Talk:Aether drag hypothesis

A note on Stellar Aberration

Perhaps this belongs in the main article on stellar aberration but the image and explanation of how stellar aberration are contradictory to aether drag may be in error. There is no angle of incidence considered at the border of entrainment. As we know through experiments with slits, light can seem to be re-emitted in a spherical fashion from what seems like a new emission point. This seems to be the model considered. Another optical effect not often considered, however, is moving mirror aberration in which it seems light is reflected with a differing angle of incidence than might be expected. (even when quantizing the re-emission as new individual spherical emanations) This effect in combination with other border condition events with light suggest a new angle of incidence would be introduced unlike the image used. IE a laser beam emitted from the source would strike the layer of entrained aether and gain a seeming bend as it gained a new angle of incidence. This is the reason why, historically, stellar aberration, when first discovered, was used as proof for an entrained ether instead of proof against it. Nemesis75 (talk) 20:19, 25 April 2013 (UTC)

Well, Young specifically introduced an immobile aether in order to explain aberration, not complete aether drag. In a similar manner, also Fresnel introduced an almost immobile aether (with partial aether drag). In contrast, it was Stokes (many years later) who considered full aether drag. See also this paper and aberration of light for a historical overview. Sure, also other effects such as "moving mirror aberration" etc. could be combined with aether drag, but this looks like original research. --D.H (talk) 20:38, 25 April 2013 (UTC)

I think the most important thing to know about this period was that they were oblivious to photons and their momentum.

If there is an aether then the speed of light within it is always c, and combining this with conservation of momentum it is soon realised that crosswinds in the aether will not effect the direction of a photon. If you add a component of lateral velocity then you would need to decrease the initial velocity to satisfy c, and there is nothing in play here to diminish the original component of velocity. i.e. there is no force/wind directly opposing the photon.

In the general case of diagonal wind, the lateral component is ignored and the parallel component adjusts speed and frequency.

Btw, this also solves all issues with Sagnac and Michelson-Gale experiments. And Sagnac could be explained by other methods (even with absolute aether drag for moving items on the earth) anyway because of the accelerating frame. Hosh1313 (talk) 14:34, 21 May 2023 (UTC)

Oops - just realised general discussions are against the rules. I was warned about this 12 years ago too - LOL - never knew! :) My apologies. Hosh1313 (talk) 14:54, 21 May 2023 (UTC)

Flat spacetime as the absence of physics?

SR cannot easily be 'wrong', being a theorem in differential geometry. loxley 08:38, 27 July 2005 (UTC)

If you are referring to the idea that any curved-spacetime problem has to reduce to flat spacetime over small regions, I think that the consequences of this tend to be misunderstood by physicists … that geometrical result does not automatically mean that curved spacetime also has to reduce to flat-spacetime physics.

The condition of flat spacetime might instead be the limit a which all meaningful physics disappears – no physical particles to play with, no identifiable field “features” to propagate or interact, a level and uniform field as a zero-particle solution. At this zero-particle limit, you don’t have to modify a smooth metric to allow “mathematical” observers to see “mathematical” particles to be obeying the principle of relativity in the region, because the geometry of the region has already told us that no such particles or observers exist there. Applying Einstein’s early approach of concentrating on the observables in a situation we can say that perhaps it’s not a law of nature that all observers see the principle of relativity being upheld, but rather that nobody sees it being broken. No observer, no breakage. That sort of thing starts to get into QM territory, but perhaps that’s not such a bad thing.

Suppose for a moment that the sort of dragging effects that we see with particulate matter and predict for gravitational fields are a fundamental aspect of moving-body problems: we take a piece of universe, zoom in on it until it becomes effectively flat, place a pair of particles in that flat “arena”, give them a relative velocity … and predicting the shift in a light signal passed between them is no longer a flat spacetime problem, because what we did in the flat spacetime region modified it.. We can zoom in further to get “flat” again, but only by refusing to look at regions that include the particles. In this scenario, flatness does not define the limit at which GR reduces to SR, it defines the limit at which physics effectively ends. We can’t reasonably prove the kinetics of moving-body problems on the basis of a geometry that is only valid when we guarantee the complete absence of moving bodies. We certainly might try that approach in the hope that the resulting relationships will then turn out to be robust enough to stand up to the introduction of more realistic particles, but in the case of SR they aren’t.

