Talk:Transverse Doppler effect

little error on classical prediction
Hi the classical Doppler prediction is not "no effect at all", but an effect that depends on one's speed relative to he ether. I hope I don't need to explain that, and that that error was just due to oversight. Harald88 09:56, 31 October 2005 (UTC)

the mess seems to be increasing
The explanation about the "why"of the effect is very incomplete: the main point to include but that is lacking is time dilation.

About the recent edits by Scienceapologist: No, IMO it certainly may NOT also be referred to as aberration redshift! And neither did I ever see such an idea in peer reviewed literature. As this may cause a lot of confusion, as well as the other related material, I reverted it. Please provide first a peer reviewed reference according to which this is so. Harald88 05:03, 17 December 2005 (UTC)

When you said "symmetric" you did not mention sign or blue or red-shift. Its your addition, so I'll let you make it more clear. Jok2000 17:49, 19 December 2005 (UTC)


 * No problem. Apart of that, the sources are in the time dilation article as well as in most text books on SRT. Harald88 19:54, 19 December 2005 (UTC)

Relativistic Doppler effect, in particular: transverse Doppler effect and 'time dilation'
Should these two articles not be merged? Harald88 18:02, 24 December 2005 (UTC)

Examples and figures
Hi all, as I read the article I found it a bit unclear: for someone who didn't study special relativity it's not easy to understand what the "trsansverse Doppler" means, since it's one of the most beautiful effects of time dilatation I would suggest to put in a figure explaining how (and why) the wavelenghts are different in the two frames (for the longitudinal Doppler effect it's straightforward)... And why the references are all around and not on the bottom? Bye Tatonzolo

Classical transverse Doppler effect
It is so simple. Relativistic effects just replace all galilean observations with proportional time transformation instead of speed transformations. Time proportions just cause chaos when referenced to more than 2 events of 2 observers with relative speed whereas speed proportions do not. Granted for 2 observers where one is stationary with respect to the source of light, SRT is so similar to galilean - esp. doppler effects. Try any relative speed (time) computation with SRT and you will fail when stretched beyond 2 objects of interest. Not so with Galilean equations.And yes it is absurd to not see how Time dialation is just a case of proper time for both observers whereas the light source has relative speed to one and not the other and how else to see the transverse doppler effect. Change in time form start of observed wave is when both observers are at 90 degrees and one is zero in relative speed to light source. The equation is exactly the same as time dialation.

