The aether theory

The aether theory was an early scientific idea proposing that space is filled with an invisible, weightless substance called "aether," which permeates all of space. Scientists believed this medium was necessary for the propagation of light waves, much like sound waves require air or water. According to this theory, light traveled through the aether, and Earth’s motion relative to it could affect measurements of light's speed. However, experiments, such as the famous Michelson-Morley experiment, failed to detect the aether, leading to its abandonment in favor of Einstein’s theory of special relativity, which explains light's behavior without needing an aether.