General Relativity (and Einstein) - needs an ether? or not?

[Nereid]

I was inspired to start this new Q&A thread by a post by turbo-1:

In his Leyden address and later in his 1924 work "Uber den Ether" Einstein insisted that GR requires an ether, and that all gravitational and inertial effects must arise from matter's interaction with it. In the 1924 work, he put forward the idea that the optical effects that we call gravitational lensing are caused by differences in the speed of light as the light traverses regions of ether of varying density.

My question in this thread has two parts:

1) In what sense does the theory of General Relativity, as it is defined today, incorporate (or require) an 'ether'?

2) In terms of how the theory of General Relativity is understood today, what was Einstein talking about in his 1924 work (mentioned above)?

[Thomas(believer)]

If I remember well, in the "early days" is was believed that the ether was the medium wherein em-waves propagate. I think Einstein is refering to this ether and this has nothing to do with GR. As Einstein did believe in the existance of this ether, I am sure he believed that GR would have had an effect on the ether. Well, that is my guess.

[Ken G]

1) There is no ether in modern GR, there is only a metric tensor and a dynamical equation that is reference-frame independent. I'm not an expert, and maybe you need one, but as I understand it, spacetime admits a metric that can be modeled as a curvature, and this curvature is also reference frame independent.
2) I have no idea. Einstein gets misquoted a lot, I'd start with that hypothesis and see what the proof is that Einstein felt you needed a preferred reference frame. On the surface, it would seem that the central idea of relativity is that there is no preferred frame, i.e., no ether. Perhaps he had some other definition of ether in mind.

[Celeritas]

Not being an expert. There is evidence that Einstein at first rejected Aether but later began to reverse his opinion. Google Einstein+Aether

An address delivered on May 5th, 1920

The notion that IF light is a wave then it must have a medium through which to propogate etc. But Einstein apparently had some issues with "Action at a Distance". The "Butterfly Effect" apparently violated c as the fastest method of propogation. There are some references to him having refered to it as 'spooky'. Probably stared by Mach.

But generally speaking 'Aether' seems to have been been kicked out of the mainstream. Mostly.

Perhaps the need for a metric tensor demonstrates the need for an Aether?- or the use of metric tensor+dynamic equation that is reference-frame independant requires no Aether. Thus its rejection.

Supposedly this was written in a letter from E to Lorenz:

"I agree with you that the general relativity theory admits of an ether hypothesis as does the special relativity theory. But this new ether theory would not violate the principle of relativity. The reason is that the state [...metric tensor] = Aether is not that of a rigid body in an independent state of motion, but a state of motion which is a function of position determined through the metrical phenomena."

One man's Aether may be another's Dark Matter.

[Ken G]

It sounds like Einstein's concept of an aether was quite a bit different than the conventional view before Michelson-Morley. But you won't get dark matter from it, the properties of dark matter cannot be attributed to space itself (or we would not need both dark matter and dark energy).

[George]

Supposedly this was written in a letter from E to Lorenz:

"I agree with you that the general relativity theory admits of an ether hypothesis as does the special relativity theory. But this new ether theory would not violate the principle of relativity. The reason is that the state [...metric tensor] = Aether is not that of a rigid body in an independent state of motion, but a state of motion which is a function of position determined through the metrical phenomena."

That was written to Lorentz in 1916.

That is a cool link about ether, though.

Reading further produced Einstein's 1938 statement ...

"All our attempts to make ether real failed. It revealed neither its mechanical construction nor absolute motion. Nothing remained of all the properties of the ether except that for which it was invented, i.e., its ability to transmit electromagnetic waves. Our attempts to discover the properties of the ether led to difficulties and contradictions. After such bad experiences, this is the moment to forget the ether completely and to try never to mention its name."

They knew the ether had to be weird to exist. Propogation of a wave at 300,000 km/sec had to have an almost unbelievable tensile strength, yet must not impeed objects moving at constant velocity.

However, this does not mean there isn't at least some sort of fabric, a spacetime fabric, out there, and in here.

[Ken G]

Thanks for clearing things up with that quote George, I think that makes it crystal clear that Einstein concluded the ether was a bad idea.

