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The universe as a string-net liquid

  1. Mar 21, 2007 #1
    The universe as a "string-net liquid"

    Has anyone heard about http://www.newscientist.com/article.ns?id=mg19325954.200&feedId=online-news_rss20 [Broken]?

    A new theory that "give rise to conventional particles and fractionally charged quasi-particles -- [and] to other elementary particles, such as quarks, which make up protons and neutrons, and the particles responsible for some of the fundamental forces, such as gluons and the W and Z bosons."

    What do you people think? Does this theory have any potential?
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  2. jcsd
  3. Mar 21, 2007 #2

    Sundance Bilson-Thompson have suggested elementary particles are "braids" -- though his model doesn't account for higher generation, and it's not clear what the "braids" themselves are.

    I'd like to see papers on this, along with perhaps explanations on how it improves on the SM
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  4. Mar 22, 2007 #3

    john baez

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    No. In this theory, instead of the usual potential giving rise to the electromagnetic field, electromagnetism arises as a condensation of string networks.:tongue2:

    Seriously... it's an interesting idea. For the real thing, read:

    • Michael Levin and Xiao-Gang Wen, http://arxiv.org/abs/hep-th/0507118" [Broken].

    Xiao-Gang Wen got an http://www.fqxi.org/aw-wen.html". He's a condensed matter physicist at MIT.
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  5. Mar 22, 2007 #4


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    I'm intrigued!
    His java http://dao.mit.edu/~wen/java/dance/dance.html uses the 2d packing .... hummmm.... got to keep reading.
    I've been playing with it. It's a great way of seeing the dynamics of QMLS.
    (try it with 12 units)
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  6. Mar 22, 2007 #5
    I can't grasp that idea yet... have to read more about it. :)

    Thanks a bunch for the links, really appreciate it. I believe http://dao.mit.edu/~wen/pub/qorev.pdf is good to start with.

    How does the string-net differ from other spinfoam models, e.g. Loop Quantum Gravity?
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  7. Apr 4, 2007 #6

    The article references loop quantum gravity spin networks (page 8) as a possible basis for the lattice which particles emerge. It might be possible to relate spin foam/spin network in LQG to standard model particles with spin networks playing the role of a crystal lattice in condense matter physics. I'm a little surprised Lee Smolin hasn't commented on this.

    If you can connect spin foam formalism with Wen's string-net derivation, you can get gravity and the standard model.


    "So in their theory elementary particles are not the fundamental building blocks of matter. Instead, they emerge as defects or "whirlpools" in the deeper organized structure of space-time."

    "Now this problem is solved. If the spins that form our space organize into a string-net liquid, then the collective motions of strings give rise to light waves and the ends of strings give rise to electrons. The next challenge is to find an organization of spins that can give rise to gravitational wave."

    Perhaps a quantum gravity with chirality can explain chiral fermions (i.e neutrinos)
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  8. Apr 4, 2007 #7


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    I expect he has. The "Quantum ether" article you are talking about is July 2005. Smolin organized a workshop bringing X-G Wen to Perimeter in mid-November that year. That would have involved considerable comment :biggrin: They obviously know each other.

    Wen's talk at the November 2005 Perimeter workshop is available video at PIRSA. I watched some. Smolin also got Renate Loll from Utrecht to come and participate in the same workshop (On the Emergence of Spacetime.) She has a different way of making spacetime emerge from microscopic QG dynamics. Her talk is also available video at PIRSA.

    I first heard of X-G Wen's ideas in a September 2004 paper from Dreyer who was in Smolin's group at Perimeter at the time---since then gone to London.
    So I checked out his MIT website---it was pretty interesting back then in 2004, haven't visited lately so can't say.

    Anyway the signs are that Smolin has had a lot of response to Wen including to that July 2005 paper and may have stimulated students and people in his group to look at Wen's work. It may, as you mention, have connections to spinfoam and would naturally have been of interest to them.

    A lot has happened in QG in the intervening two years, though, and I don't know any current Wen/QG or Wen/Smolin news, except of course the FQXi grant that JB mentioned (Smolin is on the FQXi scientific advisory board IIRC)
    Last edited: Apr 4, 2007
  9. Apr 5, 2007 #8


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    There seems to be a reluctance to investigate Xiao-Gang Wen approach.
    Words are being used which scare people away. (ether ... and string ...) :smile:
    I spent time reading his papers. In my simple way, he is doing the dynamics of Quantum Minimum Length Structure with the infusion of his level of education (a "math kid").
    Since he has a number of students I would expect to see more papers on this approach.
    I would expect that the devil will get a good beating.
  10. Apr 5, 2007 #9
    It should be possible to have a rigorous derivation of string-net theory (which produces some bosons and electrons) with the spin foam formalism, hence giving lqg the standard model.
  11. Apr 6, 2007 #10


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    He has gone from an observable, phenons, to strings to explain the symmetries of our universe.
    Different string-net condensations are not characterized by symmetries, but by projective symmetry group (PSG).

    To the newbies; it’s all about Symmetries.
    Never mind the names used to represent what is believed to be happening. ( phenons, strings, mini-superspace, plaquettes, SPOTS )

    At the end of the day …. It will be an elephant.

