One thing that general relativity says about photons in matter

Let us abandon for a moment the strict epistemological standpoint of quantu m field theory, that eventually comes to declare nonsensical any question a bout the photon posed outside the quantum-theoretical framework. We can the n avail of the works by Whittaker et al. and by Synge about the particle an d the wave model of the photon in the vacuum of general relativity. We can also rely on important results found by Gordon and by Pham Mau Quan: thanks to Gordon's discovery of an effective metric these authors have been able to reduce to the vacuum case several problems of the electromagnetic theory of dielectrics. The joint use of these old findings allows one to conclude that a quantum-theoretical photon in an isotropic dielectric has a classic al simile only if the dielectric is also homogeneous.