Can loop quantum gravity see before the Bang?

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The May 20 issue of the journal Physical Review Letters will reveal the results of a National Science Foundation study by Penn State Eberly College of Science grad student, Victo Raveras and Madhavan Varadarajan, a professor at the Raman Research Institute in India that challenge the idea that spacetime is continuous and the idea that information that enters a black hole is lost, never to return. In a nutshell, the theory says that there is room for the information to reappear in the distant future on the other side of space time. Has anyone else heard about this building block model of the fabric of space time or how it may reveal conditions prior to the Big Bang?
 
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  • #2
marcus
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We've certainly been hearing about things LIKE this for some time. I don't know the specific paper you are referring to. I'll look it up.

The grad student's name is Victor Taveras, I believe.
 
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marcus
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In any case, the way we look back into the past, whether we are looking back a billion years, or ten billion years, or before the big bang, is essentially the same way.
To look back we use a model of the universe that we can TEST because it makes predictions about things we can measure in the present.
If we can validate the model, then we extrapolate back to conditions in the past by running the model backwards in time.

The vintage 1915 model, as it happened, broke down at a certain point when you ran it back. People got over-impressed by that and thought because the model broke that time didn't extend back any further :smile:

But since 2001 or so, models have been developed that don't break down and to go back prior to the big bang. And they fit the available data as far as we can tell, so far. More testing is in order.

But that is Quantum Cosmology. It eliminates the singularity and goes back before the big bang. Typically the QC model says there was a contracting phase and a bounce.
A lot of this work was in fact done at Penn State starting in 2001 by Bojowald and Ashtekar and their many collaborators.

I believe the two people you mentioned are or have been at Penn State and worked with Ashtekar's group. But I need to check this.

======================
Yeah, Madhavan Varadarajan and Ashtekar go way back. They collaborated already in 1994.
Here are some of the 25 papers by Varadarajan which the arxiv lists:

22. arXiv:gr-qc/9507044 [ps, pdf, other]
Title: Homogeneous 2+1 Dimensional Gravity in the Ashtekar Formulation
Authors: J. Fernando Barbero G., Madhavan Varadarajan
Comments: 31 pages, latex
Journal-ref: Nucl.Phys. B456 (1995) 355-376
Subjects: General Relativity and Quantum Cosmology (gr-qc)

23. arXiv:gr-qc/9503006 [ps, pdf, other]
Title: On the gauge fixing of 1 Killing field reductions of canonical gravity: the case of asymptotically flat induced 2-geometry
Authors: Madhavan Varadarajan
Comments: 25 pages, LaTex
Journal-ref: Phys.Rev. D52 (1995) 2020-2029
Subjects: General Relativity and Quantum Cosmology (gr-qc)

24. arXiv:gr-qc/9406040 [ps, pdf, other]
Title: A Striking Property of the Gravitational Hamiltonian
Authors: Abhay Ashtekar, Madhavan Varadarajan
Comments: 22, CGPG-94/6-3
Journal-ref: Phys.Rev. D50 (1994) 4944-4956
Subjects: General Relativity and Quantum Cosmology (gr-qc)

25. arXiv:gr-qc/9307006 [ps, pdf, other]
Title: The Phase Space of 2+1 Dimensional Gravity in the Ashtekar Formulation
Authors: J. Fernando Barbero G., Madhavan Varadarajan
Comments: 19 pages, preprint# SU-GP-93/64
Journal-ref: Nucl.Phys. B415 (1994) 515-532
Subjects: General Relativity and Quantum Cosmology (gr-qc)
 
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marcus
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This is probably the paper you were talking about, that will appear in print soon.
It is available already electronically, free, in PDF

http://arxiv.org/abs/0801.1811
Information is Not Lost in the Evaporation of 2-dimensional Black Holes
Authors: Abhay Ashtekar, Victor Taveras, Madhavan Varadarajan
(Submitted on 11 Jan 2008)

Abstract: We analyze Hawking evaporation of the Callen-Giddings-Harvey-Strominger (CGHS) black holes from a quantum geometry perspective and show that information is not lost, primarily because the quantum space-time is sufficiently larger than the classical. Using suitable approximations to extract physics from quantum space-times we establish that: i)future null infinity of the quantum space-time is sufficiently long for the the past vacuum to evolve to a pure state in the future; ii) this state has a finite norm in the future Fock space; and iii) all the information comes out at future infinity; there are no remnants.

Comments: 4 pages, 2 figures

If there is another different paper (that will be published in 20 May PRL) then I have not seen it.
 
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  • #5
If we can validate the model, then we extrapolate back to conditions in the past by running the model backwards in time.

The vintage 1915 model, as it happened, broke down at a certain point when you ran it back. People got over-impressed by that and thought because the model broke that time didn't extend back any further

But since 2001 or so, models have been developed that don't break down and to go back prior to the big bang. And they fit the available data as far as we can tell, so far. More testing is in order.

But that is Quantum Cosmology. It eliminates the singularity and goes back before the big bang. Typically the QC model says there was a contracting phase and a bounce.
Marcus,
I appologize for the misspelling of Victor Taveras's name. I thought I had just stumbled across something new and revolutionary, but it had been posted at space.com a while back. This was not mentioned in the book I just read. Do you know any more recent books I can read?
Thank you.
 

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