It might however not apply to the universe. We could, for instance, suggest as you have done that the distribution of material in the universe is finely adjusted to appear like a hyperbolic geometry. It seems a bit odd however to favour a 3D Euclidean space to such a degree that we are prepared to suggest effects that are specifically adjusted to make it look like hyperbolic space. loxley 08:38, 27 July 2005 (UTC)

No, I'm not suggesting we live in a 3D euclidean metric that just happens to look like the SR metric: I'm suggesting that, if we take dragging effects seriously, and treat them relativistically, we must be living in a velocity-warped non-Euclidean metric that generates equations of motion that must then be recognisably, measurably, physically different from those of SR. I'm saying that the whole SR-based structure of C20th physics may have been founded on an inadequate set of geometrical relationships that don't work properly in curved spacetime, and seem fundamentally incompatible with the general principle of relativity. We have GR, but it's been hacked about to stop it contradicting SR, and consequently doesn't "fit" QM or its original design brief. Experimental verifications of SR typically concentrate on showing that SR is better than a non-relativistic flat aether model, or showing then NM superimposed on a flat background doesn't work (which it doesn't), but there's no obvious test theory to tell experimenters how to test for SR being the wrong theory of relativity.

What I actually favour is a post-SR non-Euclidean metric redesigned from the ground up, in which GR concepts of local c and spacetime curvature apply not just to acceleration and rotation but also to conventional mechanics. Acceleration drags light, rotation drags light, velocity drags light, kinetic energy stored in the metric as spacetime curvature, no information transfer without geometry change. A single geometrical paradigm for everything, fully compliant with the general principle of relativity (unlike the rather Frankenstein-ey thing we have now). But it seems that in order to do that, we have to ditch special relativity and make the theory “curved” all the way down. To me it’s possibly the last major challenge in classical physics, with Einstein throwing down the gauntlet in 1950, but most theoreticians seem to get an attack of vertigo at the idea of losing their SR safety net and prefer not to look over the edge. I find this attitude unimpressive.

Anyway, back on topic: if you want a unified relativistic theory that can't be reached via SR, and your working assumption is that such a theory really exists, and has a wider range of applicability than SR, then a good way to proceed would seem to be to take all the things that SR can’t cope with, and presume that since they can’t be optional (or SR could do them), and can’t be forbidden, they must be mandatory. So you dig up all the effects that violate SR and turn them from bugs into features: you say: the hypothetical final theory hasn’t been found by the SR guys because it only works if you embrace dragging effects, and gravitational mass, and particulate behaviour, as essential parts of what makes mechanics work. And then you find that these bits do actually work very well together, moving particles do drag light, moving gravitational features really should drag light, light-dragging warps lightbeams and should count as a sort of spacetime curvature, and that’s why SR –based approaches can’t enter this territory and stay consistent. Light-dragging as a mechanism for local lightspeed constancy requires more complex geometry than SR, but it you can crack that, you’ve also probably got gravity and cosmology and gawd knows what else all working off the same mechanism. Next-generation single-layer physics.

If this hypothetical theory does exist, and has these characteristics, I don’t see how we’ll be able to find it by starting with the assumption that SR is correct. It seems instead that to get a full general theory of relativity you probably have to assume that the final theory can’t reduce to special relativity’s physics, and then that it can’t reduce to SR’s math, either.

So to me, these "non-SR" dragging effects are potentially quite important. Rather than being archaic C19th leftovers, they might be the key to post-SR C21st relativity theory. ErkDemon 03:09, 3 August 2005 (UTC)

I agree, but it seems both SR AND Ether Drag may be possible, rather like wave particle duality but with a physical explanation. See the DFM. In any case I've added a reference tag, some much needed reference citations and links.Docjudith (talk) 12:48, 11 February 2010 (UTC)

I'm not sure that it's geometrically possible to support both light-dragging effects and Lorentz/Minkowski. Minkowski spacetime depends critically on the assumption that spacetime (as defined by the geometry of lightbeams) is flat and that its properties remain totally unaffected when we throw masses through the region at arbitrarily-high fractions of the speed of light. Light-dragging (as demonstrated by Fizeau, and others since) shows that there is a physical, identifiable distortion of lightbeam geometry in the proximity of moving clusters of particles (water-molecules in the Fizeau experiment). ErkDemon (talk) 14:37, 18 April 2022 (UTC)

