Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Any relation between de sitter relativity and LGC?

  1. Nov 17, 2009 #1

    MTd2

    User Avatar
    Gold Member

    Does anyone know?
     
  2. jcsd
  3. Nov 17, 2009 #2

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    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?
     
    Last edited: Nov 18, 2009
  4. Nov 18, 2009 #3

    MTd2

    User Avatar
    Gold Member

    Pereira is Brazilian! Wow, nice. I don`t know why, but I assumed he was Portuguese. Certainly he should be from a country that speaks portuguese, because of that surname. As you know, I want to connect LQC with a cyclic model, so, I need to make cosmological horizon to evaporate.

    Randono did something related to cyclic models, right?
     
  5. Nov 18, 2009 #4

    MTd2

    User Avatar
    Gold Member

    No, he didn't. Damn it. But I found a thread of your with LQG and Holography.
     
  6. Nov 18, 2009 #5

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    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?
     
  7. Nov 18, 2009 #6

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    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.
     
    Last edited: Nov 18, 2009
  8. Nov 18, 2009 #7

    MTd2

    User Avatar
    Gold Member

    HMM. SO THAT IS PEREIRA THAT FIXED LQG!!! :eek: This guy is really something!!! :O
     
  9. Nov 18, 2009 #8

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    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
     
    Last edited: Nov 18, 2009
  10. Nov 18, 2009 #9

    MTd2

    User Avatar
    Gold Member

  11. Nov 18, 2009 #10

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    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.
     
  12. Nov 18, 2009 #11

    MTd2

    User Avatar
    Gold Member

    LQG has a minimum length. Marcus, why not the maximum length?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook