Do Black Holes Really Emit Radiation?

[Chronos]

This is an issue worth discussing:

http://www.arxiv.org/gr-qc/0304042
Do black holes radiate?
Authors: Adam D. Helfer

 

[marcus]

This is an issue worth discussing:

http://www.arxiv.org/gr-qc/0304042
Do black holes radiate?
Authors: Adam D. Helfer

I have been looking at it. It is a review article that cites many other articles which have questioned, or critically examined, Hawking radiation. It is hard to assess this review article without checking some of the sources.

Some of the sources can be found on line. He cites
Ted Jacobson 1993 Phys Rev D48 728–741
and this is available as
http://arxiv.org/abs/hep-th/9303103

I looked at the Ted Jacobson paper and it tended to confirm what your author Adam Helfer says. One cannot be absolutely sure that black holes evaporate. there has certainly been no empirical observation of hawking radiation, but on top of that the theoretical derivation is not certain because it extrapolates to very high energies (planck scale) where the physics is not known.

my impression of Jacobson is that he is very reliable and does not say things lightly. his papers are highly cited.

Helfer's bibliography seems good----he has stuff from Ashtekar, Unruh, Bekenstein.

He also cites authors like Carlip who support that Hawking radiation should be just like Hawking says, and that any problems with the theoretical derivation can be fixed. In other words scholarly evenhandedness.

I still think that it is kind of maverick to question hawking radiation. But I have to acknowledge that this Adam Helfer paper is scholarly. As far as I have been able to tell he makes the case that one still has to allow for the possibility that there isn't as much radiation, or that it has a different spectrum (not the simple thermal spectrum) and maybe even that the holes do not finally evaporate.

Personally I picture them like drops of water bouncing around on a hot skillet, and i like the idea that they evaporate, so I am disappointed to learn that this is questionable and i hope that evaporation will be vindicated.

 

[meteor]

The text mentions the notion of almost-black hole, an object that is near to shrink under its Schwarzschild radius, but its saved of the disaster by reamining above that limit. I wonder if almost-black hole is a synonym of neutron star, or perhaps is a new class of object that i hadn't knowledge about

 

[Chronos]

Agreed, marcus. My initial impression was ... skeptical. I was not aware there was any serious dissent over Hawking radiation. I too checked citatations. I was rather surprised to find 13 citations by several different authors to this paper. Maverick theories do not generally gather much attention from serious researchers. So I went ahead and read the thing at face value. It was illuminating... [couldn't resist].

I am also resistant to the notion of evaporation going away. It just does not seem thermodynamically viable. I can see how it may be different, possibly much different than generally thought. Perhaps a decent quantum gravity theory will make it possible to fill in the blanks. It would be nice [then again maybe not so nice] if GLAST happened to find one near and small enough to get a good look. I was thinking though [which is risky since it tends to confuse me], doesn't many-worlds predict a Planck mass black hole could be stable [non-radiating]?

The thought that meteor had is also intriguing. Could it be that a true black hole is merely a mathematical artifact, not a real object? Perhaps if we knew all the physics involved, we would find an upper density limit for matter, a state of nearly, but not quite a black hole. Would that be a dark matter candidate?

 

[turbo]

Here is another paper by Helfer, examining the interface between quantum theory and GR. Like many studying this area, he sees extremely high energies (trans-Planckian problem) that make reconciliation impossible without a theory of quantum gravity.

http://arxiv.org/abs/gr-qc/0407055

If these extreme energies are to be avoided, there must be a UV cutoff, perhaps imposed by the fine structure of our universe.

 

[selfAdjoint]

If these extreme energies are to be avoided, there must be a UV cutoff, perhaps imposed by the fine structure of our universe.

For example LQG.

 

[Nereid]

Call me old-fashioned, but papers by theoreticians - no matter how illustrious or elegant (the paper, not the persons!) - are just that. Well before Planck scales there are many, many OOM of physics that haven't been tested - even between a magnetar or GRB (whatever they are) and Planck, let alone LEP/Tevatron and Planck. Who can say what rich physics awaits the exploration of the next 3 to 5 OOM of energy? Of course, if GLAST (or something else) sees a nice evaporating BH in our neighbourhood tomorrow ...