Advanced · ABOUT 2 MINUTES READING
Dark Matter and Dark Energy
These names describe two different problems in cosmology. Neither is a synonym for ordinary matter that happens to be hard to photograph.
Evidence for additional gravitating matter
Galaxy motions, gravitational lensing and large-scale structure indicate more gravitating matter than visible stars and gas can explain in the standard model. Dark matter does not interact with light as ordinary luminous matter does. Its microscopic identity remains unresolved; a gravitational inference is not a confirmed particle detection.
Evidence for accelerated expansion
Observations of expansion history motivate a component called dark energy in the standard cosmological model. A cosmological constant is one possible description. Dark energy is not a reservoir that powers stellar fusion or spacecraft. Its inferred role concerns the dynamics of expansion on the largest scales.
Different roles, open questions
Dark matter clusters and contributes to structure formation. Dark energy, in the simplest model, is smooth and affects expansion differently. Researchers compare multiple measurements and consider alternatives, but an unresolved physical identity does not mean there is no evidence for the phenomena. State clearly which inference is measured and which explanation is uncertain.
Key takeaways
- Dark matter is inferred through gravitational evidence.
- Dark energy describes accelerated-expansion behavior.
- Neither microscopic explanation is settled.
Make this knowledge yours
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Knowledge check
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Take the Galaxies and Cosmology quiz ↗Sources and further reading
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Connect the ideas
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