Phase Cavitation Theory (PCT v3.0): Unified physical model where observable universe emerges as coherent cavitation within elastic crystalline plenum (ρ_P=10^96 kg/m³, K_P→∞, S=0). KEY RESULTS:• Derives c = √(K_P/ρ_P) = 299,792,458 m/s exactly [Eq.17]• Resolves 45 cosmological tensions (H0 8σ, S8, σ8, etc.) • Verifies 15 GR tests: Shapiro (248.9μs), Mercury (42.98"/cy), LIGO (h=10^-21)• Plenum (S=0 eternal) → BE-membrane → Cavitation (S>0) ontology Preprint presents core mathematics, 15+ observational verifications, LISA/PIXIE predictions (2030+). PCT offers rigorous framework inviting academic scrutiny across theoretical physics, cosmology, and information conservation. Non-commercial use only (CC BY-NC-ND 4.0). **NC-ND license preserves author's commercial rights for potential future applications.** Academic review and non-commercial citation encouraged. Commercial inquiries: contact author. Keywords: unified theory, vacuum elasticity, phase cavitation, cosmology crisis, S=0 conservation