Predicted Ringdown Echoes from Wormhole-Saturated Horizons in the Foam–Plexus Model

In general relativity, black hole mergers settle into quasinormal mode (QNM) ringdowns with exponential damping. In the Foam–Plexus framework, however, the event horizon is not a singular surface but a stack of wormhole-saturation layers—nested shells of finite connectivity. These shells act as partially reflective boundaries just outside the classical horizon. Gravitational waves emitted during merger can therefore produce a sequence of “echoes” following the primary QNM. We derive expected echo delays, include the effect of layer thickness set by maximum foam density, and show how oscillator damping produces spectral reddening. The result is a distinctive, non-uniform multi-echo train, testable with LIGO/Virgo/KAGRA and LISA.