The first paper I found drawing a sharp difference is On Ehrenfest's paradox, by V. Varićak, 1911:
The occurrence of Ehrenfest's paradox is understandable, when one clings to the standpoint taken by Lorentz in the formulation of his contraction hypothesis, i.e., when one sees the contraction of moving rigid bodies in the direction of motion as a change which takes place in an objective way. Every element of the periphery will be changed independently of the observer according to Lorentz, while the elements of the radius remain non-contracted.He refers to this 1909 paper, which mostly treats Lorentz and Einstein as having the same theory but adds:
However, if one employs Einstein's standpoint, according to whom the mentioned contraction is only an apparent, subjective phenomenon, caused by the manner of our clock-regulation and length-measurement, then this contradiction doesn't appear to be justified.
That Ehrenfest took the Lorentzian standpoint in his argumentation is concluded by me from ...
I allude e.g. to the work of Lewis and Tolman, who especially emphasized the radical difference in the views of Lorentz and Einstein. There one can also see, by which considerations the stationary observer is forced to assume the contraction of the moving rod. But he remains conscious, that this contraction is so to speak only a psychological, not a physical fact, i.e., that the body experienced no change in reality.
When Lorentz first advanced the idea that an electron, or in fact any moving body, is shortened in the line of its motion, he pictured a real distortion of the body in consequence of a real motion through a stationary ether, and his theory has aroused considerable discussion as to the nature of the forces which would be necessary to produce such a deformation. The point of view first advanced by Einstein, which we have here adopted, is radically different. Absolute motion has no significance. Imagine an electron and a number of observers moving in different directions with respect to it. To each observer, naïvely considering himself to be at rest, the electron will appear shortened in a different direction and by a different amount; but the physical condition of the electron obviously does not depend upon the state of mind of the observers.While this might seem like a deep insight on how Einstein had a superior understanding, Einstein denied that there was any such difference:
Although these changes in the units of space and time appear in a certain sense psychological, we adopt them rather than abandon completely the fundamental conceptions of space, time, and velocity, upon which the science of physics now rests. At present there appears no other alternative.
The author unjustifiably stated a difference of Lorentz's view and that of mine concerning the physical facts. The question as to whether length contraction really exists or not is misleading. It doesn't "really" exist, in so far as it doesn't exist for a comoving observer; though it "really" exists, i.e. in such a way that it could be demonstrated in principle by physical means by a non-comoving observer.Lewis, Tolman, and Varicak are making a legitimate point about how the FitzGerald length contraction can be interpreted, and how such an interpretation could be different from Lorentz's. But their interpretation cannot be attributed to Einstein, as you can see from his denial. Einstein's interpretation was the same as Lorentz's, and Einstein's papers never drew the distinction described in the above papers.
Calling the length contraction "psychological" is not the best term, but what these papers are saying is that the contraction is a property of the coordinates being used on spacetime, and not of the physical object. That view was presented by Poincare in 1905 and Minkowski in 1908, but Einstein still did not seem to understand or accept it in 1911.
Post a Comment