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What's wrong with Michelson's explanation of ether dragging?

  1. Mar 14, 2008 #1
    The null result of the Michelson-Morley experiment led Lorentz to believe that the ether can never be detected because it distorts things in the direction that they move with respect to it. But from what I've read, Michelson himself explained the result by saying that the ether must somehow be "dragged along" by the movements of the earth. Although this explanation seems rather simplistic, perhaps there is some deeper truth to it (such as, the gravitational fields and the light propagation medium/ether are "connected" at the most fundamental level).

    Isn't this explanation at least as sensible as one that says that space and time are relative? (I'm still not sure what the heck that's supposed to mean!)
     
  2. jcsd
  3. Mar 14, 2008 #2
    Nothing was wrong with the Ether dragging explanation. It followed the normal route of physical enquiry. It was proposed, experimentally tested and found to be incorect.

    Matheinste.
     
  4. Mar 14, 2008 #3

    JesseM

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    See the problem with stellar aberration discussed here.
    Basically it means that the different inertial coordinate systems related by the Lorentz transform disagree about distances and times between events, but the laws of physics are found to work exactly the same in all these coordinate systems, so there's no reason to label one system's measurements as more correct than any other's. Did you read my last comment on the Problem with thought experiment thread? If so, did you have an answer to this question?
     
  5. Mar 14, 2008 #4
    I'll read up on the phenomenon of stellar aberration. I don't think it'll change my basic point that, assuming that a light-propagation medium exists (which even Einstein assumes), there must be a fundamental relationship between it and the "gravity-propagation medium" (for want of a better term).

    (Jesse, I know it means those series of words, but I just can't wrap my mind around those series of words. That is, I can't "feel it", if you know what I mean!)
     
  6. Mar 14, 2008 #5

    JesseM

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    I don't think Einstein assumed there was a medium for the propogation of either! What quote of his are you thinking of?
     
  7. Mar 14, 2008 #6
    The problem is that it was falsified experimentally. See here.
     
  8. Mar 14, 2008 #7
    And not only did the Michelson-Morley experiment invalidate the existing ether theories of that time but relativity was confirmed, not just in general but with very specific predictions like the precession of the perihelion of Mercury, and since then by all sorts of astronomical phenomena and by the relativistic effects experienced by satellites orbiting the Earth.
     
  9. Mar 15, 2008 #8
    It is a difficult thing to wrap your mind around without practice. There also must be a good intuitive reason for practicing which seems to be what you are searching for. Just being asked to believe the Lorentz transform explains it is not good enough for many of us. So let's take a closer look.

    The problem with stellar aberration has already been pointed out. Even if we assumed that Special Relativity (SR) and Lorentz Ether Theory (LET) agreed in all predictions there are problems. On closer inspection it is no different than defining a certain object in the Universe as not moving and the speed of everything else must be measured relative to that one object. Only in LET this object/s we are supposed to use for this cannot be detected much less measured in any way so we can't even know what is moving relative to it. On Earth we use ground speed to do this but ground speed is a very poor choice when doing orbital mechanics of the solar system or our galaxy. We could still use ground speed and correctly say the Earth is not moving and say everything orbits around the Earth using some VERY complex math, but why? It would, like LET (mostly), make the same predictions. LET runs into similar difficulties when we talk about many phenomena. LET is even worse because it uses something we cannot detect, measure, or determine any aspect of how it works to define what is at rest. At least we can see and measure ground speed. What use is something we can't measure to define what is at rest when another observer can say its motion is different (because there is no way to measure it) and this other observer is just as correct as the first, even if they both claim the ether as their rest frame? This alone means that it doesn't even make a good interpretation as claimed, even if stellar aberration didn't falsify it.

    Suppose that at some level there is something to the ether idea. Suppose you could re-define some kind of ether that successfully predicts stellar aberration, gravity consistent with General Relativity, etc. What value would that be? If all it did was tell us what we already know it would be of no value whatsoever. It would still leave us with no way to test if it really was the right explanation. It would just be an ontological construct designed to soothe the philosophical prejudices of a few. If you think such a model could make new testable predictions that couldn't be predicted by standard means then I for one will hear you out. Before you can even dream of doing something like that it is imperative that you fully understand why the ether as conceived is not a viable construct to explain relativistic effects. So the main reason for objecting to postulating a classical ether connection to gravity is not because it is fundamentally impossible, though it probably is, but history has shown it to be at best superfluous and at worse flat out wrong. If you want to object then deliver the goods. If you wish to pursue this model then more power to you, just don't claim what you haven't got.
     
