# What dark matter is

- kind: problem
- status: open
- year: 1933
- authors: Fritz Zwicky; 1970s, Vera Rubin's rotation curves

**Statement.** What is the substance that makes up about 85% of the matter in the universe?

Its gravity shows up in galaxy rotation, gravitational lensing, the cosmic microwave background and the growth of structure, all consistent with the same amount. Direct detection experiments have ruled out much of the favored parameter space for WIMPs without a signal. Axions, sterile neutrinos and primordial black holes remain candidates, and a minority argue for modified gravity instead.

Posed 1933, Fritz Zwicky; 1970s, Vera Rubin's rotation curves.

## What would settle it

A direct-detection signal confirmed by independent experiments

## Sources

- [Wikipedia: Dark matter](https://en.wikipedia.org/wiki/Dark_matter)

[The dark sector](/wiki/Space:dark-sector.md) · [Cosmos](/wiki/Continent:cosmos.md)

## Relations to this page

- related to [strong-cp](/wiki/Problem:strong-cp.md) — The original curation links this problem to What dark matter is; the argument for the link has not been written yet.

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