We formalize the theorem that physics terminates at the Reflexive Fixed Point. We define a "Master Loop" as a physical framework where the law-description, record semantics, and execution mechanism are internally co-realized without external separation. We prove the Theorem of Foundational Finality: any attempt to explain a Perfectly Self-Contained (PSC) universe from the "outside" (e.g., via a simulator, a multiverse measure, or an external runner) must either violate self-containment, be physically redundant, or be isomorphic to the original universe. Within PSC frameworks, any purported external explanation is either non-foundational, redundant, or isomorphic to the original closed structure. We further demonstrate that the universe is a literal fixed point of the map from ontology to semantics and back to optimal ontology. This establishes that no foundational explanation can rely on external model selection without ceasing to be foundational. All definitions and conditional theorems are formalized and machine-checked in Lean 4. This overview presents the core NEMS theorem engine and selected applications; stronger domain-specific derivation and ontological synthesis claims belong to separate release surfaces with their own premise bundles and formal artifacts. Trust boundary. Foundational finality is stated relative to the Master Loop and PSC predicates formalized here; "no outside explanation" is a no-external-model-selection claim in that sense, not a sociological limit on theorizing. Machine-checked alignment is nems-lean . See .
Nova Spivack (2026) studied this question.