I'm no cosmologist and my understanding of dark energy is probably below that of a layperson's. But I'm misunderstanding not only what dark energy is (which apparently nobody understands), but even the concept of it. The main thing I don't get is that they say it makes up ~70% of the mass/energy of the universe, because I guess that's how much energy is required to accelerate the galaxies away from each other. However, my understanding it that the galaxies are NOT accelerating away from each other...just that the expansion of space between them is. Does this mean that if I expanded the space between two objects, would that require the same energy as simply moving the two object apart by the distance of the expansion? That doesn't seem right...from lay-reading of the big-bang, inflation, and proposed Alcubierre drives, I didn't think that expansion of space required any energy.