Sean Carroll

I've often said that many worlds is not mostly about the worlds.

The worlds come along.

They're there, no doubt.

But what Many Worlds is really about is saying there's no such thing as collapse.

There's no such thing as a special cordoned off concept of measurement in quantum mechanics.

There's just the Schrodinger equation, letting the wave function evolve as it will.

And Everett's brilliant idea was if you count the observer as part of the quantum system,

you get a very different answer than the Copenhagen story.

And again, people like Heisenberg and Bohr, they're not dummies.

They're very, very smart people who thought about this stuff really, really deeply and carefully.

And they knew that if you treated the observer as part of the quantum system, you were going to quickly go down a very strange road.

Because what happens is when the observer measures the electron, let's say, let's say, forget about the proton, okay?

Let's say you have an electron that's in a superposition of,

box A and box B. So there's no such thing as where the electron really is.

You can solve the equations for what happens when an observer measures the position of the electron.

And what you get is a superposition of the combined system of electron and observer.

No one disagrees with this, like the solving the equations is not something that you have optionality about, okay?

The equations are what the equations say.

So if you solve the Schrodinger equation, when you measure the position of the electron, the wave function of the universe turns into a quantum superposition of the electron was in box A and the observer measured it in box A, plus the electron is in box B and the observer measured it in box B.

People like Bohr and Heisenberg didn't want to put up with that.