September 18, 2015

Black Holes, information and What happens Beyond the Event Horizon

The black hole information paradox results from the combination of quantum mechanics and general relativity. It suggests 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 commonly assumed tenet of science—that in principle complete information about a physical system at one point in time should determine its state at any other time. A fundamental postulate 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. This is the strictest form of determinism.

Main approaches to the solution of the paradox
Information is irretrievably lost

    Advantage: Seems to be a direct consequence of relatively non-controversial calculation based on semiclassical gravity.
    Disadvantage: Violates unitarity, as well as energy conservation or causality.

Information gradually leaks out during the black-hole evaporation

    Advantage: Intuitively appealing because it qualitatively resembles information recovery in a classical process of burning.
    Disadvantage: Requires a large deviation from classical and semiclassical gravity (which do not allow information to leak out from the black hole) even for macroscopic black holes for which classical and semiclassical approximations are expected to be good approximations.

Information suddenly escapes out during the final stage of black-hole evaporation

    Advantage: A significant deviation from classical and semiclassical gravity is needed only in the regime in which the effects of quantum gravity are expected to dominate.
    Disadvantage: Just before the sudden escape of information, a very small black hole must be able to store an arbitrary amount of information, which violates the Bekenstein bound.

Information is stored in a Planck-sized remnant

    Advantage: No mechanism for information escape is needed.
    Disadvantage: To contain the information from any evaporated black hole, the remnants would need to have an infinite number of internal states. It has been argued that it would be possible to produce an infinite amount of pairs of these remnants since they are small and indistinguishable from the perspective of the low-energy effective theory

Information is stored in a baby universe that separates from our own universe.

    Advantage: This scenario is predicted by the Einstein–Cartan theory of gravity which extends general relativity to matter with intrinsic angular momentum (spin). No violation of known general principles of physics is needed.
    Disadvantage: It is difficult to test the Einstein–Cartan theory because its predictions are significantly different from general-relativistic ones only at extremely high densities.

Information is encoded in the correlations between future and past

    Advantage: Semiclassical gravity is sufficient, i.e., the solution does not depend on details of (still not well understood) quantum gravity.
    Disadvantage: Contradicts the intuitive view of nature as an entity that evolves with time.



New Proposal that information is bounced form Blackhole

The mechanism by which black holes return the absorbed information to the outside world is reconsidered, and described in terms of a set of mutually non-interacting modes. Our mechanism is based on the mostly classical gravitational back-reaction. The diagonalized formalism is particularly useful for further studies of this process. Although no use is made of string theory, our analysis appears to point towards an ensuing string-like interaction. It is shown how black hole entropy can be traced down to classical gravitational back-reaction

Arxiv - Diagonalizing the Black Hole Information Retrieval Process




SOURCES - Wikipedia, Arxiv

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