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Hard Science

The Length Of a Second is Being Redefined

Because losing a nanosecond a month is just too much to bear.

Jelor GallegoJune 3rd 2016

Changing Clocks

While the science behind the concept of time is mired in the nuances of pretty strange physics, the science behind keeping time isn’t really that complicated. Simply define what a second is, and make something that measures that accurately. Currently, said device is atomic clocks, but that may soon change.

Researchers have developed a system that is more accurate than our current atomic clocks. Instead of using atomic clocks, the researchers used optical clocks that measure atoms or even ions that vibrate faster than the current versions.

Current atomic or microwave clocks measure the vibrations of a cesium atom. They define a second as 9,192,631,770 cycles of those vibrations. However, current atomic clocks still accumulate an error—about 1 nanosecond over a month.

In contrast, optical clocks measure oscillations of atoms or ions that vibrate at frequencies about 100,000 times higher than microwave frequencies—which is a whole lot faster, and therefore more accurate. But this comes at a price. The clocks experience downtime from a few minutes up to two days. Meaning in that period, the clock can’t be used to tell the time. That is why optical clocks were never a viable option.

Considering Combinations

In a study published in Optica, the researchers described a system that uses optical clocks to tell time more accurately. They proposed the combination of a commercially available atomic clock device called a ‘maser’ with a strontium optical lattice clock. The maser, which is less accurate than an optical clock, would compensate for the downtime of the optical lattice clock.

To overcome the gap between the accuracy of the two clocks, the team used an optical frequency comb, which divides the slower optical-based ‘tick’ to match the faster ‘ticks’ of the optical clocks.

“We compared the continuously running maser with our optical clock and corrected the maser frequency as long as we had data available from the optical clock,” said one of the researchers, Christian Grebing. “During the optical clock’s downtimes, the maser runs on its own stably.”

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