The Substrate Field: A Physical Inference from the Finite Speed of Light

The constancy of the speed of light in vacuum is a fundamental empirical fact, yet its origin remains unexplained. Adopting the first-principle view that any finite speed must be mediated by a physical medium, this paper proposes the existence of a universal substrate field that pervades all space. The rigidity of this field determines the speed of light, while its uniformity ensures its isotropy and constancy. Using elementary optical data – the refractive indices and densities of air, water, and glass – the effective density ρ₀ and the rigidity K of the substrate field are derived. The calculation yields ρ₀ ≈ 4386 kg/m³ and K ≈ 4.0×10²⁰ Pa, consistent with c = √(K/ρ₀). The substrate field is presented as a physically plausible entity whose existence can be inferred directly from the finiteness of the speed of light and whose parameters can be obtained from ordinary optical measurements.Part I of the Substrate Field Theory series