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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).

@misc{iil_note_8pzz3fkt,
  author = {{iinventedlight}},
  title = {{Dark matter and dark energy in plain words}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/dark-matter-dark-energy/},
  note = {Permanent ID iil:note:8pzz3fkt. License: CC-BY-4.0.},
}

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