I'll have to come back. Short of time. But this is interesting. Haven't had time to get click the links yet.

Tim, very briefly. Dark Matter is proposed to account for observations regarding gravtational lensing and galaxy rotation, and is said to comprise something like 90% of all the matter in the universe.

Dark energy is proposed as a force that accounts for accelerating expansion of space.

"Time is what prevents everything from happening at once" - John Wheeler