Talk:Length contraction/Archive 1

Archive 1

Archive 2

Different definitions of L?

Your L in the Derivation does not correspond to your L in the introduction! — Preceding unsigned comment added by Ad van der Ven (talk • contribs) 15:17, 1 June 2011 (UTC)

Length contraction explains magnetism?

I just read this blog post, and I remember a friend of mine who was a physicist describing something remarkably similar several years ago (though I wasn't paying too much attention unfortunately). Is this true? http://skepticsplay.blogspot.com/2007/12/relativity-electrostatics-magnetism.html Jotaf (talk) 02:32, 2 May 2011 (UTC)

Yes, the topic is an issue in education. See relativistic electromagnetism for references and some editors' efforts to show the way.Rgdboer (talk) 21:11, 1 June 2011 (UTC)

LT given incorrectly?

Hm, looks to me as if the Lorentz transformation states $x'=\gamma \cdot (x-vt)$ with $\gamma ={\frac {1}{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}.$

So setting t = 0 yields $x'={\frac {x}{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}$, which would describe quite the opposite effect.

What's wrong?

---

You have to set t' = 0, not t.

---

The equation above is correct. The moving observer measures the length of a rod as the rest length $l_{0}$ (all measuring rods are comtracted) so $x^{\prime }=l_{0}$. The rest frame measures the length of the rod $x-vt$ as contracted. Hence $x-vt<l_{o}$. Fot $t=0$ and $x<x^{\prime }$.

I don't know since when these comments are sitting here and who wrote them, but they are utterly faulty.

In the frame in which the rod is moving, the length is measured by subtracting the distances to the end points when measured simultaneously. In the rest frame of the rod its length is measured by subtracting the distances to its end points at arbitrary times. When we decide to use the equation $x'=\gamma (x-vt)\,$ we assume that one end point is measured at event (x,t) = (x',t') = (0,0), and another endpoint at some event (x,t) for which the x'-coordinate is given by this transformation equation. Since the variable t' is not present in the equation, it is arbitrary, and the equation therefore establishes the (x',t')-frame as the rest frame of the rod. The (x,t)-frame is the frame in which the rod is moving. This also establishes x' as the proper length and x as the coordinate length.

So, to make sure that in the (x,t)-frame the distances to the endpoints are measured simultaneously, we have to put t = 0 in the equation, and get $x'=\gamma x\,$ , giving $x=x'{\sqrt {1-v^{2}/c^{2}}}<x'\,$ , or in coordinate free language: coordinate length < proper length. DVdm 14:01, 20 January 2007 (UTC)

New section

Was imported by me from Ehrenfest paradox during my second rewrite of that article. In that and other contexts (e.g. Thomas precession), two spatial dimensions are essential, hence discussion of E^1,2 rather than E^1,1.

I realize the present exposition has shortcomings and will eventually try to address these, e.g. by writing a background article explaining more fully the three trigonometries, their relation with Kleinian geometry and Cayley's projective metric.---CH 15:05, 5 June 2006 (UTC)

Merge?

The articles called Lorentz-FitzGerald contraction hypothesis and Length contraction are both rather short and partly discuss the same subject. As the title "Length contraction" is a bit ambiguous, I propose to merge the articles into a new article called Lorentz contraction. Harald88 14:46, 11 July 2006 (UTC)

I second that motion, 14 Nov 2006

• • Comment: This message is unsigned. Please sign all messages.

• This is a bad idea. Everything should be merged into Length contraction as it is simple, more popular, and less prone to argument. Moving the page to one that does not have a history and credits Lorentz but does not credit FitzGerald's contribution will not work out. I am going ahead and merging it.--JEF 02:31, 20 January 2007 (UTC)

Talk:Lorentz–FitzGerald contraction hypothesis

There is one phrase that I left but think is erroneous:

"Lorentz was not particularly satisfied with his hypothesis because he realized that it was ad hoc and not testable by experiment."

Anyone has a direct reference? I think to have read the contrary, which is consistent with fact that it was *not* ad-hoc, as explained. Thus I will take it out if after some time nobody proves its correctness; or if I find the source I read, I'll adppt it accordingly and include the ref. Harald88 06:56, 14 October 2005 (UTC)

OK I found it: http://www.mpiwg-berlin.mpg.de/litserv/diss/janssen_diss/Chapter3.pdf - in particular p.41. I'll rewrite that part accordingly to the here presented facts. Harald88 18:47, 17 October 2005 (UTC)

It IS "ad-hoc". Please read the final resolution given by the Trouton-Rankine experiment that proves that, contrary to what Lorentz belived, the contraction is "aparent" , not "real". The TR experiment was the final nail in the coffin for the FitzGerald contraction.

"Ad-hoc" is nonsence, as explained in the above reference as well as in this article. And I have read Trouton-Rankine; with others I tried to explain the logical flaw in your reasoning, but you didn't pay attention. Here is another try: please formulate the Kennedy-Thorndike experiment as seen from the solar frame, accounting for the fact that time dilation is as "real" as the Ives-Stillwell experiment demonstrated. Harald88 17:02, 8 January 2006 (UTC)

Harald, looks like you are mixing up Lorentz's theory with FitzGerald's. I explained the error in your thinking:

1. Lorentz (at least in the current acception) is "subjective" (i.e. it is an artifact of judging the experiment from a frame moving wrt to the frame of the experiment)

2. FitzGerald is "objective", i.e. the contraction really "happens" (or at least, this is what FitzGerald thought) within the frame of the experiment. Interestingly enough, Lorentz thought the same thing, at least until he accepted Einstein's explanation. Your post is conveniently missing this "detail" leaving the reader with the wrong impression that Lorentz died clinging to his theory.

Now, since you asked, here is BOTH MM and KT explanation as viewed from the Sun:

http://www.wbabin.net/sfarti/sfarti12.pdf

Hope that this will clear any lingering confusion.

PS: it would be good if you made the logical separation between the FitzGerald and the Lorentz contraction. they are not the same thing.

PPS: You are also somewhat confused about Ives-Stilwell. The time dilation is real , not "real" (as in "subjective"). For an explanation, please check here:

http://www.wbabin.net/sfarti/sfarti17.pdf

If you don't mind me asking, are you a relativist or an "aetherist"? Reading your posts I am having a hard time figuring out.

[all the above apparently written by no-name, 12.36.122.2]

12.36.122.2, to me it is clear that you confuse a single hypothesis with a complete theory. Waht is, according to you, "subjective" about the "real" expansion of an object? The impression that Lorentz saw no reason to replace his metaphyisics for that of Einstein the general opinion as supported by his writings.

from your answer on my question about your explanation with an internet article, does that mean that you are the author? I think that you mistakingly gave the wrong link, as I could not find a description of the KT experiment in the light of Ives-Stillwell.

About "real", I put it like that, as it has different meanings for different people. Einstein's "real" was apparently more like "reality" as in the film Matrix. What Lorentz at first overlooked but later understood from Poincare and Einstein is that --assuming that the theory is correct-- for consistency reasons, length contraction and time dilation must be equally real. That was also an important argument of Ives.

And for your question: some die-hard Etherists call me "Relativist", while some die-hard Relativists call me "Etherist". Instead, I am a technical physicist. True scientists are against dogmas. And may I ask, what are you? Harald88 22:38, 9 January 2006 (UTC)

"as I could not find a description of the KT experiment in the light of Ives-Stillwell." What? This question seems to make no sense at all.You must mean accounting for time dilation. It is all there, read the MM+KT paper. Anyway, what I gave you are my own explanations of KT and IS. I am a die-hard relativist (to use your terms) and I see no reason in the ambiguity that is perpetrated by "etherists" (we can explain this experiment if, and we can explain that experiment if..., and Lorentzian relativity would be perfectly equivalent to STR if ....)

"The impression that Lorentz saw no reason to replace his metaphyisics for that of Einstein the general opinion as supported by his writings.". Yes, right. Check this out:

"If I had to write the last chapter now, I should certainly have given a more prominent place to Einstein's theory of relativity (p 189) by which the theory of electromagnetic phenomena in moving system's gains a simplicity that I had not been able to attain. The chief cause of my failure was my clinging to the idea that the variable t only had to be considered as the true time and that my local t' must be regarded as no more than an auxiliary mathematical quantity." in "The Theory of Electrons," by H. A. Lorentz second edition (1915). Page 197 in the original 1915 edition, page 321 in Dover Publications 1952 reprint.Ati3414 19:08, 2 February 2006 (UTC)

[who wrote this last comment? I get tired of unsigned comments, and it's against the rules... Harald88 00:25, 10 January 2006 (UTC)]

It is clear who wrote it, it is a continuation of my posting (ati3414).

