Ever since their inception, black holes have sparked the imagination of physicists, sci-fi authors, and artists alike. Thus, it was a particularly big event when only very recently the first image of a black hole was released, which gave a scientifically grounded face to these mysterious regions of space. A major obstacle in the understanding of space-time singularities is that the usual paradigms of measurement cannot be applied directly. All measurements in physics rely either on intercepting some intrinsic emission or on observing the response to an outside perturbation. The only emission from a black hole is the rather faint Hawking radiation, which is very hard to observe. The second technique is further debilitated by the fact that, to date, no clear consensus has emerged on what exactly happens to a signal sent toward a black hole once it crosses the event horizon.
A possible resolution of this “information paradox” has been suggested by quantum information theory. It has been argued that all information crossing the event horizon is essentially instantaneously and chaotically “scrambled” across the entirety of the horizon and eventually leaves through wormholes connecting the interior of the black hole with the Hawking radiation. Whether or not this is what really happens in the cosmos remains to be seen. However, the concept of quantum information scrambling has opened the door to all kinds of fundamental questions. Rather remarkably, its study has attracted significant attention in various other fields of physics, including, but not limited to, high-energy physics, quantum information theory, and condensed matter and quantum many-body theory.
- Information scrambling vs. decoherence – two competing sinks for entropy
Akram Touil and Sebastian Deffner
PRX Quantum 2, 010306 (2021) [arXiv:2008.05559]