Dark Matter vs Ether: What's the Difference?

[thomasxc]

how is dark matter different from the old "ether" theory

 

[seycyrus]

In what ways do you suppose they are the same? Do you believe that the speculation is offered in the same manner, or do you mean something else?

 

[thomasxc]

im not exactly sure...could you maybe differentiate between the two please?

 

[cristo]

This is a ridiculous premise for a thread. What do you understand about dark matter? What do you understand about the aether? What makes you think they are similar?

 

[Janus]

Dark matter interacts gravitationally but not with light.
The ether was supposed to provide the medium for light transmission, but wouldn't have interacted gravitationally.

 

[thomasxc]

thnx. what janus said is all i needed to know.

 

[Garth]

how is dark matter different from the old "ether" theory

You might have been thinking about "Dark Energy v ether?"

In which case the difference would be that the aether in its original form would have been a medium against which an absolute frame of reference could be measured.

DE would provide no such absolute frame of reference.

The original aether theory was proved false by the Michelson–Morley experiment but was further revived for a short time by Lorentz. In its new guise the Lorentz transformations of moving rulers and clocks would render the aether always unobservable.

However, the standard interpretation was that if the aether was always unobservable then it did not exist and the theory of Special Relativity took its place on the world scientific stage.



Garth

 

[thomasxc]

mmkay. thnx

 

[brokensphere]

Dark matter and ether have one thing in common they both are ways to explain why our equations are not working.

 

[russ_watters]

Not really, no. Ether theory was rejected because with it, our equations didn't work. You have it backwards.

 

[pbannister]

Backwards?

Both "ether" and "dark matter" were offered as - in some respects - similar explanations. In the end the purposed theory for "ether" was rejected when what we knew advanced enough that the equations did not work out. We are not yet that far along with "dark matter". Both "ether" and "dark matter" are metaphors for something we do not understand. Both were presented as a sort of universal seemingly undetectable medium - and proposed as an answer to a current question.

Give the subject another fifty years, and they might both share the same chapter in a Physics textbook. Could just as meaningfully call "dark matter" and "dark energy" the "new theory of ether". The denotation is the same, only the connotations differ. :)

Guess it bugs me somewhat that "dark matter" and "dark energy" are talked about as though real and some sort of answer, when so far as I call tell all we have is the question. A vast and interesting question to be sure ... but so far only that.

Seems to me the question that started this thread is entirely reasonable.

 

[granpa]

the aether in its original form would have been a medium against which an absolute frame of reference could be measured.
Garth

why would motion relative to the aether be absolute?

 

[russ_watters]

why would motion relative to the aether be absolute?

Because the ether was thought to be the very fabric of space, acting much like air as a medium for sound.

 

[granpa]

Because the ether was thought to be the very fabric of space, acting much like air as a medium for sound.

so? that's still relative not absolute.

 

[russ_watters]

Backwards?

Both "ether" and "dark matter" were offered as - in some respects - similar explanations. In the end the purposed theory for "ether" was rejected when what we knew advanced enough that the equations did not work out. We are not yet that far along with "dark matter". Both "ether" and "dark matter" are metaphors for something we do not understand. Both were presented as a sort of universal seemingly undetectable medium - and proposed as an answer to a current question.

The ether was not introduced to explain an error in a theory, it was assumed to exist based on the way previous theories worked. It was discarded when it was found that it didn't exist.

Dark matter, on the other hand, was theorized because previous theories produced inaccurate predictions, but scientists didn't think the error was big enough to scrap the entire theory.

There's another difference: there is evidence that dark matter exists. There was never any evidence that the ether existed. The very first attempt to find it failed.

If dark matter is eventually abandoned, history will likely view it as similar to Einstein's cosmological constant, not as similar to the ether.

Give the subject another fifty years, and they might both share the same chapter in a Physics textbook.

Perhaps, but one way to look at the advancement of science is a narrowing of error margins. Because of the narrowing of error margins, the potential for error in current theory is much smaller than in the theories that existed 110 years ago.

Seems to me the question that started this thread is entirely reasonable.

You seem to be taking the question figuratively. We read it and answered it literally.

 

[pbannister]

Perhaps, but one way to look at the advancement of science is a narrowing of error margins. Because of the narrowing of error margins, the potential for error in current theory is much smaller than in the theories that existed 110 years ago.

