Alok Jha, science correspondent
Saturday November 5, 2005
Scientists believe they are on the verge of measuring gravitational waves, one of the most elusive phenomena in the universe, for the first time.
Albert Einstein predicted the existence of these waves as part of his general theory of relativity. He argued that when a mass accelerates, it causes the fabric of spacetime around it to stretch and squeeze. The waves have remained elusive to scientists for a simple reason: gravity is such a weak force that it produces extremely tiny waves, and no instrument has usually been sensitive enough to detect them.
But that limitation may soon be over. Yesterday, scientists at Hanford in the US kicked off an experiment with a $350m (£200m) machine called Ligo which they are confident will bring the first evidence for the existence of Einstein's elusive waves. Next month, Ligo will be joined by the Geo 600 detector in Hanover, which cost €7m (£4.7m) and is being run by scientists from Glasgow, Cardiff, Birmingham and Hanover universities.
The first attempt to detect the waves was made in the 1960s by University of Maryland physicist Joseph Weber. His experiment involved suspending a 1 ton aluminium bar in a vacuum and waiting to see if any passing gravity waves caused it to expand and contract. Unfortunately, he got too many false alarms and his detections were discredited. Modern detectors use lasers to measure the change in distance caused by gravity waves between two test masses. The Ligo and Geo 600 systems are so sensitive they can detect changes in distance which are less than 1/3000th of the width of a proton - or less than a thousand billion billionths of a metre. Scientists know any true observation of gravity waves will need simultaneous recordings in all the detectors.
But they have never been more confident. "Experiments are just getting to the stage where first results are possible," said Jim Hough of Glasgow University. It is a confidence that surprised Ladbrokes. In August last year, New Scientist asked the bookie for odds on the chance of scientists discovering gravity waves by 2010. Ladbrokes offered 500 to one, prompting scientists to pile in with bets.
By the time Prof Hough joined the rush, the odds had dropped to 100 to one. Later that afternoon, they were cut to six to one, and by the end of the next day, Ladbrokes had stopped taking bets.
Detection of gravity waves has profound implications for cosmology. They will give cosmologists a new understanding of the universe immediately after the big bang.
In its first few hundred thousand years, the universe was so dense and hot that electromagnetic radiation such as light did not penetrate very far. As a result, there is nothing from that time which reaches the Earth and no way to understand it directly. But gravity waves passed through the universe unhindered and can provide a new window on the early universe.