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I have begun performing several edits, and have forgotten to comment the edits. The initial few edits were adding relativistic invariance. Apologies for any inconvenience caused.
Masud15:32, 22 December 2005 (UTC)reply
I have added relevant sections. They still need touching up, which I may do later, and I have yet to add the source lagrangian for the EM field and general relativity.
Masud16:23, 22 December 2005 (UTC)reply
Perhaps a better title for this article might be "Lagrangian formulation of electrodynamics". In fact, I'd strongly recommend that change.
linas16:37, 24 December 2005 (UTC)reply
But the page has information on general classical fields. I can then add a GR section too. And if we did rename it, we'd lose a page on classical fields in general, which I think is as necessary as the (much higher profile) quantum field theory page.
Masud16:42, 24 December 2005 (UTC)reply
You are new to WP, so allow me to make some suggestions and pointers. First, WP is not a book, and shouldn't be written as if it were one. The article is already fairly long, and it deals with just one topic (electromagnetism). Adding GR would only make it longer. Thus, I would suggest that you write two articles; a second on the lagrangian formulation of GR.
Next, you are currently rather far form an article on "classical fields" in general. First, the article assumes four space-time dimensions. That is a strange limitation. Next, there are a vast number of possible lagrangians; focusing on E&M or GR may have physical importance, but cuts out oceans of other interesting things. Also, note that the modern mathematical understanding of E&M is as a
line bundle over
U(1). The pdf
Line Bundles by Micheal Murray provides an excellent overview of electrodynamics in this context, and you might do well to study that.
Based on these remarks, I suggest that you try to narrow your focus to something more humble, a limited-scope, single-topic article, something for which you do have a good grasp, rather than attempting an over-arching, reviews-all-human-knowledge type of an article. (I note that Landau and Lifshitz, "the Classical Theory of Fields", is hundreds of pages long, and dense to boot. Each section of that book might make an appropriate WP article: that would result in 50 or 100 of articles.)
That's actually quite patronising. I've been a member of Wikipedia longer than you, and have been editing before that.
Masud09:48, 26 December 2005 (UTC)reply
I'm sorry, based on your edit history, it seems that you've been here a few weeks. I've been here for almost a year.
linas20:33, 3 January 2006 (UTC)reply
Apology accepted; but just for the record, my edit history starts from 5 July 2004, and your earliest edit is 30 December 2004.
Masud02:45, 4 January 2006 (UTC)reply
Article name is fine; major cleanup needed though
I'm with Masud on the issue of the article containing more than just a description of one field theory. The article is called 'classical field theory' and this includes more than just any particluar field theory - EM, GR etc. and Newtonian gravitation; yes, that's right, Newtonian gravitation is a classical field theory. Which brings me to another point: classical field theories are not necessarily Lorentz covariant as the article claims (and incorrectly gives the example of the string). Depending on how much information we want to include on each classical field theory, other articles on EM, GR etc. may be needed.
MP (talk)09:57, 3 January 2006 (UTC)reply
I agree with you on the cleanup. Am attempting to separate relativistic and non-relativistic fields. Note that the electric field (also initially treated non-relativistically) was the first field recognised as a field, then the gravitational field was described in the same way. Then came magnetic fields, etc.
Masud15:13, 3 January 2006 (UTC)reply
Have tried to add some to the non-rel. grav. field. I'm not sure if I like the arrow-on-top or heavy type notation for vectors. Is there a Wikipedia convention for which one to use?
Masud15:40, 3 January 2006 (UTC)reply
I'm still concerned about the scope. Classical fields include sound-waves/acoustics in air, ocean, and earth (geophysics). Classical fields also include wind fields, humidity fields, pressure fields, etc. for predicting weather. Then, in supernova research, one solves classical field equations for a detonation front (supersonic burning) (of nuclear material, biut that's besides the point). Note that in burning, the number of particles are not constant. (Ditto for rainfail). One also has lots and lots of clasical fields in KdV and fluid dynamics and turbulence and etc. One uses classical (albeit fractal) fields to model the stresses in a sheet of metal, thus leading to the propagation of stress fractures in solids (which are fractal). Speaking of fractals and classical fields:
DLAdiffusion-limited aggregation. Then, the
diffusion-reaction equation. and etc. By focusing on E&M and gravity, this article is ... very very incomplete.
linas20:29, 3 January 2006 (UTC)reply
You make a very good point. But clearly we are attempting an article on fundamental classical fields. I also note that the article on
QFT does not have sections on every imaginable quantum field either. People who know about and are looking for propagation of stress fractures in solids would probably look that up independently as opposed to coming to this page to find it; besides assuming someone has written this content, we could easily have short paragraphs and subsections which link to these pages.
Masud02:53, 4 January 2006 (UTC)reply
I beg to differ. The article on QFT makes an attempt, in the introduction, and then in the body, to actually list every possible QFT. Its misses a few of the minor ones but after a quick skim, seemed to touch all the major ones. I'd also like to point out that the QFT article is a rather poor role model for what a WP article should look like; its in pretty nasty condition, and poorly structured. It has all the symptoms of an ambitious editor who couldn't/didn't finish the job that was started.
