I was thinking of an idea in my head about a week ago, but it would need the rate of the expansion of the universe to increase over time (this is different from it just expanding at a constant rate). Today, i was reading about dark matter and it had stated that it might be the reason why the rate of expansion is increasing. Can someone clear things up? Is the rate increasing or is the universe expanding at a constant rate and is there already a confirmed explanation to this? Thanks in advanced!