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Wrong claims?

  1. Sep 14, 2004 #1
    in the sticky above about wrong claims, chris hillman attempts to debunk the idea that "GR is an aether theory". however, his argument seems a bit disingenuous when compared to einstein's own writing on the topic.

    einstein stated, in "Ether and the Theory of Relativity", an address delivered on May 5th, 1920, in the University of Leyden:

    "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. But this ether 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."

    for those interested in this, the original article can be accessed here - http://www.mountainman.com.au/aether_0.html
     
  2. jcsd
  3. Sep 14, 2004 #2

    selfAdjoint

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    That quote from Einstein is forever being resurrected by ether fans. Einstein meant, as you will see if you read carefully, that his SPACETIME, which he identified with his FIELD, was the new ether. It had nothing at all to do with the luminiferous ether that was overthrown by special relativity.
     
  4. Sep 18, 2004 #3
    i dont think i can agree with your interpretation of this issue. the original luminiferous aether was always considered some type of underlying "fabric" whihc permeated the universe, providing a medium that "waved" with the passage of EM radiation. einstein's aether for GR is exactly that - an underlying fabric by which fields and their interactions are propagated. he does not seem to be waffling at all with his language in the cited article. i certainly wouldnt claim to understand GR fully, but i do believe that for chris to claim that GR is not an aether theory contradicts what einstein says in the article.
     
  5. Sep 18, 2004 #4

    russ_watters

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    No, it isn't, jnorman. Einstein's "ether" does not provide a medium for the transmission of EM radiation. Your understanding is incorrect.

    And SA is also correct about this being a very commonly cited (and misinterpreted) quote. A search of this forum will reveal a number of references to it...
     
  6. Sep 18, 2004 #5
    There are other Einstein quotes which confirm the views of selfAdjoint and russ_watters.
     
  7. Sep 19, 2004 #6
    sorry - i didnt say that very well. i didnt mean to imply that the GR aether was the medium by which EM radiation was propagated (though i dont think it is very clear just how photons are propagated considering their dual nature, wierd little critters that they are...). i meant that the aether of GR is (at least as i read it) an underlying fabric which conveys the shape of spacetime (ie, i gues it is that aether that is "waving" if there are such things as gravity waves). i am not trying to be dense or troll here - it just sounds like einstein is saying in no uncertain terms that there is an aether associated with GR, and chris seems to be saying that is not the case. thanks for your responses - this is a fine forum. i will admit freely that i really do not have any idea what gravity is, or what time is, or what damn near anything is anymore... point particles, virtual particles, higgs bosons, monopoles - jeebus!!
     
  8. Sep 20, 2004 #7

    russ_watters

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    Yes, obviously Einstein said GR is an ether of sorts. But "ether theory" refers to an ether as a medium for propagation of light. Important difference.
     
  9. Sep 27, 2004 #8
    I will jump in here and say first - that SR did not do away in any sense of the word, with the notion of an ether - the point was that it was not necessary to Einstein's development of the transforms. Einstein firmly believed in the concept of an ether - it was a necessary thing -- indispensible to an explanation of an inertial field that pervaded all space as opposed to Mach's principle that relied upon distant matter to act instantaneously upon locally accelerated masses. The ether has many properties that define electromagnetic propagation (a characteristic impedance) a capacitance per unit length - and an inductance per unit length that, taken together, determine the speed of em waves. Dirac held out for a dynamic ether (as opposed to Einstein's static but warpable ether) - one that actually moved in a manner that would explain the vector potential and other mathematically related phenomena. SR yields the same transforms as ether theory - moreover the experimental evidence cannot distinguish between SR transforms and other transforms based upon different postulates that are related to different ether based theories such as in-flow. We ae spending money to determine in gravity probe B whether the ether will exhibit a rotational property in the proximity of rotational matter.
     
  10. Sep 28, 2004 #9

    selfAdjoint

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    Have you got any citation at all for this? And don't quote that post-GR paper when E. calls the gravity field a new ether. Special relativity specifically did away with "an inertial field that pervaded all space."
     
