Reuter: plancksize black holes are stable

1. Feb 16, 2006

marcus

weird result
http://arxiv.org/abs/hep-th/0602159
Spacetime Structure of an Evaporating Black Hole in Quantum Gravity
A.Bonanno, M.Reuter
23 pages, 7 figures
MZ-TH/06-04
"The impact of the leading quantum gravity effects on the dynamics of the Hawking evaporation process of a black hole is investigated. Its spacetime structure is described by a renormalization group improved Vaidya metric. Its event horizon, apparent horizon, and timelike limit surface are obtained taking the scale dependence of Newton's constant into account. The emergence of a quantum ergosphere is discussed. The final state of the evaporation process is a cold, Planck size remnant."

2. Feb 17, 2006

Chronos

Indeed a weird result, marcus - and one I find questionable. I think it is speculative and weakly unsupported. For example, observational consequences are acknowledged by Bannano/Reuter here:

. . . It would be interesting to investigate the possible astrophysical implications of a population of stable Planck size mini-black holes produced in the Early Universe or by the interaction of cosmic rays with the interstellar medium [59, 60]. We hope to address these issues in a subsequent publication . . .

I think these issues [especially with regard to gravitational lensing] will prove difficult to address. I am further concerned by the generous reliance upon approximations. For example:

. . . if we approximate the stress-energy tensor near the horizon as a radial influx of negative energy which balances the outward Hawking flux at infinity, the event horizon is located inside the AH [5] . . . The apparent horizon (AH) is defined as the outermost marginally trapped surface for the outgoing photons . . .

I think it very risky to approximate anything near the plackian realm. Subsequent works by the author of reference 5 [Hajicek] appear to affirm this conclusion:

Time evolution and observables in constrained systems
http://arxiv.org/abs/gr-qc/9512026
. . . The resulting non-unitarity is different from that known in the field theory (Hawking effect): state norms need not be preserved so that the system can be lost during the evolution of this kind . . .

Another example from Bannano/Reuter:
. . . According to the analysis by York [2, 3] the AH continues to coincide with the TLS for a spherically symmetric emission, but the EH is different from AH=TLS. . .

York too has published subsequent papers that appear to question some of the assumptions relied upon by Bannano/Reuter:

Path Integral Over Black Hole Fluctuations
http://arxiv.org/abs/hep-th/0505125
. . . This establishes the existence of blurred horizons and a thermal atmosphere. It has been argued previously that the existence of a thermal atmosphere is a direct concomitant of the thermal radiation of black holes when the temperature of the hole is greater than that of its larger environment, which we take as zero . . .

Action and Energy of the Gravitational Field
http://arxiv.org/abs/gr-qc/0010024
. . . We present a detailed examination of the variational principle for metric general relativity as applied to a quasilocal'' spacetime region . . . Finally, we present several new examples of quasilocal energy--momentum, including a novel discussion of quasilocal energy--momentum in the large-sphere limit towards spatial infinity.

3. Feb 17, 2006

marcus

I suspect you of intentionally calling Signore Bonanno a bannana
by spelling his name Bannano

I feel compelled to give a severe pedantic look in your direction and say that Bon Anno is simply the Italian equivalent of GOODYEAR, like tires and rubber and the famous blimp.

Yeah, who can say?

However there has been a convergence of results between Reuter QEG ("quantum einstein gravity") with its strange renormalization razzledazzle AND other kinds of quantum gravity.

they are working out the consequences of various theories, you have to let them do this, even if the results sometimes are strange. they dont have to be RIGHT after all. one just wants to have the consequences of each approach worked out so one can compare and maybe eventually find something to check and so on.

I guess the received wisdom from people like Stephen Hawking is that black holes eventually explode. as they evaporate they get smaller and as they get smaller they get hotter and that makes them evaporate faster and finally they go "kaboom"------a temperature and radiation spike.

but that is a semiclassical analysis---I guess vintage 1980s or so----and so one has to wait for a more quantum analysis-----and who knows? maybe maybe evaporation, weird as that sounds, stops

I reserve judgment for now.

4. Feb 17, 2006

Staff Emeritus
Tsk, tsk Marcus. It's renormalization GROUP, not renormalization, and whether it's razzle-dazzle or not the RG is very pukka physics. Reuter's use of it may be what's razzle-dazzle.

5. Feb 17, 2006

marcus

pukka is a nice word----the Victorian British Empire version of "kosher".

Naturally a Victorian gentleman wouldn't want to say "kosher", so how to express the idea with just the right light mockery combined with respect for propriety?

in any case, have to wait and see how Reuter's results wear.

6. Feb 18, 2006

Chronos

Oops, I Freudian-slipped on the name thing, marcus . I doubt there are any observable consequences of non-evaporating black holes. Unless the observable universe is unimaginably ancient [which is very doubtful], or a mechanism capable of producing sub-stellar mass black holes exists; planckian mass black holes do not exist in the observable universe. Hawking's postulate of tiny, primordial black hole creation in the early universe is the only viable candidate and there is no observational evidence supporting that model.