The Oneness Zone

Quintessence Is a Dynamic/Life is Random

What is the nature of the mysterious dark energy which is accelerating expansion of the Universe? In a recent study published in the Physical Review Letters, physicists are proposing two scenarios: thawing and freezing. In thawing, the expansion of the Universe should eventually come to a stop, and maybe even reverse. In "freezing", the acceleration should continue indefinitely. A new mission: the Joint Dark Energy Mission (JDEM) has been proposed by NASA and the US Department of Energy, and should be able to determine which of these two scenarios is correct.

Today's universe is expanding at an accelerating rate because dark energy counteracts the force of gravity. In the early universe matter was closer together, and gravity still slowed its expansion.

"The cosmological constant was a vacuum energy (the energy of empty space) that kept gravity from pulling the universe in on itself," says Linder. "A problem with the cosmological constant is that it is constant, with the same energy density, pressure, and equation of state over time. Dark energy, however, had to be negligible in the universe's earliest stages; otherwise the galaxies and all their stars would never have formed."
For Einstein's cosmological constant to result in the universe we see today, the energy scale would have to be many orders of magnitude smaller than anything else in the universe. While this may be possible, Linder says, it does not seem likely. Enter the concept of "quintessence," named after the fifth element of the ancient Greeks, in addition to air, earth, fire, and water; they believed it to be the force that held the moon and stars in place.

"Quintessence is a dynamic, time-evolving, and spatially dependent form of energy with negative pressure sufficient to drive the accelerating expansion," says Caldwell. "Whereas the cosmological constant is a very specific form of energy — vacuum energy — quintessence encompasses a wide class of possibilities."
http://arxiv.org/abs/astro-ph/0505494

posted by fusionlin @ 10:33 AM