Special relativity, which takes the invariance of the speed of light as an underivable fundamental axiom, successfully constructed the modern theory of spacetime. However, it has never explained three core questions: why the speed of light is constant, why it takes its current value, and why all massless particles propagate at exactly the speed of light. Existing quantum field theory and quantum gravity frameworks have also failed to provide the microscopic dynamical origin of the speed of light. Based on the experimentally verified physical ontology of vacuum quantum fluctuations, this paper follows the fundamental assumptions of the λ-field coherent dynamics and the Boltzmann transport theory framework established in the previous Pi Universe system. By introducing the physical picture of three primordial phase modes and the steady-state transport equilibrium condition, we rigorously derive the origin formula of the speed of light: c=D₀₀. This formula reveals that the speed of light is not an intrinsic property of massless particles, but rather the characteristic velocity at which the intrinsic diffusion power of the sustained coherent mode reaches equilibrium with the joint damping of the other two primordial modes: random fluctuations and transient coherence. This paper rigorously proves that the model naturally satisfies Lorentz invariance, is fully compatible with special relativity, can naturally explain core phenomena such as the constancy of the speed of light, the velocity unification of massless particles, and the cosmic limit of the speed of light, and provides 4 falsifiable predictions with clear 5σ falsification criteria that can be tested in laboratories and astronomical observations. This model does not overthrow special relativity, but only provides a complementary explanation of its microscopic dynamical origin. As a natural extension of the λ-field coherent dynamics system, it achieves a complete and self-consistent connection with the Pi Universe quantum gravity unified framework. (A full Chinese version of this work is included as an additional file. )
Zhengrong Luo (Fri,) studied this question.