[hackinthebochs]

It's not about fields specifically, but about particular problems within fields. An example is neuroscience discovering the function of some unknown functional unit of the brain. We have all the conceptual machinery to solve the problem, we just need to fill in the details. On the other hand, the problem of consciousness doesn't even have the conceptual machinery in place such that more details will lead to the solution. A solution here will require conceptual leaps that we can't put a boundary on like we reasonably can when the conceptual groundwork is already established.

[mantap]

In mathematics the word used for these kinds of problems is "inaccessible", e.g. Reimann Hypothesis or (previously) Fermat'a Last Theorem. I don't know if Carmack's chances are as good as Wiles' were but certainly better than the average joe. It's also the case that AI is a substantially younger field (arguably it was only possible to correctly evaluate ideas since powerful GPUs were released this decade) and so the difficulty of open problems including AGI is not yet known.