The story I remember about the state of Physics back 110 years ago (or a bit before), was a belief that pretty much everything had been discovered, and all that was left was a narrowing of error margins (more precise measurements). What we got a bit later was some fairly large conceptual leaps.

You could count that as just a narrowing of error margins, but I think conceptual leaps should count as non-linear - not linear - progress.

We use a lot of metaphors in trying to explain physical reality. Humans are only really good at understanding physical processes with which we have direct experience. To understand physics outside the range of human experience, we apply metaphors. If the metaphor is a reasonably close approximation to reality, what we "understand" advances (at least well enough to manipulate).

The comparison of "ether" to "dark matter" may be particularly appropriate if - once again - the old metaphors are in for a major revision. So far as I can tell, there is no evidence (past the initial set of observations) that "dark matter" is the right metaphor. A good first-approximation, yes, but no basis to assume this going to yield useful results.

 

[Chronos]

See Michelson-Morley for how 'aether' was pinned to the theoretical mat -
http://nobelprize.org/educational_games/physics/relativity/experiment-1.html

 

[russ_watters]

so? that's still relative not absolute.

No, it's not. The speed of sound is constant only relative only to the air that it is traveling through. It is not constant between objects moving though the air. Thus, the air is the one and only special/absolute rest frame from which the speed of sound can be measured to be constant.

Works the same for light and the aether.

 

[granpa]

No, it's not. The speed of sound is constant only relative only to the air that it is traveling through. It is not constant between objects moving though the air. Thus, the air is the one and only special/absolute rest frame from which the speed of sound can be measured to be constant.

Works the same for light and the aether.

not if objects shrink, become time dilated, and experience loss of simultaneity when moving through it. I really don't think that you've thought this through.

 

[Chronos]

Michelson-Morley was a brilliantly designed experiment that works just fine in air, or any other 'ponderable' media, granpa. See
http://galileoandeinstein.physics.virginia.edu/lectures/michelson.html

 

[russ_watters]

not if objects shrink, become time dilated, and experience loss of simultaneity when moving through it. I really don't think that you've thought this through.

Me? This is Relativity I'm talking about. This is one of the most well-researched theories in science. I don't have to think it through, I'm just telling you what those thousands of physicists for the past 100+ years have figured out. And the belief that there was an absolute frame of reference (like for sound in air) is one of the primary reasons for it's creation - when that belief was found to be wrong (by the MM exp, as posted above).

There really isn't anything to discuss here. What you are arguing against isn't really even the theory itself, it is the historical facts of why these theories were developed. You may want to peruse the wiki on the aether for the history:
http://en.wikipedia.org/wiki/Luminiferous_aether

It makes specific mention of the history of the aether and it being believed to be a "universal" reference frame. In particular, the section on the aether and classical mechanics. They even use the analogy of sound traveling through air.

 

[granpa]

Michelson-Morley was a brilliantly designed experiment that works just fine in air, or any other 'ponderable' media, granpa. See
http://galileoandeinstein.physics.virginia.edu/lectures/michelson.html

I never said it didnt.

 

[granpa]

I don't think that the argument against the aether was that it required absolute motion. my motion relative to the aether would be no more absolute than my motion relative to the earth.

rather the argument was simply that, due to relativity (which it does not contradict), it can't be empirically observed and therefore can't be assumed.

 

[russ_watters]

Please read the references provided, granpa. You are wrong on both counts.

 

[Chronos]

Well grounded knowledge of classical physics is necessary to appreciate the MM experiment, and why it refutes the classical 'aether' concept. Part of the confusion arises from what was meant by 'aether' up to the early 20th centuries. It's worth reading up on, granpa. We will all be on the same page then.

 

[oldman]

...knowledge of classical physics is necessary to appreciate the MM experiment, and why it refutes the classical 'aether' concept... We will all be on the same page then.

I'm just not quite sure which page this is.

By now the "classical 'aether' concept" is indeed dead and buried, but there are still some mysteries and puzzles. There does now seem to be an accepted 'absolute' frame of reference --- the CMB frame in which an observer is at rest with respect to the Cosmic Microwave Background.

This CMB frame is strictly a 'personal absolute' that depends on observer location. Separate observers in the consensus expanding universe may each be at rest in their own CMB frame and yet find their distance apart to be increasing. This is a mystery that you can't understand in the context of normal experience. You just have to trust GR as the best way to describe gravity invented so far .

