The Ontology of Mass: Constrained Energy, Inertial Interface and the Emergence of Gravitation

What is mass? In classical physics, mass was a primitive property of matter. In relativity, it became equivalent to energy. In the Standard Model, it emerges from couplings to the Higgs field. Yet the ontological status of mass—what it is, not merely how it behaves—remains unresolved. Energy-Efficiency Theory (EET) provides a first-principles answer grounded in the dynamics of constraint networks. Mass is not an independent substance but the \textbf{scalar interface} through which ontological inertia becomes externally measurable. Inertia is the resistance of constrained-state energy to constraint reconfiguration (Inertia Ontology v3.2). Mass is the scalar quantity that encodes this resistance for use in…