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The chemistry of geometry (Braid and Preon Update)

  1. Apr 6, 2007 #1


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    "the chemistry of geometry" (Braid and Preon Update)

    I just finished listening to the 3 April seminar in the ILQGS series.

    the audio was MP3 and there were 62 carefully prepared informative slides so the format worked very well.

    A lot of it was a conversation between Lee and Abhay and Laurent Freidel with Sundance Bilson-Thompson speaking up now and then. Lee was the main speaker and Abhay was acting as the moderator or seminar chairman.
    Again the format worked remarkably well---both at the people level and the audiovisual media level.

    To get it you can just google "ILQGS" for international loop quantum gravity seminar and that gets you right thru to the main page, and Smolin's seminar
    "Update on braids and preons" is the most recent so its at the top of the menu. So you just click on PDF to get the slides and once you are ready with the slides you click on MP3 for the audio.

    Yidun Wan who has posted here sometimes spoke up once or twice in the seminar. Some of the work being discussed was his. Parampreet Singh contributed several questions and comments.
    The seminar takes place at several locations linked by wire. A "conference call" where you have the slides to refer to.

    Abhay at one point quoted John Archibald Wheeler saying
    "Elementary particle physics is the chemistry of geometry.
    Last edited: Apr 7, 2007
  2. jcsd
  3. Apr 7, 2007 #2
    Hi Marcus,
    I know you've been following LQG at least since 2000, thanks for the link, I've been wondering if there was ever a followup to the Bilson paper. Which approach do you think is more promising for incorporating the SM in LQG, Bilson-Thompson preon braiding, or Xiao-Gang Wen's condensed matter-lattice approach for example, http://arxiv.org/abs/cond-mat/0407140, page 8, where Xiao-Gang Wen states spin networks already have the properties of string networks, which particles can arise from collective phenomenon, and he derives fermions and bosons in this and other papers? (He concedes his model to date do not account for chiral fermions, but it can account for gravitons). Perhaps we need Bilson-Thompson ribbons for chiral fermions and SU(2) gauge bosons, and Wen's approach for everything else, including gravitons, and the Higgs boson (both of which are unaccounted for in Bilson's preon braiding scheme) in spin foam formalism. (All this without using unobserved SUSY or higher dimensions)


    From new states of matter to a unification of light and electrons


    A lattice bosonic model as a quantum theory of gravity
  4. Apr 7, 2007 #3


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    I normally don't rate things as "promising", ensabah. I wouldn't call any development in string I've heard of in the past few years promising either, just to be clear.

    You have to listen to Smolin's talk to appreciate the attitude. He has quite a few people working on this now and there are two cases TRIVALENT and FOUR-VALENT. My guess is he doesnt think EITHER is a final answer, he just senses intuitively that both must be explored and worked out.
    IOW perhaps neither are "promising" but both are important and interesting and need to be studied (because they will increase the researchers understanding and potential for new physical models) and the four-valent case looks like it is connecting with recent braid-group work of John Baez (with Crans, Wise, Perez etc.)

    When I was listening, and going along thru the slides (he keeps letting you know which slide he is on), I saw a surprising amount of connection with Renate Loll work! Pachner-like "moves" with tetrahedra. Loll's montecarlo computer simulations of spacetime used massive amounts of these different moves where tets combine and transform into other tets---two can breed four, six can breed two, and so on. But Loll's model was purely geometry and now some of Smolin's people are working on something that has a similar flavor but seems to involve MATTER at a fundamental level.

    I would not call it promising---no more would I call John Baez recent 2 or 3 papers promising, but I would call them extremely fruitful new lines of investigation in the sense the young people now working on these things are going to be prepared to see new connections and get new ideas

    I think Smolin has an unusually deep physical intuition about what approaches need to be explored. I think he is systematic about it.
    He lays the groundwork, does one or two papers, gets people started on something, and (often as not) moves on to break ground on another approach.
    Last edited: Apr 7, 2007
  5. Apr 7, 2007 #4
    hi Marcus,

    Okay, I'll use your term "fruitful", since on the issue of "promise" I myself agree that I'll suspend judgment on string theory until LHC goes online, finds SUSY, and there are current research teams searching for dark matter or microscale deviations of Newton's gravity (predicted by some string models) or violations of GR's strong equivalence principle, or cosmic strings, or maybe protons do decay after all.

    You know things on the inside that I have no way of knowing, such as Smolin inviting Xiao-Gang Wen to come visit at the Perimeter institute. I'd have no way of knowing about these events myself.

    On the topic of "fruitfulness" Do you know if Smolin, Baez, or other LQG researcher has been pursuing Xiao-Gang Wen's suggestion, first published 6 Jul 2004 http://arxiv.org/abs/cond-mat/0407140v2 Page 8 "Remarkably, it appears that the theory of loop quantum gravity can be reformulated in terms of a particular kind of string net [condensation]...in addition to gauge interactions and Fermi statistics, string net condensation can give rise to gravity"

    Has any LQG' researcher pursued this line of "fruitful" inquiry, since Jul 2004 -- reformulating string net condensation in terms of spin networks/spin foam? Wen has already shown how certain string net condensation models give rise to some bosons and non-chiral fermions, including gravitons and Higgs boson, (Bilson's preon braiding scheme does not offer a braiding that corresponds to gravitons nor Higgs boson) so all that needs to be done is to connect string net condensation with spin foam.

    Wen's intuition is that there is no "smaller" or more "fundamental" structure to SM particles, as there is with preon and string theory models. Rather SM particles are the result of "collective" properties of spacetime in analogy to solid state physics and lattice. Wen's intuition is that photons and electrons are not made of tiny superstrings vibrating in 10 D's, whose properties depend on the topology Kaluza-Klein compactification of 6 of those dimensions (or preons) and scale and mechanism of SUSY breaking, but emerging as the result of the lattice like structure of spacetime, (by analogy to phonons arrise from the vibration of the lattice structure of solids -- it would be fruitLESS to find a smaller substructure of phonons, it is the lattice and a mechanism that gives rise to phonons) something LQG has some research in through BF spin foam type formalism.

    A common criticism of gravity on a lattice models and discrete gravity models, models with cut-off scales, is that it would appear this would break lorentz invariance, (the whole DSR project is exploring the ramifications of this), which is clearly in contradiction to all known observation, but one fruitful line of inquiry is whether Wen's approach would preserve Lorentz invariance.
    Last edited: Apr 7, 2007
  6. Apr 7, 2007 #5


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    Two recent Perimeter papers (by Konopka and Markopoulou, and also by K&M with Smolin) have cited two X-G Wen papers.

    When one bunch of research papers cites another, that shows there is some crosstalk. These two of Wen were cited by the Perimeter people:

    I would say that the LQG-community has been aware of Wen since at least 2004 and has been making all the use they can of his work. But I don't know how deep that goes or how much actual use it has been. My impression is that X-G has lots of ideas, not all rigorously formulated and some (at least superficially) similar to ideas that QG people already have--so there is at least on the superficial level a kind of convergence. The QG people may or may not have derived inspiration and suggestive speculation from Wen. But besides just finding inspiration, I don't know how much more the QG people can get. You would have to dig that out yourself. Citations are the best clue.

    Here is another Perimeter paper that cites X-G Wen
    this time the citation is to Wen's 2004 book
    Last edited: Apr 7, 2007
  7. Apr 8, 2007 #6
    Thanks, that was what I was looking for (citations to his papers) I'd be interested in seeing how all this plays out (i.e the project of reducing SM to strings, preons, braids, or string-net condensation)
    Last edited: Apr 8, 2007
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