The fate of the Universe theory:

"Dark energy is making the expansion of the Universe accelerate. If this continues-and there is no reason to think it will not-the expansion will get faster and faster as time passes. At first, it will not directly affect matter. Within galaxies, stars will still be born, live out their lives, and die. However, as the stuff from which the stars are made is used up, galaxies will get fainter, and more matter will be locked up inside various forms of dead stars-white dwarfs, neutron stars, and black holes.
But, while all this is going on, clusters of galaxies will be moving apart faster and faster, disappearing from each others view. Our own Milky Way galaxy is part of a small cluster know as the Local Group. Within a couple of hundred billion years, there will be nothing visible outside this cosmic archipelago.
Eventually, space will be expanding so fast that it will overcome gravity and other forces, and material objects will get torn apart. The result will be a rapidly expanding space in which matter has been spread so thin that it is essentially empty-ideal conditions for the birth of one or more new universes through inflation."