Agobot writes:
Why do we have to have Dark Energy to explain the expansion of the universe?
I don't think anyone has given you a clear enough answer yet.
First of all, you need to know a couple bleedingly obvious facts.
(1) The universe is expanding at an accelerated rate.
(2) There isn't any force that we know of that could account for such a universal acceleration.
In order for all the matter in the universe to accelerate like that despite the force of gravity being present, there needs to be some kind of energy responsible for it. Hence, we call it
dark energy. It's sort of like dark matter. We don't know what the hell it is but we sure as hell could see what it's doing to our universe.
The best suggestion I've heard is that perhaps the universal accelerated expansion of the universe is caused by the virtual particles popping in and out of existence. The total combination of all this causes an outward "pressure" that is enough to cause everything to expand.
I'm trying to see things your way, but I can't put my head that far up my ass.