The Casimir Effect as Boundary-Mode Resonance Lock in USP Field Theory: From Vacuum Pressure to Surface Cohesion and Cold-Welding Limits

This document presents a standalone USP Field Theory interpretation of the Casimir effect as boundary-mode resonance lock. The standard Casimir and Lifshitz frameworks remain the predictive baseline, while USP provides an interpretive dictionary that maps the measured pressure to effective surface-stress imbalance, boundary-compatible mode-density difference, and mean-square frequency mismatch. The paper emphasizes dimensional guardrails, non-circular calibration, material-response dependence, and falsifiable experimental pathways using AFM, MEMS, Lifshitz-kernel modeling, surface characterization, and clean-surface contact tests. The central idea is that closely spaced boundaries restrict the compatible oscillatory modes in the gap relative to the exterior field. This produces an inward pressure that is interpreted in USP language as a boundary-mode compatibility imbalance. The ideal parallel-plate Casimir pressure is retained in its standard form: Pc (d) = -π² ħ c / (240 d⁴). For a 100 nm ideal plate separation, this gives an approximate pressure magnitude of 13 Pa. In the USP mapping, this pressure corresponds to Δσₑff (d), the effective stress imbalance between exterior-supported and gap-supported modes. The document also separates the Casimir regime from van der Waals attraction, adhesion, electron-cloud overlap, and cold welding. These are presented as distinct regions of a broader surface-cohesion ladder, not as one identical mechanism. Casimir attraction is treated as a pre-contact boundary-mode pressure, while cold welding is treated as a contact-level lattice-lock state that requires clean, compatible metallic surfaces and removal or absence of surface barriers such as oxides and contamination. The work is compatibility-first: it does not claim that the ideal d⁻⁴ Casimir law applies at atomic contact, nor that cold welding is caused by the Casimir effect alone. Instead, it proposes a regime-based bridge from boundary-mode pressure to surface compatibility and contact-level lattice resonance lock. The proposed tests require fixed calibration transfer across separations or materials, explicit comparison against Lifshitz-only, patch-potential, roughness, instrument-noise, and chemistry/adhesion null models, and predeclared residual thresholds.