Obviously I am part of neither camp. The fact is that according to KT as well as mainstream literature, the Lorentz contraction and time dilation are a pair, and this combined Lorentz contraction and time dilation was assumed to have been demonstrated (thanks for the above citation, that was what I meant further above with "later understood" - concerning physics). Thus whatever you may think, it's up to you to show that your opinion can be found in respectable literature, and that it is notable. Harald88 00:25, 10 January 2006 (UTC)

"The fact is that according to KT as well as mainstream literature, the Lorentz contraction and time dilation are a pair, and this combined Lorentz contraction and time dilation was assumed to have been demonstrated"

Yes, the time dilation and length contraction of STR form a pair in the explanation of the KT experiment. This does not mean that they always form a pair (look at the MM experiment, time dilation is not needed in explaining the experiment). Though that they are both part of STR, as I explained to you numerous times time dilation is objective (as per IS experiment) while length contraction is subjective (as demonstrated by TR experiment). I don't know exactly how to sign this, so I will add my name: ati3414

You are here turning a historical account into a philosophical debate, but without referring to this debate. The article already cites Lorentz' final opinion; a citation of a different opinion by a notable scientist could be interesting. Harald88 08:08, 10 January 2006 (UTC)

"The chief cause of my FAILURE was my CLINGING to the idea that the variable t only had to be considered as the true time and that my local t' must be regarded as no more than an auxiliary mathematical quantity." by....H.A.Lorentz

Harald, I gave you Lorentz CONCEDING speech,IN PRINT, from HIS OWN BOOK, what else do you need? ati3414

Hi Ati, I am not the only editor here; but I'm the only one who bothers to reply to your personal interpretations, which differ from the common one. I already told you that I refered to that passage in my reply to you. That still doesn't ring a bell? Lorentz had inconsistenly regarded time dilation as somehow more [oops, I meant LESS] real than Lorentz contraction. Now you try to suggest that a similar (only, inversed) inconsistency would be the general opinion. To the cvontrary: KT would have concluded the absence of time dilation if they had assumed that Lorentz contraction does not occur, and Ives would not have regarded his positive time dilation result as evidence for the reality of Lorentz contraction. Harald88 19:07, 10 January 2006 (UTC)

Harald, the concession I am referring to is that Lorentz admits SR's superiority. The reference to time dilation is incidental, ok?

Harald, I am having a hard time following your logic, especially when you put words in my mouth. I am a "mathematical formulas" man , so I let my math do the speaking for me. As to what I believe to be the truth, I found it encapsulated on another wiki posting, here:

http://en.wiki.x.io/wiki/Lorentz_ether_theory

This is the view I ascribe to. OK? ati3414

Ati, I think that that article describes it pretty well, and your above citation may be a useful complement to Lorentz ether theory. Note that, as mentioned, no "LET" was known at the time: it is revisionist history. Similarly, we could invent a "MET" for Maxwell Ether Theory, and state that it has been replaced by Electrodynamics. Also, the LET article isn't about the math, and thus it shouldn't speak according to you. Your recent argument is definitely not about the formulas but about your personal metaphysics.

I reformulated your words in the way that makes sense to me, to let you know what I received. Again, in my words: it is very much inconsistent, in the same way as Lorentz had been inconsistent, to propose that according to SRT t and l in the same equation would not have similar reality for the same physical description.

I have nothing else to add. I repeat: if you can find a respectable article's opinion to your taste, you may cite that and see if others agree that it improves the article (applicable, notable, balanced). Harald88 22:13, 10 January 2006 (UTC)

OK : applicable,notable,balanced and reputable:

http://www2.slac.stanford.edu/vvc/theory/relativity.html

If you look at the caption at the bottom, under Length Contraction it is clear that these people do not think in terms of rods shortening (actually every place on the web gives a resounding NO to this question for SR and YES for LET, you know many of these places since you've posted your ideas there). They think in terms of particle flightpath shortening as a reciprocal to time dilation (particle lifetime lengthening). So, from the perspective of Trouton-Rankine AND from the perspective of SR , rods DO NOT GET SHORTER, and ATOMS DO NOT BECOME OBLATE (Cleonis, are you reading this?). The internal clock of the particles does run slower, though therefore the particle lifetime gets longer. I know that you, like any physicist likes symmetries but this is a subtle case, there is symmetry but it is not perfect.

Ati:

- you disagree with Einstein (see my quote on the other talk page where he argues that atoms flatten)

Really? can you give me the link?

Look at my replies to you of yesterday or the day before...

Ah, I found it.

BTW, according to Einstein, For v=c all moving objects --VIEWED from the "stationary" system-- shrivel up into plane figures.

VIEWED is key. As in "aparent". I have said it numerous times that I agree with SR, there is an "apparent" length contraction. Now, how did you divine from the above that "see my quote on the other talk page where he argues that atoms flatten"? He certainly is saying something DIFFERENT.

Now, the funny thing is that, had he lived a few more years , he could have read Terrell's paper that says that VIEWED from another reference frame an object does not appear only forshortened but also rotated. The LET proponents haven't caught on on this one yet to incorporate it. So SR and LET might show some differences after all :-)

Maybe I'll write an entry on Terrell's paper :-) ati3414

- you suggest an asymmetry that I never found in literature (you do claim that time dilation is real, but that length contraction is an artifact, right?); thus your metaphysics is your personal POV, and apparently original research.

He,he,he you've been told about this by many others in many other places where you posted on the web. But, no, you wouldn't accept it. To refresh your memory:

"Does the length of the object really change? According to SR, No. According to ether theory, Yes. John Anderson "

Come on , Harald, you are not impartial, you are clearly a LET epigone, hoping that maybe one day, when SR/GR continues to falter in the difficult and not yet attained quest of unification with QM, LET will spring back to life (see your earlier posting on this). So, keep LET in a refrigerated state awaiting the opportunity to supplant SR/GR.

Ati, there is a never ending debate in mainstream literature about relativistic effects being "real" or not, and what "real" means. But sorry to break the news to you, your asymmetrical approach is entirely yours -- and thus not notable for Wikipedia. Harald88 23:34, 11 January 2006 (UTC)

- as many people, you confuse the principle theory that Einstein labeled "special relativity" with Einstein's interpretation of it; and you confuse Einstein's interpretation of that theory with that of others.

Well, it is not the first time you are resorting to personal attacks when you don't get your way. You started this way, when I first posted, you are ending this way (see this last posting). So, what's wrong with the Stanford Linear Accelerator link I gave you?

That's fruitless: it's you who attemps to make this a personal matter; I won't cooperate with turning this Wikipedia page into a boxing match. At first sight that link is not bad for its purpose: teaching the physics of special relativity.Harald88 23:34, 11 January 2006 (UTC)

On a different topic, have you ever wondered why M.Janssen spent hundreds of pages on the Trouton-Noble experiment just to conclude that SR gives a more ellegant and natural explanation than LET while he made not one mention of Trouton-Rankine? Not one page. Not one reference. Nothing. Regards from ati3414

It's a different experiment, involving different physics. Probably he deemed tit wise to leave that for someone else's thesis subject of another 200 pages. Maybe you want to try it? But I warn you, one page won't do! ;-)

Nope, not interested. It was me who suggested it first for other people. ati3414

I leave further comments to other editors. Good luck.

Harald88 23:34, 11 January 2006 (UTC)

Regards, Harald

I have a question for you, Harald:

Suppose that I have a spring . I look at the spring and then I decide to run very fast by it. Does the spring compress and if so, will it push an object next to it when I stop running? Ati3414 19:10, 2 February 2006 (UTC)

This may seem like a dumb posting, especially in the midst of all out philosophical war, but unequivocally sidestepping interpretational issues of the hypothesis itself, who want's to rename the effect, the "FitzGerald-Lorentz contraction hypothesis". I'm not aware of any physical institution that states any preference, it is just habit. The physical community has a shameful tendancy to forget the contributions of less successful physicists, and Lorentz himself always accredited the hypothesis to FitzGerald alone. So, let's give FitzGerald his due.

Ati3414, stealing Harald's question, I don't think the spring extends past it's equilibrium position in either frame (although that equilibrium distance will itself contract). Thus, no forces will be exerted from anyone's point of view ( I hope!).

Krea 20:41, 10 March 2006 (UTC)

I'm worried that the section on "A trigonometric effect?" may be badly sourced. Not to disparage Hughston, but the source listed for that section is co-authored by that author and does not discuss the issues listed in that section. Additionally, I'm not sure that the geometry of the transformations is really that modern and interpretation; it seems very basic geometry, but I'm not up on the specific history of that discussion. It would be nice to have a reference to the development of the geometry here if it is to presented as a "modern view". (Worryingly, the image in the section is similar to a figure in Minkowski's original paper on the subject.) BangPhys Feb 20, 2008 —Preceding comment was added at 18:41, 20 February 2008 (UTC)

Merge?

The articles called Lorentz-FitzGerald contraction hypothesis and Length contraction are both rather short and partly discuss the same subject. As the title "Length contraction" is a bit ambiguous, I propose to merge the articles into a new article called Lorentz contraction. Harald88 14:45, 11 July 2006 (UTC)

This is a good idea. --EMS | Talk 18:51, 15 August 2006 (UTC)

• This is a bad idea. Everything should be merged into Length contraction as it is simple, more popular, and less prone to argument. Moving the page to one that does not have a history and credits Lorentz but does not credit FitzGerald's contribution will not work out. I am going ahead and merging it.--Jorfer 02:29, 20 January 2007 (UTC)

I have suggested a merge for the article space contraction as well, since it is a synonym for Lorentz contraction. Tnxman307 (talk) 14:57, 11 December 2007 (UTC)

Space contraction is not really a synonym but in fact the contrary: if a ruler contracts, the measured space increases as illustrated by for example bell's spaceship paradox. Thus space contraction is really a misnomer. However, it may be useful to mention it inside the length contraction article, if the term is notable in the literature. Harald88 (talk) 15:52, 6 April 2008 (UTC)

First person plural tone

This article reads like a professor's lecture with two occurrences of the word "we" and its plural first person viewpoint. I feel it would better represent the subject if passive voice were used. I've tagged the article for inappropriate tone. Binksternet (talk) 17:40, 21 November 2008 (UTC)

good call, i trivially replacd the two WEs and dropped the tag. done —Preceding unsigned comment added by 83.196.101.199 (talk) 13:43, 13 January 2010 (UTC)

The "object's length" , not "the object"

The sentence: "Note that in this equation it is assumed that the object is parallel with its line of movement." should be changed to "Note that in this equation it is assumed that the object's length is measured parallel with its line of movement."