[George]

We aren't to mention its name.

[Nereid]

Slightly OT (this thread is about GR, not SR), this thread - Aether theories which are experimentally indistinguishable from SR - contains some interesting discussion and links (note that the wisp idea which wisp is pushing in this thread has been debunked).

[Nereid]

For anyone interested (and who hasn't already discovered it), Living Reviews in Relativity is a marvelous site, containing a wonderful collection of pretty much up to date reviews of many aspects of relativity.

For the historical context, Living Einstein may be a good place to start.

FWIW, I think the "ether" turbo-1 is quoting Einstein on is a very different thing than what most folk understand when they read the term. Is it possible to re-write GR (i.e. same theory, just a different presentation) is such a way as to allow an 'ether' to appear? Perhaps (but the theory - GR - would produce the same predictions, and pass the same experimental tests equally well).

One man's Aether may be another's Dark Matter.

In the quote you gave, a more accurate summary might be "One man's Aether is another man's geometry of space-time" (as Ken G has already noted).

More on the Lorentz-Einstein debate/discussion.

[noha]

whats a heliochromologist?????

[Argos]

Something that´s always bugged me: The MM experiment assumed that when the Earth travelled transversely to the "flow" of the aether a beam of light would deviate to some extent. Good. They found that it does not. But why did they assume that the aether would have any special direction of flow?

[SeanF]

Something that´s always bugged me: The MM experiment assumed that when the Earth travelled transversely to the "flow" of the aether a beam of light would deviate to some extent. Good. They found that it does not. But why did they assume that the aether would have any special direction of flow?

The MM mechanism used two beams of light, one reflecting in an East-West direction and the other in a North-South. They then rotated the mechanism 90 degrees, so the EW beam was now travelling NS, and vice-versa.

Regardless of the relative directions of the Earth's orbit and the ether's motion, they should have seen a change in the interference pattern when the apparatus was turned.

[turbo-1]

FWIW, I think the "ether" turbo-1 is quoting Einstein on is a very different thing than what most folk understand when they read the term. Is it possible to re-write GR (i.e. same theory, just a different presentation) is such a way as to allow an 'ether' to appear? Perhaps (but the theory - GR - would produce the same predictions, and pass the same experimental tests equally well).

True. Einstein was pretty frustrated about the fact that when he invoked an ether, people visualized the ether of the 19th century and rejected the idea as disproven and anachronistic. He was absolutely convinced that the mathematical expressions describing space-time were modeling something real, and that "empty" space has real physical properties. He took care to separate the mathematics of his model from the reality that the model described.

"The general theory of relativity removes a defect of classical dynamics: in the latter, inertia and weight appear as totally different manifestations, quite independent of one another, in spite of the fact that they are determined by the same body-constant, i.e. the mass. The theory of relativity overcomes this deficiency by the dynamical behaviour of the electrically neutral mass-point by means of the law of the geodesic line, in which the inertia and weght effects can no longer be distinguished. Thereby it attributes to the ether, varying from point to point, the metric and dynamical properties of the points of matter, which in turn are determined by physical factors, to wit the distribution of mass or energy respectively. The ether of the general theory of relativity therefore differs from that of classical mechanics of the special theory of relativity, in so far as it is not 'absolute', but is determined in its locally variable properties by ponderable matter. ... The fact that the general theory of relativity has no perferred space-time coordinates which stand in a determinate relation to the metric is more a characteristic of the mathematical form of the theory than of its physical content.

"On the Ether" is chapter 1 of Saunders and Brown's book "The Philosophy of Vacuum" and it was written when Einstein was arguably at his peak. I highly recommend it.

On the necessity of the varying density of the ether to explain refraction as observed in gravitational lensing, he wrote:

In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust. But in reality this is not the case. We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity; its result hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (e.g. of light).

