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The atomic clocks that keep satellites and your smartphone on time

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The US Naval Observatory is home to a set of incredibly precise atomic clocks that record America's official time. Its clocks are relied upon for a vast range of functions, from providing the time on your smartphone lock screen to keeping GPS satellites accurate in their calculations. The clocks, and the service they provide, are presided over by Dr. Demetrios Matsakis, chief scientist for the observatory's time services department. Matsakis describes their importance and operation in a video interview with The Atlantic.

Dr. Matsakis calls the clocks of the observatory his "babies." The most advanced are so accurate that they won't lose or gain a second over 300 million years of operation, but Matsakis says more precise clocks are coming. He says these devices will eventually become "10 to 100 times more accurate" but that the advance will bring new problems to time's measurement. Einstein's theory of relativity states that time will run slower or faster within levels of a gravitational field — so on a 3-foo-tall clock time would run faster at the top than at the bottom.