Prof Stephen Hawking celebrates gravitational wave discovery
11 February 2016 Last updated at 15:31 GMT
Scientists are claiming a stunning discovery in their quest to fully understand gravity.
They have observed the warping of space-time generated by the collision of two black holes more than a billion light-years from Earth.
The international team says the first detection of these gravitational waves will usher in a new era for astronomy.
One of the UK's foremost experts on black holes, Prof Stephen Hawking, told the BBC's Pallab Ghosh that the discovery was groundbreaking.