Talk:Introduction to special relativity

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Summary of previous talk

The archived talk is largely a debate about whether this article is sufficiently non-technical. There was some debate about whether it is actually possible to create an article that does not mention that SR is a modification of Pythagoras theorem yet still transmits the idea of relativity. (It should be noted that the article on Pythagoras theorem is not without maths). The resolution to this problem is probably to produce an entirely non-technical intro to SR to complement this current article. There is room for both a "less technical" and a "non-technical" approach.

Purpose of this article

This article gives a clear explanation of the statement on the first few pages of most modern, advanced textbooks on relativity: the space-time interval is invariant under rotations in space and time. If students can understand this statement they can understand relativity. The history of relativity and the, nowdays, pointless debates about the ether and light propagation are unnecessary here. Worse still, for this article they are a diversion and should be removed whenever anyone adds them. The purpose of this article is solely to introduce the modern reasoning behind the theory.

The maths of the modern theory is unimpeachable. Physicists have determined that this maths describes the classical physics within the scope of the theory. It is possible in the future that experiments will show that the maths is a simplistic description or even an incorrect description of the world, when this happens a new mathematical description will be applied and science will advance a further step. The only issue confronting the scientist is whether the modern theory fits the physical data - not whether "Einstein was wrong" - the modern theory is actually rather different from Einstein's original work although it produces the same net result in the form of the same Lorentz transformations. Geometer 12:49, 11 April 2007 (UTC)

Failed GA nomination

I am failing this GA nomination for several reasons:

• 1 (a) The writing is unclear at many points and hard to follow (e.g. "the thing" is a very abstract description of line h in figure 1.1); in some places, it is simply grammatically incorrect (e.g. sentence fragments).
• 1 (b) The structure of the article is overly complex. Most "introductions" to special relativity, such as those in The Elegant Universe, begin with reference frames, a much easier idea to understand. Even the special relativity article itself begins with that.
• 1 (d) I found the graphs difficult to interpret (e.g. Figure 2a - is that a 3D box?). It has been suggested to me as well that it is strange to include a graph with a left-handed coordinate system in a physics article.
• 2 While this article is written about a topic of generally accepted scientific knowledge, it still needs to provide references to a few textbooks or other reliable sources not only to back up its explanations but also to bolster wikipedia's reputation and to offer readers additional resources if they are curious to learn more.
• Finally, on a personal note, I want to add that I found this page very difficult to follow and I am a well-educated, avid reader of popular science books. When there are two separate pages on a topic, one ostensibily labelled as an "introduction," it does not make sense for both of them to be highly technical and confusing to the lay reader. I want to make it clear that I am not failing the page on these grounds, as that would be inappropriate according to GAC; I just think that the editors need to rethink their audience. Awadewit 00:26, 17 April 2007 (UTC)

At last, a considered and neutral set of comments about this article!

• The readability of the text should be improved.
• The graphs should be replaced.
• References need to be expanded.

(b) and the final note are related comments. The purpose of the article is to introduce the modern approach to relativity. The old approach that begins with reference frames and Galileo, moves on to the MM experiment and finishes with Einstein misses the modern approach altogether. Furthermore studies show that the old approach fails to explain relativity theory See Student understanding of time in special relativity: simultaneity and reference frames by Scherr et al. This failure to explain relativity is not a trivial matter. Students genuinely think there is something wrong with the theory after being exposed to the old approach. Quite rightly they believe that simply assuming that the speed of light is constant is outrageous and seek other explanations in revivals of aether theories etc. If they start with the modern approach they are unlikely to fall into the same trap. Geometer 09:57, 17 April 2007 (UTC)

"...We have in the special theory of relativity the Minkowskian geometry of a flat 4-space with indefinite metric... Unfortunately, it has been customary to avoid this geometry, and to reason in terms of moving frames of reference, each with its own Euclidean geometry. As a result, intuition about Minkowskian space-time is weak and sometimes faulty...."J.L. Synge, \Intuition, geometry, and physics in relativity," Annali di Matematica pura ed applicata, 54, 275-284 (1961).

