Why no Ęther

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Offline syhprum

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Why no Ęther
« on: 01/01/2012 12:36:40 »
Why is it heresey to talk of an ęther, we are told space is pervaded by the Higgs field, masses of virtual particles, we know the CMBR is there because we can measure it not to mention Mach's generalised gravitational field and lots of dark matter and Neutrino,s.
Surely we have something to refer to.
« Last Edit: 03/01/2012 11:44:04 by syhprum »
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Offline JP

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Re: Why no Ether
« Reply #1 on: 01/01/2012 14:16:41 »
The luminiferous ether was a theory that light behaved like water or sound waves.  The ether would act like water or air, and would wave up/down or back/forth as light moved through it to carry the wave, just like air does for sound waves.  Part of this theory is that, like sound waves, if you move quickly in the ether, you would eventually overtake light.  That proved false, and the ether theory fell out of favor. 

Now, we do know that there are all sorts of fields pervading the universe and that space-time itself also has properties that keep the speed of light constant, but none of these have anything to do with the above theory of luminiferous ether.  Some people propose to use the word "ether" to describe space-time, but that's not really accurate, and it can be necessarily confusing to name it after a defunct and unrelated theory.

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Offline syhprum

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Re: Why no Ether
« Reply #2 on: 01/01/2012 16:27:27 »
Are we not as guilty as the pre copernicans when we assume the characteristics of space in our local area are the same over the whole universe, if it is correct that dark matter holds the rotating galaxy together are we not immersed in that same dark matter yet we assume that every thing is the same in the universe that is mostly outside it.
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Offline JP

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Re: Why no Ether
« Reply #3 on: 01/01/2012 20:18:14 »
Are we not as guilty as the pre copernicans when we assume the characteristics of space in our local area are the same over the whole universe . . .

How so?  Pre-Copernicans made assumptions without considering observational or experimental fact.  Today we use observations and experiments to develop theories that are in accordance those facts. 

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Offline Phractality

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Re: Why no Ether
« Reply #4 on: 02/01/2012 04:08:23 »
Sour grapes! Many attempts were made to describe the ether and how both waves and particles move thru it. All proposed ether models were proven wrong, or at least inadequate. Then Einstein came up with a mathematical description of space-time which made it unnecessary to describe the physical nature of space. The mathematical description works well, so we now pretend that space is nothing but math. We couldn't reach the grapes, so they were probably sour, anyway!

In his Leyden address, Einstein reluctantly conceded that, if there is an underlying ether, it lacks the property which he called "immobility". Every reference frame is equivalent, and all known phenomena work the same in every reference frame. As long as no faster-than-light (FTL) phenomenon is proven to exist, his argument remains valid. However, if we ever do prove the existence of an FTL phenomenon (such as quantum entanglement, which some claim is instantaneous), that will mean that there is only one preferred frame of reference in which the FTL phenomenon has the same speed in every direction. In other words, that frame of reference will be immobile, and the ether must have the property of immobility. If the ether is immobile, then it will no longer make sense to ignore its existence. 

Some scientists (myself included) are still pursuing the quest to adequately describe the ether, but they are the black sheep of the scientific community. Their ether models are outside the mainstream of science; on this website, they are relegated to the New Theories forum.

« Last Edit: 02/01/2012 19:39:00 by Phractality »
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Offline JP

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Re: Why no Ether
« Reply #5 on: 02/01/2012 13:52:32 »
Phractality, we asked you (on several occasions) to move your posts to New Theories because you were preaching new theories and that's the appropriate forum for new theories.  Constantly complaining about being asked to do so won't convince us otherwise and will only annoy the moderators.

As for whether the properties of space-time constitute "ether" or not, you're missing the point.  The point is that the word ether is strongly associated with "stuff" that supports light propagation and has a preferred reference frame in which it's immobile.  Unless you're talking about that stuff, why use the word ether?

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Offline simplified

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Re: Why no Ether
« Reply #6 on: 02/01/2012 18:43:28 »
Very fast gravitational winds are "ether".

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Offline Phractality

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Re: Why no Ether
« Reply #7 on: 02/01/2012 19:28:15 »
JP,
There is nothing new about the theory that there is a substance which is the medium of light. If you read Einstein's Leyden address, you would know that he, too, was a firm supporter of that theory. (Here, I am using the term "theory" loosely; "notion" would be a better description.) What's new is a variety of new ether models, each of which properly belongs in "New Theories". I have carefully avoided mentioning any particular ether model, new or old, while answering the question, "Why no ether?"

