How GPS Knows Exactly Where You Are (Satellites, Atomic Clocks & Einstein)

How does a phone in your pocket know exactly where you are? It listens to 32 satellites orbiting 20,200 km above us. Each one broadcasts its position and the exact time, and your phone turns the signal’s travel time into distance. Four satellites solve your position and your clock error, and Einstein’s relativity keeps the whole system accurate. Without it, the error would grow by more than 11 km a day. 0:00 The clock above your head 0:56 The satellite constellation 1:38 A short history of GPS 2:12 Satellites don’t track you 2:38 Turning time into distance 3:06 Trilateration 3:36 The clock problem 4:00 The fourth satellite 4:40 Atomic clocks in orbit 5:09 Ground control 5:48 Einstein: special and general relativity 6:31 11 km a day, and the fix 7:13 What limits accuracy 8:13 How accurate is your phone? 8:48 GPS is the world’s clock 9:17 Recap Sources: gps.gov; U.S. Space Force (April 2026); NOAA; FAA; Ashby, Living Reviews in Relativity (2003); Penn State GEOG 862; BIPM. Full list of sources in the pinned comment. Images: NASA and gps.gov (public domain). Stock footage: Pexels & Pixabay. Original music. This video is for general education. Facts are drawn from the published sources listed in the pinned comment. Animations are illustrative and not to scale. Spotted an error? Let us know in the comments. #GPS #Science #Einstein