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Why GPS wouldn't work without Einstein's theory of relativity

One technology you probably use everyday that wouldn’t work if it wasn’t for Einstein’s theories is GPS, or the global positioning system.

GPS is a network of satellites orbiting Earth. The satellites are constantly emitting signals with their location and the time the signal is emitted. A GPS receiver on Earth uses that information to determine how far it is from different satellites and triangulates that information to find your location. General relativity tells us that gravity affects time, and because the pull of gravity is stronger on Earth than in the satellite’s orbit, time is passing faster up where the satellites are than on Earth. GPS technology corrects for this discrepancy, which, unaccounted for, would make the location determined by your GPS receiver inaccurate.

Kip Thorne, Feynman Professor of Theoretical Physics, Emeritus, at Caltech, explains how GPS works, and why it wouldn’t if we were ignorant of relativity.

Fusion’s original Relatively Speaking series celebrates the 100th anniversary of Albert Einstein’s general theory of relativity.

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