The nature of dark matter

What makes this fascinating

• Most matter is invisible — About 85% of the universe's matter emits no light; we only know it's there from its gravity.

• It holds galaxies together — Without unseen mass, galaxies spin so fast their stars would fly apart.

• Detectors keep coming up empty — Decades of experiments hunting candidate particles like WIMPs have found nothing conclusive.

Frequently asked questions

What is dark matter?

An unseen form of matter that emits no light but whose gravity holds galaxies together and bends light. It makes up about 27% of the universe — far more than ordinary matter.

Has dark matter been detected?

Its gravitational effects are well established, but no one has identified what it is made of. Direct-detection experiments and collider searches have not confirmed a particle.

What could dark matter be?

Leading candidates include WIMPs, axions, and sterile neutrinos; some researchers instead propose modified gravity (MOND). None is confirmed.

More summits in Physics

• Quantum gravity

  Our two best theories of reality contradict each other. Uniting them is physics' deepest quest.

• The nature of dark energy

  Something is pushing the universe apart, faster and faster. We have no idea what.

• The quantum measurement problem

  Why does a particle's haze of possibilities snap into one outcome when we look?

• High-temperature superconductivity

  Some materials carry current with zero loss — and we still can't explain why.