I vote for leaving the tone of the article the same. One of the virtues of the Wikipedia is that it can emphasize being useful information as opposed to being dry and "authoritative" information. It's never going to be authoritative. The sponsors have grown very defensive, however. You even see the Wikipedia warning banners in mathematics articles when the authors give examples. How silly. —Preceding unsigned comment added by 4.240.141.41 (talk) 17:25, 27 February 2009 (UTC)

Length is not an appropriate term for all objects

Not all objects can be said to have 'length'. A sphere, for example, does not have length, because its dimensions are all equal and/or equitable. 'Length' is a term applied to everyday objects where one dimension is much bigger than the others. Thus I believe that a more universal term would be 'size' or c. Majopius (talk) 15:20, 29 March 2009 (UTC)

You are right about 'length' being a term applied to objects where one dimension is much bigger than the others. However, traditionally the object in question is rod-shaped and (silently) aligned with the direction of motion, so length is of course the only meaningful dimension. Your 'size' or 'distance' suggestions fail because they effectively hide the (implicit) direction of motion prerequisite. Tricky, but sticky <== double pun intended :-) DVdm (talk) 16:22, 29 March 2009 (UTC)

Why is the object in question a rod? If the terms "size" and "distance" do not work (I'm fine with them!), then maybe a better term would be "the dimension parallel to the direction of motion". If you meant that my suggestions don't work because they might mean ALL the dimensions, not only one, than this term clearly states ONE direction. Neither is length always parallel to the direction of motion - the object could be moving sideways. So I think that the term 'length' fails too. Majopius (talk) 03:41, 31 March 2009 (UTC)

"Why is the object in question a rod?" => Perhaps our great-grandfathers took a rod because it was a short word and because rods have only one interesting dimension, automatically implying direction of motion. But yes, perhaps they expected far too much goodwill from their audience. Maybe all the books should be rewritten and "length contraction" replaced with "dimension parallel to the direction of motion contraction", and then, a few years later we can finally change this article's name into dimension parallel to the direction of motion contraction. I'm sure we could find a suitable replacement for "time dilation" as well. DVdm (talk) 13:18, 31 March 2009 (UTC)

For me, the object of investigation is a ball. And for a sphere, length and height are the least appropriate terms.Majopius (talk) 03:11, 14 April 2009 (UTC)

I don't see any Length Contraction in the following ??

Consider two space ships A and B of same length instead of train in the following link. http://www.youtube.com/watch?v=wteiu...eature=related

Both A and B started their same computerized journey from stationary observer “Os” station but moving in opposite direction to each other in a closed loop. All clocks as shown below, used by respective observers are synchronized at Os station before their journey into their respective ship. After certain time A and B crosses each other at the crossing facility in a loop such that one is exactly above the other (front of upper ship is exactly above the rear of lower and rear of upper is exactly above the front of lower). Here is the detail of crossing facility (For simplicity imagine a parallel circuit diagram for crossing)

“A” leave the normal loop and move up grade, straight, down grade and then enter the normal loop from where“ B” left

“B” leave the normal loop from opposite direction but move down grade, straight, up grade and then enter the normal loop from where “A” left.

            End------------------------ship A---------------------------Front
           LSae, Mae, e, Cae, Oae _______________________f,Caf, Oaf, LSaf,Maf

           Mbf, LSbf, f, Cbf, Obf,________________________e,Cbe, Obe,Mbe, LSbe
          Front------------------------ship B---------------------------End                                  

Where e = end of ship, f = front of ship, Af = A front, Bf = B front, Ae = A end, Be = B end

Oae = Observer of A at its e, Oaf = Observer of A at its f, Obe = Observer of B at its e, Obf = Observer of B at its f.

LSae = Light Source at the bottom of A at its e (emit downward vertical flash), LSaf = Light Source at the bottom of A at its f (emit downward vertical flash), LSbe = Light Source at the top of B at its e (emit upward vertical flash), LSbf = Light Source at the top of B at its f (emit upward vertical flash).

Mae = Mirror at the bottom of A at its e which detect LSbf during line up of Bf/Ae, Maf = Mirror at the bottom of A at its f which detect LSbe during line up of Af/Be, Mbe = Mirror at the top of B at its e which detect LSaf during line up of Af/Bf, Mbf = Mirror at the top of B at its f which detect LSae during line up of Bf/Ae.

Cae = Clock of A used by Oae during line up of Ae/Bf, Caf = Clock of A used by Oaf during line up of Af/Be, Cbe = Clock of B used by Obe during line up of Be/Af, Cbf = Clock of B used by Obf during line up of Bf/Ae.

For Os, in elevation or top view

LSae is well above Mbf and Mae is well above LSbf, LSaf is well above Mbe and Maf is well above LSbe.

As for Os both A and B are equally longer therefore he would see both new flashes from the f and e of both ships at the same time. And also at the same time

Downward vertical flash of LSae is detected by Mbf and upward vertical flash of LSbf by Mae, Downward vertical flash of LSaf is detected by Mbe and upward vertical flash of LSbe by Maf.

Now consider the event from A frame of reference

For Oaf, the front light strike the Af/Be followed by Ae/Bf. This means Mbe is struck by downward vertical flash of LSaf and that Maf by upward vertical flash of LSbe Caf is paused by Oaf when Af even with Be but Since Oae is still waiting for Bf to be even with Ae, therefore Cae is not yet paused by Oae, and Downward vertical flash of LSae hasn’t yet touched B and or Mbf while Upward vertical flash of LSbf has touched A but not yet reach Mae and thus Oae is still waiting for the event to be occurred at Ae

Obf and Obe have an exactly symmetrical experience but sees flash Bf/Ae first followed by Be/Af

Here is the detail of event as seen from B frame of reference

For Obf, the front light strike the Bf/Ae followed by Be/Af. This means Mae is struck by upward vertical flash of LSbf and Mbf by downward vertical flash of LSae Cbf is paused by Obf when Bf even with Af but Since Obe is still waiting for Be to be even with Af, therefore Cbe is not yet paused by Obe and Upward vertical flash of LSbe hasn’t yet touched A and or Maf while Downward vertical flash of LSaf has touched B but not yet Mbe and thus Obe is still waiting for the event to occurred at Be

Later on both Oaf and Obf come back from their mission to Os station and starts claim for observing first front strike Both are right in their perspective frame of reference but still there is disagreement between two

Oaf claim that he has paused his Caf before Obf while Obf also claim that he has paused his Cbf before Obf

Now Os advises Oaf and Obf to compare their Caf and Cbf reading. Since Oaf is the witness for the Af even with Be ( For the front strike of Af and rear strike of Be) Obf is the witness for the Bf even with Ae (For the front strike of Bf and rear strike of Ae) So both Caf and Cbf should show same reading because they went through the same computerized journey and thus there should no length contraction

Here is the answer about those clocks from one of reputable physics forum. It's true that when lightning struck next to Af, A's clock at that location read -5, and when lightning struck next to Bf, B's clock there read -5, but since these are clocks from two different observers this does not mean the strikes were simultaneous in either frame--this is your crucial mistake, each observer only defines simultaneity using multiple clocks of his own at different locations”.

So here are my questions..

If each front observer deny the lining up of the front of the other ship with the end of his ship then how comes abovementioned mirrors detects all those vertical flashes from their respective opposite light sources??? OR

Event from A frame of reference

If Oae is still waiting for Bf to be even with Ae, then how come Mae was struck by upward vertical flash of LSbf and Mbf by downward vertical flash of LSaf from B frame of reference

Event from B frame of reference

If Obe is still waiting for Af to be even with Be then how come Mbe was struck by downward vertical flash of LSaf and Maf by upward vertical flash of LSbf from A frame of reference?? 96.52.178.55 (talk) 04:14, 12 May 2009 (UTC)khattak

1/(1-v^2/c^2)^1/2

When v=c then it would be (1-1)^1/2 which of course would equal 0 and a number when divided by 0 is undefined not nothing, so the length of an object traveling at the speed of light would be undefined not zero. —Preceding unsigned comment added by 66.32.10.145 (talk • contribs)

Remarks:

• ( Please sign your posts on talk pages with 4 tildes ~~~~ - Thanks )
• The case v=c is excluded. No object can move at the speed of light. This case is not within the scope of the theory. So your removal of the paragraph was okay, but not for the reason stated:
• Assuming that the case v=c would be inluded in the theory, notice that the proper length L is not divided by the factor (1-v^2/c^2)^1/2, but mutiplied by it, so the "length of an object traveling at the speed of light" would indeed be zero. Thus there was no logical falacy.
• I reverted your removal but I introduced a little safety line.

