Hi guys, I'm a bit confused. The initial motivation for including dark energy seems to be: "The Friedmann equation requires a flat universe to have a mass/energy density exactly equal to the critical density. Yet, observationally, including both the baryonic and dark matter, we can only find less than a third of this value." So a dark energy term is added so the universe can be flat. But then they say the dark energy has negative pressure and so is responsible for expansion which would result in an open universe! So they put in something to make the universe flat, then give it the characteristic which would result in an open universe. So the dark energy is not going to result in a flat universe after all. So what's that all about?? Thanks a lot.