Vacuum dispersion and invariance of speed of light

PS to answer Murad's or is it Z's question?

In classical GR the vacuum is assumed to be non-dispersive in the coupling 8piG/c^4 of applied stress-energy current density's ability to manipulate the local geometrodynamical field Ruvwl and its global patterns of geodesic deviation.

If one makes the vacuum's virtual electron-positron pairs disperse light with strong magnetic fields etc in a small region - then it's the same problem as in my DARPA-NASA Star Ship "Low Power Warp Drive" paper for real meta-materials.

It's clear from Richard Tolman's 1934 classic "Relativity, Thermodynamics, & Cosmology" that

1) the macroscopic theory of EM fields is not completely derived from the microscopic theory.

2) the way to proceed is to renormalize all the couplings into zero rank tensor (scalar invariant) form - as I do in my paper - and to keep the local dynamical Euler-Lagrange field equations of all the matter fields generally covariant as well as locally Lorentz invariant - which I do.

3) of course we now know as Tolman did not in 1934 about P.W. Anderson's More is Different ---> Higgs-Goldstone spontaneous breakdown of continuous dynamical symmetries - modifying Noether's theorem etc. in which the ground states need not manifest all the symmetries of the Euler-Lagrange field equations from the Action Principle.

For example, we have an absolute cosmic frame of rest with global time (isotropy of CMB with a temperature measure of time) not in violation of GR but as a valid solution of the GR Euler-Lagrange field equations.