The comment about stress fractures reinforces my point, instead of weakening it. The reader of an article on weather prediction, or somesuch, does indeed start there, not here. On reading, they realize that they now have a general question about the theory of continuous media, and would thus hopefully be linked here. They come here, and rather than learning about the classical theory of fields, they see nothing but a sea of gravity and electromagnetism.
I'll say it a third time, and then I'll grit my teeth: either write the general survey article that the title promises this to be, or change the title to reflect its actual contents (which currently is rather narrow, a mix of "the classical theory of electromagnetic fields in a vacuum with no boundary conditions", and some newtonian gravity, which, honestly, to me, are rather unrelated.) Honestly; I'm not trying to be offensive; I'm trying to be helpful: you'll have a better article if you narrow the scope.
linas05:14, 4 January 2006 (UTC)reply
The term 'classical field theory' is most commonly used for things like electromagnetism and GR and the article should certainly discuss these. Having said that, Linas' point about including other fields (humidity, pressure etc.) can't be ignored. I think a compromise is in order here. Be aware, however, that when a physicist comes across a 'classical field theory' nowadays, they also come across Lagrangians and this point should be emphasised when discussing more up to date classical field theories. This article should have links going to the other less well-known classical fields, but a big deal should not be made of them here (for example, I don't believe meteorologists - or anyone for that matter - ever use Lagrangians to determine how a test particle moves in a wind field). Let's keep things in perspective.
MP (talk)08:17, 4 January 2006 (UTC)reply
Some questions
See the to-do box, I've duplicated here for convenience and permanence.
Question: do we derive the field equations given the Lagrangians? Or do we delegate that to some other article? (eg. GR's field equations derivations are presented in other pages on Wikipedia).
Question: do we include more details on the non-relativistic fields? Those sections are looking quite thin at the moment.
Hi Masud. Good questions; I propose that we don't derive the field equations in this article (as this would be too much detail for this article and) as the equations for GR are derived in
Einstein-Hilbert action. However, the Lagrangians, field equations and conservation laws should be mentioned (as they're obviously worthy of mention). It may even be too much to mention all the different Lagrangians and field equations for one classical field theory - vacuum and non-Einstein vacuum equations (and similarly for EM). Perhaps we could state the most general Lagrangian for each theory and just briefly mention the vacuum cases).
Recent edits
I've edited the EM section to include source terms in the equations, re-organised the headers, and feel that the tags are not required as much anymore.
I'm not sure if it would be a good idea to add the magnetic field as a non-relativistic field theory. Anyone have any thoughts on the matter?
Masud02:05, 14 February 2006 (UTC)reply
I had a question: Please get back to me if I am wrong User:Bnmouli
* there can be higher order differential w.r.t same coordinate.
* Max oder is not limited to 4.
* There can not be higher order differentials w.r.t time.
This page is showing up on the speedy deletion list
presumably because something that has been listed for speedy delete has been transcluded on it, but I cannot find it. DGG (
talk)
16:12, 11 July 2008 (UTC)reply
It was to delete the to-do list that was no longer necessary. You'll notice I've removed the todo template from this page now that the todo list is gone. --
Masud (
talk)
01:02, 12 July 2008 (UTC)reply
Classical fields and radiation of energy
Wikipedia articles on radiation emphasize the particle point of view. It would be useful to say something about classical fields of force and the concept that energy can be radiated by such fields. Is there a classical model that explains the radiation of energy or must it attached to the theory of classical force fields by some independent postulates?
For example, the electric field at point in space can be defined as a force on a "unit test charge", but a time varying electric field doesn't do work (in the sense of work = force times distance ) on a conceptual test charge and it doesn't do work on an actual charge that is not free to move. I suppose the field has the "potential to do work" so perhaps the classical view is that it can transmit potential energy.
The term "field equation" is used in both classical field theory and quantum field theory. There is also
relativistic wave equations, which describes equations in classical field theory, relativistic quantum mechanics, and quantum field theory, according to spin.
I think this alternative wouldn't serve most users, since the vast majority of hits for "field equation" in a Google search are to Einstein field equations. Now that I think of it, it may even make sense to make
Einstein field equations the primary subject with a hatnote going to a disambig page. RockMagnetist(
talk)17:00, 21 September 2015 (UTC)reply
My second alternative wasn't brilliant, just something to think about, although "field equation" is used much more widely than general relativity. I strongly oppose making
Einstein field equations the primary subject.
The article on classical field theory includes (or at least should include) the Einstein field equations, the non-relativistic gravitational field equations (Newton's and Gauss' laws), and Maxwell's equations of the electromagnetic field will certainly be a target also. Your original idea of merging
field equation with
classical field theory was much better.
M∧Ŝc2ħεИτlk17:16, 21 September 2015 (UTC)reply