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C, P, and T of Braid Excitations in Quantum Gravity (Song He, Yidun Wan) 
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#1
May1208, 01:54 PM

Astronomy
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PF Gold
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http://arxiv.org/abs/0805.1265
C, P, and T of Braid Excitations in Quantum Gravity Song He, Yidun Wan 28 pages, 5 figures (Submitted on 9 May 2008) "We study the discrete transformations of fourvalent braid excitations of framed spin networks embedded in a topological threemanifold. We show that fourvalent braids allow seven and only seven discrete transformations. These transformations can be uniquely mapped to C, P, T, and their products. Each CPT multiplet of activelyinteracting braids is found to be uniquely characterized by a nonnegative integer. Finally, braid interactions turn out to be invariant under C, P, and T." I think this is an important paper. It is the companion of another HeWan paper that I nominated last week for this quarter's MVP (most valuable nonstring QG research) prediction poll. The braidmatter program is high risk. It began as a long shot with only a slim chance of working out. It was not at all clear that braids (in this case in fourvalent networks used to describe states of geometry and gravity) would turn out to reproduce some of the basic patterns of matterkey symmetries and invariants. This paper is, for me, the first sign that braidmatter might work. Others might see differently and I would be glad to have some comments. In any case the whole thing is very new. It goes back only to BilsonThompson's work in 2005which had braids but without the context of fourvalent networks. 


#2
May1308, 12:09 AM

Astronomy
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PF Gold
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I should list the paper by He and Wan which immediately precedes this one
http://arxiv.org/abs/0805.0453 Conserved Quantities and the Algebra of Braid Excitations in Quantum Gravity Song He, Yidun Wan 25 pages, 2 figures (Submitted on 5 May 2008) "We derive conservation laws from interactions of braidlike excitations of embedded framed spin networks in Quantum Gravity. We also demonstrate that the set of stable braidlike excitations form a noncommutative algebra under braid interaction, in which the set of activelyinteracting braids is a subalgebra." There is also a solo paper by Yidun Wan and another coauthored by Jon Hackett and Wan. One of the references says there is also a paper in preparation by Smolin and Wan. So far, to my knowledge, there is no evidence either that the 4valent braidmatter approach of Wan et al is right, or that it is wrong. One thing that can be said is that, if it is right, matter arises as knots in geometry, in other words matter is a topological complication in space. It is a daring idea, with a high risk of not working out, and I think Yidun Wan and the others deserve a lot of credit for undertaking such a research venture. Yidun has posted several times here at PF, and subsequently set up his own blog. 


#3
May1308, 12:22 AM

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PF Gold
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Here is a Perimeter online video lecture by Yidun about braid matter,
http://www.physicsforums.com/showthread.php?t=184400 it is a good easy audiovisual way to learn about braid matter. Here is our announcement of Yidun's blog back in May 2006. Has it been two years already?! http://www.physicsforums.com/archive.../t120127.html At that time Yidun was posting at PF with the name "lqg". I see a post from him there. The blog is named "Road to Unification". Perimeter has a new catalog of video talks called Pirsa. If you go here: http://pirsa.org/speaker/Yidun_Wan You will find TWO available video talks by Wan. One of them is more recent 31 January 2008. PIRSA:08010044 ( Windows Presentation, Windows Video File , Flash Presentation , MP3 , PDF) Which Format? Braidlike Chiral States in Quantum gravity Speaker(s): Yidun Wan  University of Waterloo Abstract: There has been a dream that matter and gravity can be unified in a fundamental theory of quantum gravity. One of the main philosophies to realize this dream is that matter may be emergent degrees of freedom of a quantum theory of gravity. We study the propagation and interactions of braidlike chiral states in models of quantum gravity in which the states are (framed) fourvalent spin networks embedded in a topological three manifold and the evolution moves are given by the dual Pachner moves. There are results for both the framed and unframed case. We study simple braids made up of two nodes which share three edges, which are possibly braided and twisted. We find three classes of such braids, those which both interact and propagate, those that only propagate, and the majority that do neither. These braids may serve as fundamental matter content. Date: 31/01/2008  2:00 pm Series: Quantum Gravity URL: http://pirsa.org/08010044/ PIRSA:07090011 ( Windows Presentation, Windows Video File , Flash Presentation , MP3 , PDF) Which Format? Propagation and interaction of topological invariants on embedded 4valient spinets Speaker(s): Yidun Wan  University of Waterloo Abstract: The study of particlelike excitations of quantum gravitational fields in loop quantum gravity is extended to the case of four valent graphs and the corresponding natural evolution moves based on the dual Pachner moves. This makes the results applicable to spin foam models. We find that some braids propagate on the networks and they can interact with each other, by joining and splitting. The chirality of the braid states determines the motion and the interactions, in that left handed states only propagate to the left, and vice versa. Date: 07/09/2007  3:00 pm URL: http://pirsa.org/07090011/ Over the years I've found the Perimeter online video lectures quite helpful, so if anyone wants to learn more about braidmatter and the current research, I'm suggesting this. there is also online talks at the ILQGS (international loop quantum gravity seminar). 


