General Relativity and the Global Positioning System Despite what you might suspect, the fact that time passes at different rates at different altitudes has significant practical consequences. An important everyday application of general relativity is the Global Positioning System. A GPS unit finds out where it is by detecting signals sent from orbiting satellites at precisely timed intervals. If all the satellites emit signals simultaneously, and the GPS unit detects signals from four different satellites, there will be three relative time delays between the signals it detects. The signals themselves are encoded to give the GPS unit the precise position of the satellite they came from at the time of transmission. With this information, the GPS unit can use the speed of light to translate the detected time delays into distances, and therefore compute its own position on earth by triangulation. But this has to be done very precisely! Bearing in mind that the speed of light is about one foot
This is the end of the preview.
access the rest of the document.