Talk:Special relativity/Archive 13

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This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

1 New image
2 reference frame definition
3 Lorentz-Fitzgerald contraction
4 c in the section Special relativity#Physics in spacetime
5 Four forces
- 5.1 Four force, part 2
6 relativity of simultaneity
7 little help?
8 GA Re-Review and In-line citations
- 8.1 just another header
- 8.2 Did she get one right?

New image

Image:SphereAberration01.gif

(Linkified animation in response to complaints about load time. --Christopher Thomas 04:30, 30 August 2006 (UTC))

We need a better description of this image. What exactly does it illustrate? What do the background curves represent? It was placed in the external links section, which doesn't make sense; if we use it, it should be incorporated into the text. —Keenan Pepper 07:59, 6 August 2006 (UTC)

I'm the beginner and still working on text for the images, sorry. But everybody are welcome to use my images in their own articles. At the first time I did place this image in a little bit weird section. Actually it represents visualization of rapidly moving sphere.

Image:XYCoordinates.gif

(Linkified animation in response to complaints about load time. --Christopher Thomas 04:30, 30 August 2006 (UTC))

Demonstration of Aberration of light and Relativistic Doppler effect‎

Animation: Image:Lcprojection1m.gif

This picture can help to understand the background curves. I've put the image and short description into Relativistic Doppler effect I'll be very appreciated for any comments. TxAlien 16:56, 14 August 2006 (UTC)

That's much better. I cleaned up the text a little for Relativistic Doppler effect, but it looks fine now. It would be nice if you added a summary of how you created the images to the image description pages. Other than that, keep up the good work! —Keenan Pepper 02:44, 25 August 2006 (UTC)

I'm very appreciated for the text improvement. Thank you. I've started to add the summary [1]. It is not finished yet. I think to make a few new images to illustrate the long formulas.--TxAlien 04:26, 28 August 2006 (UTC)

I think I've found the right image in the end. Now, I have to find the shortest formulas and the right words. It is Image:Lcprojection01.jpg --TxAlien 06:52, 30 August 2006 (UTC)

I am about to finish the text How this image was created I'll be glad if those images will be useful to anyone and thankful for any comments. --TxAlien 21:37, 4 September 2006 (UTC)

reference frame definition

In "Reference frames, coordinates and The Lorentz transformation" section the reference frame is defined as "a point in space at rest, or in uniform motion...". There is no absolute rest, so I would suggest omitting the word and change to "a point in uniform (non-accelerating) motion..." --Michagal 12:03, 9 August 2006 (UTC)

Lorentz-Fitzgerald contraction

An editor made an edit changing "Lorentz contraction" to "Fitzgerald contraction". I have never heard this effect called the "Fitzgerald contraction". Admitedly Fitzgerald published it first [2], but it was Lorentz who promoted it and got people to notice it. That is how it became known as the "Lotentz contraction". The other common title for it is the "Lorentz-Fitzgerald contraction". Even the "Fitzgerald-Lorentz contraction" in the reference web article is an anachronism.

If this editor wants to push this change, then proper csources need to be cited. The best that I can offer is to refer to length contraction instead. --EMS | Talk 18:51, 15 August 2006 (UTC)

That is OK. I will not fight about it. I just remembered that it was called the "FitzGerald contraction" when I learned about it, but that was many decades ago and I cannot find the books that I learned it from. I thought that "Lorentz" was a mistake, but I see that the article on Lorentz-FitzGerald contraction hypothesis says that Lorentz also discovered it independently shortly after FitzGerald. JRSpriggs 03:23, 16 August 2006 (UTC)

c in the section Special relativity#Physics in spacetime

I do not like the placement of "c" in this section. Using "ct" instead of "t" as the time coordinate leads to equations which are hard to understand because the time coordinate is given in meters (even though proper-time is still measured in seconds). There is no point in doing this because one is forced to distinguish between contravariant and covariant anyway due to the minus sign. Please allow me to rewrite the section to change the placement of "c" so that we are using International System of Units consistently. JRSpriggs 08:31, 19 August 2006 (UTC)

First, I will make some fixes which do not affect the units or "c"s. If no one objects here in the next few days, I will move on to change the units. JRSpriggs 05:03, 21 August 2006 (UTC)

