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name: will baker blogrollin' other sites: |
taking "precision" to a whole new level
Yesterday, NASA successfully launched Gravity Probe B, an orbital probe that will test two of the more interesting unverified implications of Einstein�s General Theory of Relativity. In 1905, Einstein�s Special Theory of Relativity shattered our commonsense assumptions about the relationship between space and time in a Newtonian universe. A decade later, in 1916, he expanded his original work into the General Theory of Relativity, which described gravitation as a warping of space-time by matter and energy. GR has consistently provided accurate predictions about the behavior of matter, space, and time in the macro-universe, and is a foundation of modern physics and cosmology. Some of its most basic predictions remain untested, though, because the extent to which the earth and sun warp space-time is relatively slight (or at least difficult to measure with available instrumentation). Gravity Probe B will attempt to measure the distortion of space and time around the earth as caused by the earth�s mass. More interestingly, the probe will attempt to measure the extent to which space-time is twisted by the earth�s mass as it rotates on its axis. The probe itself is as fascinating as the experiments it will conduct. It contains four gyroscopes consisting of spheres of fused quartz coated with niobium. These spheres are the most perfectly round objects ever manufactured. In fact, they are probably the most perfectly round objects within hundreds of light years. If the spheres, which are about the size of ping-pong balls, were expanded to the size of the earth, the distance between the lowest valley and highest peak on their surfaces wouldn�t be more than 16 feet. These spheres are suspended in chambers in the fused quartz block by saucer-shaped electrodes that apply a fraction-of-a-volt charge to the spheres, the niobium coating of which will become superconducting at the near-absolute-zero temperature at which the experiments will be conducted. In inner surface of the spherical cavities have channels through which helium gas will be shot to spin the rotors up to 10,000 rpm. After the rotors are spun up, the helium will be pumped out, leaving the rotors to spin in a near-perfect vacuum. The final pressure will be so low that after spinning for 1,000 years the gyroscope would lose barely 1% of its initial speed. A telescope is attached to one end of the fused-quartz block containing the gyros. This telescope is constructed of smaller fused-quartz blocks, the connecting surfaces of which are machined to such a precise smoothness that when they are pressed together, the fuse to create an incredibly strong, permanent, molecular-level bond. In effect, it is as if the entire final assembly was carved from a single block of fused quartz. This is accomplished by natural molecular adhesion alone�no adhesives, no welding, no nothing. Just the binding of molecules between some of the smoothest surfaces ever produced. This entire assembly is encased in a series of lead �bags� that will keep the interior mechanisms almost completely isolated from the earth�s magnetic field. These �bags�, in turn, will be encased in a gigantic Dewar flask which will maintain the instrumentation at a temperature near absolute zero. A telescope gyroscopically aligned toward a single star should never lose its alignment, because gyroscopes maintain their axial alignment in space. But the warping of space itself should cause a minute deviation that will allow for the measurement of spatial warping and the frame-dragging effect (caused by the earth�s mass and rotation, respectively).
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