The stochastic gravitational-wave background (GWB) can come from inspiraling SMBH binaries plus early-universe processes (inflation, phase transitions, cosmic strings) (Maggiore 2000; Romano & Cornish 2017; Caprini & Figueroa 2018; Christensen 2019). Recent PTA detections suggest GWB signals stronger than standard galaxy-merger expectations would produce, fitting the signal within ΛCDM constraints from CMB, BBN, PTAs, and ground-based detectors without overproducing energy density or invoking fine-tuned new physics is challenging.
The standard model attributes the nHz GWB to SMBH binary inspirals at galaxy-merger rates. The observed signal strength demands either higher merger rates or larger SMBH masses than standard hierarchical-galaxy-formation predicts, or contributions from new-physics sources (cosmic strings, inflation), 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, the GW background spectrum is the unified signature of pre-existing SMBH binaries plus mesh-dissipation orbital evolution plus constructive GW interference. The cascade thermalized pre-existing matter from prior cycles (P25, P28), inheriting a substantial population of SMBH binaries that already existed in the parent pockets. These binaries continue inspiraling under the combined action of standard gravitational-wave emission plus mesh dissipation (P14, P15, P16) operating on their orbital evolution.
The mesh-dissipation contribution provides the additional inspiral channel that allows binaries to traverse the parsec gap (recid 151) and complete their merger sequences over cosmic time. Constructive GW interference between binaries in the same comoving frame (P49) enhances the signal from comoving-source populations relative to incoherent sums, contributing additional amplitude to the observed PTA signal. The same mechanism produces the megamaser-NanoGrav unified signal (recid 55).
The GWB spans nHz (PTA) to mHz (LISA) frequencies through the cascade-deposited SMBH binary population at all mass scales. The signal eliminates merger-rate fine-tuning because the binary population was inherited (not assembled gradually through hierarchical merging) and the inspiral path is completed by mesh dissipation (not requiring CDM-halo dynamical-friction tuning). The same M5 framework that resolves the Hubble tension family, the cosmic-noon star formation cliff (recid 121), and the SMBH-binary final-parsec problem (recid 151) accounts for the GWB.
If precision PTA + LISA observations find the GWB spectrum fully consistent with hierarchical-galaxy-merger predictions plus standard GR inspiral at the 5% level (no mesh-dissipation contribution, no pre-existing-SMBH-population signature), the M5 unified-source explanation is refuted. The signature SCT prediction is the GWB spectrum across nHz-mHz matching the cascade-seeded plus mesh-driven inspiral population.