Possible fates of the Universe, computer illustration. Astrophysicists envisage four possible fates for the Universe in the distant future (clockwise from top left): closed, flat, open low-density and open high-density. In these schematics the Universe is represented as a 2-dimensional surface opening out from a point, somewhat like a funnel. The green line represents where we are now. In a closed universe, with positive curvature, it will collapse in an infinitely hot, dense singularity in a reverse of the Big Bang (???ig Crunch??scenario). In a flat scenario, the universe expands forever, asymptotically, slowing down but never quite stopping. And in an open universe, the universe expands forever accelerating as it does. If the density is higher than a critical value, the future acceleration will cause it to tear itself apart in what has been called the ???ig Rip??