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skydivephil

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In summary: The current data (from WMAP, etc.) is already enough to constrain inflation somewhat, and Planck will improve this, but probably not enough to really constrain LQC. The basic reason is that one of the key parameters of inflation (the "tensor-to-scalar ratio") is not something that LQC affects very much, so Planck will be able to measure it fairly well with the current best theories. However, if Planck finds some surprising new anomalies in the data, then it's possible that LQC could start to play more of a role in trying to explain them. In other words, Planck is unlikely to directly shed much light on LQC, but it could indirectly do

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skydivephil

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Space news on Phys.org

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marcus

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If you don't want to rely on the words of non-specialists, look up the work of Barrau and others (experts on this question.)

You should learn how to use arxiv.org if you don't already.

Google "arxiv search" and you get

http://arxiv.org/find

Put in the name "Barrau" and you get the papers of Aurelien Barrau

http://arxiv.org/find/all/1/au:+Barrau_A/0/1/0/all/0/1

==quote sample==

3. arXiv:1003.4660 [pdf, ps, other]

**Inflation in loop quantum cosmology: Dynamics and spectrum of gravitational waves**

Jakub Mielczarek, Thomas Cailleteau, Julien Grain, Aurelien Barrau

Comments: 11 pages, 14 figures. Matches version published in Phys. Rev. D

Journal-ref: Phys.Rev.D81:104049,2010

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

4. arXiv:1001.2973 [pdf, ps, other]

Very high energy gamma-rays and the Hubble parameter

A. Gorecki, A. Barrau, J. Grain, E. Memola

Comments: Proc. of the 12th Marcel Grossmann meeting on general relativity. 3 pages, 1 figure

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

5. arXiv:0911.3745 [pdf, ps, other]

**Loop quantum gravity and the CMB: toward pre-Big Bounce cosmology**

Aurelien Barrau

Comments: Proceedings of the 12th Marcel Grossman Meeting on General Relativity. 3 pages, no figure

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

6. arXiv:0910.2892 [pdf, ps, other]

**Fully Loop-Quantum-Cosmology-corrected propagation of gravitational waves during slow-roll inflation**

J. Grain, T. Cailleteau, A. Barrau, A. Gorecki

Comments: 9 pages, no figure, minor corrections

Journal-ref: Phys.Rev.D81:024040,2010

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

7. arXiv:0902.4810 [pdf, ps, other]

Internal structure of a Maxwell-Gauss-Bonnet black hole

S. Alexeyev, A. Barrau, K.A. Rannu

Comments: 5 pages, 5 figures, published version with minor changes

Journal-ref: Phys.Rev.D79:067503,2009

Subjects: General Relativity and Quantum Cosmology (gr-qc)

8. arXiv:0902.3605 [pdf, ps, other]

**Inverse volume corrections from loop quantum gravity and the primordial tensor power spectrum in slow-roll inflation**

J. Grain, A. Barrau, A. Gorecki

Comments: 15 pages, 5 figures, published version with minor modifications, results unchanged

Journal-ref: Phys.Rev.D79:084015,2009

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

9. arXiv:0902.0145 [pdf, ps, other]

**Cosmological footprints of loop quantum gravity**

J. Grain, A. Barrau

Comments: Accepted by Phys. Rev. Lett., 7 pages, 2 figures

Journal-ref: Phys.Rev.Lett.102:081301,2009

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)

==endquote==

EACH ONE OF THOSE PAPERS HAS A LINK TO THE ABSTRACT AND A LINK TO THE PDF

And each one of Barrau's co-authors is a link to the work by that co-author, so you can get a list of the work of Julien Grain, and of Jakub Mielczarek etc.

You should learn how to use arxiv.org if you don't already.

Google "arxiv search" and you get

http://arxiv.org/find

Put in the name "Barrau" and you get the papers of Aurelien Barrau

http://arxiv.org/find/all/1/au:+Barrau_A/0/1/0/all/0/1

==quote sample==

3. arXiv:1003.4660 [pdf, ps, other]

Jakub Mielczarek, Thomas Cailleteau, Julien Grain, Aurelien Barrau

Comments: 11 pages, 14 figures. Matches version published in Phys. Rev. D

Journal-ref: Phys.Rev.D81:104049,2010

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

4. arXiv:1001.2973 [pdf, ps, other]

Very high energy gamma-rays and the Hubble parameter

A. Gorecki, A. Barrau, J. Grain, E. Memola

Comments: Proc. of the 12th Marcel Grossmann meeting on general relativity. 3 pages, 1 figure

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

5. arXiv:0911.3745 [pdf, ps, other]

Aurelien Barrau

Comments: Proceedings of the 12th Marcel Grossman Meeting on General Relativity. 3 pages, no figure

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

6. arXiv:0910.2892 [pdf, ps, other]

J. Grain, T. Cailleteau, A. Barrau, A. Gorecki

Comments: 9 pages, no figure, minor corrections

Journal-ref: Phys.Rev.D81:024040,2010

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

7. arXiv:0902.4810 [pdf, ps, other]

Internal structure of a Maxwell-Gauss-Bonnet black hole

S. Alexeyev, A. Barrau, K.A. Rannu

Comments: 5 pages, 5 figures, published version with minor changes

Journal-ref: Phys.Rev.D79:067503,2009

Subjects: General Relativity and Quantum Cosmology (gr-qc)

8. arXiv:0902.3605 [pdf, ps, other]

J. Grain, A. Barrau, A. Gorecki

Comments: 15 pages, 5 figures, published version with minor modifications, results unchanged

Journal-ref: Phys.Rev.D79:084015,2009

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

9. arXiv:0902.0145 [pdf, ps, other]

J. Grain, A. Barrau

Comments: Accepted by Phys. Rev. Lett., 7 pages, 2 figures

Journal-ref: Phys.Rev.Lett.102:081301,2009

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)

==endquote==

EACH ONE OF THOSE PAPERS HAS A LINK TO THE ABSTRACT AND A LINK TO THE PDF

And each one of Barrau's co-authors is a link to the work by that co-author, so you can get a list of the work of Julien Grain, and of Jakub Mielczarek etc.

