SpaceViews: The Online Publication of Space Exploration

Contradictory Findings on Accelerating Universe

Published: 1999 January 1
12:00 pm EST (1700 UT)

The discovery that the expansion of the universe may be accelerating, and not slowing down as once thought, was named the top science story of 1998 by the journal Science Thursday, December 17.

However, data released just one day later contradicts those earlier findings by showing that the universe's expansion is slowing down as predicted by theory.

Work by two separate international research groups showed that the rate of expansion of the universe appears to be accelerating. Astronomers measured the Doppler redshift of distant supernovae and compared the light with similar, nearby supernovae to determine the distances to the distant objects, and hence the expansion rate.

Most astronomers believed that the results would show that the rate of expansion had decreased since the Big Bang some 15-20 billion years ago. Instead, they found that the rate of expansion was increasing, meaning galaxies were flying away from each other at higher rates now than ever before. It also means that there is far less mass than necessary to ever stop the expansion.

The results have strong implications for theories of the Big Bang. Inflation theory, the leading theory to explain the sudden growth of the universe a tiny fraction of a second after the Big Bang, requires a universe with just enough mass to stop its expansion, or more than what recent observations show.

The acceleration also implies that an unknown force is at work to cause galaxies to speed up. A leading explanation is the "cosmological constant", a term introduced into general relativity by Albert Einstein to prevent the expansion of the universe, which his theories predicted. Einstein later retracted the constant, calling it his "greatest blunder."

Jeffrey Peterson, an astronomer at Carnegie Mellon University, announced at an astrophysics conference in Paris December 18 findings that contradicted earlier results using data from the Viper Telescope, an submillimeter-wavelength telescope located in Antarctica.

Peterson reported that observations of distant gas clouds showed that their angular size -- about one-half of a degree of arc -- was exactly that predicted for a universe whose rate of expansion is slowing as predicted by inflation theory.

"These findings indicate that the material of the universe was given just the right kick by the Big Bang to expand forever, never collapsing, but also never becoming so dilute that gravity can be ignored," Peterson said.

"This delicate balance is hard to understand unless inflation theory, or something akin to it, is correct," he concluded.

Astrronomers used observations of the redshift of distant supernovae, like this one above, to discover that the universe was accelerating.

Related Stories:
New Data Contradicts Accelerating Universe Findings -- 1998 December 18
Accelerating Universe Top Science Story of 1998 -- 1998 December 17
Related Sites:
Science magazine press release on top ten science stories of 1998
High-z Supernova Search Team Web site
Supernova Cosmology Project Web site
European Southern Observatory press release
NOAO press release
National Science Foundation press release on discovery
Viper Telescope Web site
Center for Astrophysical Research in Antarctica Web site