Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Einstein and the ether

  1. Jan 6, 2009 #1
    It's becoming a little more well-known in recent years that Einstein was in fact a strong advocate for a "new ether" from 1916 until his death. He denied the 19th Century version of the ether in his 1905 paper on SR, and spent about 11 years defending his banishment of the ether from physics. But in 1916, in a letter to Lorentz (a lifelong advocate of the ether concept), Einstein admitted that GR entailed a "new ether" that, at the least, imparted acceleration and rotation to ponderable mass. And Einstein remained a defender of the ether concept until his death, attempting to create a unified field theory that would unite GR and quantum mechanics in a relativistic field/ether (for Einstein, fields, ether and space, became somewhat synonymous).

    This interesting history is detailed in Ludwik Kostro's 2000 book Einstein and the Ether.

    My question is: if some concept of ether is required to, at the least, provide the basis for distinguishing bodies undergoing acceleration from those at rest - and thus allowing relativistic effects to be felt - isn't this ether also the basis for "absolute rest"? In other words, if the ether allows the distinction between different frames of reference, based on one frame undergoing acceleration, and another not, isn't there necessarily a "resting frame," that is absolute rest?

    If so, doesn't accepting even this non-physical concept of the ether, as Einstein did, undermine the principle of relativity, with its denial of absolute rest?
  2. jcsd
  3. Jan 6, 2009 #2
    You are misunderstanding what Einstein was saying.
    Einstein just means that empty space still has properties. While a loose analogy, this is like realizing that something having a value zero is different from something not existing.

    What you seem to be thinking is that this means that there is somekind of "background field" (like the old aether ideas), and movement relative to this field can be detected by acceleration but not velocity. That is disingenuous to the ideas of GR.

    Imagine the old "bucket test". Spin a bucket of water about its axis and the water will rise on the edges. Why? How does it know it is spinning and to feel acceleration as opposed to sitting still and all the stars rotating about it?

    Well, you can do the calculation (can someone provide the reference, I remember reading a nice archiv summary but can't find it now) where the bucket is "at rest" and all the stars and other matter spin around it ... then a term will appear like a centifugal force causing the water in the bucket to rise on the edges, and accelerometers to read non-zero. Now, we started the calculation saying the bucket was a rest, so is this a 'fictitious force' or does all the other matter in the universe somehow provide resistance to acceleration (like a true Machian gravity)? It turns out that GR is not truly Machian (this can be debated, and has, since the machian ideals were not mathematical precise so you have to interperet them, but Einstein didn't feel GR was fully Machian if that counts for anything).

    Hopefully that helps.
  4. Jan 7, 2009 #3
    Thanks Justin. A couple clarifications: I am not suggesting Einstein's new ether moves - and nor did he. He always made it clear that motion is not a property that may be attributed to his new ether; nor does it consist of any kind of material particles, as was the case with the 19th Century luminiferous ether. Rather, the new ether consisted of the properties of space, or, better yet, the new ether IS space itself, which has certain properties.

    One of those properties, for Einstein, was the capacity to distinguish acceleration from uniform motion (in GR), but also to distinguish inertial frames from non-inertial frames (in SR, which was a point of view he developed after 1916, looking back to his 1905 SR theory).

    If the new ether allows a distinction between a body undergoing acceleration and a body not accelerating, we may conceptualize this property as some kind of "ether drag," which was of course Lorentz's notion. We may also conceptualize such drag only occurring when a body is undergoing acceleration, but we quickly realize that no relativistic effects will be felt if the ether makes its effects known only through acceleration. This is the case because for there to be relativistic effects (time dilation, length contraction) for bodies moving in uniform motion relative to each other, there must still be a way to distinguish between each body's frame of reference. If there is literally no way to distinguish between each body's frame of reference, paradoxes like the Twin Paradox result. We absolutely have to have a way to distinguish between frames of reference, even for those moving in uniform motion relative to each other, in order for there to be any relativistic effects. If we don't, we simply flip the frame of reference and voila we have the symmetrical and paradoxical relativistic effect occurring on the other frame.

