Gravitational waves cannot be directly seen or detected in the same way as light or electromagnetic waves. This is because gravitational waves are a different type of wave that arises from disturbances in the fabric of spacetime itself, caused by accelerating masses. They do not interact directly with light or other forms of electromagnetic radiation.
To indirectly observe gravitational waves, scientists use highly sensitive instruments called interferometers. The most famous example is the Laser Interferometer Gravitational-Wave Observatory (LIGO). These interferometers consist of two perpendicular arms with lasers bouncing between mirrors at the ends of each arm. When a gravitational wave passes through, it causes tiny fluctuations in the distances traveled by the lasers, resulting in an interference pattern that can be detected.
By measuring these interference patterns, scientists can infer the presence of gravitational waves. The detectors are extremely sensitive, capable of measuring changes in distance as small as one-thousandth the size of a proton. Multiple interferometers, such as LIGO and Virgo, are used to cross-validate the signals and pinpoint the source of the gravitational waves.
Since the first direct detection of gravitational waves in 2015, several gravitational wave events have been observed, including mergers of black holes and neutron stars. These observations have opened up a new way of studying the universe and have provided valuable insights into phenomena such as the nature of black holes, the behavior of matter under extreme conditions, and the origins of the universe itself.