Resolution of the Cosmological Constant Problem: Non-Gravitating Hydrostatic Pre-Stress, Absence of Zero-Point Divergences, and the Geometric Origin of Cosmic Acceleration in an Elastically Pre-Stressed Vacuum

The Cosmological Constant Problem constitutes the most acute quantitative failure in theoretical physics: summing zero-point quantum vacuum fluctuations up to the Planck cutoff predicts an energy density ρ_vac^QFT ≈ Λ_UV^4 / (16π^2) ~ 10^71 GeV^4 ≈ 10^96 kg/m^3, which exceeds the observed dark energy density ρ_Λ^obs ≈ 10^-47 GeV^4 ≈ 10^-27 kg/m^3 by 120 orders of magnitude. Standard resolutions invoke 120-decimal-place fine-tuning or anthropic multiverse landscapes. Building upon our foundational series on the physical vacuum as an elastically pre-stressed continuum, we show that the 10^120 catastrophe is an ontological artifact of equating static thermodynamic pre-stress with an active gravitational mass source. In continuum elastodynamics, the vacuum possesses a homogeneous hydrostatic holding pre-stress P_0 ≈ 7.48 × 10^24 Pa and bulk modulus K_v. In static Cauchy stress equilibrium, the divergence of the stress tensor vanishes identically: ∇ · σ_0 = ∇(-P_0 I) ≡ 0. Because a uniform pressure exerts zero body force, it produces zero gravitational acceleration. Microscopic zero-point modes are symmetric acoustic lattice vibrations whose spatial and temporal averages vanish identically on the discrete unit cell ℓ_0, eliminating quartic loop divergences (ρ_ZPE^grav ≡ 0). Furthermore, we derive the observed cosmic acceleration as the macroscopic boundary relaxation strain of the finite causal Hubble horizon R_H ~ c/H_0, yielding ρ_Λ = (5/6) P_0 (ℓ_0 / R_H)^2 ≈ 2.25 × 10^-47 GeV^4 ≈ 10^-27 kg/m^3 without fine-tuning, resolving the crisis under Occam's razor.