After having researched on many different Websites the Many Worlds Interpretation of Quantum Mechanics, it seems to me as if there are two positions defended by physicists: Position 1: All the outcomes of a system actually happen in reality. That is, every time a choice is made all possible choices are actually realised and these branch off into alternate Universes to create the multiverse. Position 2: All the outcomes of a system can happen in reality but only the most probable outcome (I think this is given by the sum-over-histories approach) happens in reality so that although it is possible that all these alternate Universes can be created the only existent Universe is the one we live in (i.e. there is no multiverse in reality). An article that helped me to come to this conclusion is one titled "Multiverses and Blackberries" by Martin Gardner. It can be viewed online here: http://www.csicop.org/si/2001-09/fringe-watcher.html [Broken] I would appreciate any help and any clarification needed, as I find this MWI quite confusing!