  10. Mar 15, 2008 #9

    turbo

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    If you will read his Leiden address of 1920 and/or his essay "On the Ether" from 1924, you will see that he was quite explicit about the need for an ether to support the propagation of EM through "empty" space. He also claimed that gravitation and inertial effects arise from matter's interaction with the local ether in which it is embedded, and not from some Machian "spooky action-at-a-distance". These ideas are given little notice these days, and in fact are generally dismissed out-of-hand, but that was his line of reasoning for many years. He felt that this was a viable route to incorporate electromagnetism into GR, though he never managed to accomplish it in his lifetime. Here's the final paragraph of the Leiden address.

     
  11. Mar 15, 2008 #10

    JesseM

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    That quote doesn't say what you're saying it all--it only says that space has its own properties, and in that sense it's like an ether. But he doesn't say it's like an ether in the crucial sense of having its own distinct local rest frame.
     
  12. Mar 15, 2008 #11

    turbo

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    He was far more specific in his essay "On the Ether", which is Chapter One of "The Philosophy of Vacuum" by Saunders and Brown. The translation is copyrighted material, but here is an authorized preview. Unfortunately, two critical pages are missing, but you'll get the gist of it. Some of the missing material deals with his rejection of the Machian notion of action-at-a-distance. He kept pursuing this line of reasoning for many years, and I wish more of his works from this period were available in English translations.

    http://books.google.com/books?id=ZU...ig=82St7DUG9LXyCKuuKiS8BU4smkA&hl=en#PPA17,M1
     
  13. Mar 15, 2008 #12

    JesseM

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    Specific about what? Did he claim that there was an ether with a single definite local rest frame? If you've read this book, can you provide a relevant quote?
     
  14. Mar 15, 2008 #13

    turbo

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    He said in part "The fact that the general theory of relativity has no preferred 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."

    and

    "The metric tensor which determines both the gravitational and inertial phenomena on the one hand and the tensor of the electromagnetic field on the other, still appear as fundamentally different expressions of the state of the ether: but their logical independence is probably more to be attributed to the imperfection of our theoretical edifice than to a complex structure of reality itself."
     
  15. Mar 15, 2008 #14

    JesseM

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    Looking at the context on p. 17-18, I don't think the first quote is talking about the issue of a single preferred frame at all, when he says "no preferred space-time coordinates" I think he's comparing it to special relativity which has a family of preferred coordinate systems, namely the inertial frames (see the preceding discussion on p. 17 where he talks about the specialness of inertial coordinate systems in SR); so in that quote I think he's talking talking about the fact that general relativity is stated in a "generally covariant" form which works the same in all coordinate systems, but as I talked about in post #8 on this thread, it was indeed realized after Einstein formulated this principle that it was really more a feature of the mathematical formulation, and not a physical feature, because it's possible to rewrite any theory (including Newtonian mechanics) in a generally covariant tensor form which will work in arbitrary coordinate systems.
    This second quote from p. 18 doesn't talk about the issue of a preferred frame at all, I think he's talking about the issue of whether gravity and electromagnetism can be unified or whether they're two separate forces (note that the preceding sentence is 'Furthermore, in my opinion, we have not as yet succeeded in going beyond a superficial integration of the electromagnetic forces into the general scheme of relativity', so it's clear he's making a speculative comment about the idea that in the future we might find a new theory which unifies them, perhaps by treating electromagnetism in terms of curved spacetime as in the Kaluza-Klein theory). He does state this idea in terms of "ether", but throughout the paper it's clear that he's using the word "ether" just to refer to the notion of space having intrinsic properties and fields associated with it, without implying the additional notion that there is a single preferred frame as in pre-relativistic notions of the ether. I note that on p. 17 he says:
    So, I think you've misinterpreted the two quotes you posted if you thought Einstein was suggesting an ether with a single preferred rest frame, and I think he makes it clear in the article that he isn't defining "ether" in this way.
     
