Dark Energy

As you look up into the sky at the blackness beyond, you are totally unaware of the immense weight of energy permeating every inch of everything. It starts as a faint tickle on the back of your neck that soon runs down your spine giving you chills. You didn't realize it then, but you just came into contact with the greatest power in the universe, dark energy. In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding at an accelerating rate. In the standard model of cosmology, dark energy currently accounts for 73% of the total mass-energy of the universe. The nature of this dark energy is a matter of speculation. The evidence for dark energy is only indirect coming from distance measurements and their relation to redshift. It is thought 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. A recent survey of more than 200,000 galaxies appears to confirm the existence of dark energy, although the exact physics behind it remains unknown. This sound uses the following file from Freesound: http://www.freesound.org/samplesViewSingle.php?id=126173