Michelson interferometer
The Michelson interferometer was invented by the American physicist Michelson.
Although it has a simple structure, it can measure very small distance differences, such as the size of an atomic nucleus.
The Michelson interferometer consists of the following parts.
- Light-emitting device use a single wavelength light source, such as a laser.
- A splitter placed in the center reflects some laser light and passes the rest.
- Two vertically placed mirrors reflect light and send it back to the splitter.
When the two lights are mixed with the same phase, a bright pattern appears on the screen. Conversely, a dark pattern appears if the phases are not the same.
Even a tiny change in the distance of the mirror results in a significant change in phase, so we can measure the distance difference even if it is very slight.
Using this device, it turns out that the direction of Earth’s travel and the speed of light are independent. In other words, we discovered that the medium (ether) that transmits light does not exist.
Afterward, based on this fact, Einstein developed the theory of relativity.
Recently, we have measured gravitational waves from binary black holes. (LIGO project)