The voltage surge that happens in one of the two universes could cause some of the neurons in a passenger’s brain to misfire. As a result, in that universe, that passenger spills a cup of intergalactic coffee on another passenger. They then have a shared experience which they do not have in the other universe, which can lead to anything – maybe a romance or a new course of history. In fact, quantum theory states that every individual universe in the multiverse will have its own unique history