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Gravitational Waves have been detected, after a long search, a century after they were first said to exist by Einstein.
Like the ripples seen when a stone is dropped into a pond, Gravitational Waves are ripples in the fabric of spacetime, moving through the Universe at the speed of light away from catastrophic events in the cosmos.
Predicted to exist by Einstein in his theory of General Relativity, published a century ago in 1906, they are the result of massive objects causing distortions in spacetime. This effect is felt by us as gravity. But until now their existence had only been inferred not directly detected.
The waves are incredibly weak so most have no measureable effect. The only sources which were believed to possibly emit strong enough signals that could maybe be detected are those with incredibly strong and varying gravity, for example black holes.
Today their discovery has been formally reported by scientists working at LIGO (Laser Interferometer Gravitational Wave Observatory) in USA. The signals originating from the combining of two black holes almost a billion light years ago have reached Earth and were detected by LIGO.
The Ligo experiment is rather simple, and has an L-shaped design. A laser beam at the centre is split into two and the parts sent in perpendicular directions (at 90°) along identical tunnels, in which they bounce back and forth. Graviational waves travelling through the equipment may cause disturbances by stretching or squeezing space, meaning that the light in one of the beams will travel a distance a tiny bit different to that of the other. This change of size will be only about the width of an atom, but due to the length of the paths (about 4km) and the incredible sensistivity of the LIGO setup this can be detected.
The two parts of LIGO are sufficiently separated to allow noise such as traffic or Earth tremours to be disregarded and ensure any signal is only from the faint gravitational waves. The first run of LIGO from 2002-2010 was unable to detect anything, but since being upgraded in 2015 to Advanced LIGO the significantly increased sensitivity of the detectors has enabled the detection of gravitational waves now reported.
To appreciate what LIGO is able to achieve, if it could measure the distance between the sun and the nearest star Alpha Centauri about 3 light years away, LIGO is capable of measuring this distance to the accuracy of the width of a single human hair. It is this incredible sensitivity which is required to detect gravitational waves.
Detection of gravitational waves promises great advancements in astronomy, providing a new way to observe the Universe. Becuase these waves travel through matter, there are no shadows which can hide their source. Gravitational wave astronomy will be able to provide a better view of mysterious objects such as black holes, things previously invisible by use of optical telescope, and further understanding of the early Universe just moments after the Big Bang. Gravity can be better undersoood, and lead to the long desired Theory of Everything.
The findings are reported here in Phys. Rev. Lett.
Image credits:
Ripple Effect - sea turtle, Flickr
Aerial photo of LIGO - NASA
