GP-B Post-Flight Analysis—Final Report - Gravity Probe B - Stanford ...

In Einstein’s view, space and time are relative entities, inextricably woven together into a “fabric” which Einsteincalled “spacetime.” Furthermore, spacetime and matter interact—spacetime tells matter how to move, andmatter tells spacetime how to curve and twist. Thus, in Einstein’s universe, gravity is not an attractive force, butrather the interaction of bodies moving through curved spacetime. This concept is illustrated in Figure 2-6below.Figure 2-6. Einstein’s Universe: Space and time are relative entities, interwoven into a spacetime fabric whosecurvature we call gravity. Objects follow the straightest possible lines, called geodesics, through curvedspacetime.2.1.3 Why perform another test of Einstein?With the general theory of relativity, acclaimed as one of the most brilliant creations of the human mind,Einstein forever changed our Newtonian view of gravity. However, even though it has become one of thecornerstones of modern physics, general relativity has remained the least tested of Einstein’s theories. Thereason is, as Caltech physicist Kip Thorne once put it: “In the realm of black holes and the universe, thelanguage of general relativity is spoken, and it is spoken loudly. But in our tiny solar system, the effects ofgeneral relativity are but whispers.” And so, any measurements of the relativistic effects of gravity around Earthmust be carried out with utmost precision. Over the past 90 years, various tests of the theory suggest thatEinstein was on the right track. But, in most previous tests, the relativity signals had to be extracted from asignificant level of background noise. The purpose of GP-B is to test Einstein’s theory by carrying out theexperiment in a pristine orbiting laboratory, thereby reducing background noise to insignificant levels andenabling the Probe to examine general relativity in new ways.Gravity is the most fundamental force in nature; it affects all of us all the time. But, gravity is still an enigma—wedon’t completely understand it. Einstein’s 1916 general theory of relativity forever changed our notions of spaceand time, and it gave us a new way to think about gravity. If the Gravity Probe-B experimental resultscorroborate the geodetic and frame-dragging predictions of general relativity, we will have made the mostprecise measurement of the shape of local spacetime, and confirmed the theory of general relativity to a newstandard of precision. If on the other hand, the results disagree with Einstein's theoretical predictions, we maybe faced with the challenge of constructing a whole new theory of the universe’s structure and the motion ofmatter.32 March 2007 Chapter 2 — Overview of the GP-B Experiment & Mission