Our ideas met fierce opposition in the beginning, but later our ideas were accepted. The resistance was caused by the fact that everybody knew that resonance delay for electrons does not show up in the diffusion constant. Phase, group and transport velocities relative to the speed of light. The size parameter is a measure of the sphere diameter. It is quite difficult to find media in which one can get short mean free paths.
Nature puts some serious constraints on the experimentalist.
One cannot just make the volume fraction of scatterers larger and larger, in order to increase the amount of scattering. Furthermore there are some fundamental limits on the magnitude of the cross-section for scattering. An important parameter for the experimentalist is the contrast in index of refraction. Diederik Wiersma et al. The index of refraction is there 3.5.