  16. Mar 16, 2008 #15
    Let me just say that I am not advocating a literal phenomenon of "ether dragging" whereby mass and the ether simply interact with one another. I am thinking more along the lines of the notion that the null result of the MM experiment simply tells us that the ether is perfectly at rest with respect to the surface of the earth. Instead of going full steam ahead into "relativity mode", can't we consider the possibility that the ether is an extraordinarily dense, yet highly fluid medium? Lorentz assumed it to be more like a static, solid block. Can't we have more imagination than that?

    Imagine the surface of a body of water in which vortexes are embedded inside of vortexes. Inside of each particular vortex, water energy waves will always propagate at the same rate with respect to a frame of reference that is swirling along with it.

    We can now correlate our water vortexes with local, inwardly directed compressions of the light propagation medium. Likewise, the entire body of water can be equated with the totality of the universal ether.
     
  17. Mar 16, 2008 #16

    Mentz114

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    Joey_m:
    General relativity, relativistic electrodynamics and quantum theory work without an aether. So why introduce this complicated thing when it isn't needed, and probably won't work in any case.
     
  18. Mar 17, 2008 #17
    No, see here. Why do you keep reposting the same ideas and you refuse to read?
     
  19. Mar 17, 2008 #18
    I think it is needed because when theories don't quite fit observation then people start artificially modifying them to an absurd degree. Relativity and quantum theory are both very successful models up to a point. I think replacement is inevitable.

    Incidentally, the Michelson Morley experiment failed because the aether moves towards the centre of the earth. The earth is not travelling through it so no modification to the speed of light beams would be expected.

    Nick
     
  20. Mar 17, 2008 #19
    That second to last sentence of yours gives away the model you speak of as if it has authority. Personally I like analyzing aether theories and seeing exactly when where and how they break down empirically. The version you are speaking so authoritatively about fails any basic comprehension of thermodynamics, even at the level of aerodynamics.

    Isn't the model you are implying here "artificially modifying" a theory over a hundred years old? What do you mean by replacement? Even if some version of an aether theory actually worked it does not imply a replacement for the standard formalism.

    Hint: Steer clear of your personal theories unless you think your prepared to defend it in the Independent Research thread. Learn everything you can about the standard formalism you can. I can almost guarantee it's not what you think it is from reading descriptions.

    Good luck...
     
  21. Mar 17, 2008 #20
    Hi,

    There are two versions of aether being discussed in this thread.

    1) Old aether

    This version of aether is a fluid medium that llight waves travel in, rather like waves in an ocean or sound in air. The problem with this version was that the motion of the Earth would be expected to leave a detectable wake as the Earth moved through it and that it would cause the Earth to slow down in its orbit as the aether dragged on it. The null result of the MM experiment caused people to conjecture that the aether was dragged along with the Earth rather like the atmosphere. This conjecture was disproved by measurements of stellar aberration.

    2) Lorentz aether.

    Lorentz proposed a more sophisticated version of the aether. His aether had the properties that anything moving relative to the Lorentz aether is length contracted and time dilated according to the Lorentz transformations. His aether is completly frictionless and so is not dragged along and does not leave a wake. (It passes through normal matter with little or no interaction rather like the WIMP particles that are proposed as an explanation of dark matter). Mathematically, the results of assuming a Lorentz aether are (for most trivial calculations) identical to those of Einstein. Einstein correctly claimed that since the mathematical results of not assuming an aether are no different to assuming an aether, then there is no need of an aether. It is also correct to state that it is not possible to detect the aether by any experimental means and therefore it is not possible to determine an absolute reference frame.

    However, even though Einstien correctly points out that there is no (mathematical) need of an aether, for some people an aether might be helpful for intuitively viewing relativity (even if just to prove to themselves that it is undetectable). Often, it is suggested (as hinted at by Metz114 and my_wan) that assuming a Lorentz aether would produce incorrect results in some situation, yet I have never seen a clear demonstration of where classic relativity and assuming a Lorentz aether produce different results, mathematically. Can anyone here demonstrate (or point to a link) where they are not mathematically equivalent?
     
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