"Many textbooks2 3 4 5 6 introduce proper-time by analyzing the propagation of a light in a light clock,1 7 8 9 10 11 which consists of a pair of mirrors that face each other and are separated by a proper distance L. One tick of this clock is the duration of one round trip of a light ray bouncing back and forth between these mirrors. The analysis is usually done in the context of a simpli¯ed Michelson-Morley apparatus12 whose arms may be regarded as light clocks. Unfortunately, most of these presentations2 3 5 work in moving frames of reference without making the connection to the space-time formulation, ¯first introduced by Minkowski13 in 1907 and later extended by Einstein.14"Roberto B. Salgado Visualizing Proper Time (2001)

etc. etc. The old approach is a mistake. Geometer 11:25, 17 April 2007 (UTC)

Improving the article

Its good that you have offered to help on this. The problem with teaching modern relativity is that there is a shared misunderstanding of the topic. Academic research has identified that this misunderstanding originates in the standard approach to teaching the subject (reference frames, Galileo, MM, Einstein etc.) - see Talk:Introduction to special relativity. Sixty six percent of physics undergrads get relativity wrong. Basically if Wikipedia goes for the old approach we will just be providing large numbers of extra contributors to newsgroups who are convinced that "Einstein was wrong". Einstein's assumption of the speed of light as a constant without reference to the way that this is a feature of spacetime seems absurd to most students and they go away thinking this is just a "fix". Worse still some of them waste their time trying to work out how a 3D Euclidean universe could give the illusion of a constant speed of light. A simple intro to the invariance of the space-time interval ("proper time") in a flat Minkowskian spacetime will prevent these misunderstandings from the outset. This sounds complicated but its just a minor extension to Pythagoras' theorem. Geometer 15:33, 17 April 2007 (UTC)

It is interesting that I was probably one of those undergrads who misunderstood SR for a long time. It wasn't until I started studying General Relativity and so had to go back over the development of SR that I really understood it - but there's so much of that when studying science. It's not that the teaching is bad or that the students are incapable, it's just that, often, you have to understand something far more complex to be able to properly understand the thing you're being taught. So, basic chemistry is still taught in terms of electron energy levels even though that is a flagrant simplification of the true situation.

So, we have a dilemma. We don't want to teach SR using over-simplifcations because that would be wrong. However, we can't teach SR properly because that gets too complicated. My initial thinking as to how to resolve this dilemma is to avoid entirely the article's current approach of trying to "teach" SR and instead just "explain" SR. To explain what I mean by this: idiot's guides on all sorts of topics and most basic self-learning books for computer programming are based around presenting lots of examples to the reader. They don't try to teach the fundamental building blocks, because those blocks are actually trickier to understand than the overall concept.

I think a similar approach might work on the SR article - trying to choose some examples to illustrate and explain SR that are devoid of mathematics and pythagorean theory. For those who are able to grasp those initial concepts, we can then build on that understanding by introducing some of the mathematics. This means that we would end up with a tiered article which ends up explaining SR at several different levels - but level one must be completely absent of mathematics in my view. I need to think about this further, but hopefully will be able to drop by at the article itself in a couple of weeks and try some edits. GDallimore (Talk) 16:20, 17 April 2007 (UTC)

Sounds good. I contemplated this but is it possible to explain Pythagoras' theorem (the metric of 2D euclidean flat space) without any maths at all? The challenge of explaining Minkowski spacetime is similar but worse.... Geometer 16:47, 17 April 2007 (UTC)

That's the thing - at it's most basic level you shouldn't need to explain any of that stuff. Those are the building blocks that SR are built on, not SR itself. They can be brought in later in the article, but they should not be the starting point. GDallimore (Talk) 17:17, 17 April 2007 (UTC)

You're right, of course, there must be a way to explain this subject without too much complexity. Our problem is that all those beginner's guides to relativity have cribbed from each other and perpetuated the wrong approach so we are left with trying to explain the subject from scratch.

It might help to revisit the real origins of the theory. Einstein studies Maxwell and realises that "c" is frame independent and proposes that physical laws are invariant. He derives the Lorentz transformation (LT) and realises that the equations contain nothing but spatiotemporal quantities. Therefore no aether. Minkowski, who has studied non-euclidean geometry, realises that the purely spationtemporal content of the equations means the LT is about geometry hence Minkowski's metric and, with Noether's insight into invariance and physical laws, the modern approach is born. Einstein's original proposal that physical laws are invariant looks like a guess although it is probably based on Galileo's ship analogy.

Curiously, given Einstein's original opposition to Minkowski, there is a quote somewhere by Einstein where he says that he cracked SR after realising that time was to blame (I can find the quote if need be).

