As I read on various sites ,all of them say that Black Holes emit Hawking radiation as one of the instantly created virtual particles near Event Horizon escapes from it.One goes inside it and other particle escapes and this particle(which escapes) constitutes Hawking radiation. So while engulfing Normal BODIES,does it emit something,so that the information preserves somehow?

  • $\begingroup$ No offense to Hawking, Susskind, John Rennie and Wikipedia, but not even a cup of coffee preserves information about the sugar falling into it, so take the "information paradox" with a strong cup of tea, you will need it to find anything of physical relevance in there... to this day I have not (and neither have any of the aforementioned). $\endgroup$
    – CuriousOne
    Jul 27, 2016 at 7:32
  • $\begingroup$ @CuriousOne: are you claiming that quantum mechanics is non-unitary when you dissolve sugar in coffee? Because that's the technical definition of "information loss". If you think the dissolution of sugar is non-unitary and you can prove it experimentally, go ahead and do it and get your Nobel Prize. $\endgroup$ Jul 27, 2016 at 10:53
  • $\begingroup$ @PeterShor: I am not claiming anything of the sort. What I am saying is that a black hole is the worst system to test whether it is or not. The entire discussion is completely unphysical. Indeed, one can't even decide that question using a cup of coffee and sugar cubes, neither theoretically nor experimentally, so it's really just a matter of having the boring phrase "cup of coffee" replaced with "black hole" while ending up with the same non-physics. If somebody comes up with a precision tabletop unitarity experiment, then I am all ear. $\endgroup$
    – CuriousOne
    Jul 27, 2016 at 18:55
  • $\begingroup$ @CuriousOne: just because it's impossible to test whether dissolving sugar in a cup of coffee is non-unitary, it doesn't mean that you can claim that the information is not preserved, as you did. The laws of quantum mechanics, which preserve information, have passed every experimental test performed so far. $\endgroup$ Jul 30, 2016 at 11:13
  • $\begingroup$ @PeterShor: See the definition of science for the practical distinction between a hypothesis and "it's not even wrong". This is the latter. $\endgroup$
    – CuriousOne
    Jul 30, 2016 at 11:17

1 Answer 1


Have a read through the answers to An explanation of Hawking Radiation to get a better idea of what Hawking radiation is. The popular explanation of virtual particles falling into the black hole is just a metaphor and should not be taken literally. The proper explanation for Hawking radiation is I'm afraid far more complicated than that.

A black hole does not necessarily emit anything when an object falls into it. If the falling object has a non-zero angular momentum there will be gravitational waves emitted, but these are unrelated to the information paradox.

At the moment there is no widely accepted explanation for the information paradox. There are many suggestions including a recent one from Hawking himself, but none of them are sufficiently convincing to have become widely accepted.

  • $\begingroup$ Aren't there always gravitational waves emitted when something falls into a black hole? (Except when what is falling in is a perfectly symmetrical spherical shell of matter.) I thought that if the mass falling in is not symmetrical, the black hole has to redistribute the mass that falls in, and that this process creates gravitational waves. Certainly, black holes colliding head-on produce gravitational waves. See this Caltech web page $\endgroup$ Jul 27, 2016 at 11:07
  • $\begingroup$ Thanks for explaining now I have 2 questions: 1) ingoing bodies have nothing to do with Hawking radiation? It is a spontaneous process? 2) I learnt in my school that red shift is just the loss of travelling wave's energy,so the wave expands but this wave has lesser energy ,so the wave with Infinite red shift will become just NULL kind of thing,so it wont escape,but with finite Red Shift one can escape,but still it must have enough energy to escape Event Horizon? Is this correct? $\endgroup$ Jul 27, 2016 at 12:25
  • $\begingroup$ @Śȟůbȟäm Ŗäĵpůț: There's no theoretical minimum to the energy a photon can have. $\endgroup$ Jul 30, 2016 at 11:23
  • $\begingroup$ But at zero energy ,The photon simply doesn't exist so infinite red shift means zero energy,So the photon will be gone. $\endgroup$ Jul 31, 2016 at 15:54

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