eli5: “choice” in the Many Worlds theory.

Question

From what I’ve read, according to the Many Worlds theory, every time I make a choice, a new universe springs into being in which I make a different choice. But what constitutes a choice? Does it have to be a conscious, binary choice? For example, there are a large number (infinite?) of things I’m NOT doing right now, including running around my workplace naked except for clown makeup. Does that mean that there’s a universe in which I am doing that? And am I just getting lucky to keep ending up in the universe in which I’m behaving well? Or does the theory only apply when I have to actually consider what to do next? (Until now I’ve never considered running around naked at work with clown paint on).

In: 8

Answer 1

It’s not about choices, and it’s not on a macro level like that.

Journalist and science communicators talk about it like that because it makes sense to a layperson, but it’s really not that accurate.

It’s much *much* smaller scale than that. Like individual atoms bumping into each other.

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When people talk about the “many worlds theory” what they are referring to is the “many worlds *interpretation* of quantum mechanics”. I pointed out the word “interpretation” there because it’s not really a theory. The math doesn’t tell us this is true, and we have no way of testing it (as far as I know). But it’s one way to *interpret* what might be going on.

What MWI says is that there is no *wave function collapse*. You can probably already see why science communicators are oversimplifying it. Because now you need to understand what a wave function is.

But basically (this is *also* going to be not entirely correct but hopefully less incorrect than what you have heard before) in quantum mechanics we can never know the exact position and velocity of a particle until it interacts with another particle. But what we can do is describe where it probably is and what it’s most likely to be doing. This is called the wave function, it’s basically a list of all the possible states the particle could be in. Like “moving quickly coming for the left, Moving slowly coming from the top.”

Once that particle interacts with another we know where it is at that moment. There is no longer a wave function.

So what MWI says is that there is a universe out there for every single one of the state that wave function said it could be in.