E=mc²=Work: A Classical-Mechanics-Based Ontological Reinterpretation of Mass-Energy Equivalence

This paper demonstrates that the mass-energy equivalence equation E=mc² is not an exclusive discovery of relativity theory, but rather a necessary consequence of the classical mechanics definition of work (W = F × d) under the boundary conditions of light. Using only F=ma and W=Fd, substituting the boundary condition of "a unit mass accelerated to the speed of light in 1 second, traveling a distance of 1 light-second," E=mc² can be derived in three steps without relativity, Lorentz transformations, or the constancy of light speed as a postulate. Building on this derivation, this paper reveals a systematically overlooked definitional network in contemporary physics: the units of length, time, mass, and energy are all anchored in the properties of light, meaning that the "1 unit" of multiple fundamental physical quantities points to the same origin. This paper argues that this convergence is not a historical coincidence, but stems from physics' failure to strictly distinguish between "real quantities" and "human-defined metrics." Real quantities refer to objectively existing entities, properties, or relations in the physical world; human-defined metrics are scales, parameters, or concepts created by humans for description, recording, or computational convenience, which do not correspond to independent physical realities. Confusing the two is the root of many conceptual contradictions and "inexplicable mysteries" in contemporary theoretical physics. Based on this ontological framework, this paper draws five conclusions: (1) E=mc² is a special case of the definition of work at the light boundary, serving as a unit conversion formula between mass and energy rather than a universal physical law describing mass-energy conversion; (2) the speed of light c is the origin constant of spacetime, and its constancy is a mathematical necessity of self-referential unit definition rather than an irreducible empirical postulate; (3) "time bending with space" in general relativity is essentially the influence of spatial structure differences on the rate of physical change, rather than the bending of time itself; time is a typical human-defined metric; (4) light is pure energy moving in straight lines at speed c, its wave nature arises from spacetime medium perturbation, and its point-like delivery arises from the discrete quantization of matter energy absorption; "photon rest mass equals zero" is a mathematical fiction lacking physical correspondence; (5) the fine-structure constant α≈1/137 is not a fundamental physical constant, but an apparent product of the artificial choice of charge units; after redefining charge units, α=1 and disappears from all related formulas. All conclusions are verified by substitution into known physical formulas, with no exceptions. Compared to traditional physics requiring at least five independent postulates, this framework requires only one ontological position, offering significant simplicity advantages under identical empirical results.