







During the ten black hole mergers detected by the LIGO and Virgo interferometers in the last two years, each of the black holes involved lost a fraction of total mass during the process, around 5% on average. If the information is encoded in the mass of black holes, then it should be lost.





In any case, this is what general relativity says. When a particle falls into a black hole, all its properties - baryonic number, leptonic number, isospin, etc. - no longer play any role in the physics of the black hole. Information related to these properties is believed to be lost. In other words, according to Einstein's theory, the entropy of a black hole is zero.





Black hole and entropy: information stored on the event horizon



However, this consideration contrasts with the laws of thermodynamics and quantum mechanics. Any object with a defined temperature, energy and physical properties has a non-zero entropy, which can never decrease. If the material from which the black hole originates has a non-zero entropy, then throwing material into it would only increase its entropy. The black hole must therefore have a finite, positive and non-zero entropy.

