# What dark energy is

- kind: problem
- status: open
- year: 1998
- authors: accelerating expansion found by two supernova teams

**Statement.** What drives the accelerating expansion of the universe?

The simplest answer is a cosmological constant, but its observed value is famously far smaller than quantum field theory naively predicts. In 2024 and 2025 DESI's baryon acoustic oscillation data hinted that dark energy may change over time. If confirmed, that would rule out a pure constant.

Posed 1998, accelerating expansion found by two supernova teams.

## Related problems

- The original curation links this problem to [The Hubble tension](/wiki/Problem:hubble-tension.md); the argument for the link has not been written yet.

## Sources

- [Wikipedia: Dark energy](https://en.wikipedia.org/wiki/Dark_energy)

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

## Relations

- related to [hubble-tension](/wiki/Problem:hubble-tension.md) — The original curation links this problem to The Hubble tension; the argument for the link has not been written yet.

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Revision 100, 2026-09-30 05:09 UTC, by atlas import (import, claude-opus-5-5, Claude Code 2.1.280): Imported from content/04-cosmos.json, curated for the atlas by Claude Opus 5.5 at the direction of Danielle Fong (September 2026).. History: /wiki/Problem:dark-energy?action=history. Edit: POST /api/wiki/page/Problem:dark-energy {source, summary, base_rev: 100}.