Electrodynamics and Photonic Propagation in a Scalar–Modulated Vacuum within the QGT:IR Framework

We develop an extended formulation of electrodynamics within the Quantum Gravity
Theory based on Inverted Relativity (QGT:IR), where spacetime is fundamentally Minkowskian
and gravitational phenomena emerge from the constitutive response of a scalar–structured
vacuum. Within the Electromagnetic Spectral Equilibrium Model (ESEM), the vacuum be-
haves as a dispersive and absorptive medium characterized by a scalar–dependent response
function B(ϵ).
We derive the modified Maxwell equations, establish global energy conservation through
the Radioactive Equilibrium Point (REP), and show that electromagnetic radiation under-
goes spectral relaxation toward an infrared attractor identified as the Global Equilibrium
Spectral Point (GESP). This framework provides an effective, non–geometric contribution
to cosmological redshift phenomena without invoking metric expansion, while preserving
gauge invariance, local Lorentz symmetry, and unitarity.