As additional data-points we have the fact that general relativity's "relativity of rotation" requires moving masses to have a velocity-dragging component (the receding side of a star pulls more strongly than the approaching side), and that the relativity of acceleration requires accelerated bodies to exert a dragging effect on nearby masses (Einstein 1921). Einstein's acceleration-dragging effect represents an intrinsic curvature of spacetime, which cannot exist unless there is also an underlying velocity-dependent dragging effect. Since acceleration can be "mocked up" using multiple velocity stages, if the relative velocity of masses is inherently a flat-spacetime problem (SR description), then an accelerated body must mark out a curved path in flat spacetime. But GR requires it to mark out a path in intrinsically curved spacetime, so Einstein's 1921 result demonstrates that if general relativity is correct, special relativity must have the wrong geometry, and therefore also the wrong equations. ErkDemon (talk) 14:37, 18 April 2022 (UTC)

General relativity doesn't mesh geometrically with special relativity. We can have one or the other, but we can't have both (at least, not as exact solutions). ErkDemon (talk) 14:37, 18 April 2022 (UTC)

A further data-point is that under GR, a moving mass must drag light due to gravitomagnetism, and the gravitomagnetic dragging effect must be total for a moving horizon - this is represented in spacetime diagrams by drawing in little Minkowski light-cones, and showing them being increasingly tipped over in the vicinity of a rotating or moving black hole. If we treat fundamental massed particles as little pointlike masses enclosed by horizons, and we identify the effective particle interaction surface with the horizon surface, then those particles ought to drag light totally when they move. ErkDemon (talk) 14:37, 18 April 2022 (UTC)

This article is messed up: it confounds two different, competing hypotheses

In the middle of the 19th century there were two competing ether models, those of Stokes and Fresnel.

The Stokes ether was completely entrained by matter ("entrained ether"), while Fresnel's was essentially a stationary ether; however, inside refractive media it was slightly dragged along, the more the higher the refractive index.

The experiment of Fizeau decided between these two models, as Fizeau explained with much elaboration (see the references of the article on Fizeau). Harald88 (talk) 23:51, 6 August 2010 (UTC)

That's true. I wanted to rewrite the article, but afterwards I forgot about it... It will be fixed. --D.H (talk) 08:46, 7 August 2010 (UTC)

Thanks! The cause of the confusion is in the literature as the same word "drift" is used for two contrary things - a drift of ether "relative" to the earth as in Stokes' entrained ether (the extreme of fully entrained = no drift), and a partial drift of ether with matter inside transparent media as in Fresnel's stationary ether (the extreme of complete drift = full entrainment inside but none outside). Perhaps such a disambiguation would be useful at the start.

Another shortcoming that could easily mislead readers, is what appears to be a carefully constructed set of omissions about the Lorentz electron theory and special relativity. Lorentz's 1895 electron theory provided an alternative to ether drift: in that theory there is no ether drift at all, instead the effective speed of light is affected by moving matter. The article fails to make that clear, instead the reader is informed about less relevant aspects of Lorentz's electron theory. Also, special relativity and modern textbooks do not propose a different physical explanation. Special relativity provides a mathematical shortcut to derive "Fresnel drag" and its second postulate is based on the 1895 Lorentz electron theory. The article appears to falsely suggest otherwise on all these points. Harald88 (talk) 13:36, 8 August 2010 (UTC)

I see no "carefully constructed omissions" as I've only tried to reflect mainstream opinion about this subject. BTW: This is a wiki - so if one wants to know more about the connection of Fresnel's theory and that of Lorentz, he should click on the provided link to Lorentz ether theory and History of special relativity and then he will see the section on "local time" and the "Fresnel coefficient". Now to the "omissions":

1. It is clearly said in the article (even in the lead!) that in Lorentz's theory that "there is no ether drift at all".
2. The last point is unclear to me. To which "physical difference" are you referring to? To that between Fresnel and Lorentz, or between Lorentz and Einstein? Well the first is clearly explained in the article, the other (at least within current understanding of relativity) is, that in Lorentz's theory the effects of a "stationary aether" are responsible for the Lorentz transformation, while in Einstein's theory the Lorentz-transformation tells us something about the nature of space and time. As Einstein himself wrote (see 1909 paper).

