GEP Prediction: Angular Anisotropy of Photon Phase Velocity

We derive the quantitative prediction of Granular Entropic Physics for the angular dependence of the photon phase velocity. The tetrahedral bipartite network at the Planck scale uniquely determines the leading Lorentz-violating correction as the j=4 cubic harmonic Q4, which is the lowest rotationally non-invariant term allowed by the tetrahedral symmetry group at operator mass dimension d=6. The key result is a parameter-free ratio: the phase velocity anisotropy in the 111 crystal direction relative to the 100 direction equals exactly minus two thirds, independent of the wormhole fraction, photon energy, and all other model parameters. This follows purely from the tetrahedral geometry. The angular pattern has fourfold azimuthal symmetry, in contrast to the twofold symmetry of the minimal Standard Model Extension. The amplitude scales as the square of photon energy, providing a further discriminator from the energy-independent minimal SME prediction. Although the absolute amplitude is far below current experimental sensitivity, the angular pattern, the parameter-free ratio, and the energy scaling together constitute falsifiable signatures that uniquely identify the tetrahedral universality class of spacetime. If Lorentz-violating birefringence is ever detected, GEP requires the pattern to be Q4 with the ratio minus two thirds.