AFTER more than 90 years, scientists believe they may have found experimental proof for general relativity, one of Albert Einstein’s greatest theories.

Scientists announced yesterday that early results from Gravity Probe B (GP-B), the £400m space mission carrying the first experiments capable of testing the theory, suggested that Einstein was right.

The researchers cautioned that they still had several months of work to confirm the result. However, the announcement, made at the annual meeting of the American Physical Society, is seen as highly significant.

Since its launch by Nasa in April 2004, GP-B has been using four ultra-precise gyroscopes to measure two effects predicted by Einstein’s theory. One is the “geodetic” effect, the amount by which the Earth warps space and time. The other, called frame-dragging, measures how the Earth “twists” space as it spins.

Both effects were predicted by Einstein in 1905 but are so tiny that only recently has it become possible to measure them.

Professor Francis Everitt, a Stanford University physicist and principal investigator of the GP-B mission, said the gyroscope data confirmed the predicted geodetic effect to a precision of better than 1%.

“It’s fascinating to be able to watch the Einstein warping of space-time in the tilting of these gyroscopes,” said Everitt.

However, the frame-dragging effect, which is more interesting to scientists, is 170 times smaller than the geodetic effect and Stanford scientists are still trying to filter out the relevant information from the mass of data sent back by the spacecraft.

“We anticipate it will take about eight more months of detailed data analysis,” said William Bencze, GP-B programme manager. “Understanding this data is like an archeological dig. A scientist starts with a bulldozer, follows with a shovel, and then finally uses dental picks and toothbrushes to clear the dust from the treasure. We are passing out the toothbrushes now.”

Einstein’s theories of special and general relativity are among the greatest achievements of 20th-century physics.

Special relativity explained how space and time are linked and showed that nothing could travel faster than the speed of light. This is easy for scientists to verify experimentally in particle accelerators.

However, this left Einstein with a problem: how to explain gravity? It appeared to behave like a force that was transmitted instantly over vast distances, but this was impossible if nothing could travel faster than light.

In 1916 Einstein came up with general relativity, which reinterpreted gravity not as a force but as a “field” generated by objects such as planets and which distorted nearby space according to the mass of that object.

However, general relativity has many weaknesses. One is that it seems incompatible with quantum mechanics, the theory that addresses how matter behaves at sub-atomic levels. Another is that it has proven impossible to find a way of verifying it experimentally.

It was these problems that led researchers to design GP-B to find out if Einstein’s theory needed amending or replacing. The craft was first proposed in 1959 but it has taken more than 40 years to bring the project to fruition.

At the heart of GP-B is the most precise gyroscope ever made. Once a gyroscope is pointed in a certain direction and set spinning, it should hold that alignment for ever. If Einstein were right, however, the distortion of space caused by the nearby Earth should slowly bring such a gyroscope out of alignment through a combination of the geodetic and frame-dragging effects.

Such effects are very small. According to Everitt, over the course of a year the geodetic effect caused the gyroscopes to change alignment by just 0.0018 degrees.

The frame-dragging effect is predicted to change the gyroscope’s alignment by about 0.000011 degrees. This is the width of a human hair viewed from a quarter of a mile away.

Dr Clive Speake, an experimental gravity researcher at Birmingham University, said the most interesting results — on the frame-dragging effects — were yet to come. “If the probe can measure how the spin of the Earth has affected the spin of the gyroscopes to the accuracy they claim, it would be the strongest test yet devised for general relativity,” he said. “We shall have to wait a few more months.”

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