BigSnap CLASS Tests — Series 2: The Universe is Clumpier in the Past Than Today — and We Can Measure Why

The standard model of cosmology has a problem. When astronomers measure how clumped together matter is in the universe today, they get a lower number than what the Big Bang predicts. Two different measurements of the same universe disagree. Nobody has a clean explanation for why.This deposit presents a second series of CLASS Boltzmann code tests of the BigSnap dark matter pressure model. All tests use the same parameter point as Series 1: r = 5×10⁻⁴, γ = 1.5, Planck 2018 cosmology. No parameters were retuned between tests. The key result: the pressure model produces a scale-dependent, redshift-evolving suppression of matter clustering — strongest at small scales today, negligible at early times and large scales. This is not a uniform amplitude shift. It is a shape change in the matter power spectrum that neutrino mass cannot reproduce. The model is consistent with all current data tested and makes specific, falsifiable predictions for DESI and Euclid. Tests performed in this series: CMB lensing consistency, full growth trajectory D(z), fσ₈ growth rate likelihood, neutrino mass degeneracy, tomographic S₈ tilt, joint fσ₈ + tomography discriminant, MCMC posterior from KiDS-1000, BOSS DR12 BAO chi2, parameter space degeneracy structure, CMB temperature-lensing cross correlation, scale-dependent growth suppression, and Lyman-α forest forward model. The honest summary: the model is consistent with everything tested, makes a distinctive prediction that differs from neutrino mass, and that prediction is testable with current and near-future surveys. It has not been proven right. It has not been ruled out. It has earned the right to be tested.All numerical results, CLASS implementation details, parameter scans, validation tables, stress test outputs, and figures are included in the downloadable files accompanying this deposit. Companion papers: BigSnap Framework (Snider 2026), CLASS Series 1 — Implementation and First Results (Snider 2026).