  11. Sep 29, 2004 #10
    Selfadjoint - you and I have an entirely different understanding of Einstein's words - he specifically referred to the ether as being necessary for the propagation of light in the 1920 Layton address. Here is a quote therefrom:

    “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....space without the ether is unthinkable, for in such space there would not only be no propagation of light, ..."

    and from his address in honor of Faraday:

    “..every attempt to deny the physical reality of space collapses in the face of the law of inertia. For if acceleration is to be taken as real, then space must also be real within which bodies are conceived as accelerated."


    “...The ether was invented, penetrating everything, filling the whole of space, and admitted as a new kind of matter. ... it was overlooked that by this procedure, space itself had been brought to life...It (the ether) was thus to some degree identical with space itself.... In this way the field theory was born as a illegitimate child of Newtonian physics.”

    “To become fully conscious of this change in outlook was a task for a highly original mind whose insight could go straight to essentials, a mind that never got stuck in formulas. Faraday was this favored spirit. His instinct revolted at the idea of forces acting directly at a distance which seemed contrary to every elementary observation.” If one electrified body attracts or repels a second body, this was for him brought about not by a direct action from the first body to the second, but through an intermediary action. The first body brings the space immediately around it into a certain condition which spreads itself into more distant parts of space according to a certain spatiotemporal law of propagation. This condition of space was called ‘the electric field.’ The second body experiences a force because it lies in the field of the first, and vice versa. The ‘field’ thus provided a conceptual apparatus which rendered unnecessary the idea of action at a distance. Faraday also had the bold idea that under appropriate circumstances fields might detach themselves from the bodies producing them and speed away through space as free fields; this was his interpretation of light.”
     
  12. Sep 29, 2004 #11
    This may be wrong,but I wish to suggest the following:-Instead of looking upon the ether as some kind of a fluid which would produce an ether wind when bodies move through it,think of it as a membrane--a 3D elastic membrane with stresses and strains produced by gravitating bodies.In this picture the metric tensor would be akin to the elasticity tensor.Let me have your feedback on this.

    Jagmeet Singh
     
  13. Sep 29, 2004 #12
    gptemjms - I think your comment has much merit - if Space (the ether) whatever, is a necessary factor as Einstein opined, in the propagation of light, it would seem that the fluid model leaves something to be desired - specifically, fluids do not support shear forces and therefore are not able to function as a medium for transverse waves. A membrane by contrast, can be in tension (e.g., like a violin string) only in three dimensions. I like to think of space as loosly coupled micro vortices each attracted to the other but being pulled apart by expansion so as to result in a negative pressure (stress).
     
  14. Oct 1, 2004 #13
    yogi,there's ,however, a problem in equating the metric tensor with the elasticity tensor--the former is in 4 dimensional space(spacetime) while the latter is 3D.Should we then treat this elastic membrane as really 4 dimensional with time being its fourth dimension?What would that mean?
     
  15. Oct 1, 2004 #14

    russ_watters

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    yogi, how do you reconcile that with the last sentence of the quote:
    "The idea of motion may not be applied to it."?
     
  16. Oct 2, 2004 #15
    Hi Russ - I cannot. The two statements have always seemed to be in conflict to me.
     
  17. Oct 27, 2004 #16
    To add to this:-if you look up a book discussing elasticity you'll find that the tensor of elastic coefficients is of rank 4.Now what could be the analogue of stress,strain and the tensor of elastic coefficients in GR. We could take T_{mu,nu} as the stress tensor and since the left hand side of Einstein's equation contains R_{mu,nu} - .5 g_[mu,nu} R,may be we should take the whole thing as the strain tensor(?)--in which case the tensor of elastic coeficients is just replaced by a constant.Would this lead to the correct wave equation for gravitational waves?May be not--then what should be the correct form--I am sure some of the GR experts here can arrive at it--so please help!
    It would be really interesting if we could look upon gravitational waves as elastic waves,in which case the graviton would just be a quantum of these elastic vibrations(much like the phonon).
    Jagmeet Singh
     
  18. Oct 28, 2004 #17
    I guess we should work on R_{mu,nu}=0,the equation for empty space.T_{mu,nu} is too localized,moreover we are looking for stresses and strains in this space(spacetime).
    Hope to hear from you all soon.
    Jagmeet
     
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