|Oct15-04, 01:47 AM||#1|
Blackhole Ex-singularity (Ashtekar + Bojowald)
Martin Bojowald got rid of the Bigbang singularity in 2001 while
at Penn State----on postdoc working for Ashtekar. Now he is at the Albert Einstein Institute in Germany.
This year he has been working on getting rid of the Blackhole singularity and has posted one or two preliminary papers.
Now Ashtekar has announced two BH papers, co-authored with Bojowald, in preprint form but not posted at arxiv. Ashtekar has given some sketchy indications of the results. Maybe we should write Ashtekar or Bojowald and ask for the preprints. Or maybe the thing to do is just wait patiently. At least one of the papers is about what is down inside the blackhole instead of a classical singularity. A quantum "ex-singularity".
look at the two references at top of page 37 of
 Ashtekar A and Bojowald M 2004 Non-Singular Quantum Geometry of the Schwarzschild Black Hole Interior Preprint
 Ashtekar A and Bojowald M 2004 Black hole evaporation: A paradigm Preprint
Ashtekar addresses the problem of BH information loss, which was arrived at based on semiclassical ideas. and he says:
---quote from bottom of page 30---
However, loop quantum gravity considerations suggest that this argument is incorrect in two respects. First, the semi-classical picture breaks down not just at the end point of evaporation but in fact all along what is depicted as the final singularity. Recently, using ideas from quantum cosmology, the interior of the Schwarzschild horizon was analyzed in the context of loop quantum gravity. Again, it was found that the singularity is resolved due to quantum geometry effects . Thus, the space-time does not have a singularity as its final boundary...
|Oct15-04, 03:32 AM||#2|
Ashtekar recently gave a talk where he discusses this a bit:
Hopefully that's a static link.
|Oct15-04, 09:54 AM||#3|
Please correct me if I am mistaken on the following basics: IH stands for isolated horizon. DH stands for dark hole. there is no such thing as a black hole. there is no such thing as an event horizon. these concepts are convenient classical or semiclassical approximations. the event horizon exists only as a semiclassical approximation where one declines to wait for the hole to evaporate and "approximates" by saying it lasts for an infinite time.
there is no information loss paradox, and Ashtekar Bojowald resolution looks strangely like the Hawking resolution, except it is more mathematically worked-out with a lot of Penrose diagrams and spin-networks and formulas. So there is not so much mystery or handwaving, but it comes to something rather like Hawking conclusion---or so it looks to me.
this is a real nice talk, thanks Stingray!
|Oct15-04, 10:44 AM||#4|
Blackhole Ex-singularity (Ashtekar + Bojowald)
DH stands for Dynamical Horizon.
There is a nice recent review
|Oct23-04, 11:44 AM||#5|
Stingray told us about this talk by Ashtekar
The talk was given 20 September at Penn State and is called
Black Hole Evaporation and Information Loss: Recent Advances
As you listen to the audio you have to step from one slide to the next
in synch with the talk. In this talk you get a foretaste of two papers by Ashtekar and Bojowald which are not on arxiv yet.
Ashtekar A and Bojowald M 2004 Non-Singular Quantum Geometry of the Schwarzschild Black Hole Interior Preprint
Ashtekar A and Bojowald M 2004 Black hole evaporation: A paradigm Preprint
Two recent Ashtekar papers from arxiv are relevant:
nonunitary provided a link to an article giving the definitions of dynamical horizon and isolated horizon. Ashtekar uses these concepts in his talk
Abhay Ashtekar, Badri Krishnan
Isolated and dynamical horizons and their applications
And then there is the one that started this thead:
Gravity and the Quantum
|Nov11-04, 02:17 PM||#6|
Thanks due to both nonunitary and Stingray for making this thread better!
Ashtekar and Bojowald are not the only people working on what you get when you quantize and remove the Black Hold singularity.
There is also Leonardo Modesto, postdoc at Rovelli's institute in Marseille.
He has written a couple of papers removing the BH singularity. There is a tension between the Modesto picture (where spacetime continues at the pit of a black hole, where the classicial singularity used to be, and may inflate from there to form a new universe)
and the pictures that Ashtekar drew in his online seminar talk (where a "deep planck regime" forms at the pit, and eventually participates in evaporation so that seemingly all the information is ultimately recovered and a paradox is solved)
So there is a kind of bifurcated approach and the picture could go either way. I feel that I should keep paying attention to Modesto approach (he only recently moved over from string to LQG so he has almost no QG trackrecord, but you never know.)
here is the conclusions paragraph from Modesto most recent paper:
In this work we have applied the quantization procedure of  to the Kantowski-Sachs space time  with space topology R×S 2. This space time contains the part of Schwarzschild solution on the other side of the horizon as a particular classical solution. The quantization procedure is alternative to the Schr?odinger quantization and it is suggested by loop quantum cosmology. The main results are : 1. the inverse volume operator has a finite spectrum near the point b = 0 that in the case of Schwarzschild black hole solution produce a singularity, 2. the solution of the Hamiltonian constraint gives a discrete difference equation for the coefficients of the physical states and we can have many scenarios to connect our universe to another.
I have bolded for emphasis what is strange here. Ashtekar and Bojowald do not talk about connecting to a new universe! For them, it all evaporates in the end. Could both happen?
Modesto picture is in line with Smolin Multiverse which is called "Cosmic Natural Selection" or CNS.
Scientific alternatives to the anthropic principle
According to CNS our universe may have formed down inside somebody else's toilet, or black hole. The thing is, this idea is kind of inescapable because when you remove the collapse-singularity of a BH it looks rather like the expand-singularity of a BB. One looks like it might be the prior condition of the other. Heady stuff, if you are familiar with nautical terminology.
Basically LQG provides the plumbing connectors to connect all our black holes to baby universes and to give them all the generic capability to do an inflation stage (creating a lot of matter by Guth's free lunch) and then doing a graceful exit from inflation. The BB stuff has been gone over repeatedly by a number of researchers and seems OK. So LQG gives the a readymade set of connectors---it would seem, at least in Modesto picture---for CNS.
We had a thread about this
"a scientific multiverse theory"
Modesto's second, and latest, paper on this is
The Kantowski-Sachs Space-Time in Loop Quantum Gravity
For me, the interesting feature right now is that Modesto is in marked contrast with the Ashtekar and Bojowald picture, or seems so anyway.
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