The editing will take several days. So when I am changing the units, the section will be inconsistent. That is some formulas will have the SI units and some will still have the units which are there now where time is measured in meters. JRSpriggs 05:51, 21 August 2006 (UTC)

OK. Now I have changed the units of time from meters to seconds in the "Physics in spacetime" section. I have also made a number of other changes to try to use contravariant and covariant indices correctly. Please take a look at it and say what you think. Especially check the equations of electromagnetism which I think may be in a form superior to those in the special relativity section of the article "Maxwell's equations". JRSpriggs 06:06, 25 August 2006 (UTC)

Four forces

I have some concerns about the following remark. Rather than spoil an active edit session, I'm going to put my concerns on the talk page and drop a note to the active editor.

"Force presents a problem because there is no (reasonable) tensor in 4D which contains the components of the 3D force vector among its components."

The four-force is a reasonable and standard tensor expression for force in SR, and it's even in the Wikipedia (and probably deserves a link). I think a remark explaining how to interconvert the three-force and the four-force would be much more useful than the above remark. A simple scale factor should not be made so mysterious - if that's the concern.

Possibly there may be other concerns here, a reference or a note here in reply might help clarify matters. Pervect 07:51, 28 August 2006 (UTC)

As the text of the article correctly says, $\vec F = d\vec p/dt$ is the appropriate notion of force in special relativity. The four-force, to which you referred, is $F^\alpha = {dp^\alpha \over d\tau}$ which is indeed a tensor. However, it is merely the force in the particle's rest frame transformed into the observer's frame. It is not force in the observer's frame in any meaningful sense. Furthermore, if you look at what I said, you will see that the components of the 3-force are NOT components of the four-force. The "scale factor" you mentioned is $dt/d\tau = \gamma \!$ which is NOT an invariant scalar, i.e. it is observer-dependent. JRSpriggs 05:52, 29 August 2006 (UTC)

The thing which makes momentum physically significant is the fact that it is a conserved quantity (or integral of the motion, as they say). The thing which makes force important is the fact that it is the rate at which this conserved quantity is transferred from one entity to another, i.e. Newton's second and third laws of motion. For this conservation to work, the RATE of transfer must be calculated with respect to the same time coordinate for all entities involved. That is why the Newtonian definition is correct even for special relativity. And that is why "four-force" is useless; its rate is measured with respect to the proper time of each object which varies from object to object (remember the twin paradox). JRSpriggs 03:48, 30 August 2006 (UTC)

Calling the 4-force useless is very WP:POV. It's a standard approach in many textbooks, as well as an existing article crying out for a link. I think the section as written is too unclear. I'm going to try rewriting it the way I think it should be written, then we can argue about it more if we must. It looks like your editing has died down a bit, so I can get my edits in without an edit conflict. Pervect 08:56, 30 August 2006 (UTC)

Dividing by $d\tau\!$ wont work for particles travelling at c such as photons (in vacuum), gravitons, and neutrinos (for practical purposes). And to integrate the four-force to get the change in momentum you have to keep changing reference frames as the particle accelerates (or go to general relativity and use an accelerating frame reference). With the 3D force, you just stay in the same reference frame and do not worry about whether proper-time is defined or not. JRSpriggs 07:51, 1 September 2006 (UTC)

Massless particles do not have a rest frame, but then they don't accelerate, either. One can certainly use four forces to deal with radiation pressure, etc, the fact that the energy and momentum of massless particles depends on their frame is a feature, not a problem.

The four force is a standard textbook approach to forces. See for instance http://cosmo.nyu.edu/hogg/sr/sr.pdf. Or any of several other textbooks that take this approach. - any approach that treats forces and uses the 4-vector concept, basically.

You seem to have some personal biases in this matter that don't represent standard textbook usage. You are certainly entitled to your personal opinions, but the Wikipedia isn't a place for them, it's a place for standard textbook usages.

