A Substrate Interpretation of Dark Sector Phenomenology: Baseline Tension, Structural Response, and Observer-Limited Detectability

This paper develops a unified substrate-based interpretation of dark-sector phenomenology grounded in the author’s previously established framework of continuous non-zero substrate ontology, finite deformation capacity, continuity-preserving admissibility, and observer-limited reconstruction. The analysis addresses a central operational question: if the substrate is physically real, why do some of its most consequential large-scale properties remain inaccessible to internal observers? Three core principles are formulated. The Operational Baseline Inaccessibility Principle states that internal observers composed of substrate excitations cannot directly isolate perfectly uniform substrate baselines; operational access is restricted to gradients, contrasts, boundary responses, and induced geometric deviations. The Baseline Tension Principle holds that a uniform non-zero substrate stress may manifest geometrically as a cosmological-constant-like contribution to the large-scale metric, providing an ontological interpretation of dark-energy-like behavior. The Differential Response Principle holds that spatial variations in effective substrate response may generate curvature enhancements that mimic dark-matter-like gravitational signatures without requiring additional matter species. Taken together, these principles yield a unified interpretation in which dark-energy-like and dark-matter-like phenomena arise as distinct observational regimes of one continuous physical substrate. The framework does not modify General Relativity, does not introduce new particle species, and does not claim exclusion of the standard ΛCDM cosmological framework. Instead, it establishes structural admissibility, operational consistency, and empirical constrainability as the necessary foundations for future quantitative development. This Version 1.0 release presents the conceptual and structural foundations of the dark-sector interpretation while identifying the empirical burdens required for future testing across galactic dynamics, gravitational lensing, cluster-merger phenomenology, large-scale structure formation, gravitational-wave propagation, and cosmological stability.