Why did Albert Einstein’s theory of relativity undermine Hermann von Helmholtz’s ether-based theories?

Hermann von Helmholtz’s work contributed to the development of 19th-century ether theories, which posited that a weightless, universal medium was necessary to transmit electromagnetic waves like light. Helmholtz’s mathematical analysis of vortex motions in fluids influenced the hypothesis that the ether could serve as the fundamental substance of the cosmos, potentially accounting for all physical phenomena.12

Albert Einstein’s special theory of relativity undermined these ether-based theories by demonstrating that the ether was unnecessary. Einstein’s theory established that the speed of light is a universal constant, a conclusion supported by the null results of the Michelson-Morley experiment, which failed to detect Earth’s motion through any such medium. By removing the need for a stationary reference frame or transmission medium, Einstein’s work effectively rendered the ether hypothesis obsolete in modern physics.13