I've been waiting a bit to see where you are going with this. It appears to me that you may be attempting to present some form of the "Lorentz force density". (Jackson, pg 611). This works fine for E&M, though it is somewhat complicated to derive. It does not work in isolation, the definition you are giving is not the correct covariant way to describe a general force. What the Lorentz force density says is that when an electromagnetic field interacts with charged particles, the energy and momentum locally lost by the field is equal to that gained by the particles it interacts with. It is not a general definition of force, it does not describe how forces transform covariantly. The 4-force does that job.

I don't have any objection to putting a discussion of the Lorentz force density in the appropriate place, when fully and properly motivated, but it doesn't belong as the general definition of force, it just doesn't work right, and it's not standard. Pervect 17:50, 2 September 2006 (UTC)

"Massless particles do not have a rest frame, but then they don't accelerate, either" - it is not quite correct. Even massless particle can change velocity direction. The equation $\frac{d^{2}x^{i}}{d\tau ^{2}} = \alpha F^{ik}\frac{dx_{k}}{d\tau }+g^{i}$ is still correct to massless particles. Only $\tau \,$ wont be the proper time anymore.--TxAlien 20:10, 4 September 2006 (UTC)

The density of force (which may or may not be Lorentz force) in continuous matter exerted by a force-field is important in its own right and should be mentioned. It is not intended as an alternative to four-force. They apply to different things. Four-force and three-force are applicable to particles or entire objects (if the internal structure is negligible). The density of force is applicable to continuous mediums. The density of force is a tensor (actually covariant 4-vector) density of weight +1 (it is not necessary in SR to distinguish between tensor densities and ordinary tensors) and in SR it transforms like any other covariant 4-vector. This is because the measure of a hyper-volume (dt·dx·dy·dz) is unchanged by a Lorentz transformation, rotation, or translation.

Your statement "Massless particles ... don't accelerate ..." is not accurate. Photons are deflected when they pass thru materials which have a refractive index which varies. And even in a vacuum, gravity can deflect them (although their acceleration is perpendicular to their direction of motion). JRSpriggs 08:12, 3 September 2006 (UTC)

David Hogg's paper gives four-force just one column, doing little more than defining it. He does not use it for anything. I would like you to show me an application of it which cannot be done just as well or better with the three-force. JRSpriggs 08:26, 3 September 2006 (UTC)

Four force, part 2

Photons are deflected by gravity, but they do this because the follow geodesics. There are not any "forces" involved. This is as it should be, for the concept of force depends on the frame used, and a photon has no frame. Matter does change the directions of photons, but this has to be explained in the matter frame, again, photons don't have a frame.

For starters, try "Griffiths, Introduction to Electrodynamics", where four-forces are called Minkowski forces. Also, Misner, Thorne, Wheeler, "Gravitation", which uses them a lot, and explains the concept of "geometric objects" on page 48, of which four-forces are an example. Jackson, "Classical Electrodynamics", uses 4-forces to derive the Faraday tensor (see Force, Lorentz, Covariant form) though otherwise he doesn't use them very much.

Geometric objects, of which four-forces are an example are quite useful to relativity, i.e the following quote from "Gravitation"/

(References) have expounded the mathematical theory of geometric objects. But to understand or do research in geometrodynamics, one need not master this elegant and beautiful subject. One need only know that geometric objects in spacetime are entities that exist independently of coordinate systems or reference frames. A point in spacetime ("event") is a geometric object. The arrow linking two neighboring events ("vector") is a geometric object in flat spacetime, and its generalization, the "tangent vector", is a geometric object even when spacetime is curved. The "metric" (machine for producing the squared length of any vector) is a geometric object. No coordinates are needed to define any of these concepts.

Four forces are the expression of the concept of force as a geometric object. It's that simple, ultimately.

I'm pretty sure Taylor & Wheeler "Spacetime Physics" uses four-forces, but I don't own a copy to double-check. Most of my SR books are really E&M books - or GR books.

Return the challenge - name a reference that supports your POV?

In the same vein, Re "Density of force". It would be helpful here as well to quote a reference. I have never seen a reference to "density of force" outside the concept of electromagnetism. Do you have some reference which supports your usage here?

