Delanceyplace.com 01/04/07-Einstein

In today's excerpt, a practical application for Einstein's theory of relativity:

"Incredibly, the GPS [global positioning satellite] system now in use [in applications such as cars] requires Einstein's theory of general relativity to achieve its one-meter accuracy ... [otherwise it] would build up errors at the rate of more than 10 kilometers each day. ... Determinations of the variation in snow depth on Mars using laser-ranging data from orbiting spacecraft also incorporate general relativity and yield values with an unbelievable precision of 10 centimeters. Certainly, at the time it was developed, no one--not even Einstein--anticipated such practical applications of a theory as abstract as general relativity."

Lisa Randall, Warped Passages, Harper Collins, 2005, pp. 84-5