  Let us abandon for a moment the strict epistemological standpoint of quantum
field theory, that eventually comes to declare nonsensical any question about
the photon posed outside the quantum theoretical framework. We can then avail
of the works by Whittaker et al. and by Synge about the particle and 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 classical simile only if
the dielectric is also homogeneous.
