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Proof of the non-existence of ether

  1. Jun 8, 2010 #1
    Guys, I have started reading Special Relativity and used the Feynman Lectures as my starting point. As I noted, he started well with the concept of ether and told about Michelson-Morley experiment. There, to explain the results of experiment, he told Lorentz Contraction and supposed it to be true whatsoever. Then came Poincare's Hypothesis and from there on he continued to develop the the theory taking Lorentz Contraction and Poincare's Hypothesis as postulates. Nowhere did he gave any sign whether the concept of ether is correct or incorrect.

    So, I want to know whether there is any proof that the concept of ether is falty? And moreover what is the proof of Lorentz Contraction?
  2. jcsd
  3. Jun 8, 2010 #2


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    Here is some information about the experimental basis of special relativity: https://www.physicsforums.com/showthread.php?t=229034

    The experiments referred to above agree with SR. There is no aether theory that succeeds in predicting the observed results.
  4. Jun 8, 2010 #3
    The ether in Lorentz Ether Theory is, even in theory, undetectable. LET and SR predict exactly the same results for time dilation, length contraction etc. and can be used interchangeably as a matter of choice. I personally prefer the SR formulation for reasons of simplicity and aesthetics.

    Lorentz himself wrote of the ether "This incertitude, this impossibility of even disclosing a movement in relation to the aether, led Einstein and numerous other modern physicists to abandon completely the notion of an aether. There, it seems to me, is a question towards which each physicist must take a position which best accords with the manner of thinking to which he is accustomed."

  5. Jun 8, 2010 #4
    Nicely stated. Depending on one's preferences, either the ether doesn't exist or, if it does, Nature elegantly conspires to prevent our determination of its rest frame. I read somewhere that Poincare quipped, "A complete conspiracy in Nature is a Law of Nature." Maxwell conceived of all of space as being filled with an equal continuum of positive and negative charge within which restorative stresses are engendered by free charges (the origin of which he never gets into). The idea is that free charge displaces one sign or the other in the "sea" of continuous charge distributions, and that this displacement is the same as a current of free charge while the displacement is under way. His development of the stress mechanisms, in his "Treatise on Electricity and Magnetism", is elegant. But ultimately his sea of displacement charges probably ranks with the ether. If it exists, we can't determine its rest frame. But we can scarcely be faulted for postulating that it is essentially one and the same thing as the ether.
  6. Jun 8, 2010 #5
    There is no "proof "that the aether concept is "falty". There is ample proof that the concept is irrelevant. SR replaced the Lorentz Aether Theory about 100 years ago by being a much simpler explanation.

    To date, there is no direct experimental proof of Lorentz contraction. This is due to the enormous experimental difficulties associated with setting up such an experiment.
  7. Jun 8, 2010 #6
    Well, I myself first understood the effects of time dilation and lorentz contraction through the ether theory. But if we assume Poincare's Hypothesis to be true then the results about the simultaneity of two events in different frames do not match with the result arrived from ether. So, if the principle of relativity is true, then the theory of ether must be wrong, if this is the case. That's why I asked for the proof that ether doesn't exist.
  8. Jun 8, 2010 #7
    I am not familiar with Poincare's Hypothesis but I will check it out. The generally held belief is that LET and SR both produce the same results and so one being true does not exclude the other being true.

  9. Jun 8, 2010 #8


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    Keep in mind that there is not a single ether theory. The ether that Michelson and Morley's experiment argues against has different properties from the ether of the "Lorentz Ether Theory" whose experimental predictions are indistinguishable from SR.
  10. Jun 8, 2010 #9
    Ok, how do u explain simultaneity of events by Lorentz Ether Theory?
  11. Jun 8, 2010 #10


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    There is no experiment that can directly measure simultaneity. You can make measurements but then you have to perform a calculation. The calculation you make in Lorentz Ether Theory is different to the calculation you make in relativity, so the fact you may get different answers proves nothing.

    (And, in fact, if you choose to use what Lorentz called "local time", you get the same answer in both theories.)
  12. Jun 8, 2010 #11
    Two completely opposing opinions.

    I think SR and the LET are equivalent. The numbers come out the same and that is what is important, not what the theory claims is going on behind the curtains, whether it is spacetime, ether or invisible pink unicorns. Arguing about such things is philosophy or (even worse) politics.

    For GR it is different, as far as I know no one has been able to extend LET to be compatible with GR.