DVdm (talk) 07:15, 19 August 2009 (UTC)

Yes, your mistake is that you are thinking that because Lorentz factor is undefined in this case, the original formula is undefined, when this is not the case.--Jorfer (talk) 16:02, 19 August 2009 (UTC)

No object with mass can travel at the speed of light?

This article seems to state that no object with mass can travel at the speed of light because its length would then be reduced to zero. But a singularity has a length of zero and a LOT of mass. Does this mean that a black hole could travel at the speed of light despite having mass? Or am I completely misunderstanding all this? 68.200.98.166 (talk) 02:41, 13 January 2010 (UTC)

Good catch. I have removed the misleading phrase "Among other reasons, this suggests that objects with mass cannot travel at the speed of light.", as there is indeed nothing in the preceding text that suggests this, since mass isn't even mentioned. And of course, the form of an equation can never be a reason for someting. It can at best model some fact. I have also slightly reworded another related phrase. DVdm (talk) 08:56, 13 January 2010 (UTC)

Pardy paper and LHC in Observability

This draft is of poor quality, has a large fraction of references to single-author paper by the same author, shows no signs of being published, and shows no clear case that the LHC which is designed to smash nuclei together and which works best with protons is technically capable of smashing lightly ionized nanostructures together. 209.131.48.66 (talk) 18:35, 6 April 2010 (UTC)

If the referenced paper is indeed nothing more than a draft, the comment and its reference can be removed from the text per WP:RS. Afaic, go ahead. DVdm (talk) 18:51, 6 April 2010 (UTC)

Thanks -- I reviewed Google Scholar and confirmed that it was not apparently even published nor was any reference to it apparently published in the two years since it first came out. (Early hint that it's less than scholarly: the first word of the title has too many S's.) 209.131.48.66 (talk) 19:07, 6 April 2010 (UTC)

I'm confused about length contraction

--JamesBowlin (talk) 06:42, 10 May 2010 (UTC) Hi,

I'm not a professional physicist and come here to learn, but I'm leaving confused. Here are examples of the type of questions that I am looking for answers to.

1. (Not a question, but) It seems to me that the title ought to at least mention relativity (or relativistic) as this is the only type of contraction which is discussed. There are other types of length contraction (e.g. pressure, low temperature), so it seems the title should be more specific. I'll leave the argument over Lorentz and/or Fitzgerald to others.

2. The derivation is very confusing, mixing math, rhetoric, and hard to reproduce fonts. Could you employ a straightforward diagram? (Basis in Relativity section.)

3. I am curious about the "reality" of the contraction, and reading the article and the discussion does not help. Most of the reality arguments involve very old papers and concepts (e.g. Lorentz, his contemporaries, and/or aether) and do not seem to present modern viewpoints The modern viewpoint, as it is argued, makes it appear that length contraction is simply the result of definitions and trigonometry, which makes it sound as if it has no basis in underlying physical reality. (I know, "reality" is a loaded word.) This point of view seems to be disputed elsewhere (sorry, no references at hand).

4. The textbook derivation of length contraction often ties it closely to time dilation. Time dilation seems to have real evidence: muons and clocks (although often when tied to non-inertial frames - in gravitational fields or in rotary or orbital motion). Does the reality of time effects say anything about length contraction? A related question, as inertial speed and momentum increase, would this increase the overall energy, change the curvature of space-time, and cause a length effect - in either SR or GR?

5. Although time and length are usually analyzed in terms of a rod and a mirror, I can't help wondering about old-fashioned engineer's stop watches. One is composed mostly of planar disks. When the stationary observer looks at the watch face-on (perpendicular to its motion), wouldn't he also see length-contracted oval gears, unable to turn - or do the gears change shape as they turn? Is this possible in a real material? Conversely, a watch turned so it's hands face the direction of motion should not contract in any dimension which affects its operation.

6. Don't Terrell's results (Phys. Rev. 116, #4) argue that the true length contraction effect is unobservable by a real viewer, and that the object may actually look longer or rotated instead of contracted? I understand that this is an illusion of observation, but it muddies my conceptual waters about how I would "observe" Lorentz-Fitzgerald contraction separately from motion illusions. (All of the simple derivations have me "observing" something in motion, possibly over an interval of time.) What is the physical status of an unobservable phenomenon?

7. Finally, I'm back to the old pole in the barn problem. I have found explanations of it which range from a fully contracted, unrotated, pole fitting exactly in short stationary barn with both doors momentarily and simultaneously closed (assume the pole just touches each closed door and that if I froze time and walked around the barn, I'd find both doors shut - or glued to the pole, or something else physically continuous...), to explanations where the doors open and close out of synchrony in such a way as to allow a long pole to appear that it was momentarily contained inside with both doors closed, to statements that it is not possible to compare two frames (in some ways) and that the question (may be) meaningless. How would you analyze this situation? - Best, Bruce H.

Original research

I have removed a poorly worded, "unencyclopedicly" written, lecture style, example from a section twice ([1], [2]). If this is not original research, then a source for it should be easiy found. DVdm (talk) 11:55, 10 October 2010 (UTC)

It provides no new information, so it's not "original research". It was a simple attempt to describe the consequences of relative motion in connection with length contraction (at least, I thought the example might be helpful for people who have problems to imagine the consequences). However, I won't revert your changes, as it is no essential part of that article. --D.H (talk) 14:24, 10 October 2010 (UTC)

No new information, but nevertheless, whithout a source, a classical case of original research. Thanks for not reinserting it.

By the way, it looks like you have done an excellent job here, although the example was a bit of a tache de beauté. Cheers and keep up the good work. DVdm (talk) 15:23, 10 October 2010 (UTC)

Reality of Lorentz contraction

This section is unclear. To show that contraction is indeed very much real, one must explain with pictures how the electric field (and hence all interatomic distances in a body) contracts, in the longitudinal but not in transverse direction, as a result of the standard electrodynamics. The contraction of the electric field was described somewhere in The Feynman Lectures on Physics, unless I am missing something (I am not an expert in this area).Biophys (talk) 21:34, 23 October 2010 (UTC)

The section is about terminology, as different people ascribe different meanings to the words "real" and "apparent". Now, you say that length contraction is "very much real" - but you must bear in mind that this contraction of the electric field only arises in reference frames, in which the field is in motion - not in its rest frame. BTW: The contraction of the Coulomb field and its consequence is already mentioned in the section "experimental verifications". --D.H (talk) 09:48, 24 October 2010 (UTC)

All right. I mean the explanation of length contraction by Lorentz, which he did without the postulates. No, that does not require to assume the existence of ether. In other words, the original Maxwell equations can be applied to relativistic electrons without any modifications (see The Feynman Lectures on Physics, 21-13 and 26-13, for example).Biophys (talk) 14:28, 24 October 2010 (UTC)

Question

New figure in this page ... Although bodies A, B, C change their lengths, the distances between the bodies should remain the same, should not they? Biophys (talk) 00:26, 26 October 2010 (UTC)

No, the diagram is correct. Length contraction is a coordinate effect, not something that happens to objects. You can imagine a measuring stick underneath and with the same velocity as the moving objects (even touching them if you want), and the stick will also be Lorentz contracted. The positions of the objects as measured by the stick will not change. Tim Shuba (talk) 03:04, 26 October 2010 (UTC)

@Biophys. Look at the definition at the beginning of the section: "At first, it is necessary to carefully consider the methods for measuring the lengths of resting and moving objects, where "object" simply means a distance with endpoints that are always mutually at rest, i.e., that are at rest in the same inertial frame of reference." That is, the right end of A and the left end of B have the same velocity, so they are at rest in the same frame. Therefore also the distance between the rods contract. --D.H (talk) 09:38, 26 October 2010 (UTC)

Thank you for response! This is an important question related to my previous posting on this page. Now I know where you are. It's not that simple. I will probably bring more (with references) on this subject, maybe in a few weeks. Just to clarify, I am talking about something like this, and there are other similar publications. What follows is that distances between the centers of mass of the bodies would not change. But I have to check it.Biophys (talk) 14:58, 26 October 2010 (UTC)

In relativity (as it is currently understood by the leading experts, and whose papers are the only reliable sources for this article) effects like length contraction are kinematic effects. See for example the "orthodox" view described in this article by M. Janssen. So please forget this "physical explanation" stuff, because the fact that one can derive the Lorentz transformation from electrodynamics does not mean that this "causes" the contraction. And Wikipedia-Talk pages are not the right place to discuss alternative theories. --D.H (talk) 16:31, 26 October 2010 (UTC)

We are talking about special theory of relativity, which is not an alternative theory by any accounts. No one is trying to disprove anything in this theory. As about understanding and teaching relativity, yes, there are different approaches that must be described per WP:NPOV because they were shared by many notable scientists. Yes, that "physical explanation" stuff is precisely what I am interested in. Why? Because that would be also interesting for wikipedia readers. Each effect in physics must have its causes. Using Einstein's postulates (something like Energy conservation law) does not eliminate the physical causes of length contraction and other relativistic effects, as Einstein admitted himself Biophys (talk) 17:23, 26 October 2010 (UTC)

