Revision 1

Accepted · first revision · record

Title: What is dark matter made of?
Plain: Galaxies, clusters and the cosmic microwave background all require extra unseen mass, about five times the ordinary matter. The task is to find out what that mass physically is.
Precise: Determine the microscopic identity (mass, spin, non-gravitational couplings, production mechanism) of the non-baryonic component with $\Omega_c h^{2} = 0.120 \pm 0.001$ inferred from the CMB in LCDM. An answer is a candidate confirmed by a reproducible non-gravitational signal (direct, indirect or collider detection, or a compact-object census) whose abundance accounts for $\Omega_c$.
Settled by: A reproducible non-gravitational detection of a candidate whose inferred cosmic abundance matches $\Omega_{c}$.
Kind: phenomenon
Answer type: identification
References: (empty)
Literature status: open
Status note: No candidate has been detected as of 2026; the leading searches (xenon detectors, axion haloscopes, gamma-ray telescopes, microlensing) report null or contested results.
Posed since: 1933