writes "Discover magazine has an interesting article on the multiverse theory — a synthesis of string theory and the anthropic principle that explains why our universe seems perfectly tailored for life without invoking an intelligent creator. Our universe may be but one of perhaps infinitely many universes in an inconceivably vast multiverse. While most of those universes are barren, some, like ours, have conditions suitable for life. The idea that the universe was made just for us — known as the anthropic principle — debuted in 1973 when Brandon Carter proposed that a purely random assortment of laws would have left the universe dead and dark, and that life limits the values that physical constants can have. The anthropic principle languished on the fringes of science for years, but in 2000, new theoretical work threatened to unravel string theory when researchers calculated that the basic equations of string theory have an astronomical number of different possible solutions, perhaps as many as 101,000, with each solution representing a unique way to describe the universe. The latest iteration of string theory provides a natural explanation for the anthropic principle. If there are vast numbers of other universes, all with different properties, at least one of them ought to have the right combination of conditions to bring forth stars, planets, and living things."
So far xkcd is simulating just one single universe