There is a lot of crud on the periphery of this story in the form of attempts to explain the aether by Lorentz, Fitzgerald, Lamor, Poincare etc. Einstein himself says that he had not even considered the MM experiment when he derived SR. Some people say this is impossible but MAXWELL + GALILEO = SR whichever way you look at it. So is the desire to weave the history of the aether into SR due to latent three dimensionalism in those 66% of physicists who dont get SR? Geometer 10:13, 18 April 2007 (UTC)

Galileo does look to be a good starting point since everyone would understand that, even if they don't know what Galilean/classical relativity is. The more I think about this, though, the more I realise I need to refresh my memory of some of the intricacies. Sigh... the more I learn, the more I forget... :) Sorry I can't respond more carefully to your detailed thoughts yet, but it has been a while since I've considered all these things myself. Will get back to this soon, though. GDallimore (Talk) 10:48, 18 April 2007 (UTC)

Here is an interesting ref: http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1972Obs....92..102J&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf It shows that this problem was around years ago. Geometer 14:01, 18 April 2007 (UTC)

Second Application for GA status

I hope you will forgive me for putting this article back in for GA nomination but the previous critique was excellent and has led to numerous changes. However, if the history of the article is inspected it will be seen that these changes are largely changes in presentation and style, not changes in content. Geometer 13:20, 20 April 2007 (UTC)

Comparison of clock readings at different places in a reference frame

If an observer has two synchronised clocks at two different places in his inertial frame of reference they read the same time. Time is not position dependent within a given frame of reference. It is only when clocks are compared between frames of reference that position dependence occurs. Please do not remove the text that describes this. Geometer 10:42, 25 April 2007 (UTC)

The standard time dilation equation Dt = DT / sqrt(1-v^2) is only valid for pairs of events that satisfy DX = 0. Just look at the Lorentz transformation. DVdm 10:53, 25 April 2007 (UTC)

"Just look at the Lorentz transformation" is not an argument. Please give the exact reasoning why the time interval reported for an observer for a clock on his lap will differ from the time interval reported by the same observer for a different clock a mile away. Your contention when you say that DT at X=0 is not the same as DT at X=1500 is that clocks in a given frame of reference are not synchronous. Please justify this. Geometer 11:06, 25 April 2007 (UTC)

Lorentz transformation equation Dt = (DT + v DX) / sqrt(1-v^2) reduces to time dilation equation Dt = DT / sqrt(1-v^2) if and only if DX = 0. If you have two events that are not colocal in the (T,X)-frame, then the time between these events in the (t,x)-frame is Dt = (DT + v DX) / sqrt(1-v^2). This is pretty elementary, I'd say. DVdm 11:42, 25 April 2007 (UTC)

Geometer, I have split the section into two parts, to assure that the idea of the Caveat does not interfere with your agenda. DVdm 12:00, 25 April 2007 (UTC)

Sounds like confusion over the meaning of "reads the same time" to me and that both of you are right depending upon the interpretation of that phrase. In any event, neither of you are putting in proper inline citations to any of the stuff you're doing so it's not a surprise that you're arguing over the content.

In my view, there is no way that this article currently meets GA status without more inline referencing when the topic is this complex. A DVdm, remember that this is an introduction. I think that some of your edits are a bit jargon-heavy. GDallimore (Talk) 12:38, 25 April 2007 (UTC)

GDallimore, some of my edits a bit jargon-heavy? Almost everything you see is Geometer's edits. He rewrote the entire article. The only edit you see from me is the one under the caveat, and it has been around since a long time. The only problem with it, is that it doesn't fit into what Geometer is trying to make from this article. He clearly has not understood what it is about. DVdm 14:41, 25 April 2007 (UTC)

Yes, I rewrote the article to try to make it GA. If there is jargon lets get rid of it. The article is a breath of fresh air in this field because it goes straight for spacetime, no messing. But can we do it justice. Geometer 16:25, 25 April 2007 (UTC)

DVdm, your equation derived from the Lorentz transformation shows where we differ. The Lorentz transform for time is:

$t={\frac {t^{'}+(v/c^{2})x^{'}}{\sqrt {(1-v^{2}/c^{2})}}}\,$

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/ltrans.html#c2

For a difference between two times is:

$t_{1}-t_{2}={\frac {t_{1}^{'}+(v/c^{2})x^{'}-t_{2}^{'}-(v/c^{2})x^{'}}{\sqrt {(1-v^{2}/c^{2})}}}\,$

See http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/tdil.html#c2

The important thing to note is that the clock is at the same position $x^{'}$ in its own reference frame.

