Including many cavity modes that obey an FP cavity dispersion, we generalized the theory of k VSC (Eq. 16) to a many-mode version that explains the normal-incidence condition (Fig. ). This is because, for a 2D FP cavity, the finite in-plane momentum of the mode effectively decreases the effective lifetime of the thermal photon in a given mode volume. This leads to a sharp resonance at ω c = ω Q when k ∥ = 0. All of the above discoveries bring to a potential first microscopic theory k 2D VSC in Eq. 22, which successfully explains all observed phenomena in VSC experiments so far, including (1) The resonance effect ω c = ω Q , (2) the normal incidence effect, where the VSC effect only happens at k ∥ = 0, and operate under (3) collective coupling condition and (4) the thermal activation regime.