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Doesn't light's constant speed dictate an 'ether'?

  1. Mar 26, 2004 #1
    firstly, i'm an ignoramus

    secondly, doesn't the fact that lights speed cannot be affected by the speed of a body that emits it suggest the existence of an ether? sound waves wouldn't exist without the 'ether' of air and so you can say that the air is the only thing that slows down sound waves...what slows down light waves? or is it something in the energy of radiation itself? even so, it is slowed, it must be slowed, or a fast body would give off fast light...

    help me out?
  2. jcsd
  3. Mar 26, 2004 #2
    You'd think so, wouldn't you?

    Here is what Special Relativity supposes:
    Assume you are at rest. I'm in a rocket ship coasting past you. Just as I pass, you turn on a light. According to your measurements, the light travels away from you at c. The strange thing is if I measure how fast light is going I observe that light travels at c relative to me.

    Where is the aether?
  4. Mar 27, 2004 #3
    The free space velocity of light as determined by Maxwell depends upon the permeability and permittivity of the vacuum void - so in this sense, there is a medium - give it whatever limitations you will. Moreover, if you consider space as being in tension (e.g. as would be the case in a false vacuum under any of the ongoing inflationary theories), then you can justify, at least in principle, how this spatial structure can support a transverse wave. While ether theories are out of vogue, they are not dead - and the adherents are not all crackpots - there appear to be more ether based articles coming out of the universities - contrary to common opinion, SR did not disprove the existence of an ether.
  5. Mar 27, 2004 #4
    very interesting, thank you :)
  6. Mar 27, 2004 #5


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    SR did disprove the existance of CLASSICAL ether*.In modern physics it is more convinient to talk about complex structure of QM vacuum then about ether.Vacuum turns to be far from being physically nothing.But,I stress again relativity does not describe QM phenomena.Properties of QM vacuum support to the great extent relativity,but link with spacetime concept in relativity and QM vacuum is still troublesome to reach.
    *Maxwell's ether constructed of ideal cog wheels and similar ideal fluid funny
  7. Mar 27, 2004 #6
    okay, so in quantum mechanics we understand that there is something more than nothing in a vacuum but we can't easily marry that with relativity...

    this is making things much clearer to me...i refuse to accept that a vacuum can possibly be empty for light to pass through it...if light is truly a wave then it must be a wave "in" something...a ripple in spacetime or in the dynamic vacuum...no?...and for light's speed to be reactive, as in constant regardless of relative velocity, it must be reactive against something...
  8. Mar 27, 2004 #7
    Billy boy 999

    Very much so, Maxwell's equations were developed using an elastic ether medium and they predicted that electromagnetic waves travel at speed c, which turns out to be the same as light.
    Up until Einstein's SR, everyone was thinking in terms of light propagating through the ether. Now everyone thinks in terms of spacetime, which doesn't require an ether.
    But there is no proof that space and time are joined together and no experiment has been done to prove the ether doesn't exist, so maybe your right.


    "particles of nothingness"
  9. Mar 27, 2004 #8
    billy boy 999 said: "if light is truly a wave then it must be a wave "in" something"

    Why? Do you feel the same about a static electric (or even magnetic) field. Does there have to be "something" around an electric charge for you to believe that there can be an electric field extending out from the charge?

    Another thing. Suppose you had never heard of waves (any kind of wave), and then you saw Maxwell's equations for the electric and magnetic fields and how you can combine them into an equation which has solutions of the form Asin(kr-wt). Then you realize this means that if at a certain time and place the field has a given strength, that at some later time and at a point further out on the r axis it will have this same value. Now you know all there is to know about this field. Do you think it would occur to you at that point to suggest that this field that varies periodically in time and space "must be in something"? I don't think it would.

    I think the reason that people insist on thinking that an EM wave needs a medium is just because other waves (although not all other waves) have them.

