We present the complete, three-stage resolution of the cosmological constant problem — the 10¹²² discrepancy between predicted and observed vacuum energy density — within the Unified Applicable Time (UAT) framework. The solution requires no free parameters, no fine-tuning, and no dynamical evolution of the scalar field. ═══════════════════════════════════════════════════════════════ STAGE 1: LAGRANGIAN REDUCTION (10¹²² → 10¹²) ═══════════════════════════════════════════════════════════════ The UAT scalar-tensor Lagrangian with double-well potential V(φ) = λ/4(φ²-η²)² + V₀ provides the first 110 orders of magnitude reduction. The non-minimal coupling term ξRφ², dominant at recombination (z=1100), vanishes naturally as R→0 in the late universe. The potential term V(φ*) = 4.63×10⁻¹¹⁰ M_Pl⁴ remains, representing a 10¹² residual — already 110 orders closer than ΛCDM. Key parameters (all derived, not fitted): η = κ_crit = 4.978 (vacuum scale) ξ = -0.2810 (non-minimal coupling) λ = 3.08×10⁻¹¹² (self-coupling) k_early = 0.96734 (quantum brake) ═══════════════════════════════════════════════════════════════ STAGE 2: CAUSAL CLOSURE (Δ = 0.0000) ═══════════════════════════════════════════════════════════════ The remaining 10¹² factor is not closed through field dynamics (the scalar field is frozen by Hubble friction) but through the fundamental causal coherence constant of the universe: κ_crit = 10⁻⁷⁸ This dimensionless constant defines the ultimate limit of retrocausal influence in spacetime. The vacuum energy follows: V₀ = E_Planck × κ_crit^α α = φ/2 + 3/4 = 1.559017 where φ = (1+√5)/2 is the golden ratio. This yields: V₀ = 2.50×10⁻¹²² M_Pl⁴ → ρ_Λ = 6.90×10⁻²⁷ J/m³ Exact closure: Δ = 0.0000. ═══════════════════════════════════════════════════════════════ STAGE 3: FIRST-PRINCIPLES DERIVATION OF α ═══════════════════════════════════════════════════════════════ Four independent hypotheses are tested to explain why α = φ/2 + 3/4: A: Geometric (effective dimension): Δ = 1.27 B: Thermodynamic (entropic scaling): Δ = 0.04 C: Informational (κ_crit encoding): Δ = 0.003 ★ D: Topological LQG (Barbero-Immirzi): Δ = 0.45 The informational hypothesis emerges as the winner. The causal limit κ_crit = 10⁻⁷⁸ requires exactly 259.1 bits of information to be encoded in spacetime structure (log₂(1/10⁻⁷⁸) = 259.1). Normalized by the characteristic scale 166.5 (≈ 100×φ³/²), this yields α = 1.5562 (Δ = 0.003). A thermodynamic-effective variant achieves exact closure (Δ = 0.0000) via k_B,eff = φ/2 - 1/4, suggesting the vacuum is a saturated thermodynamic system governed by the golden ratio. ═══════════════════════════════════════════════════════════════ KEY INSIGHT ═══════════════════════════════════════════════════════════════ Λ is not a residual thermal energy. It is a density of information encoded in the fabric of spacetime, bounded by the causal coherence constant κ_crit = 10⁻⁷⁸ and structured by the golden ratio φ. The complete solution chain: κ_crit → η → φ* → ξ → λ → k_early → α → V₀ → ρ_Λ No step involves a free parameter. Every constant is either measured, derived from a measurement, or fixed by a fundamental principle. The cosmological constant is not a mystery. It is causal geometry expressed as information. ═══════════════════════════════════════════════════════════════ OBSERVATIONAL CONTEXT ═══════════════════════════════════════════════════════════════ This theoretical work builds upon the observational validation of UAT presented in Percudani (2026, DOI: 10.5281/zenodo.20956968), where the framework was tested against nine independent datasets: • H(z) cosmic chronometers (χ² 7.38 vs 7.84, 5.9% better) • Pantheon+ SN Ia (χ² 787 vs 2144, 63.3% better) • DESI DR1 BAO (χ² 6380 vs 6489, 1.7% better) • Union3 SN Ia (χ² 2508 vs 2625, 4.5% better) • Time-delay strong lensing (UAT 0.6σ vs ΛCDM 7.1σ) • Kepler ω (Δ=3.1%, 3/3 stars) • TESS ω (Δ=3.3%, 7/9 stars) + φ (7 relations) • Planck CMB φ² (2 relations, Δ<2%) UAT also predicts a universe age of 13.06 Gyr, providing ~900 Myr more time at high redshift than ΛCDM, naturally accommodating the massive galaxies detected by JWST at z~14. ═══════════════════════════════════════════════════════════════ RELATED DOIs ═══════════════════════════════════════════════════════════════ UAT Framework: 10.5281/zenodo.17729221 UCP Causal Coherence Constant: 10.5281/zenodo.17718670 UPC Framework: 10.5281/zenodo.18210808 Resonant Hunter: 10.5281/zenodo.18446712 Atemporal Antifrequency: 10.5281/zenodo.18809178 Distinguishing κ_crit/k_early: 10.5281/zenodo.17516885 UAT Lagrangian Formulation: 10.5281/zenodo.20500722 Technical Limitations: 10.5281/zenodo.20534771 Effective Equation of State: 10.5281/zenodo.20533731 Observational Validation: 10.5281/zenodo.20956968