Sean Carroll

They didn't want to accept that.

And to be fair, they had a little bit of experience on their side, right?

No experimenter has ever felt like they were in a superposition, like that they had both measured the spin up and the spin down of some spinning particle.

You always seem to get a definite outcome.

And Everett's genius philosophical jujitsu move was to say the problem is not that you need to change the equations to add in this wave function collapse and whatever.

The problem is you have to think carefully about identifying yourself in the wave function of the universe.

And he said you should treat those two different parts of the wave function.

One says the electron is in box A and the observer saw it in box A.

The other says the electron's in box B and the observer saw it in box B. You should treat that as separate worlds.

You, the observer, are not the superposition of both of them.

You are one or the other.

And there's another observer who shares a past with you who is in the other thing that we call the other branch of the wave function.

So that's many worlds.

I didn't even mean to get into many worlds that much.

But the point is that the formalism of many worlds just says there are wave functions and they obey the Schrodinger equation.

Everything else is derived from that.

In the Copenhagen view, you postulate a whole bunch of other things.

You postulate the existence of something called measurement.

the wave function collapses, that there's a probability rule, the Born rule for how often they collapse, all this extra postulates.

And in Everett, you have no extra postulates.