Echo in a Wormhole express
A wormhole is a tunnel that pierces through curved space and connects distant regions of the Universe. Recently, Juan Maldacena and his colleagues proposed a working model of such a hole based on a special combination of spatial curvature and quantum particles. Physicists wanted to find out what an observer would hear if they sent a signal into such a tunnel.
It turned out that the wormhole acts like an echo chamber: its throat is sandwiched between two near-black holes — regions with monstrous gravity. These regions act as mirrored walls. A wave that gets inside bounces between them, each bounce producing a new, weaker burst — an echo. The more twisted the wave (the greater its angular momentum), the higher the gravitational barriers become, and the longer the sequence of echoes rings out. A simple, untwisted wave slips through almost without an echo.
This echo pattern is unique: ordinary black holes swallow the signal immediately, without repetition. If astronomers ever detect similar series of gravitational waves or other pulses, it would be a strong hint of wormholes. Curiously, even gravitational tremors passing through the Earth right now could echo in the same way if there were a traversable tunnel nearby.
Original abstract
as written by the authors arXiv:2511.22671
We study linear scalar perturbations of the four-dimensional, traversable wormhole solution of Maldacena, Milekhin, and Popov(arXiv:1807.04726). The geometry is constructed by matching an asymptotically flat, near-extremal Reissner--Nordstr\"om region to a throat described by $$AdS_2 \times S^2$$, supported by charged massless fermions. We derive the effective scalar potential governing wave dynamics, which when viewed in the tortoise coordinate, exhibits two extremely sharp and widely separated barriers. These barriers form a resonant cavity and are a direct consequence of the near-horizon geometry of the wormhole mouths. Using time-domain integration, we analyze the wormhole's response to an initial scalar wave packet inside the throat. We find that the late-time signal contains a distinct train of echoes whose amplitude depends on the angular momentum number $$l$$. We show that higher $$l$$ modes produce significantly stronger echoes, as the corresponding potential barriers are taller and more reflective, which results in more efficient trapping of the wave within the wormhole throat.
The echo from a wormhole resembles the famous 'whispering gallery' in St. Paul's Cathedral: sound, reflecting off curved walls, repeats many times at the other end.
In the movie 'Interstellar,' the wormhole is a bridge to another galaxy. Now scientists have shown that a real wormhole could reveal itself through a series of echo signals, like a cosmic sonar.