Which instrument was used to detect gravitational waves for the very first time?

LIGO

The correct answer is option 2. LIGO.

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a groundbreaking scientific experiment designed to detect gravitational waves. Gravitational waves are ripples in the fabric of spacetime caused by the acceleration of massive objects, such as merging black holes or neutron stars. These waves were predicted by Albert Einstein's theory of general relativity over a century ago but had eluded direct detection until the advent of advanced technology and experimental techniques.

LIGO consists of two identical interferometers located in Livingston, Louisiana, and Hanford, Washington, separated by thousands of kilometers.

Each interferometer consists of two perpendicular arms several kilometers in length, arranged in the shape of an "L." A laser beam is split and sent down each arm, where it reflects off mirrors at the end of each arm and returns to a central location where the beams recombine.

Gravitational waves passing through the Earth cause slight changes in the lengths of the interferometer arms, stretching one arm while compressing the other. This results in tiny differences in the arrival times of the laser beams at the recombination point.

LIGO uses a technique known as laser interferometry to detect gravitational waves. When a gravitational wave passes through the interferometer, it induces phase shifts in the laser beams due to the changes in arm lengths. These phase shifts are detected as interference patterns when the laser beams recombine.

The interferometer is extremely sensitive, capable of detecting changes in length as small as one-thousandth the diameter of a proton.

On September 14, 2015, LIGO made history by detecting gravitational waves for the first time. The waves were produced by the merger of two black holes, located about 1.3 billion light-years away from Earth.

This groundbreaking discovery provided direct evidence of the existence of gravitational waves, confirming a key prediction of Einstein's theory of general relativity and opening a new era in astrophysics and cosmology.

Since its initial detection, LIGO has made several additional detections of gravitational waves from various astrophysical events, including the merger of neutron stars and black holes.

These detections have provided valuable insights into the nature of black holes, neutron stars, and the universe's most extreme phenomena.

LIGO's success in detecting gravitational waves has revolutionized our understanding of the universe, allowing scientists to study phenomena that were previously inaccessible. It has opened a new window to explore the cosmos and has the potential to uncover even more mysteries of the universe in the future.

In summary, LIGO is a groundbreaking experiment that uses laser interferometry to detect gravitational waves, providing direct evidence of these elusive phenomena and ushering in a new era of gravitational wave astronomy. Its discoveries have deepened our understanding of the universe and offered new avenues for scientific exploration.