A gravity wave (or gravitational wave) is a ripple in the curvature of the space-time continuum (the enmeshed combination of our three perceived physical dimensions, plus time) created by the movement of matter.
Long thought to exist before they were detected, gravity waves were first hypothesized in Albert Einstein's general theory of relativity, which predicted that an accelerating mass would radiate gravitational waves as it lost energy. For example, it would be expected that two pulsars (celestial bodies that emit radiation in regular pulses) in orbit around each other should emanate gravity waves as their orbits decay. In accordance with the first law of thermodynamics, which states that neither matter nor energy can be created or destroyed although either may be transformed, the energy loss associated with the orbit's decay is radiated as gravitational waves. According to theory, gravity waves propagate at approximately the speed of light and pass through matter unchanged, alternately stretching and shrinking distances on an infinitesimal scale. Their strength decreases as a function of distance from their source. The study of gravitational waves could yield an incredible amount of information about the universe and lead to many practical applications. For example, their ability to pass through matter unaltered could enable the transmission of a signal over vast distances in space.
Around the world, several countries have constructed gravity wave detectors, highly sensitive instruments designed to detect gravity waves and identify their sources. In the United States, the detector project is called LIGO (for Laser Interferometer Gravitational-Wave Observatory). LIGO researchers have been working to establish the existence of gravitational waves and prove whether or not they actually propagate at the speed of light and cause the displacement of matter that they pass through.
The LIGO system consists of suspended weights with mirrored surfaces that can move freely horizontally. If a gravitational wave passes through, the distance between the weights (which is measured by a laser beam moving back and forth between the mirrors and then recombined at a photodetector) is altered. The LIGO project uses the resources of volunteered personal computers collaborating through distributed computing. PC users can download the software from LIGO; the project is called Einstein@home.
On February 11, 2016, David Reitze, executive director of LIGO reported that researchers had detected gravitational waves. Reitze said the waves were created by the merging of two black holes, one of which had the mass of 29 suns and the other 36.
Researchers from the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT) have developed a LIGO prototype sensitive enough to detect a tiny movement (many times smaller than the diameter of a single hair) in a test weight 40 meters away. Other gravitational wave detection projects include a collaborative effort by France and Italy called VIRGO, another by Germany and Great Britain called GEO 600, a project in Japan called TAMA 300, one in Australia called ACIGA, and NASA's LISA project.
The Verge explains how gravity waves work and how they were detected: