Gravity and Time

Why GPS needs Einstein

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Clocks run slower deeper in gravity.
• GPS clocks run fast by a net 38 µs per day.
• Uncorrected, that would cause errors of about 11 km per day.

Steps

1. Clocks run slower low down
2. A clock on Everest
3. GPS satellites
4. Getting lost
5. Near a black hole
6. The two effects together