The universe, it turns out, may be the most provincial notion of all. The latest cosmological evidence suggests that our universe is one among many universes. Within this multiverse, there will be universes, like our own, hospitable to intelligence, and among these, as one physicist explains, "there will be some in which technological civilizations advance to the point of being able to simulate consciousness. Eventually, entire virtual worlds will be created inside computers, their conscious inhabitants unaware that they are the simulated products of somebody else's technology. For every original world, there will be a stupendous number of available virtual worlds -- some of which would even include machines simulating virtual worlds of their own, and so on ad infinitum." Within such a multiverse, there is no reason to suppose that you are real and not a simulation.