By Ron Cowen
Four years ago, cosmologists reported the most startling finding about the universe since the late 1920s, when Edwin P. Hubble discovered that the cosmos is expanding. Most researchers assumed that gravity was slowing this expansion, but in 1998 two teams presented evidence that the universe is revving up its expansion rate. By measuring the brightness of distant supernovas, they concluded that some mysterious source, dubbed dark energy, must be opposing gravity’s braking action (SN: 3/21/98, p. 185).
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Now, using entirely different evidence, another team has also found that cosmic expansion is accelerating.