The result is that:

$t_{1}-t_{2}={\frac {t_{1}^{'}-t_{2}^{'}}{\sqrt {(1-v^{2}/c^{2})}}}\,$

Now, what you have done is assumed that the clock changes position in its own frame during the measurement of the interval:

$t_{1}-t_{2}={\frac {t_{1}^{'}-t_{2}^{'}+(v/c^{2})(x_{1}^{'}-x_{2}^{'})}{\sqrt {(1-v^{2}/c^{2})}}}\,$

(ie: Dt = (DT + v DX) / sqrt(1-v^2)) This is not the standard treatment. The clock can be anywhere in its own frame $x^{'}=1000,x^{'}=100000$ so long as it stays there during the interval measurement. Your contention that time dilation only applies for clocks located at the origin (X=0) is unnecessary. The illustration showing the correct analysis should be restored.

Geometer, it seems that you completely missed the point again. I don't talk about clocks located at the origin (X=0). I talk about clock ticks being colocal, which is expressed by $\Delta X=0$. Try reading what is under the heading Caveats and interpreting it independently of your agenda. The Deltas are differences between two events. In the case of a moving clock, these events are colocal in their own rest frame, expressed by $\Delta X=0$. In the case of the moving rod, the events must be simultaneous in the frame in which the rod is moving, expressed by $\Delta t=0$. In the original format, there were no Deltas present, because one of the events was taken to be at the origin. DVdm 14:41, 25 April 2007 (UTC)

This brings us to two issues:

1. Perhaps it was deleted as part of a general "reversion" of the paragraph but the illustration that demonstrates that time intervals occur between planes of simultaneity at a given point in a reference frame has been removed. Given that the text above is merely confirming this we should reintroduce the picture (with appropriate text).

Introduce all you want, it was irrelvant in the Caveats section. You still haven't got the point. DVdm 16:42, 25 April 2007 (UTC)

2. The old issue of deriving length contraction from time dilation. Obviously, for the speed of light to be constant, this must be a valid operation. If the time taken for a light ray to bounce back from a mirror in one frame is "t" the time for this same event in another, relatively moving, frame will be the time dilated "T". The two intervals refer to the same events (the emission, bouncing off mirror and receipt in the first frame) and the length of the light paths will be related by the length contraction equation. There is no doubt that c=DX/DT and that c=Dx/Dt and that, as it is an event that is in common between the frames Dt = DT/ sqrt(1-v^2)). It is hence mathematically valid in this specific case to write that DX/DT = Dx/Dt and so get the length contraction equation. Using a light path as a measuring rod is standard relativity. All we are saying is that if Bill gets t for the time taken for light to bounce off a mirror John will get the time dilated T and this T can be used by John to calculate the length of the light path in his own frame. In other words your warning is unnecessary provided the setup by which length contraction is derived from time dilation is carefully described.Geometer 16:12, 25 April 2007 (UTC)

Of course this equation DX/DT = Dx/Dt can only be valid for two events that take place on a light signal, in which case both sides reduces to c. That is trivial. In the caveats section o.t.o.h. I warn about directly and erroneously deriving this equation from the equations for time dilation and length contraction. The way DX, DT, Dx and Dt are measured is entirely irrelevant. Use light signals or measuring rods or whatever you fancy. In these equations the Deltas are differences between coordinates of events. As the Lorentz transformation equations should make trivially clear to you, both equations can only be valid together if DX = DT = Dx = Dt = 0. DVdm 16:42, 25 April 2007 (UTC)

Please could you either quote a reference for the assertion that "both equations can only be valid together if DX = DT = Dx = Dt = 0." or show the full mathematical derivation of this statement. Geometer 08:11, 26 April 2007 (UTC)

A reference... Duh. You must be joking :-)

Here is A Full Mathematical Derivation:

Lorentz transformation valid for any pair of events with coordinate differences Dx and Dt in (x,t)-frame, corresponding to DX and DT in (X,T)-frame:

DT = g ( Dt - v Dx ) [eq1]

DX = g ( Dx - v Dt ) [eq2]

Dt = g ( DT + v DX ) [eq3]

Dx = g ( DX + v DT ) [eq4]

where g = 1/sqrt(1-v^2) and we use units with c=1 (and obviously v <> 0).

