Séminaire de Physique Théorique

Some thoughts on the information loss paradox

by Prof. Shinji Mukohyama (Yukawa Institute for Theoretical Physics, Kyoto University)


After reviewing basic concepts such as black hole thermodynamics, entanglement entropy and entropy bounds, we revisit the assumptions leading to the information loss paradox. The paradox is usually stated as an incompatibility between general relativity and quantum mechanics. However, the assumptions leading to the problem are often overlooked. Indeed, we present a thought experiment involving a black hole that emits radiation and, independently of the nature of the radiation, we show the existence of an incompatibility between (i) the validity of the laws of general relativity to describe infalling matter far from the Planckian regime, and (ii) the so-called central dogma which states that as seen from an outside observer a black hole behaves like a quantum system whose number of degrees of freedom is proportional to the horizon area. We critically revise the standard arguments in support of the central dogma, and argue that they cannot hold true unless some new physics is invoked even before reaching Planck scales. Therefore, if the central dogma holds then we may have chances to see O(1) deviations from general relativity far from the Planckian regime, providing new observational windows to quantum gravity. As an alternative, we also suggest a possible scenario for the recovery of information without need for the central dogma.