Note the bold text. This effect has already been demonstrated with superb accuracy by the Pioneer anomaly. The farther the probes got from the Sun, the thinner the "ether" and the faster EM traveled. Assuming a constant speed of light, physicists have been modeling the shortened return times as if the probes are slowing down with a very smooth coordinated sunward acceleration. The shortened return times have resulted in an apparent positional error of ~40 ppm at a radius of 70 AU if we hold that the speed of light in a vacuum is constant. If we consider that the speed of light is dependent on the physical properties of the vacuum through which it propagates, the Pioneer anomaly has mapped the density of the local vacuum for us. From the quote above: Einstein did not believe that the speed of light in a vacuum is constant, but instead the speed of light is dependent on the physical properties of the vacuum, as conditioned by the masses embedded in it. It has taken over 80 years for his prediction to be borne out, and it will probably take until the end of my life (or longer) to convince others that the experimental proof is both real and definitive.

I think that these points make it pretty clear that GR does need an ether - the most likely culprit is the quantum vacuum, which quantum theory tells us suffuses all of "empty" space. I will not wander into my own theory about how this can work, but wish to note that Einstein was revolted by the necessity of uncertainty and indeterminance of quantum theory, so even if the quantum vacuum had been as well understood as it is today, he may not have pursued it as his GR ether. He was so far ahead of his time...

[George]

whats a heliochromologist?????

Heliochromology is an advanced field of solar astrophysical physics focused on ascertainable derivations from the narrow band of electromagnetic radiation known as “visible” light, which is emitted uniquely from our non-nocturnal star. The apex of this research is to find that one attribute so amazingly illusive to astronomy since man first noticed its color changes – the Sun’s true intrinsic color.

Greek helio-, from helios, sun
+
(chrom(o)-) [Gr. chr[omacr]ma color] a combining form denoting relationship to color
+
Chromatography is a family of analytical chemistry techniques for the separation of mixtures. [In this case, it is light we are separating to obtain spectral irradiance data.]
+
“Gist” - effect: the central meaning or theme of a speech or literary work. A person who is dedicated to finding the central meaning, in this case, to the sun's light which will produce its color. [pronounced "jest"]
+
“jest” - a humorous anecdote or remark intended to provoke laughter. [Both meanings must be incorporated to be a true heliochromologist.]

Helio-chrom-ologist: Sun + color + person who discovers meaning to these two parameters in a humorous way.

Yet, it is still a serious study with the secret, outside of BAUT, goal of determining the sun's true color to eliminate other fields of science from off-color remarks towards astronomers for their lack of this knowledge. You will only find heliochromology discussed on BAUT; within the confines of the local astronomical order, and away from several potentially chidding physicists.


Does that answer your question?

Current research does indicate the Sun's true color ain't yellow. However, direct observations from space under proper attenuation conditions have yet to be conducted.

There are numerous threads about the Sun's color.

[BTW, this is not related to ether, well... other than light-headedness, so I won't elaborate further. ]

[noha]

thanks George that makes sense!!!!!!!!!!
i think that whole electromagnetic spectrum is sooooooo complicated i`m still trying to understand it
it looks like you have memorized

[George]

thanks George that makes sense!!!!!!!!!!
i think that whole electromagnetic spectrum is sooooooo complicated i`m still trying to understand it
it looks like you have memorized

Actually, I think you may be the first to actually ask the question; which gave me a chance to fabricate define a clear explanation for it.

turbo-1, it is unclear to me what Einstein is saying in your second quote of his. Isn't he just saying SR is limited when light bends (relative to us)? He understood light did not need a medium, aether, for propogation; are you saying he changed his mind?

[swansont]

Something that´s always bugged me: The MM experiment assumed that when the Earth travelled transversely to the "flow" of the aether a beam of light would deviate to some extent. Good. They found that it does not. But why did they assume that the aether would have any special direction of flow?

The observation of stellar aberration (Bradley, 1728) had already ruled out us being stationary with respect to the ether. From it you can tell we are moving ~30 km/s around the sun. And, as SeanF explained, the MM device was rotated to different orientations to measure the movement.

[noha]

Actually, I think you may be the first to actually ask the question; which gave me a chance to fabricate define a clear explanation for it.

turbo-1, it is unclear to me what Einstein is saying in your second quote of his. Isn't he just saying SR is limited when light bends (relative to us)? He understood light did not need a medium, aether, for propogation; are you saying he changed his mind?

