This paper presents a rigorous, information-theoretic extension of the Planck Core Framework to the search for extraterrestrial intelligence. I argue that black hole event horizons—being the densest information-storing surfaces allowed by nature, encoding up to 10791079 qubits for a stellar-mass black hole—constitute the most fertile environments for the emergence, evolution, and ultimate transcendence of complex informational structures that meet any reasonable definition of "civilisation." I analyse how such "horizon civilisations" could evolve under the intense selective pressures of matter infall (resource acquisition) and Hawking evaporation (information erasure), developing self-replicating computational structures, encoding their informational essence into the Planck core remnant, and potentially achieving a form of informational immortality across cosmic epochs. Critically, I demonstrate how such highly advanced civilisations could actively communicate with humanity using two principal mechanisms: (i) the deliberate modulation of gravitational wave echoes by controlled manipulation of the host black hole's entanglement structure, and (ii) the construction of a cosmic-scale communication network using Planck core remnants as entangled information nodes distributed throughout the dark matter halo. I provide a concrete, falsifiable observational roadmap for detecting these signals using gravitational wave observatories (Einstein Telescope, LISA), Hawking radiation spectroscopy (CTA, LHAASO), and dark matter distribution surveys (Euclid, Roman Space Telescope). The Fermi paradox is resolved as a consequence of humanity's sensory immaturity: we have been searching in the wrong domain, with the wrong instruments, for the wrong kind of entity. The search for extraterrestrial intelligence must now enter its gravitational era.
Wengang Yu (Mon,) studied this question.