Gravitational Wave Background

The gravitational wave background (GWB) detectable by ground-based interferometers like LIGO-Virgo-KAGRA encompasses contributions from the integrated population of compact binary mergers — binary black holes, neutron star mergers, and neutron star-black hole systems — across cosmic history. The predicted amplitude of this astrophysical background, computed from observed merger rates and mass distributions, is approaching the sensitivity threshold of current detectors. Tension arises from the fact that the inferred merger rate densities at various redshifts, combined with the mass function of merging binaries, produce a background spectral amplitude that is sensitive to the assumed cosmic star formation history and delay time distribution between binary formation and merger. ΛCDM-calibrated star formation histories predict a specific background level that will be testable within the next detector generation, and any significant deviation would require new physics or revised merger population models.

Successive Collision Theory predicts a gravitational wave background amplitude that exceeds the ΛCDM astrophysical prediction due to the contribution of pre-existing compact binary populations from the colliding pockets. The two spacetime pockets contained stellar populations that had been forming, evolving, and producing compact remnants for an indefinite prior epoch within eternal infinite spacetime. When the collision thermalized these populations, their compact remnants — particularly the binary systems that had already hardened through prior stellar evolution — were incorporated into the post-collision debris with merger timescales set by their pre-collision binary properties. This pre-existing binary population begins merging from the earliest post-collision epochs, contributing to the GWB at redshifts higher than any ΛCDM star formation history can produce compact binary mergers, thereby boosting the total background amplitude.

The spectral shape of the GWB in SCT also differs subtly from the pure ΛCDM astrophysical prediction. The pre-existing binary population contributes to the background at higher frequencies corresponding to the compact object mass scales inherited from the pre-collision stellar populations, while the tensor mesh dissipation mechanism adds a low-frequency component from frame-scale orbital decay. The combined spectrum has a composite shape — dominated by the standard binary merger contribution at LIGO frequencies but with an excess at high frequencies from pre-existing compact remnants and a low-frequency excess from mesh dissipation that merges into the nanohertz pulsar timing signal. This multi-frequency spectral shape is a unique SCT prediction distinguishable from both a pure astrophysical background and from cosmological backgrounds postulated in inflationary models.