Atomic Clocks May One Day Crack One of the Universe’s Greatest Mysteries

When it comes to dark matter, scientists are much more certain of what it isn’t than what it actually is. But physicists do believe that it exists and that the universe consists of roughly 27% dark matter (the rest being dark energy at 68%, and normal matter—the stuff we know like planets and stars—make up just 5% of the known universe). But why does dark matter, well, matter? Because its existence helps explain how our galaxies can spin as fast at they do without tearing themselves apart.

The idea that dark matter exists in our universe isn’t exactly a modern notion. In 1933, a Swiss astronomer by the name of Fritz Zwicky made a discovery that first introduced dark matter, or what he called “dunkle Materi,” into the lexicon. While studying a galaxy cluster, he calculated that the gravitational mass of the galaxy must be far greater than what he was actually observing, because otherwise, the cluster would be ripping itself apart. He concluded that something must be holding these celestial bodies together, something that we cannot observe. This something is what is now commonly referred to as dark matter. Though Zwicky’s initial calculations have since been adjusted, his conclusions remain sound.

In the many decades that followed, numerous scientists have built on Zwicky’s early work, offering varying explanations for dark matter, everything from WIMPS (weakly interacting massive particles) to primordial black holes. But despite our best efforts, dark matter remains extremely elusive. As far as we understand, it does not interact with electromagnetic forces, making it incredibly difficult to spot. Now a group of researchers in Poland have put forth an idea that we may be able to use optical atomic clocks—the most accurate timekeepers in existence—to track dark matter.

We wrote about atomic clocks and how they work here, but to summarize, atomic clocks keep time by measuring the oscillations of atoms, which are predictably consistent and are less likely to be affected by outside physical forces when properly shielded. The result is that we get a much more accurate representation of time, and since 1967, the International System of Units has defined the second as the time that elapses during 9,192,631,770 cycles of radiation that is produced by the transition of cesium 133 between two energy levels. Scientists have since developed clocks more accurate than atomic clocks called optical clocks. These state-of-the-art devices measure ions that vibrate at even faster frequencies, about 100,000 times faster than those of atomic clocks. This allows for great precision as these clocks should only lose one second every three hundred million years.

One of the theories about dark matter is that it permeates space much like the way gravity does. Within it, there are “topological defects,” or structures that formed and stabilized in the early moments of the universe and today exist in its vast expanse (to give you a better sense, imagine a pocket of air between a phone screen and a plastic cover). These defects have a different set of quantum fields operating within them. If Earth were to pass through one of these defects, which can be as large as a planet, it would theoretically trigger quantum reactions in the physics of an atomic clock, causing glitches that would cause it to tell time differently. These glitches could give scientists a better understanding of the nature of dark matter and our universe.

Earlier proposals have suggested that there would need to be a network of synchronized atomic clocks to test this idea, which would, in theory, create a wide enough spread so that some clocks would remain unaffected and serve as a reference. Theoretical physicists Andrei Derevianko and Maxim Pospelov are currently using atomic clock networks onboard GPS satellites to look through a decade’s worth of data for signs of dark matter signatures.

However, the team from Poland led by physicist Piotr Wcislo argues that this approach is limited by our current ability to synchronize such a large scale network of atomic clocks via fiber links. His team suggests that a single optical atomic clock, based on the fundamental nature of its design, could be enough to detect such signatures. As Wcislo explains, “our approach makes the idea of building a global network of such detectors possible without any further developments in experimental apparatus.”

All of this is, of course, still largely theoretical. But if pursued, it could help shed light to one of the universe’s darkest mysteries.