Light as a Density-Bound Carrier

The speed of light c is treated in modern physics as a universal invariant — the anchorof spacetime, the metronome of causality, and the foundation of the relativistic framework.The Cohesion UFT (Gilbert 2025–2026) predicts that this invariance is local rather thanuniversal: c is the propagation rate of light within Earth’s density layer, not a property ofempty space as such. In a substrate-driven universe, light is a carrier whose propagation rateis governed by the resistance of the substrate it traverses. Higher substrate density produceshigher resistance and slower propagation; lower density produces lower resistance and fasterpropagation.This paper develops the formal operator set for density-bound light propagation, derives two new cosmological consequences not yet stated in the Cohesion UFT series, andpresents the resulting experimental predictions. The two new contributions are: (1) adensity-dependent redshift decomposition z = zvel + zdens that separates the velocity-drivenand density-driven components of observed redshift; and (2) a distance correction factorΛc = cE/vvoid that relates Earth-frame distance measurements to the true distances in avariable-propagation universe. Both are falsifiable with existing or near-future observationalprogrammes.This paper is an extension of the Scaling GR framework 3 and the Cosmological Dynamic 5. The GPS argument establishing the locality of c is developed in 3 and is notrepeated here.Scope and Prior Work. The variable-propagation hypothesis — that the effective speedof light varies with substrate density — was introduced in the Scaling GR paper 3, whichestablished the GPS argument: all precision measurements of c have been made withinEarth’s gravitational and density envelope, and GPS validates c only within that envelope.This paper accepts that argument as established and extends it to derive specific cosmologicalpredictions. The claims here are predictions of an unvalidated hypothesis. They are statedas predictions, not established results.