Last edited:

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marcus

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For each paper there is the abstract summary, and the introduction, and the conclusions paragraph at the end that generally gives an overview.

These people are interested in what can be learned from

That is their job. They are not Loop specialists, they are phenomenologists, interested in

As you may know, LQC has undergone radical changes since 2006 (a new dynamics) and even more since 2008 (spin foam cosmology, getting rid of simplifying assumptions of homogeneity and isotropy, merging with full LQG theory).

For the most recent advances in LQC, look up the papers of Rovelli with coauthor Vidotto

(also those of Ashtekar, Henderson, Wilson-Ewing).

There is a recent (October 2010) paper by Rovelli, Vidotto, Henderson, and Wilson-Ewing on spinfoam LQG cosmology.

This goes somewhat beyond what we used to think of as LQC a couple of years ago.

It has references to other papers so you can work back if you want:

http://arxiv.org/abs/1010.0502

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skydivephil

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Wow that's a lot to be getting on with, thanks.

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marcus

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skydivephil said:Wow that's a lot to be getting on with, thanks.

But Phil! You don't have to even glance at any of it!

My feeling about this is that you have asked an extremely interesting question, that we should be following over the next 12 months. And that right now IMHO we don't know the answer. Even experts don't yet know what bearing Planck will have on LQG/LQC.

The only thing I know to do is to read (or skim) the brief summaries, and the conclusion sections, of the papers by phenomenologists like Barrau. (and Grain, Mielczarek etc.) And get a sense of it, how definite are they being, how reserved, what do they think?

I don't think there is a sure conclusive answer to the question yet. But it is something to watch.

I do know that two major leaders in LQG are Rovelli and Ashtekar---and before 2006 Ashtekar was doing comparatively little in cosmology, now it is his main focus. And before 2009 Rovelli was not doing LQC at all---now LQG application to cosmology is a major interest of his (several papers per year). People get to be leaders by knowing what to work on---it is a sign that Loop cosmo is ripe when it has drawn their attention away from the main theory. From the general to the critical application.

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Chalnoth

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The short answer is: probably not much. It will add further constraints to the available parameter space, but it isn't likely to be enough to really constrain inflation (which is where LQC comes into play).skydivephil said:

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skydivephil

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marcus said:But Phil! You don't have to even glance at any of it!

My feeling about this is that you have asked an extremely interesting question, that we should be following over the next 12 months. And that right now IMHO we don't know the answer. Even experts don't yet know what bearing Planck will have on LQG/LQC.

The only thing I know to do is to read (or skim) the brief summaries, and the conclusion sections, of the papers by phenomenologists like Barrau. (and Grain, Mielczarek etc.) And get a sense of it, how definite are they being, how reserved, what do they think?

I don't think there is a sure conclusive answer to the question yet. But it is something to watch.

I do know that two major leaders in LQG are Rovelli and Ashtekar---and before 2006 Ashtekar was doing comparatively little in cosmology, now it is his main focus. And before 2009 Rovelli was not doing LQC at all---now LQG application to cosmology is a major interest of his (several papers per year). People get to be leaders by knowing what to work on---it is a sign that Loop cosmo is ripe when it has drawn their attention away from the main

theory. From the general to the critical application.

As somone who is not a professional comsologist,Im a bit worried that any results from Planck might be ad hocly re interpreted as consistent with one framework or another. I doubt Id be any the wiser. What I think would be really exicting would be if there were any specific predictions of what we will find in the data Planck will provide. Or maybe even LISA if it ever gets funded (anyone know what the current situation is with that?)

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wolram

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Lisa launch date 2018, if all goes well.

Launch Scheduled for 2018, the mission is currently planned to launch from NASA’s Kennedy Space Centre in the USA on board an Atlas 531 rocket.

Loop Quantum Cosmology (LQC) is a theoretical framework that combines principles of quantum mechanics and general relativity to study the evolution of the universe on a small scale. It proposes a discrete structure of space-time, where space is made up of tiny loops and time is quantized into discrete units.

The Planck Satellite is a space observatory launched by the European Space Agency in 2009 with the primary goal of studying the Cosmic Microwave Background (CMB). The CMB is the oldest light in the universe and contains valuable information about the early universe. The Planck Satellite has provided precise measurements of the CMB, which can be used to test and refine theories such as LQC.

LQC proposes that the Big Bang was not a singularity, as predicted by general relativity, but rather a "bounce" from a previous contracting phase. This bounce occurs when the universe reaches a minimum size, and the repulsive forces of quantum gravity cause it to expand again. This avoids the singularity and provides a more complete understanding of the early universe.

One of the main differences between LQC and other theories, such as String Theory, is that LQC is based on a discrete structure of space and time, while other theories assume a continuous space-time. LQC also provides a more complete and self-consistent framework for studying the universe on a quantum level, while other theories may have limitations or require additional assumptions.

One of the main challenges is that the Planck Satellite was not specifically designed to test LQC, so the data must be carefully analyzed and interpreted in the context of the theory. Additionally, LQC is still a developing and evolving theory, so there may be discrepancies or uncertainties in predicting certain phenomena. Further research and collaboration between cosmologists and quantum physicists is needed to fully explore the potential of LQC with the data from the Planck Satellite.

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