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The dominant component (about 70 percent) of the universe. Its nature is not well understood, but it differs from matter in being gravitationally repulsive. Dark energy is detected by its effect on the rate at which the universe expands. Many explanations have been proposed for dark energy; the simplest is that it is an energy density inherent to empty space.
This entry comes from Encyclopædia Britannica Concise. For the full entry on dark energy, visit Britannica.com.