Multiverses and Many Worlds

Most recent answer: 10/30/2013

OK. So I have been reading some simple articles about String Theory and the whole Multiverse thing. OK so firstly lets make the assumption that there are Multiple Universes. My question is that when I hear this described/fictionalised it always comes from the perspective that each of these Multiverses exists because of choices we make in our Universe. So for example if I have eggs this morning some guy like me in another Universe is having cereal. So why are the two linked or is this just a misconception? Why do the two universes have anything at all to do with each other? If they do exist why do our choices have any bearing on what happens in another Universe? Sorry if this is over simplifying it!
- Jason (age 42)

It sounds like you've scrambled two different ideas. One is the multiverse idea. We don't really know the overall spacetime geometry in which our universe is embedded. There are theoretical reasons to suspect that there may be many universes connected together, sort of like bubbles in a foam. In fact, there might be infinitely many. In that case there would be ones just like this one, down to what's for breakfast, and all other major and minor variants as well.

The other is the Many Worlds interpretation of quantum mechanics. Since the basic time-dependence of quantum field theory is linear, a literal reading of the output of quantum processes would say that all of the possible quantum outcomes occur. If, despite the difficulty of accounting for the observed  probability rule for the outcomes, this interpretation is correct, one also gets an enormous range of different things happening in parallel.

Lenny Susskind has argued that somehow these two different parallelisms will be united in one picture, but for now we usually view them as two distinct possibilities.

In the multiverse picture I don't think there's any reason at all for the guy in the next universe to be systematically different from you. There's a similar extremely tiny chance that he's also having eggs as that he's like you but having cereal. No matter how tiny that chance, if you add it up over an infinite number of universes, it becomes a certainty to happen somewhere.

Mike W.

(published on 10/30/2013)

Follow-up on this answer