Gravity Probe B is a relativity experiment developed to test two parts
of Albert Einstein's General Theory of Relativity. To make
the experiment work, a wide range of technologies were created
to help construct a satellite with instruments that explore
the basic foundations of space-time.
To
conduct the experiment, four gyroscopes will be placed in
Earth orbit to study their behavior outside the pull of
gravity. The gyroscopes will be precisely checked for tiny
changes in their direction of spin caused by their interaction
with the Earth. The gyroscopes will be contained in a satellite
orbiting at 400-miles over the Earth's poles. The gyroscopes
will be so free from interference that they will provide
a nearly perfect system for measuring the Earth's effects
on them.
The
gyroscopes will check for two effects that have far-reaching
implications for our understanding of the structure of the
Universe.
- Frame
Dragging - A rotating massive body drags space and time
around with it. A gyroscope orbiting Earth tends to tilt
away from the plane of its orbit because the Earth is
dragging it. GP-B will be the first experiment able to
sense the frame-dragging effect and will measure it to
1% precision.
- Geodetic
Effect - According to Einstein's General Theory of Relativity,
space and time in the vicinity of a massive body is distorted.
For a gyroscope orbiting near the Earth, this distortion
leads to a tilting of the gyroscope's spin axis in the
plane of the orbit. This effect is predicted by general
relativity theory to be 150 times larger than the frame
dragging. GP-B will measure this effect to a part in 10,000.
Gravity
Probe B, in measuring how space and time are warped by the
presence of the Earth and how the Earth's rotation drags
space-time around with it, will provide the most precise
test of Einstein's theories ever attempted.
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