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wywong
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When the apparent horizon differs from the event horizon, as in the case of an observer falling into a black hole, does Hawking radiation take place at the former, the latter, or both?
wywong said:When the apparent horizon differs from the event horizon, as in the case of an observer falling into a black hole
wywong said:does Hawking radiation take place at the former, the latter, or both?
PeterDonis said:I assume you mean an object falling in with significant enough mass to change the hole's mass, so that the horizons change during the process, correct?
Thanks for enlightening me.Hawking's original derivation gave the answer that it's the event horizon; however, other treatments have made it seem like it's the apparent horizon... I don't know that we'll know for sure until we have a confirmed theory of quantum gravity.
As far as everything I have read goes, that's incorrect, but if I have been misled I'll happily stand corrected.wywong said:Sorry to have confused you. I actually mean the horizon perceived visually by the falling observer, which always seems some distance below the observer. It appears that "apparent horizon" is not the correct term. Is "visual horizon" a better term?.
wywong said:When the apparent horizon differs from the event horizon, as in the case of an observer falling into a black hole, does Hawking radiation take place at the former, the latter, or both?
wywong said:I actually mean the horizon perceived visually by the falling observer, which always seems some distance below the observer.
wywong said:Will he still see Hawking radiation coming from below?
wywong said:What puzzles me most is how the observer perceives the Hawking radiation as he crosses the event horizon. Will he still see Hawking radiation coming from below?
jartsa said:Observer hovering near the event horizon feels a large acceleration, therefore he must observe Unruh-radiation. The black hole is the only possible energy source for that radiation.
jartsa said:Mathematically: Observer hovering at distance D from event horizon absorbs X % of all the radiation emitted by the black hole. When the observer starts free falling, he starts absorbing X% / K of all the radiation emitted by the black hole. As D approaches zero, K approaches infinity.
rootone said:As far as everything I have read goes, that's incorrect, but if I have been misled I'll happily stand corrected.
The generally accepted idea is that the infalling observer does not see an apparent or visual horizon which is always below him, he sees nothing at all below him.
He passes right though the place where the event horizon was deemed to be before he started his journey. then continues deeper into the hole.
In his own frame of reference he shouldn't see any significant increase in radiation when crossing the event horizon.
Edit: Although it does seem that Hawking is himself now not so sure.
The Penrose diagram shows that the horizon is really two distinct entities, the Horizon, and the Antihorizon.The Antihorizon might reasonably called the illusory horizon. ...The diagram shows that when you look at a black hole from the outside, you are looking at its Antihorizon, or illusory horizon. When you fall through the horizon, you fall not through the Antihorizon, but rather through the Horizon, or true horizon. The Horizon becomes visible only after you have fallen through it. The Antihorizon continues to remain ahead of you, and you never fall through it.
Observers crossing a black hole event horizon can calculate the moment they have crossed it, but will not actually see or feel anything special happen at that moment. In terms of visual appearance, observers who fall into the hole perceive the black region constituting the horizon as lying at some apparent distance below them, and never experience crossing this visual horizon.
wywong said:According to http://jila.colorado.edu/~ajsh/insidebh/penrose.html
rootone said:it seems to me that you cannot see anything deeper into the black hole than you are yourself
rootone said:Doesn't this also contradict the notion of 'spaghettification' ?
But by the time you get there, wouldn't the light itself have gone still deeper into the well?PeterDonis said:No, that's not really true. What is true is that you won't see the light from anything deeper than yourself, until you have fallen to where the light is.
rootone said:But by the time you get there, wouldn't the light itself have gone still deeper into the well?
rootone said:by the time you get there, wouldn't the light itself have gone still deeper into the well?
PeterDonis said:Can you show math for this? Or give a reference?
jartsa said:This paper seems to say that the closer an observer goes to the event horizon of a black hole, the more Hawking radiation will look like Unruh-radiation to him.
jartsa said:if an observer in a lab hovering near an event horizon jumps into the air, he observes almost no Hawking radiation during the jump, because Unruh-radiation would completely disappear during a jump, I mean during the free fall part of the jump.
Hawking radiation is a phenomenon proposed by physicist Stephen Hawking that states black holes emit radiation due to quantum effects near the event horizon.
The apparent horizon is a theoretical boundary around a black hole where the escape velocity is equal to the speed of light. It is often used interchangeably with the event horizon, but they are not the same.
The exact location where Hawking radiation takes place is still a topic of debate. Some theories suggest it occurs at the event horizon, while others propose it happens at the apparent horizon.
Hawking radiation has a significant effect on black holes, as it causes them to lose mass and energy over time. This process is known as black hole evaporation.
Hawking radiation has not been directly observed, but there is strong theoretical and mathematical evidence supporting its existence. It is still a subject of ongoing research and experimentation.