Sean Carroll

We're trying to figure out how the actual world works.

And so I think that I'm happy to imagine all sorts of other worlds.

And the job of science is to figure out which one of those imaginations matches the world around us that we actually see.

Polina Vino says, can you explain what the classical limit is and how it's calculated?

Sure.

So in quantum mechanics, as you know, we have this idea that the world is described by a state.

That's a very vague way of saying things.

And it is a very vague way of saying things.

And it's intentional because it's very hard to talk about what the quantum state is without either being very mathematical sounding or being

prejudicing your physical view of what the quantum state is.

So here are two different ways of saying what the quantum state is.

One way is to say it's a vector in Hilbert space, okay?

That's what we were talking about earlier in the AMA.

So what that is simply saying is that we have this view of the fundamental ontology of reality

that we can represent mathematically in a certain way.

And there's a big old vector space, you know, either infinite dimensions or a very, very large number of dimensions, unless you're Daniel Harlow and you think it's one dimension.

But most of us think it's a very large number of dimensions, 10 to the power 10 to the 122, at least, or much bigger than that.

And it's a vector.

It's a little thing with a direction and an arrow with a length and a direction.

It's moving around in that space according to some law of physics.