Perfect timing is more complicated than you think. Most clocks slow down over time (few people notice) and tiny imperfections in the manufacturing process ensure that no two watches are truly in sync. Atomic clocks are currently the most advanced timekeepers we have designed. Or at least they were, before the invention of nuclear clocks.
Earlier this month, researchers developed a prototype “optical nuclear clock,” a timekeeping device that would be even more precise than the standard atomic clocks NASA uses in its satellites. The researchers detailed the new clock and how it works, and published their work on arXiv. Basically, nuclear clocks measure time with the oscillations of a laser, tuned to the precise frequency that swaps the nucleus of thorium-229 atoms (stored in a calcium fluoride crystal) between quantum states. If the frequency drifts, fewer atoms change state and the laser must be readjusted to maintain accuracy.
As the device is a prototype, it is far from ready for large-scale use. However, it has potential applications in the search for the invisible theoretical material that binds the universe and its laws, known as dark matter. Think of The Force from “Star Wars” but less mystical. However, we cannot normally detect dark matter because it interacts with most particles to an almost infinitesimal degree. That being said, a thorium-229 optical nuclear clock is so sensitive and precise that oscillations of its constant fine structure (the electromagnetic force between particles) that do not match those of similar clocks could be taken as evidence of the presence of dark matter. The fine structure constant is assumed to be constant for all elements. Then again, some scientists claim that dark matter doesn’t exist, so this is all theoretical at this point.
A timing that took a long time to come
Although it seems like it came from the pages of a “Star Trek” script (or at least like an invention inspired by science fiction novels), atomic clocks were invented in the 1950s. Likewise, nuclear clocks have been around longer than most people think. At least, the theory behind them.
The idea of an optical nuclear clock was launched in 2003 (you can read the article in Europhysics Letters). The original idea predicted that thorium-229 atoms could be hosted in radio frequency traps. The scientists who wrote the paper believed that thorium-229 would make the ideal core for a nuclear clock because the element is unaffected by external magnetic and electric fields. Not far from the current iteration of the optical nuclear clock.
So why did it take scientists so long to capitalize on this theory? Our technology had to catch up with our imagination. Thorium-229 has a very specific energy jump suitable for stimulation with a laser, but this laser must be frequently monitored and readjusted, ideally without human interaction or intervention. Without this feedback loop, you would just have a laser pointing at the item without doing any real timing. But now that we have the required technology, not only can we produce prototype nuclear clocks, but researchers are confident that this field will advance rapidly. Fingers crossed, these advances will revolutionize the search for dark matter.
