New research is bringing fresh insights to one of cosmology’s most enduring mysteries: the question of whether dark matter behaves like ordinary matter.
The findings, presented by University of Geneva (UNIGE) researchers, appeared in a recent paper in Nature Communications, where they report that hypothetical dark matter falls into gravitational wells just like ordinary matter, based on current observations. Still, the authors caution that an unexpected interaction or previously unknown force may yet be revealed with future, more precise data.
Fundamentally, the study suggests that on the largest scales observable today, dark matter appears to follow the same physical laws as regular matter, while leaving open the possibility of subtle, undiscovered forces at play.
Dark Matter
Due to the fact that dark matter neither emits nor reflects light, it remains invisible and has never been directly detected. Scientists infer its existence because it fills massive gaps in our understanding of gravity and galactic structure—its effects are observed, but not the substance itself.
However, one of the greatest remaining questions about dark matter is whether it follows the same laws as ordinary matter.
Four well-known forces interact with traditional matter: gravity, electromagnetism, the strong nuclear force, and the weak nuclear force. Presently, it remains uncertain whether dark matter responds to these forces the same way, and some theories even propose a fifth, undiscovered force acting only on dark matter.
Gravity Wells
At the center of the team’s research was the cosmic phenomena known as gravity wells. When extremely massive objects occupy space, they bend that space around them, creating these gravitational phenomena. Current physics, from Einstein’s general relativity to Euler’s equations, accurately predicts how visible matter behaves in these wells. But does dark matter follow the same rules?
“To answer this question, we compared the velocities of galaxies across the Universe with the depth of gravitational wells,” explained co-author Camille Bonvin, associate professor in the Department of Theoretical Physics at UNIGE’s Faculty of Science. “If dark matter is not subject to a fifth force, then galaxies — which are mostly made of dark matter — will fall into these wells like ordinary matter, governed solely by gravity.”
“On the other hand, if a fifth force acts on dark matter, it will influence the motion of galaxies, which would then fall into the wells differently,” Bonvin said. “By comparing the depth of the wells with the galaxies’ velocities, we can therefore test for the presence of such a force.”
Dark Matter Behavior
The team’s analysis of real-world cosmological data shows that dark matter appears to fall into gravitational wells in line with Euler’s equations, behaving just like ordinary matter. However, small deviations remain possible.
“At this stage, however, these conclusions do not yet rule out the presence of an unknown force,” said lead author Nastassia Grimm, a former postdoctoral researcher at the Department of Theoretical Physics at UNIGE’s Faculty of Science. “But if such a fifth force exists, it cannot exceed 7% of the strength of gravity — otherwise it would already have appeared in our analyses.”
Future measurements, including upcoming data from the LSST and the Dark Energy Spectroscopic Instrument (DESI), will allow researchers to detect forces as weak as 2% of gravity’s strength. Those high-precision surveys may finally confirm whether dark matter truly follows the same laws as normal matter—or whether a faint but fundamental new force shapes the universe.
The paper, “Does Dark Matter Fall in the Same Way as Standard Model Particles? A Direct Constraint of Euler’s Equation with Cosmological Data,” will appear in Nature Communications on November 7, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.