Deriving the Cosmic Microwave Background via Substrate Loss in Phase-Shift Cosmology

This paper presents the thermodynamic closure of Phase‑Shift Cosmology (PSC), demonstrating that a dual‑channel energy loss mechanism — geometric phase‑shift loss and harmonic substrate loss — naturally drives the vacuum reservoir to a stable equilibrium temperature of 2.73 K without invoking cosmological expansion. The harmonic substrate loss coefficient is derived directly from the background wave spectrum via a Helmholtz relation and coarse‑grained modal integration. The resulting steady‑state thermal field provides a present‑day physical explanation for the Cosmic Microwave Background.