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In General Relativity, white holes arise when one formulates Maximal extensions (the process by which coordinate singularities are mapped to new non-degenerate coordinates) to a geometric solution (say, Schwarzschild metric). As classical solutions, they are not expected to be physical.

On the other hand, if one were to imagine some sort of regularization process that smoothes the singularity, one can imagine trajectories of radiation falling into the black hole and exiting into the white hole, and there is no known argument to expect white hole solutions to disappear once a physically sound regularization takes place.

If Hawking radiation is a real physical process that can happen in nature, is hard to ignore the analogy that exists between what we classically expect from white holes, and a black hole that is spitting its guts in its final moments before total evaporation.

Do white holes encode the future evaporation of the black hole?

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  • $\begingroup$ This is a known idea, but there is no definite answer. The Hawking radiation may not exist, but even if it does, there is no reason why white holes would be limited to produce only this radiation. Also, the Schwarzschild solution defines the white hole radiation as emitted in the infinite coordinate past that is incompatible with the finite age of the universe. This may be a strong argument against the existence of white holes. $\endgroup$
    – safesphere
    Commented Sep 19, 2018 at 19:07
  • $\begingroup$ the infinite versus finite issue does not worry me since Schwarzschild solutions are built upon the assumption of BH being formed also in the infinite past, a realistic model or computation of gravitational collapse would remove those assumptions $\endgroup$
    – lurscher
    Commented Sep 19, 2018 at 21:11
  • $\begingroup$ With these assumptions the realistic model would also remove the white hole side of the solution. $\endgroup$
    – safesphere
    Commented Sep 19, 2018 at 21:18
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    $\begingroup$ I'm interested in any reference or argument you might have regarding that assertion $\endgroup$
    – lurscher
    Commented Sep 19, 2018 at 21:29
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    $\begingroup$ "Because a thermal-equilibrium state is time-reversal-invariant, Stephen Hawking argued that the time reverse of a black hole in thermal equilibrium is again a black hole in thermal equilibrium. This may imply that black holes and white holes are the same object. The Hawking radiation from an ordinary black hole is then identified with the white-hole emission." - en.m.wikipedia.org/wiki/White_hole $\endgroup$
    – safesphere
    Commented Sep 20, 2018 at 5:25

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Assuming Hawking radiation do exist.

A black hole then evaporate slowly and the evaporation rate will be proportional to inverse of its mass. At the end it will eventually vanishes with a flash of radiation. This leads to the quantum information paradox.

There are ways to resolve the paradox, one of them is that there exist a object called white hole counter to a black hole such that every single in-going quantum information to the black hole exits through the white hole so that quantum information will conserve. In this way, a respective white hole do encode the information going into the Black hole. There are other ways to resolve the paradox without invoking the hypothetical white hole. One of the popular solution is : information leakage through perturbations in event horizon.

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  • $\begingroup$ right, the point here is to identify the semi-classical idea of a black hole evaporating with the classical idea of a white hole as one and the same thing, modulo thermodynamic considerations $\endgroup$
    – lurscher
    Commented Sep 20, 2018 at 2:32
  • $\begingroup$ @lurscher So if you satisfied with this answer please accept it by up-voting it. $\endgroup$
    – Aman pawar
    Commented Oct 4, 2018 at 11:14

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