The Michelson-Morley experiment, conducted in 1887 by Albert A. Michelson and Edward W. Morley, was a landmark in physics that disproved the existence of the “luminiferous ether”—a hypothetical medium once believed to carry light waves through space, similar to how air carries sound.
Background: What Was the Ether?
Before Einstein’s theory of relativity, scientists believed that light waves, like mechanical waves, needed a medium to travel through. This invisible substance was called the luminiferous ether, and it was thought to fill all of space, acting as a stationary frame of reference for light.
The Experiment:
Michelson and Morley designed an interferometer to detect differences in the speed of light based on Earth’s motion through the supposed ether.
- The idea was that if Earth moved through the ether, light moving with or against this motion would travel at different speeds.
- The interferometer split a beam of light into two paths—one aligned with Earth’s motion, one perpendicular.
- After reflecting off mirrors, the beams were recombined to create an interference pattern that would shift if the light speeds differed.
Result:
No such shift was observed. The speed of light remained constant, regardless of the direction of Earth’s motion.
Impact on Physics:
- The null result of the Michelson-Morley experiment dealt a serious blow to ether theory.
- It paved the way for Einstein’s special theory of relativity (1905), which proposed that the speed of light is constant in all inertial frames and does not require a medium to travel through.
- The experiment is now considered one of the foundations of modern physics.