When do you actually have time to learn this
see i`m sorta new to the whole cosmology thing cause i`ve been more of a amature astronomer and learing about the night sky, planetary science, still in Einstein`s theory of realitivity.
your a pro:surprised
Bye~noha

[George]

When do you actually have time to learn this
see i`m sorta new to the whole cosmology thing cause i`ve been more of a amature astronomer and learing about the night sky, planetary science, still in Einstein`s theory of realitivity.
your a pro:surprised
Bye~noha

On the contrary, I am an amateur much as yourself. Some on this thread, however, are real astronomers. They've learned me some stuff real good, though. You'll find them very helpful and tolerant; my survival is a true testament to this.

[noha]

well i`ll be sure to do that
thanks for your support.
I love Astronomy!!!!!!!!!
and does anyone know any good books or magazines i can get to help w/mylearning about the cosmos, i got the book Bad Astronomy its great.
Bye~bye
noha

[turbo-1]

turbo-1, it is unclear to me what Einstein is saying in your second quote of his. Isn't he just saying SR is limited when light bends (relative to us)? He understood light did not need a medium, aether, for propogation; are you saying he changed his mind?

Yes, he certainly did change his mind, which has led to a tremendous amount of confusion on the subject.

But on the other hand there is a weighty argument to be adduced in favour of the ether hypothesis. To deny the ether is ultimately to assume that empty space has no physical qualities whatever. The fundamental facts of mechanics do not harmonize with this view. For the mechanical behaviour of a corporeal system hovering freely in empty space depends not only on relative positions (distances) and relative velocities, but also on its state of rotation, which physically may be taken as a characteristic not appertaining to the system in itself. In order to be able to look upon the rotation of the system, at least formally, as something real, Newton objectivises space. Since he classes his absolute space together with real things, for him rotation relative to an absolute space is also something real. Newton might no less well have called his absolute space ``Ether''; what is essential is merely that besides observable objects, another thing, which is not perceptible, must be looked upon as real, to enable acceleration or rotation to be looked upon as something real.

It is true that Mach tried to avoid having to accept as real something which is not observable by endeavouring to substitute in mechanics a mean acceleration with reference to the totality of the masses in the universe in place of an acceleration with reference to absolute space. But inertial resistance opposed to relative acceleration of distant masses presupposes action at a distance; and as the modern physicist does not believe that he may accept this action at a distance, he comes back once inore, if he follows Mach, to the ether, which has to serve as medium for the effects of inertia. But this conception of the ether to which we are led by Mach's way of thinking differs essentially from the ether as conceived by Newton, by Fresnel, and by Lorentz. Mach's ether not only conditions the behaviour of inert masses, but is also conditioned in its state by them.

As for the necessity of an ether through which light can propagate:

Recapitulating, we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense.

By 1924, Einstein had given the ether concept a great deal more attention and was far more specific about its properties and about the necessity for its existence. If you can borrow Saunders and Brown's book "The Philosopy of Vacuum", read chapter one and you will see what I mean. It is Saunders' translation of "Uber den Ather" (variant spelling with umlauts) - I have read that work at least a hundred times and it has convinced me that we can model the universe with an ether with real physical properties in Euclidean space. If you are an adherent of the concordance view of relativity, you will need multiple readings and reflection to see why Einstein held these views. The mathematical tools of relativity have attained a status seemingly higher than the physical processes that they model. Einstein took great pains to explain in "Uber den Ather" that the seeming incompatibility of GR gravitation and electromagnetism are due to inadequacies in GR. He spent decades trying to understand where the problems lay so that he could reconcile the theories. If you read that chapter, you will see that he had very real expectations that quantum theory would ultimately overthrow GR.

[George]

Why do I get the feeling ether comes in different flavors? As was mentioned, Mach had one view of it, contrary to Newton and others. As per your quote of Einstein:
"...space is endowed with physical qualities; in this sense, therefore, there exists an ether."

