Sean Carroll

Ooh, now you're getting deep.

So I like it because you're invoking not what the system is, but counterfactual properties of what would happen to the system if you changed it a little bit, which is fine.

It's a fine thing to do.

Look, you're absolutely right that there is no pre-existing definition of the word nothing to which we're referring here.

You could have different ideas.

I think at the deepest level of this question,

is why is there a universe at all versus complete non-existence, not even space?

I mean, even you had to preface your question by saying, like, imagine there was no quantum mechanics.

And for that matter, secretly imagine there's no general relativity either because... Okay, yeah.

You're throwing away all of known physics to even ask your question.

But of course, within known physics, you can ask plenty of questions about why isn't space empty?

Why is space three-dimensional?

Those are perfectly good physics questions.

It's a little bit different than the question of why there's a universe at all.

You can ask both of them separately.

It's not a right or wrong thing to ask.

Right.

Yeah.

All right.

Yeah, there's a science answer here and a philosophy answer here.