Time as Phase Flow IV: Observational Signatures and Falsifiability in Late-Time Cosmology

The concordance ΛCDM model faces a persistent S8 tension between Cosmic Microwave Background (CMB) and late-time weak lensing observations. We propose a fundamental resolution via Geometric Dissipation within the Information-Geometric Spacetime (IGS) framework, where irreversible entropy production arises intrinsically from spacetime deformation. This mechanism generates an effective cosmic viscosity characterized by β = 1/ (π√3) ≈ 0. 1837, a value derived purely from geometric and information-theoretic considerations without free tuning parameters. The resulting suppression kernel, PIGS / P_ΛCDM = exp -2β k² (1+z) ^-3, operates specifically at late times (z ≲ 2) and quasi-linear scales (k ≳ 0. 1 h/Mpc), effectively alleviating the S8 tension while preserving consistency with early-universe Planck data. Fisher matrix forecasts indicate that upcoming surveys such as Euclid and LSST will be capable of constraining β with a precision of σβ ≈ 0. 0002, allowing for a decisive falsification or confirmation of the IGS hypothesis with extremely high statistical significance.