Talk:Spin network

message: Recursion, see Recursion.  String-net directs here, yet the only place where string-nets are mentioned is in a link to string-nets.  I am going to break the redirect and hope that someone with more in depth knowledge of string-nets can make a more specific article. Hillgiant 20:32, 15 March 2007 (UTC)
thread_title:  Recursion

message: 'A spin network, immersed into a manifold, can be used to define a functional on the space of connections on this manifold. One simply computes holonomies of the connection along every link of the graph, determines representation matrices corresponding to every link, multiplies all matrices and intertwiners together, and contracts indices in a prescribed way. A remarkable feature of the resulting functional is that it is invariant under local gauge transformations.'
Clear as mud and twice as thick.  Is it any wonder that other scientists think that theoretical physicists are getting up to nothing of any relevance to the scientific community, let alone the real world outside academia?
::This fragment assumes that the reader is familiar with terms "manifold", "functional", "connection", and "local gauge transformation". In other words, familiar with GR and QFT. It is possible in principle to describe spin networks without making any statements that require knowledge of GR and QFT, but it would not do justice to the subject (and would not make sense in a quantum gravity related article). --Itinerant1 11:30, 30 June 2007 (UTC)
replies: text: Agreed.  This article, and others like it, should, among other things, start with an introduction that includes a statement as to what the everyday meaning of the subject-matter is, that is, what does it mean in simple terms to a person who is not a specialist in the field. Tmangray 07:50, 6 November 2007 (UTC)
thread_title:  Exactly who is this article intended for? 

message: Suggestion: use Figure 2 in http://math.ucr.edu/home/baez/penrose/Penrose-AngularMomentum.pdf for an illustration. Also, base a definition of spin network on that article.  —Preceding unsigned comment added by 66.245.58.135 (talk) 05:07, 3 February 2008 (UTC)
replies: text: I think this is nice as an elementary introduction. But I have a few comments. I think the spin network norm is defined only if the spin network is closed. Also, I'm not sure adding in the conditions on integer labels is beneficial since it doesn't really relate to anything else that is discussed, so it may appear to the uninitiated as an arbitrary set of rules. From the mathematical POV, this is the Clebsch-Gordan formula. Perhaps it could be phrased as relating to the permissible interactions between particles. A nice way to state the rule is that a,b,c must be permissible as integer side lengths of a Euclidean triangle.  —Preceding unsigned comment added by Triathematician (talk • contribs) 20:39, 3 February 2008 (UTC)
thread_title:  Suggestion for figure and definition 

message: Would Scientific American or Lee Smolin let us use one of the picures from their article (The one in the 2006 special edition)? *Max* (talk) 03:30, 22 February 2008 (UTC)
thread_title:  Image 

message: This article really confuses me.  I'm not a physicist but I don't like to think of myself as completely ignorant, either.
* Spin networks are described as the world lines of particles that come together in threes.  But the illustration shows a network of triangles - so I assume the vertices in the text are actually the centers? of the triangles in the illustration.
* Two rules are given for the numbers in spin networks, but making the above assumption, the illustration still breaks both of them.  For example 4, 2, and 1 on the second triangle up on the right edge.
* The article on loop quantum gravity says "In this context, spin networks arose as a generalization of Wilson loops necessary to deal with mutually intersecting loops. Mathematically, spin networks are related to group representation theory and can be used to construct knot invariants such as the Jones polynomial."  This at least should be incorporated, and preferably... explained.
* Please explain in very simple terms: do the axes on this graph represent physical dimensions?  Is, say, up at a later time?  Does the left-right axis represent the movement of particles in one dimension?  Or is the map only conceptual, and does the mention of knot invariants mean that somehow these networks can encode knot patterns in higher dimensions?
This article is a node between several unapproachable articles; yet the simple diagram gives the impression that it is a topic that can be understood by a novice without great sophistication. Wnt (talk) 03:19, 25 March 2009 (UTC)
thread_title:  Basic information needs to be added 

message: I see a number of apparent inconsistencies between the figure and the definition given in the current page.
I am not familiar with the subject so I cannot judge whether it is due to a confusing wording in the definition(s), a problem with the figure, or something else. Yet it would be nice if someone knowledgeable could address this. The problems include:
1. The "formal definition" states the graph is directed, the figure shows an undirected graph. (The "directed" word is in parenthesis but the meaning of the parenthesis is unclear).
2. The "Penrose's original definition" states that exactly three segments join at each vertex; if this is not true for a general definition (as the figure suggests) it should be stated explicitly. 
3. Again, "Penrose's original definition" includes a "triangle inequality", violated even for those vertices in the figure for which it is defined (e.g. 4 > 2+1), and undefined for all the vertices joining more than three lines. Would be nice to explain this.
4. More generally, the "formal definition"  may be hard to understand even to a person familiar with the basic ideas like Lie groups etc. Thus, if the conditions implied by that definition are less restrictive than those stated in the "Penrose's original definition", this should be commented upon.  —Preceding unsigned comment added by 128.97.82.220 (talk) 02:11, 29 July 2009 (UTC)
replies: text: Here we are 13 years later and as far as I can tell not one of these inconsistencies has been addressed. This article needs serious pruning until someone can replace it with a consistent account. — Cheers, Steelpillow (Talk) 18:23, 21 June 2022 (UTC)
thread_title:  How the definition relates to the figure? 

message: I thought I would add to the previous mentions that the diagram is pretty, but confusing, since it is inconsistent with the article definitions.  I'm sure the diagram is simply a more advanced development, but the article needs to connect these, or the diagram detracts from the overall message.  Oh, and for the record, mad props to Roger Penrose!  70.247.164.231 (talk) 03:26, 28 August 2010 (UTC)
thread_title: (Another) confused reader

message: In the Formal Defintion section where it says "can be used to define a functional on the space of connections on this manifold", I linked "connection" to "Levi-Civita connection".  Is this correct? 18:05, 15 April 2017 (UTC)
thread_title:  "Connection" linked to "Levi-Civita connection" - correct?