Proposal for an Experimental Test of the Casimir Effect — Identical Surface Coatings with Variable Internal Mass Density

A benchtop experimental proposal is presented to test the coupling between vacuum quantum fluctuations and internal substrate mass density — while maintaining identical surface electromagnetic boundary conditions. Two Casimir–Lifshitz cavities are fabricated with identical gold coatings (>100 nm) but differing substrate bulk densities (1.2–2.7 g/cm³ vs. 19.2–21.4 g/cm³). Standard quantum electrodynamics predicts zero force difference (ΔF = 0); the Field‑Code framework predicts a measurable residual force (ΔF ≠ 0) arising from differential vacuum damping by internal mass density. Measurements via atomic force microscopy and torsion balance with ≥10⁴ acquisitions per trial, thermal and vibrational isolation. Result implications span quantum vacuum, dark matter, and cosmological information structure.