The Dark Energy Principle: A Falsifiable Reinterpretation of Relativity’s Invariant

Abstract Einstein’s relativity enshrined the speed of light, c, as the universal invariant. We propose instead that the invariant is the speed of dark energy, cDE. Photons are contingent travelers whose effective speed depends on the cosmic environment. This principle predicts achromatic traveltime delays ∆t that scale with path length L and mean offset µ, producing millisecond to hourscale lags across voids, filaments, and clusters. The framework preserves Lorentz symmetry while offering clean falsification via fast radio bursts (FRBs), gamma-ray bursts (GRBs), and strong lensing time delays.