- #1

MTd2

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Does anyone know?

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- Thread starter MTd2
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- #1

MTd2

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Does anyone know?

- #2

marcus

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The first things to notice, I think, are the human links between the two. Like for example Andy Randono.

Andy Randono has done a lot of LQG-related research, and postdoc'd at Penn State and Perimeter. Maybe you had this paper in mind. It is not strictly speaking LQG, but what he is looking for would feed into LQG, perhaps produce a**new deSitter version** of LQG.

There are also some writings by John Baez and by his former PhD student Derek Wise. Randono may have references to Derek Wise' work. In this general area there is a paper by Macdowell-Mansouri, and one by Laurent Freidel and Artem Starodubtsev, but nothing I can dredge up is precisely what you asked for.

A propos of "deSitter relativity" one also thinks of two Brazil guys, Aldrovandi and Pereira. They have some papers on that, but I don't know if their version of deSitter relativity would connect with LQG.

When you raised the question, what deSitter relativity did you have in mind? Presumably something**like** General Relativity, but with the local Lorentz symmetry replaced by local deSitter group symmetry.

That's intrinsically very interesting IMHO. But did you have any specific papers in mind?

http://arxiv.org/abs/0909.5435

de Sitter Spaces

Andrew Randono

(Submitted on 29 Sep 2009)

"We exploit an interpretation of gravity as the symmetry broken phase of a de Sitter gauge theory to construct new solutions to the first order field equations. The new solutions are constructed by performing large Spin(4,1) gauge transformations on the ordinary de Sitter solution and extracting first the tetrad, then the induced metric. The class of metrics so obtained is an infinite class labelled by an integer, q. Each solution satisfies the local field equations defining constant positive curvature, and is therefore locally isometric to de Sitter space wherever the metric is non-degenerate. The degeneracy structure of the tetrad and metric reflects the topological differences among the solutions with different q. By topological arguments we show that the solutions are physically distinct with respect to the symmetries of Einstein-Cartan theory. Ultimately, the existence of solutions of this type may be a distinguishing characteristic of gravity as a metric theory versus gravity as a gauge theory."

Andy Randono has done a lot of LQG-related research, and postdoc'd at Penn State and Perimeter. Maybe you had this paper in mind. It is not strictly speaking LQG, but what he is looking for would feed into LQG, perhaps produce a

There are also some writings by John Baez and by his former PhD student Derek Wise. Randono may have references to Derek Wise' work. In this general area there is a paper by Macdowell-Mansouri, and one by Laurent Freidel and Artem Starodubtsev, but nothing I can dredge up is precisely what you asked for.

A propos of "deSitter relativity" one also thinks of two Brazil guys, Aldrovandi and Pereira. They have some papers on that, but I don't know if their version of deSitter relativity would connect with LQG.

When you raised the question, what deSitter relativity did you have in mind? Presumably something

That's intrinsically very interesting IMHO. But did you have any specific papers in mind?

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- #3

MTd2

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Randono did something related to cyclic models, right?

- #4

MTd2

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No, he didn't. Damn it. But I found a thread of your with LQG and Holography.

- #5

marcus

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Pereira is Brazilian! Wow, nice. I don`t know why, but I assumed he was Portuguese...

There is a Pereira who writes papers with Aldrovandi. Both are located in Brazil. I don't know where he was born or what his citizenship. I only know he lives and works in Brazil, at the same institute as Aldrovandi. Both of them are senior people with lots of publications.

There is also the postdoc named Pereira who is in Marseille and works with Rovelli. This is someone else. I don't know anything about him. And he could certainly be Portuguese.

If you are interested in deSitter relativity then we should take a look at the papers by the team of Aldrovandi-Pereira. They were promoting the deSitter GR idea. They are either crazy or extremely creative, or both. But how can two dignified established senior Brazil physicists both be crazy at the same time at the same institute?

To me it is not even clear that you can do deSitter GR in the first place. I mean do General Relativity with the local symmetry being deS instead of Lorentz. I simply don't know enough to have an opinion about whether it is possible.

Derek Wise wrote a paper trying to do that, around 2 years ago. I think of it as something that people try unsuccessfully to do from time to time. I respect them without being very hopeful.

I will get some Aldrovandi Pereira links. Or do you already have them?

- #6

marcus

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You probably know the work of both these people, but I want to avoid all possible confusion with the Marseille Pereira who is co-author of the EPRL spin foam (Engle-Pereira-Rovelli-Livine). The EPRL spin foam has turned out to be really important.

Let's take a careful look at this Sao Paulo team. They are at the ITP at Sao Paolo.

Instituto de Física Téorica, São Paulo State University

Here is a sample paper. It will have references to other papers by them, going back several years

http://arxiv.org/abs/0812.3438

**De Sitter Special Relativity: Effects on Cosmology**

Ruben Aldrovandi, Jose Geraldo Pereira

12 pages

(Submitted on 18 Dec 2008)

"The main consequences of de Sitter Special Relativity to the Standard Cosmological Model of Physical Cosmology are examined. The cosmological constant Lambda appears, in this theory, as a manifestation of the proper conformal current, which must be added to the usual energy-momentum density. As that conformal current itself vanishes in absence of sources, Lambda is ultimately dependent on the matter content, and can in principle be calculated. A present-day value very close to that given by the crossed supernova/BBR data is obtained through simple and reasonable approximations. Also a primeval inflation of polynomial type is found, and the usual notion of co-moving observer is slightly modified."

