Talk:Gauge theory

section "2.1 Global and local symmetries"

How is that an appropriate title for this section? At no point does this section make the slightest attempt to define what a global or local symmetry is, or what the difference is between them. In fact, neither the word "global" nor the word "local" ever appears in it, except to say that the idea can be generalised to include local as well as global symmetries. Quite what that's actually supposed to mean is left entirely unclear. — Preceding unsigned comment added by 131.169.205.156 (talk) 15:34, 2 February 2015 (UTC)

section "2.2 Gauge Fields"

This needs to be rewritten. You cannot begin the first paragraph of a new section using vague pronouns instead of specific subjects. The topic is confusing enough, there's no reason to make the text indecipherable. "The "gauge covariant" version of a gauge theory accounts for this effect by..." What effect? Michael McGinnis (talk) 21:50, 15 September 2016 (UTC)

semi-gauge field

A semi-gauge field has a finite range of transformative invariance. — Preceding unsigned comment added by 2A02:587:410D:7800:A54E:6F32:59F7:49A1 (talk) 15:58, 30 September 2016 (UTC)

This page vs. Introduction to gauge theory

Why is there a separate Introduction to gauge theory page? Shouldn't an encyclopedia article be an introduction to a subject? It seems like it'd be better to combine them into a single page, or split this main article out into more specific technical pages and replace it with the introduction. — Preceding unsigned comment added by 2601:647:4D03:3CA7:A860:47C9:1D45:B8DD (talk) 10:34, 15 June 2017 (UTC)

   The first sentence is a great example of how Physics articles on Wikipedia can be utterly incomprehensible. The first sentence of this article: "In physics, a gauge theory is a type of field theory in which the Lagrangian is invariant under certain Lie groups of local transformations." contains four terms I don't understand: "field theory", "Lagrangian", "Lie groups", "local transformations". I guess I could read up on those terms on their respective pages. Let's take "Lie groups", the first sentence of that article is: "In mathematics, a Lie group is a group that is also a differentiable manifold, with the property that the group operations are compatible with the smooth structure." Three terms I don't understand: "Differential manifold", "group operations", "smooth structure". It just keeps branching out! How can an uninformed reader ever grasp what is being said? 

Although I applaud the creation of the Introduction to gauge theory page, I completely agree with the above comment: encyclopedia articles should be an introduction to a subject. 217.76.25.109 (talk) 22:11, 19 July 2017 (UTC)

This would be very difficult, but I'll see if I can come up with something when I have time. So far, here are the issues:

* We could improve the description of the Lie group article to be more familiar to non-mathematicians who use it for other purposes (your average physicist would have trouble fully understanding that introduction). I think knowing what is a Lie group is important to understanding this; although one could give a rough idea of it just by using the term "infinitesimal local transformation" and ignoring Lie groups. (see below for more elaboration on this)

* Field theories are just physical theories about fields; like how fields evolve over time, interact with each other, etc? Quantum field theory and classical field theory are so structurally different that it's hard to say "X is precisely and exactly what a field theory is", so explaining that further will get people to argue over the definition of words. Usually field theories are quickly summarized in this function called a "Lagrangian". I don't think Lagrangians are strictly necessary for a gauge theory (I'm not sure about this, can someone verify?), but all the treatments of gauge theories that I have ever seen use Lagrangians.

* "local transformation" in this context is simultaneously not notable enough to merit its own article, but also kind of hard to define on its own. Essentially, we want too say that if we have a (vector field) $f(x)$, a local transformation takes $f(x)$ to $g(f(x))$ for some (typically linear) function from the vector space to itself $g$, as opposed to a transformation that takes $f(x)$ to $f(x+a)$ for example. Essentially, we want the transformed field at x to only depend on the original field at x. (erm, does that work/make sense?)

If we want to make this article more comprehensible, we could add a section starting with a simple introduction; in fact the article titled Gauge Fixing gives a very intuitive but also kind of badly written introduction to this. We could also be like the math pages and define terms like "gauge" (a basis for our vector space at any particular point), and define everything clearly enough so that it becomes understandable? (but then we would have to link fibre bundles and whatnot to make the mathematicians happy) Physics undergraduates don't touch gauge theories until they do their Ph.Ds (so, for some of them, it's just "never"), so this is difficult to explain in a simple way that is also correct. Qwyxivi (talk) 03:25, 28 September 2019 (UTC)

Not so difficult, anything that is PhD-level only can safely be removed from the encyclopedia.134.160.214.17 (talk) 08:18, 9 March 2020 (UTC)

84.114.240.91 (talk) 14:40, 21 June 2020 (UTC) The subject is very difficult, indeed. To help at least physics students with just basic (BS) knowledge to get a grip on it, I added a link into the "external links" section to here: https://www.goldsilberglitzer.at/Rezepte/Rezept008E.pdf. It explains it without "Lie groups", "Lagrangian", etc. However, the link was immediately removed. Maybe this decision should be re-considered. — Preceding unsigned comment added by 84.114.240.91 (talk) 14:33, 21 June 2020 (UTC)

The pdf is just a non peer-reviewed blog of conventional material on electromagnetism already in Wikipedia. Do you have any COI in the matter? Xxanthippe (talk) 22:34, 21 June 2020 (UTC).

"under certain"

In physics, a gauge theory is a type of field theory in which the Lagrangian is invariant under certain Lie groups of local transformations.

Under certain wider range transformations we have dark matter and Roger Penrose's Big Bang (suddenly, after an energy threshold overflow of an extremely old expanding universe, that Universe is caught by police, and the only way to make its Lagrangian invariant again is to implode).

Under certain allows room for new theories. — Preceding unsigned comment added by 2A02:587:411C:3400:6121:B908:16E1:BD7 (talk) 03:44, 12 July 2018 (UTC)