  12. Apr 12, 2007 #11

    General Relativity and Quantum Cosmology
    Title: A lattice bosonic model as a quantum theory of gravity


    A local quantum bosonic model on a lattice is constructed whose low energy excitations are gravitons described by linearized Einstein action. Thus the bosonic model is a quantum theory of gravity, at least at the linear level. We find that the compactification and the discretization of metric tenor are crucial in obtaining a quantum theory of gravity.
  13. Apr 12, 2007 #12


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    Wen's string-nets use trivalent vertices and string crossings, and so fit quite naturally into the categorified knot theory framework. Single strands are appropriate for the U(1) case.
  14. Apr 12, 2007 #13
    LQG's spin network and spin foam also used categorified knot theory, how close is spin foam formalism to Wen's string net's formalism? Is a derivation or refumulation possible? Certainly desirable.
  15. Apr 12, 2007 #14


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    When I googled spin foam and knotted trivalent just now, I got only 3 hits, one of which was a general discussion by a large group of mathematicians, and one of which was my blog. Perhaps you could provide me with further references.
  16. Apr 12, 2007 #15
    John Baez
    http://arxiv.org/abs/gr-qc/9504036 p 22

    Tomas Liko, Louis H. Kauffman
    Knot theory and a physical state of quantum gravity

    We discuss the theory of knots, and describe how knot invariants arise naturally in gravitational physics. The focus of this review is to delineate the relationship between knot theory and the loop representation of non-perturbative canonical quantum general relativity (loop quantum gravity). This leads naturally to a discussion of the Kodama wavefunction, a state which is conjectured to be the ground state of the gravitational field with positive cosmological constant. This review can serve as a self-contained introduction to loop quantum gravity and related areas. Our intent is to make the paper accessible to a wider audience that may include topologists, knot-theorists, and other persons innocent of the physical background to this approach to quantum gravity.

    John Baez

    Recent work on the loop representation of quantum gravity has revealed previously unsuspected connections between knot theory and quantum gravity, or more generally, 3-dimensional topology and 4-dimensional generally covariant physics. We review how some of these relationships arise from a `ladder of field theories' including quantum gravity and BF theory in 4 dimensions, Chern-Simons theory in 3 dimensions, and the G/G gauged WZW model in 2 dimensions. We also describe the relation between link (or multiloop) invariants and generalized measures on the space of connections. In addition, we pose some research problems and describe some new results, including a proof (due to Sawin) that the Chern-Simons path integral is not given by a generalized measure.

    Jorge Pullin

    These notes summarize the lectures delivered in the V Mexican School of Particle Physics, at the University of Guanajuato. We give a survey of the application of Ashtekar's variables to the quantization of General Relativity in four dimensions with special emphasis on the application of techniques of analytic knot theory to the loop representation. We discuss the role that the Jones Polynomial plays as a generator of nondegenerate quantum states of the gravitational field.
  17. Apr 13, 2007 #16


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    Thanks, ensabah6. I apologise for not making myself clearer: I was using the term categorified knot theory in a more technical sense, to refer to recent work in Khovanov homology. Cheers.

  18. Apr 20, 2007 #17


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    Oriti's plenary talk at Loops '07 advertises a connection between spinfoam and condensed matter physics

    Here are the plenary talk abstracts


    they are alphabetical so Oriti is more than halfway down the page. I'll paste it in here for convenience.

    Daniele Oriti: Group field theory: spacetime from quantum discreteness to an emergent continuum

    Group field theories are non-local quantum field theories on group manifolds, and a generalization of matrix models. Having been first introduced in the context of simplicial quantum gravity, have gained attention as being potentially of much interest in the context of loop quantum gravity and spin foam models. After a brief introduction to the group field theory formalism, I review some of the results already obtained in this approach. I will then try to offer a new perspective on how group field theories should be interpreted and used towards a complete theory of quantum gravity. In particular, I will argue that group field theories can represent on the one hand a common unifying framework for loop quantum gravity, spin foam models and simplicial approaches, like quantum Regge calculus and dynamical triangulations, and on the other hand a consistent microscopic description of spacetime considered as a condensed matter system. From this, a novel approach to the issues of the emergence of the continuum and of General Relativity as an effective description of spacetime, in this approximation, is proposed. Finally, I will briefly report on some recent results and work in progress inspired by and supporting this new perspective.
    Last edited: Apr 20, 2007
  19. Apr 20, 2007 #18


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    Also from the list of plenary talk abstracts for the same conference there is:
    Artem Starodubtsev: Some physical results from spinfoam models

    Given the known mathematical fact that a spinfoam is a Feynman diagram the data relevant for particle scattering amplitudes could be identified in it.

    this may not be directly relevant to what is being discussed in this thread but it might nevertheless be of interest. It involves unifying how one approaches quantum geometry (e.g. spinfoam) with how one approaches matter (e.g. Feynman diagram.)
    Last edited: Apr 21, 2007
  20. Apr 21, 2007 #19
    Thanks Marcus for bringing this to my attention. I've got my doubts about SUSY and higher dimensions, given that Tevatron has not seen them nor has proton decay been observed. It's too bad though Wen hasn't been invited to this conference since he has produced papers describing the emergence of gravitons from a lattice, as well as some SM particles, and he describes his string net condensation model as a spin network.
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