Gravitational Wave Standard Sirens

Binary neutron star mergers detected by LIGO-Virgo emit gravitational waves whose waveform amplitude encodes the absolute luminosity distance to the source independently of any calibration chain. When combined with an electromagnetic redshift of the host galaxy, the luminosity distance yields H₀ directly. The first such event, GW170817 with its kilonova counterpart in NGC 4993, produced H₀ = 70 ± 12 km/s/Mpc — central value intermediate between the SH0ES and Planck results but consistent with both at that uncertainty. Subsequent binary black hole events analyzed statistically also yield values broadly consistent with the high-H₀ end of the tension range. As detector sensitivity improves and the sample grows toward the tens or hundreds of events needed for precision cosmology, the standard siren H₀ will become a decisive arbitrator — and the current central values already lean toward the higher local measurements.

Successive Collision Theory predicts that the gravitational wave standard siren H₀ will converge toward the locally enhanced value measured by SH0ES and time-delay cosmography rather than the globally averaged Planck value. The reason is geometric: all LIGO-detected binary mergers lie at redshifts z ≲ 0.5, within the same local volume that is underdense relative to the cosmic mean. The expansion rate probed by sources at these redshifts is the locally enhanced Λ_eff reflecting the KBC supervoid environment, not the globally averaged value encoded in the CMB. As the standard siren sample grows, SCT predicts no convergence toward Planck's value — the persistent offset will confirm that the Hubble tension is a real, environmentally induced spatial gradient in the expansion rate rather than a systematic error in the distance ladder.

The SCT framework makes a further testable prediction: standard siren H₀ values should show mild anisotropy correlated with the orientation of the local void structure, because the enhancement of Λ_eff is stronger along the least-dense directions of the KBC void than in the directions where the void boundary brings denser structure closer. This anisotropy signal, at the level of a few percent, will become accessible to third-generation gravitational wave detectors such as the Einstein Telescope and Cosmic Explorer, providing a direct spatial map of the locally enhanced expansion rate that is the hallmark of the SCT tensor mesh dissipation mechanism.