The transverse Doppler effect is by definition the effect which is observed when an observer being in uniform rectilinear motion observes a point source from the lateral direction under an angle of 90° with respect to his line of motion. Contrary to what the present author of the Wikipedia article on the transverse Doppler effect asserts (and contrary to what is stated in almost any textbook on SRT), the optical transverse Doppler effect is known since the year of 1842, when Christian Doppler published his famous article (translation from German) "On the coloured light of the binary stars and of some other celestical bodies - Attempt of a general theory including Bradley's theorem as an integral part". The article is contained in Doppler's collected papers (edited by H. A. Lorentz). Bradley's theorem, also known as his law of velocity aberration or as his theorem for the addition of the velocity of light, reads:  c'  = c - v. It defines the direction under which the wave fronts of a distant light source arrive at normal incidence. During the astronomical observation of a fixed star for example the observer's telescope, therefore, is aligned in the direction antiparallel to light's relative phase velocity c' . The transverse Doppler effect is observed during the short moment when the vector c'  is aligned precisely perpendicularly with respect to the velocity vector v. Bradley's theorem then leads to a rectangular vector triangle  the hypotenuse of which is c. From the proportionality relation f ' / f = c' / c (where f ' is the Doppler shifted frequency of oscillation) and the Pythagorean law follows then the well known formula for the transverse Doppler effect, which in the framework of classical optics of moving bodies is exactly the same as in SRT. Now, a second order type of effect which is very well known already since the year of 1842 can hardly be a consequence of the phenomenon of time dilatation, as currently asserted in textbooks on SRT. The proposal that the transverse Doppler effect should be regarded as a pure effect of time dilatation was put foreward by Albert Einstein in a short note published in 1907 in Annalen der Physik. In that note Einstein had by no means asserted that the transverse Doppler effect should be regarded as a novel phenomenon. He rather suggested indirectly that from now on this well known aberration effect should be re-interpreted as an effect of time dilatation. That his proposal should merely be regarded as a bad joke can best be seen from the fact that the Lorentz contraction would have to be simultaneously zero when the transverse Doppler effect is observed, because solely if this were the case the transverse Doppler effect could be interpreted as a "pure" effect of time dilatation. This, however, is by no means the case: The Lorentz contraction is zero not if c'  is perpendicular on v, but rather if c is perpendicular on v, i.e., not if the inclination angle of the observer's telescope amounts to 90° but rather when the emission angle of the light ray amounts to 90° (because only then the relative velocity between source and observer passes through zero). In the latter case, however, a second order blue shift is predicted (both by classical theory and by SRT; for the case of SRT compare Pauli's encyclopaedical article - Pauli presented a formula for "his" transverse Doppler effect, which predicts a second order blue shift), not the desired second order red shift. It should be noted, however, that Doppler's original optical Doppler theory indeed requires modification because from historical reasons it ignored the transverse character of light waves. (It is strictly valid solely for longitudinal waves, such as acoustic waves). In the case of transverse waves (not solely of light waves) an additional aberration phenomenon enters the scenery, which may qualitatively be described as "velocity aberration of angular velocity". It is responsible for effects which in the framework of SRT are wrongly attributed to "time dilatation". If the former (classical) phenomenon is taken into account, the classical formula for the Doppler effect of transverse waves resembles very much the formula predicted circumstantially by means of SRT. Readers interested in this discussion should first consult a review of the classical optics of moving bodies, such as the one presented in Miller's historical account of SRT. Another suitable review article, written by one of the pioneers of SRT, Max von Laue, is available in Handbuch der Experimentalphysik. The content of the "Textbook quotes" (Mould, d'Inverno) has nothing to do with reality, but is what authors of textbooks on SRT like to "believe" (since now one century). Other textbook authors try to "prove" that for the case of lateral oberservation the relation f ' = f is obtained in classical physics (among them is J. D. Jackson). The "proof" works in fact in the case of a plane wave, but a point source, such as a fixed star, does not emit plane waves, and if one resorts to plane waves then this is from the very beginning only an approximation. A "proof" based on approximately valid relations is inacceptable, however. The confusion in the literature, which concerns the transverse Doppler effect, can be traced back to the circumstance that so-called "authorities" of SRT, like Max von Laue and Max Born, had misinterpreted (in blind trust) Einstein's proposal of 1907 and had asserted in their textbooks indirectly (Max von Laue) or directly (Max Born) that the transverse Doppler effect is due to "time dilatation". Later textbook authors then relied on these "authorties". In the many editions since 1932 of the textbook on theoretical physics by Joos the erroneous interpretation of Einstein's proposal of 1907 leads to a direct contradiction. Thus, in the section on the acoustic Doppler effect Joos writes down correctly the aberration law valid in acoustics. Moreover, he also states explicitely the formula for the relative phase velocity valid for the special case of lateral observation. About ten pages further on, in the section on the relativistic Doppler effect, Joos then, however, states that in acoustics the relation f ' = f is strictly valid for lateral observation from a moving platform. A sketch of the different telescope inclinations required during the observation of a fixed star from a moving platform may be found in the article "Temptative Galilean Synthesis of the Optical Doppler Effect", Existentia XV, 127 - 139 (2005).84.154.74.1 19:07, 13 April 2006 (UTC)


 * KraMuc (assuming that it's you), you may have a point that "transverse Doppler" is a rather general expression that is likely to be used for the classical effect for a moving observer as well - which is a very different definition than the one that this article uses.
 * If indeed you can show (by citing a source) that the term was also used for the classical effect, then it must be mentioned in the article. BTW, the article's current development lends itself very well to such an addition, as that would enable to clarify better how "time dilation" affects the predictions and it would justify not merging this article with other articles. Harald88 12:49, 20 May 2006 (UTC)


