Sunday, October 4, 2009
"The exact nature of dark energy is a matter of speculation. It is known to be very homogeneous, not very dense and is not known to interact through any of the fundamental forces other than gravity. Since it is not very dense — roughly 10−29 grams per cubic centimeter — it is hard to imagine experiments to detect it in the laboratory. Dark energy can only have such a profound impact on the universe, making up 74% of universal density, because it uniformly fills otherwise empty space. The two leading models are quintessence and the cosmological constant. Both models include the common characteristic that dark energy must have negative pressure.
"Negative pressure does not influence the gravitational interaction between masses - which remains attractive - but rather alters the overall evolution of the universe, typically resulting in the accelerating expansion of the universe despite the attraction among the masses present in the universe."