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The question Why is a black hole black? states that stuff can't escape the event horizon and must ceaselessly pull inwards towards the singularity. At the singularity the forces become infinite. However, I heard that Hawking radiation (but not information) can escape the event horizon. Can something similar to Hawking radiation escape the inside of the event horizon and the singularity? Would a person inside the event horizon see Hawking radiation emitted from the singularity?

It is hard for me to understand this because I think as soon as one photon is emitted one quantum step out away it starts to fall back to the singularity at the center of the black hole again.

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    $\begingroup$ In the Schwarzschild metric the singularity is a future region for a geodesic that has crossed the horizon. Nothing comes out of it as a result. $\endgroup$ – Lawrence B. Crowell Aug 23 '16 at 2:11
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Hawking radiation escapes the horizon through quantum tunneling. Hawking calculated the radiation escaping through a quantum field theory in a general relativity classical background. It can also be understood as virtual particles escaping from outside the horizon and falling in with negative nergy, equivalent to positive energy particles escaping. These quantum effect causes the black holes to loose mass and energy in the form of different kinds of radiation escaping.

Note that it does not violate the theorems of black holes because those do not apply to quantum effects.

The calculations he and many other have done were done in the gravitational field near the horizon, which can be represented as a classical general relativity metric, with the matter being a quantum field. Closer to the singularity it does not apply - as you get closer to the sigularity the classical general relativity metric becomes less and less valid, as quantum gravity effects enter in and we do not know how to represent or calculate those. General Relativity becomes invalid as you approach the singularity. It has nothing to say about what happens there or nearby.

The above is now commonly accepted in black hole physics (though possibly I didn't state it all perfectly. The next paragraph is a little surmising on my part, at least on the conclusion, and may or may not be commonly accepted. Either way, what happens at the singularity, or anywhere near where quantum gravity could enter in, is just unknown at this time.

Now, if the Hawking black body radiation theorem is right, it says the black hole radiates at a temperature determined by his effect, and nothing else enters in. Since whatever happens at the singularity, if it is causal (a real singularity would not be, but then there would be no physics for it), it could only affect the energy coming out of the horizon through interactions with the classical gravitational field near it, it seems that anything else that happens inside the horizon might be accounted through the Hawking blackbody radiation already calculated.

EDIT after comment below: the explanation in the paragraph before the last that the 'above is commonly accepted in black hole physics' is just that. It's the theory of black holes, some of which has been observed. But Hawking radiation has not yet been observed, it may be difficult to observe it for macroscopic black holes but it is not impossible that astrophysical observations of the density of black holes and their masses over the time of the universe's evolution could confirm that they'd have to evaporate at the Hawking rates. Again, nothing measured at th time.

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  • $\begingroup$ "The above is now commonly accepted in black hole physics" -- yet none of it has been confirmed through experimental observations, right? $\endgroup$ – flippiefanus Aug 23 '16 at 4:08
  • $\begingroup$ Correct. And so nobody can ask any questions about black hole radiation? Or questions are ok but no answers allowed? Still, I edited and said in the context of the theory. $\endgroup$ – Bob Bee Aug 23 '16 at 4:31
  • $\begingroup$ Sorry, it was not meant to be a criticism. I just wanted to know if I'm still allowed not to believe any of it. ;-) $\endgroup$ – flippiefanus Aug 23 '16 at 4:42
  • $\begingroup$ Sorry myself. There is a tendency to not accept any statement not experimentally proved on this site. Good question: there is some hope they can see some relatively light black holes from the big band or way in the past tHat might be at the end of their life now, and see some X rays etc. but nothing on that yet. Also micro black holes at the LHC but I'M not sure how likely, and nothing of course. If there were any measurements it'd be big news and a Nobel prize for Hawking. My thought is that black holes can give us some ideas of how to get to quantum gravity, nothing there either. AdS/CFT? $\endgroup$ – Bob Bee Aug 23 '16 at 4:49
  • $\begingroup$ Thanks for the update. Problem with a field when it proceeds for so long without experimental confirmation is that one does not know whether any of it has any correlation with what actually happens in nature. $\endgroup$ – flippiefanus Aug 23 '16 at 5:08

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