All of our clocks are wrong

The length of a second might not be what we think it is. New optical clocks aim to improve timekeeping over inaccurate, traditional atomic timepieces.

All of our clocks are wrong
Mark Hachman

The gold-standard for time measurement—the 500 or so atomic clocks in use—might be on its way out. The clocks' days, if not their hours or seconds, are numbered.

Optical clocks are a better way to measure time, say researchers who published their findings in Optica, the Optical Society's journal. The scientists say the optical technology is more accurate than the previous best-tech, which uses microwave frequency atomic oscillations.

“Clocks work by counting a recurrent event with a known frequency, such as the swinging of a pendulum,” the society explains in a press release. Atomic clocks use the natural movement of a cesium atom.

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It’s a pretty good method, and better than the watch on your wrist, however smart, but not 100 percent accurate. The atoms are off by a nanosecond each month. A nanosecond is a billionth of a second. That might not sound like much, but it’s enough to make a second not really a second.

And indeed data sent through networks, financial transactions, navigation and the legal system are just some examples of human endeavors that require accurate timekeeping. Seconds, and fractions of seconds, count.

Optical clocks keep better time

The scientists say optical clocks are better. Optical clocks don’t use microwave, but use visible spectrum. That frequency is higher, therefore the recurring event—the tick—is more frequent, the scientists explain. That makes them more accurate and the seconds they measure more like an actual second.

The only problem is that the optical clocks haven’t been very reliable—they’re complicated. And that’s one reason that up to now, the ions and atoms of the optical tech haven’t replaced atomic, microwave clocks.

But the researchers say they’ve made a breakthrough and can reduce the downtime, thus making optical timekeeping a practical alternative to the incumbent.

Their system, developed at the National Metrology Institute of Germany (Physikalisch-Technische Bundesanstalt, or PTB), uses a maser optical device. A maser is like a laser, but in a microwave band. The optical-clock-substituting maser kicks in during the optical clock’s frequent downtime. It’s “a type of reliable pendulum with limited accuracy to bridge the downtime of the optical clock,” the release says.

Even with the optical clock running only half the time, with the combination maser and optical clock, accuracy was still greater than a classic atomic clock.

“The researchers calculated a time error of less than 0.20 nanoseconds over the 25 days,” the release says.

Optical clocks keep time about a hundred times better than atomic clocks, Christian Grebing of PTB adds.

One question is whether time will actually be newly defined through use of the now-reliable maser-optical combination technology. Time will tell, but Grebing says “a true redefinition of a second” is 10 years away.

There are arguments in favor.

“A more accurate global timekeeping system would allow financial networks to use more precise time stamps and thus handle even more transactions in shorter amounts of time,” the release says. “It would also allow GPS and other satellite-based navigation systems to provide even more precise location information.”

It's about time.

Copyright © 2016 IDG Communications, Inc.

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