Book 8, Question 83
Why Do GPS Satellites Need Einstein's Help?
GPS satellites need Einstein's help because their clocks tick a little differently from clocks on the ground! Clocks tick slightly differently up high and at high speed, so engineers correct them every day. Without the fix, maps would drift by kilometers within a day.
More fun facts
- Every GPS satellite carries an atomic clock.
- Because the satellites move so fast, Einstein's ideas say their clocks should fall behind clocks on Earth by about 7 millionths of a second a day.
- But gravity is weaker up there, which makes their clocks run faster.
- Put together, GPS clocks run about 38 millionths of a second per day faster than clocks on the ground.
- If engineers did not correct for this, tiny time errors would quickly add up to wrong locations.
- GPS could be seen as the longest-running test of Einstein's ideas.
Questions kids ask
Do clocks in space really tick differently?
Yes. GPS clocks run about 38 millionths of a second per day faster than clocks on Earth.