Nuclear timekeeping may reveal hidden traits of dark matter

Nuclear timekeeping may reveal hidden traits of dark matter
by Sophie Jenkins
London, UK (SPX) Jul 22, 2025

For nearly a hundred years, scientists have sought dark matter, the unseen material believed to account for 80 percent of the universe's mass. Despite extensive efforts-including particle accelerator experiments and cosmic radiation searches-its properties remain largely unknown. Although dark matter doesn't interact directly with light, it may subtly influence visible matter, making it extremely difficult to detect.

Now, physicists believe that a nuclear clock-an ultraprecise timekeeping device based on an atomic nucleus-could serve as a tool to expose these hidden interactions. Recent progress in nuclear physics has opened a new pathway for researchers at the Weizmann Institute of Science, working in collaboration with scientists in Germany and the US, to search for signs of dark matter without needing a fully operational nuclear clock.

The key lies in thorium-229, a radioactive element whose resonance frequency-its natural oscillation rate between quantum energy states-is unusually low. This allows scientists to probe it using standard ultraviolet lasers. Since the 1970s, thorium-229 has intrigued physicists for this very reason, and it has long been considered a prime candidate for constructing a nuclear clock.

Measuring the resonance frequency with extreme accuracy is essential to building such a clock. It also provides a potential way to detect dark matter, which could subtly alter this frequency. However, for nearly five decades, scientists couldn't obtain precise enough readings. That changed last year when German researchers at the PTB institute and a team from the University of Colorado made major advances in measuring thorium-229's resonance frequency-improving precision by several million times.

Recognizing the significance of this achievement, Prof. Gilad Perez's theoretical physics group at Weizmann proposed using these enhanced measurements to hunt for dark matter. "In a universe with only visible matter, the absorption spectrum of a nucleus would stay constant," said Perez. "But dark matter may cause minute shifts. Detecting those shifts in thorium-229 could reveal its presence."

The team, led by Dr. Wolfram Ratzinger, calculated how dark matter might influence the full absorption spectrum of thorium-229. They concluded that this method could detect interactions as much as 100 million times weaker than gravity. "We're probing a region no one has accessed before," said Ratzinger. "Even though we haven't seen these changes yet, our work provides the framework to identify them once they emerge. From the size and frequency of any deviation, we'll be able to determine the dark matter particle's mass."

Their study also explores how various dark matter models would impact thorium-229's spectrum. This groundwork could ultimately help physicists determine the nature of dark matter itself.

While precision measurements continue in labs worldwide, the eventual development of a thorium-based nuclear clock could transform navigation, communication, power grid control and fundamental science. Unlike conventional atomic clocks that depend on electron transitions-and are vulnerable to environmental interference-a nuclear clock would be more stable and less prone to disruption.

According to Perez, "a thorium-229-based nuclear clock would be the ultimate detector. It could sense forces 10 trillion times weaker than gravity and achieve a resolution 100,000 times greater than current dark matter detection methods."

Research Report:Nuclear Glow Illuminates Dark Matter