In 2007, Ruben Aldrovandi and Jose Geraldo Pereira took the dangerous step of deriving a prediction of energy-dependent speed of light, from their theory. They said their deSitter relativity would make very energetic photons arrive a little later than the more normal photons. I pointed this out in a thread. I admire their courage but I think it will tend to discredit their deSitter relativity theory. I made a thread about this:

https://www.physicsforums.com/showthread.php?t=198890

It has links to other papers by them about the deSitter idea.

Let's take a careful look at this Sao Paulo team. They are at the ITP at Sao Paolo.

Instituto de Física Téorica, São Paulo State University

Here is a sample paper. It will have references to other papers by them, going back several years

http://arxiv.org/abs/0812.3438

Ruben Aldrovandi, Jose Geraldo Pereira

12 pages

(Submitted on 18 Dec 2008)

"The main consequences of de Sitter Special Relativity to the Standard Cosmological Model of Physical Cosmology are examined. The cosmological constant Lambda appears, in this theory, as a manifestation of the proper conformal current, which must be added to the usual energy-momentum density. As that conformal current itself vanishes in absence of sources, Lambda is ultimately dependent on the matter content, and can in principle be calculated. A present-day value very close to that given by the crossed supernova/BBR data is obtained through simple and reasonable approximations. Also a primeval inflation of polynomial type is found, and the usual notion of co-moving observer is slightly modified."

In 2007, Ruben Aldrovandi and Jose Geraldo Pereira took the dangerous step of deriving a prediction of energy-dependent speed of light, from their theory. They said their deSitter relativity would make very energetic photons arrive a little later than the more normal photons. I pointed this out in a thread. I admire their courage but I think it will tend to discredit their deSitter relativity theory. I made a thread about this:

https://www.physicsforums.com/showthread.php?t=198890

It has links to other papers by them about the deSitter idea.

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- #7

MTd2

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HMM. SO THAT IS PEREIRA THAT FIXED LQG!!! This guy is really something!!! :O

- #8

marcus

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It is possible that I am not communicating clearly enough. The Marseille Pereira who helped Rovelli to fix the spinfoam version of LQG is just a PhD student. He does not even have his PhD yet. His name is Roberto Pereira. I don't know where he comes from or anything.

Let's talk about**Jose Geraldo** P. who is at Sao Paolo. Do you know his papers? Does the name ring a bell for you? Did you know there was this Brazilian team of Aldrovandi-Pereira that was promoting deSitter relativity?

Brazil is a huge country. I don't know where you live. Maybe it is 1000 kilometers from Sao Paolo. If by some rare accident you lived in Sao Paolo, I would ask if you would please visit the ITP there and meet Jose Geraldo. It would be interesting to learn your impressions.

Most of the time I think the deSitter relativity idea is hopeless. But now that Andy Randono has written this paper about it, I am inclined to take a second look.

Hmmm, here is a picture of Jose Geraldo Pereira: http://www.ift.unesp.br/users/jpereira/biography.html#

He looks quite sensible. I wonder if he knows Andy Randono's paper and what he thinks of it.

Also I wonder if he knows Derek Wise' papers. For some reason he did not make a citation to Derek Wise 2006, as if maybe he didn't know of the paper. The disconnectedness is curious.

Look at pages 22-24 of Derek Wise 2009. He talks about gravity with a deSitter symmetry group. He talks about Macdowell-Mansouri gravity. He cites an earlier treatment by Andy Randono, and he cites his own 2006 paper. This is good scholarship and good writing.

http://arxiv.org/abs/0904.1738

**Symmetric Space Cartan Connections and Gravity in Three and Four Dimensions**

Let's talk about

Brazil is a huge country. I don't know where you live. Maybe it is 1000 kilometers from Sao Paolo. If by some rare accident you lived in Sao Paolo, I would ask if you would please visit the ITP there and meet Jose Geraldo. It would be interesting to learn your impressions.

Most of the time I think the deSitter relativity idea is hopeless. But now that Andy Randono has written this paper about it, I am inclined to take a second look.

Hmmm, here is a picture of Jose Geraldo Pereira: http://www.ift.unesp.br/users/jpereira/biography.html#

He looks quite sensible. I wonder if he knows Andy Randono's paper and what he thinks of it.

Also I wonder if he knows Derek Wise' papers. For some reason he did not make a citation to Derek Wise 2006, as if maybe he didn't know of the paper. The disconnectedness is curious.

Look at pages 22-24 of Derek Wise 2009. He talks about gravity with a deSitter symmetry group. He talks about Macdowell-Mansouri gravity. He cites an earlier treatment by Andy Randono, and he cites his own 2006 paper. This is good scholarship and good writing.

http://arxiv.org/abs/0904.1738

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- #9

MTd2

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http://maps.google.com/?ie=UTF8&ll=-22.492257,-44.939575&spn=2.821634,3.532104&t=h&z=8

- #10

marcus

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http://maps.google.com/?ie=UTF8&ll=-22.492257,-44.939575&spn=2.821634,3.532104&t=h&z=8

I think you are fortunate to live in a beautiful and lively city. Don't worry about the Sao Paolo people. It is much much too far to visit. I would be reluctant to go 480 km to visit my Aunt, although I might go that far to visit my Grandfather. It depends on the degree of relationship. I personally would not go 480 km to visit Jose Geraldo Pereira.

But I find his vision and courage admirable.

- #11

MTd2

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LQG has a minimum length. Marcus, why not the maximum length?

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