#4
May1408, 02:27 PM

P: 1,667

C, P, and T of Braid Excitations in Quantum Gravity (Song He, Yidun Wan)
What dynamical stuff constitutes the braids ??? Or is it just old fashioned symmetry braking ?



#5
May1408, 03:10 PM

Astronomy
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PF Gold
P: 23,083

This is a useful question. I don't think anyone has spelled out what dynamical stuff. One response would be the same primitive "material" that embedded spin networks themselves are made of. You get braids whenever you have the network embedded. A braid is like a knot. You get the possibility of knots whenever you have a circle that is embedded in R^{3}. You Careful know this. I'm saying it in case anyone else is reading the thread and doesn't know. I personally don't like that response to the question either, but that would be one answer. We should think about it, but for now I think there is no answer. A spin network is too fundamental for it to be "made" of any "material". Likewise braids in a spin network, they don't seem to be made of any thing. they are mathematical ways of representing information, I guess. ======================= A 4valent network can be thought of as a simplicial complex. but as you mentioned there is a kind of generalized symmetry breaking in the way you glue the simplexes together. You can glue them together in some naive straightforward way, I suppose, or you can twist them as you are bringing face to face. There can be crisscross contorted ways that you join face to face. ======================= Something I am curious about, well two things: One is how this braidmatter business might parallel Connes Chamseddine NCGSM. They say that spacetime is M x F where M is just a smooth 4D manifold and F is a finite discrete sort of geometry that is representable only algebraically (not as a manifold). Well it seems to me that 4valent networks (conventionally representing 3D geometry in Looptalk) correspond vaguely to the manifold M, and that MAYBE Connes finite geometry F corresponds to the TWISTS AND BRAIDS. The dimensions don't match perfectly and the fit may not be very good but I see some possibility of the two approaches joining. The other thing I am curious about is how braidmatter could tie in with Ambjorn Loll CDT. They both use Pachner moves.. Yidun Wan uses a dynamics of local moves made on the network which looks similar to the local moves on the simplexes that Ambjorn Loll usee.g. join two tets and then split the result into three (to take a lower dimensional example). It seems possible that the CDT spacetime brickworks are basically the same thing as braidmatter 4valent networks and that Wan could be showing Ambjorn Loll a way that they could include matter in their CDT picture. this is very tentative on my part. havent thought it out much. 


#6
May1408, 03:54 PM

P: 1,667

There is a definite distinction between spin networks and say causal sets in this regard. The causet itself is a dynamical object and questions like braiding could in principle be asked (albeit it would be difficult) in such framework. 


#7
May1508, 11:26 AM

Astronomy
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PF Gold
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I was reluctant to cover up your post, unresponded to, but want to continue with a bit more discussion. 


#8
May1508, 11:43 AM

Astronomy
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PF Gold
P: 23,083

There is another bit of unfinished business, so to speak, from a previous braidmatter thread. That thread got a lot of discussion going in different directions by different people and this comment by Saltlick didn't get a response. It also points up some potentially interesting topics and it would be great if anyone who knows the referenced literature could respond



#9
May1608, 04:52 AM

P: 1,667

It might be in this way that particles change species if observers change, which would definetly be problematic. Since I haven't read the papers (or given it any further thought), I would welcome any comment on this (and set me straight if necessary). 


#10
May1608, 01:23 PM

P: 859

The problem is that people continue to associate the embedding space with some fixed classical geometry that is supposed to reflect the nature of an emergent spacetime. Bad idea to put in by hand what you want to get out. The only way to treat braids in a truly observer dependent way (this is seen as a feature, not a problem), is to view the imbedding space as a reflection of the measurement constraints for that particular observer, ie. as an abstract template completely independent of the properties that we like to attribute to space on large scales. I don't see how you can do this without incorporating category theory, so that the embedding space can be, eg., a configuration space.



#11
May1608, 01:47 PM

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#17
May1808, 01:49 AM

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#18
May1808, 04:23 AM

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