The New York Times Science section features a nice article looking at one of the odder speculations of cosmology--the Boltzmann brain hypothesis. As the Times reports:
It could be the weirdest and most embarrassing prediction in the history of cosmology, if not science.
If true, it would mean that you yourself reading this article are more likely to be some momentary fluctuation in a field of matter and energy out in space than a person with a real past born through billions of years of evolution in an orderly star-spangled cosmos. Your memories and the world you think you see around you are illusions.
This bizarre picture is the outcome of a recent series of calculations that take some of the bedrock theories and discoveries of modern cosmology to the limit. Nobody in the field believes that this is the way things really work, however. And so there in the last couple of years there has been a growing stream of debate and dueling papers, replete with references to such esoteric subjects as reincarnation, multiple universes and even the death of spacetime, as cosmologists try to square the predictions of their cherished theories with their convictions that we and the universe are real. The basic problem is that across the eons of time, the standard theories suggest, the universe can recur over and over again in an endless cycle of big bangs, but it's hard for nature to make a whole universe. It's much easier to make fragments of one, like planets, yourself maybe in a spacesuit or even — in the most absurd and troubling example — a naked brain floating in space. Nature tends to do what is easiest, from the standpoint of energy and probability. And so these fragments — in particular the brains — would appear far more frequently than real full-fledged universes, or than us. Or they might be us.
This kind of thing can make Plato's Theory of the Forms look reasonable. Of course, Jim Holt reports that when he asked a group of elite mathematicians how many of them are Platonists, three-quarters held up their hands.
Enjoy the Science Times article here.
Addendum: Besides Plato's speculations, there is always Hindu cosmology. As the Hindu Wisdom website explains:
Prior to the creation of the universe, Lord Vishnu lies asleep on the ocean of all causes. He rests upon a serpent bed with thousands of cobra-like hoods. While asleep, a lotus sprouts from His navel. Upon this lotus is born Brahma the creator of the universe. Lord Brahma lives for a hundred years and then dies, while Lord Vishnu remains. One year of Brahma consists of three hundred and sixty days. At the beginning of each day Brahma creates the living beings that reside in the universe and at the end of each day the living beings are absorbed into Brahma while he sleeps on the lotus.
FYI, the calculation for Brahma's 100 year lifetime in divine terms is 311,040,000,000,000 years.