OUR COSMOS

The gyroscopes used in Gravity Probe B are 'the most perfect spheres ever made'.

Einstein was right, probe shows

Early results from a Nasa mission designed to test two key predictions of Albert Einstein show the great man was right about at least one of them. It will take another eight months to determine whether he got the other correct say scientists analysing data from Nasa's Gravity Probe B satellite.

One of these effects is called the geodetic effect, the other is called frame dragging. A common analogy is that of placing a heavy bowling ball on to a rubber sheet.
In the analogy, the geodetic effect is similar to the shape of the dip created when the ball is placed on to the rubber sheet.
If the bowling ball is then rotated, it will start to drag the rubber sheet around with it. In a similar way, the Earth drags local space and time around with it - ever so slightly - as it rotates.
Over the course of a year, these effects would cause the angle of spin of the gyroscopes to shift by minute amounts.

[Other experiments are due to test the equivalence principle which stems from the observation that when two objects are dropped, they will accelerate at the same rate.
"Here there is a theoretical framework where one might expect to see a departure from the equivalence principle," said Professor Sumner. "This might give us pointers as to the way forward."]