Hugh Pickens writes: "Einstein's theory of general relativity predicts that when large objects such as black holes collide, ripples in space and time flow outwards called gravitational waves. Now the Telegraph reports that the Laser Interferometer Space Antenna (LISA) consisting of a fleet of three spacecraft flying in formation three million miles apart, will be able to detect gravitational waves of very low frequencies due to the huge distance between the three spacecraft in the largest scientific instrument ever built. "Gravitational waves are the last piece of Einstein's theory of general relativity that has still to be proved correct," says Professor Jim Hough, an expert on gravitational waves at Glasgow University and a member of the committee that drew up the plans. "Unfortunately we haven't been able to detect them yet because they are very weak. However, the new experiments we are working on have great potential to allow detection." A small test mission will be launched next year to demonstrate the technology to be used to detect the waves paving the way for the more ambitious mission to be launched after 2020. Each spacecraft will house floating cubes of gold platinum and laser beams fired between the spacecraft will measure minute changes in the distance between each of the cubes caused by the weak waves of gravity that ripple out from catastrophic events in deep space. "Black holes are so dense that no light or radiation escapes from inside them. Gravitational waves from the warped spacetime around black holes could give us new ways of looking at them," says Professor Sheila Rowan. "We could also learn about the state of matter inside collapsed stars.""