The problem is, that you questioned one of the most basic applications of the Lorentz transformation: the calculation of the simultaneous positions of endpoints. So if you have a theory that predicts other results (as you suggested), then this is of course an alternative theory, not simply an alternative "interpretation". And besides WP:NPOV you should also look at WP:UNDUE and WP:PRIMARY. The articles must rely on reputable secondary sources, and they must reflect the opinion stated in this source. Now, the overwhelming majority of secondary sources tell me that special relativity is a kinematic theory, and length contraction is therefore a consequence of the properties of relativistic space-time (electrodynamic explanations like those of Lorentz, Larmor and Poincaré can be found in the History section). --D.H (talk) 19:34, 26 October 2010 (UTC)

Yes, special relativity is understood as a kinematic theory, but there is nothing wrong with giving a physical explanation. Perhaps we should wait and see what he proposes, before rejecting it. Roger (talk) 04:42, 27 October 2010 (UTC)

Thank you all for response. I will add something later. No one disputes the Lorentz transformation (this is just a math), and no one claims that length contraction was caused by the Lorentz transformation. The length contraction is caused by contraction of electric fields of the molecules that compose the body. The contraction of electric field follows from the standard electrodynamics (the relativistic effects are already there - see textbook by Feynman). What contracts or changes are the rulers, clocks and other material objects rather than empty space or mystic time. Or at least this is so in the special theory of relativity. I am not going to discuss theory of gravitation (general relativity) at this page, since that's a very different theory. Let's keep apples and oranges separately.Biophys (talk) 14:15, 28 October 2010 (UTC)

Be careful when you say that "the length contraction is caused by contraction of electric fields of the molecules that compose the body." You forget that no body needs to be present for the transformation to predict length contraction. Assume two stars at rest w.r.t each other. In special relativiy no body is present (or assumed to be present) between the stars, yet the distance between the stars depends on the velocity of whom is passing by and making measurements of distances of simultaneous (according to those who make the measurements) events on the stars. No rulers are needed to make those measurements, since times and distances can be measured with nothing more than a clock and some light. DVdm (talk) 16:00, 28 October 2010 (UTC)

The replacing rulers by clocks is a separate story and may be beyond this article. I only wanted to tell that some of the historical explanations are interesting and valid because they are based on the classical electrodynamics (rather than ether) which has not been disproved by relativity. But your point is taken: I am going to be very careful with editing in this area.Biophys (talk) 16:06, 29 October 2010 (UTC)

Hm, I don't think that the replacing of rulers by clocks should or even can be seen as a separate story. It is 100% special relativity, which is, by the way, derived from classical electrodynamics. But anyway, I don't think that we can add statements about such explanations and say something about them being interesting and/or valid. We can just say (sourced of course) that such and such explanation was put forward at some time by X or Y. When we would do that, in order to avoid wp:undue weight, we should of course also say something about the current mainstrain view. DVdm (talk) 19:49, 29 October 2010 (UTC)

Oh yes, absolutely. If there are alternative explanations what causes length contraction of bodies, we must provide them all per NPOV. But I know only one cause, and that is contraction of electric fields.Biophys (talk) 13:11, 30 October 2010 (UTC)

I think that the mainstream view of the "cause" lies just in the way we measure things. Remember that at a certain level physics is not interested in why things are what they are, just in how they are. The ultimate why-problems tend to be pondered in religion and philosophy. DVdm (talk) 13:23, 30 October 2010 (UTC)

The measurement or calculation is the way to define things in physics. Identifying the causes is the way to understand things and has always been one of the most important parts of physics like here and in a lot of other cases.Biophys (talk) 14:36, 30 October 2010 (UTC)

Yes, I agree that parts of physics like this and many other cases indeed are why-cases. That is the reason for the qualifications "at a certain level" and "ultimate" in my previous remark. Anyway, I think we are wandering a bit off-topic on this article talk page here. So.... cheers - DVdm (talk) 15:09, 30 October 2010 (UTC)

Re: "Derivation" section: Why not just use Einstein's two postulates directly?

The current discussion of Fitzgerald-Lorentz length contraction in Wikipedia is based entirely on the Lorentz transformation (LT) of the special theory of relativity (SR). I object in particular to the section entitled "Derivation" which begins with "Length contraction can simply be derived from the Lorentz transformation as it was shown, among ..."

I would like to point out that it is possible to use Einstein’s two postulates of relativity directly to predict changes in the lengths of objects upon acceleration without involving the LT.

The method of choice for measuring distances is the Global Positioning System (GPS). Atomic clocks are used to measure the elapsed time for light to travel between two points and this value is multiplied with the speed of light (c) to obtain the corresponding distance. Although this technique is designed to measure distances on the earth’s surface, it can also be adapted to make a definitive test of the relativistic length contraction hypothesis, as shown below.

The length of a metal bar is measured by using two identical (proper) clocks on the ground. The elapsed time for light to traverse the metal bar is found to be L/c s for both clocks, indicating that the length of the bar is L m at this point in the experiment. The bar and one of the clocks are then put into orbit and the measurement is repeated. Consistent with the relativity principle (Einstein’s first postulate [1]), no change in the length measurement is found on the satellite. However, because of the effects of time dilation, it is known that the onboard clock has slowed by a factor of Q>1 (the effects of the gravitational red shift are neglected at this stage of the argument). The corresponding elapsed time on the clock left behind on the earth’s surface is therefore deduced to be Q times L/c s, a larger value than before. The speed of light on the satellite is still equal to c for the observer on the ground (Einstein’s second postulate [1]). The conclusion is therefore that the bar has expanded as a result of being accelerated into orbit; its length has increased from L m to QL m. Moreover, the increase in length is the same in all directions because the local time measurement on the satellite is completely independent of the orientation of the metal bar to the observer on the ground. The observer on the satellite is unaware of this change, which simply means that the lengths of all objects on the satellite have increased by the same factor (uniform scaling of distance and time).

Confirmatory evidence is found in the results of transverse Doppler measurements. They show that a decrease in light frequency (caused by time dilation at the light source) is always accompanied by a corresponding increase in the wavelength of the radiation. Again, the effect is the same in all directions. This result is clearly a consequence of the constancy of the speed of light, just as in the GPS example considered first. The slowing down of clocks can be looked upon as an increase in the unit of time in the moving rest frame. In order for the speed of light to be unaffected by this change, it is obviously necessary for the unit of velocity to remain constant, which means that the unit of distance, i.e. the length of the meter stick, must increase in the same proportion as the unit of time.

The above examples show that isotropic length expansion accompanies time dilation, not the anisotropic length contraction predicted by Einstein in his 1905 paper.[1] Deduction of length expansion is based solely on the two relativistic postulates (relativity principle and the constancy of the speed of light). Since the latter have received extensive experimental verification, not the least through the experience with GPS distance measurements, there is no reason to doubt the correctness of this conclusion.

What it shows is that the theory of special relativity is not internally consistent. If one uses the above postulates directly to predict changes in length upon acceleration, the answer is opposite to what is deduced on the basis of the Lorentz transformation (LT). There is a simple explanation for this discrepancy. Einstein made an assumption in deriving the LT which was not declared as such. He claimed [see the four equations at the bottom of p. 900 in his original paper[1]] that a function φ defined there only depends on v, the relative speed of the two rest frames under discussion (S and S’). One obtains a qualitatively different result if one chooses φ instead so as to satisfy the basic assumption of the GPS methodology: the rates of clocks in relative motion are strictly proportional to one another, i.e. t=Qt’ in the notation used in the above example. The resulting alternative LT still satisfies Einstein’s two postulates, but predicts that the lengths of objects expand rather than contract when clock rates slow as a result of acceleration. More details may be found elsewhere.[2]

[1] A. Einstein, Ann. Physik 17, 891 (1905).

[2] R. J. Buenker, Apeiron 15, 254 (2008).
--Rjbuenker (talk) 20:39, 14 May 2011 (UTC)

The preceding crackpot sewage by Rjbuenker is a good example of why citing one's own material is frowned upon. Apeiron is not considered to be a reliable source, both here and in the general science community. There is no way any of it belongs in this article. Tim Shuba (talk) 00:22, 16 May 2011 (UTC)

Experiments on the variation of cosmic-ray intensity with altitude provided one of the first confirmations of time dilation [1,2]. Rossi and Hall [1] found an absorption anomaly of “mesotrons” due to spontaneous decay and used relativity theory to show that the effect must be more pronounced for particles of relatively low energy because of their shorter lifetimes. They also made a connection with relativistic length variations. Specifically, they pointed out that the “average range before decay” L, i.e. the average distance traveled by the particles before disintegrating, must be proportional to the observed lifetime τ and their speed β = v/c: L = β τ. This formula shows that the distance traveled by the particles has a different value for two observers in relative motion. Specifically, it shows that the observer with the slower clock (and therefore the shorter corresponding measured lifetime τ) must find a smaller value for the distance L traveled by the particles before decay. This conclusion follows from the fact that the speed β is the same for all observers, as expected from application of Einstein’s velocity transformation (VT [3]).