 * PS your claim that that classical transverse Doppler shift is the same as that of SRT is easily shown to be erroneous; but I simply checked it (again) for myself, as I don't have a source at hand where the classical Doppler shift is calculated in sufficient detail (your above cited article makes the same error as you and even doesn't provide enough detail to either confirm or rebut it; Mathpages only shows it indirectly and it can hardly be considered as Wikipedia source). Harald88 17:24, 20 May 2006 (UTC)

Harald88, you are mixing up everything again like an autodidact, and you don't want to listen. You know once again everything in advance and much better than anybody else. What you are stating here, however, is nonsense again. The classical forerunner of SRT has been optics of moving bodies, a discipline dealing with the observation of  point source from a moving platform, which is governed by Bradley's law of velocity aberration. A point source emits spherical waves, not plane waves.

In none of the references stated in the nonsensible Wikipedia article on the transverse Doppler effect, to which you have contributed, a proof is delivered, but it is simply asserted there that the transverse Doppler effect has been unknown in classical physics. In dozens of textbooks this nonsense is repeated without proof because authors tend to write off from one another.

'Proofs' of the nonsense are delivered in Chapter 11 of J. D. Jackson's book on clsssical electrodynamics as well as in a German book on SRT by Greiner/Rafelski who probably have copied the 'deduction' offered in Jackson's book (who himself probably got that 'deduction' from somewhere else). These 'deductions' boil down to direct betrayal of naive students, because the students are made to believe that a point source, such as a fixed star, does emit plane waves rather than spherical waves. Nobody tells them that the plane wave approximation is only an approximation and that it is, therefore, completely useless to 'prove' anything in a context of this paramount importance.

The nonsense of the 'non-existing classical Doppler effect' spreads in the literature since Einstein published in 1907 a short note, where he had stated that the transverse Doppler effect, which already Stark wanted to measure (why, if it is unknown in classical optics of moving bodies?), is "important", but not that it is "unknown" in classical physics. It apparently has to do with the hystery which seems to capture most people who get in touch with the special relativity nonsense.


 * Einstein's general knowledge of the history of physics seemed to be a bit ropey during his "productive" period. Fr'instance he may well have been ignorant of earlier work on subjects like light-bending, and seems to have been totally ignorant of the contents of Newton's Opticks until the 1930's. ErkDemon 03:04, 26 February 2007 (UTC)

In reality SRT departs from classical optics of moving bodies solely for the case of longitudinal observation.

This I was going today to demonstrate in the article Modern Galilean relativity.

Because of your current unprofessional and grandfatherly interference with that article I stopped today contributing to it.

Since you have the big mouth and know everything better, I suggest that you finish the article now. Perhaps you should do this in close cooperartion with Philosphus who has a similar big mouth (with little behind it). KraMuc 13:47, 18 June 2006 (UTC)


 * The general rule is, that if we assume that light travels at fixed speed wrt the observer, we get a zero "transverse" redshift, if we assume that it travels at fixed speed wrt the emitter, we get a Lorentz-squared redshift, and if we believe that it moves with some intermediate speed, we get a redshift somewhere in the middle of this range. SR's predictions in this situation aren't qualitatively novel (as sometimes claimed), they are numerically slap bang in the middle of the range given by the broad spread of earlier theories. What is novel with SR is its interpretation of why the redshift happens.


 * In experiments designed to verify SR's transverse redshift effect, nasty old emission-theory would have predicted a stronger redshift value than SR does. Really. :) But test theory invoked by experimenters in these situations usually doesn't actually take into account how SR compares with real, historical theories, but compares SR against a convenient reference model, referred to as "classical theory", which assumes that lightspeed is totally fixed wrt the observer. Most pre-SR theories didn't assume this. So when SR texts compare SR's predictions with those of "classical theory", they usually aren't making a fair comparison between SR and earlier theories.