Quote
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 Aether. According to the General Theory of Relativity space without Aether 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. But this Aether may not be thought of as endowed with the quality characteristic of ponderable media, as consisting of parts which may be tracked through time. The idea of motion may not be applied to it.
A. Einstein, from Leyden address

It is now widely claimed that, through quantum entanglement, a cause at A can instantaneously produce an effect across a finite distance at B. (Whether this may permit FTL communication is irrelevant to the question at hand.) What the popular news media fail to mention is that the effect cannot be instantaneous in every reference frame. Clocks which are synchronized in a different reference frame, having a component of motion parallel to the line A-B, will indicate that the cause and effect are not simultaneous. That is just basic special relativity, not new theory;

t'= γ(t-vx/c^2).

Proof of an FTL phenomenon would prove the existence of an immobile preferred reference frame, and the ether described by Einstein would then have the quality of immobility. Therefore, it would be a ponderable substance whose parts may be tracked through time. 

Einstein answered the question, "Why no ether?" based on the lack of any known FTL phenomenon. As long as no such phenomenon is proven to exist, his conclusion remains valid, and without introducing any new theories, that's why we have no ether in today's mainstream physics.
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Offline Phractality

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Re: Why no Ether
« Reply #8 on: 02/01/2012 19:31:29 »
Very fast gravitational winds are "ether".
Now, that's an example of new theory for you.
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Offline simplified

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Re: Why no Ether
« Reply #9 on: 02/01/2012 20:01:54 »
Very fast gravitational winds are "ether".
Now, that's an example of new theory for you.
Gravitation exists in space and has fast speed.It is not new theory. :P

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Offline JP

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Re: Why no Ether
« Reply #10 on: 02/01/2012 22:11:37 »
JP,
There is nothing new about the theory that there is a substance which is the medium of light. If you read Einstein's Leyden address, you would know that he, too, was a firm supporter of that theory.

The Leyden address was given over 90 years ago.  Einstein's use of (a)ether in that address bears no resemblance to how it's used in modern physics.  These days, the word ether means luminiferous ether (http://en.wikipedia.org/wiki/Luminiferous_aether), which I described above, and which isn't taken seriously as a theory because it requires that light speed isn't constant (and from extensive testing, it appears to be constant).  Citing an outdated use of the term, even if that use is by Einstein, doesn't change its modern definition. 

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Offline Phractality

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Re: Why no Ether
« Reply #11 on: 03/01/2012 00:32:12 »
JP,
There is nothing new about the theory that there is a substance which is the medium of light. If you read Einstein's Leyden address, you would know that he, too, was a firm supporter of that theory.

The Leyden address was given over 90 years ago.  Einstein's use of (a)ether in that address bears no resemblance to how it's used in modern physics.  These days, the word ether means luminiferous ether (http://en.wikipedia.org/wiki/Luminiferous_aether), which I described above, and which isn't taken seriously as a theory because it requires that light speed isn't constant (and from extensive testing, it appears to be constant).  Citing an outdated use of the term, even if that use is by Einstein, doesn't change its modern definition.
The way the word "ether" is used by people who don't believe in it has little to do with the way the word is used by people who have theories about what ether is. I agree that the speed of light is the same in every direction in every reference frame. I only disagree with the mainstream belief that there is no preferred reference frame. Detecting something special about that special reference frame may not be possible until it is proven that certain FTL phenomena are real.

Syphrum posed the question, "Why no ether?" He wants to know why mainstream physics has abandoned the idea that light requires a ponderable medium. I have merely provided the historical context which has led the mainstream to that conclusion. The reasoning that went into the Leyden address remains valid, given that no one has yet proven the existence of FTL phenomena. Because of recent experiments which claim to have detected FTL phenomena, I think it is prudent to prepare ourselves for the implications in case they are proven right. Those implications are not new theory, but straightforward corollaries to the accepted theory of relativity.
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Offline JP

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Re: Why no Ether
« Reply #12 on: 03/01/2012 01:25:09 »
The way the word "ether" is used by people who don't believe in it has little to do with the way the word is used by people who have theories about what ether is.

