Michelson Morley Experiment - Concept and Virtual Lab
Channel: Physics Partner
Date: 09/08/2022

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During the 19th century, scientists had hypothesized a medium that supposedly permeated all of space. They called it aether. They felt obliged to think this, because it offered a plausible explanation of how light is able to travel (propagate) through space. After all, sound has to use air molecules to propagate, hitching a ride from molecule to molecule in a wave-like fashion. And since they thought light was a wave also, it was only natural to think it required a propagation medium too.

Scientists did not think that this aether was anything that was attached to Earth or its atmosphere. This meant  as the Earth orbits the Sun, it must cut through this aether. If this is so, why do we not feel some sort of aether wind then? Perhaps the speed of our orbiting is not fast enough. Certainly as one moves through a medium like air, the opposing force felt from the air resistance increases directly with the speed at which one is traveling. Surely, light traveling at its incredible speed must encounter some measurable level of resistance as it travels head-on into this medium called aether.

A light source sent a ray of light to the half-silvered mirror that acted as a splitter. The splitter, in turn, sent two light rays simultaneously on paths that are perpendicular to each other. When each respective beam strikes its respective mirror, each is reflected back in such a way to combine the two rays of light at the half-silvered mirror. This sends a single combined beam into the detector. The distances from the half-silvered mirror to each reflection mirror are exactly the same. The combination of all these things comprises the interferometer. One of the light beams is meeting the hypothesized aether wind vector head-on, while at the same time, the other beam is transverse to that vector field. At that point, we have a situation analogous to the swimming round-trips
Experiment 
According to Michelson’s experiment theory, the light should travel at different speeds through ether. The speed at which light moves depends on the relative motion through space. Michelson Morley designed an interferometer to spot the minute differences in the arrival time of light beams. Out of all these beams, one can take a long time to reach the sensor while travelling through ether.  

The experiment performed compared the speed of light to notice the relative motion of Earth through ether. However, the conclusion of the Michelson Morley experiment comes out to be negative. It means that they found no difference between the speed of light while travelling through ether. 
Conclusion
Michelson–Morley type experiments have been repeated many times with steadily increasing sensitivity. These include experiments from 1902 to 1905, and a series of experiments in the 1920s. More recently, in 2009, optical resonator experiments confirmed the absence of any aether wind at the 10−17 level.