Hammar experiment

The Hammar experiment was an experiment designed and conducted by Gustaf Wilhelm Hammar (1935) to test the aether drag hypothesis. Its negative result refuted some specific aether drag models, and confirmed special relativity. Experiments such as the Michelson–Morley experiment of 1887 (and later other experiments such as the Trouton–Noble experiment in 1903 or the Trouton–Rankine experiment in 1908), presented evidence against the theory of a medium for light propagation known as the luminiferous aether; a theory that had been an established part of science for nearly one hundred years at the time. These results cast doubts on what was then a very central assumption of modern science, and later led to the development of special relativity. In an attempt to explain the results of the Michelson–Morley experiment in the context of the assumed medium, aether, many new hypotheses were examined. One of the proposals was that instead of passing through a static and unmoving aether, massive objects like the Earth may drag some of the aether along with them, making it impossible to detect a "wind". Oliver Lodge (1893–1897) was one of the first to perform a test of this theory by using rotating and massive lead blocks in an experiment that attempted to cause an asymmetrical aether wind. His tests yielded no appreciable results differing from previous tests for the aether wind. In the 1920s, Dayton Miller conducted repetitions of the Michelson–Morley experiments. He ultimately constructed an apparatus in such a way as to minimize the mass along the path of the experiment, conducting it at the peak of a tall hill in a building that was made of lightweight materials. He produced measurements showing a diurnal variance, suggesting detection of the "wind", which he ascribed to the lack of mass making while previous experiments were carried out with considerable mass around their apparatus. To test Miller's assertion, Hammar conducted the following experiment using a common-path interferometer in 1935.

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Expérience de Fizeau

On désigne sous le nom d'expérience de Fizeau l'une des trois expériences mémorables destinées à mesurer la vitesse de la lumière. Sans autre précision, elle désigne la première, effectuée en 1849 par le physicien français Hippolyte Fizeau, et qui donne la première mesure terrestre de la vitesse de la lumière. Il utilise pour cela son appareil, appelé l'appareil de Fizeau et la méthode dite de la roue dentée.

Effet Sagnac

On appelle effet Sagnac le décalage temporel de la réception de deux signaux lumineux tournant en sens inverse autour de la circonférence d'un disque en rotation (par rapport à un référentiel inertiel), quand ils sont émis par un émetteur-récepteur fixé sur ce disque. L'effet Sagnac a été découvert par Georges Sagnac en 1913. En physique classique, il est interprétable comme une asymétrie de la vitesse des signaux lumineux par rapport à la circonférence du disque en rotation.

Aether drag hypothesis

In the 19th century, the theory of the luminiferous aether as the hypothetical medium for the propagation of light waves was widely discussed. The aether hypothesis arose because physicists of that era could not conceive of light waves propagating without a physical medium in which to do so. When experiments failed to detect the hypothesized luminiferous aether, physicists conceived explanations, which preserved the hypothetical aether's existence, for the experiments' failure to detect it.

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