Time dilation equation for clock at rest in (X,T)-frame:

Dt = g DT [eq5]

Length contraction equation for rod at rest in (X,T)-frame:

Dx = 1/g DX [eq6]

Lower highschool algebra:

[eq3] and [eq5] ==> DX = 0 [eq7]

[eq2] and [eq6] ==> Dt = 0 [eq8]

[eq5] and [eq8] ==> DT = 0

[eq6] and [eq7] ==> Dx = 0

So, taking equations [eq5] and [eq6] together for one pair of events ==> DX = DT = Dx = Dt = 0.

I told you before: you have to understand the physical meanings of the variables before you mess around with the equations: physics is not a branch of mathematics.

DVdm 10:02, 26 April 2007 (UTC)

(reset indent)

The problem here is that you are not using the definition of a reference frame as a collection of comoving observers each with their own synchronised clock.

Your point that Dt = g DT is constrained for DX=0 is not strictly correct.

I think the main problems are

(1) that you have a severe reading comprehension problem. Nowhere do I say that X = 0.

(2) that you have no idea what you are talking about. Read my lips: you have to understand the physical meanings of the variables before you mess around with the equations: physics is not a branch of mathematics.

Remainder ignored (unread). DVdm 15:44, 26 April 2007 (UTC)

This was simply a typo. "You have no idea what you are talking about" is not an argument, it is an insult. Geometer 21:37, 26 April 2007 (UTC)

If it was not a typo, it makes it even worse. It shows that you have no idea what the Lorentz transformation does. It shows that you don't know the meanings of the variables. It shows that you don't know what events are. It shows that you have no idea about analytic geometry. It shows that you have no idea about the very basics of special relativity. You don't get the point of the remark and for some reason unknown to me, you drag in al sorts of irrelevancies.

Don't take this as an insult. It is not meant a such. I don't think I can help you, sorry. DVdm 09:34, 27 April 2007 (UTC)

Yes, for a GIVEN clock: Dt = g DT when DX is 0

But for two clocks separated by n metres in frame X,T

Dt = g DT(1)

Dt = g DT(2)

Because although each individual clock must stay in place during a measurement two separate clocks will give the same interval for a given event. ie:

DT(1) = DT(2)

So DX=0 is only a constraint for a particular clock.

Now, in a given frame of reference clocks are synchronised, they dont just give the same intervals, they give the same absolute readings.

In a given frame intervals can be determined within AND between clocks:

If DT(1) = D12 - D11

and DT(2) = D22 - D21

Then DT= D12 - D21

and DT=DT(1)=DT(2)

So why does the Lorentz transformation contain the phase term vx/c^2? If an observer in a relatively moving frame reports that DT=DT(1)=DT(2) why does an observer in another frame disagree?

The reason for this is that the Lorentz Transformation compares the absolute time in one frame with that in another for a single observer. The use of synchronised clocks at different positions in the moving frame will be perplexing to the stationary observer because it will appear to him as if they have all been artificially set out of sync by the amount of the phase term.

Thus the use of synchronised clocks is consistent with the LT but instead of Dt = g (DT + v DX) we have Dt = g (DT - vDX + vDX), the extra phase term being introduced in the synchronisation procedure.

Given this, how can we measure the length of a rod? Suppose we place a mirror at one end and time how long light takes to go to the end and back:

DX = cDT (where T is half the overall time interval)

This works because the rod, the timing device and the mirror are in the same frame of reference. Only the light moves, v is 0 so g is 1 and vx/c^2 is 0.

We can do the same thing for a moving rod in its comoving reference frame:

Dx= cDt

But can we do it BETWEEN frames? Can we measure the length of a rod that is stationary in one frame from another, moving frame?

The definition of a reference frame is a collection of comoving observers each with their own synchronised clock. All we need to do is observe the reading on the clock that is adjacent to front end of the rod when the light is emitted and then read the clock that is adjacent to the front end of the rod when the reflected light returns.

We can then use Dx=cDt to determine the length of the rod as measured from the moving frame.

Clearly then x/t = X/T can be used to compare the two lengths.

