Late-time weak-lensing surveys (KiDS-1000, DES Y3, HSC, DESI) consistently measure the matter-clustering amplitude S₈ ≈ 0.76. Planck CMB extrapolated forward through ΛCDM predicts S₈ ≈ 0.83. The 3.4σ deficit means the late universe is measurably less clumpy than the standard model says it should be.
The standard model assumes smooth, scale-invariant matter perturbation growth driven by a constant Λ from CMB-set initial conditions through to today. The growth rate must be the same in every environment. If observations show the late universe is less clumped than that growth rate predicts, the model has nowhere to put the difference.
SCT replaces the hot-dense-center with a superluminal collision and the thermalized debris field that became our visible universe. The same mechanism that resolves the Hubble tension resolves S₈, because both tensions are surface manifestations of the same underlying fact: Λ is not a constant, and the gap between "what we see locally" and "what CMB-extrapolated ΛCDM predicts" is exactly what a dynamical Λ_eff(x,t) field is supposed to produce.
The Λ_eff(x,t) ratio is set by the local-to-parent gravitational binding energy ratio (P17). Inside our local KBC supervoid, U_local is suppressed and Λ_eff is locally enhanced. Enhanced Λ_eff suppresses gravitational structure-growth rate in our local volume. Gravity has to work against a stronger effective dark-energy contribution to pull matter together (P18, P19). The result: late-time clustering measurements made from inside our supervoid naturally yield a lower S₈ than the CMB-anchored extrapolation predicts. The CMB sees the volume-averaged growth from outside; weak lensing surveys see the locally-suppressed growth from inside.
This is the same physics as the Hubble tension, just measured on the matter-clustering side instead of the expansion-rate side. The 3.4σ S₈ deficit and the 5σ H₀ tension are not two independent problems requiring two independent fixes. They are two observational projections of one mechanism that emerges naturally once the hot-dense-center assumption is replaced. The same field-equation extension that explains why void observers measure higher H₀ explains why void observers measure lower S₈. There is no need to invoke massive neutrinos at Σm_ν near 0.3-0.6 eV (which conflict with other constraints) or to fine-tune feedback prescriptions in cosmological simulations. The tension was always an artifact of forcing a fundamentally inhomogeneous Λ_eff field into a single-number constant-Λ framework.
SCT predicts the S₈ tension should diminish as observations probe higher redshift, where the line of sight extends progressively outside our local KBC supervoid. Specifically, ΔS₈ (CMB minus weak-lensing) should decrease from about 0.05 at z ≈ 0.3 to less than 0.01 at z ≈ 1.5, following a smooth decline with redshift. If the S₈ tension persists at full magnitude at z ≈ 1.5 (in measurements from Euclid photometric weak lensing), the M5 local-environment explanation is wrong.