Admissibility as the Boundary Between Physics and Metaphysics

This paper establishes admissibility as the boundary condition separating physics from metaphysics. It shows that the distinction is not disciplinary, methodological, or semantic, but structural: claims belong to physics if and only if they are admissible under standing-preserving reference and scope constraints. Claims that exceed these constraints are not speculative physics; they are metaphysical in the strict sense of being inadmissible to empirical or theoretical grounding. Within a closed admissibility framework, the boundary is binary and fail-closed. There is no gradient between physical and metaphysical description, and no legitimizing move by which inadmissible claims can be softened into admissibility through interpretation, probability, or explanatory appeal. When representational demands exceed what standing can support, the claim does not become less physical—it exits the space of licensed description altogether. The analysis is eliminative. No demarcation criteria, methodological rules, or philosophical doctrines are proposed. Instead, the paper establishes a necessity result: admissibility itself enforces the physics–metaphysics boundary, independent of empirical success, mathematical elegance, or explanatory ambition. By locating the boundary in admissibility rather than in content or intent, the paper dissolves debates over speculative realism, multiverse ontology, and foundational excess. It closes these debates by showing that what distinguishes physics from metaphysics is not what is being talked about, but whether the talk is admissible at all.