The Tully-Fisher relation links a spiral galaxy's rotational velocity to its luminosity, providing a relative distance indicator that requires absolute calibration to yield H₀ (Tully & Fisher 1977; McGaugh 2012). TF-derived H₀ sometimes lands between Cepheid/TRGB and CMB values, exposing a complex web of rotation-width, inclination, mass-to-light, and selection systematics. There are also hints of environmental dependence (cluster vs void galaxies show different TFR zero-points).
The standard model assumes one universal H₀ that the TFR must converge on after rotation-curve and inclination systematics are controlled. Environmental dependence has no place in the model except as a calibration error or a galaxy-evolution effect that cannot be cleanly disentangled.
SCT replaces the hot-dense-center with a superluminal collision and the thermalized debris field. From this single change, both the TFR scatter and the apparent H₀ offset are real physical effects, not calibration artifacts. The TFR itself emerges from grazing-collision angular-momentum inheritance (P31, P32): J = μ(b × v_rel) deposits an isothermal density profile ρ ∝ r⁻² that produces flat rotation curves without invoking a CDM particle. Coherence amplification through gravitational superposition (P50, P52, P54) gives A* = 5.970 in fully virialized halos (Paper 13, zero free parameters from Euler's e and the cosmic baryon fraction).
Different host environments sit at different points on the coherence-amplification curve. Cluster-stripped galaxies have reduced A; void-environment galaxies retain a slightly different A; field galaxies sit near the virialized-halo asymptote. The TFR zero-point inherits this environmental variability through the rotation-velocity-vs-luminosity relation, producing the observed environment-dependent scatter at the few-percent level. The inferred H₀ from TF-calibrated distances inherits the same environmental dependence through Λ_eff(x,t) (P17, P19) along the line of sight.
Once the M5 framework is applied, TF-derived H₀ converges on the SCT/CAR consensus value of 70.4 ± 0.4 km/s/Mpc (Paper 16), intermediate between Planck and SH0ES. The TF intermediate result is the predicted location for a method that samples a mixed environment of cluster, void, and field hosts. There is no need for unidentified rotation-width systematics or for new galaxy-evolution physics.
If environment-stratified BTFR surveys (Cosmicflows + DESI hosts) find zero correlation between host environment and inferred H₀ (after rotation-curve corrections) at greater than 2σ, the M5 environmental explanation is refuted. Equivalently, if the predicted A* = 5.970 amplification is found to be inconsistent with cluster baryon fractions at greater than 3σ, the M5 superposition framework loses one parameter-free anchor.