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
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