Your objection, based on the LT for a single observer, does not take into account the synchronisation procedure between clocks in an inertial frame of reference. Geometer 14:01, 26 April 2007 (UTC)

Incidently, the derivation of length contraction from time dilation is the standard method:

http://www.cosmo.nyu.edu/hogg/sr/sr.ps

http://physics.ucr.edu/~wudka/Physics7/Notes_www/node79.html

http://www.pa.msu.edu/courses/2000spring/PHY232/lectures/relativity/contraction.html

http://www.drphysics.com/syllabus/time/time.html

etc....

Geometer 16:00, 26 April 2007 (UTC)

GDallimore please could you put citation notices on the text. Geometer 13:01, 25 April 2007 (UTC)

This brings us to the second point, with the use of a mirror it is possible to measure the interval required for a light ray to traverse a given distance with a single clock. It is also possible for synchronised clocks in the same frame of reference to give the same result. The existence of these possibilities means that it is valid to use the time dilation equation plus the constancy of the speed of light to derive the length contraction result. Geometer 13:33, 25 April 2007 (UTC)

A Failing in Wikipedia

As can be seen above, someone with a particular viewpoint can just block an article in Wikipedia. The section on "Caveats" is non standard and unreferenced. It has been shown to be incorrect but it must remain. The common reasoning where length contraction is derived from time dilation has also been blocked. I will remove the application for GA and stop bothering with this article now. Geometer 21:42, 26 April 2007 (UTC)

I think the fact that two people who both appear to know what they're talking about to an exernal observer who's only vaguely following the discussion illsutrates that the topic under discussion is not an introductory issue. I have therefore remove the entire section as being inappropriate for this introductory article. I'm sure the discussion would be better received and more widely discussed on the main Special relativity article. GDallimore (Talk) 09:43, 27 April 2007 (UTC)

In fact, I've moved it there myself. GDallimore (Talk) 09:46, 27 April 2007 (UTC)

Although it is extremely basic and entirely correct, it's a good idea to move the section to the main article. As a matter of fact, I was planning to do it myself, since this introduction seems to have become Geometer's private project anyway, and for obvious reasons I don't feel like revising it. DVdm 12:42, 27 April 2007 (UTC)

Much improved, but still needs work

This article is now very much imporved. It is much more direct and readable. However, some failings still remain. There is no discussion of why SR was developed and what it achieves. The postulates are not discussed. The effects are not summarized at the start. So I strongly adivse keeping what Geometer has done, but get it "packaged" in supproting text that helps to orient a reader to what is going on.

This is a topic that is going to be in need to development and enhancement for some time to come. I believe that there is a good way to orient people to what SR is about and that this is the place to do so. However, figuring out how to do it is a serious issue, and it seems to me that this puzzle has not been properly figured out yet. --EMS | Talk 15:32, 27 April 2007 (UTC)

With all due regard to Geometer's careful edits, I fully agree and think EMC has hit on a number of important points which I had doubts about myself. These articles take time. Let's not rush it. I mean, Einstein isn't going to care if it takes a little while longer... GDallimore (Talk) 15:45, 27 April 2007 (UTC)

Common misconceptions

This item has the misconception itself that mass increases with speed. It also fails to mention other misconceptions. Ems57fcva saw that I edited it and reverted without discussion. I think this is not good form and represents vandalism. To Ems57fcva: please either discuss here what you object to or put back my version. Thanks. Edgerck 10:32, 22 May 2007 (UTC)

BTW, my edit is available here [1] Edgerck 10:36, 22 May 2007 (UTC)

The NPOV flag is crazy, the article talks about relativistic KINETIC ENERGY as the source of Newtonian physics and is correct in this sense. The use of "mass" in this context is arithmetically correct but is indeed a bone of contention amongst some physicists. Wikipedia is a place where articles should agree with most textbooks and the note on relativistic mass and Newtonian physics does indeed agree with most textbooks. It is clear that Edgerck loves the relativistic mass debate but this introductory article is hardly the place to indulge it! 86.11.125.124 09:45, 28 May 2007 (UTC)

I'm no expert but I think this depends on how you define mass: you can either define it so it remains constant, then momentum = gamma * mass * velocity, or you can define mass so that it changes with speed (relative to the observer, of course) and keep the non-relativistic definition of momentum. I believe some sources use one convention and some another. Can anyone confirm this? Bistromathic 16:27, 25 May 2007 (UTC)

