The Invariant Substrate: A Non-Zero Baseline Model for the Vacuum as an Interaction-Carrying Medium

This paper develops a conservative reinterpretation of the physical vacuum as a non-zero, invariant baseline rather than a true null state. The framework emphasizes gradient-based observability, distinguishing what is operationally silent from what is ontologically absent. Observable physics is treated as arising from deviations relative to a uniform interaction-carrying substrate, while remaining compatible with standard quantum field theory and relativity. Version 1.4 introduces targeted refinements that improve conceptual clarity, methodological discipline, and referee readability. Major updates include:• Integration of the measurement principle into the main section hierarchy.• Formal introduction and repeated use of the four-way zero taxonomy (observational, ontological, baseline, effective).• Addition of an explicit baseline admissibility condition.• Clarification of reference-state invariance versus dynamical symmetry.• A topology-sensitive caveat based on the Aharonov–Bohm effect.• Expanded Lorentz/reference-frame language excluding detectable preferred-frame effects under uniform conditions.• Reorganization of the vacuum-energy discussion around baseline assignment and effective-zero conventions.• A new constraint section identifying conditions under which the framework would lose physical motivation. This version does not expand the physical scope of the model. It stabilizes the manuscript as a disciplined, foundations-oriented interpretive framework with clarified assumptions, explicit methodological boundaries, and a more precise account of how observational silence differs from ontological absence.