Einstein: It is completely unnatural to distinguish the two reference frames $K^{\prime }$ and K by introducing an ether that is at rest in one. A satisfying theory can only be reached if we dispense with the ether hypothesis ....Superficial consideration suggests that the essential parts of Lorentz's theory cannot be reconciled with the relativity principle. According to Lorentz's theory, if a light beam propagates through space, it does so with a speed c in the resting frame K of the ether, independently of the state of motion of the emitting object. Let's call this the invariance of the speed of light principle....Hence, the hitherto prevailing transformation equations in passing from one frame to another moving relative to it rest on arbitrary assumptions. If these are abandoned, the essence of Lorentz's theory or, more generally, the "invariance of the speed of light" principle can be reconciled with the relativity principle....Relativity theory has changed our views on light. Light is conceived not as a manifestation of the state of some hypothetical medium, but rather as an independent entity like matter.

So he took light speed invariance (the "essence") from Lorentz, but the aether is rejected as inconsistent with the relativity principle. As far as I know, this still reflects the opinion of leading physicists and historians of relativity. --D.H (talk) 14:47, 8 August 2010 (UTC)

I agree with you that a number of physics textbooks (which are notorious for historical accuracy) present history the way this article presented it; I did not accuse you personally, sorry if you felt it that way. The lead was just now put in by you it seems, as I did not see it last time:

http://en.wikipedia.org/w/index.php?title=Aether_drag_hypothesis&oldid=377567419

The presentation in the lead is very good IMHO. Also the main text is strongly improved, and the summary looks fine too - thanks! The main text should normally include this information and elaborate on it. Most relevant is the still lacking precision that since Lorentz we explain the "Fresnel drag" effect as a dragging of light with moving matter instead of dragging of ether; in modern terms, the scattering of light on moving matter. That is the physical explanation of what happens, since the scattering is different for moving matter.

Note: Einstein as well as a number of other physicists admitted later that the Lorentz ether is consistent with the relativity principle; but that discussion is hardly relevant for this article. And I think that an encyclopedia should primarily report about facts; I see no reason here to report about opinions.

PS: great references, thanks! Good references are the lifeblood of Wikipedia and make it most valueable. Harald88 (talk) 22:36, 8 August 2010 (UTC)

Agree with Harald88. @D.H. Yes, you quote what Einstein have written in his earlier works. But that is what he thought later: [1] (I just included it).Biophys (talk) 17:31, 23 October 2010 (UTC)

Your quotation was out of context (therefore I rewrote the section and included also the 1924-paper). Einstein wrote several papers on the aether, and although he later said that the spacetime-structure of special relativity is "absolute" (in the sense that the properties of spacetime are not affected by the presence of matter), he clearly said that space is not absolute in general relativity anymore. Anyway, Einstein's subsequent definitions of "absolute space" and "aether" were not accepted by the scientific community, and are therefore of secondary importance (see Luminiferous aether#Einstein's views on the aether) --D.H (talk) 11:14, 24 October 2010 (UTC)

I am not quite sure what you are talking about. This particular view by Einstein is very much obvious and clear. He tells that the absolute space as a privileged entity from which accelerations, but not velocities should be counted, and which remains undetectable as long as everything moves by inertia. What that ever challenged or disproved? By whom and where? Note that he tells nothing about time or spacetime here.Biophys (talk) 14:06, 24 October 2010 (UTC)

It was challenged by Einstein himself by inventing general relativity

1924: "Thus the aether of general relativity differs from those of classical mechanics and special relativity in that it is not ‘absolute’ but determined, in its locally variable characteristics, by ponderable matter.")

This is of course the same what he already wrote in 1920, after your quotation

1920: What is fundamentally new in the ether of the general theory of relativity as opposed to the ether of Lorentz consists in this, that the state of the former is at every place determined by connections with the matter and the state of the ether in neighbouring places, which are amenable to law in the form of differential equations;

So you only have to carefully read both papers, that of 1920 and that of 1924 (both have principally the same content, but the latter is more precise). --D.H (talk) 15:13, 24 October 2010 (UTC)

Thank you! This is very instructive. So, let's look at his 1924 article. It tells:

When we speak here of aether, we are, of course, not referring to the corporeal aether of mechanical wave-theory that underlies Newtonian mechanics, whose individual points each have a velocity assigned to them....