The above experience has been discussed in various textbooks in connection with length contraction. Weidner and Sells [4] considered a case in which the decaying particles move with speed β=0.98 at a height of L=2260 m toward the earth’s surface. The authors point out that the measured lifetime of the particles is therefore 5.0 τ₀ in this rest frame (S) which is long enough so that exactly one-half of them reach the earth. An observer traveling with the particles (in S’) must also find the same fraction, even though the lifetime from his vantage point is much shorter (τ₀). The explanation is that the corresponding distance traveled is also smaller by the same factor of 5.0, in agreement with the above range formula [1]. The authors [4] conclude: “because of the space-contraction phenomenon, the Earth’s distance from him is contracted.” Another version of the same argument is given in an introductory textbook [5]. In this case, the example of a rocket ship passing between two fixed points in space is used. Consistent with the VT, it is assumed that two observers agree on the velocity (speed and direction) of the rocket. It is concluded that the observer in S’ with the slower clock measures the smaller value for this distance. The following equations in standard notation for the two rest frames S and S’ summarize these results [γ= (1-v²/c²)^-0.5]: t’= t/γ, x’=x/γ and y’= y/γ. Note that the direction of travel is immaterial in computing the distance.

In his 1905 paper [3], Einstein derived the length contraction effect and time dilation from the Lorentz transformation (LT). The following equations summarize these results: t’= t/γ, x’= γx and y’= y. Although both textbooks [4,5] conclude that their example serves as a verification of the phenomenon of relativistic length contraction, comparison of the above two sets of formulas shows that the opposite is the case. In Einstein’s result lengths measured by the observer in S in the x direction are contracted, whereas in the textbook examples, lengths measured by the observer in S’ are contracted in all directions. It is clearly necessary to resolve this discrepancy.

[1] B. Rossi and D. B. Hall, Phys. Rev. 59, 223 (1941).

[2] B. Rossi, K. Greisen, J. C. Stearns and D. K. Froman, Phys. Rev. 61, 675 (1942).

[3] A. Einstein, Ann. Physik 17, 891 (1905).

[4] R. T. Weidner and R. L. Sells, Elementary Modern Physics (Allyn and Bacon, Boston, 1962), p. 410.

[5] R. A. Serway and R. J. Beichner, Physics for Scientists and Engineers, 5th Edition (Harcourt, Orlando, 1999), p.1262.
--Rjbuenker (talk) 11:11, 28 May 2011 (UTC)

How does a photon see things?

According to the Lorenz equation, it appears that for something traveling at the speed of light (i.e. a photon) distances have shrunk to zero – in other words, the universe would be like a singularity, and in the photon’s frame of reference, it doesn’t ‘go’ anywhere. All photons would automatically be ‘everywhere’, separated only by their time of occurrence. However, I have heard that matter slows light by some means, which suggests that to a photon, matter has ‘size’. Does this mean that to a photon all the objects in the universe are somehow ‘there’, but the separation we see between them does not exist? Guccio (talk) 02:06, 8 September 2011 (UTC)

Questions about the subject can and should be asked at the science reference desk. This article talk page is for discussions about the article itself, not about the subject. Cheers, DVdm (talk) 06:32, 8 September 2011 (UTC)

Reality of Lorentz contraction

I think this section is somewhat misleading. There are optical illusions caused by the finite speed of light. For example, something moving towards you will appear longer, and something moving away from you will appear shorter. This "effect" will go away if you account for the time it takes light to reach you, and consider the where thing are, rather than where they were when they emitted the light you're recieving. I would consider Lorentz contraction to be real, in contrast to this effect, which is apparent. — DanielLC 05:06, 9 July 2012 (UTC)

Yes, optical effects are not the same as relativistic effects. Regarding the question is general, it depends on the reference frame you choose. As Einstein put it: Contraction doesn't exist for a co-moving observer (it cannot be measured), but it exists for a non-comoving one (it can be measured). I've included the relevant Einstein quote, and trimmed down the "terminology" part.. --D.H (talk) 08:37, 9 July 2012 (UTC)

Physical?

The first line of the article refers to a 'physical' effect. What is this intended to mean?

Also, 'according to Hendrik Lorentz', should be part of the history. Martin Hogbin (talk) 10:07, 6 October 2013 (UTC)

Thanks. The term "physical" (which was used in the article for years) can lead to misunderstandings, since in relativity it's only a geometric effect. --D.H (talk) 11:36, 6 October 2013 (UTC)

Evidently the above phrase "only a geometric effect" (meant by me in terms of "frame dependent" or "coordinate dependent") leads to misunderstandings as well. Anyway, whatever word one chooses, the article explains that it is a frame dependent effect based on the Lorentz transformation and certain operational procedures, as described in standard mainstream textbooks. So it's more secure to follow the textbook formulas and to avoid philosophical talking about the meaning of words (physical, geometrical, apparent, real), unless sourced as per WP:Sources and WP:undue. This effect expresses itself in a frame dependent manner in areas such as relativistic electromagnetism (contraction of the Coulomb field); longer travel path of moving muons (in the other frame it's due to time dilation); contracted heavy ions in motion; increased ionization capability of charged particles in motion due to contraction of the Coulomb field; contraction is consistent with the negative result of the Michelson-Morley experiment in relatively moving frames; contraction is consistent with the Ehrenfest rotating disc as viewed in the laboratory frame (in the co-rotating frame general relativity implies non-euclidean geometry in presence of a pseudo-gravitational field) etc. --D.H (talk) 07:53, 16 October 2013 (UTC)

I think you are correct in concluding that we should avoid saying, 'only a geometric effect' as is does lead to misunderstandings, mainly because people will assume a 3+1 geometry rather than 4D spacetime. We could though add a bit more to the 'Reality of length contraction' section. I will start a new section here on that. Martin Hogbin (talk) 08:34, 16 October 2013 (UTC)

The "Reality of Length Contraction" section ends with this quote: "John Bell and Harvey Brown have argued that there are some advantages to explaining relativity in a more constructive way, with the length contraction being caused by electromagnetic forces pulling atoms closer together." This perpetuates the misunderstandings by "explaining relativity in a more constructive way" as physical compression physically shortening objects. Also this Wiki reference to the Ehrenfest paradox insists that there are no rigid bodies in relativity... more of the argument for physical contraction, leading to more misunderstanding: “Another famous paradox is the Ehrenfest paradox, which proves that the concept of rigid bodies is not compatible with relativity.” Length contraction can not have it both ways,..."only a geometric effect" and a physical shortening of objects (and distances between them.)This basic contradiction in presentation of length contraction is in dire need of "disambiguation." LCcritic (talk) 18:23, 10 October 2013 (UTC)

Nowadays (i.e. since a century or so), "physical" and "real" (and even "geometrically") all mean "operationally and reproducibly measurable". Anything beyond that seems to have become what we could call arm-chair philosophy, i.e. wasting one's time on the usage of words. Just like velocity and energy, length is a coordinate dependent property. That does not make it "unphysical" or "unreal" or "merely geometrical". - DVdm (talk) 21:27, 10 October 2013 (UTC)

Maybe Bell and Brown are misleading with their arm-chair philosopher. I have no quarrel with either of you. I put that sentence in because I thought that it is useful to have a reference to how some credible sources have discussed the reality of the contraction. Roger (talk) 23:17, 10 October 2013 (UTC)

Many modern introductory text books have a section where they address the question of whether the Lorentz contraction and other effects of relativity are 'real' or 'physical'. The facts are fairly clear; lengths of objects in relatively moving frames do everything they should do if they were contracted, nuclear bombs really do make big bangs, and the GPS system continues to work. No one argues that a rod experiences any effect in its own rest frame just because it has been observed from another frame. The days when motion through some aether might be considered responsible for 'really' (whatever that means) making rods get shorter for are long past. Whether you chose to call the effects of relativity, 'real', 'physical', or 'geometrical' is purely a matter of taste and, as DVdm says, only of interest to philosophers. Martin Hogbin (talk) 08:37, 11 October 2013 (UTC)

In reference to: "Reality of length contraction

Another issue that is sometimes discussed concerns the question whether this contraction is "real" or "apparent". However, this problem only stems from terminology, as our common language attributes different meanings to both of them. Yet, whatever terminology is chosen, in physics the measurement and the consequences of length contraction with respect to any reference frame are clearly and unambiguously defined in the way stated above.[15] [15]: “^ See for example Physics FAQ: "People sometimes argue over whether the Lorentz-Fitzgerald contraction is "real" or not... here's a short answer: the contraction can be measured, but the measurement is frame dependent. Whether that makes it "real" or not has more to do with your choice of words than the physics."