The density of energy and momentum expressed as a geometric object is not a 4-vector, but a rank 2 tensor, the stress-energy tensor. The geometric representation of a volume element is not a scalar, but a vector - the dual vector to a 3-form. The 3-form represents the volume element, so does its dual. Basically, a volume can be defined by its magnitude, and the direction of the "time vector" orthogonal to the volume. Thus "energy / momentum per unit volume" is covariantly expressed as (rank 2 tensor) * (vector representing volume) = (four-vector energy and momentum contained in volume). This is explained in MTW's "Gravitation".

One can take the divergence of this stress tensor to come up with a vector. This turns out to be zero in general $\nabla_a T^{ab} = 0$ , where T is the stress-energy tensor. So this isn't a very interesting vector, it's zero. It represents the differential conservation laws of energy and momentum.

The concept of force density, as I have seen it derived, comes from breaking up the stress-energy tensor T^ab into two parts, a part representing the stress-energy tensor of the electromagnetic field, and a part representing the stress-energy tensor of the particles only. The equation says that the divergence of the field part is equal to the negative of the divergence of the particle part. This defines the "force density". To define it in this manner comprehensibly, one must first introduce the stress-energy tensor. Again, if you have a reference that says differently, it might help clarify what you are trying to say to quote it. Pervect 18:19, 3 September 2006 (UTC)

Modifying the equation at geodesic equation, we get:

$\frac{dp_\mu}{dt} = \Gamma^{\nu}_{\mu\alpha} p_{\nu} \frac{dx^\alpha}{dt} + q F_{\mu\nu} \frac{dx^\nu}{dt} + \operatorname{other}\,\operatorname{forces}$

where p^μ is the 4-momentum at time t and $\Gamma^{\mu}_{\nu\alpha}$ is the Christoffel symbol. The Christoffel symbol is the force-field of inertial forces, such as gravity, centrifugal force, and Coriolis force. It is not a tensor. One can say that these forces are a fiction which disguises the curvature of space-time, but this might well be true of all other forces also. The equivalence principle implies that curvature and inertial force are equivalent descriptions of reality.

If you had bothered to read to the bottom of my subsection on electromagnetism, you would see that I mention the stress-energy tensor and show how it is related to the force density. They are two different things. The stress-energy tensor gives the flux of momentum and energy thru a THREE dimensional boundary. While the force density gives the amount of momentum and energy changing form (from electromagnetic to material form, say) within a FOUR dimensional body. You are confusing them and then blaming me for your confusion. JRSpriggs 06:11, 4 September 2006 (UTC)

relativity of simultaneity

The relativity of simultaneity article is in very bad need of attention. It is currently poorly written, and the last half is an anti-Einstein diatribe which belongs in relativity priority disputes if it belongs anywhere in Wikipedia. I made an attempt to reduce this article to a stub, but other editors objected and reverted it back.

This is an important sub-topic of relativity, and it is a disgrace to have this important article in the hideous shape that it is now in. I am hoping that others can help me to correct it. Otherwise, I will attempt to have it deleted. --EMS | Talk 02:36, 8 September 2006 (UTC)

The last half of the page is not an anti-relativity diatribe, but a calm presentation of the pre-history of relativity of simultaneity. It may be out of place, or irrelevant, or many other things, but hardly a diatribe. E4mmacro 06:37, 9 September 2006 (UTC)

An article with such a general title and scope should not be treated as a sub-topic of Special relativity theory - instead it is (or should be!) much wider in scope, as discussed on its Talk page. Harald88 13:21, 9 September 2006 (UTC)

little help?

currently im only a year1 math undergraduate so dont laugh as i ask this. in the section

This suggests what is in fact a profound theoretical insight as it shows that special relativity is simply a rotational symmetry of our space-time, very similar to rotational symmetry of Euclidean space. Just as Euclidean space uses a Euclidean metric, so space-time uses a Minkowski metric. According to Misner (1971 §2.3), ultimately the deeper understanding of both special and general relativity will come from the study of the Minkowski metric (described below) rather than a "disguised" Euclidean metric using ict as the time coordinate.

as it says the space of SR uses the Minkowski metric, it doesnt necessarily mean the actually space is a metric space right? because the distance is negative along timelike worldlines, and you have 0 distance between lightlike worldlines so it should be atleast called a pseudo metric space or something. can someone please just say a yes or no to my question? --I got scammed 09:08, 10 September 2006 (UTC)

