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Dark energy Dark energy is one of two concepts (the other is dark matter) that Big Bang cosmologists and astrophysicists have invented to explain the most serious differences to date between astronomical observations of an expanding universe and their own expectations. It is "the most popular way to explain recent observations that the universe appears to be expanding at an accelerating rate";[1] Astronomers and cosmologists have been speculating on the nature of this dark energy for ten years.

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