The Geometric Origin of the S8 Tension: Void Pressure from Vacuum Lattice Sintering

Abstract The “S8 Tension” describes a persistent discrepancy where the late universe appears smoother (S8 ≈ 0.77) than predicted by the Cosmic Microwave Background (S8 ≈ 0.83). We propose that this suppression of structure growth is the mechanical inverse of the Hubble Tension. In the Selection-Stitch Model (SSM), cosmic voids are not passive empty space but active domains of “sintered” vacuum lattice (K = 13) that exert a topological pressure against gravitational collapse. We derive a zero-parameter suppression factor of ξ−1 = 12/13 ≈ 0.923, representing the geometric resistance of the thawed lattice. Applying this factor to the Planck 2018 baseline (S8 = 0.832) yields a predicted late-universe value of S8 = 0.768, which aligns precisely with Weak Lensing measurements from DES Y3 (0.776) and KiDS-1000 (0.766).