The Michelson-Morley experiment does not prove that space is a vacuum; rather, it demonstrates that the speed of light is constant regardless of Earth's motion. The experiment aimed to detect the presence of the luminiferous ether, a medium through which light was thought to propagate. Results showed that light's speed remained unchanged in all directions, contradicting the ether theory. This consistency indicates that light does not require a medium for propagation. Ultimately, the experiment supports the idea that space does not contain a medium affecting light's speed.