Λ Ground Mode of the Cosmic Boundary

Einstein introduced Λ in 1917 to hold the universe static. When Hubble proved expansion, Einstein removed it, calling it his "biggest blunder." A century later, standard cosmology revived Λ as dark energy. This note completes the arc: there is no dark energy nor mysterious force. Λ is the ground-mode eigenvalue of the cosmic boundary; the geometry of the universe itself driving "expansion" as expressed through the Friedmann equation. Einstein was right the first time, for reasons then unknown. The Möbius surface selects half-integer modes; the lowest yields Λ_top · ℓ_P² ≈ 2Ω_Λ⁻¹, where Ω_Λ = (R_Λ/ℓ_P)² ≈ 10¹²² is the de Sitter-to-Planck hierarchy. The observationally inferred Λ_obs differs by a factor of 3/2, derived from Gauss-Codazzi embedding of the 2D surface in 3D space under minimal embedding and isotropy. Prediction: 3.0 × 10⁻¹²² - Observed: 2.84 × 10⁻¹²² - Agreement: ~5% Latest derivation of this paper can be found at github.com/cosmological-constant v5 update: Λ correctly references the de Sitter scale Ω_Λ (epoch-independent) rather than the Hubble scale Ω_H (epoch-dependent). New section on topological protection: the logarithmic slope of C(Θ) vanishes exactly at the antinode, the reason Λ is constant. The 3/2 Gauss-Codazzi factor now carries a dual interpretation: face stabilizer order (3) to edge stabilizer order (2) in the icosahedral group native to S³. Phase position (Θ) notation aligned to MITv6. COMPACT reference updated to arXiv:2510.05030 (2025).