Galaxy major merger rates rise from z = 0 to z ≈ 1 to 2 but show only weak further increase or even a plateau and decline beyond z ≈ 2, contrary to ΛCDM expectations of a steeply rising merger rate at earlier times driven by rapidly growing dark-matter halo merger rates (Conselice 2014; Dalmasso 2024). Hierarchical models can be tuned to match parts of the data but the combination of modest high-z merger fractions, abundant massive disks, and the detailed redshift evolution shows tensions with simple hierarchical merging prescriptions.
The standard hierarchical model has galaxies growing primarily by mergers, with merger rate scaling with halo merger rates that increase steeply at high z. The observed plateau and decline at z > 2 demands either modified halo-merger physics or selection-bias explanations, neither of which reproduces all the high-z observations cleanly.
SCT replaces the hot-dense-center with a superluminal collision and the thermalized debris field. From this single change, high-z galaxies are NOT assembled through gradual mergers but emerge as cascade-seeded proto-galaxies with substantial pre-existing baryonic content (P22, P25). The cascade-seeded population dominates the high-z galaxy budget: stars, disks, and morphology are present at deposition rather than built up through merger sequences over cosmic time.
The merger rate at z > 2 therefore reflects only the late-time gravitational interactions among already-formed cascade-seeded galaxies, plus a smaller contribution from the residual hierarchical assembly of the smaller cascade-stage products. Predicted excess over ΛCDM expectations at z > 2 by a factor of 2 to 5 (because cascade-seeded galaxies dominate); flatter decline at z = 4 to 6 because the cascade-seeded population continues to dominate over the hierarchical-merger contribution at these redshifts.
Angular-momentum inheritance (P31, P32) gives the cascade-seeded galaxies their disk morphology directly at deposition, explaining the abundance of massive disks at high z without requiring late-time disk reformation after major mergers. The same M1 framework that resolves the JWST early-galaxy mass crisis (recid 7, 108) and the SMBH-seed problem (recid 109) accounts for the merger-rate decline. There is no need for modified halo-merger physics or selection-bias corrections.
If precision JWST + Euclid + Roman pair-fraction surveys at z > 2 find merger rates fully consistent with hierarchical halo-merger predictions at the 10% level (no factor-of-2-to-5 excess from cascade-seeded population), the M1 cascade-deposition explanation is refuted. The signature SCT prediction is a flatter merger-rate decline at z = 4 to 6 than the standard hierarchical prediction.