Introduction

In the mid-19th century, French physicist Léon FoucaultFoucault, Léon demonstrated experimentally that, contrary to Isaac Newton’s assertionNewton, Isaac, light is not a flow of corpuscles but a wave. This remarkable result was not without its paradoxical problems. Indeed, while it was already known that a wave (e.g. sound) does not propagate in a vacuum, it had to be admitted that light (e.g. from the Sun) does propagate in supposedly empty interstellar spaceInterstellar space. In ancient Greece, AristotleAristotle, observing the movement of animals, whether walking on the ground, flying through the air or swimming in water, deduced a general principle according to which a body needs a material support to move. To the four original elements: earth, air, water and fire, he added a fifth, which he called etherEther. This hypothetical fluid was supposed to fill the void and thus justify the movement of the planets in the cosmos. Taking up this idea, 19th-century physicists imagined a substance that would serve as a medium for the propagation of light. They called it luminiferous etherLuminiferous ether. Between 1881 and 1887, American physicists Albert MichelsonMichelson, Albert and Edouard Morley carried out a series of experiments to demonstrate the “ether wind”Ether wind produced by the Earth’s revolution around the Sun.