But then what's the difference between a brain and, say, a rock, in this case? Both exist in this world, and neither is external. Can we therefore not understan

But then what's the difference between a brain and, say, a rock, in this case? Both exist in this world, and neither is external. Can we therefore not understand or do a full simulation of a rock? Not being sarcastic here, genuinely curious what you think and why. edit: Oh, I think I understand a bit more now: we're not talking about creating a simulation of "a brain", but a simulation of a specific brain, and whether that's still the same "person" as the original person the brain belonged to. That's a very different discussion.