The above reflects the *opinion* that whether or not length contraction is "real" or physical is merely a philosophical debate about semantics. If a student of special relativity comes to Wiki looking for an answer with that question in mind, what does he find?: The ultimate ambiguity. I have shown two examples of contradictory Wiki answers. I am new here. Wiki talks a lot about disambiguation, but on this issue, the senior editors delete all attempts at such disambiguation, calling it armchair philosophy. Either physical objects shrink or they don't. If they do, physics is required to provide the physical explanation for it. If not, it must be clearly labeled as an observer-dependent phenomenon, and those differeces in observations and measurements must be distinguished from actual physical changes in the objects observed. LCcritic (talk) 18:40, 12 October 2013 (UTC)

The issue is somewhat confusing. If you have any suggestions for improving the article, please propose them. Roger (talk) 23:08, 12 October 2013 (UTC)

Opinions about possible contradictions in the length contraction concept must be based on reputable sources, (WP:Sources, WP:OR), otherwise they are not relevant for the improvement of the article. If someone wants to make substantial additions, one has to cite such sources. --D.H (talk) 08:19, 13 October 2013 (UTC)

It does not require a "reputable source" to have general, reasonable agreement that, as I said, either physical objects shrink or they don't. Wiki on length contraction remains ambiguous on that, and I already cited examples. I would improve the article on length contraction (if I were so allowed) by prefacing the discussion with clarification of the "physical or not" issue. Martin Hogbin asked for clarification on that, opening this talk page. D.H answered that it was "only a geometric effect." Yet mainstream SR still treats length contraction as a physical effect, the most popular example of which may be the "barn and ladder/pole" example, confusing different measurements from relativistic frames with a physical shortening of the ladder or pole. Shortened distances between bodies in space (as measured by theoretical relativistic frames) is also frequently argued by SR physicts. I need feedback on whether or not I am allowed to disambiguate this issue as a preface to the length contraction section. Must I first reveal my credentials as a philosopher of science specializing in relativity? (I value my anonymity very highly.) Thanks ahead for any feedback offered. LCcritic (talk) 19:54, 14 October 2013 (UTC)

Alas, your "credentials as a philosopher of science specializing in relativity" don't mean much at Wikipedia, so really there is no need to reveal them. One of the pilars of Wikipedia is that contributors' credentials are entirely irrelevant. See wp:reliable sources, wp:primary sources and wp:NOR. If I'm not mistaken, I think that, as someone with impressive credentials, you might be welcome at Citizendium, which, as far I as understood, was created because specialists with relevant credentials were not really welcome to expose their work here. - DVdm (talk) 21:23, 14 October 2013 (UTC)

Thanks but Citizendium is 'off the radar' for anyone searching length contraction, and I am not willing to give my real name and credentials as a critic of length contraction anyway. Seems no one here cares about disambiguating whether physical objects actually, physically shrink or not (in the context of length contraction,) much less sort out the philosophical difference between the realism of things and distances with length independent of all differences in observation and the idealism Einstein's world where there is no "reality" independent of differences in observation. Seems that SR could grant that proper length is valid physical measurement and that relativistic measurement requires the Lorentz transformation to achieve the correct and valid value of the length of objects and distances... rather than insisting that all frames yield equally valid measurements of length. I would give it a try (disambiguation) if there were any indication that such a try would not be dismissed and deleted out of hand as irrelevant philosophy. Still open to feedback on that. LCcritic (talk) 19:34, 15 October 2013 (UTC)

I do not understand your point. If you are an expert on this subject, then you know that more than one point of view is possible. I added a sentence so that readers could learn more about the difference between the views. If you are an expert, then you probably know of a better reference on the subject than the one I put in. If so, please add your reference and propose your clarifications.

You say, "either physical objects shrink or they don't." Well, they do for one observer and not for another. Maybe you prefer to think of it as a geometrical or a physical effect, I cannot tell from your comments. Roger (talk) 20:32, 15 October 2013 (UTC)

LCcritic, again, what you first need are relevant, reliable, mainstream, secondary sources (again, see wp:RS and wp:secondary sources). When you have those, you can propose here to make some change or addition to the article. Then perhaps, if the proposed content is sufficienctly relevant (see wp:DUE) and is not fringe (see wp:FRINGE), we can find some consensus (see wp:CONSENSUS) to get it in the article. That's how Wikipedia works. Good luck. - DVdm (talk) 20:52, 15 October 2013 (UTC)

Expansion/reorganisation of the 'Reality of length contraction' section

I think this section might be reorganised and expanded a little to cover this subject.

For a start I think the sentence about Bell and Brown's thoughts should moved from the end of the section be put into a historical perspective. At the moment this sentence suggests that this topic is of interest to physicists and is still under active discussion. Martin Hogbin (talk) 14:48, 16 October 2013 (UTC)

Yes, go ahead. Not really a topic under relevant active discussion anymore. - DVdm (talk) 15:12, 16 October 2013 (UTC)

I think that you are reading too much into that sentence. Brown is a philosopher, and wrote a well-received book on the subject in 2005. Of course philosophers write lots of books on subjects that are not of interest to most non-philosophers. The issue is discussed in textbooks and students often ask about it. Go ahead and add historical perspective. Roger (talk) 16:12, 16 October 2013 (UTC)

Maybe we need to separate philosophical musing on the subject from the physics. Martin Hogbin (talk) 16:28, 16 October 2013 (UTC)

Maybe an introduction to length contraction in Wiki could include this from “The State of Experimental Evidence for Length Contraction, 2002” by Delbert Larson, (renowned physicist and designer of particle accelerators): Abstract: "The idea that physical objects become shorter as they move is now well established in physical theory. Both the classical theories of Lorentz, Larmor, Fitzgerald and Poincare and the more radical special theory of relativity of Einstein incorporate a physical length contraction into their worldview. However, no direct measurement of length contraction has ever been done..." Conclusion: “As of July, 2002, it is still not proven that a length contraction exists.”

Roger, to clarify as you requested: To my, "Either physical objects shrink or they don't," you said, "Well, they do for one observer and not for another." The whole point of my proposed clarification is to distinguish differences "for one observer" vs "for another observer" (no argument on that) from differences (changing lengths) in physical objects themselves, if any.LCcritic (talk) 19:44, 16 October 2013 (UTC)

I don't think that such an addition would be due (see wp:DUE). After all, no "direct measurement" of you or me falling from a tall building when dropped, has been done either. Conclusion: as of October, 2013, it is still not proven that you or I will fall from a tall building when dropped. So what? If some renowned physicist and designer of particle accelerators would write that in some article, would we put that in our article on gravitation? The entire body of physics is consistent with you or me falling under such circumstances, just like that same body is consistent with length contraction. - DVdm (talk) 20:47, 16 October 2013 (UTC)

I agree. this website shows that Larson is far from being a mainstream physicist. Martin Hogbin (talk) 21:27, 16 October 2013 (UTC)

LCcritic, if you want to contradict a century of physics textbooks, it is going to take more than an off-hand comment cherry-picked from an unpublished rant. The paper says, "By looking at all of the experimental evidence, it is clear that Einstein's relativity is the most in doubt, because of the experimental tests (reference 6) of Bell's Theorem (reference 7)." Most of the paper is an analysis of an experiment that is claimed to be inconclusive. The point you want to make about direct experiment seems to be already made in the section on "Experimental verifications". The point about observer dependence is also made. Roger (talk) 21:42, 16 October 2013 (UTC)

There is still no clarification (disambiguation) on whether length contraction is "only a geometric effect," as D.H said or whether a physical ladder 20 feet long will fit inside a physical barn 10 feet long as claimed by length contraction advocates. The physics of such shrinkage must be clarified if the claim is that physical objects do in fact shrink. It must also apply to a shortened Earth diameter as measured by an approaching relativistic frame. Disambiguate that.LCcritic (talk) 19:48, 17 October 2013 (UTC)

Are you saying that some sort of ladder-barn experiment could disprove the view that the contraction is only a geometrical effect? Has anyone done such an experiment, and proven the standard textbooks wrong? As usual, just cite some reliable sources, as WP will normally stick to what the textbooks say. Roger (talk) 21:38, 17 October 2013 (UTC)

LCcritic, why not read some good relativity text books. They will explain why length contraction is a geometrical effect (in 4-D spacetime) as D.H. says and how a 20 foot long rod will fit into a 10 foot barn. Martin Hogbin (talk) 22:21, 17 October 2013 (UTC)

Roger, I am saying that Wiki on length contraction remains extremely ambiguous as to whether length contraction is a *physical phenomenon* (that physical objects/distances actually physically get shorter as in "thought experiments" such as the popular barn and ladder/pole example)... or whether it is strictly an observer/frame-of-reference dependent *appearance* of contraction. I have studied relativity for many years and understand the 4-D spacetime *model* (Martin Hogbin, please note, regarding your false assumption about my knowledge of relativity.) I endorse the latter, i.e., only *apparent*, not physical contraction. If the former (physical shrinkage) were true, physics would be required to give a physical/mechanical explanation for shrinking physical objects and the distances between them as per "length contracted space" between bodies in space... as measured by theoretical relativistic frames traveling through space. My intent as a critic of physical shrinkage of objects is simply to make the above distinction clear in the Wiki spirit of disambiguation.LCcritic (talk) 17:51, 18 October 2013 (UTC)LCcritic (talk) 19:24, 18 October 2013 (UTC)

So, we are full circle now — see [3]. This can continue for ages, and it's called talk page disruption — see wp:talk page guidelines. DVdm (talk) 18:03, 18 October 2013 (UTC)

I just reviewed those guidelines. Thanks. It has never been my intention to disrupt "talk" on length contraction but rather to clarify exactly what it means in the context of 'actual, physical' versus 'apparent, observer-dependent' contraction. This was made clear above. (Edit: That reply to Roger and to Martin Hogbin was deleted, and I re-inserted to clarify the conversation.) Your reply is consistent with your *opinion* that I am an anti-relativity crank whose clarification/contribution you would like to censor (delete) in defense of your idea of "mainstream" SR. I suggest that your opinion/bias in that regard has no place in a discussion of what Wiki presents as Length Contraction.LCcritic (talk) 18:58, 18 October 2013 (UTC)