 * The SR community's attitude to stuff in the analysis and testing literature seems to be a bit like the major Christian churches' attitude to what's in the Bible. If they can get away with it they'll insist that everything in the literature is absolutely true, and woe betide anyone who suggests different, ye Heretical Evil-Doers and Enemies of Physics! Until you can pin them down and force them to accept that a lot of this stuff, point by point, is frankly, mathematically and historically, a little bit crappy. And then they backtrack and say, well, it was never meant to be taken literally, nobody really said those things, at least, if they did, they didn't mean them seriously ... (sigh) ErkDemon 03:04, 26 February 2007 (UTC)

Assertions found on the classical transverse Doppler effect in textbooks on SRT are indeed misleading
The classical forerunner of SRT is the discipline of "Optics of moving bodies", compare, e.g., A. I. Miller's historical account of SRT. This theory which is based on Bradley's aberration theorem does, of course, also predict the so-called transverse Doppler effect. Velocity aberration brings about that the apparent direction of the light source observed never coincides with its true geometrical direction. Thus, if the apparent direction of the light source makes a right angle with respect to the observer's line of motion (which is the condition under which the "transverse Dopper effect" is measured), its true direction deviates from the axis of the telescope by a small angle, the aberration angle. This discrepancy between apparent and true directions gives rise to the transverse Doppler effect, a redshift of second order. But at that time, little attention was focused on effects of second order. In his original paper of 1842, C. Doppler simply approximated Bradley's theorem with the help of a cosine function. If this crude approximation is made, the transverse Doppler effect is suppressed.

Apart from this, the classical transverse Doppler effect does also exist in acoustics, where also the aberration law has to be observed; compare, e.g., the corresponding section in the book ''Theoretical Physics" by Georg Joos.84.153.104.56 14:31, 12 September 2006 (UTC)

what happened?
For a while I didn't look and now, among other things, the whole section on reciprocity has disappeared while anti-mainstream ideas are promoted as matter-of-fact. What happened? Harald88 00:14, 13 September 2006 (UTC)


 * Undetected KraMuc activity. --Pjacobi 11:57, 13 September 2006 (UTC)


 * Yeah I guessed so. I see you already reverted.
 * Note to Kramuc: personally I don't mind compact mention of an extreme minority view (even if it's in fact wrong), but by now you should understand that Wikipedia has a zero tolerance level for deletion of majority views. Harald88 20:27, 13 September 2006 (UTC)

Students be aware
The critical comments and modifications are not from Kramuc. A lot of phantastic rubbish is written in the article which neither agrees with the common views of modern physics nor with the views currently expressed by Kramuc. What dos it mean to say that "transverse" is the key to "reciprocal"? This is certainly not asserted in any of the references mentioned or in textbooks on special relativity, but seems to be a private opinion of a very small minority consisting solely of Harald88. The so-called transverse Doppler effect is observed when light's relative phase velocity governed by the aberration law arrives at the observer's line of rectilinear motion under normal incidence. In order to receive maximum light intensity, the observer's astronomical telescope has then to be aligned at a right angle with respect to his line of motion. Kramuc is right in saying that this is known since 1842, when C. Doppler published his famous paper "On the coloured light of the binary stars and of some other celestical bodies - Attempt of a more general theory including Bradley's theorem as an integral part", reprinted in Abhandlungen Christian Dopplers (H.A. Lorentz, ed.), Leipzig 1907, pp. 1 - 24.

In acoustics the transverse Doppler effect is observed too, compare, e.g., Georg Joos, Lehrbuch der Theoretischen Physik 11. Auflage, Leipzig 1959, Zweites Buch, Sechstes Kapitel, § 4: '''Bewegte Bezugssysteme in der Akustik. Der Doppler-Effekt'''.

The majority of theoretical physicists knows all this. A small minority of arrogant and ignorant textbooks authors, however, who feel obliged to mystify physics and to fool naive students, asserts the contrary. For these textbooks authors, who since generations copy the terrible and irresponsible nonsense propagated on relativity by authors of the older generation, it is not necessary to study Doppler's orginal paper of 1842 or to look into the chapter on acoustics of the book by G. Joos. For these arrogant members of the physical society this is not necessary because they a very much convinced that they know everything much better.

