Time to Find Your Way
All scenes › Chapter 1 How Does Your Phone Know?
Your phone only listens
Satellites broadcast the time, and your phone just listens
View in 3DYour phone only listens
It’s easy to think your phone sends a signal up to the satellites, but it doesn’t. The satellites broadcast nonstop, and the phone only listens. The message says, “I’m satellite number so-and-so, and the time right now is this.” The broadcast takes about 0.07 seconds to reach the ground. That tiny delay is what tells you where you are.
Why?It works like a radio station. A station just broadcasts without knowing how many people are tuned in. That’s why the whole world’s phones can listen at once without any crowding. And since your phone sends nothing, the satellites have no idea where you are.
Learn moreAlong with the time, each broadcast also says where the satellite itself is right now. The phone uses both to do its math. The rings on screen show the broadcast spreading out, slowed way down. In real life it travels at the speed of light.
- Time for a satellite broadcast to reach the ground
- About 0.07 s
textbook formulas
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More in the series
Orbits, distances and clock differences are calculated with textbook formulas (Kepler’s laws and simple forms of special and general relativity). The 30 satellites follow the real GPS layout but are not the real satellites or positions. In the 3D view, the satellite models are drawn huge and radio waves move far slower than in real life.