---
source: https://iinventedlight.com/library/notes/dark-matter-dark-energy.md
title: "Dark matter and dark energy in plain words"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "US government work, public domain; restated in our own words"
attribution: "Summary by iinventedlight (AI-assisted). Sources: NASA, Dark Matter, US government work, public domain; NASA, What is Dark Energy? Inside Our Accelerating, Expanding Universe, US government work, public domain."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-04
as_of: 2026-11-04
confidence: medium
untested: "No observation or experiment was done; only the fetched government pages were read."
category: coverage-gaps
topic_area: "science-explain: cosmology"
tags: science, cosmology, dark-matter, dark-energy
sources:
  - id: S1
    title: "Dark Matter"
    publisher: NASA
    url: https://science.nasa.gov/universe/dark-matter-dark-energy/
    accessed: 2026-11-04
    license: "US government work, public domain"
  - id: S2
    title: "What is Dark Energy? Inside Our Accelerating, Expanding Universe"
    publisher: NASA
    url: https://science.nasa.gov/dark-energy/
    accessed: 2026-11-04
    license: "US government work, public domain"
---
# Dark matter and dark energy in plain words

## Short answer
Ordinary matter is only about 5% of the universe. Dark matter, about 27%, is invisible but has mass and pulls on things with gravity. Dark energy, about 68%, is whatever makes the universe's expansion speed up. [S1][S2]

## Key points
- Dark matter does not give off or reflect light; we infer it from its gravity on galaxies and clusters. [S1]
- Dark energy was discovered in the late 1990s. [S2]
- Nobody yet knows what dark energy is, but its effect is measured. [S2]

## Claims
- id: C1
  claim: The universe is about 5% normal matter, 27% dark matter and 68% dark energy.
  source: S1
  evidence: "normal or visible matter (5%), dark matter (27%), and dark energy (68%)"
- id: C2
  claim: Dark matter takes up space and holds mass.
  source: S1
  evidence: "It takes up space and it holds mass."
- id: C3
  claim: Dark energy is making the universe expand at an accelerating rate.
  source: S2
  evidence: "it’s making the universe expand at an accelerating rate"
- id: C4
  claim: Dark energy was not discovered until the late 1990s.
  source: S2
  evidence: "Dark energy wasn't discovered until the late 1990s."

## Sources
- [S1] Dark Matter. NASA. https://science.nasa.gov/universe/dark-matter-dark-energy/ . License: US government work, public domain. Accessed 2026-11-04.
- [S2] What is Dark Energy? Inside Our Accelerating, Expanding Universe. NASA. https://science.nasa.gov/dark-energy/ . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).