For roughly half a century, the length of one second – assuming you don’t take into account the effects of relativity – has been measured in precisely the same way: by a swinging pendulum. Generations ago, this pendulum hung down from a grandfather clock; nowadays, the most accurate clocks are atomic, but the pendulum concept still holds strong, as these digital boxes are essentially recording the back and forth movements of atoms of cesium.
Now, writing in the journal Optica, a team of researchers has announced that it has designed an atomic clock that uses strontium atoms effectively. With the ability to “tick” faster than cesium, it could form the basis of unprecedentedly accurate timekeeping – one in which only 0.008 nanoseconds are lost each day.
Although almost everyone won’t directly notice the increase in accuracy of humanity’s timekeeping, this clock, if officially adopted as the definer of “one second”, will improve GPS navigation by up to one or two orders of magnitude – say, from 1 meter to 1 centimeter, in certain situations.
Tick tock. Brian A Jackson/Shutterstock
“We want to improve the timekeeping infrastructure all over the world by building better and better clocks and integrating them into the time-keeping infrastructure,” Christian Grebing, a researcher at the Physikalisch-Technische Bundesanstalt in Germany and lead author of the study, said in a statement. “What we demonstrated is a first step towards a global improvement of timekeeping.”
Traditional atomic clocks, as mentioned, rely on the element cesium. When exposed to microwaves – or any other type of sufficiently energetic radiation – the electrons orbiting atoms of cesium become excited, and jump up to a higher energy state before emitting some radiation and “falling down” again.
This electron-based back and forth motion is somewhat like a pendulum. This motion frequency is fixed and can be used to define how long a second is.
In fact, ever since 1967, “one second” has been defined as 9,192,631,770 of these electron movements, or “cycles”. Within the United States is one of the world’s most accurate atomic clocks, the NIST-F1. It’s so ridiculously precise that its time error per day is about 0.03 nanoseconds, meaning that in 100 million years it would have only lost about a second.
Although remarkably precise, this cesium clock is about 3.8 times less precise than the proposed strontium clock. Operating in a similar way, an atom of strontium will experience 429,000,000,000,000 cycles when energetically excited, which is roughly 47 times faster than that of cesium.
With more cycles comes more precision. Theoretically, this new clock can keep time so well that only 100 seconds would have been lost if it began ticking at the birth of the universe 13.8 billion years ago.
A chip-sized atomic clock, unveiled in 2004 by NIST. Svdmolen/Wikimedia Commons; Public Domain
This clock uses radiation within the optical part of the electromagnetic spectrum, which features lower wavelengths, higher frequencies, and higher energies. As such, it is known as an “optical clock.” Optical clocks aren’t new, but they have always been seen as inferior to microwave-based atomic clocks as they require significant maintenance and downtime, thanks to their higher technical complexities.
Combining a microwave laser (a “maser”) with a “frequency comb”, a technique that directly links optical frequencies with lower ones, the team managed to overcome these delicate intricacies to produce a continually operational, low-maintenance optical clock. Only time will tell if it’s ultimately welcomed with open arms by the most stringent timekeepers in the world.