Dark energy

[alokmohan]

On Jan. 12, 1998, just before leaving for his honeymoon, astronomer Adam Riess e-mailed his colleagues that the universe appeared to be completely dark and utterly repulsive. Fortunately, he was talking about a matter of gravity. http://www.sciencenews.org/articles/20080202/bob10.asp<br /><br /> <br /><br />NASA/STScI, E. Roell<br /> <br /><br />Riess was part of a team of astronomers viewing distant supernovas to study the expansion of the universe. Researchers have known since the 1920s that the universe is expanding, with distant galaxies fleeing from each other at a rate proportional to their distance. That expansion, driven by the energy released during the Big Bang, ought to have been decelerating ever since, braked by the mutual gravity of all the matter in the cosmos. <br /><br />But that's not what Riess, along with astronomers from a rival team, had found. Instead of slowing, cosmic expansion was speeding up. Gravity had somehow transformed from an attractor to a repeller, forcing matter to fly apart at an ever-faster rate. <br /><br />"I still recall feeling very excited—excited that it was true and also very anxious, because most things you discover in science are wrong," says Riess of the Space Telescope Science Institute in Baltimore. <br /><br />But with another team, led by Saul Perlmutter of the Lawrence Berkeley (Calif.) National Laboratory, coming to the same conclusion, astronomers had to accept—and even embrace—the notion that gravity has a flip side. <br /><br />Some kind of invisible, mysterious substance—which University of Chicago cosmologist Michael Turner dubbed dark energy—fills the universe, turning gravity's pull into a comic push. This mystery material, thought to pervade all of space, comprises 74 percent of the universe's mass and energy. <br /><br />Understanding dark energy "is the most profound problem in all of science," says Turner. Solving it even might unite qua

 

[richalex]

Astronomers were astonished to discover in 1998 that the expansion of the universe is happening at an ever-increasing rate. The mysterious repulsive force responsible for this was dubbed dark energy, though scientists still do not know what it is (see Dark energy: seeking the heart of darkness).<br /><br />Now, physicist Syksy Rasanen of CERN in Geneva, Switzerland, says we might not need dark energy after all. As counter-intuitive as it sounds, the increasing rate of expansion might be due to the collapse of small regions of the universe under gravity, he says.<br /><br />Gravitational brake<br /><br />Cosmologists have long assumed that the overall expansion of the universe is not affected by the properties of small regions within it, since these properties should average out on the largest scales.<br />But in any given region of space, the force of gravity between bits of matter acts as a brake on expansion. This means that expansion should slow down quickly in regions with lots of matter, while continuing without much change in mostly empty regions.<br /><br />It is this difference in the expansion rate between different regions that could produce the illusion of dark energy, Rasanen says. Strangely enough, even though the expansion rate decreases or stays about the same in every region, the average rate of expansion for the universe as a whole can increase.<br /><br />New Scientist: Is dark energy an illusion?

 

[primordial]

alokmohan ! Yes it does look like the cosmological constant is dependent on many unknown variables, as in the distribution of interactions, through entropy of this complex system. The article about the flow of gravitational diffused potential to a more concentrated isolated potential, may be such a step in the entropy of gravity, but could this affect the cosmological constant in the places where the gravitational density is less as a result of this change, presenting its self with the evidence we see in the inflation between the large systems. <br />