The Accelerating Expansion

The accelerating expansion of the universe, the notion that the big bang enlargement of spacetime is not slowing down but actually gathering speed, has received new experimental support in the form of supernova observations made by the Hubble Space Telescope (HST).

Previous evidence for such a cosmic acceleration consisted of studies of the dimness of remote supernovas (Update 355), and represented a major revision for some scientists who had long thought that the mutual gravity among galaxies would slow or even reverse the cosmological expansion. The new HST observations consist of reexaminations of 170 previously studied supernovas and the announcement of 16 new objects, including 6 of the 7 most distant type Ia supernovas yet recorded.

The new data are in line with the accelerating-expansion hypothesis employing the mysterious mechanism usually referred to as "dark energy." The energy of the universe would be divided up as follows: 29% in the form of matter (dark plus luminous) and 71% as dark energy. (NASA press conference, 20 Feb; Riess et al., preprint astro-ph/0402512 )