Einstein and Gravity Probe B proves space-time warps

William Atkins
Monday, 16 April 2007 05:54

Science - Space

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Gravity Probe B (GP-B) was a satellite whose sixteen-month mission was to measure the distribution and motion of matter (what is called stress-energy tensor) around the Earth. The GP-B satellite used four very precise gyroscopes that are one million times more accurate than any inertial navigation gyroscopes. The gyroscopes measured the geodetic effect, which is the amount that Earth’s mass distorts the fabric of space and time in the general vicinity of the Earth.

Einstein’s General Theory of Relativity is a theory that predicts gravitation is not due to an attractive force but instead is a consequence of the distortion of space and time (that is, the curvature of space-time), specifically by the mass-energy and momentum content of space-time. In other words, Einstein did not see, for example, the solar system’s planets being pulled in by the Sun. Instead, he saw them following the curvedness of space-time due to the distorting effects of the Sun’s mass.

Developed by NASA and Stanford University (California), it was launched on April 20, 2004, from Vandenberg Air Force Base in California. It orbited at about 400 miles, traveling over the North and South Poles. However, GP-B was first began in 1959 by Stanford University professors and funded by NASA starting in 1964. Consequently, it is considered the longest lasting physics-research programs at Stanford and NASA.

One measurement made by GP-B is the geodetic effect, which is the amount by which the mass of the Earth warps the local space-time in which it resides. Space-time is a math model that brings together the three dimensions of space and the one dimension of time into one single entity called the space-time continuum. The other effect, called frame-dragging, is the amount by which the rotating Earth drags local space-time around with it.

According to Einstein’s theory, over the course of one year, the geodetic warping of Earth's local space-time causes the spin axes of each gyroscope to shift from its initial alignment by a minute angle of 0.0018 degrees (6.606 arc-seconds ) in the plane of the spacecraft’s orbit. Likewise, the twisting of Earth’s local space-time causes the spin axis to shift by an even smaller angle of 0.000011 degrees (0.039 arc-seconds) in the plane of the Earth’s equator.

These important scientific results were announced at the American Physical Society (APS) meeting in Jacksonville, Florida, which was held on April 1417, 2007. Although the distortion effects of space-time have been considered true for years, this experiment proves these two previously unverified prediction from Einstein’s General Theory of Relativity. Such knowledge means an enormous amount with respect to the structure of the universe.

The home Web page of Gravity Probe B is: http://einstein.stanford.edu/.