Please Help Me!!

[mooberrymarz]

:cry: HEYA. wOTS THE DENSITY PARAMETER/OMEGA.?? I DONT REALLY UNDERSTAND WOT IT IS... AND IF U GUYZ COULD SEND ME ANY USEFUL LINKS ON THE EXPANSION OF THE UNIVERSE, IN REGARDS TO DARK MATTER... THAT WOULD BE HELPFUL. CHEERS ALL. :biggrin:

[wolram]

Average density of mass in U to the critical density.

Omega>1 bound U
Omega<1 unbound U
Omega =1 balanced U
Bound U = big crunch
Unbound U =expands forever
balanced U = expands forever but expantion slows

[Phobos]

The contents of the universe affect the fate of the universe. Omega is a ratio of the contents to the balance point of very different fates (as explained by wolram). If there is a lot of stuff (and therefore a lot of gravity), the universe will be "closed"...the ongoing expansion would eventually stop and collapse back on itself. If there's a lot less stuff, then the expansion will go on forever. There's more to it, but that's the basic idea.

[meteor]

balanced U = expands forever but expantion slows

This is not correct, as the actual universe has omega=1, but is supposed that the expansion is accelerating.
When there wasn't thought that a thing like dark energy could exist, then omega=1 really meant an slowing of the expansion. But if you insert dark energy in the formula, then omega=1 can mean an accelerated universe, like is the actual case.
All the books written until 1997 really say "Omega=1 means an slowing of the expansion", perhaps your confusion comes from here