Everything we can detect, every star, planet and person, makes up only about 5% of the universe. The rest is 'dark matter' and 'dark energy'. We can measure their effects, but nobody knows what they are.
Truth label: Established. Strong evidence and broad agreement among experts.
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Dark matter
Galaxies spin so fast they should fly apart. Something unseen, with gravity, holds them together.
Dark energy
The universe's expansion is speeding up. Something is pushing it, and we call that dark energy.
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- Names for unknowns. Both terms are placeholders. They describe what we observe, not what the stuff actually is.
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Roughly how much of the universe is ordinary matter?
5%. Only about 5% is the matter we know.
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