The Boundary-Mediated Origin of Inertia

This paper presents a mechanism-first explanation for the physical origin of inertia using only established principles of modern physics. It argues that inertia is not an intrinsic, unexplained property of matter, but a necessary consequence of relativistic causality and local conservation. Because momentum and information cannot propagate instantaneously, any interaction that changes a system’s state must redistribute momentum across a finite interaction region. The resulting, non-dissipative momentum density gradient during this redistribution is what is observed as inertial resistance. In this framework, inertia emerges as the operational cost of enforcing conservation laws in a universe with a finite speed of light, providing a physical “why” behind Newton’s laws without modifying existing equations or invoking speculative physics.