Black Hole Information Paradox - Wikipedia - en.wikipedia.org  ## Metadata - Author: **en.wikipedia.org** - Full Title: Black Hole Information Paradox - Wikipedia - Category: #articles - Tags: #physic - URL: https://en.wikipedia.org/wiki/Black_hole_information_paradox ## Highlights - The information paradox appears when one considers a process in which a black hole is formed through a physical process and then evaporates away entirely through Hawking radiation. Hawking's calculation suggests that the final state of radiation would retain information only about the total mass, electric charge and angular momentum of the initial state. Since many different states can have the same mass, charge and angular momentum this suggests that many initial physical states could evolve into the same final state. Therefore, information about the details of the initial state would be permanently lost. However, this violates a core precept of both classical and quantum physics—that, in principle, the state of a system at one point in time should determine its value at any other time.[3][4] Specifically, in quantum mechanics the state of the system is encoded by its wave function. The evolution of the wave function is determined by a unitary operator, and unitarity implies that the wave function at any instant of time can be used to determine the wave function either in the past or the future. - The loss of information can be quantified in terms of the change in the fine-grained von Neumann entropy of the state. A pure state is assigned a von Neumann entropy of 0 whereas a mixed state has a finite entropy. The unitary evolution of a state according to Schrödinger's equation preserves the entropy.