This article originally published in
Air and Space Magazine

Everitt is 58; he wears his black and silver hair down to his shoulders, and he sports a bushy Einsteinian mustache. Speaking in an authoritative British accent, he says, "If you ask me to speculate-Will we confirm or will we deny general relativity? -I must say Iím an experimentalist; all Iím interested in is the truth."

Isnít that rather too modest?

"Well, surely itís the right kind of scientific modesty in this circumstance," he replies. "If I were completely modest, or if any of us were completely modest, we wouldnít do an experiment of this kind. But on the other hand, you know, we are undertaking a rather difficult enterprise, which seems worthwhile from many different points of view."

In a nutshell, what the experiment will attempt to do is measure two effects that Einsteinís general relativity theory predicts. That theory contradicts Newtonís vision of gravity as a force instantaneously traversing great distances and redefines it as a field that warps the space-time fabric. If space and time are woven together the way Einstein envisioned, then the shape of that fabric should be affected by the gravitational forces exerted by rotating bodies. A comparatively small body like Earth wonít affect the space-time fabric very dramatically; nonetheless, GP-B will try to determine if Earth is exerting the two primary effects Einstein hypothesized. The first is the geodetic effect, the degree to which a planetís mass bends space-time. The second is frame-dragging, the degree to which a planetís rotation drags space-time around. Both should be observable in fractions of a milliarc-second, aptly described by one graduate student as "a gnatís whisker of a measurement."

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