“Ladies and Gentlemen, we have detected gravitational waves” David Reitze, executive director of LIGO announced to the world at a press conference this afternoon.
It is a momentous occasion as all of the predictions of Einstein’s general theory of relativity have now been finally verified. The last prediction of his 1915 theory of general relativity, that of gravitational waves, was the most difficult to confirm. Einstein’s theory of general relativity says that gravity is caused by the distortion of space and time around objects with mass (illustrated above). Gravitational waves are like a ripple in the space-time caused by a massive cosmic event such as the formation of a neutron star, a supernova explosion, or as LIGO has detected, the collision of two black holes. Unfortunately the events that cause these ripples are rare, far away and difficult to observe because by the time the ‘ripple’ reaches Earth it is very small. In fact, LIGO’s experiment is the first time that the collision of two black holes has been observed. The other predictions of general relativity – gravitational lensing, time dilation, and frame dragging – have been physically tested and verified several times over the last century with the first proof given in 1919 by Sir Arthur Stanley Eddington. Although every other prediction that came from Einstein’s general theory of relativity has been proven true, without the detection and proof of gravitational waves the theory as a whole still stood in uncertain territory.
As I complained in a previous HeadStuff article rumours have been rife recently from scientists not involved with the LIGO project that the detection had been made. But the official line from LIGO was silence until today. At the press conference in Washington DC the director of LIGO David Reitze announced that his team has found proof of gravitational waves by detecting the ‘ringing’ of two black holes spiralling into one another. One of the black holes was 36 times the mass of our Sun. The discovery was first observed by physicist Marco Drago at the Max Planck Institute for Gravitational Physics in Hannover, Germany, in September before the advanced upgraded LIGO system had even been turned on. As a worldwide project LIGO has several detectors and the ‘ringing’ of the gravitational wave on their interferometers was picked up by LIGO at Livingston Louisiana and in Hanford in Washington State at the same time. LIGO managers had routinely injected false signals into the system to ensure quality control but this signal was no fake. A series of further checks were run since September to confirm that this really was a gravitational wave
Scientists are very excited about the possibilities this confirmation of Einstein’s theory opens up. A lot of theories will now gain greater ground and the discovery opens up new avenues of research into black holes, gravity, and the very early universe. After 100 years of uncertainty, proof of the last remaining prediction of Einstein’s general theory of relativity is a feat certainly worthy of a Nobel Prize next November and the announcement is a special occasion in the history of physics.
Here’s a video NASA put together on what two black holes colliding and creating gravitational waves looks like!
Image: Spacetime curvature by World Science Festival Youtube