[ExI] dark constant

[Damien Broderick]

<http://www.cosmosmagazine.com/news/2447/dark-energy-expands-and-contracts-our-universe>


Dark energy expands and contracts universe

Thursday, 18 December 2008
Agence France-Presse


WASHINGTON: Mysterious dark energy works simultaneously to expand the 
universe and shrink objects inside it, astronomers have found.

"This result could be described as 'arrested development of the 
universe'... Whatever is forcing the expansion of the universe to 
speed up is also forcing its development to slow down," said Alexey 
Vikhlinin of the Smithsonian Astrophysical Observatory in Massachusetts.

Vikhlinin was the lead researcher of the study, to be published next 
year in the Astrophysical Journal.

By studying how gravity competes with the expansion of galaxy 
clusters, using NASA's Chandra X-ray Observatory, "a crucial 
independent test of dark energy" has been found, said the researchers.

After years of research, scientists now believe that dark energy 
makes up about 70 per cent of the universe, and is "a form of 
repulsive gravity that dominates the universe," the researchers 
wrote, "although [we] have no clear picture of what it actually is."

The discovery of dark energy's dual effects of expansion and 
contraction sheds light on changes in the universe to come: "What 
this means for the future of this universe is that accelerated 
expansion will proceed forever but will probably not result in a Big 
Rip," said Vikhlinin.

"That is, nearby galaxies will eventually disappear from our sight, 
but the structures already formed by clusters of galaxies and our own 
galaxy will not be torn apart, not in the near future anyway."

The new research provides the "strongest evidence yet that dark 
energy is the cosmological constant," Vikhlinin said, being similar 
to the energy of empty space. "Or in other words, that 'nothing 
weighs something."