Phase Wave Cosmology

We present Phase Wave Cosmology (PWC), a continuous single-fluid framework that replaces separate cold dark matter particles and dark energy vacuum fields with a mass-energy fluid medium undergoing thermodynamic phase relaxation. Using first-law thermodynamic conservation (∇_μ T^{μν} = 0), we show that an infinitely smooth (C^∞) double-hyperbolic tangent equation of state w(a) maintains true 0.0000% energy conservation violation across seven orders of magnitude in scale factor (a ∈ [10^-7, 1.0]), resolving the 10^120 quantum field theory vacuum energy problem. Integrating linear perturbations over this smooth background with fluid shear viscosity (ν_0 = 5.0 × 10^26 m^2/s) yields k^2 scale-dependent damping that reduces the top-hat window variance σ_8 by 4.12%, shifting S_8 = 0.797 ± 0.008 and resolving the 3σ weak lensing tension. Intrinsic field kinetics yields a microscopic cross-section σ/m = c_s / (3 ρ ν_0) = 0.10 cm^2/g, satisfying Bullet Cluster bounds (σ/m < 0.13 cm^2/g) without arbitrary macroscopic length scales. We define quantitative Popperian falsification criteria for Stage IV surveys (Simons Observatory, Euclid, Rubin LSST, JWST) and present a mock likelihood parameter forecast for Planck 2018 + KiDS-1000.