LIGO Discover Gravitational Waves

Einstein’s Gravitational Waves have finally been heard.
100 years ago Einstein predicted that his theory of general relativity gives rise to gravitational waves, but until now these hadn’t been directly observed. On February 11th 2016, physicists at the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) announced that their detectors heard “the gravitational ‘ringing’ produced by the collision of two black holes about 400 megaparsecs (1.3 billion light-years) from Earth”.
Einstein’s prediction told that “any cosmic event that disturbs the fabric of space-time with sufficient force should produce gravitational ripples that propagate through the Universe. Earth should be awash with such waves — but by the time they reach us, the disturbances that they produce are minute.”
So what is General Relativity? It is a relativistic theory of gravity which describes gravity as the curvature of four dimensional spacetime.
Unlike the Newtonian view of space which is based on matter pulling on other matter across empty space, Einstein’s theory introduced the idea of the fabric of curved spacetime, which interacts with matter and matter with it. In other words mass and energy shape the geometry of spacetime and the geometry of spacetime shapes the motion of mass and energy.
Imagine the planets moving around on a sheet of spacetime. As the planets move, their mass curves the sheet whilst curvature in the sheet can determine the paths and distribution of planets. This is a non-Euclidean world of geometry based on curvature, where the shortest path is a curve, a “geodesic” and not a straight line. Even the path of light is subject to being warped: light passing a massive object will follow a curved path.
The Theory of General Relativity comes down to this: Einstein’s field equations describe the mathematical measure of curvature, which is the same thing as the strength of the gravitational field, and its relation to energy. They give a complete description of a gravity matter system. General Relativity describes gravity as the distortion of space and time and in turn spacetime depends on the velocity and energy (mass) of an object. Don’t forget Einstein’s famous equation E=mc2 which shows the relation of Energy (E) to mass (m).
General Relativity predicts and explains some amazing phenomena such as the existence of black holes, the perihelion advance of Mercury, gravitational lensing and wormholes. It is also the basis of the present cosmological models of our expanding universe.
But back to our gravitational waves. How were they detected? The waves are created by moving masses and propagate at the speed of light. Whilst travelling through spacetime the waves “squash and stretch spacetime in the plane perpendicular to their direction of propagation.” (http://physics.aps.org/articles/v9/17#c1) However the distortions created are minute and are therefore difficult to detect. Their effect could easily be classified as noise or sheer experimental error.
The LIGO experiment consists of two Michelson interferometers, one in Washington and one in Louisiana, with each detector consisting of two 4km long arms shaped like an “L”. A laser beam is split, with half travelling down the horizontal arm and the other half down the vertical arm. Both get reflected by mirrors. The light takes the same time to travel up and down each arm. As the beams are 180 degrees out of phase their waves will cancel each other out resulting in the absence of a signal. Gravitational waves would change the travel times for the beams. They would be propagating perpendicular to the plane of the lasers and would disturb the perfect phase difference between the two laser beams. The waves would lengthen and shorten the arms of the detector resulting in the survival of part of the signal, which reaches the detector. As there are two detectors, the result can rule out any physical disturbances localised to just one detector. The sensitivity of the detector is at the frequency of approximately 100 Hertz, audible for humans. We can actually listen to the universe.
The exciting part of this discovery is that it opens the door to a whole new field of research: gravitational wave astronomy. We will be able to hear before we can see. The sound heard by LIGO came from two black holes spinning into oneness, and further research could give us a previously unimaginable insight into black holes, their mergers and the formation of binary systems. There are rumours that LIGO has already detected another event, and it is likely that it is the sound of a black hole binary system. We might eventually obtain more knowledge on gravity itself from gravitational waves emitted from black holes.This would answer questions about what happens to gravity inside a black hole, or ultimately the origin of the universe as a singularity. Imagine gaining knowledge on the origin of spacetime itself.