Why Are Scientists Building a Nuclear Clock? Because Atomic Clocks Aren't Perfect

The task of building a clock that accurately keeps time is totally unlike clockwork. Normal clocks help serve us pretty well for day-to-day practical needs, but scientific research and technology based on sensitive measurements require clocks that are able to gauge the passage of time with utmost precision. Thus, scientists invented atomic clocks — and while they are more accurate at keeping time than conventional systems, there remained significant room for improvement. Now, scientists are moving from the atomic world to the nuclear one. A new study published in Nature shows that German physicists have developed a timepiece capable of losing less than a tenth of a second every 20 billion years. That’s — depending on how you look at it — 10 times better than current atomic technologies

But before we dub atomic clocks obsolete, let’s consider what makes them different from the pendulum-flaunting ancestors.

Every clock uses a resonator to keep track of time. A resonator is a mechanism that, for the sake of simplification, “ticks” on a regular basis. Old clocks used a pendulum and gears as a resonator. Digital clocks use the oscillations on the power line or of a quartz crystal as the resonator. An atomic clock takes this idea a few steps forward by using resonance frequencies of atoms themselves as the resonator. In this system, the resonator is regulated by the electromagnetic radiation emitted by the quantum transition of an atom. In other words, an atomic clock keeps track of time by measuring the energetic changes in an atomic particle.

For some elements and their isotopes, this happens at consistent frequencies. Cesium-133, for instance, oscillates at exactly 9,192,631,770 cycles per second. That’s why it was used to build the first atomic clock at the National Physical Laboratory in the UK, in 1955.

Since then, a number of technological advances have led to more accurate atomic clocks — including laser cooling and trapping of atoms, more precise laser spectroscopy, and figuring out other isotopic elements that exhibit even more consistent resonant frequencies. The current record holder for the most accurate atomic clock bases readings on ytterbium ions.

The reason atomic clocks are so critical has to do with the fact that clocks measure time differently at different elevations. The farther a clock is from the main source of gravity, the faster time passes (i.e. a clock will run faster at Mount Everest than at sea level). The difference is seemingly negligible, but can add up as more time passes.

So much of our technology these days operates as global applications, like GPS. In order to ensure they run on the same time no matter where someone is, they have to be tied directly to an accurate clock. There’s no better way to ensure that than to use atomic clocks as a standard. In the latest study, the German research team outlines an idea to directly measure the oscillations of the element’s atomic nucleus itself (as opposed to the electrons surrounding the nucleus). An atomic clock based on this design could avoid being influenced by external forces. The research team identifies an excitation state in the isotope of thorium, Th-229m, that could work — and illustrates experimental findings that support this notion.

There’s just one problem: Th-229m doesn’t occur naturally. Though the results of the new study are nevertheless impressive, it’s unclear exactly how researchers can harvest enough of Th-229m to build and maintain a nuclear clock. The researchers derived Th-229m in this case by using uranium-233 as a source. It’s not an easy process.

If scientists figure out how to resolve that little issue and generate a sustainable amount of Th-229m, we’re looking at a new generation of atomic clocks that will undoubtedly play a major role as we build more and more technology that spans the globe and serves people in every corner of the world.