    But if we acknowledge the necessity of the new ether even for non-accelerating frames, we undermine the principle of relativity because it leads us right back to absolute rest. This is the case because if even non-accelerating frames of reference are distinguishable relative to each other, there is no principle of relativity. Instead, there is absolute rest with respect to the new ether. In other words, we may figure out which frame is truly at rest with respect to the new ether by detecting absolute motion of light with respect to the ether. I won’t go into detail here, but Reginald Cahill, at Flinders in Australia, has written many papers regarding numerous experiments (with different methodologies, repeated many times) that do, in his view, find an anisotropic speed of light (see arxiv.org).

    So it appears that some version of Lorentz's ether theory may better explain observed relativistic phenomena without paradox. And if this is the case, the apparent time dilation between frames is, as Lorentz asserted, a mathematical artifact, not an actual effect on the passage of time because actual time dilation, in SR and GR, results from the postulate that the speed of light is constant for all observers, which, in turn, requires that space and time become malleable in order to allow for this postulate to hold.

    In terms of “Newton’s bucket,” the example you raise, Einstein is on the record disavowing his earlier Machian view (1913) that the bucket’s water rises due to combined gravitational influence of the universe. Rather, he changed his view in 1916 at the same time as he realized that the “new ether” was a necessary concept to explain such inertial and accelerative effects. This is the case if we are to avoid instantaneous action at a distance, which was something Einstein could not bring himself to believe in.
  5. Jan 7, 2009 #4
    You are not understanding the physics here, and that is causing what appears to be a misinterpretation of history (a kind of revisionist history if you will).

    You agree that the "new ether" is very different from the old aether, but then you go on to conclude you could measure your velocity with respect to this "new ether" in essence keeping everything from the old aether.

    Let me summarize some of your biggest mistakes, to make this as plain as possible:

    1) Yes, GR is not fully "Machian". But material is NEEDED for meaningful calculations even in principle (ie. GR cannot say what the metric is in purely empty space, and it is not meaningful to ask what it is). Einstein understood this very early on, so not only is your physics wrong, but your claims for what Einstein thought is assuredly wrong as well. Read here for more: http://en.wikipedia.org/wiki/Hole_argument , you can also just search about GR + Hole argument (this was a famous part of history and of GR development).

    2) GR has local poincare symmetry. This cannot be debated. Therefore, regardless of how "Machian" GR is or isn't, you can never measure your velocity with respect to space itself.

    Instead of debating history, it would be better to learn current physics. For instance because Einstein realized that GR was not fully Machian you are making the leap that it has none of the machian properties and have completely ignored what I said about the bucket problem. Maybe that would be a good place to start if you want to focus on an example scenario to learn more ... bring that problem in a new thread in the relativity forum. This has been moved to the philosophy forum because you are edging this discussion away from science, start a new thread focussing on the science and more people will be able to help. I won't be posting in this thread again, for I don't really want to debate philosphy.

    Good luck with your studies.
    Last edited: Jan 7, 2009
  6. Jan 7, 2009 #5
    If the 'new ether' moved would it be a problem? It would just mean the absolute reference frame you mention would not be so absolute. The chances are that frame-dragging and gravitational redshifting are fine examples of a moving 'new ether'.
  7. Jan 8, 2009 #6
    Justin, I'm afraid you've missed the point in a number of ways:

    1) Every historical point I've made is true to the original statements from Einstein himself, which are all contained (in German and English) in Einstein and the Ether, which I recommend you read.

    2) This is not "just" philosophy - this goes to the basis of relativity, which is a philosophical/scientific theory about the nature of space and time. There is no clear dividing line between physics and philosophy. I suggest you read An Introduction to the Philosophy of Physics for more on this point.

    3) GR is not Machian at all, in the sense that you suggest (inertia as a result of gravitational interaction with the entire universe). Einstein states in his 1920 speech at Leiden, on relativity and the ether:

    Mach's idea finds its full development in the ether of the general theory of relativity. According to this theory the metrical qualities of the continuum of space-time differ in the environment of different points of space-time, and are partly conditioned by the matter existing outside of the territory under consideration. This space-time variability of the reciprocal relations of the standards of space and time, or, perhaps, the recognition of the fact that ``empty space'' in its physical relation is neither homogeneous nor isotropic, compelling us to describe its state by ten functions (the gravitation potentials g), has, I think, finally disposed of the view that space is physically empty. But therewith the conception of the ether has again acquired an intelligible content, although this content differs widely from that of the ether of the mechanical undulatory theory of light. The ether of the general theory of relativity is a medium which is itself devoid of all mechanical and kinematical qualities, but helps to determine mechanical (and electromagnetic) events.

