Friday, March 30, 2012

What Lorentz meant by the aether

Historians regard the Lorentz aether theory as inferior to special relativity mainly because it is alleged that Lorentz believed in a stationary aether and Einstein did not. For example, a scholar argues that the "fundamental assumption of Lorentz's theory" of 1895 was the stationary aether. The support for this is Einstein's 1907 paper (pdf):
... through the brilliant confirmations which the electrodynamic theory of H.A. Lorentz has experienced. That theory is founded, namely, on the assumption of a stationary immobile aether: ...
The quote is misleading. Here is what Lorentz said in his 1895 paper:
It is not my intention to ... express assumptions about the nature of the aether. ... That we cannot speak about an absolute rest of the aether, is self-evident; this expression would not even make sense. When I say for the sake of brevity, that the aether would be at rest, then this only means that one part of this medium does not move against the other one and ...
Einstein said the same thing in his 1909 paper:
This contradiction was chiefly eliminated by the pioneering work of H. A. Lorentz in 1895. Lorentz showed that if the ether were taken to be at rest and did not participate at all in the motions of matter, no other hypotheses were necessary to arrive at a theory that did justice to almost all of the phenomena.
Thus they both say that Lorentz needed no hypotheses about the aether except that it did not participate at all in the motions of matter. Some people read a lot into that "at rest" phrase, but Lorentz explicitly disavows meaning an absolute rest of the aether. He only means that he is rejecting Stokes' view.

Einstein's 1907 paper takes a little more explanation. That Einstein quote on Lorentz's assumption is from a paragraph on Galilean invariance. "That theory" refers to Maxwell's equations, which Einstein goes on to say "are not so constructed that they go over into equations of the same form upon application of the above transformation equations."

Einstein only starts discussing the Lorentz 1895 theory in the next paragraph. The paragraph after that says that the Lorentz-FitzGerald contraction was "ad hoc", and then "It appeared thus that Lorentz's theory had to be abandoned again, and replaced by a theory whose foundations agreed with the principle of relativity". He then credits that replacement theory to Lorentz 1904 and Einstein 1905.

I read this as saying that there are 3 Lorentz theories. Lorentz-1 is Maxwell's equations, aka Maxwell-Lorentz theory, with Galilean transformations for a different velocity frame. Lorentz-2 is the Lorentz 1895 relativity paper. Lorentz-3 is the Lorentz-1904 paper and Einstein 1905 paper. When Einstein says "Lorentz's theory had to be abandoned again", he means that Lorentz was abandoned once going from Maxwell-Lorentz to Lorentz-1895, and abandoned a second time going from Lorentz-1895 to Lorentz-1904.

Thus I do not agree that the "fundamental assumption of Lorentz's theory" of 1895 was the stationary aether. I do not think that Lorentz or Einstein would have made such a statement.

Lorentz said in that 1895 introduction, "so far none of the two contested theories, neither that of Fresnel, nor that of Stokes, were fully confirmed with respect to all observations ... By that I was long ago led to believe that with Fresnel's view, i.e. with the assumption of a stationary aether, we are on the right way." Lorentz was scrupulous about crediting others. He was careful to distinguish Fresnel from Stokes, and to say he preferred Fresnel. He goes on to explain the "difficulties for Fresnel's theory". So he likes Fresnel better than Stokes, but Fresnel is not the foundation for his proposed theory. The foundation is Maxwell's equations, Fizeau, and Michelson-Morley.

By comparison, Einstein's 1905 paper said only this about the aether:
The introduction of a “luminiferous ether” will prove to be superfluous inasmuch as the view here to be developed will not require an “absolutely stationary space” provided with special properties, nor assign a velocity-vector to a point of the empty space in which electromagnetic processes take place.
Einstein was saying essentially the same as what Lorentz said -- that he was avoiding assumptions about the aether, that there is no absolute rest, and that motion is relative.

As Lorentz's theory was well-known in 1905, the burden was on Einstein to explain how his theory was any different from Lorentz's, if indeed he was claiming a difference. Einstein's 1907 paper describes his 1905 paper as being essentially the same as Lorentz's 1904 paper. Einstein only claims minor differences with Lorentz. The main one was where Einstein claims a terminological advantage over Lorentz's 1895 paper:
It required only the recognition that the auxiliary quantity introduced by H.A. Lorentz, and called by him "local time", can be defined as simply "time."
This point about time was not original to Einstein. Poincare wrote in a 1900 paper that Lorentz's local time is the same as the time measured by clocks. (And Einstein acknowledged in 1906 having read Poincare's 1900 paper.)

Most of these points are also discussed in my book. Einstein's 1905 relativity paper is widely considered to be one the greatest scientific papers ever written, but it is hard to find anything original about it. The original work was done by Lorentz and Poincare, and Einstein added nothing substantial.

6 comments:

  1. John Bonaccorsi, PhiladelphiaMarch 31, 2012 at 12:59 AM

    Hold on a second, Roger. My sense is that either you're missing something or you're engaging in semantic sleight of hand. Let's take a look at the whole of Lorentz's statement. I mean the one you quote and whose last part you leave off. It is this:

    "That we cannot speak about an absolute rest of the aether, is self-evident; this expression would not even make sense. When I say for the sake of brevity, that the aether would be at rest, then this only means that one part of this medium does not move against the other one and that all perceptible motions are relative motions of the celestial bodies in relation to the aether."

    By that statement, you say, Lorentz is merely rejecting Stokes's view. I'm afraid I don't know what that means. If you will explain Stokes's view, maybe I will agree with you; but without knowledge of that, I will presume to tell you what I take Lorentz to be saying.

