Scientists have made significant strides in understanding dark matter, revealing that it may behave similarly to ordinary matter. A research team from the Université de Genève and collaborating institutions conducted a study published in Nature Communications on November 16, 2025, analyzing the movement of galaxies through cosmic gravitational wells. Their findings suggest that dark matter adheres to established physical laws, although the existence of a potential fifth force remains a possibility.
Dark matter, an invisible substance making up approximately five times more mass in the universe than ordinary matter, has long puzzled researchers due to its elusive nature. The fundamental question remains: Does dark matter respond to the same physical forces as ordinary matter? The UNIGE-led team embarked on this inquiry to determine if dark matter follows familiar behavior on cosmic scales or if other undiscovered forces might play a role.
Examining Gravitational Wells
The researchers focused on whether dark matter sinks into gravitational wells similarly to ordinary matter. These wells are created by massive objects that distort the fabric of space. As planets, stars, and galaxies fall into these wells, they do so according to established principles, including Einstein’s general relativity and Euler’s equations.
Camille Bonvin, an associate professor in the Department of Theoretical Physics at UNIGE and co-author of the study, explained, “To answer this question, we compared the velocities of galaxies across the Universe with the depth of gravitational wells. If dark matter is not subject to a fifth force, then galaxies—mostly composed of dark matter—will fall into these wells like ordinary matter, governed solely by gravity.”
In examining modern cosmological data, the researchers found that dark matter indeed behaves similarly to ordinary matter, confirming that it is consistent with Euler’s equations.
Possible Fifth Force Remains Uncertain
Despite these findings, the researchers caution that they cannot entirely rule out an unknown force influencing dark matter. According to Nastassia Grimm, the first author of the study and former postdoctoral researcher at UNIGE, “If such a fifth force exists, it cannot exceed 7% of the strength of gravity—otherwise, it would have already appeared in our analyses.”
This research represents a crucial advancement in the quest to understand dark matter’s role in the universe. The next objective is to ascertain whether a subtle fifth force genuinely affects dark matter. Upcoming experiments, such as LSST and DESI, are expected to provide valuable data.
Isaac Tutusaus, a researcher at ICE-CSIC and IEEC, as well as an associate professor at the Midi-Pyrénées Observatory, noted, “These experiments will be sensitive to forces as weak as 2% of gravity, allowing us to learn even more about the behavior of dark matter.”
As scientists continue to unravel the mysteries of dark matter, these findings contribute to a deeper understanding of the universe and the fundamental forces that govern it.
