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

Figure 2-4. GP-B Principal Investigator, Francis Everitt, receiving the NASA Distinguished Public Service Award atan awards ceremony at NASA Headquarters in April 2005.2.1.2 Einstein Stands on Newton’s ShouldersIn a letter of 1676, written to his lifelong enemy, Robert Hooke, Isaac Newton made the now famous remark: “IfI have seen farther, it is by standing on the shoulders of giants.” In 1687, Newton published his three-volumePhilosophiae Naturalis Principia Mathematica—universally regarded as the most important work in the historyof science—in which he fused the work of Copernicus, Galileo, Kepler, and others into the first comprehensivetreatise on theoretical physics. In the Principia, Newton defined the three laws of motion and derived theformulae that, for practical purposes, describe the motion of celestial bodies, as well as the motion of everydayobjects (e.g., apples falling from trees). Newton believed that space and time are distinct and absolute entities,and although he could not explain the mechanism by which it works, he thought that gravity is an attractiveforce, somehow acting instantaneously at a distance between bodies, as illustrated in Figure 2-5 below.Figure 2-5. Newton’s universe: Space and time are absolute or fixed entities. Gravity is a force that actsinstantaneously between objects at a distance, causing them to attract one another.About two centuries later, in 1905, Einstein published his special theory of relativity, which is based on thepremise that the speed of light is a universal “speed limit”—nothing can travel or propagate faster than the speedof light. Realizing that Newton’s idea of gravity violated this basic premise of his special theory of relativity,Einstein spent the next 11 years developing his general theory of relativity—his theory of gravity—whichutilized the equivalence principle to go beyond the concepts of inertia and weight to describe how gravity makesthings fall.Gravity Probe B — Post Flight Analysis • Final Report March 2007 31