Ever since my days of experimentation with hallucinogens (this was quite a few years ago), I've been highly skeptical of the notion that ours is the only universe. Whether all about us was born of the mind of God or of nothing, it always struck me as rather improbable that there aren't other variations on the theme somewhere. In fact, I've despaired at the thought that our universe, large as it may appear from our little cinder, may only be a tiny and unique piece of flotsam amidst an endless sea of timeless nothingness.
It was thus with considerable enthusiasm that I recently read Brian Greene's, "The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos", a heroic attempt to explain in terms comprehensible to minds as blunt as my own some of the most profound thinking of physicists, mathematicians and cosmologists on the subject of multiple universes. According to Greene, the existence of multiple or parallel universes, perhaps an infinity of them, is at least consistent with current and respected thinking in quantum physics, string theory, artificial intelligence, and other fields of science. This stuff ain't the monopoly of sci-fi writers anymore.
One of the many mind-bending ideas offered by the book is that, with the exponential growth of computing power, a trend which shows no signs of abating, we may in the foreseeable future be able to simulate universes on our computers. Further, if conscious intelligence is not inextricably dependent on our biological goo, simulated universes could be inhabited by intelligent, conscious creatures whose experience of reality is indistinguishable from our own. This is "Sim City" writ very large indeed. Any pimply faced adolescent gamer with a MacBook could step into the shoes of God.
Lest this wine get too heady, though, there is no guarantee we are not ourselves simulated creatures in a Sim Universe.
Not that it really makes all that much of a difference.