Sean Carroll

It is reality.

It's sort of unique in that way.

But it is represented mathematically as a vector in Hilbert space.

So any question you could ask about reality can be turned into a question about that vector in Hilbert space and how it evolves with time.

Now that's an especially simple version of ontology.

More complicated versions of ontology are also entertained by plenty of people.

And the question about high-dimensional classical phase space is very well put.

People argue about that, okay?

If I say, if I didn't know about quantum mechanics and I was a Newtonian physicist and I thought that the world was made of these particles moving in three-dimensional space.

They're N particles, capital N particles.

What is the ontology of that theory?

And someone might say, well, it's N point particles moving in three-dimensional space.

Someone else might say, actually, it's a single point in a 6n dimensional space.

That 6n dimensional space is the phase space for the whole system, the positions and velocities of every single particle.

I know that people actually do argue over which of those is a better description or more real or whatever.

To me, those are the same.

They're mathematically completely equivalent.

It's like saying, is Hamiltonian mechanics or Lagrangian mechanics real, right?

Or are numbers real when they're in base 10 or base 2?

It's just a translation from one point of view to another.