The Non-Fundamental Nature of Electron Rest Energy: Independent Derivation of 0.511 MeV from Stable Nuclide Data

Electron rest energy m_ec² = 0.511 MeV is treated as a fundamental input parameter in the Standard Model of particle physics, whose origin is not questioned by the theory. This paper demonstrates that 0.511 MeV can be independently derived from publicly available stable nuclide data, without assuming any intrinsic property of the electron. The derivation uses only five known data: the atomic masses of deuterium and hydrogen-1, the photodisintegration threshold of the deuteron, the rest mass of the free neutron, and the neutron decay energy. Through four steps of algebraic operations, 0.511 MeV is precisely obtained. The result shows that electron rest energy is not an intrinsic property of the electron, but the energy share released by the constraint network when a neutron is bound into an atomic nucleus. This discovery calls for a fundamental re-examination of the concept of "fundamental constants."