Quantum Gravity: No BH Singularity with Modesto's Program - L. Modesto at MITP

[marcus]

this just out

L. Modesto, basically following Bojowald's program
and a variant of it started by Husain and Winkler
says he has gotten rid of the Black Hole Singularity
by quantizing the spacetime model

http://arxiv.org/gr-qc/0407097

this is what Bojowald did with the Big Bang singularity
(it has always been expected that when there was a successful
quantum theory of gravity----that is, a quantization of Gen Rel---
that it would get rid of GR singularities and extend on past them.

I thought Bojowald was preparing to address the BH singularity
because of a couple of preparatory papers he just posted that
were in that direction.

I am surprised that Modesto has apparently gotten to the goal
first. But it is only an 8-page paper and there is surely a lot more
to be done in ironing out the BH singularity in all possible cases and
seeing what is beyond it!

Modesto is at Rovelli's Marseille University Institute of Theoretical Physics.
I expect that Rovelli may be advising Modesto, who AFAIK is new.
There are a bunch of new authors in LQG and allied research areas.

the Husain and Winkler paper that Modesto uses to some extent as a guide is one that Olias flagged for us here at PF:

"On singularity resolution in quantum gravity"
http://arxiv.org/gr-qc/0312094

 

[marcus]

I'll post the abstract for Modesto's paper

Disappearance of Black Hole Singularity in Quantum Gravity
Leonardo Modesto
8 pages

"We apply techniques recently introduced in quantum cosmology to the Schwarzschild metric inside the horizon and near the black hole singularity at r = 0. In particular, we use the quantization introduced by Husain and Winkler, which is suggested by Loop Quantum Gravity and is based on an alternative to the Schrödinger representation introduced by Halvorson. Using this quantization procedure, we show that the black hole singularity disappears and spacetime can be dynamically extended beyond the classical singularity."

the weird thing is that spacetime can be extended beyond where the classical singularity used to be

it is somehow an echo of the "wormhole" idea of stuff falling into a black and spewing out a white "at the other side"

We have been told by various authorities that this is not possible.
Indeed in Hawking's recent Dublin talk he made the point explicitly that nothing can't get thru the BH singularity. He said "sorry to disappoint you sci-fi fans". Morally I find prohibitions and impossibilities vaguely satisfying and too much permissiveness offends my sense of propriety. No no that is the wrong smiley I mean

at this point do not know what to think about Modesto paper.
Probably others will redo the same thing and after a while the situation will get focussed better

 

[Olias]

this just out

L. Modesto, basically following Bojowald's program
and a variant of it started by Husain and Winkler
says he has gotten rid of the Black Hole Singularity
by quantizing the spacetime model

http://arxiv.org/gr-qc/0407097

this is what Bojowald did with the Big Bang singularity
(it has always been expected that when there was a successful
quantum theory of gravity----that is, a quantization of Gen Rel---
that it would get rid of GR singularities and extend on past them.

I thought Bojowald was preparing to address the BH singularity
because of a couple of preparatory papers he just posted that
were in that direction.

I am surprised that Modesto has apparently gotten to the goal
first. But it is only an 8-page paper and there is surely a lot more
to be done in ironing out the BH singularity in all possible cases and
seeing what is beyond it!

Modesto is at Rovelli's Marseille University Institute of Theoretical Physics.
I expect that Rovelli may be advising Modesto, who AFAIK is new.
There are a bunch of new authors in LQG and allied research areas.

the Husain and Winkler paper that Modesto uses to some extent as a guide is one that Olias flagged for us here at PF:

"On singularity resolution in quantum gravity"
http://arxiv.org/gr-qc/0312094

Interesting that the outcome seems to provide an 'un-tangled' state , exactly what I sated on many previous threads, this quote from their closing remarks:It is interesting to observe that beyond the classical singularity the function b ≡ x is negative. One can speculate, extrapolating the form of the metric that “on the other side” of the singularity there is no horizon: a black hole and a white hole are connected.

This is really..really interesting thanks Marcus for keeping the correlation of so many great papers.

 

[Chronos]

Apologies, Marcus is right. Stay here a few more days and learn. We welcome you to the club.

 

[marcus]

Hi Chronos, Olias,
I looked for past work of Leonardo Modesto and found 6 papers
going back to 2002.
The first 3 papers were in string theory (D-branes) and then
he got out of that and in late 2003 and early 2004 posted a couple
in some kind of perturbative QFT type of quantum gravity.

All that time he was at Torino. Now he has moved to Marseille
where Rovelli is, and has posted his first non-perturbative QG paper---
his first paper where he is taking a background independent approach
akin to Loop. So he is a comparative newcomer to quantum gravity proper (i.e. approaches that actually quantize General Relativity, instead of whatever stringy theories do). he's probably a postdoc working with Rovelli.

I am still completely at a loss as to what it means to remove the BH singularity. I would like to believe that everything that falls into a BH stays there at a kind of "quantum bottom" of the hole---and the hole gradually evaporates and let's the energy back out into OUR universe, as nondescript thermal radiation.
Emotionally and intuitively, I want the hole to have a quantum bottom, whatever that means. But Modesto is talking about a "continuation" of spacetime and he speculates that (although he hasnt made the continuation and does not know) it might lead to an opening of some kind. this opens up a can of worms I would rather not confront. How can a black hole evaporate and produce its nice thermal Hawking radiation if it is simultaneously leaking energy through its now-cured and now-unplugged classsical ex-singularity? Or is stuff still prevented from leaking? this line of thought bewilders me.

I assume that rovelli is keeping track of Modesto's research and if there were something really questionable he would have advised not posting.

 

[marcus]

... How can a black hole evaporate and produce its nice thermal Hawking radiation if it is simultaneously leaking energy through its ... classsical ex-singularity? Or is stuff still prevented from leaking? this line of thought bewilders me.
...

Can this be one of the rare cases where we appear to have our cake and eat it too?

maybe when a star collapses to form a BH the matter goes down the drain and the event horizon can STILL make Hawking radiation until the hole has evaporated.

maybe the matter that collapsed can go down the drain and thru the quantum blender at the classical ex-singularity and even COME OUT somewhere helping feed a baby universe, and still the black hole we see
can continue to exist and make hawking radiation.

Suppose that finally the hole evaporates and in a sense heals, by which time our universe has gotten all the energy back. It seems that we have lost nothing and yet in the meantime something new has been created.

Excuse the speculativeness. If Modesto has indeed gotten rid of the BH singularity then it will take me (and perhaps others as well) some time to assimilate what this means. the first obstacle for me, at least, is this "something-for-nothing" aspect if the BH does not trap everything that falls into it but seems to let it out a kind of backdoor and then proceeds to evaporate.