Kirshner, Robert P. Department of Astronomy, Harvard University, Cambridge, Massachusetts.
Last reviewed:May 2018
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- Discovery of an expanding universe
- Discovery of an accelerating universe
- Candidate drivers for an accelerating universe
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An increase in the expansion rate of the universe, attributed to dark energy. In 1998, astronomers presented evidence that the universe's expansion is not slowing down, as would be expected due to the gravity from the abundances of matter strewn throughout the cosmos. Instead, the observations of distant, exploded stars revealed that cosmic expansion is accelerating (Fig. 1). Since this initial discovery, multiple other lines of evidence, including observations of the afterglow of the big bang, known as the cosmic microwave background, and in the clustering of galaxies over cosmic history have made the case for this surprising result more secure. See also: Big bang theory; Cosmic background radiation; Cosmology; Matter (physics); Physics; Universe
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