Now that scientists are fairly settled on the theory of the Big Bang, they've turned their attention to how they believe the universe is most likely to come to an end - and the options don't sound too appetizing.
One model, termed the Big Crunch, speculates that when gravitational forces within the universe reach their outermost limit, they'll simply collapse back on themselves and shrink with incredible speed and force, condensing everything the universe contains into one microscopically tiny point, before ceasing to exist completely. The other option, the Big Rip, doesn't really hold all that much appeal either. This theory posits that the universe will eventually reach a heat death - a point where thermodynamic activity ceases and gravitational bonds fail. Eventually even the particles in atoms would lose their bond and simply float away from each other, as everything dissipates to nothing. On the plus side, this isn't scheduled to occur for billions upon billions of years, so neither we nor you will be around to see it.