My interest has been concerned with the prospect that it has been established with some certainty that light speed will vary when the light encounters certain mediums. If the speed of light, other than in a vacuum, can effect the result of the energy produced by application of the formula how can the outcome of the application of the formula be predictable and reliable?
REP: Speed of Light as they say in classical GR remains the same.Certain mediums change it due to interaction with photons(changing the state of atoms). But the underlying fact remains same with respect to light.