    But of course if someone would come out with an extension of LET which lets us calculate accurately the bending of light around the Sun and the anomalous rate of precession of the perihelion of Mercury's we could possibly get a competing theory. But as far as I know no one has presented such a theory.
    Last edited: Jun 8, 2010
  13. Jun 9, 2010 #12
    MMx did not disprove the existence of some sort of ether - the notion of an ether was superfluous to Einstein's development of SR - nowdays it is sort of bad taste to speak in terms of an ether - at least in the context of a light propagating medium - but by the same token, its vogue to muse about dark energy and dark matter - so what is the difference - Whatever space is, there appears to be no difference between standing still and moving at a uniform velocity - and if the velocity of light is not affected by uniform motion, we have to view whatever space is as something different that a wind or flow that that can be detected. It would seem that the invariance of the interval precludes any type of measurement that would reveal absolute motion - for example if two oppositly directed spaceships pass each other at copnstant velocity, each will measure a spacetime interval in their own frame as equal to what the other would measure in his frame - this would seem to rule out any chance of measuring velocity with respect to space.
  14. Jun 9, 2010 #13
    Ok, well SR is validated by experiments.. And it is proved that if two events are simultaneou s in one frame then they may not be simultaneous in another frame. And this fact is not explained by Lorentz Ether, so can't we take it as an evidence against it? There must also exist other facts which aren't explained by LET or do they not??
  15. Jun 9, 2010 #14


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    But to say two events are simultaneous depends on what your definition of simultaneity is. As I said before, there is no experiment that can decide whether two events are simultaneous or not without you deciding which of the two theories you are going to apply to calculate the answer from your measurements.
  16. Jun 9, 2010 #15


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    Let me develop a little as I try to follow you.

    Which calculation do you make in LET? Well, if one believes in an aether, one may also believe that one can make a calculation in the aether frame. If one applies therein the Einstein-Poincaré convention for clock synchronization, one could argue that when the light beams hit the distant clocks in their go-trips, they do it with a sort of "absolute" simultaneity, in the sense that... Difficult to express... Maybe in the sense that if, for example, each light beam has triggered a mechanism that has made a bomb go off, then it is impossible that a signal departs from one clock, which has already exploded, and arrives in time to avoid the explosion of the other clock, even if such signal travels at superluminal speed, even if such signal displaces (I know this is absurd) "instantaneously".

    ... whereas in SR one would say that a superluminal speed is impossible and so the two events, the two explosions, whose separation is spacelike, are not causally connected, which amounts to the same practical result, i.e. a signal cannot depart from one clock after its explosion and arrive in time to avoid the other's explosion. But if -nevertheless- one day someone found out that superluminal speeds were possible, then... I get lost as to what SR would say in this case. Maybe the answer is nothing, since SR simply rejects that possibility = nothing can travel FTL.

    And well in fact, according to LET itself, the hypothesis considered earlier (one makes a calculation in the aether frame and claims to have obtained absolute simultaneity) is impossible to consider in practice, because it is impossible to make any experiment betraying whether one is at rest with the aether or at which speed one moves wrt the aether. Hence in fact one HAS to choose what Lorentz called "local time", which is equivalent to SR's "time without any adjective".

    Conclusion: in practice, as it has been mentioned, there is no difference between LET and SR. But that doesn't mean there is no aether, some sort of thing, which is not material, not ponderable matter, pervading space! Who knows? I remember Lorentz said something like this: the great merit of Einstein was making aether fully unnecessary and thus preventing us from wasting time in guessing its mysterious features. But really I think some authors are misleading when they say that SR disproves the aether. It doesn't. It just makes discussions about it superfluous.

    Similarly, I also think it is incorrect to say that SR is "preferrable" over LET. The two theories cannot be made to battle against each other because they are situated at different levels. Anything that SR says is also said by LET. It simply happens that LET goes one step further in an attempt to find a causal explanation and makes a hypothesis ("it's all like that because there is an aether"), although it does humbly accept that such hypothesis appears to be unprovable, because everything indicates that such aether would be undetectable. On the other hand, one should also recognize that LET is useful for didactic purposes: it helps to visualize and understand the postulates of SR.
  17. Jun 9, 2010 #16


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    Neither dark energy nor dark matter are a propagation medium for light. So not only are they different from aether, they are completely unrelated to it.
  18. Jun 10, 2010 #17
    Since no one knows what form dark energy and dark matter might take - how do you know its not tension stress - and if it is tension, then it comports with the attributes required for supporting a transverse wave.
  19. Jun 10, 2010 #18
    The concept that is faulty is that the medium moves independently with respect to a particle emitting radiation. In other words there is no "ether wind".

    Maxwell said in effect that in the second volume of his treatise. He declared that the physical motion of a particle may not be directly associated with a location of the electromagnetic forces. Sorry, I don't have my notebook with me at the moment so I'm not able to post the exact words.
  20. Jun 23, 2010 #19
    Maybe the ether affects atoms from all directions. It's atomic size vector sum is zero, yet it's subatomic effect is directional. At some size it might add shear forces to atoms and shake things up. For example an electron is about to fall into the nucleus and gets hit by an ether vector force and shot into a higher orbital. If ether affects the space between the lowest electron orbital and the nucleus, how can we observe it?
  21. Jun 23, 2010 #20


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    What you're talking about has nothing to do with the lumeniferous aether under discussion. You're mis-identifyng the 'quantum vacuum' as an aether, which identification is a daft idea promulgated by certain crackpots.
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