Fizeau Experiment - Controversy

Controversy

Although Fresnel's hypothesis was empirically successful in explaining Fizeau's results, many leading experts in the field, including Fizeau (1851), Éleuthère Mascart (1872), Ketteler (1873), Veltmann (1873), and Lorentz (1886) were united in considering Fresnel's partial aether-dragging hypothesis to be on shaky theoretical grounds. For example, Veltmann (1870) demonstrated that Fresnel's formula implies that the aether would have to be dragged by different amounts for different colors of light, since the index of refraction depends on wavelength; Mascart (1872) demonstrated a similar result for polarized light traveling through a birefringent medium. In other words, the aether must be capable of sustaining different motions at the same time.

Fizeau's dissatisfaction with the result of his own experiment is easily discerned in the conclusion to his report:

The success of the experiment seems to me to render the adoption of Fresnel's hypothesis necessary, or at least the law which he found for the expression of the alteration of the velocity of light by the effect of motion of a body; for although that law being found true may be a very strong proof in favour of the hypothesis of which it is only a consequence, perhaps the conception of Fresnel may appear so extraordinary, and in some respects so difficult, to admit, that other proofs and a profound examination on the part of geometricians will still be necessary before adopting it as an expression of the real facts of the case.

Despite the dissatisfaction of most physicists with Fresnel's partial aether-dragging hypothesis, repetitions and improvements to his experiment (see section above) by others confirmed his results to high accuracy.

Besides the problems of the partial aether-dragging hypothesis, another major problem arose with the Michelson-Morley experiment (1887). In Fresnel's theory, the aether is almost stationary, so the experiment should have given a positive result. However, the result of this experiment was negative. Thus from the viewpoint of the aether models at that time, the experimental situation was contradictory: On one hand, the Fizeau experiment and the repetition by Michelson and Morley in 1886 appeared to prove the (almost) stationary aether with partial aether-dragging. On the other hand, the Michelson-Morley experiment of 1887 appeared to prove that the aether is at rest with respect to Earth, apparently supporting the idea of complete aether-dragging (see aether drag hypothesis). So the very success of Fresnel's hypothesis in explaining Fizeau's results helped lead to a theoretical crisis, which was not resolved until the development of the theory of special relativity.