LCcritic, the length contraction is ambiguous because more than one view is possible. I tried to make that clear by adding a sentence and reference. You say, "physics would be required to give a physical/mechanical explanation for shrinking physical objects". Yes, physics does precisely that in the constructive view. The point is commonly made in philosophical discussions of relativity, and sometimes also in textbooks. The history of this point goes back to Lorentz and Einstein. If you are really a "philosopher of science specializing in relativity", then you ought to be able to provide a reference that supplements or clarifies the article on this point. Or if you have some other suggestion for improving the article, then please tell us. I really don't see what you want to add, because everything you say is already in the article. Roger (talk) 23:41, 18 October 2013 (UTC)

I want to add an historical perspective on the philosophical basis for the assumption that the length of objects and the distance between objects in space "depends on how you look at it"... in denial of an objective world with intrinsic properties independent of observation. Then I would like to point out that the "view" that the "contracted distances" between atoms in a physical object (varying with velocity), as an "explanation" of physical contraction, has no basis in physics, and that it does not address the issue of applying the principle to contracted distances between objects in space. If these suggestions are still considered simply "disruptions" of Wiki's attempts at disambiguation, then I am done, and Wiki will continue to be ambiguous on length contraction. Thanks anyway. I did my best to clarify the contradictions in this subject as presented.LCcritic (talk) 18:03, 22 October 2013 (UTC)

LCcritic, you are as free to add your wisdom as anyone else. But it is not true that the atomic distance contraction explanation has no basis in physics. There are papers showing it to be a completely legitimate explanation of the length contraction. While the view is out of favor today, it is historically important and deserves to be mentioned as a valid alternate view. If you think that I am wrong, just produce a reliable source that shows that I am wrong. Roger (talk) 04:28, 24 October 2013 (UTC)

Roger, I am familiar with what Bell and Brown "have argued" regarding atomic distance contraction. Please cite the papers showing empirical, experimental verification of same (making it a "valid alternative view"), specifically object length varying with velocity. Another similar "argument" is often applied to distances between objects in space, contracted in proportion to the velocity of observing relativistic frames. Shall Wiki also endorse contraction of distances between stars as theoretically measured from such frames as also "legitimate" according to SR theory? Have you no comment on the philosophy that the length of things depends on how you look at them, as the basis of length contraction? That is the historical basis of SR and the "elephant in the living room" being ignored in the Wiki presentation of length contraction. LCcritic (talk) 18:27, 24 October 2013 (UTC)

LCcritic, the article already has a section on "Experimental verifications". Just read that for the empirical evidence. Yes, the contraction also applies to "distances between objects in space", according to all the textbooks. The article does not mention stars, but yes, SR applies to stars also. You want to say that the "length of things depends on how you look at them"? The very first sentence of the article says that the contraction is measured relative to an observer. The concept is then explained in greater detail. I have no idea what you mean by the "elephant in the living room". If there is some aspect to this subject that is in the textbooks but not in the article, you have not told us. Roger (talk) 20:34, 24 October 2013 (UTC)

(My edit did not copy correctly. Another try:

Roger, From the Experimental Verifications section: "In addition, even in such a non-co-moving frame, direct experimental confirmations of Length contraction are hard to achieve, because at the current state of technology, objects of considerable extension cannot be accelerated to relativistic speeds. And the only objects traveling with the speed required are atomic particles, yet whose spatial extensions are too small to allow a direct measurement of contraction."

There is no empirical evidence cited, as there is none available. It should read, "has never been achieved" rather than merely "hard to achieve." The reference to atomic particles is also wrong, because the "pancaked" effect has been detected in "clouds" of subatomic particles, but that is clearly due to extreme electromagnetic force accelerating them to near lightspeed, and no such force is involved in the hypothetical length contraction on macro-scale, as for instance the distance between stars as theoretically observed from relativistic frames. Furthermore, a different distance between stars would be measured by every possible different velocity of observing frames... which is clearly absurd.

I am sorry that I was not more clear about the statement,"the length of things depends on how you look at them." This denies the objective world with properties independent of observation and insists that length of objects and distances between them depends on the observer. This would have stars varying in distance between them and Earth's diameter varying with all varieties of theoretical observing relativistic frames. This is not objective science but rather a consequence of Einstein's philosophy that there is no objective world, and that all "subjective" perceptions (relativistic frames of reference) are equally valid. That is the "elephant in the living room" being ignored by SR. This philosophy is relativity's version of subjective idealism in denial of realism... an objective world independent of how differently the same object/distance might be measured. SR insists that physical objects shrink, as per the MMX example cited: "Therefore, in the longitudinal direction the interferometer is supposed to be contracted, in order to restore the equality of both travel times in accordance with the negative experimental result(s)." Likewise the 20 foot ladder fitting into a 10 foot barn... a common thought experiment perpetuated by physical length contraction advocates. From the Reality of Length Contraction section: ..." though it 'really' exists, i.e. in such a way that it could be demonstrated in principle by physical means by a non-comoving observer.[16]" "By physical means?" Not so. Finally, from the History section:

"Eventually, Albert Einstein (1905) was the first who completely removed the ad hoc character from the contraction hypothesis, by demonstrating that this contraction was no dynamical effect in the aether, but rather a kinematic effect due to the change in the notions of space, time and simultaneity brought about by special relativity." So contraction must be clarified as not a physical, dynamical phenomenon but an imaginary, conceptual result of the 4-D spacetime model, which depends on SR's "notions of space, time and simultaneity," not a shortening of the actual distances between bodies in space or of the physical lengths of ladders, planet diameters or an arm of the MM apparatus. These criticisms of length contraction deserve to be presented in Wiki's treatment of the subject in service to clarification of the difference between an observed image of an object/distance (varying with observational perspective) and actual physical shrinkage of objects and distances. LCcritic (talk) 18:04, 25 October 2013 (UTC)

LCcritic, re "So contraction must be clarified as not a physical, dynamical phenomenon but an imaginary, conceptual result of the 4-D spacetime model", only if you have a relevant non-fringe wp:reliable source for that. Many times you have been asked to provide such. If you cannot do that, you are wasting everone's —including your own— time here, and, per wp:talk page guidelines, abusing this talk page. Please stop. - DVdm (talk) 18:18, 25 October 2013 (UTC)

LCcritic, you say that the length contraction is not physical. Then you contradict yourself by saying that the pancaked ion effect "is clearly due to extreme electromagnetic force". Then you are wrong again by saying "no such force is involved in the hypothetical length contraction on macro-scale", because that same electromagnetic force applies to the rigidity of macro objects. You are also quite wrong when you say that the objective world is denied, as Minkowski space is the objective world. I have wasted my time on you because I thought that you would provide some useful references to philosophical or interpretational views. You have not. Roger (talk) 19:16, 25 October 2013 (UTC)

Roger, I don't think we should point out contradictions in their analysis. Unless they produce a solid source backed article change proposal, I think it's best to just stop responding. I have put a second level chat warning on their talk page. - DVdm (talk) 20:09, 25 October 2013 (UTC)

Apparently I have misunderstood the Wiki guidelines. No reputable encyclopedia would allow a presentation on how modern science theorizes that Earth's diameter physically shrinks or that stars move closer together as a result of being observed and measured from various relativistic frames of reference. So as a philosopher of science with a focus on relativity, I have suggested several changes in the presentation on length contraction in order to point out such nonsense from a philosophical perspective. These suggestions have been disregarded in the same way that science forums ban all critics of SR, as if the constant speed of light requires that physical objects shrink as well as the distances between stars, planets and all objects in space... depending on how each possible frame might see them. (This is just wrong.) This does not serve better understanding of relativity. At least such a presentation should include such a philosophical perspective as I have tried and failed to present here. I'm done. DVdm, Please do not delete this final note to the editors of length contraction here just because you personally think I am a crank. (I was a well respected professor of the philosophy of science.) Such censorship has no place in science. (Ps: There is no evidence of length contraction on macro-scale and no explanation for it in physics. Future... theoretical fast moving frames traveling through space can never make massive bodies move closer together.... or planets shrink... in the direction of the observer's travel, of course... so shrunken differently "for each observer." Such absolute nonsense!) LCcritic (talk) 21:03, 25 October 2013 (UTC)

Yes, you have misunderstood the Wiki guidelines. Speakers' corner is over here. - DVdm (talk) 21:07, 25 October 2013 (UTC)

Physics FAQ

The section on the "reality" of length contraction contains a quote from the Physics FAQ. Is that really a suitable reference for Wikipedia? I don't recall ever seeing the Physics FAQ referenced in a Wikipedia article before (although admittedly I haven't read too many Wikipedia articles). Web pages usually aren't considered suitable references, are they? Some parts of the Physics FAQ are pretty good, and some parts are not too good, so I'd be careful. I don't have a problem with that specific quote, but I think the quote by Einstein is probably sufficient.Fiddlefofum (talk) 20:33, 28 October 2013 (UTC)

Yes, both quotes are essentially saying the same, so I removed the FAQ quote. --D.H (talk) 09:02, 29 October 2013 (UTC)

I think we could do with a good modern secondary source. I have looked through everything that I have and found nothing suitable. I think the Einstein quote should stay as it is but anything else we add should be in our own words but supported by good quality reliable secondary sources. Any suggestions? Martin Hogbin (talk) 09:45, 29 October 2013 (UTC)