    It appears to me Lorentz is merely saying that he is not going to get into some sort of metaphysical question whether the cosmos -- i.e., the ether-filled cosmos -- is in some sort of absolute fixed spot. When a historian or scholar says that Lorentz's theory involved a "stationary" ether, he or she is not saying that Lorentz was maintaining such a thing. He or she is merely saying that Lorentz was maintaining exactly what he (Lorentz) appears (to me) to be saying in that quote, i.e., that every point in the ether is at rest relative to every other point therein and that "all perceptible motions are relative motions of the celestial bodies in relation to the aether."

    I'll repeat that: Lorentz is taking the ether to be a cosmos-filling substance every point of which is at rest relative to every other, a substance to which "all perceptible motions" -- his words -- are relative. Is the moon "really" moving, i.e., moving in relation to some cosmos-filling substance relative to which "all" perceptible motion of material bodies may be said to be taking place? I think Lorentz's answer to that question would be yes. That's why he's struggling to come up with formulae for "contractions." He's thinking he needs such to explain why the "position" of the ether can't be determined. He hasn't made the imaginative leap Einstein will make, i.e., the leap to recognition that all length is observed length and that contraction of a body in motion relative to its observer is merely in the nature of space and time. The contracted length is no more or less real than the greater length that the body has when it is at rest relative to the observer.

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  2. John, are you a mindreader? You keep attributing to Lorentz and Einstein opinions that they never stated. Tell me this: if they had these opinions, why didn't they say so?

    Stokes had the view that the aether moved along with the Earth, as the atmosphere moves with the Earth.

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  3. John Bonaccorsi, PhiladelphiaMarch 31, 2012 at 12:13 PM

    Your question is unreasonable, Roger. I'm not mindreading; I'm reading. If my interpretation of Lorentz's statement is incorrect, then what do you take him to be saying? What does he mean when he says the question whether the ether is at "absolute" rest is senseless? As I've said, he seems to me to be saying that he is not going to get into the question whether the ether-filled cosmos -- i.e., all of space -- is itself within some greater space, with respect to which it may be said to be at rest or not. He says that such a question -- whether all of space is within some greater space -- "would not even make sense." That's his very phrase. Because I'm taking trouble to grasp his point, you attempt to put me in the position of the lout. Lorentz certainly does not appear to be denying that the ether is "at rest" with respect to every material body in motion. Those are his very words: "all perceptible motions are relative motions of the celestial bodies in relation to the aether."


    So -- if Stokes had the view that the ether is moving along with the Earth, and if Lorentz is rejecting that view -- fine, great. In fact: so much the better for my point. Lorentz is saying the ether is a fixed framework -- i.e., that "one part of [it] does not move against the other one"; he's saying that "all perceptible motions" are motions within that framework, i.e., are movement "in relation to the ether." That's what I would mean if I were to say that Lorentz speaks of a "stationary" ether; I should think that that's what scholars mean when they say the same thing. If you ask me what I think Lorentz was getting at when he said he will not get into the question whether that framework is at "absolute" rest, I respond with what I've already said: He wants to make clear that he's not going to get into a philosophical question whether space itself is within another space, which might be, in turn, within yet another space and so on.

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  4. Lorentz did not say that the moon is really moving. Einstein did not say that the contraction is merely in the nature of space and time. Einstein did not say whether the contracted length was real.

    I go by what they say. Lorentz explicitly said that he was not expressing assumptions about the nature of the aether. Then you insist on pretending that he was making such assumptions.

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  5. John Bonaccorsi, PhiladelphiaMarch 31, 2012 at 2:12 PM

    You and I are "just going back and forth" again, Roger. Well, I will say it again: I am very pleased I've come to know of your blog. From visiting it and from exploring some of the questions you have raised in my mind, I have profited. Good luck to you.

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    1. I am a physicist who has studied this issue for years.
      Here is what Physics Forum says on this issue:
      “Debates about the superiority or "truth" of modern Lorentz Ether Theory (LET) and the Block Universe (BU) concept are outside the scope of PF because: There is little or no debate among professional physicists about these issues. Positions on these issues are based on personal philosophical preferences and cannot be addressed (even in principle) by experiment. The core of a scientific theory is a mathematical model which can be used to predict the outcome of experiments… Often a single theory is compatible with many different philosophical interpretations. There is no possible way to resolve a dispute between different philosophical interpretations through appeal to experiment because all of them make the same predictions for all experiments. The choice between philosophical interpretations is therefore entirely a matter of personal philosophical preference… Both BU and LET use the Lorentz transform, etc., to make all of their experimental predictions, and therefore they are scientifically indistinguishable, making the same experimental predictions in all cases. Because of this experimental equivalence, there is little if any serious ongoing debate between the two in professional physics circles …”

      Reference https://www.physicsforums.com/threads/what-is-the-pfs-policy-on-lorentz-ether-theory-and-block-universe.772224/
      I see no mathematical difference between LET or BU. Both are internally consistent with no ad hoc interpretations. It is true that Lorentz did have ad hoc terms in his equations in his first two forms of his theory but by 1904 these were eliminated and matched Einstein’s 1905 paper mathematically. I can get all the results of time dilation, space contraction, velocity addition, Relativistic Doppler Shift, light aberration, simultaneity, etc. from LET (or BU).
      I have extensively worked on the math for Special Relativity, LET, and GR. I can mathematically show you that SR and LET are mathematically equivalent. I would personally say LET is simpler philosophically but SR is simpler in basic principles. Both are scientifically valid. It has been over 100 years and no one has shown either (in their current form) to be invalid.
      LET opens up another method to understand the math. Its framework may also allow and explain differences (SR/GR can’t) at extreme velocities (something like 99.9 with about 30 more 9s the speed of light) or extreme gravity etc.

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