The black hole information paradox is a puzzle resulting from the combination of quantum mechanics and general relativity. Calculations suggest that physical information could permanently disappear in a black hole, allowing many physical states to devolve into the same state.
This is controversial because it violates a core precept of modern physics—that in principle the value of a wave function of a physical system at one point in time should determine its value at any other time.
A fundamental postulate of the Copenhagen interpretation of quantum mechanics is that complete information about a system is encoded in its wave function up to when the wave function collapses.
The evolution of the wave function is determined by a unitary operator, and unitarity implies that information is conserved in the quantum sense.
In 2014, Chris Adami argued that analysis using quantum channel theory causes any apparent paradox to disappear; Adami rejects Susskind's analysis of black hole complementarity, arguing instead that no space-like surface contains duplicated quantum information.
In 2015, Modak, Ortíz, Peña and Sudarsky, have argued that the paradox can be dissolved by invoking foundational issues of quantum theory often referred as the measurement problem of quantum mechanics. This work was built on an earlier proposal by Okon and Sudarsky on the benefits of objective collapse theory in a much broader context.The original motivation of these studies was the long lasting proposal of Roger Penrose where collapse of the wave-function is said to be inevitable in presence of black holes (and even under the influence of gravitational field). Experimental verification of collapse theories is an ongoing effort.
In 2016, Hawking et al. proposed new theories of information moving in and out of a black hole. The 2016 work posits that the information is saved in "soft particles", low-energy versions of photons and other particles that exist in zero-energy empty space.