According to Wang's theory, Minkowski photon is a kind of "quasi-photon", and its "four-momentum formula_10 denotes the macroscopic average of the properties of photons absorbed and re-emitted by the material subsystem". formula_10 only denotes the momentum and energy of a "pure" radiation field, because the momentum and energy of a "non"-radiation field (owned by the material) cannot constitute a four-vector. This explanation is completely different from the argument by Feigel and Kemp, where Minkowski momentum is thought to include both the field part and material part.