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Crystal clocks and atomic ticks

By , 29 August 2014

Strontium atomic clock

This experimental atomic clock uses strontium atoms and laser light. The image is made from many photos taken with long exposure times and other techniques to make the lasers more visible.
Image: Ye group and Baxley/JILA

One of our readers requested an article about time keeping devices, and it’s a great time for the topic. Scientists set a new record in clock precision early this year with an atomic clock that ‘ticks’ 430 trillion times in a single second.

Most wristwatches and wall clocks today use a quartz crystal to keep time. The cool thing about quartz is that it bends when you give it an electric charge. The tiny quartz in a clock is trimmed with a laser so that, when you give it electricity, it vibrates 32 768 times a second.

It’s not just a random number. If you halve 32 768 and then take the answer and halve it again, and again, and again, eventually the answer is one. Clocks use a chain of divide-by-two counters to turn the quick quartz vibrations into a steady second.

As rapidly as quartz vibrates in a watch, it’s nothing compared to an atomic clock. Our definition of a second is now measured using the light from caesium atoms, which has a frequency of exactly 9 192 631 770 cycles each second.

Atomic clocks are very precise and are put in satellites that orbit Earth as part of the global positioning system (GPS). Power stations, mobile phones and wireless networks can use the clocks in GPS satellites to keep everything synchronised – working at the same time. The clock on your computer may well get the right time by connecting through the internet with a computer server that uses an atomic clock as a reference.

Scientists from the USA set a new record in precision and stability early this year with an experimental strontium clock. Led by a physicist from the National Institute of Standards and Technology, the clock contains a few thousand atoms of strontium. The strontium atoms were arranged in a column of pancake shapes, held in place using lasers. When bathed in red laser light, they ‘ticked’ 430 trillion times a second.

The experimental strontium clock was so precise that scientists say it wouldn’t lose or gain a second in about five billion years. That’s longer than the age of the Earth, estimated at four and a half billion years!

More information

Strontium atomic clock sets new records.
How atomic clocks work.
How quartz watches work.

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How do you usually check the time? Do you wear a watch, check your phone, or watch a wall clock ticking?

This article first appeared in Science by Email. Get your weekly dose of science by subscribing here.

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