Monday, December 26, 2011

Poincare supposedly did not understand his theory

I criticized a new paper by Emily Adlam. Her conclusions are strange:
In summary, Poincaré’s use of the Lorentz transformations differed from Einstein’s in two key ways. First, for Poincaré, the transformations are not used to give relations between any two inertial frames of reference - they are defined only relative to the ether rest frame, so that the velocity v appearing in the formula must always refer to a velocity with respect to the ether rest frame, i.e. an absolute velocity.
Poincare stress that the Lorentz transformations form a group. The first fact about groups is that any group element is just like any other. He never mentions the aether because the group makes any particular reference frame irrelevant. So Adlam is wrong -- Poincare knew that Lorentz transformations connect any two frames.
Moreover, even if we restrict ourselves to transformations involving the ether rest frame, Poincaré’s usage does not coincide with Einstein’s, since for Einstein the transformations express a relationship between coordinate systems, whereas for Poincaré they are merely a means of predicting the physical changes that a system undergoes when set in motion relative to the ether.
So I guess that she is trying to say that Einstein's transformations act only mathematically on the coordinates, while Poincare's act physically. But then she says:
Thus Poincaré not only failed to give a physical interpretation to the Lorentz transformations, he also failed to appreciate the full range of situations in which they can be applied.
This is weird. She says that Poincare's transformations were physical, and then says that he had no physical interpretation.
1.3 Assessment
In light of Poincaré’s limited understanding of the relativity principle and the Lorentz transformations, it seems inaccurate to say that he had any significant intimations of special relativity before Einstein’s 1905 papers.
Except for Einstein's rivals, I don't know of any other scientists who get insulted in this way. Usually historians just give them credit for what they did, and do not concoct explanations for how they did not understand what they were doing.

She goes on to concede that, while Poincare did not understand what he was doing, his discoveries were essential to all further developments in relativity:
This is not to deny that he made extremely important contributions to the development of the theory, but his achievements in this area were largely mathematical: formulating the notion of the Lorentz group and finding its invariants, formulating the notion of a four-vector and finding quantities that transform like four-vectors, interpreting the Lorentz transformations as rotations in four-dimensional space. These are results that follow from the mathematical structure of the equations, not from any physical understand-ing of their significance; they paved the way for the powerful mathematical formalism developed by later workers in the field, but did not provide the essential physical insight that provides the formalism with its application.
She is describing the core of special relativity. Poincare published this, and neither Einstein nor anyone else, except for Minkowski and others who got it from Poincare. She is saying that the modern mathematical formulation of relativity was discovered by someone who did not have any physical understanding of the significance of the formulas. This is like saying that Shakespeare wrote great plays, but he did understand the content of what he wrote. Adlam concludes:
Special relativity is first and foremost a physical theory, and in the absence of an understanding of the physical significance of the Lorentz transformations, Poincaré cannot be said to have formulated a theory approximating special relativity.
Wow. So Adlam not only gives Poincare less credit than Einstein, she denies that Poincare had any physical understanding or relativity theory.

Poincare's 1905 relativity theory was superior to Einstein's. The only way to explain it away is to argue that Poincare somehow did not understand what he was saying. Adlam does this by alternately arguing that Poincare's papers were too mathematical or too physical. Her argument does not even make any sense.

Even if she were right that Poincare's explanation had some philosophical defect, the reasonable thing is to just describe the defect and give him credit for the rest. But that won't leave much credit for Einstein, and no one has been able to find any defect in Poincare's work. So Adlam has to somehow claim that Poincare did not understand what he was doing with a very contrived argument.

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