This is fortunate.  Science would be a confusing mess if anyone could redefine terms to fit their personal theories.  Since this is a science forum, it's probably best to stick to scientific terminology.

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Offline Phractality

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Re: Why no Ether
« Reply #13 on: 03/01/2012 06:33:10 »
The way the word "ether" is used by people who don't believe in it has little to do with the way the word is used by people who have theories about what ether is.

This is fortunate.  Science would be a confusing mess if anyone could redefine terms to fit their personal theories.  Since this is a science forum, it's probably best to stick to scientific terminology.

Let me use a metaphor to describe our difference of opinion; okay? A century ago, the lack of physical evidence for the existence of a real person named Santa Clause caused grownups to declare that Santa does not exist. Faced with open rebellion from their children, the grownups conceded that Santa exists but only as an idea, not as a real person. But some kids grew up still believing that Santa is a real person. Of course each true believer has a different idea of what Santa looks like, where he lives, how many reindeer pull his sleigh, and whether his sleigh actually flies, but they all believe Santa is a real person, not just an idea. You are accusing those true believers of changing the meaning of Santa Clause to suit their own pet theories. They're not the ones who changed the meaning of Santa; it's the unbelievers who changed the meaning. Someday, the real Santa may reveal himself, and he probably won't resemble any of the popular legends about him.
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Offline Geezer

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Re: Why no Ether
« Reply #14 on: 03/01/2012 07:00:15 »

Let me use a metaphor to describe our difference of opinion; okay? A century ago, the lack of physical evidence for the existence of a real person named Santa Clause caused grownups to declare that Santa does not exist. Faced with open rebellion from their children, the grownups conceded that Santa exists but only as an idea, not as a real person. But some kids grew up still believing that Santa is a real person. Of course each true believer has a different idea of what Santa looks like, where he lives, how many reindeer pull his sleigh, and whether his sleigh actually flies, but they all believe Santa is a real person, not just an idea. You are accusing those true believers of changing the meaning of Santa Clause to suit their own pet theories. They're not the ones who changed the meaning of Santa; it's the unbelievers who changed the meaning. Someday, the real Santa may reveal himself, and he probably won't resemble any of the popular legends about him.


True, but religions are based on belief. Science isn't.
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline Phractality

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Re: Why no Ether
« Reply #15 on: 03/01/2012 07:28:38 »
True, but religions are based on belief. Science isn't.
If scientists change the definition of God, are priests then wrong to continue using their old definitions? Would you accuse the Pope of changing the definition of God when he continues to define God the way his predecessors have done for two millennia, instead of the definition made up by scientists a century ago?
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Offline Geezer

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Re: Why no Ether
« Reply #16 on: 03/01/2012 07:55:26 »
If scientists change the definition of God, are priests then wrong to continue using their old definitions? Would you accuse the Pope of changing the definition of God when he continues to define God the way his predecessors have done for two millennia, instead of the definition made up by scientists a century ago?


That seems to be entirely hypothetical. I do not understand what it has to do with science. I'm not aware of any science that purports to change the definition of any god.

Science is really very simple. All we have to do is come up with a testable theory and put it to the test. Until it passes the test, it's supposition.
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline Phractality

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Re: Why no Ether
« Reply #17 on: 03/01/2012 09:01:03 »
Science is really very simple. All we have to do is come up with a testable theory and put it to the test. Until it passes the test, it's supposition.
They dreamt up a number of tests (like Michelson-Morley) to find out if aether is a ponderable substance. Unfortunately, all the tests were flawed because they lacked a valid model of the aether. The test failed, so they declared that the aether does not exist. Then, they resumed using the term "aether", but with a whole new meaning. If they had a proper model of aether, they might have dreamt up a valid test and gotten a positive result. However, since the math works sufficiently well, they see no reason to try and fix the model. As far as they're concerned, it ain't broke, so don't try to fix it. I look forward to the day when they discover that the model has been broke all along.
Imagination is more important than knowledge. Einstein

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Offline JP

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Re: Why no Ether
« Reply #18 on: 03/01/2012 09:09:35 »
Phractality, if you keep moving the goalposts, of course you'll always be able to win the game.  As Geezer says, science doesn't work that way.  Continue moving the goalposts all you like, but you've left the realm of science.

