TUNIS—A physicist in Tunisia wants to build the most accurate clock on the African continent. For him, measuring time by the second isn’t precise enough. He wants to get down to a nanosecond; that’s one-billionth of a regular second.
To do that, he needs an atomic clock, a device which at its most accurate is 10 billion times more accurate than a wristwatch. There are currently none in Africa or in any Arab state.
“Atomic clocks have very real-world applications,” says the physicist, Haikel Jelassi, an associate professor at the National Center of Nuclear Science and Technology in Tunis.
GPS systems rely on atomic clocks: Each satellite needs to agree on the exact time to within a few nanoseconds for the technology to work. Atomic clocks are also used to calibrate complex scientific instruments like high-power telescopes, and they are also used to synchronize the networks that make up the Internet.
In an atomic clock, the natural oscillation of a cesium atom replaces the role of a pendulum in a traditional clock.
Low-energy cesium atoms are subjected to radiation, which transforms some of them into a high-energy state. The percentage of atoms that change their state depends on the frequency of the radiation—the closer it is to matching the natural oscillation frequency of cesium, the more atoms will change state. The aim is to tune the frequency of the radiation so it is a perfect match with the oscillation of the cesium atoms and then measure it.
Precisely 9,192,631,770 cesium oscillations equal one second.
Just a handful of countries can produce a “standard second” like this, which allows them to keep tabs on the world’s time, and the clear majority are developed nations like the United Kingdom and the United States in the so-called “global north.”
“A lack of an atomic clock in Africa is bad because gravity isn’t the same all over the world,” says Jelassi.
That’s a problem because time is influenced by gravity, meaning that time differs ever so slightly depending on geographical location. This is not enough to be noticeable in everyday life, but enough that it can be measured by an atomic clock.
That’s why Jelassi wants to build an atomic clock in Africa. “The more atomic clocks we have, the more accuracy we have,” he says.
“Some of it is about prestige,” he confesses, “but we also want to have data from an atomic clock in Africa because it will give different data.”
Jelassi learned how to construct and operate some of the components needed to make an atomic clock during a postdoctorate placement at the Laboratoire Collisions Agrégats Réactivité in Toulouse, which is part of the National Center of Science Research in France.
“He gained the skills to build an atomic clock when here,” says Matthias Büchner, a physicist at the Toulouse center and Jelassi’s former supervisor. “There are many common features in what he wants to do in Tunisia and what he did here.”
The most accurate atomic clock in the world is currently housed at the National Institute of Standards and Technology in the United States. It’s so accurate that had the clock begun counting at the time of the big bang, it would be off by less than one second today—although this is a record that is rarely held for long before another clock in another institution takes the lead, as scientists are constantly pursuing ever more perfect time keeping.
Elizabeth Donley, a physicist at the National Institute of Standards and Technology, says that Tunisia would be able to contribute to the international atomic time if Jelassi succeeds in his quest to build an atomic clock.
“The world agrees on time because the countries with these atomic clocks constantly compare their clocks and come up with an average,” says Donley.
Jelassi says he has been fortunate in his collaborators at the research center in France, who have provided him with some of the materials needed to construct the atomic clock.
“They have given some components like the pumps, electronic devices, optic elements like lenses and mirrors,” says Jelassi. “They have been generous with us.”
He is currently in the process of acquiring, assembling, testing and calibrating these parts. “It’s a science in itself to build an atomic clock,” he says.
He hopes to record the first reasonably accurate signal of his atomic clock by 2021. After that he will try to improve the accuracy even further, which could take several more years. “To have an atomic clock that is finished and working will take maybe 10 years,” says Jelassi.
“He is very capable of doing this but he will need a lot of support both financial and collaborative,” says Büchner, while adding that Jelassi’s aim for signals in just three years will be a challenge.
Even with an ambitious time frame, Jelassi says it’s tough to convince the government and funders that the project is worth their backing. “We do what we can and we’re grateful for the help we get. That’s why networking is very important to obtain components from European colleagues.”