What could students do about this situation? Perhaps soon they do find out themselves ... --84.154.94.153 17:17, 14 September 2006 (UTC)


 * Opinions of editors don't matter, but just for the record: It's not my opinion that "transverse" is the key to "reciprocal".
 * It is however my opinion, based on style and contents, that the above section is by KraMuc.
 * Cheers, Harald88 17:49, 14 September 2006 (UTC)


 * KraMuc is a bleeding double-crosser, isn't he? I also strongly believe that this is from KraMuc. The longer I think about his ideas the more I get the impression that at the end he might be right.---PaolaDiApulia 18:15, 14 September 2006 (UTC)

Quote of 19th century mention of the term "Classical Doppler" required
Eventhough in classical physics a Doppler effect exists by detection under a right angle with a moving detector, that does not mean that the term "transverse Doppler" is or was notably used for that case. So far no quote has come forth to verify that this term was used in classical physics. If no 19th century source can be found that uses that term, no more mention of it should be made in the article than is necessary to explain its existence in principle. Harald88 18:51, 14 September 2006 (UTC)


 * Harald88, your viewpoint is incorrect. You have to study the paper of J. Stark cited in Einstein's paper of 1907. Stark wanted ro measure the transverse optical Doppler effect under an observation angle of 90 degree. Stark's intention gave rise to Einstein's nonsensible proposal of re-interpretation of the classically well known effect. Another quote is Emden or Emde, Naturwissenschaften, about 1927. The paper is probably cited in Liebscher's Homepage article "Fallstricke beim Thema Aberration". It is among the Weblinks to "Anti-relativity", I believe. What is written under "Reciprocity" does hardly agree with the mainstream viewpoint and sounds to me rather clumsy. Thanks for Michelson's paper which arrived here some time ago.--84.154.87.22 08:38, 15 September 2006 (UTC)


 * Hi 84, under this header (and in fact, inn Wikipedia!) no editor's viewpoint is discussed: instead correct sourcing is required. Thus if you can come up with such a citation, please do so thanks! Harald88 11:44, 15 September 2006 (UTC)
 * Note: Einstein clearly explained that SRT predicts a time dilation effect on top of classical Doppler - it's erroneous to call an aditional effect a "reinterpretation". Harald88 11:48, 15 September 2006 (UTC)

Harald88, the first of these four comments is correct: Classical Doppler theory based on the law of velocity aberration $$\vec{c_{r}} = \vec{c} - \vec{v}$$ (in optics of moving bodies called "Bradley's theorem", cf. A.I. Miller's historical account of SRT) predicts a second-order shift toward lower frequencies for the situation $$\vec{c_{r}} \perp \vec{v}$$ corresponding to the "transverse Doppler effect". Since in the 19th century nobody had been interested in this completely unimportant quadratic effect, which originates from velocity aberration, the effect had not been given a special name at that time. The quadratic effect had also been known in acoustics since a long time, where it follows from velocity aberration too, cf. the section "Bewegte Bezugssystem in der Akustik. Der Doppler-Effekt" in Lehrbuch der Theoretischen Physik by G. Joos. Also here it is completely uninportant, und everybody neglected it. At that time the angular dependence of the Doppler effect was not derived exactly from the aberration law, as would be required if effects of second order are of interest, but approximated by  assuming a cosine dependence. Because of these historical circumstances the term "transverse Doppler effect" was not yet coined in the 19th century. Therefore, you will not find the term in literature of the 19th century.

What you say in the fourth note is incorrect and in direct contradiction of the content of the first note: Since the quadratic effect, nowadays called "transverse Doppler effect", was already implicated in classical Doppler theory (for the observation of point sources) based on the law of velocity aberration, it is certainly not the result of putting something "on top of" something else. The transverse Doppler effect existed already in the 19th century, because it was implicated in the Doppler theory available at that time, but it had not yet been given the particular name "transverse Doppler effect".

Since the transverse Doppler effect is implicated in the older Doppler theory (which is a Doppler theory for longitudinal waves), it has absolutely nothing to do with "time dilatation". The "time dilatation" nonsense is bluff: Einstein knew of course that the square root expression for the transverse Doppler effect was already implicated in the older Doppler theory based on the law of velocity aberration. As far as literature indicates, after his nonsensible indirect suggestion of 1907 in Annalen der Physik, Einstein apparently has nowhere again directly or indirectly asserted that the transverse Doppler effect is a novel phenomenon predicted by SRT, or  a phenomenon "on top of" classical Doppler theory. If you know of a later publication, where Einstein  repeated his nonsensible interpretation of 1907, then please tell me.

