Dark Matter Follows Gravity on Cosmic Scales — New Analysis Narrows the Window for a Fifth Force

Dark matter obeys gravity across the universe, new study finds

Researchers report that dark matter — the invisible substance that makes up roughly five times more matter than ordinary atoms — falls into large-scale gravitational wells in the same way visible matter does. The result places strong limits on any hypothetical long-range "fifth force" acting on dark matter and strengthens the case that gravity (as described by general relativity) governs dark matter's motion on cosmological scales.

Why this matters

Everyday matter is built from atoms (protons, neutrons and electrons) and interacts via four known forces: electromagnetism, gravity, the strong nuclear force and the weak nuclear force. Dark matter, by contrast, appears not to interact with light — or does so only extremely weakly — which makes it detectable mainly through its gravitational effects. Determining whether dark matter follows the same gravity rules as ordinary matter across vast cosmic distances is crucial because dark matter drove much of the universe's large-scale evolution.

How the team tested the idea

Scientists from the University of Geneva (UNIGE) and partner institutions compared galaxy velocities with the depths of cosmic "gravity wells" — regions where massive objects warp spacetime and create stronger gravitational attraction. If dark matter were subject to an additional long-range force, galaxies (which are dominated by dark matter) would fall into these wells differently than ordinary matter.

"To answer this question, we compared the velocities of galaxies across the universe with the depth of gravitational wells," said Camille Bonvin (UNIGE). "If a fifth force acts on dark matter, it will influence the motion of galaxies and produce measurable deviations from pure gravitational infall."

Findings and limits

Using contemporary cosmological datasets, the researchers found that dark matter sinks into gravitational wells in the same way visible matter does. The analysis shows no evidence for a new long-range interaction affecting dark matter, though it cannot rule out every possible model.

Nastassia Grimm (Institute of Cosmology and Gravitation, University of Portsmouth) cautioned: "These conclusions do not yet rule out the presence of an unknown force. 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."

What's next

Future surveys will tighten these constraints. Isaac Tutusaus (University of Toulouse) says upcoming experiments such as LSST (the Legacy Survey of Space and Time at the Vera C. Rubin Observatory) and DESI (the Dark Energy Spectroscopic Instrument) should be sensitive to forces as weak as ~2% of gravity and will therefore probe dark matter's behaviour even more precisely.

Publication: The study was published on Nov. 3 in Nature Communications.

Implications

These results bolster the view that gravity, as currently understood, governs the large-scale motion of dark matter and narrow the range of viable alternatives. While they do not absolutely exclude exotic interactions, they significantly constrain any additional long-range force's strength and encourage future observations to push these limits even lower.