Gravity device probes universe

Scottish scientists have begun work on one of the most sensitive scientific instruments ever built - so delicate it could measure a fly stretching its legs on a planet in another solar system.

With German colleagues they are building the giant structure at a fruit farm near Hanover and in 1999 it will begin delving into the mysteries of the universe. The structure will measure "gravitational waves", which were predicted by Einstein but whose existence could until now only be suspected as nothing could measure them.

The waves are faint ripples of gravity, reaching earth millions of years after events like exploding stars or the appearance of black holes. The structure that will measure the ripples is formed from two stainless steel tubular arms, each 600 metres long and set at right angles to each other.

Each contains an almost-perfect vacuum, in which the world's most perfect mirrors will bounce laser light up and down the length of the tubes.

Professor James Hough, of Glasgow University's department of physics and astronomy, said the arrival of a gravitational wave should alter the length of each tube by a fraction of the diameter of the nucleus of a single atom. This will be measured with the latest laser and optics technology, using techniques pioneered in Glasgow, where a prototype was built.

The University of Wales in Cardiff will be involved in analysing the data. The British team will also be working with German colleagues from the University of Hanover, the Albert Einstein Institute in Potsdam and the Max Planck Institute at Garching.

Britain's contribution to the pounds 7m project includes a pounds 1m grant from the government-funded Particle Physics and Astronomy Research Council.

Four more structures are to be built, including an American one which will have arms 4km long, but the Hanover device - so sensitive that it should be able to detect waves from 45 million light years away- will be the first in operation.