The Cosmic Refrigerator: Gradient-Driven Diffusion of Zero-Point Energy Across the Cosmological Horizon as Dark Energy (Version 3.0)

This is Version 3. 0 of The Cosmic Refrigerator: Gradient-Driven Diffusion of Zero-Point Energy Across the Cosmological Horizon as Dark Energy. This major update significantly strengthens the theoretical foundation and adds several new results: • Full first-principles derivation of the effective diffusion coefficient \ (D\) from quantum field theory in curved spacetime, using 4th-order adiabatic regularization of long-wavelength perturbations on a de Sitter background. • Complete linear perturbation analysis demonstrating that the FLRW background remains linearly stable under the diffusive flux. • Quantitative prediction of a horizon-aligned cosmic dipole with amplitude \ (T/T 0. 01-0. 02\), naturally accounting for the observed >5–6σ anomaly in radio galaxies and quasars. • Explicit far-future numerical integration (\ (a\) up to \ (10⁶\) ) confirming that the model reproduces the standard \ (\) CDM Big-Freeze evolution exactly. • Expanded comparison with interacting-vacuum and running-vacuum models, plus full in-text citations and professional formatting throughout. The Cosmic Refrigerator proposes that cosmic acceleration arises from the natural thermodynamic diffusion of zero-point vacuum energy across the cosmological horizon. Our observable universe occupies a slightly higher-vacuum-energy patch left over from eternal inflation; the minute super-horizon gradient (\ (10^-30\) ) drives an outward Fickian flux that produces effective negative pressure inside our patch. The model reproduces the full Planck 2018 \ (\) CDM expansion history to better than 0. 01% accuracy while providing a simple, minimalist, and thermodynamically intuitive explanation for both the present acceleration and the widely accepted Big Freeze fate of the universe.