clock menu more-arrow no yes mobile

Filed under:

Scientists just got one step closer to building the world's most perfect clock

Brian Resnick is Vox’s science and health editor, and is the co-creator of Unexplainable, Vox's podcast about unanswered questions in science. Previously, Brian was a reporter at Vox and at National Journal.

Scientists are inching closer and closer to perfecting the clock, one of humanity's oldest and most useful inventions. The latest advance is a new way to keep strontium clocks, finicky but amazingly accurate timekeeping devices, ticking.

Clockmakers have forever been chasing increasingly greater precision. In the 1500s, clocks with mechanical gears were prone to lose or gain whole minutes every day. Quartz clocks are much better: Even the cheapest ones are accurate to less than one second a day (and a cheap Casio is more accurate than a $10,000 mechanical Rolex).

The world's current standard clock — the atomic cesium clock — keeps near-perfect time, only losing or gaining a second every 300,000,000 years.

That's pretty good. But we can do better.

Why strontium may make a better atomic clock


For years, scientists have been toying with the idea of replacing the cesium clock with a clock based on the strontium atom. As Vox has reported, the best strontium clocks would keep time to within one second for around 15 billion years. For reference, the Earth is around 4.5 billion years old.

Atomic clocks — whether they run on strontium, cesium, or even aluminum — keep time by counting the frequency at which the atoms vibrate. This frequency never, ever changes, which is great for making precise time measurements. The international standard unit of one second is defined as 9,192,631,770 (9.2 billion) cesium oscillations.

Scientists say strontium clocks are more accurate because strontium's atoms vibrates much faster: at around 430 trillion of these atomic "tics" per second. That makes for more precise timekeeping. (Think of it like adding a whole lot of decimal points to a number. It allows you to describe that number more accurately.)

The problem with strontium clocks (sometimes called "optical clocks," because this frequency is in the visible light range) is that due to their complexity, they can't be run 24/7. "These are fairly complex systems with dozens of lasers that need to be frequency locked at the same time, and they simply break sometimes," Christian Grebing, a scientist with Germany's National Metrology Institute, told CNN. Which kind of defeats the point.

Grebing and his colleagues now think they've found a solution. Reporting in the journal Optica, the researchers say they've found a way to keep these strontium clocks ticking even when the atom's vibrations aren't being measured.

This diagram is a bit confusing, but basically it's showing how just as a maser can be programed to help a cesium clock keep time, it can also be used in an optical strontium clock.

The research group found they could temporarily duplicate the frequency of the strontium in a maser (a laser beam made of microwaves instead of light). The maser then acts as a "flywheel" to keep the ticking going steady for when the clock needs to be turned off. When the strontium clock then turns back on, it can then "retrain" the maser for the next bout of downtime.

The results were impressive. The Optical Society, which publishes Optica, explains:

the study found that, even with the optical clock running less than 50 percent of the time, with downtimes ranging from minutes to several days, the maser/optical-clock combination accumulated time errors of less than 200 picoseconds over 25 days, a nearly fivefold improvement relative to the best cesium atomic clocks.

That could make these clocks a viable replacement for the cesium ones.

But why do we need such precise clocks?

For one, science is the pursuit of perfection. Why shouldn't we have the most ridiculously accurate clocks imaginable?

The other reason is more practical. Some of our day-to-day technologies are actually sensitive to extremely small changes in time measurements. GPS technology, for instance, is sensitive to the changes in time predicted by Einstein's theory of general relativity. That is, even the infinitesimally small changes in time wrought by orbiting the Earth can make a difference in a GPS system determining your location. If these systems had even more precise measurements of time, they could judge your location more accurately.

It's important to note: It's unlikely the definition of a second is going to change anytime soon. The German scientists themselves report it would take a decade more work before a case can be made to redefine the second in terms of strontium.

We probably shouldn't watch the clock while we're waiting.

Sign up for the newsletter Sign up for Vox Recommends

Get curated picks of the best Vox journalism to read, watch, and listen to every week, from our editors.