Multiple Gravitational Wave Interferometry (MGWI): A Proposal for Ensemble Analysis of Post-Merger Residuals

Abstract

Gravitational wave astronomy has confirmed the predictions of General Relativity in the strong-field regime, yet the precise structure of the event horizon remains obscured by the signal-to-noise limitations of individual merger events. Current searches for post-merger “echoes”—signatures of quantum-gravitational corrections at the horizon scale—have returned null results. We argue that these null results may be expected on theoretical grounds: the internal dynamics of black holes likely degrade the phase coherence of any reflected radiation, rendering phase-coherent echo templates potentially suboptimal in the scrambledresponse regime. We propose Multiple Gravitational Wave Interferometry (MGWI), a data analysis framework that extends interferometric principles from single events to the entire gravitational wave catalog. The core methodological contribution is a phaseless power stackingprotocol for post-merger residuals, analogous to Hanbury Brown–Twiss intensity interferometry, which bypasses the scrambled phase to search for persistent spectral structure in the horizon’s resonant spectrum. Unlike existing coherent mode stacking methods, which target known quasinormal mode frequencies, this protocol requires no a priori frequency target and is designed for the case where no coherent template exists. By normalizing residuals onto a dimensionless manifold scaled by remnant mass, the protocol forces any universal horizon signature to constructively reinforce across events while incoherent detector noise averages to a flat floor. We describe the stacking algorithm, selection criteria for a curated event set, a rigorous time-shifted null control, and projected sensitivity estimates from injection studies. We additionally outline broader applications of cross-catalog interferometry, including identification of strongly lensed gravitational waves and intensity correlations sensitive to the quantum state of primordial radiation. MGWI represents a natural extension of the aperture synthesis paradigm into gravitational wave population statistics, and provides a near-term, falsifiable test of horizon structure using existing LVK catalog data.

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