    The EM wave is just a solution to some equations that tells what the force is on charges at points in space. Just because the same sort of solution shows up as a disturbance in media that have mass, should in no way lock us into to insisting that it always has to.
  10. Mar 27, 2004 #9
    wisp - yes - maxwells first papers were developed along the lines of an elastic medium - vortex tubes and the like - but later on he abandoned much of what he thought was necessary for propagation - reducing it to the intrinsic properties of permeability and permittivity. To me, the thing that has to be abandoned about the notion of an ether is that it consists of entities like the molecules of a gas or a fluid that has a positive pressure - the properties of the spatial medium are "sui generis" ...we seem to be perpetually engaged in trying to relate it to something we have experience with - I can concur with the idea that an oscillating magnetic and electric field could be self sustaining without the presence of a medium - but space has measurable properties aside from the above electrical values - Dirac for example, argued that the vector potential must involve the rotation of something (consider the voltage induced in a loop of wire by a changing magnetic flux- the induced voltage is the same no matter how large the loop) - the entire magnetic field can be confined to a small iron core passing through the loop at its center, but the loop can be a mile in diameter - yet the induced voltage is always equal to the time rate of change of the flux passing through the loop - how does the confined flux communicate with the loop? The vector potential leads to a circulation - but there is no electrical field measurable outside the confining iron core - So if you believe that this is due to some form of ethereal spatial circulation as suggested by Dirac, you are in pretty good company -
  11. Mar 30, 2004 #10
    Yes, a medium that allows force to transmit through it is better than having nothing (absolute emptiness). Consider two small pieces of matter separated by absolute empty space. Now, how can these pieces be pulled together by gravity or electric forces. Only the ether medium through which forces can act can explain this. Without the ether medium, forces cannot act.

    If you accept that forces are some magical things that are attributed to bodies then we must assume that the speed of light is dependent upon the motion of the source. And we know that this is not true and so the ether must be the medium through which light travels.
  12. Mar 30, 2004 #11

    Chi Meson

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    I don't agree. First of all, the notion of force-carrying particles is no less "magical" than the notion of ether. Furthermore, the assumption of the existance of these particles does not say that their speed will be dependant on the motion of the source; in fact, it makes much more sense to me that their speed should not be dependant on the motion of the source.

    The introduction ofthe classical, incompressible super-fluid ether presents problems that are no less evasive than the SR & GR model. Supporters of the ether have come up with their own elaborate models that do appear to be quite valid, and ultimately I (personally) have to admit that there is a stalemate as to the final proof.

    This is a good time to point out the sticky thread at the top of this forum: the section that describes Einstein's re-introduction of "Aether" would serve this thread very well. It's too bad Einstein and Maxwell never got to work with each other.
  13. Mar 30, 2004 #12


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    I agree,classical incompressible super-fluid concept impose more questions and paradoxes in physics than simple spacetime geometry concept.
    Is there a single measurable observable phenomenon in physics that contradicts GR or quantum physics predictions ,that requires introduction of ether as some sort of must existing medium structure that is advantageos over usual spacetime concept?If there's not,why to complicate things than?
    Btw,spacetime concept from the physical (and metaphysical) standpoint is even more mysterious than "ether" to me.From the mathematical standpoint it is simple ,and that's why for use.
  14. Mar 30, 2004 #13

    It is possible that permeability and permittivity are properties of the ether.
    It is quite amazing that Maxwell developed his equations on an elastic ether model and the equations then reduce to terms that become independent of the ether.

    You are right in that the first problem in encountered with traditional ether is that of positive pressure slowing matter down (ethereal drag). But matter doesn't push through the ether, it is part of the ether and its motion through it is in the form of waves (the ether is displaced perpendicular to matters motion, and so the opening forces are equal and opposite to the closing forces). And so matter can move through solid ether without being impeded.
  15. Mar 30, 2004 #14
    Wisp - yes - I agree that there is no impediment to motion vis a vis the aether - actually, we are only 300 years behind the times in coming to this conclusion -
    D Alambert's showed that there is no drag in an ideal fluid - irrespective of the shape - this was a shocking revelation at the time - but if the ether functions as a propagation medium, must be the ideal fluid, and that should obviate the problem commonly brandied about re ether drag.

    With regard to Chi meson - there is a bias that strems from analogy with velocity in water that is always taken to heart when discussing the ether - i.e., that the ether must be nearly incompressible in order for light to propagate at c ----- this is not at all necesary - in fact it overlooks the low value of the average cosmic density i.e., the modulus can be highly compressible because the density is so low v = (B/rho)^1/2 where B is the modulus and rho is the density - using a density that corresponds to a critical universe (10^-26 kgm) and a modulus about equal to G, you get the velocity of light c.
  16. Mar 31, 2004 #15


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    Neither do I. Wisp, you (as I'm sure you know) are searching for a classical explanation for a non-classical phenomenon. Light simply does not and cannot work the way other waves do.

