Some of them have provided the means to probe more and more deeply into the nature and evolutionary history of the universe. Observations with such instruments have yielded one surprise after another, and they raise perplexing questions about missing mass, the age of the universe, and the circumstances giving rise to the large-scale d istribution of matter in space. In the past, laws of nature previously considered sacrosanct have sometimes been found deficient when subjected to much closer scrutiny or applied to new phenomena. As long as some discoveries defy understanding, it is im portant to continue testing nature's most fundamental laws. The frame-dragging effect predicted by our principal theory of space and time, general relativity, has a deep conceptual significance involving the connections between rotation, distant matter, and absolute space.
Frame dragging is a direct manifestat ion of gravitomagnetism.
Its consequences have found important astrophysical applications in, for example, models of relativistic jets observed streaming from the cores of quasars and active galactic nuclei. Gravity Probe B is one of the few space missions NASA has conducted with relevance to fundamental physics. If successful, it would assuredly join the ranks of the classical experiments of p hysics. By the same token, a confirmed result in disagreement with GR would be revolutionary. Since GP-B was conceived, significant progress has been made through experimental studies of gravity, both in improved precision and in performing qualitatively new tests.