eli5: “choice” in the Many Worlds theory.


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

It seems entirely unfair that a person and a universe springs into being in which they will be punished because of the good decision made by their counterpart in another universe.

Many Worlds has nothing to do with choices or consciousness or willpower or anything human.

In order to get normal, classical mechanics out of quantum mechanics, you need something called wavefunction collapse – in effect, a particle whose state was uncertain has (some part of) its state become certain upon measurement, with the result of the measurement reflecting that certain state. This is weird, because why would a fuzzy smeared-out thing suddenly become sharp when measured?

Many Worlds just says that it doesn’t – that, in fact, the world we see with definite states is just one possible state of us along with the rest of the Universe and that, like a particle whose position is uncertain, the Universe is in fact a smeared out combination of every such possible timeline. There are many yous in the same way that an electron can be in a mixture of different orbitals in an atom.

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.


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.

“Many Worlds” theory is not falsifiable and not even testable. Common sense tells us there is only one universe. Theories like these simply highlight the difficulty of using human language to try and describe certain aspects of physics, quantum mechanics, and the like.

Every time you flip a coin in a many worlds multiverse the universe splits into the potential outcomes. Heads, Tails, being most probable (But the coin can also land on its side lol). 6 heads (H, H, H, H H, H) is less probable than any combination of 3 heads and 3 tails as there is only 1 way to get 6 heads and many to get 3 heads and 3 tails eg. (H T H T H T), (H H H T T T)

Your choices are no different than the coin flips. Just more complex. Based on your personality, experience, physical body, certain things are more probable than others. An introverted, risk avoident accountant might sky dive, but it’s unlikely. However the probability isn’t zero.

If universes are truly infinite a universe exists where all coin tosses end with heads as the outcome. Heads, Always, all coin throws purely due to chance come up as heads. However universes with more typical coin flip outcomes would be much more common.

The universe you exist in is probably very average because it’s more common. Most your choices yield pretty normal outcomes. You win some you lose some but things will typically average out to your skill level etc (think chess rating).

If you deal in risky behaviors the probabilities on average will play out it you play them enough. If you deal with smart behaviors on average these behaviors will average out. Consistency is important.

On a side note. Our solar system is pretty average, our sun is pretty average.
If simulations exist. It’s unlikely that you would be the true world, but in a simulation, simulating a simulation, but you would be somewhere in the middle of the stack of simulations because that is most probable.