    You like to argue that there is no proof that there is no ether and that SR doesn't completely rule one out. That's quite true. The part you ignore is that science requires positive proof, not negative proof: ether has not been observed and the equations work just fine without it, therefore it must be assumed to not exist.

    The question I have for you is: When? When will you abbandon ether? When has enough effort been put into failed attempts to find it that you will conclude it doesn't exist? If the answer is 'never,' and I rather suspect it is, you may want to re-examine the mindset from which you approach science.
  17. Mar 31, 2004 #16
    Chi Meson:
    why is this? why does it make more sense this way?

    it seems that this topic elicits a little civil scientific rancor from some people, which is good to read, i like it, keep it coming guys... :wink:

    and i'm hearing that maxwell's equations - while originally formulated on the basis of an ether - actually drop the necessity of one...a pretty intuitive thing to think is - hey, the equations are trying to tell us something! so that feels like an intuitive argument against 'ether'

    it seems like one of the problems is a confusion about the word 'ether' because its a historically loaded word, but can we not toy with the idea of permittivity and permeance of vacuum as being qualities of a much different and dynamic vacuum that we can - for the sake of a visualization - call 'ether'?

    one of the reasons i brought up this topic of 'ether' (which i know almost nothing about but definitely more than i did! thanks guys) was because there seem to be some fundamental things about EM radiation and why c is the value it is that at least i don't well understand, and it sounds like there are still some things that are universally not well understood also...

    so is it then not useful to consider the existence of an 'ether' or a medium of a kind we haven't been able to articulate in science to help us imagine why light acts the way it does? i am now sorry i began using the word 'ether' but i don't think a theory should ever be abandoned if it it is still the object of useful debate...
  18. Mar 31, 2004 #17
    I wouldn't count out the ether - it probably doesn't have a particle structure as other mediums - but it exerts a reactionary force when masses are accelerated - and it is itself conditioned by matter as Einstein told us so many times - it has a characteristic impedance that we match to antennas to radiate max power transfer, a capacitance, an inductance that combined, dictate the velocity of light - that in and of itself is significant in terms of its reality - it is probably in tension as would be the case if space is a false vacuum, and accordingly this explains why it can support transverse wave propagation. Nothing in SR reveals why time proceeds differently in different reference frames - ether theory provides a physical link - although none of the various versions are necessarily correct - yet they do encourage us to seek to understand the nature of the void, and to endeavor to find a physical explanation for relativistic effects. If it is in tension, then it exhibits stress - stress fields imply stored energy - probably most of the cosmic energy exists in aetheral stress - so the dark matter that is sought for critical density may be exist in the form of stress energy. I will bet on some form of ether - we now know that there are several reasons why MMx and other experiments failed to detect the earths motion relative thereto, and we now have the CBR that gives good reason to suspect that we are moving relative to a stationary medium - in fact we can even detect the yearly variation in the CBR to show that we are moving relative to something
  19. Apr 1, 2004 #18
    I agree this does suggest an ethereal spatial circulation. However, I believe the ether has mass and so it is not the ether that rotates, but rather the magnetic pattern rotates in a "stationary" ether. This is similar to a sine wave pattern moving down a fixed string. A crude analogy - think of an electric field as a bicycle spokes pattern. The spokes rotate about an axis creating a magnetic effect. In this case the rotating pattern doesn't cause ether rotation.
  20. Apr 1, 2004 #19


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    In theory of relativity magnetic and electric fields a sort to say "the same things".
    IOW,what is E-field in first reference frame can appear to be B- field in another in relative motion to the first one and vice versa.Even though relativity, doesn't explain origin of Maxwell's EM (matter of fact it is the opposite case),classical EM gets nice interpretation through it.
    QED rise electromagetics to yet another level,and not just that:P. Dirac predicted possibility of magnetic monopoles.(Yet to be detected).I just thought it is worth mentioning it.
    I'm cuirious to know how pushers of any kind of "(a)ether" theory explain the absence(?) of retarded EM radiation of charge accelerated by gravity field?
  21. Apr 1, 2004 #20


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    To be more specific on the last sentence:consider "centripetal force" orbiting motion of charge in gravity field of say spherical mass object.Ie. charged particle in the geodesics trajectory of external G-field doesn't emit EM radiation.
    How an aetherist explain this?
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