Causal Field Theory II: A Unified Framework for Dark Matter, Dark Energy, and the Hubble Tension

In Paper I, we demonstrated that the causal field model explains galactic rotation curves through the saturation of a dimensionless field φ at φₘₐₓ=0.429, producing gravitational amplification e^2φₘₐₓ=2.357 without invoking particle dark matter. Analysis of 1572 measurements from 134 SPARC galaxies confirmed the characteristic speed c₀ = 104.3 km/s as a new fundamental constant. Building on this empirical foundation, Paper II develops the complete cosmological framework of the causal field theory. Starting from the Principle of Causal Optimality, we derive the full field equations, including modified Einstein equations with an optimality tensor Cμν[φ], the causal field equation, and the causal potential V(φ) = β(e2φ - 1 - 2φ). Applying these to a homogeneous and isotropic universe yields the causal Friedmann equations, describing cosmic evolution with a dynamical field φ(t). We show that the same field φ explaining galactic dynamics also accounts for cosmological phenomena. The field stabilizes at φvac = 0.3476, giving dark energy density ρΛ = V(φvac) = 0.689ρc0, in exact agreement with Planck observations. The coupling constant β = 1.900 × 10⁻²⁶\ kg/m³ ~ 3.68 × 10⁻¹²³ MPl⁴ is directly derived from observations, not fine-tuned. The environment-dependent coupling λ(φ) = λ₀ eαφ with theoretical values λ₀ = 5.65 × 10⁻¹³ G and α = 69.2 (numerically implemented as λ₀ = 2.74 × 10⁻⁹ G, α = 70 for stability) unifies galactic (λgalactic = 4.40 G) and cosmic (λcosmic = 0.0157 G) regimes. The model resolves the Hubble tension through Hlocal/HCMB = e^φlocal - φCMB. Numerical integration yields Δφ = 0.0796, predicting Hlocal/HCMB = 1.0829, in excellent agreement with the observed $1.0837$. The fine-tuning problem is eliminated because β is a coupling constant whose smallness follows from the small Hubble parameter H and moderate φvac = 0.3476. The coincidence problem is addressed as dark energy domination occurs inevitably when matter density drops below ρΛ. The equation of state ω(z) = -1 + 2φ̇²/(3H² + φ̇²) deviates from $-1$ at z ~ 0.5-1.0, but these deviations are extremely small ($<0.02%$) and lie below the sensitivity of upcoming surveys like Euclid. The model makes four distinct predictions: (1) evolution of φ(z) with JWST/ELT; (2) modified gravitational lensing enhanced by eφ; (3) gravitational wave speed vGW = c eφ; and (4) the Hubble tension itself. All are falsifiable within 5-15 years. If confirmed, the causal field model unifies dark matter, dark energy, and cosmic structure within a single theoretical framework rooted in a first principle, eliminating the need for separate components while resolving major observational tensions.