Listening to black mirrors with gravitational radiation (2508.13272v1)

Abstract: The existence of curvature singularities and the information and firewall paradoxes are significant problems for the conventional black hole model. The black mirror hypothesis provides a CPT-symmetric alternative to the classical description of black hole, offering a novel solution to these long-standing issues. We show that classical black holes can, in principle, be distinguished from black mirrors observationally, by using gravitational waves. The principal challenge is to identify a unique, testable signature of the black mirror's reflective horizon that can be detected by current or future observatories. The horizon singularity of the black mirror model necessitates that no energy flux is propagated beyond the horizon, which can be described effectively by imposing specific boundary conditions at the event horizon. Our analysis demonstrates that the quasi-normal mode spectrum of the black mirror is fundamentally different from that of classical black holes, as purely ingoing modes are forbidden. Moreover, we show that the reflectivity of the black mirror does not depend on any free parameter; it is given precisely by the Boltzmann factor, which is independent of the dissipation parameter, indicating a universal behaviour regardless of the specific underlying quantum dynamics at the horizon. A definitive detection of the predicted gravitational wave echoes would provide compelling evidence distinguishing the reflective boundary of a black mirror from the perfectly absorbing horizon of a classical black hole. Extreme Mass Ratio Inspirals (EMRIs) are ideal probes for this test, as their long-duration signals allow for the secular accumulation of these faint echoes, offering a concrete pathway to challenge the classical paradigm and revolutionise our understanding of spacetime.