That depends. If there is enough matter in the universe (and currently there doesnt appear to be ) then mutual gravity will pull the universe back together in what will be "the big crunch." However, with the discovery of dark energy, whatever it is, it appears to be overpowering the pull of gravity so that the universe will die a cold, dark, and very lonely death. In other words, dark energy will cause the universe to expand forever. Boohoo.