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Second: The Present

With the atomic clock, scientists continued on their quest to split the second into even smaller parts. Employing innovations in laser cooling developed in part by Bill Phillips at NIST, for which he shared the 1997 Nobel Prize in Physics, NIST’s first “fountain clock,” NIST-F1, was put into operation in 1999. This then-new type of atomic clock used lasers to slow cesium atoms from several hundred meters per second to just a few centimeters per second. This makes them far easier to control and get in tune with microwaves of the right frequency. This innovation improved the accuracy more than threefold over NIST-7 to one second in 20 million years (1/20,000,000th of a second per year). 

Since then, atomic clocks have steadily improved. Another giant leap in accuracy was achieved in 2014 when NIST-F2 was launched. Among other improvements, this fountain clock introduced a cooled chamber to further reduce thermal effects. The accuracy of NIST-F2 is about three times that of the final iteration of F1 and will not gain or lose a second in 300 million years (1/300,000,000th of a second per year). Learn more about how NIST-F2 works.

NIST uses F2 and F1 to keep the official civilian U.S. time, and their time signals, along with the U.S. Naval Observatory’s atomic clocks, are used to determine Universal Coordinated Time, or UTC, the world’s clock.

But why do we need to keep building more and more accurate and precise atomic clocks?

For one, the Global Positioning System (GPS) wouldn’t be possible without them. Each of the 24 satellites in the GPS Network has four atomic clocks that are synchronized with atomic clocks on the ground and each other daily. GPS satellites continually broadcast information about their position and the time they broadcast that position. When a GPS unit such as the one in a car receives signals from four of these satellites, it can use the time and position signals to determine where it, and thus you, are on the globe with a high degree of accuracy. 

Precise timekeeping also enables split-second financial transactions, synchronized electrical power grids, and high-speed communications.

Created April 9, 2019, Updated April 22, 2019