The Thomson scattering optical depth to reionization τ from Planck 2018 is τ ≈ 0.054, implying late reionization ending at z ≈ 7.7. JWST discovered an abundance of bright massive galaxies at z > 10 that, with standard escape fractions, should have reionized the universe much earlier (τ > 0.08) (Planck 2020; Naidu 2020; Muñoz 2024). The photon-budget crisis: late CMB reionization conflicts with early JWST cosmic dawn.
The standard model assumes a single smooth reionization epoch driven by the first stars + galaxies. Reconciling the late CMB τ with the early JWST galaxy abundance requires fine-tuning escape fractions or invoking inefficient reionization despite abundant ionizing-photon production, neither of which is parsimonious within minimal ΛCDM.
SCT replaces the hot-dense-center with a superluminal collision and the thermalized debris field. From this single change, τ_reion is the integrated multi-phase cascade-stage thermalization signature rather than a single smooth-reionization parameter. Cascade-stage events thermalize at multiple epochs through post-collision reheating (P36, P37, P38, P47), producing a multi-phase reionization history.
The CMB integrated optical depth measured by Planck (τ ≈ 0.054) reflects the cumulative effect of cascade-stage reheating across all post-recombination epochs. JWST observes the bright cascade-seeded galaxies at z > 10 (recid 7, 108) but their reionization contribution is partial: cascade-seeded SMBH (P46) plus early stellar populations contribute to the multi-phase reionization signal but do not fully ionize the universe at any single epoch. The reionization process spans z ≈ 6 to 15 in cascade-stage steps rather than completing at z ≈ 7.7.
The Plasma Equivalence Theorem (P29, P30) ensures the CMB observables match ΛCDM at l > 30 modulo the multi-phase signature, with the integrated τ consistent with observations. The high-z JWST galaxy abundance is naturally accommodated because cascade-seeded galaxies emerge with substantial baryonic content at deposition (M1, recid 108), producing the observed bright populations without needing 100% reionization-efficient escape fractions. The same M2 framework that resolves the polarization-bump anomaly (recid 39) and the optical-depth scatter (recid 41) accounts for reionization optical depth as a multi-phase cascade signature.
If precision SKA + HERA-2 + 21-cm tomography finds reionization proceeded smoothly from a single redshift onset z ≈ 7.7 with no multi-phase structure (no cascade-stage reheating signature), the M2 multi-phase explanation is refuted. The signature SCT prediction is reionization spanning z ≈ 6 to 15 in cascade-stage steps consistent with the integrated τ constraint.