Scientists are looking in an unlikely place for clues to one of the universe’s most enduring mysteries, as billion-year-old geologic formations have become a new target in the search for dark matter.
The effort, led by physicists at Virginia Tech, proposes that evidence of dark matter’s interactions with Earth over time may be discoverable within subtle clues left behind in ancient rock formations.
“It’s crazy,” said theoretical particle physicist Patrick Huber, who is the Director of the Center for Neutrino Physics at Virginia Tech. “When I first heard about this idea, I was like—this is insane. I want to do it.”
Now, Huber and his team are hoping to reveal that rock formations that originated billions of years ago—normally the focus of geologists—could soon prove to have a dual use as unlikely natural dark matter detectors.
The Hunt for Dark Matter
Scientists have had little success in making direct detections of dark matter, a hypothetical nonluminous material that physicists nonetheless expect to comprise around 85% of the mass in our universe. Despite decades of experiments aimed at revealing it, this mysterious invisible matter remains elusive.
While much of the search for dark matter remains focused on the distant cosmos, Huber and his collaborators decided to take a different approach: one that would look within the Earth, rather than beyond it, for the long-sought evidence of this mysterious “missing” matter.
Specifically, evidence of interactions with dark matter could be found hidden within some of Earth’s oldest stone formations, a hypothesis that Huber and his team are now exploring with the help of funding from the National Science Foundation and the National Nuclear Security Administration.
The approach, while unorthodox compared to past efforts aimed at revealing the most elusive matter in the cosmos, warrants consideration, given that only around 5% of the universe falls within the portions that astronomers can easily observe. While the dark matter comprising the larger remaining percentage of the universe cannot be seen directly, its gravitational influence on the surrounding cosmos can be inferred from the behavior of galaxies and other celestial objects.
Along similar lines, if Earth has also been affected by the influence of dark matter in its 4.6-billion-year history, there could be evidence of these ancient interactions left within mineral structures deep below ground.
A Costly Search for Dark Matter
Thanks to a $3.5 million Growing Convergence Research award from the National Science Foundation, the ambitious plan to search deep within the Earth for evidence of a longstanding cosmic mystery will soon be underway, with additional funding provided by the National Nuclear Security Administration.
The research effort will include the construction of a new lab in Robeson Hall at Virginia Tech, which will be uniquely designed according to the needs of Huber’s ambitious project.
Scientists like Huber know all too well the kinds of challenges such research can present. Since dark matter only interacts weakly with ordinary forms of matter, detections of the invisible material are notoriously difficult, and to date, no direct evidence for its existence has been found. Still, several anomalies observed throughout the cosmos, including the spin of galaxies at rates that exceed what should occur based on their visible mass alone, have kept the search for dark matter alive.
Rising to the challenge, Huber and his team are planning to employ advanced imaging technology to help them search for evidence of microscopic damage trails that result from collisions between dark matter and the crystalline lattice of ancient minerals.
A Novel Approach
In theory, when high-energy dark matter particles collide with the nucleus of other particles located within rocks, a recoil effect is produced, which should displace the nucleus and produce a microscopic structural defect.
Vsevolod Ivanov, one of Huber’s collaborators on the project, said the team plans to search for evidence of such defects within ancient crystals, which have been exposed collisions with various different kinds of particles over the vast periods of time that have elapsed since their creation.
“We’ll take a crystal that’s been exposed to different particles for millions of years and subtract the distributions that correspond to things we do know,” Ivanov said in a statement.
“Whatever is left must be something new, and that could be the dark matter,” he says.
An additional challenge arises in the search for suitable rocks that can be identified as likely natural dark matter “detectors.” One problem involves how radioactive decay occurring deep within the Earth can sometimes affect crystal structures. To help find rocks that have not been impacted by background radiation, University Distinguished Professor Robert Bodnar, a recent inductee into the National Academy of Sciences, plans to work alongside Huber’s team to help find samples that show minimal signs of such Earth-based influence.
Capturing Imagery of the Invisible
Currently, Huber’s team has announced a partnership with the University of Zurich’s Brain Research Institute, a collaboration that will facilitate state-of-the-art imaging technologies for the project. With 3D imaging capabilities originally developed for the analysis of the nervous systems of animals, early efforts through the collaboration have already revealed images of high-energy particle tracks detected in synthetic lithium fluoride crystals.
Lithium fluoride, which unfortunately is not an ideal substance for use in the search for dark matter interactions, was selected for these early imagery tests because it does have beneficial qualities that make it ideal for creating a baseline for the kinds of promising signals the team hopes to find.
Even beyond the search for dark matter, the team’s novel approach toward resolving this mystery could have other useful applications. For instance, the new imaging capabilities they plan to use could also be used in the promotion of nuclear transparency, particularly with devices designed for compact monitoring of nuclear reactors.
Huber and his team are hopeful that by thinking outside the box, their new approach could be the one that will ultimately reveal the extent of dark matter’s influence on the Earth over long periods, and ultimately, a discovery that could offer unprecedented new perspectives on its role in shaping the structure of the universe.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. He can be reached by email at micah@thedebrief.org. Follow his work at micahhanks.com and on X: @MicahHanks.