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Offline syhprum

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Re: Why no Ether
« Reply #19 on: 03/01/2012 09:43:53 »
This discussion seems to have taken paths that I really did not intend it too, I had in mind was there a fixed reference against which our motion could be measured and was our conception of intergalactic space coloured by our presence in a galaxy.
Hertz tells us that the speed of light is determined by the permittivity and permeability of the vacuum if we constructed  a vacuum capacitor and measured is capacitance at our present location immersed in a sea of dark matter and in intergalactic space would it be the same.     
« Last Edit: 03/01/2012 19:21:30 by syhprum »
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Offline Bill S

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Re: Why no Ęther
« Reply #20 on: 03/01/2012 18:25:31 »
Quote from: Syphrum
was there a fixed reference against which our motion could be measured

What about the CMBR?

There never was nothing.

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Offline Phractality

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Re: Why no Ether
« Reply #21 on: 03/01/2012 19:54:23 »
Hertz tells us that the speed of light is determined by the permittivity and permeability of the vacuum if we constructed  vacuum capacitor and measured is capacitance at our present location immersed in a sea of dark matter and in intergalactic space would it be the same.   
The permittivity and permeability of the vacuum are defined in terms of the speed of light, not the other way around. Turning the equations around to derive the speed of light from the permeability and permittivity of the vacuum only proves that you know how to rearrange the variables to get back where you started. It gives no insight into why the speed of light is what it is.

There is a striking similarity between the formula for speed of light in the vacuum ( in terms of permittivity and permeability of the vacuum) and the formula for the speed of acoustic shear waves in a solid medium (in terms of shear modulus and inertial density of the solid).

c^2 = 1/εoμo      
cs^2 = G/ρ   

(I must refrain from drawing any conclusions from this, lest I be accused of introducing new theory or arguing for the existence of a substantive aether.)

Since the speed of light in the vacuum is the same in all reference frames by definition, and since the permeability and permittivity of the vacuum are defined by the speed of light, there can be no difference in the capacity of that hypothetical vacuum capacitor anywhere in the universe. To claim otherwise would contradict the definitions.
« Last Edit: 04/01/2012 09:34:00 by Phractality »
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Offline David Cooper

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Re: Why no Ęther
« Reply #22 on: 03/01/2012 20:52:45 »
I can't see what's so scientific about claiming something doesn't exist on the basis that it can't be detected. If nothing could travel faster than the speed of sound because all the forces between atoms acted at the speed of sound, accelerating something up towards the speed of sound would automatically slow down any kind of clock you tried to devise and contract things in the direction of travel, and if it was also impossible to detect the air directly, you'd have the same kind of situation in which many scientists would step beyond their competence and declare that the air does not exist, all based on an experiment (Michelson-Morley) which fails because the equipment is contracted by its own motion through the medium it's trying to detect. Claiming that that aether doesn't exist on the basis of MM is philosophy, not science.

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Offline Phractality

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Re: Why no Ęther
« Reply #23 on: 03/01/2012 21:02:12 »
Quote from: Syphrum
was there a fixed reference against which our motion could be measured

What about the CMBR?
The CMBR would be my first choice for a preferred reference frame. However, all phenomena which are limited by the speed of light behave the same in that frame as they do in all other frames. So until we discover something that can cause an effect across a finite distance faster than the speed of light, the dipole asymmetry of the CMBR remains the only thing that distinguishes it from any other reference frame.

One Wikipedia article says our peculiar velocity relative to the comoving cosmic rest frame is about 627 km/s toward Virgo. (According to another Wikipedia article, our solar system's apparent velocity relative to the is about 370 km/s. I don't know which is more accurate.) The figure of 627 km/s corresponds to a relativistic gamma of 1.0000022. It means that clocks synchronized in Earth's reference frame differ from clocks synchronized in the CMBR reference frame at the rate of about 9 ns/km. In other words, in the CMBR frame, Earth clocks which are closer to Virgo, indicate earlier times than Earth clocks farther from Virgo. (Earth's orbital velocity causes up to ±30 km/s annual variation in our velocity relative to the CMBR.)

