An astrophysicist explains the often-misunderstood nature of dark energy

Produced and directed by Corey Eisenstein. Click here for transcript. (video link)

Ars' Edge of Knowledge series looks at important aspects of our Universe that we still understand poorly, like dark matter and the origin of life. This week, our host Paul Sutter bravely ventures into the area we probably understand the least: dark energy. Dark energy accounts for about 75 percent of the stuff in the Universe, but we still don't have even the slightest idea what it is and are a bit stumped as to how to even go about finding out.

Paul goes into how we accidentally discovered that the Universe's expansion is accelerating when astronomers looked for an indication that the expansion was slowing down. Dark energy is simply the term we're using for the big unknown here: What's driving that acceleration?