Nasa set to test theory of relativity; Satellite is 'most

Almost 90 years after Albert Einstein published his theory of relatively, Nasa scientists are ready to launch a satellite that will put it to the test.

If all goes to plan tomorrow, the state-of-the-art satellite, Gravity Probe-B - which has taken more than 40 years to develop - will lift off from California's Vandenberg Air Force Base on a 16- month mission.

Described by the programme manager, Gaylord Green, as "the most sophisticated thing the human race has ever tried to put into space", the test is as much one of accuracy as it is of relativity.

The satellite is equipped with four gyroscopes which will allow scientists to detect tiny changes in an angle to an accuracy of 0.0001 degrees - equal to the width of a human hair as seen from 10 miles away.

In 1916, Einstein rocked the world of physics with his theory that space and time are distorted by the presence of massive objects. According to the theory, gravity does not only distort space but can also make time run slower, so that each second on a clock may not always last exactly one second.

If Einstein's theory is correct, relativistic forces will gradually change the direction of the gyroscopes' spin, which would otherwise be constant.

The Gravity Probe-B was developed by Nasa's Marshall Space Flight Centre, Stanford University and Lockheed Martin. The unmanned spacecraft will test both the geodetic effect (how space and time are warped by the presence of the Earth), and frame dragging (how the Earth's rotation drags space and time around with it).

A good simile is to think of a tautly stretched sheet, representing space-time, and a large, heavy ball representing a star or planet. Placing the ball in the centre of the sheet would cause it to warp and nearby objects would move towards it. If the ball was rotating at the same time, this motion would twist the sheet - a phenomenon know as frame dragging.

Since Einstein's theory first emerged, scientists have wanted to test it using the Earth itself, but until now there has been no technology capable of dealing with such accurate information.

Dr Anne Kinney, director of Nasa's astronomy and physics division, said: "Gravity Probe-B has the potential to uncover fundamental properties of the invisible universe, a universe which seems very bizarre and alien to our everyday perceptions, yet one that Einstein tried to show us almost a century ago."

Studies have already been conducted on the warp theory, but the twisting effect of frame dragging has never been directly detected. Nasa hope to measure both during their mission.

The Gravity Probe-B has taken longer to finish than any other Nasa project and it is armed with some of the most precise instruments ever built. Since being introduced, the project has been delayed and cancelled on several occasions due to technical problems.

Norman Gray, researcher at Glasgow University's physics and astronomy department, said: "This is a massive experiment that is due to take place.

"The Gravity Probe-B will prove, in fact rather than theory, if Einstein was indeed correct.

"However, it would be very exciting if it proved this isn't the case. This is one of the main theories that sits at the heart of physics.

"Proving the theory wrong would knock so many other theories out as well."

The gyroscopes on board the satellite are approximately the size of ping-pong balls and are the most perfectly round objects ever created, according to Nasa. Once the gyroscopes are set rotating they will be aligned to a star tracked by the satellite's onboard telescope. To ensure accuracy, liquid helium will be used to chill the gyroscopes to -271.4(degrees)C, slightly above absolute zero - and they will be stored in the largest vacuum flask ever taken into space.

This will be by far the most accurate test of any of the predicted effects of Einstein's theory. Robert Reasenberg, associate director of the Harvard-Smithsonian Centre for Astrophysics, is helping calculate key astronomical measurements for the project. "Everyone involved in the project is expecting to see some sort of movement during the experiment," he said.

"It's not possible to prove Einstein's theory of relativity but it is possible to disprove it. If this was the case I think the results would be absol-utely astounding, it would turn the world of physics upside down."

Some scientists have been critical of the project's $700 million budget but Reasenberg disagrees. "I'm aware that there are scientists who have criticised the amount of money being spent on this project but I think that's unfair," he said.

"It was known at the time it was funded in March 1964 that technologies had to be developed and this would take time.

"It is a very important and worthwhile project."

Copyright 2004 SMG Sunday Newspapers Ltd.
Provided by ProQuest Information and Learning Company. All rights Reserved.