“As an analogy one can imagine an intelligent amoeba with a good memory. As time progresses the amoeba is constantly splitting, each time the resulting amoebas having the same memories as the parent. Our amoeba hence does not have a life line, but a life tree.” -Hugh Everett
We only have the one Universe, despite all the quantum possibilities out there. We have to accept that, at a fundamental level, the Universe is indeterminate, and that the act of measuring — or otherwise making a quantum decision — selects which quantum path our Universe takes. But according to the many-worlds interpretation of quantum mechanics, every quantum possibility that can happen does happen, just somewhere else. The key necessity for this interpretation is a large enough, perhaps even infinite number, of parallel Universes.
The multiverse idea states that there are infinite numbers of Universes like our own, and infinite ones with differences. Image credit: Lee Davy of flickr.
This might seem absurd, given the sheer number of interactions and particles present in our Universe over its 13.8 billion year history. But as large as that number is, it’s still finite. And perhaps the Universe is infinite. Or perhaps it’s finite, but it’s been around for an infinite amount of time. Or perhaps it’s finite in both space and time, but old and large enough that parallel Universe are still real… for now.
Even though inflation may end in more than 50% of any of the regions at any given time (denoted by red X’s), enough regions continue to expand forever that inflation continues for an eternity, with no two Universes ever colliding. Image credit: E. Siegel.