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Gravity Probe B
Definitive tests of general relativity were beyond the science
of his day, but his equations were so compelling to other scientists
that his theory won almost immediate acceptance. So confident was he in the
rightness of his insight that in a divorce settlement with his first
wife he promised to split the proceeds from the Nobel Prize he felt
certain it would help him earn. Indeed, in 1921 - three years after
the divorce became final - he was awarded the Nobel Prize in
physics.
In the years since, researchers have labored diligently in
experiments of such bewildering complexity that it is easy to conclude
that, in the matter of relativity, Einstein had the easy part.
To test general relativity, scientists have, among other things,
pondered variations in the orbit of the planet Mercury, measured
microwaves as they warp around
the sun, bounced signals off Mars and the moon, monitored the
radioactivity of superdense stars and studied the attractions between
the stellar partners of a binary pulsar.
The Stanford experiment - decades in the making due to its
unprecedented precision - entails the first direct measurements of
several relativity effects.
A FAINT BREEZE CAN RUIN IT ALL
 n
one point at least, the project's backers
and detractors agree: Gravity Probe B is science at its most
fundamental.
The relativity mission entails some of the most sophisticated aerospace
engineering and applied physics of the past two decades, yet at the
center it is no more complicated than a spinning crystal ball.
At the heart of the relativity experiment are four supersensitive,
superchilled gyroscopes, which fit into a block of fused quartz.
Engineered to be almost completely free from disturbances, the
gyroscopes will form an almost perfect space-time reference system as
they orbit Earth within the supercooled probe. The rotor of each
gyroscope is a polished sphere of electrically neutral quartz crystal
about the size of a ping-pong ball.
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