Einstein made this very clever. Already in the first sentence of his paper of 1907 he called Stark's efforts to measure the transverse Doppler effect for canal rays "very important". Everybody likes to hear things like that! But compliments like this make you blind for the intention behind it, namely bluff.

What you say in the fourth note is correct for all directions of observation except for the observation angle of 90 degree (transverse Doppler effect). For all other angles of observation the Lorentz transformation actually does predict new effects of second order. But these novel quadratic effects have nothing to do with "time dilatation" either, but originate from the transverse character of electromagnetic waves. How does this happen?

A transverse wave has a period of oscillation, T. For an observer at rest the corresponding phase of the wave rotates in the transverse plane. In order to be able to detect the phase rotation the observer needs a suitable sensor, such as an electric dipole antenna. The two arms of the dipole antenna are then aligned in the wave's transverse plane, i.e. perpendiculary to its direction of propagation. The best thing to do here is to visualize an elliptically or circularly polarized wave, where the additional component (rotating in phase quadrature) is detected by means of a second dipole antenna arranged orthogonally to the first one. Then, if you wanted to, you could really measure the phase rotation occuring in the transverse plane. If the frequency of oscillation is slow enough, you also could make the phase rotation visible by separately amplifying the two signals and by connecting the outputs of the two amplifiers to the two input terminals of an oscilloscope.

Let the observer equipped with the two orthogonal dipole antennas now move in the direction of propagation (or against it) with constant rectilinear velocity v. This is motion perpendicular to the transverse plane of the transverse wave. Phase locking can take place solely in the transverse plane, but the antennas escape continuously from the transverse plane, where the phase rotation of the wave occurs! The Doppler signal received by the observer is a forced oscillation, but what rotating component of the wave steers the Doppler signal? It is certainly not the rotating phase observed by an observer at rest, because the moving observer cannot get hold of that phase (because he continuously escapes from the transverse plane). It is a vectorial fraction of the wave's angular velocity $$\vec{\omega}$$, to which the Doppler signal received is phase locked. Independently of the direction of motion of the observer, that angular frequency which is effective in the process of phase locking, is always smaller than the nominal angular frequeny $$\omega\,$$ of the wave. In other words, Harald88, if you watch a transverse wave from a moving platform, you always find that its angular frequency seems to be lower than it is in the rest frame.

From mere historical reasons, in the framework of SRT the latter effect is erroneously attributed to "time dilatation". Since the well known root expression (Lorentz factor) turns up in the analysis of the latter effect, which also is known from the transverse Doppler effect, it was wrongly concluded that the origin for this root expression is in both cases the same: "time dilalation". In physical reality, the root expression enters the theory from two entirey different reasons: In the case of the transverse Doppler effect (lateral observation of a point source) its direct cause is the classical law of velocity aberration. In the case of longitudinal observation of a transverse wave it originates from the aberration of angular velocity. Visualize a point rotating in the transverse plane on a circular or elliptic orbit, and assume that the rotating point is driven by a transverse wave. Now, as the observer moves, this rotating point is, of course, also influenced by velocity aberration! Unfortunately, this had been overlooked in classical Doppler theory (of transverse waves). ---84.153.118.133 11:37, 16 September 2006 (UTC)

The fact that the correct phase relationship $$c' ^{2} = c^{2} - v^{2}\,$$ valid for the transverse Doppler effect does follow also from Bradley's classical aberration theorem $$\vec{c'} = \vec{c} - \vec{v}$$ is explicitely stated in R. Emde, "Aberration und Relativitätstheorie", Die Naturwissenschaften 14, 327 - 335 (1926). For the corresponding case of acoustics the same phase relationship is explicitely stated in G. Joos, Lehrbuch der Theoretischen Physik; Section "Bewegte Bezugssysteme in der Akustik. Der Doppler-Effekt". The statement is found in Joos' book in all its editions from 1932 to 1989.


