Quasar optical polarization vectors align coherently over Gpc regions (Hutsemekers 1998 onward, chance below 0.1 percent), and VLBI parsec-scale jets, set by black hole spin axes and immune to propagation effects, align across 400 to 900 Mpc at over 99.5 percent significance (Mandarakas et al. 2021). Tidal torque theory coheres angular momentum to 30 to 50 Mpc at most: the observed spin organization exceeds the model's reach by a factor of 20 to 30.
Angular momentum in ΛCDM is acquired locally, by tidal torques during collapse, and processed stochastically, by mergers and accretion, making black hole spin axes the noisiest vectors in the universe. Gigaparsec spin coherence has no mechanism at any epoch: the model cannot create it late and did not install it early.
SCT installs the coherence at the source: the collision deposits a global angular momentum J = μ(b × v_rel) whose direction is inherited down every level of condensing structure (P31, P32), and supermassive black holes, fed by filamentary accretion from the rotating debris field, lock their spin axes to the inherited local J (P56). Jet and polarization alignments over Gpc scales are then the J-field made visible: quasars across a billion light-years share an axis because their spins descend from one deposition geometry, the same inheritance measured in cluster spins, filament rotation, and satellite planes at smaller scales. The redshift-dependent rotation of the optical alignment angle reads as the line of sight sampling the large-scale structure of the J field.
The radio-optical agreement is the mechanism's signature: propagation exotica affect photons in flight, but VLBI jets are geometry at the source, so only a genuine spin-axis field explains both samples at once. The registered geometric cross-check sharpens it: the CMB dipole should lie perpendicular to the large-scale angular momentum coherence axis these alignments trace (P64), a comparison of two existing datasets.
This is the keystone evidence of the J-inheritance family, the largest-scale member of the same pattern as spin-filament alignment. There is no need to invoke axion mixing for a signal the radio jets carry without any propagation at all.
The registered kill: new large-sample SKA and LOFAR polarization surveys showing the alignment coherence collapses below 100 Mpc once unrecognized systematics are controlled, or VLBI jet alignment significance dropping below 3σ with improved calibration, would remove the gigaparsec J field. The cross-check cuts independently: the dipole-perpendicularity test (P64) failing at more than 3σ breaks the collision-geometry link between the alignment axis and the frame velocity.