In 1954, a doctoral candidate at Princeton University named Hugh Everett III came up with a radical (全新的) idea. There exist parallel universes, exactly like our universe. These universes are all related to ours; indeed, they branch off (分支) from ours, and our universe is branched off of others. Within these parallel universes, our wars have had different results than the ones we know. Species that are extinct in our universe have evolved and adapted in others.