 * It is important to know that the common use of the term indeed is the additionally predicted effect by SRT and not the classical effect. The article should reflect the common meanings of the word.
 * Apart of that - and filtering out editor's opinions - I still see no citation forthcoming that backs up the claim that some notable sources disagree with Einstein. As I (and probably most editors) don't have those sources that you mention and on which you base your claims, that would be helpful. Harald88 14:16, 17 September 2006 (UTC)


 * In physics, "classical" is a term that is usually applied retrospectively, or only after some other scheme has come along that considers itself to be more "modern". When we discuss QM, we describe pre-QM theory as "classical", and when we have QM effect "X", and find a counterpart in pre-QM theory, it is natural to refer to it as "classical X", to distinguish it from the default, assumed "modern" effect "X". Similarly, if an effect is associated with "modern" relativity theory, and we find an older counterpart, it is natural to apply the prefix "classical" to the older effect to distinguish it from its modern version. But before the newer theory comes along and gets accepted, nobody will be referring to an effect in the contemporary literature as "classical", and sometimes an effect won't be considered important enough to even have a special name until a new theory comes along and decides to give the effect a new significance. The importance of an effect in older theory is sometimes assigned retrospectively. Certainly people predicted a "transverse" effect in older theory, and this is documented in contemporary sources, but the subject probably wasn't considered all that important until SR came along and gave its transverse predictions more significance, so those older mentions will tend to refer to the effect descriptively, and rather casually. Not everyone is hung up on naming rituals.


 * In the early days of what we now call "classical music", I'm sure that nobody actually called it classical music. The ancient Egytians didn't recognise a country called "ancient Egypt" as theirs. But the lack of contemporary references to the phrase doesn't mean that these things didn't exist, and shouldn't be documented. Insisting otherwise seems unreasonable.


 * Another question: Should Wiki be limited only to articles about subjects whose title is an iron-clad technical term? I don't think so. If Wiki was a dictionary we'd be entitled to insist that people didn't create entries with novel titles, but Wiki is not a dictionary with strict titles and definitions, its an encyclopaedia, and sometimes it's important to split articles into distinct sub-articles with composite titles. If someone has assembled a very long article on "black holes in science fiction" and it doesn't count as original research, this may be fascinating material for sci-fi fans and film buffs, but shouldn't be merged en masse into the main "black hole" article aimed at people only interested in actual physics theory. Hence there would then be a need for a separate article with this name, even though "black holes in science fiction" isn't an established technical term (and currently only gives three hits on Google). A subject can be interesting or important without having a special "technical" name. ErkDemon 04:21, 26 February 2007 (UTC)

Questions
The paragraph "Reprocity" is unclear. During the measurement of the TDE the wavefronts arrive from the lateral direction (with respect to the observer's line of motion). If in this lateral direction a light beam would be sent (emission angle is 90 degrees), it would not suffer a red shift at the other end of the transmission path, but a blue shift. Thus, what is meant by reciprocity? --195.30.184.67 11:27, 17 September 2006 (UTC) --195.30.184.67 10:54, 17 September 2006 (UTC)


 * Hmm, I thought that it was clear that it's the observation (measured frequency) that is reciprocical - but perhaps it needs to be elaborated. Harald88 14:03, 17 September 2006 (UTC)


 * Harald88, if meant like this, "reprocity" would be a feature of the relativistic Doppler effect in general, not solely of the so-called transverse Doppler effect, a special case. Why, then, stressing this feature so very much in the context of the transverse Doppler effect (lateral observation under an angle of $$\pi/2$$)? It is also not clear, why radiation should arrive at the emitter "perhaps accidentally". In a realistic thought experiment things could be arranged such that at both ends of a transmission path both an emitter and a receiver are available. Why is the formula for the transverse Doppler effect
 * $$f' = f \sqrt{1 - v^2/c^2\,}$$
 * removed again and again, e.g. by user Pjacobi, if some other user has correctly inserted it? Is the reason for this perhaps that it follows also from Bradley's classical aberration theorem $$\vec{c'} = \vec{c} - \vec{v}$$? Cheers, --84.154.109.236 10:16, 18 September 2006 (UTC)


