Sean Carroll

And I have a particular point of view that I put forward in –

the big picture and elsewhere, but people don't agree.

So I think that good philosophers are very careful when they use words like that to explain what sense they're saying that something is real or not.

Ontology is more clearly defined and more sort of uniformly used.

It's the set of ingredients in your most fundamental description of reality.

It's what exists according to that more or less physical version of reality.

Of course, if you're not a physicalist...

then your ontology might include supernatural beings and things like that.

But I don't think that most people include numbers in their ontology, even if they're mathematically realists.

That I'm not sure.

When you hear people say things like reality is a vector in Hilbert space, those people are more likely to be physicists like myself than real card-carrying philosophers.

Although, of course, I dabble back and forth.

And what that means is that reality, whatever it is, is exactly modeled, is exactly represented by a vector in Hilbert space evolving according to the Schrodinger equation.

Sometimes that sentence is shortened to just saying reality is a vector in Hilbert space.

And then I think there's some tedious discussion that happens about, well, are you saying that the mathematical structure is real or whatever?

Like, no.

That's not actually what is being said.

We're just trying to get through our day without having every single caveat attached to every single sentence that we say.

What we're trying to say is there's reality, physical world, and it is what it is.

It's not sort of expressible in terms of anything else.