Global Complexity–Stability Theory (GCST): A Unified Framework for the Evolution of Complex Systems Across Scales

Global Complexity–Stability Theory (GCST) introduces the universal stability index G = γ / (α C) and derives the critical boundary G_c = 1 from fundamental constants c, G, ħ and cosmological expansion H(t). Structural debt D unifies dark matter (high ∇C) and dark energy (low ∇C), yielding ρ_D / ρ_crit ≈ 0.95. After aligning gradient sign, GCST predicts δw(z) > 0 at late times (w > –1 today, amplitude +0.02…+0.07), matching DESI DR2 2025 preference (w₀ > –1, wₐ < 0 at 2.8–4.2σ). The theory extends to galactic stability, planetary habitability (PSI ≈ 1) and a thermodynamic Fermi paradox resolution. Testable with Euclid, DESI, Rubin, JWST, ARIEL, PLATO, including positive δw(z) at late times consistent with DESI DR2 2025 preference for w₀ > –1 and wₐ < 0 at 2.8–4.2σ.