Chinese experiments with quantum entanglement, last year, claimed to have produced an effect which preceded the cause (according to Earth clocks). This cause-effect relationship is touted as being instantaneous. If it is instantaneous in the reference frame of the CMBR, we should expect the effect to precede the cause (according to Earth clocks) by 9 ns for each kilometer that the effect is closer to Virgo than the cause. If the effect is 16 km closer to Virgo than the cause, Earth clocks would indicate that effect preceded the cause by 144 ns. (Whether this method enables instantaneous communication is irrelevant to the question of whether there is a preferred reference frame.)
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Offline Phractality

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Re: Why no Ęther
« Reply #24 on: 03/01/2012 21:09:02 »
I can't see what's so scientific about claiming something doesn't exist on the basis that it can't be detected. If nothing could travel faster than the speed of sound because all the forces between atoms acted at the speed of sound, accelerating something up towards the speed of sound would automatically slow down any kind of clock you tried to devise and contract things in the direction of travel, and if it was also impossible to detect the air directly, you'd have the same kind of situation in which many scientists would step beyond their competence and declare that the air does not exist, all based on an experiment (Michelson-Morley) which fails because the equipment is contracted by its own motion through the medium it's trying to detect. Claiming that that aether doesn't exist on the basis of MM is philosophy, not science.
Well, at least the newbie is on my side. Thanks for your support, David.
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Offline acsinuk

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Re: Why no Ęther
« Reply #25 on: 04/01/2012 07:57:14 »
Yes, I think that space is not empty as Einstein envisaged; this is because free space has a magnetic permeability constant that does not appear in any of the gravitational attraction equations.  If space is magnetized then transmission of electromagnetic light is possible; if not magnetized then no medium is there to transmit the light.  Happy new year
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Offline JP

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Re: Why no Ęther
« Reply #26 on: 04/01/2012 09:35:15 »
I can't see what's so scientific about claiming something doesn't exist on the basis that it can't be detected. If nothing could travel faster than the speed of sound because all the forces between atoms acted at the speed of sound, accelerating something up towards the speed of sound would automatically slow down any kind of clock you tried to devise and contract things in the direction of travel, and if it was also impossible to detect the air directly, you'd have the same kind of situation in which many scientists would step beyond their competence and declare that the air does not exist, all based on an experiment (Michelson-Morley) which fails because the equipment is contracted by its own motion through the medium it's trying to detect. Claiming that that aether doesn't exist on the basis of MM is philosophy, not science.
Well, at least the newbie is on my side. Thanks for your support, David.

Again, this is an argument that amounts to moving the goalposts by redefining aether.  The aether theory assumes the speed of light isn't constant and therefore time dilation and length contraction don't exist.  If you redefine things so they both exist from the start, then you're not dealing with the aether theory.  Therefore, a null result of MM does scientifically contradict the aether hypothesis. 

Since its a matter of definitions here, no amount of arguing is going to win this one for you.

On the other hand, the question of preferred reference frames is interesting, particularly of co-moving coordinates.  Of course these ideas don't have much to do with the definition of aether.

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Offline Phractality

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Re: Why no Ęther
« Reply #27 on: 04/01/2012 17:45:13 »
I can't see what's so scientific about claiming something doesn't exist on the basis that it can't be detected. If nothing could travel faster than the speed of sound because all the forces between atoms acted at the speed of sound, accelerating something up towards the speed of sound would automatically slow down any kind of clock you tried to devise and contract things in the direction of travel, and if it was also impossible to detect the air directly, you'd have the same kind of situation in which many scientists would step beyond their competence and declare that the air does not exist, all based on an experiment (Michelson-Morley) which fails because the equipment is contracted by its own motion through the medium it's trying to detect. Claiming that that aether doesn't exist on the basis of MM is philosophy, not science.
Well, at least the newbie is on my side. Thanks for your support, David.

Again, this is an argument that amounts to moving the goalposts by redefining aether.  The aether theory assumes the speed of light isn't constant and therefore time dilation and length contraction don't exist.  If you redefine things so they both exist from the start, then you're not dealing with the aether theory.  Therefore, a null result of MM does scientifically contradict the aether hypothesis. 
It is true that SOME aether theories deny the constancy of the speed of light in all directions, and those particular aether theories were falsified by MM. Those theories are based on flawed aether models or flawed understanding of aether models.
Some modern aether models (at least my own) make it evident WHY the speed of light must be the same in all directions in all reference frames, despite propagating in a substantive medium.
Since its a matter of definitions here, no amount of arguing is going to win this one for you.
You're the one changing the definition of aether, here, claiming that a substantive medium cannot propagate light the same in all directions. Aether never was DEFINED as requiring light to propagate at different speeds in different directions. By definition, aether is just the medium for the propagation of light. That definition is not changed by denying that the medium is substantive. Advocates of aether models are saying that the medium IS substantive, and that doesn't change the definition, either. Substantive or not, the medium for propagation of light is aether. (And Santa Clause exists, whether or not he is a real person.)
On the other hand, the question of preferred reference frames is interesting, particularly of co-moving coordinates.  Of course these ideas don't have much to do with the definition of aether.
No, but they may have something to do with the detection of aether. Detecting a preferred reference frame is evidence for the immobility of aether. Aether's apparent lack immobility is what persuaded Einstein to reluctantly accept that aether is not substantive.
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Offline David Cooper

