The Causal Composition of Mass

This theory provides a mechanism-first clarification of what mass is, using only established principles of modern physics. Rather than treating mass and inertia as intrinsic properties, it identifies them as unavoidable consequences of finite signal speed, local conservation laws, and the impossibility of perfectly rigid bodies. Any change in motion must propagate causally through a system, producing a temporary internal momentum redistribution that manifests as inertial and gravitational resistance. Mass is therefore defined operationally as a causal cross-section: the volume-latency structure governing how a system enforces conservation during interaction. The framework unifies inertia and gravity under a single internal process, explains mass additivity, mass defect, and the role of internal energy, and reframes mass as a necessary structural feature of a causal universe—without introducing new particles, equations, or speculative physics.