Then there is the puzzle of postulated non-interacting 'dark matter' particles belonging to our galactic halo, thought by the DAMA dark matter hunters to be streaming through us in a way that varies annually. Is this perhaps the 'absolute frame' referred to here? Surely it's too local to be called absolute, though?

 

[Chronos]

That is the sort of drivel that makes me want to push the 'report' button, oldman. All you are doing is 'moving the goal posts'.

 

[oldman]

That is the sort of drivel that makes me want to push the 'report' button, oldman. All you are doing is 'moving the goal posts'.

In making your quite offensive remarks about 'drivel', 'report button' and 'moving goal posts', Chronos, you are ignoring the fact that this is a cosmology forum and that the title of this thread includes the nineteenth-century concept of the ether. The correct and helpful clarifications you and Russ Watters have made in this thread about the ancient Michelson-Morley experiment arise from Special Relativity (SR), which in cosmology is concerned only with local physics.

Cosmology is based on General Relativity, rather than SR. In this context the only ether-like entity is the Cosmic Microwave Background (CMB) that I drew attention to. Indeed the very concept of co-moving observers, which is fundamental to modern cosmology, has turned out to be of observers who are at rest with repect to the CMB. Such observers may use the CMB as their fixed reference frame relative to which 'peculiar' motions take place. It was high time that somebody made mention of the CMB as a reference frame in this thread.

As to the puzzle of dark matter or energy: although, as perhaps in the OP, this could be mistaken for ether (which it is not), it is indeed a galaxy-cluster-scale puzzle that is a bit ether-like and concerns cosmology. This was why I mentioned it. You may be able to access the article in August 2008 Physicsworld (via physicsworld.com) about the DAMA-detection-of-dark-matter controversy. If so, you may find it interesting.

 

[George Jones]

To illustrate oldman's point about CMB, consider the balloon analogy for the expanding universe, in which the surface of an expanding balloon represents the universe. Suppose that the balloon has a grid of lattitude and longitude lines painted on its surface. In a perfectly homogeneous and isotropic universe, the galaxies would stay at fixed positions with respect to the grid. In reality, however, the glaxies have small random motions. A galaxy that doesn't move with respect to the grid is said to have zero peculiar velocity, while a galaxy that moves with respect to the grid has non-zero peculiar velocity.

If galaxy A has zero peculiar velocity, then, for observers in A, the cosmic microwave background radiation (CMB) appears the same in all directions, and if galaxy B has non-zero peculiar velocity, the CMB exhibits a Doppler pattern, blueshifted in one direction and redshifted in the opposite direction. The blueshift occurs in the direction (with respect to the grid) that B is moving towards, and redshift occurs in the direction from which B moves away. If galaxy C has peculiar velocity opposite to the peculiar velocity of B, then C's Doppler pattern is the opposite of B's.

Consequently, the CMB establishes a frame at all times and places in the universe, the frame that consists of all observers who see the CMB as the same in all directions. These observers just ride along with the expansion of the universe.

Observers on the Earth are not in the CMB frame, and by observing the CMB we have determined our motion with respect this frame. The Earth orbits the Sun, the Sun orbits the centre of the Milky Way, the Milky Way is a in a cluster of galaxies that has non-zero peculiar velocity, etc., and the effects of all thes motions have to be subtracted in order to produce the nice pictures of the CMB that we usually see referenced.

 

[The riddler]

Ether was known as the medium in which light waves travel through and was said to exist everywhere and be spread out equally throughout the universe, while dark matter is not known as light's medium and is not spread out equally in the universe but is more dense in gravitational fields. In other words the two theories of ether and dark matter are barely alike.

 

[yogi]

I couple of comments - the MMX didn't actually disprove the ether - nor did the success of SR - Einstein simply turned the surprising results from a problem to a postulate - similar to what is being done by inventing a something that explains the apparent flatness of the universe - so there is an analogy - Einstein did the same thing in deriving the General Theory - he knew the answer was in curvature - so he simply postulated that inert matter curves static space - the equations work - but there seems to be some missing physics - maybe dark energy will turn out to be tied to the stress of space - and maybe the stress of space will ultimately be connected to the velocity of light -