However, there is Einstein's later statement, per Celeritas link, and shown in my prior post , where Einstein, in 1938, disavows the ether. However, maybe it is a different "flavor" of ether.

[RussT]

It sounds like Einstein's concept of an aether was quite a bit different than the conventional view before Michelson-Morley. But you won't get dark matter from it, the properties of dark matter cannot be attributed to space itself (or we would not need both dark matter and dark energy).

KenG, you have a unique ability of being able to define things down to the crux of the matter!

[It sounds like Einstein's concept of an aether was quite a bit different than the conventional view before Michelson-Morley.]

And so it appears that Albert will once again be proven to be correct!

[Celeritas]

Some may find this interesting from Lois Essen the inventor of the Atomic Clock.

But moreso: It doesn't appear that this site has an axe to grind and it tells a story that seems more like investigative journalism regarding Dayton Miller's Ether-Drift light-beam interferometry experiments complete with access to some of the data from same. According to this author, siting Miller, those experiments never gave "null" results. There always remained a positive effect that altered depending upon altitude.

It is a very worthwile read.

As well as:

This report

[turbo-1]

Why do I get the feeling ether comes in different flavors? As was mentioned, Mach had one view of it, contrary to Newton and others. As per your quote of Einstein:
"...space is endowed with physical qualities; in this sense, therefore, there exists an ether."

However, there is Einstein's later statement, per Celeritas link, and shown in my prior post , where Einstein, in 1938, disavows the ether. However, maybe it is a different "flavor" of ether.

Einstein was convinced that an ether was necessary to explain the behavior of the universe. His ether was a vacuum with real physical properties that were determined by the mass and energy embedded in the vacuum. Without an ether, gravitation, inertia, and centrifugal effects suddenly became subject to spooky "action-at-a-distance" forces, which Einstein categorically denied. The ether also supplied the transmissive medium that allows the transmission of light across "empty" space.

Einstein rejected the 19th C ether as popularly conceived, but insisted on an ether for GR. Ethers certainly do have flavors, and we need to recognize that.

[George]

Einstein was convinced that an ether was necessary to explain the behavior of the universe. His ether was a vacuum with real physical properties that were determined by the mass and energy embedded in the vacuum. Without an ether, gravitation, inertia, and centrifugal effects suddenly became subject to spooky "action-at-a-distance" forces, which Einstein categorically denied. The ether also supplied the transmissive medium that allows the transmission of light across "empty" space.

Einstein rejected the 19th C ether as popularly conceived, but insisted on an ether for GR. Ethers certainly do have flavors, and we need to recognize that.

That would help explain his statement..."After such bad experiences, this is the moment to forget the ether completely and to try never to mention its name." No doubt, the other flavor ether is intrinsic to spacetime. Did he give his flavor a special name after 1938?

[turbo-1]

No he did not give his ether a special name (to my knowledge), but he seemed really frustrated about the inability of other physicists to give his GR ether a fair hearing. He was far ahead of his time, and when he realized that the vacuum has physical properties, he pursued this with some vigor. His acolytes have ignored this, and have acted like the mathematical constructs of GR are real.

[north]

from my book "Einstein's Theory of Relativity" by Max Born(Dover Publishing)

pg.224 and i quote;

"from now on ether as a substance vanishes from theory. in its place we have the electromagnetic field as a mathematical device for conveniently describing processes in matter and their relationships*.

*Einstein in later years proposed calling empty space equipped with gravitational and electromagnetic fields the "ether", whereby, however, this word is not to denote a substance with its tradtional attributes. Thus, in the "ether" there are to be no determinable points, and it is meaningless to speak of motion relative to the "ether". Such a use of the word "ether" is of course admissable, and when once it has been sanctioned by usage in this way, probably quite convenient."

[Spherical]

Einstein was a Parmenideaen. When you look at a Minkowski diagram what do you see? That according to SR/GR, you can move, but not enough to perturb anything important. It seems entirely likely to me that Einstein very much wanted to fill the vacuum with "something", even that meant declaring space-time to be literally be the "fabric" of the universe. Parmenides held that the universe was a finite plenum.