In contrast to geometry and kinematics, the ‘space’ of Newton’s theory of motion possesses physical reality. We will call this physical reality which enters the Newtonian law of motion alongside the observable, ponderable real bodies, the aether of mechanics. The occurrence of centrifugal effects with a (rotating) body, whose material points do not change their distances from one another, shows that this aether is not to be understood as a mere hallucination of the Newtonian theory, but rather that it corresponds to something real that exists in nature. ...The mechanical aether--which Newton called ‘absolute space’--must remain for us a physical reality. Of course, one must not be tempted by the expression aether into thinking that, like the physicists of the 19th century, we have in mind something analogous to ponderable matter.

(consistent with his quote I included)Biophys (talk) 20:11, 24 October 2010 (UTC)

After long and fruitless efforts, physicists became convinced that light was not to be understood as the motion of an inertial, elastic medium, that the electromagnetic fields of Maxwell’s theory could not be construed as mechanical...

But there were two difficulties that could not be overcome. Firstly the Maxwell-Loretz equations could not explain how the electric charge constituting an electrical elementary particle can exist in equilibrium in spite of the forces of electrostatic repulsion. Secondly electromagnetic theory could not give a reasonably natural and satisfactory explanation of gravitation...

the aether of general relativity differs from those of classical mechanics and special relativity in that it is not ‘absolute’ but determined, in its locally variable characteristics, by ponderable matter...

But even if these possibilities do mature into an actual theory, we will not be able to do without the aether in theoretical physics, that is, a continuum endowed with physical properties; for general relativity, to whose fundamental viewpoints physicists will always hold fast, rules out direct action at a distance. But every theory of local action assumes continuous fields, and thus also the existence of an aether...

Thus, not only the "absolute space" exists (as a privileged entity from which accelerations, but not velocitiee should be counted), but it must appear in the theory of gravitation, although in a different manner. He does not disprove himself.Biophys (talk) 20:11, 24 October 2010 (UTC)

Fine. If you replace "absolute space" with "aether" in your statement, then it is correct what you say. So nobody disputes the fact, that Einstein clearly introduced (in this two papers) the word aether for all his theories (i.e. that acceleration proves that there are physically real "properties of space".) But I was alluding to Einstein's investigation, whether this aether (regarding the different theories) is "absolute" or not. Einstein's definition of an absolute aether: "we would call this aether ‘absolute’, i.e. by its nature independent of any influence". Thus he concludes for the three theories:

• Newtonian physics has an absolute aether ("For the inertia-giving property of this aether is, according to classical mechanics, not susceptible to any influence, neither from the configuration of matter nor anything else. Hence the term ‘absolute’.").
• Special relativity has also an absolute aether ("According to special relativity too, the aether was absolute, since its influence on inertia and the propogation of light was thought of as being itself independent of physical influence. ").
• General relativity has a relative aether ("Thus the aether of general relativity differs from those of classical mechanics and special relativity in that it is not ‘absolute’ but determined, in its locally variable characteristics, by ponderable matter.).

And of course Einstein "didn't disprove himself", he simply challenged the view that the aether is "absolute" (in general relativity). --D.H (talk) 09:18, 25 October 2010 (UTC)

Agree. Perhaps we need to quote Einstein in this section to explain better his views.Biophys (talk) 16:08, 25 October 2010 (UTC)

Agree. The complication is, of course, that Einstein's "aether of general relativity" does show dragging effects when you move or forcibly-accelerate matter through it. It's a case of Wheeler's "Space tells matter how to move, matter tells space how to bend." Move a lump of matter through a region and you create curvature, and the curvature then influences other matter to move somewhat in the direction of the first lump. Hence gravitationally-coupled momentum exchange, and the gravitational slingshot effect. ErkDemon (talk) 14:48, 18 April 2022 (UTC)

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Problems with Airey's disproof?

Airey is supposed to have proved that the moving Earth's influence does not drag light.

However, according to the extinction theorem (which seems to be tailored to fit known phenomena),

The characteristic "extinction length" of a medium is the distance after which the original wave can be said to have been completely replaced. For visible light, traveling in air at sea level, this distance is approximately 1 mm.

This suggests that ... even ignoring gravitational dragging and aether dragging and whatnot ... light approaching Airey's telescope ought to have been completely dragged along with the Earth, if only because of the dragging effect of the Earth's surrounding envelope of atmosphere! So how did he manage to prove the absence of dragging? I'm assuming that he didn't build an airtight wall around his telescope 100km high and and pump out all the air! This all seems a bit dubious. ErkDemon (talk) 15:25, 18 April 2022 (UTC)