Einstein’s final prediction confirmed

Scientists have announced the detection of gravitational waves, a century after they were predicted by Albert Einstein.

Forming part of his general theory of relativity, in which Einstein theorised the space-time continuum, gravitational waves are ripples that stretch the fabric of space-time. The waves were detected on 14th September 2015.

Caused by the movement of mass, these waves are so weak they require highly sensitive equipment to detect them. The Laser Interferometer Gravitational-Wave Observatory (LIGO) was built for this purpose. Consisting of two interferometers in Washington and Louisana working in tandem, it was upgraded last year and soon afterwards, rumours suggested the scientists had detected gravitational waves.

Sir Martin Rees, writing for the Telegraph said this detection is one of the great discoveries of the decade, “up there with the detection of the Higgs particle”.

The waves were caused by the discovery of two black holes, 30 times the mass of the Sun merging 1.3bn light years ago. Black holes were previously thought to be smaller than this, so this is another discovery.

Indirect evidence of gravitational waves has been noted since 1974 from observing pulsar behaviour, but this expected announcement later today would be the first time they have been directly observed.

LIGO works by firing two laser beams in separate directions at right angles four kilometres through a vacuum. Any changes in the length of the beam that is reflected back to the detectors is monitored and noted.

A gravitational wave would stretch space in one dimension and shrink it in another at right angles. This would cause the mirrors in the interferometer to shift by very small amounts, resulting in the distance between mirrors slightly changing.

To ensure any observations are not anomalies or erroneous readings, the interferometers are 3,000 kilometres apart.

Dr Danny Steeghs, from the University of Warwick, said: “This is a fantastic technical achievement by the LIGO team, a highly deserved reward after many years of effort and technology development. A century after Einstein's theory of General Relativity was presented, we now have a convincing, direct detection of a gravitational wave signal produced by a pair of black holes.”

 What are gravitational waves?

Gravitational waves are ripples in space time caused by the movement of mass. They propagate from the source spreading outwards like ripples in a pond.

It is believed this detection will allow scientists to detect what happened at the Big Bang as electromagnetic waves can only travel back 400,000 years after the Big Bang occurred. Gravitational waves can take us right back to the actual event.

The detection of gravitational waves has created a new field of astronomy - gravitational wave astronomy.