Right. The Minkowski "metric" isn't really a metric, so Minkowski space isn't really a metric space. —Keenan Pepper 15:35, 10 September 2006 (UTC)

Just in terms of what words are actually used, I don't know that it's fair to say that it isn't really a metric. It's a different kind of metric -- one unlike the metric you talk about in set theory and basic topology. For example, the metric of Minkowski space is generally only defined with the additional stucture of a vector space. (Technically, the Minkowski metric never acts on points in spacetime, but on vectors tangent to the spacetime.) In this context, we're talking about a metric tensor, and usually call something a Riemannian metric if it's positive-definite or pseudo-Riemannian if it's not. Still, in the context of differential geometry, this is usually shortened to just "metric".

If you're taking topology, it might be of interest to note that the (pseudo-)Riemannian metric is not used to define a metric topology. Manifolds (spacetimes) usually are given a metric topology, but it's just the usual Euclidean metric used in a suitable way. Good question, though. This is a useful distinction to make that is rarely explicitly discussed in textbooks. MOBle 21:11, 10 September 2006 (UTC)

GA Re-Review and In-line citations

Members of the Wikipedia:WikiProject Good articles are in the process of doing a re-review of current Good Article listings to ensure compliance with the standards of the Good Article Criteria. (Discussion of the changes and re-review can be found here). A significant change to the GA criteria is the mandatory use of some sort of in-line citation (In accordance to WP:CITE) to be used in order for an article to pass the verification and reference criteria. Currently this article does not include in-line citations. It is recommended that the article's editors take a look at the inclusion of in-line citations as well as how the article stacks up against the rest of the Good Article criteria. GA reviewers will give you at least a week's time from the date of this notice to work on the in-line citations before doing a full re-review and deciding if the article still merits being considered a Good Article or would need to be de-listed. If you have any questions, please don't hesitate to contact us on the Good Article project talk page or you may contact me personally. On behalf of the Good Articles Project, I want to thank you for all the time and effort that you have put into working on this article and improving the overall quality of the Wikipedia project. Agne 00:08, 26 September 2006 (UTC)

Thanks you for your semi-automatic note. But in-line references are unwanted and unnecessary in in overview articles about established topics in physics. All what's stated in this article is standard textbook stuff, and attributing specific sentences to specific sources would be misleading. --Pjacobi 06:18, 26 September 2006 (UTC)

I don't think in-line citations gives the impression that said source is the only source for such information. However, they are vital in maintaining WP:V. I would even say they are more crucial in articles of science and mathematics because of constant awareness of WP:OR. Attributing important claims in the article to a reliable source best accomplishes all that and is simply good form. In light of Jimbo's and the whole of Wikipedia's push for higher standards in all articles, the GA standards are keeping in tow. An article's editors are free to decline inclusion of in-line citations for whatever reason they wish. But unfortunately the article wouldn't pass GA consideration then. Agne 08:20, 26 September 2006 (UTC)

Sorry this is nonsense. And if it is policy, it is nonsense policy. You simply cannot give an inline cite for some statement, which is in tens of textbooks of the subject. At least it would be linkspam, for one particular textbook. Whoever have had course in SR can verify this article, and whoever has not, can not. --Pjacobi 08:50, 26 September 2006 (UTC)

The tens of thousands of books provide amply resources for a cite. And it's not link spam when it is explicitedly ask for by WP:V and WP:CITE. Agne 17:39, 26 September 2006 (UTC)

Why not just provide one good paper on SR? Maybe the original one? --Kjoonlee 10:17, 26 September 2006 (UTC)

OK, I've had a look at the article, and there's not a {{citation needed}} or {{fact}} template in sight. Specifically, what sort of cites do we need? --Kjoonlee 10:21, 26 September 2006 (UTC)

But everything follows from Einstein original paper! It is true that some things, like the fact that what is simultaneous for one observer is not for another, was derived earlier by Einstein. You can choose to mention this by e.g. giving a ref. If you do that, then you are giving additional historical information. If you don't then that's ok. too because it also follows from the basic theory of special relativity which is explained in the article. Count Iblis 15:26, 26 September 2006 (UTC)

