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dimanche 25 janvier 2004

You certainly know that Einstein published two theories of relativity, the special and the general. The general theory was the one trying to explain gravity and has never really been proven. Of course, this theory has strange implications, like the space itself can curve. Now, NASA will check Einstein's theory by starting the Gravity Probe B physics experiments next April. In fact, Gravity Probe B will test "the slight warping of space by Earth's much smaller gravitational field."

Here is a rendering of the Gravity Probe B deployed in space (Credit: NASA/Stanford University).

The Gravity Probe B deployed in space

Now, let's look at some of the engineering involved in this space vehicle.

It was not until 1960 that a physicist, Leonard Schiff, working at Stanford University, came up with the idea of using gyroscopes, with their great inertial stability, to test the effects of gravity. But the relatively crude, earthbound gyroscopes of Schiff's day were not up to the task of measuring forces as exquisitely tiny as those a small planet like Earth might produce.
Gravity Probe B, however, transcends those limitations. It will send a group of small gyroscopes in a satellite into a polar orbit 400 miles high, where they will stay for some 13 months, making measurements. If the theory is correct, relativistic forces will gradually change the direction of spin of a gyroscope orbiting the Earth, which otherwise should be constant. The experiment will measure those changes to an accuracy of 1 in 10,000.
Gaylord Green, program manager of the Gravity Probe B project, puts it simply: "This is the most sophisticated thing the human race has ever tried to put into space."

The Gravity Probe B vehicle arrived at Vandenberg Air Force Base and is being assembled and tested. Here is what it looks like.

The Gravity Probe B tested on the ground

Please read the original article to discover all the technical details about the gyroscopes, the telescope and how all the data gathered by the mission will be processed.

The important thing to know is how the general theory of relativity will be proven -- or invalidated.

Once in orbit, the telescope searches for and then locks onto the exact center of a particularly distant star, which will provide a fixed reference. If the gyroscopes' spin drifts relative to that, the warping of space itself -- predicted by General Relativity -- will have been demonstrated.

If you want even more information about the Gravity Probe B experiment, you can visit these sites from Stanford University and from NASA.

Source: David Halperin, TechNewsWorld, January 24, 2004

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