The EDGES experiment reported a deep absorption trough in the global 21-cm radio spectrum at 78 MHz (z ≈ 17) with amplitude near −500 mK, twice as deep as standard ΛCDM adiabatic-cooling predictions (~−230 mK) (Bowman 2018; Barkana 2018). Explaining the depth requires either much colder primordial gas (possibly DM-baryon scattering) or much hotter Cosmic Dawn radio background (possibly early black holes). SARAS 3 failed to verify EDGES, creating experimental tension (Singh 2022).
The standard model assumes adiabatic cooling of the primordial gas plus the standard CMB radio background at Cosmic Dawn. Recovering the EDGES depth (if confirmed) demands either CDM-baryon interactions modifying gas thermodynamics or unidentified excess radio sources in the high-z universe. Neither is parsimonious.
SCT replaces the hot-dense-center with a superluminal collision and the thermalized debris field. From this single change, the 21-cm global signal acquires features from cascade-thermalized + cascade-seeded reionization signatures. Multi-stage cascade dynamics (P22, P36, P37, P38) plus cascade termination before t ≈ 1 second (P40) leave the post-thermalization plasma in a state where post-collision reheating events (P47) operate at staggered times in the early universe. These multi-phase reheating episodes contribute to the 21-cm absorption-emission profile.
Cascade-seeded SMBH (P46) inherited from prior cycles drive in-cycle reionization through early AGN activity at high z. The cascade-seeded SMBH population provides ample radio-source contribution at Cosmic Dawn, naturally producing the higher background radio temperature that the EDGES depth requires (if the EDGES signal is confirmed). Pre-existing matter (P25, P28) supplies the gas + AGN-host populations that participate in the multi-phase reionization. The Plasma Equivalence Theorem (P29, P30) preserves the post-cascade thermodynamic structure into the 21-cm-observable epoch.
The SARAS 3 non-detection is consistent with the SCT prediction that the cascade-seeded reionization signature varies with sky location and observing-instrument-systematic configuration: the 21-cm signal is real but its detailed amplitude is sensitive to the cascade-seeded source-population distribution + observing geometry. The same M2 framework that resolves the polarization-bump anomaly (recid 39), optical-depth scatter (recid 41), heated-CMB term (recid 40), and broader cascade-thermodynamics CMB signatures accounts for the 21-cm global signal as a multi-phase cascade-seeded reionization output.
If precision SKA + HERA-2 + global 21-cm experiments find the absorption depth fully consistent with standard adiabatic + CMB-only predictions across all sky locations (no cascade-seeded reionization signature, no multi-phase reheating contribution), the M2 cascade-thermalized explanation is refuted. The signature SCT prediction is depth + spectral shape consistent with multi-phase cascade-seeded reionization plus cascade-AGN radio backgrounds.