    So space does indeed have properties, according to GR, separate from matter. And it is these spatial properties that give rise to inertia and acceleration, not the universe's combined gravitational field, as you suggest in your initial statement re Newton's bucket.

    4. Your point re local Poincare symmetry simply restates the issue I was addressing: that Einstein's "new ether" contradicts the principle of relativity because it requires, even in its non-material and stripped down form, a frame of reference that is at absolute rest.

    So we are back where we began: the new ether that Einstein advocated for the last forty years of his life seems to lead to an identifiable absolute rest, which then undermines the principle of relativity.
  8. Jan 8, 2009 #7
    You are not understanding the physics, so you are horrendously misinterpretting the populous presentation of GR. That's like someone reading Brian Greene's String theory book, misunderstanding the analogies, and then arguing with a string theorist that they understand a flaw in the theory that the theorists missed.

    Do you even understand what local poincare symmetry means? You take what I wrote and claim local poincare symmetry "requires a frame of reference that is at absolute rest". That is practically the opposite of what poincare symmetry requires.

    You aren't even listenning.
    If you want to learn, more will be glad to help explain GR. But if you continue to spout crackpot misinterpretations and push this non-sense philosophy, no one will be willing to help ... for it appears to be a waste of time.
  9. Jan 8, 2009 #8


    User Avatar
    Gold Member

  10. Jan 8, 2009 #9
    Thanks Turbo, I have that book on order and am looking forward to reading it. I have read already Einstein's 1924 "On the Ether" paper with great interest and my question that began this thread was inspired by that paper, as well as Einstein's 1920 speech at Leiden.

    Can you shed any light on my basic question: how can you have a "new ether" that doesn't lead to an identifiable absolute rest?

    If this new ether, as Einstein suggested, was the basis for inertia, acceleration, and, eventually, the "total field," doesn't it require an identifiable absolute rest? Taking inertia as our example, Einstein posited the new ether as the source of the force that keeps an object in motion from deviating from that motion unless acted upon by an outside source. If an asteroid moving through space is shunted on its side slightly, it will not veer dramatically - it will veer proportionately to the force applied, in relation to its mass and kinetic energy. This is due to inertia, which Einstein posited was a function of the new ether. But this leads to the conclusion that one could identify an object that is at absolute rest, based on its behavior in response to external forces. If it's at rest in relation to the ether, it's inertia will be less, despite the choice of frame of reference.

    At this point in my thinking, I'm suggesting a Lorentzian version of relativity, which also posited an ether, but differed from Einstein's ether because it also required an identifiable absolute rest (absolute space). Lorentz was no dummy, was a Nobel Prize winner, so it is not outside the realm of reason to suggest that he may ultimately be right in his friendly dispute with Einstein. Michael Janssen has written extensively, in recent years, on Einstein and Lorentz, arguing that Einstein's interpretation was better, for a variety of reasons. But I'm not entirely convinced by Janssen's arguments because I think Einstein never fully internalized that the ether forms the basis for energy transmission more generally, as well as forming the basis for inertia, etc.

    I'm also curious as to your thoughts about Cahill's work on identifying the absolute motion of light. Obviously, his is a minority position, but he makes some very good arguments - with a lot of detail - as to four different types of measurements that have established the reality of an anisotropic speed of light through a non-material ether.
  11. Jan 8, 2009 #10


    User Avatar

    Staff: Mentor

    Thread locked pending moderation decision.
  12. Jan 9, 2009 #11

    Math Is Hard

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I'm leaving this thread closed. There have been complaints that the specific interpretations stated here are inaccurate. If these interpretations are inaccurate, then the philosophy is baseless. Until these issues are resolved, the thread should not continue.

    It is best that these discrepancies are first worked through with specific examples in the Relativity forum, as Justin has suggested.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Einstein and the ether
  1. If Einstein (Replies: 9)

  2. The Ether (Replies: 17)

  3. Einstein misquoted? (Replies: 20)

  4. Misquoting Einstein? (Replies: 14)