An interferometer is a scientific instrument that uses the principle of interference of light waves to measure small distances, changes in refractive index, or other physical properties. By splitting a beam of light into two paths and then recombining them, it can detect minute differences in the path lengths, which can indicate variations in the environment or the presence of objects. Interferometers are widely used in various fields, including astronomy, metrology, and fiber optics. One well-known type is the Michelson interferometer, which played a crucial role in the development of the theory of relativity by demonstrating the constancy of the speed of light.