Every object in the observable universe is either expanding away from every other object or falling into it, or both. The expansion of the universe causes distant objects to recede from each other at an accelerating rate, while gravity pulls objects together. The ultimate fate of the universe depends on the balance between these two forces. If expansion wins, the universe will eventually become a cold, dark place as all stars burn out and black holes evaporate. If gravity wins, the universe will eventually collapse back into a singularity.
