# What is dark matter? > Dark matter is the name for mass we detect only through its gravity: it holds galaxies and clusters together, bends light and shaped the early universe, yet emits no light. It makes up about 85% of all matter. What it is made of is unknown; no particle has been detected despite decades of searches. Author: Mikhail Savchenko Updated: 2026-10-15 Canonical: https://neuralcosmology.com/en/answers/what-is-dark-matter Locale: en Translations: en, ru, pt, es License: CC-BY-4.0 (https://creativecommons.org/licenses/by/4.0/) --- ## Mass we can weigh but cannot see Astronomers weigh things by how they move. A planet's speed around the Sun tells you the Sun's mass; a star's speed around a galaxy tells you how much mass lies inside its orbit. When this is done for galaxies and clusters, the answer comes out far larger than all the stars, gas and dust put together. The missing part is called dark matter: it pulls with gravity but neither emits nor absorbs light. ## How we know it is there The evidence comes from several independent directions, and that is why most physicists take it seriously. - **Galaxy clusters.** In 1933 Fritz Zwicky measured the speeds of galaxies in the Coma cluster and found them moving so fast that the cluster should fly apart unless it held hundreds of times more mass than its light suggested. - **Rotation curves.** In the 1970s Vera Rubin and Kent Ford showed that stars at the edges of spiral galaxies orbit as fast as those closer in. Visible matter alone predicts they should slow down. Our answer on [galaxy rotation curves](/en/answers/galaxy-rotation-curves-without-dark-matter) covers this in detail. - **Gravitational lensing.** Mass bends light. Mapping how background galaxies are distorted shows where the mass is, and around galaxies and clusters there is much more of it than we can see. - **The Bullet Cluster.** In this pair of colliding clusters, the hot gas (most of the ordinary matter) was slowed by the collision, while the mass measured by lensing passed straight through. Douglas Clowe and colleagues published the map in 2006. The mass and the visible matter are in different places. - **The cosmic microwave background.** The pattern of hot and cold spots left from the early universe depends on how much matter interacts with light and how much does not. The Planck satellite's 2018 fit gives about 5% ordinary matter, 27% dark matter and 68% dark energy. ## What it could be Nobody knows. The main candidates: - **WIMPs**, weakly interacting massive particles, which fit naturally into extensions of the Standard Model. For decades they were the favourite. - **Axions**, very light particles first proposed to solve a different puzzle in the physics of the strong force. - **Sterile neutrinos**, heavier relatives of ordinary neutrinos that feel only gravity. - **Primordial black holes**, formed in the first moments after the Big Bang. Observations rule out most mass ranges for them to be all of dark matter. ## The search so far Detectors deep underground, such as LZ in South Dakota and XENONnT in Italy, wait for a dark matter particle to knock into an atomic nucleus in tonnes of liquid xenon. ADMX listens for axions turning into microwave photons in a strong magnetic field. The Large Hadron Collider looks for energy missing after collisions. None has found anything yet, but each null result narrows where dark matter can hide. Meanwhile telescopes map dark matter through its gravity: the Euclid space telescope, launched in 2023, and the Vera C. Rubin Observatory measure weak lensing across billions of galaxies. ## Doubts and alternatives The lack of a detected particle keeps alternatives alive. MOND, proposed by Mordehai Milgrom in 1983, changes the law of gravity at very low accelerations and predicts many galaxy rotation curves from visible matter alone. Erik Verlinde's emergent gravity tries to derive a similar effect from information theory. Both struggle with galaxy clusters and the cosmic microwave background, where dark matter works well. The [rotation curves answer](/en/answers/galaxy-rotation-curves-without-dark-matter) compares them. ## Where this programme stands The research programme on this site does not propose a model of dark matter. Its preprint, *Pointer Architecture* v9.0, works at the level of a formal computational substrate; its one cosmological claim reproduces the standard holographic estimate of dark energy, which concerns the expansion of the universe and says nothing about what dark matter is made of. ## Bottom line Dark matter is a well-measured effect with an unknown cause. Its gravitational fingerprints agree across galaxies, clusters, lensing and the early universe, which is why it remains the standard explanation. What it is made of is one of the largest open questions in physics. ## FAQ ### What is dark matter in simple terms? Matter that does not shine or absorb light but still pulls with gravity. We see its effect on stars, galaxies and light, but not the matter itself. ### How much of the universe is dark matter? According to the Planck satellite's 2018 results, about 27% of the universe's energy content is dark matter, about 5% is ordinary matter and about 68% is dark energy. Dark matter is roughly 85% of all matter. ### What is the difference between dark matter and dark energy? Dark matter pulls things together through gravity and helps galaxies form. Dark energy is the name for whatever makes the expansion of the universe speed up. They are separate problems with separate evidence. ### Has dark matter been detected directly? No. Underground detectors such as LZ and XENONnT, axion searches such as ADMX and collider experiments at the LHC have found no dark matter particle so far. They have ruled out large ranges of possible masses and interaction strengths. ### Who discovered dark matter? Fritz Zwicky inferred unseen mass in the Coma galaxy cluster in 1933. Vera Rubin and Kent Ford's measurements of galaxy rotation in the 1970s turned the idea into a mainstream problem.