Pairwise kSZ measurements spent a decade marginal where forecasts promised detections, and the matured ACT-DESI signals persistently favor low amplitudes, conventionally absorbed as small optical depths: gas more blown-out than simulated. But the kSZ amplitude is optical depth times pairwise velocity, and the velocity is taken on faith from ΛCDM reconstruction of redshift surveys; slow or contaminated velocities would look identical to missing gas, and no current analysis can tell.
Reconstruction assumes every redshift gradient is motion: the model converts the survey's redshift field into velocities with no provision for non-kinematic components, then divides the kSZ measurement by that velocity to read the gas. The assumption is invisible because the model contains nothing else a redshift could be.
SCT puts a non-kinematic component in the redshift field by construction: environment-dependent Λ_eff variations (P17, P19) and frame-tree corrections (P10) contribute redshift gradients that ΛCDM reconstruction reads as infall, inflating the predicted pairwise velocities above the true motion (P15: mesh-change redshifts are observationally Doppler-like). The kSZ detector, which responds only to genuine motion of scattering electrons, then under-reads the prediction: the persistent low-side amplitudes are the gap between reconstructed and true velocities made visible, with the optical-depth reading absorbing into gas physics a discrepancy that partly belongs to the velocity factor. The decade of marginal results in the strait between forecasts and sky is the expected signature of dividing real motion by overestimated motion.
The split is testable because the two readings scale differently: missing gas suppresses kSZ uniformly at fixed velocity, while apparent-velocity contamination grows with the environmental contrast the pair sample spans, so SCT requires the suppression to correlate with the void-fraction and environment statistics of the catalog (the registered environment-tagged structure of Pred 8 and Pred 12), and to co-vary with the other reconstruction-based anomalies (bulk-flow excesses read from the same assumption). X-ray and tSZ gas masses provide the velocity-independent cross-check on tau.
This is the same apparent-expansion physics behind the Hubble-tension family, audited by the one probe that measures true motion. There is no need to blow the gas out of every halo to balance a velocity ledger written by assumption.
The degeneracy splits cleanly: independent optical-depth anchors (X-ray plus tSZ gas profiles) combined with Simons Observatory and CMB-S4 kSZ finding the full ΛCDM-reconstructed velocity amplitude, suppression entirely accounted by measured gas extension with no environment-correlated residual, would remove the apparent-velocity component and falsify this reading. The registered environment kills apply: no void-versus-overdense H(z) or flow differences at the predicted level guts the mechanism upstream.