Personally, I really don't buy it. To me, it seems fair more likely that either: 1) The universe is expanding but the explanation lies somewhere in the equations we already understand. 2)The universe is expanding and our theories need correction, but no new physical phenomenon that we label "dark energy" is actually at work. 3) Our observations, or the conclusion we've drawn from them, are wrong and the universe may not even actually be expanding at all. edit - when I say expanding, I mean expanding at an accelerating rate. I base my disbelief solely on philosophical intuition, but so long as no real explanation for what dark energy could be exists, then I think that's a fair way of addressing it. It troubles me deeply that we talk about dark energy as if it is a concretely proven phenomena, yet we have no real basis for even believing it exists, other than if we don't know the answer, it's easier to just invent an explanation. To me that isn't science, that's myth making. To this effect, I'm also doubtful about dark matter. Not that there is unseen matter out there which has a gravitational effect, but the idea that dark matter is some unknown type of matter we've never seen before.