If you think the criteria for good article candidates to be problematic, please make your voice heard at Wikipedia talk:Good article candidates#Discussion on criteria changes. Thank you. --Kjoonlee 16:22, 26 September 2006 (UTC)

If the reviewer would kindly tag some facts that need citation, we could supply references for them. Otherwise, we could easily sprinkle some around randomly, but what purpose would that serve? — Laura Scudder ☎ 17:32, 26 September 2006 (UTC)

The notice above is simply that a fuller review will come be coming and the one of the criteria is in-line citations that will pass WP:V. The simply nutshell is that if there is an important claim in the article, that article should have a source. Now you could wait till a full review comes and if the reviewers deems the article to fail because of references and verifiability they can point out those particular absences of cites. My notice is just a friendly heads up to make take a look at the article beforehand. Agne 17:39, 26 September 2006 (UTC)

I have to point out some pertinent details from the main policy that has driven this. From WP:V..."The threshold for inclusion in Wikipedia is verifiability, not truth." Followed by the Section on Burden "The burden of evidence lies with the editors who have made an edit or wish an edit to remain. Editors should therefore provide references. If an article topic has no reputable, reliable, third-party sources, Wikipedia should not have an article on that topic."

Simply put, it is not the readers job to find a mainstream physics book in order to verify any particular aspect of the article. The burden lies squarely with the editors. I think especially with Math and Science articles, the need for in-line citations is even more abundant given the weight of WP:OR. We have to expect that a significant portion of this article's readership will be "non-experts" as well and they would have no way of knowing that these are mainstream with physics. The attaching of a reliable source will at least give creed to that notion. In all honestly, this is not new. It is something that the foundational wikipedia guidelines have asked for all along and in a time when Jimbo and the rest of the Wikipedia community are steering towards more quality over quantity, the GA project is moving accordingly. I don't doubt the truth of this article or that it is mainstream physics. But it has never been about truth but rather verifiability. Agne 17:39, 26 September 2006 (UTC)

it is not the readers job to find a mainstream physics book in order to verify any particular aspect of the article

This is, in fact, is already done for them. Several good SR texts are listed at the end of the article. Any one of them can be used to verify the vast majority of the article. Inline cites would look like a sea of cites to the favorite book of whoever added the cites.

I firmly agree that any potentially controversial facts or experimental numbers need inline cites. Over at Wikipedia talk:Good article candidates suggestions were made that a certain density of cites is desirable. I am trying to point out that there are circumstances were that's unnecessary, where almost everything is easily verifiable in any one of your favorite SR textbooks. — Laura Scudder ☎ 17:52, 26 September 2006 (UTC)

I have made a request regarding this issue here. --ScienceApologist 21:11, 26 September 2006 (UTC)

just another header

I really don't understand the opposition to in-line citations here. There are statements in this article refering to pre-relativity ideas, and others that refer to consequences and elaborations on the theory that were discovered after June, 1905. (For example, E=mc² was initially propsed in late 1905, and the tensor represtantation was pioneered by Hermann Minkowski in 1908.) Even those items that relate to the 1905 article are often more effectively described and elaborated on it respected textbooks. As a result, this article would benefit from a robust program of in-line documentation. --EMS | Talk 21:45, 26 September 2006 (UTC)

Part of the problem is that it is not clear to me how many citations are necessary. After I rewrote the subsection on "Electromagnetism in 4D", I put my source Formal Structure of Electomagnetics: General Covariance and Electromagnetics by E.J.Post into the list of references and I thought that that would be sufficient. Now you are telling me that I have to convert it into a footnote? (Which I do not know how to do.) And is it sufficient to put one note at the beginning of the subsection or must I put the note on every one of the formulas in the subsection? Or what? Do you want a page number for each formula? JRSpriggs 03:50, 27 September 2006 (UTC)

@EMS: Important historical information has to be put in prose, not in footnotes alone. But sure, in "history" sections, we can as far as possible link to the original paper -- which in typical cases BTW, doesn't improve verifiability (let alone for laymen), the key argument at WP:GOOD and WP:CITE. --Pjacobi 07:21, 27 September 2006 (UTC)