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Re: Why no Ęther
« Reply #28 on: 04/01/2012 19:48:50 »
Again, this is an argument that amounts to moving the goalposts by redefining aether.  The aether theory assumes the speed of light isn't constant and therefore time dilation and length contraction don't exist.  If you redefine things so they both exist from the start, then you're not dealing with the aether theory.  Therefore, a null result of MM does scientifically contradict the aether hypothesis.

I haven't heard before this bit about the aether theory assuming the speed of light isn't constant, but then I've probably just made assumptions about what the aether theory was, based on what it most obviously should have been. I always assumed it proposed a medium through which light travelled at a constant speed, but that you might be able to measure its speed as having different values if you are travelling relative to it as the apparent speed of light should be slower when it's travelling the same way you are going and faster when coming at you head on, just like with the speed of sound - you could therefore easily imagine that you would be able to measure the speed of light as changing, although that's still based on the central idea that the speed of light is fundamentally constant. What the MM experiment then showed was that you can't actually measure light as having different apparent speeds because it so happens that travelling relative to the proposed aether contracts your measuring equipment, slows down aparent time and has all manner of other effects which similarly conspire to wipe out any possibility of measuring a difference of any kind (ignoring quantum effects which may resolve the issue some day), so it turned out that there is no detectable difference in the apparent speed of light across your measuring equipment, even though there may still be a radical difference in the amount of time taken for light to cross the equipment in one direction as compared with the amount of time taken for it to go the other way. We can never measure time properly because we always require something to do a round trip between two ticks of a clock (even with a water clock or hour glass - you have to think about forces between particles acting in both directions), so we are incapable of detecting the difference in what ought to be the aparent speed of light if it could only be made aparent.

So, MM most certainly failed to disprove the most obvious aether theory. If they were actually testing some other kind of aether theory, then that would resolve one mystery (the mystery of why people keep claiming MM proved there is no aether), but it would also pose a bigger mystery: why weren't they testing a more rational aether theory? Had they really not thought it up? Or have you got it wrong? Was the aether theory they were testing the same rational one I have just outlined? If so, what was actually proved was this: you can't detect your movement relative to the proposed aether because your equipment is controlled by forces which travel at the speed of light - this is quite different from effects which allow you to measure changes in the speed of sound where your measuring equipment is governed by forces which act far faster than the speed of sound. It was a surprising result, though it could have been predicted by a mathematician in advance if one had happened to think his way down the right route in advance. MM showed up a flaw in the theory in that they wrongly thought they'd be able to measure differences which it turned out were beyond them, but it showed up no flaw in the core of the aether theory itself.

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Offline David Cooper

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Re: Why no Ęther
« Reply #29 on: 04/01/2012 19:58:25 »
Maybe I've just made another assumption - that no mathematician had predicted that moving through the aether would shorten the equipment and slow down its apparent time. Maybe someone had, in which case the only aether theories being tested would be the crazy ones which stubbornly stuck with the idea that differences would show up even though it had been shown mathematically that they wouldn't.

I don't think my assumption can be wrong though, because from everything I've read, the MM result came as a complete surprise to everyone, including the people doing the experiment.

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Offline JP

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Re: Why no Ęther
« Reply #30 on: 04/01/2012 23:44:20 »
Aether means light is like sound in that it has a constant speed in stationary aether, but it doesn't have a constant speed to all observers.  As you point out, if aether exists you can measure the speed of light being fast or slow.  The aether theory just includes galilean relativity, and has Lorentz transformations, so nothing is length contracted or time dilated.

The MM experiment shows it isn't measured fast or slow.  Therefore, the aether theory can't hold. 

