The 'many worlds' theory

This theory holds that every time an action is taken in the Universe which could have different outcomes, the Universe splits into as many Universes as there are outcomes, with each outcome having occured in a different Universe.

This is one way of interpreting the meaning of the probabilistic nature of the wavefunction of a particle in quantum mechanics. By assuming that every possible outcome occurs in some Universe or other, some form of 'interference' between Universes leads to many confusing quantum effects.

In the Multiverse, these many worlds are only a step away from others, and some people seem to have an unusual talent from stumbling across portals to another world whilst involved in the most ordinary of activities.