posted on Jul, 12 2005 @ 09:27 AM
Implications for the fate of the universe
Cosmologists estimate that the acceleration began roughly 5 billion years ago. Before that, it is thought that the expansion was decelerating, due to
the attractive influence of dark matter and baryons. The density of dark matter in an expanding universe disappears more quickly than dark energy, and
eventually the dark energy dominates. Specifically, when the volume of the universe doubles, the density of dark matter is halved but the density of
dark energy is nearly unchanged (it is exactly constant in the case of a cosmological constant).
If the acceleration continues indefinitely, the ultimate result will be that galaxies outside the local supercluster will move beyond the cosmic
horizon: they will no longer be visible, because their relative speed becomes greater than the speed of light. This is not a violation of special
relativity, and the effect cannot be used to send a signal between them. (Actually there is no way to even define "relative speed" in a curved
spacetime. Relative speed and velocity can only be meaningfully defined in flat spacetime or in sufficiently small (infinitesimal) regions of curved
spacetime). Rather, it prevents any communication between them and the objects pass out of contact. The Earth, the Milky Way and the Virgo
supercluster, however, would remain virtually undisturbed while the rest of the universe recedes. In this scenario, the local supercluster would
ultimately suffer heat death, just as was thought for the flat, matter-dominated universe, before measurements of cosmic acceleration.
There are some very speculative ideas about the future of the universe. One suggests that phantom energy causes divergent expansion, which would tear
apart the Virgo supercluster ending the universe in a Big Rip. On the other hand, dark energy might dissipate with time, or even become attractive.
Such uncertainties leave open the possibility that gravity might yet rule the day and lead to a universe that contracts in on itself in a "Big
Crunch". Some scenarios, such as the cyclic model suggest this could be the case. While these ideas are not supported by observations, they are not
ruled out. Measurements of acceleration are crucial to determining the ultimate fate of the universe in big bang theory.
Wikipedia: Dark Energy
A couple other things you might find interesting:
Wikipedia: Hubble's Law
Wikipedia: Dark Energy Star
hope that helps
[edit on 12-7-2005 by swordsaint]