Having searched the internet vigourously, i have yet to find a satisfying description of how we can know about the existence of either Dark Matter or Dark energy.
It is frequently reasured that we neither know what dark mater and dark energy are, and have yet to prove there existence. As far as i can find out, the only thing telling me, and other inquisitive people, about how we know there is Dark matter and Dark Energy is a graph on wikipedia:and nemorous comments saying that dark energy is the cause of the unerverse expanding.
Whilst i recognise that there is no proof for dark energy, I beleive that there must be some foundation onto which the idea of Dark Matter and Dark Energy is based, as it can not possibly be that someone said "hey, i know what, I'll say theres this weird stuff that can't be seen or obsevered and i will call it dark energy, and i will say that it makes up 70% of the universe" - this just doesnt seem plausible...