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Researchers Are One Step Closer To Redefining The Second


Scientists are one step closer to redefining the length of a second. To do that, they are using atomic clocks. These super-accurate clocks enable a number of life's modern conveniences.

COLIN KENNEDY: So every time you drive down the road and you're using Google Maps, you're using a timing signal from an atomic clock.

SHAPIRO: Colin Kennedy is a physicist at the Boulder Atomic Clock Optical Network Collaboration.

KENNEDY: And I build some of the world's best atomic clocks.


And whereas a grandfather clock needs to be reset every so often, Kennedy's colleague Jun Ye says atomic clocks can be much more accurate.

JUN YE: This is a clock where, if you set it right at the beginning of the universe, it would still be ticking, right? You know, it maybe have been one second too slow or too fast.

CHANG: In other words, the world's best atomic clocks would only be a second off after ticking for more than 13 billion years.

SHAPIRO: On top of their accuracy, atomic clocks don't look much like grandfather clocks, either.

KENNEDY: There's a whole mess of wires and laser beams.

SHAPIRO: The clocks work by tapping into the natural oscillation of atoms, and different atoms tick at different speeds. The worldwide standard clock today is based on cesium atoms, which tick about 9 billion times per second.

CHANG: But a new generation of clocks tick much faster than that, meaning you can divide a second into tinier and tinier slices. That makes the new atomic clocks 100 times more accurate than the cesium clock.

KENNEDY: Ultimately, the goal is to redefine the second in terms of a more accurate and more precise standard.

SHAPIRO: Kennedy, Ye and their colleagues compared three of those next-generation atomic clocks, which use atoms of aluminum, strontium or ytterbium.

CHANG: The goal was not to see which atomic clock was the best ticker per se but to show that these types of clocks can be compared from one lab to another, perhaps from one country to another.

KENNEDY: We want to make sure that a clock built here in Boulder is the same as a clock built in Paris as in London as in Tokyo.

SHAPIRO: So to connect their clocks housed in separate parts of Boulder, Colo., the scientists did something almost straight out of a comic book. They shot a laser beam through the air across town between two laboratory buildings. Here's Ye again.

YE: It was a fun experiment for sure. And it's - by all measure, it's actually very safe. And it's very much sort of out of the way of people's daily life.

SHAPIRO: He assured us the laser was high above Boulder and that no birds were hurt that he knows of. The findings appear in the journal Nature.

CHANG: Ye says networks of clocks like this could be used as super-sensitive sensors to detect a passing wave of dark matter. And the work moves scientists one step closer to officially redefining the second with a new type of clock.

SHAPIRO: As for our day-to-day lives, well, no need to reset your watch. Transcript provided by NPR, Copyright NPR.

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