The Principle of Mediocrity
  Recent developments in cosmology suggest that much of the universe is in a state of explosive, accelerated expansion, called inflation. We live in a "bubble" where inflation has ended, and other bubbles with diverse properties are constantly being formed. Most, if not all, of these bubbles are beyond our cosmic horizon and cannot be directly observed. I discuss the origin of this new worldview, its possible observational tests, and its implications for the beginning and the end of the universe. 
Alexander Vilenkin
hep-th astro-ph.CO gr-qc