If I'm following you right, you're arguing that you can keep the idea of "stuff" through which light propagates, but introduce Lorentz transformations to keep that stuff stationary with respect to every observer (so that the speed of light stays constant).  Isn't that mathematically identical to special relativity, not experimentally testable and overly complicated?  I'm going to post this question in New Theories, so we can have a better discussion of it.

Here's the new theories post on this topic: http://www.thenakedscientists.com/forum/index.php?topic=42695.new#new
« Last Edit: 04/01/2012 23:52:07 by JP »

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Offline syhprum

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Re: Why no Ęther
« Reply #31 on: 05/01/2012 16:07:47 »
I meant to be a little provocative when I mentioned the the dreaded five and  a half letter word but am rather surprised what strange paths we have been drawn down.
syhprum

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Offline burning

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Re: Why no Ęther
« Reply #32 on: 05/01/2012 16:20:24 »
The last few posts have nicely recapitulated what the physics community went through in the wake of the MM experiment.  There were various attempts to "save" the aether by positing various mechanical properties of the aether that would explain the MM null result.  The problem was that these hypotheses didn't end up leading anywhere.  If they made predictions, the predictions didn't pan out, and you then had to posit something else to explain that failure.  Physics was left with the problem that if there was an aether, it was apparently unstudiable.

On the other hand, eventually you had relativity.  It rejected or at least ignored the aether hypothesis, and from a very lean set of assumptions was able to make a large set of predictions that, one by one, turned out to be accurate.  Against the advantages of relativity, the aether theories could offer the advantage that... they included an aether.  At that point I think the question from the OP needs to be reversed, and we need to ask "Why an aether?"

Now I agree that if by aether we mean "a medium required to support the propogation of electromagnetic waves," then, no, we can't say that science has disproved the existence of such a medium.  However, JP is completely correct that science has disproved the existence of an aether that in any way resembles what everyone from J. C. Maxell to A. A. Michelson was expecting and hoping for.

So from the fact that, as far as we can tell today, there is no studiable aether, do you conclude that there is no aether at all, or do you conclude that, despite its predictive power, relativity is metaphysically flawed and that there really is an aether.  The first choice has been dismissed in this thread as philosophy rather than science, but I can't see that the second choice can claim any different.

Now I don't actually think it is bad to select the second choice, if you are rigorous and intellectually honest about it.  It is a metaphysical preference that, at this time, does not have any objective support.  I think it could be very useful for some researchers to pursue trying to develop an aether theory, but anyone who does needs to understand what they would need to do to convince the greater physics community that their result is worth paying attention to.  It is going to need to reproduce the successful predictions of relativity while also doing at least one of two other things.  First, it could do so from a comparably streamlined set of assumptions to those of relativity.  If that's all it does, it will never be a replacement, but it would reasonably be considered a rival interpretation.  Second, it could provide a new set of predictions that could be tested.  Anything that provides neither is not going to be scientifically useful, and the existence of an aether would remain metaphysics.

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Offline simplified

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Re: Why no Ęther
« Reply #33 on: 05/01/2012 16:51:14 »
Gravitational ether exists,but it creates "space-time".

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Offline David Cooper

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Re: Why no Ęther
« Reply #34 on: 05/01/2012 21:01:02 »
Aether means light is like sound in that it has a constant speed in stationary aether, but it doesn't have a constant speed to all observers.

In what way does it make sense to say that it ceases to be aether once you've realised that the second part of that isn't going to pan out? You initially expect that it won't have a constant speed to all observers because you haven't thought it through fully, but when you eventually think through the maths of it in detail you realise that it won't actually be possible to detect those variations at all. Realising that you aren't going to be able to detect the aether so easily doesn't change the bit about light having a constant speed in stationary aether, so it makes no sense ban it from being called aether - the only thing that has changed is that you have discovered a barrier which gets in the way of identifying it.

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As you point out, if aether exists you can measure the speed of light being fast or slow.

I said you might expect that you could measure the speed of light being fast or slow, but you'd then discover you were wrong and realise why when you think it through in detail - it isn't like the speed of sound where you can use clocks governed by the speed of light to show up the difference. To show up the difference with in speed relative to the aether you'd need clocks governed by forces which act faster than the speed of light, and it isn't easy to find such clocks.

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The aether theory just includes galilean relativity, and has Lorentz transformations, so nothing is length contracted or time dilated.

