This proposal tests whether fall acceleration in vacuum depends on object density: graphene aerogel cube (ρ ≈ 0.16 mg/cm³) vs tungsten cube (ρ = 19.3 g/cm³) dropped simultaneously from 1–3 m height. Standard Newtonian/GR physics predicts identical fall times t ≈ √(2h/g) = 0.452 s (1 m), 0.639 s (2 m), 0.782 s (3 m) with a = 9.81 m/s². The alternative pressure-gradient model predicts aerogel t > 2–10 s (a ≈ 0.06–2 m/s²) due to reduced external squeeze from cosmic density gradients. Tiers: access to existing super-lab facilities, professor-borrowed classroom setups, and DIY home (~200 €). Vacuum residuals quantified. All raw data—video, pressure logs, graphs—open under CC-BY-4.0. A positive anomaly falsifies Galilean equivalence and supports gravity as external pressure, not mass-pull.