scales. Instead of taking Lorentzian geometry as a starting point, the paper develops a deductive framework based on minimal physical requirements for any viable universe. The analysis identifies a set of structural constraints—continuity of physical history, localization, interactional coherence, and internal generation of causal order—and shows that these jointly restrict the admissible forms of causal organization. Under these conditions, a shared finite causal bound emerges as a stable requirement, and relativistic spacetime appears as the most robust known realization of such bounded causal structure. The argument does not attempt a formal derivation of General Relativity, nor does it claim mathematical uniqueness. Rather, it establishes a structural selection principle: among known large-scale frameworks, Lorentzian causal geometry best satisfies the combined demands of physical intelligibility and dynamical coherence. Version 2: This revised version includes improved conceptual clarity, strengthened internal consistency, and minor corrections, particularly in the discussion of causal closure and interactional coherence.