 * As a matter of fact, the so-called transverse Doppler effect is (in its current use) nothing else but the effect of time dilation on a Doppler measurement under a certain angle. It is asserted by Einstein that + <(true) Doppler> -> <"relativistic" Doppler> ; and relativistic Doppler at a straight angle relative to the observer frame is known as "Transverse Doppler". When I have time I'll have a fresh look at that section. Harald88 22:20, 19 September 2006 (UTC)

The last sentence of Overview seems to be in conflict with the principle of relativity, according to which it should be impossible to distinguish between motion of the emitter and motion of the receiver.--Graf Grauenstein 13:56, 17 September 2006 (UTC)


 * Sure - that's what the disagreement is about. Harald88 14:03, 17 September 2006 (UTC)

It's wrong, and it isn't "discussed next". Removing. Thor2023 00:23, 18 December 2006 (UTC)

Experimental success - based on numbers or language ?
The "political" problem we have here is that differences in nomenclature, and differences in the unambiguous physical outcomes of experiments (say, the number that will be shown on a particular frequency-meter), have become all mixed up together into an ugly confused mess. That mess doesn't originate here in the article and discussion page, or with us, it originates out there in the research community. They fouled things up, and the confusion here is an accurate representation of the mess they those guys created, and never got around to cleaning up.

Some SR sources insist that the term "transverse redshift" ought properly to be reserved for effects under special relativity, because that's the common usage. We might be able to get away with that if everyone realised that the literal meaning of the term then isn't quite the same as how it is used. If we accepted this, then when other theories predicted similar or indistinguishable effects in the same experimental setup, then even though those shifts would be "transverse" and "red", they couldn't be referred to as "transverse redshifts", because their conceptual basis and explanation would be different to that of the SR effect.

But SR sources also say that we can test SR by carrying out experimental verifications of the transverse redshift effect. You see the problem. There are two slightly different understood "standard" meanings here, and they clash: One says that this effect doesn't ever appear in other theories by definition, and the other treats it as the simple uninterpreted physical outcome of an experiment that can be used to assess the relative worth of different theories.

Fuse these two different meanings together and you can get the sort of "junk logic" that sometimes appears in SR texts, where they say that SR predicts the effect, we find the effect, the effect is known to be unique to SR, and therefore ... the experimental result can only be explained by SR. It's an invalid conclusion assembled from reasonable smaller component arguments that shift the meaning of a term part-way through a chain of logic. It's a bit like saying saying that the immature fruits of the orange tree outside your window are green, apples are also green, and therefore apples are coloured "orange". One word, two meanings that overlap but aren't entirely interchangeable.

The way out of this mess would seem to be to allow the term to mean what it says without specifying a single theory (words meaning what they say -- there's a novel concept) or, as a compromise, to allow talk of "classical" transverse effects (or some other similar qualified phrase), so that SR could be allowed its default ownership of the term "transverse redshift" for historical reasons, but we would still have a way of acknowledging the existence of physically-similar predictions under other theories. There have been objections to each of these options. I do understand why some SR enthusiasts may like things exactly the way they are right now, but for things to go on as they are now is not really in the interests of the subject, or the theory. It's not good for a theory's reputation if it seems that the theory is being partly supported by a manipulation of language that makes it impossible for people to mention the existence of similar effects in previous theories. ErkDemon 06:25, 26 February 2007 (UTC)

Source & observer wrong.
If the subscript s means source and o observer, then the equation is backwards. The transverse Doppler shift increases the observed frequency, making the light bluer. Clem137 20:43, 10 April 2007 (UTC)

This Article needs To be Completely Rewritten
You guys need to get to work fixing the many problems in this article. 08:17, July 28, 2008 user:72.64.43.204 (prev unsigned/dated)

Would a diagram be useful?
Would the addition of a diagram help of just confuse? RJFJR (talk) 16:22, 18 March 2009 (UTC)

Merged and redirected
Merged and redirected to Relativistic Doppler effect