Hawking Radiation

In summary: Hawking radiation is due to virtual particle pairs that are created near the horizon. The virtual particles escape the black hole, but the black hole gains mass because it lent energy to the particle pair for a short amount of time.Hawking radiation is due to virtual particle pairs that are created near the horizon. The virtual particles escape the black hole, but the black hole gains mass because it lent energy to the particle pair for a short amount of time.
  • #1
Schreiberdk
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0
Hi PF

I was wondering, if Hawking radiation could have a different source than black-body radiation. I was wondering, if quantum tunneling could be a possible way, for energy to slip out of the grasp of the black holes gravitational attraction and slip through the event horizon. Would this be reasonable and is evidence of this seen in any QG theory or in strings?

\Schreiber
 
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  • #3
We don't really know but there are speculations about it. One thing I do want to say is that when we are talking about any such cases, there are many different proposals as to what happens to "stuff" as it falls into a black-hole, for instance the holographic principal states that it gets encoded into the event horizon and then you can deal with what happens there on. So just to make things more specific, let's say we start with a black hole that encodes information as stated, now the question becomes:

Can information (in the form of radiation) tunnel through the horizon?

It must be noted that this process being discussed is separate from Hawking radiation.
 
  • #4
Schreiberdk said:
I was wondering, if Hawking radiation could have a different source than black-body radiation. I was wondering, if quantum tunneling could be a possible way, for energy to slip out of the grasp of the black holes gravitational attraction and slip through the event horizon. Would this be reasonable and is evidence of this seen in any QG theory or in strings?
If something radiates as a black body, that's just a statement about the spectrum of radiation it gives off, not about the physical mechanism. It's very standard to think of Hawking radiation as a quantum tunneling event, and you can derive it in http://arxiv.org/abs/hep-th/9907001" [Broken] which doesn't go into the details of quantum gravity.

What's difficult is to describe black hole evaporation as a unitary process. If the black hole does radiate as a black body, then different initial states are ending in the same way, which is impossible for standard quantum mechanics. Hawking himself was the first to notice this. Twenty years later he changed his mind because of AdS/CFT - the CFT on the boundary is unitary, and it's equivalent to gravity in AdS, and the latter contains black holes, so their dynamics "must" be unitary - but exact models are still lacking. Everything written about black hole evaporation, even in string theory, seems to involve approximations and guesses.

Black hole thermodynamics - all the stuff about how a black hole has an entropy proportional to its area, and a temperature expressed in the Hawking radiation - was discovered somewhat indirectly, by studying quantum field theory in black hole geometries. The question immediately arose: what are the microscopic degrees of freedom responsible for this entropy? After many years, http://arxiv.org/abs/hep-th/9607235" [Broken].

Some other recent papers on this topic: http://arxiv.org/abs/1108.2015" [Broken].
 
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  • #5
The way I originally learned about Hawking radiation was, that it was due to virtual particle pairs being made near the horizon. Then one gets sucked in, while the other escapes... The black hole looses mass, because it lends its energy (thereby mass) for a short amount of time to the particle pair, and when it annihilates, the black hole gets its mass back. But when one particle gets sucked in and the other escapes, the black hole losses energy and thereby mass.

Therefore I thought tunneling might be a different approach than the usual? Or is my way of looking at Hawking radiation the same as tunneling? :)
 
  • #6
Therefore I thought tunneling might be a different approach than the usual? Or is my way of looking at Hawking radiation the same as tunneling? :)

Hawking suggested the virtual particle pair description...but it was apparently not directly associated with his mathematical description. Either "virtual particles" or "tunneling" are possible descriptions...Both these and the overall effect can be associated with horizons: If you take a look at ADS/CFT as Porter posted and/or Unruh Effect, say in Wikipedia, you'll get a flavor for related descriptions.
 
  • #7
Schreiberdk said:
The black hole looses mass, because it lends its energy (thereby mass) for a short amount of time to the particle pair, and when it annihilates, the black hole gets its mass back. But when one particle gets sucked in and the other escapes, the black hole losses energy and thereby mass.
Vacuum fluctuations happen in flat space, without any black holes around. If you want to think of them as drawing on energy from somewhere, you should think of the zero-point energy of the quantum fields involved, as the source of the fluctuation. What's different, when you have a black hole, is that part of the field fluctuation can cross the event horizon and fall into the black hole, rather than recombining with the other part of the fluctuation.

But http://www.physics.ucdavis.edu/Text/Carlip.html#Hawkrad". Here we have a black hole which looks like a point in the large dimensions of space, but it actually consists of a stack of branes wrapped around the extra compact dimensions at that point (e.g. these might be a Calabi-Yau space), and then there is a gas of open strings stretched between the branes that are perpetually racing round and round one of the compact dimensions. These are the degrees of freedom which give the black hole its entropy! And then sometimes these open strings, when they are moving in opposite directions, collide and form a closed string which can escape as Hawking radiation - that's what page 63 depicts.

But because we don't know the micro-geometry of our universe, we can't say what sort of bound state of branes might define a black hole here, and so we don't have an exact microphysical model of Hawking radiation for the real world.
 
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What is Hawking Radiation?

Hawking Radiation is a theoretical concept proposed by physicist Stephen Hawking in the 1970s. It suggests that black holes emit thermal radiation due to quantum effects near the event horizon, eventually causing them to evaporate.

How does Hawking Radiation form?

Hawking Radiation forms as a result of virtual particle-antiparticle pairs being created near the event horizon of a black hole. One particle falls into the black hole while the other escapes, carrying away energy and causing the black hole to lose mass over time.

Can Hawking Radiation be observed?

No, Hawking Radiation cannot be observed directly because it is extremely faint and only occurs near the event horizon of black holes. However, its effects on black hole evaporation can be observed and have been confirmed through various experiments and observations.

Does Hawking Radiation violate the laws of conservation of energy?

No, Hawking Radiation does not violate the laws of conservation of energy. While it may seem like energy is being created from nothing, the energy of the escaping particle is balanced by the negative energy of the particle that falls into the black hole.

What implications does Hawking Radiation have for black hole physics?

Hawking Radiation has significant implications for black hole physics and our understanding of the universe. It suggests that black holes have a finite lifespan and eventually evaporate, contradicting the previous notion that black holes are eternal. It also provides a link between quantum mechanics and general relativity, two fundamental theories in physics that have been difficult to reconcile.

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