1) Be sufficiently large that quantum effects are irrelevant, like a billiard ball, and thus it can be modeled deterministically inside of a computer. The Tegmark paper proposes this is how the brain works.
2) Rely on quantum mechanical effects (which are non-deterministic, but can still be simulated inside a computer if you trust a computer's opinion of "random"). Penrose, Searle, etc. would argue otherwise, that there's a method to the madness, and that there's something "special" about the quantum mechanical effect on microtubules. We still don't understand quantum mechanics very well, so if human consciousness really relies on quantum mechanics, there is arguably a bit of wiggle room here, especially if you're a physicist of the same caliber as Penrose.
Microtubules are specifically of interest because they're one of the few brain structures small enough to arguably be subject to quantum mechanical events.
Tegmark argues that they're not small enough and that it's irrelevant.
The real question is:
Is it possible to simulate a brain within a computer?
- not -
Is it really hard? Is it too hard for modern technology? Is this problem simply too complex for us to understand? Do we lack the technology to build sufficient understanding today? Etc. Etc.
This article is claiming it's IMPOSSIBLE to simulate a brain within a computer. Proving that is a tall order.
