Today we often use the word "universe" in an offhand manner, usually for a laugh. "The universe played a trick on me today" or "the universe decided my car would break down." But what if we substitute "the" for "this"? What if the universe we joke about isn't the only one we can laugh about?
The idea isn't new. American physicist Hugh Everett III proposed in 1952 his "Many Worlds" theory, stating that many universes exist parallel to our own. In a version of his Princeton doctoral thesis that Everett published in a scientific journal, the physicist theorized that each time a situation exists with more than one possible outcome, a new universe is created to accommodate that situation. In that way, all potential outcomes are accounted for, and happening elsewhere. Therefore, each time we make a choice, the universe splits into parallel universes, and we actually make all of the possible choices we could have made, in different worlds, although we are aware of our choice only in our own world.
Everett's theory involved a quantum mechanics notion called "superposition," which basically says that a particle, such as an electron, can exist in billions of positions at the same time, but when measured -- when observed and interacted with -- it shows up only in one position. Everett said the person looking at the electron clones his or herself once for each of the billions of possible positions the electron could be in. The person will exist in multiple universes [source: PBS].
So while we have no definitive proof of universes beyond our own, the idea may not be as outlandish as it sounds. Everett's isn't the only theory out there, and perhaps someday other universes will be proved. For some, it may even be a comforting thought to know that even though we make wrong decisions from time to time, somewhere else there might be a copy of ourselves making the same decision and getting it right.
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