On the Physical Origin of the Invariance of the Speed of Light

This work proposes a physically motivated explanation for the independence of the speed of light from the motion of its source, based on analyzing the speed of light as a result of the transition from a regime of local quantum interaction to the autonomous dynamics of the free electromagnetic field. Such an interpretative distinction does not alter the formalism of quantum electrodynamics but reveals the mechanism by which the propagation speed of the electromagnetic excitation becomes independent of the kinematic properties of the system that produced it. In this framework, the invariance of the speed of light appears not as a postulated property or solely as a consequence of symmetry principles, but as a direct physical consequence of the transition from interacting dynamics to the autonomous free-field dynamics.

Accordingly, the work formulates an interpretation of the invariance of the speed of light that has not been presented in the existing literature. It is based on the transition from the emission phase to the autonomous phase of free-field evolution, whose dynamics do not depend on the kinematic parameters of the source. In this interpretation, the invariance of the speed of light acquires a physical justification as a consequence of the change of dynamical regimes of the quantum system, rather than only as an axiomatically assigned and experimentally confirmed property of the theory.