delanceyplace.com 01/04/07 - einstein
In today's encore excerpt - a practical application for Einstein's theory of relativity:
"Incredibly, the GPS system now in use 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."