As far as I can tell there can't be much science behind an assumption such as parallel universes. Such things cannot be proven in the near future as we cannot travel back in time and change a decision. It seems that the theory of parallel universes is based on the fact that by changing simple variables there are a near infinite amount of outcomes, however without means or scientific justification of backwards time travel it isn't possible to change variables and observe another outcome or change the universe you reside in. Even if we could travel back in time and change a variable it would be even less possible to return to "your" future and report the outcomes.