The Structural Plenitude Theory (SPT): A Viscoelastic Substrate for Light, Gravitation, and Cosmological Redshift

This work presents Structural Plenitude Theory (SPT v1.1), introducing the foundational concepts of a viscoelastic vacuum substrate (the Pleroma) as the mediator of thermal coupling, radiative exchange, and momentum transfer. The formulation reframes heat, light, and gravitational interactions as substrate-dependent fluxes governed by structural impedance and coupling efficiency. Version 1.1 consolidates terminology (TPE → SPT), revises internal consistency, and aligns metadata for future arXiv submission. No new ontological assumptions are introduced; this release establishes the conceptual and mathematical basis required for the multi-part SPT v1.3 expansion.