I fully support the inclusion of in-line citations to this (and all) articles at Wikipedia. Agne and EMS have made their points very clear about this, and I agree with those points. I have recently been incorporating in-line citations to articles, in particular, general relativity (which, in general terms, should be an article similar to special relativity). Editors may wish to look at this article for the sort of approach to citations I think we should be aiming for. Also have a look at tests of general relativity. MP (talk) 15:15, 27 September 2006 (UTC)

I came here after reading Pjacobi's comment on WP:Cite, and although I have sympathy for the constructors of excellent articles like the one here, I don't agree that adding citations is particularly difficult or unnecessary. Yes, the blue tags look a little ugly, but as Wikipedia moves into the new referencing era (references are the only way to build trust in an encyclopedia still thought to be a dubious source of information), I'm sure it won't be long until the tags and footnotes are hideable. Though some editors may object, I suspect there is no turning back with this one, so it's worth trying to get up to pace.

I should say that I'm a nobody on Wikipedia, unconnected with any of the work behind these new policies. But my opinion is that there should always be referenced information about the historical context of any scientific article; in particular, the big breakthroughs should be referenced. The best references for these would probably not be textbooks but rather the most authoritative biographies of scientists or studies of particular scientific developments or movements. When it comes to explaining basic scientific processes, on the other hand, the best references would probably be the best or the standard textbooks. The fact that there might be thousands of textbooks explaining the same thing should make it easier, not more diffcult, to give a reference. As long as a textbook is known to be reliable, it doesn't matter which one is referred to at all.

The trouble is that this will all seem like a drag and will of course take time. In the case of the present article, much of the necessary information seems present in linked articles on the papers and on the history of relativity, however; even so, each article should, I think, be referenced in itself, even if the same reference has to be remade on linked pages. I imagine that the people who write and edit these articles have good reference books on their shelves at home with which they could easily bring articles like this back up to good-article requirement. For those who are not used to it, referencing is not hard to learn at all, and it can actually be good fun; the best references, in my opinion are those which give page numbers. The question of where to reference is a matter of common sense. For example, if several sentences in an article can be referenced from a particular page or sequence of pages in a book, it is enough to give one reference; the reader who checks the reference will soon see what part of the article that part of the book verifies. (References, of course, are not intended to verify truth; they verify that what we say in the article was already said by someone else in print.) qp10qp 15:49, 27 September 2006 (UTC)

qp10qp:...long until the tags and footnotes are hideable. I will not mind the tags when I have an option not to see them when I read the article. Until then, I strongly object to trashing a good article (indeed) with this citation needed nonsense. For this I am reverting Agne's edit. (Igny 20:24, 27 September 2006 (UTC))

I concur with this revert, because the citation tags were placed on basic, non-controversial facts about SR. They can all be found in any of the textbooks listed at the bottom of the article. WP:V does not require that every single line can be individuall verified by a person with no knowledge of the subject. -- SCZenz 20:28, 27 September 2006 (UTC)

@MP

If you can simultanously fulfill GA-expectations and the desire for a scientifically sound article, all the better. That I don't subscribe to this belief, doesn't mean I want to stop someone trying it. I've looked a General relativity and if I'm not mistaken, the footnotes are of the historical type, linking to the original paper where a result or prediction was first published. This is nice and useful, but I'm unclear whether it fits the idea of inline-citing for verifiability held by the WP:GOOD project.

But at GR, no verifying source is given for phenomena that in classical mechanics are ascribed to the action of the force of gravity [...] are taken in general relativity to represent inertial motion in a curved spacetime, just as her no source is given for two events happening in two different locations that occur simultaneously to one observer, may occur at different times to another observer. And I hope it stays so.

--Pjacobi 16:01, 27 September 2006 (UTC)

Did she get one right?

Looking over the items which Agne27 marked with "citation needed", I have to agree that most of them are common knowledge among physicists. However, there is one (second paragraph of "Status") which I doubt, namely "Because of the freedom one has to select how one defines units of length and time in physics, it is possible to make one of the two postulates of relativity a tautological consequence of the definitions, but one cannot do this for both postulates simultaneously, as when combined they have consequences which are independent of one's choice of definition of length and time.". Can someone justify this (the first clause)? JRSpriggs 05:55, 29 September 2006 (UTC)

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