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Why do modern scientists reject Fresnel’s idea of an all-pervading ether?

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The Greek philosopher Plato — Realism Plato, marble portrait bust copied from an original of the 4th century bce; in the Capitoline Museums, Rome.

Modern scientists reject Augustin-Jean Fresnel’s idea of an all-pervading ether because it was an unnecessary construct that failed to be detected experimentally.12

While Fresnel’s wave theory was highly successful in predicting phenomena like diffraction and interference, it relied on the assumption that light required a physical medium to propagate, much like sound waves require air. To account for light's properties, this ether was theorized to have contradictory characteristics—such as being highly rigid yet offering no resistance to planetary motion.1342

The hypothesis was significantly undermined by the Michelson-Morley experiment in 1887, which failed to detect the expected "ether drift" caused by Earth’s motion through space. Ultimately, the development of Albert Einstein’s special theory of relativity rendered the ether obsolete by establishing that the speed of light is a universal constant independent of any medium. Contemporary science retains Fresnel’s successful mathematical treatment of wave propagation while discarding the ether as a false, unnecessary component of the theory.13254