Have you ever wondered how different your life would be if you had made different decisions? H You may never know what may have been, but incredibly, all those ‘what if’ scenarios may have played out somewhere. Over the past few years, support for the idea that we live in a ‘multiverse’, in which our universe is just one tiny bubble among countless others, has been gaining strength.
For many people, the term ‘multiverse’ conjures up pictures of parallel realities, some with just a slight difference from our own. And that sort of multiverse is indeed predicted by the ‘many worlds’ interpretation of quantum mechanics – the strange but highly successful model of how the universe works on the smallest scales – wherein every possible quantum state branches off into a new universe. In other words, every action that is physically possible, every choice that can take place, can happen and will happen, somewhere.
Such parallel universes might exist, and evidence for this ‘many worlds’ interpretation of quantum mechanics that invokes them might one day be found, but they would be forever unobservable, separated from our universe in ways we can hardly comprehend. Cosmologists like Matthew Kleban are instead interested in a more concrete form of multiverse – something beyond the realm of our current universe, but which we might nevertheless learn about. “We have a horizon in cosmology that’s a lot like the horizon on Earth,” explains