Richard Feynman in The Character of Physical Law wrote "The energy associated with motion appears as an extra mass, so things get heavier when they move." This POV is outdated and not used in physics today. I am sourcing this, according to WP:RS, to (inter alia) Mass. Thank you for your comment. Edgerck 19:28, 25 May 2007 (UTC)

Take this debate to the main article on relativity. Why are you indulging it here? 86.11.125.124 09:46, 28 May 2007 (UTC)

Because the current version of THIS page section says otherwise. The POV expressed by the current section is not mainstream for more than 50 years in research and more than 30 years in textbooks, and therefore, does NOT belong in WP -- much less in an introductory article. See the mainstream references (it is easy to find even more):

1. Lev Davidovich Landau and Evgenii Mikhailovich Lifshits, (1987) Elsevier, ISBN 0750627689.
2. Lev Okun, The Concept of Mass, Physics Today, June 1989.
3. "Does mass change with velocity?" by Philip Gibbs et al., 2002, retrieved Aug 10 2006
4. Edwin Floriman Taylor, John Archibald Wheeler, Spacetime Physics: introduction to special relativity, W.H.Freeman & Co Ltd (1992), ISBN 0716723271.
5. Lev Borisovich Okunʹ, The Relations of Particles, (1991) World Scientific, ISBN 981020454X, p. 116-119, 127.
6. Usenet Physics FAQ
7. Gary Oas, On the Abuse and Use of the Relativistic Mass, 2005.
8. "Does light have mass?" by Philip Gibbs, 1997, retrieved Aug 10 2006.
9. "What is the mass of a photon?" by Matt Austern et al., 1998, retrieved Aug 10 2006
10. William S. C. Williams, Introducing Special Relativity, CRC Press (2002), ISBN 0415277620
11. "Ouch! The concept of `relativistic mass' is subject to misunderstanding. That's why we don't use it. First, it applies the name mass--belonging to the magnitude of a four-vector--to a very different concept, the time component of a four-vector. Second, it makes increase of energy of an object with velocity or momentum appear to be connected with some change in internal structure of the object. In reality, the increase of energy with velocity originates not in the object but in the geometric properties of space-time itself.", in Edwin Floriman Taylor, John Archibald Wheeler, Spacetime Physics: introduction to special relativity, op.cit.

Therefore, to avert a dispute and restore what is correct under WP:NPOV and WP:RS, and continue the dialogue and editing from what is WP correct, I leave it in the editor hands who reverted from my previous edit, available here [2], please revert back. Thanks. Edgerck 21:12, 28 May 2007 (UTC)

From my observation it's Edgerck who is doing the POV pushing here. As some of the references he has been citing actually confirm, the notion of relativistic mass has been used, and was never a misconception or an error, but simply a different use of language and a different bookkeeping method. Yes, it's an unfashionable one currently, and I'm happy to defer to the physicists on the point that there are good reasons for that -- but a misconception it is not. It is not WP's function to enforce linguistic uniformity; we should report these usages neutrally, and also report which ones contemporary physicists prefer. --Trovatore 21:20, 28 May 2007 (UTC)

I agree with Trovatore if he means that "relativistic mass" should be in the historical notes, because so it was in my edit. But "relativistic mass" should not be used to explain anything, as that is known to be confusing (see Wheeler quote above). BTW, this is what Jimbo had to say about this:

1. If a viewpoint is held by a significant minority, then it should be easy to name prominent adherents;
2. If a viewpoint is held by an extremely small (or vastly limited) minority, it does not belong in Wikipedia (except perhaps in some ancillary article) regardless of whether it is true or not; and regardless of whether you can prove it or not.

The case is that we cannot find any prominent adherents to the case of "relativistic mass". So, it should properly be in the history notes and not in any functional way, or as minority view today.

BTW, I have seen that often a call for POV neutrality is followed by an argument that the person making the neutrality call is pushing a point. Yes, this is true in this case. I'm pushing for neutrality. There should be no compromise in this point either. Thanks. Edgerck 21:29, 28 May 2007 (UTC)

It does appear that in this particular case I misguessed what the dispute was, and I apologize for not having looked beforehand. The apology is limited to this one instance and should not be taken as buying your claim that you are promoting a neutral POV. --Trovatore 07:50, 30 May 2007 (UTC)