Could a Black Hole Bounce Lead to a New Universe?

[marcus]

In the past two years work by Ashtekar and others in Loop cosmology has modified the LQG dynamics. Two postdocs at Portsmouth, one of whom is an Ashtekar PhD, have recently studied the Schwarzschild black hole using the improved dynamics. They got some new results which seem to point in the direction of a bounce.

http://arxiv.org/abs/0709.2129
Loop Quantum Dynamics of the Schwarzschild Interior
Christian G. Boehmer, Kevin Vandersloot
15 pages, 13 figures
(Submitted on 13 Sep 2007)

"We examine the Schwarzschild interior of a black hole, incorporating quantum gravitational modifications due to loop quantum gravity. We consider an improved loop quantization using techniques that have proven successful in loop quantum cosmology. The central Schwarzschild singularity is resolved and the implications for the fate of an in-falling test particle in the interior region is discussed. The singularity is replaced by a Nariai type Universe. We discuss the resulting conformal diagram, providing a clear geometrical interpretation of the quantum effects.


For some general background here is Andy Hamilton page on Schwarzschild black/white holes
http://casa.colorado.edu/~ajsh/schww.html

One of Hamilton's conformal diagrams resembles one of the conformal diagrams in Böhmer Vandersloot's paper.

Sidenote: if you are a US new QG PhD you pretty much have to go to Canada or Europe to continue career. (string monopolizes postdocs in the US, so no postdoc openings for QG in US). What Kevin did was win a coveted Curie postdoctoral fellowship from the ESF (European Science Foundation) which is normally just for UK and European applicants. He could choose any place in UK or Europe to take the fellowship and he chose Portsmouth.
Portsmouth is strong in QG and Cosmology and also QC phenomenology (testing by observation). Roy Maartens is there and there is a special institute. So Portsmouth is a good place to go and it's not surprising that two postdocs like Böhmer and Vandersloot go there and meet up.

I'm still trying to figure out what Kevin and Christian's new paper concludes about what happens in a black hole. The results, which are suggestive rather than conclusive, overrides the "singularity" which occurs in classical GR. They find two possibilities, both needing further exploration.
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UPDATE TO REPLY TO NEXT POST:

Hi Kurt, thanks for the NewSci link--their article is a general introduction to the "baby universe" topic--and has pictures.
You commented:

This theory of a specific type of universe being connected to a black hole isn't relatively new theory (by relative, I am referring to within the last 10 years).

That is certainly right and a BOOK has even been written about it called The Life of the Cosmos, plus also many scholarly papers.

What is new about Kevin and Christian's work is they do new analysis, use a new QG dynamics, and run a lot of numerical work on the computer. They do not START with the idea that there is a bounce-baby, they start with a leading candidate model---the best currently available to replace GR at singularities IMO---and they SEE if there is a bounce. In fact in one case they do not get it, and in the other case they get the bounce. So they are trying out different versions of a LQG model black hole to see what actually happens (with that model).

The idea of a bounce-baby is not new (I think John Wheeler proposed it several decades ago) but now we are seeing more progress studying the details.

 

[marcus]

Hello Marcus,
I got a bit lost when you mentioned bounce and bounce-baby. What exactly are you referring to?

sorry, I was speaking too informally and even a bit flippantly.
the BH BOUNCE is the topic of the thread.
The authors mention the bounce idea on page 7 of the paper we're looking at:

it means the resolution of the singularity by replacing GR with a quantized version of GR which does not break down there-----where instead of a breakdown you get re-expansion

So you get a new expanding region of spacetime often called a "baby universe"

this is a pretty common idea these days and I think your earlier posts indicate you know about that idea. And you also pointed out the fact that the idea is NOT NEW. In fact it is old and I think goes back to J.A.Wheeler which would put it perhaps as early as 1970.
Smolin was writing papers about the idea as early as 1993 and I seem to recall he cited Wheeler from much earlier.

My unserious expression "bounce-baby" just puts the two terms together to refer to a BH bounce resulting in a baby universe. I don't mean to suggest that the baby universe has to be smaller or less massive just because it is a "baby". Babies could presumably grow. Although inflation in general is still something of a mystery.

I am trying to think what might puzzle you about the term BOUNCE and perhaps you have not encountered it much in your reading yet. There is a large QG literature about it but it mostly is about the cosmological singularity. The QG models studied so far by Ashtekar, Bojowald, and their co-workers tend to replace the bigbang singularity with a bounce. Our region of spacetime, our universe, results from a prior collapsing region---during collapse the density reaches a critical level at which quantum corrections dominate and make the effect of gravity be repellent---collapse bounces and turns into re-expansion.

There are many papers about this by many people, but since this thread is about a Vandersloot (and his co-author Boehmer) I will just cite a recent Vandersloot paper about the cosmological bounce. This will have references to other bounce-related papers and will serve as one example of many:

http://arxiv.org/abs/0707.2548
The behavior of non-linear anisotropies in bouncing Bianchi I models of loop quantum cosmology
Dah-Wei Chiou, Kevin Vandersloot
15 pages, 10 figures
(Submitted on 17 Jul 2007)

"In homogeneous and isotropic loop quantum cosmology, gravity can behave repulsively at Planckian energy densities leading to the replacement of the big bang singularity with a big bounce. Yet in any bouncing scenario it is important to include non-linear effects from anisotropies which typically grow during the collapsing phase. We investigate the dynamics of a Bianchi I anisotropic model within the framework of loop quantum cosmology. Using effective semi-classical equations of motion to study the dynamics, we show that the big bounce is still predicted with only differences in detail arising from the inclusion of anisotropies. We show that the anisotropic shear term grows during the collapsing phase, but remains finite through the bounce. Immediately following the bounce, the anisotropies decay and with the inclusion of matter with equation of state w < +1, the universe isotropizes in the expanding phase."

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UPDATE TO REPLY to next post:

You mentioned that there is a lot of literature on QG which deals with the cosmological singularity, sounds interesting, what's the best book on this subject that you would recommend?

Hi Kurt, as you know there's two kinds of writing on topics like this (1) books written for general audience and (2) research papers and books written for specialists.

(1) the best general audience book I know of from a QG perspective about how the universe could result from a bounce is the one by Smolin called
The Life of the Cosmos
https://www.amazon.com/dp/0195126645/?tag=pfamazon01-20

this is quite non-technical if I remember right. It was published in 1999 and the field has developed a lot since then so that there is a lot more mathematically detailed modeling of the bounce.

however even without a detailed model he manages to make TESTABLE PREDICTIONS in this book based on assuming how the universe evolved. the predictions are subject to test by astronomical observation (e.g. measuring the masses of neutron stars) and have not yet been shown false.

but there OUGHT to be some more recent general audience books about this and there aren't as far as I know, so we are down to

(2) technical articles. For that, look in the references of that Vandersloot paper. There are plenty of articles reporting recent research by e.g. Bojowald and the group headed by Ashtekar.
You might also look in this thread
https://www.physicsforums.com/showthread.php?p=1430677#post1430677
This gives a link to recent articles in the monthly journal Nature Physics that discuss the bounce, and also they are written for other scientists who are nonspecialists---so the style is not too technical.
there's plenty more. but try those for starters