I thought Lorentz transformations were precisely about contracting lengths.

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The MM experiment shows it isn't measured fast or slow.  Therefore, the aether theory can't hold.

It shows nothing of the kind - it shows that there is an unexpected problem. When you start to think about it properly, suddenly it all makes sense, and it does so without destroying the aether theory. You imagine a space ship travelling at a substantial percentage of the speed of light and with a lamp in the middle of it. The light has much further to go to reach the front of the ship because the front of the ship is racing away from it, whereas the back wall is hurtling towards the lamp. This makes you think that the wall at the front end should be much darker than normal as the light will have had more time to spread out before hitting it, while the back wall will be much brighter than normal. But that won't happen - the lamp pushes more light forwards and less backwards, resulting in the front and back walls being equally bright. Why should this happen? Well, imagine a camera with a 50mm lens on it. Put it next to the lamp and point it towards the front wall. The light coming from the wall reaches the camera far sooner than it would if the ship wasn't moving, but the lens will also behave as if it's closer to the focal plane for the same reason, so it acts like a wide-angle lens and compensates exactly for the differences caused by the speed of travel. If you point the camera towards the back wall the opposite happens - the lens behaves like a strong telephoto, the light having to go much further after passing through the lens before it reaches the film plane. The shapes of the lenses also behave differently, ensuring that perfect focus is maintained. If you try to cheat the system by using a mirror to tap light that sets out backwards from the lamp to redirect it forwards in the hope that you can get it to send less light forwards than should be allowed, lo and behold the flat mirror behaves as if it's curved and it concentrates the light forwards. These simple optical effects illustrate how forces would likewise be concentrated increasingly forwards as an object moves faster, maintaining the normal balance with the side effect that objects have to sit closer together in the direction of travel. The slowing of time is then fully accounted for by the total distance that things have to travel at the speed of light to complete a round trip. All of this is fully compatible with the idea of aether.

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If I'm following you right, you're arguing that you can keep the idea of "stuff" through which light propagates, but introduce Lorentz transformations to keep that stuff stationary with respect to every observer (so that the speed of light stays constant).  Isn't that mathematically identical to special relativity, not experimentally testable and overly complicated?

I expect the two theories are mathematically identical. The question is, how is it less complicated to chuck the idea of an aether and then to rely on not just one aether to maintain the distances between things, but an aether for every possible frame of reference, all hidden under the simple description "spacetime"? Einstein admitted that there has to be some kind of aether to create separation between things - if they are sitting in absolute nothing, there can be no separation because there's nothing to maintain the spacings. With a single aether, it's relatively easy to do the job. With spacetime, you aren't allowed to have a single aether in a preferred frame of reference, so spacetime has to do something infinitely more complex, namely having a different aether for each frame, and that idea sounds so ridiculous that you then have to brush the idea of aether under the carpet and fool yourself into thinking you don't need one at all, backed by the fact it isn't actually necessary in the maths, regardless of whether it's necessary in actuality (but we can farm that off into philosophy and forget about it). I've always regarded Einstein's relativity as an overly-complex aether theory.

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Offline David Cooper

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Re: Why no Ęther
« Reply #35 on: 05/01/2012 21:22:35 »
So from the fact that, as far as we can tell today, there is no studiable aether, do you conclude that there is no aether at all, or do you conclude that, despite its predictive power, relativity is metaphysically flawed and that there really is an aether.  The first choice has been dismissed in this thread as philosophy rather than science, but I can't see that the second choice can claim any different.

Both can be dismissed as philosophy, as can anything in science which can't be proven by experiment. MM didn't disprove the idea of aether at all - claims that it did are both bad science and bad philosophy. Claims that it currently can't be detected may be good science (unless QM really has demonstrated faster than light phenomena, although even then it may not allow a preferred frame to be pinned down). Claiming that there must be an aether would be bad science unless there was a test that could be done to prove it, but it might not be bad philosophy to make such a claim, just as claiming that there is no need for an aether might not be bad philosophy either - that's an argument for elsewhere. What matters here is that MM didn't prove that there is no aether, and it's a pity that so many physics books say that it does, because a lot of people take everything they read in them as gospel. I'm not accusing anyone here of that - this looks as if it's the most rational group of people I've ever found on the Net.
« Last Edit: 05/01/2012 21:26:13 by David Cooper »