So here's what I'm perplexed about. There are statements in Presburger arithmetic that take time doubly exponential (or worse) in the size of the statement to reach via
any path of the formal system whatsoever. These are arithmetic truths about the natural numbers. Can these statements be reached faster in ZFC? Possibly—it's well-known that there exist shorter proofs of true statements in more powerful consistent systems.
But the problem then is that one can suppose there are also true short statements in ZFC which likewise require doubly exponential time to reach via any path. Presburger Arithmetic is decidable whereas ZFC is not, so these statements would require the additional axioms of ZFC for shorter proofs, but I think it's safe to assume such statements exist.
Now let's suppose an AI model can resolve the truth of these short statements quickly. That means one of three things:
1) The AI model can discover doubly exponential length proof paths within the framework of ZFC.
2) There are certain short statements in the formal language of ZFC that the AI model cannot discover the truth of.
3) The AI model operates outside of ZFC to find the truth of statements in the framework of some other, potentially unknown formal system (and for arithmetical statements, the system must necessarily be sound).
How likely are each of these outcomes?
1) is not possible within any coherent, human-scale timeframe.
2) IMO is the most likely outcome, but then this means there are some really interesting things in mathematics that AI cannot discover. Perhaps the same set of things that humans find interesting. Once we have exhausted the theorems with short proofs in ZFC, there will still be an infinite number of short and interesting statements that we cannot resolve.
3) This would be the most bizarre outcome of all. If AI operates in a consistent way outside the framework of ZFC, then that would be equivalent to solving the halting problem for certain (infinite) sets of Turing machine configurations that ZFC cannot solve. That in itself itself isn't too strange (e.g., it might turn out that ZFC lacks an axiom necessary to prove something as simple as the Collatz conjecture), but what would be strange is that it could find these new formal systems efficiently. In other words, it would have discovered an algorithmic way to procure new axioms that lead to efficient proofs of true arithmetic statements. One could also view that as an efficient algorithm for computing BB(n), which obviously we think isn't possible. See Levin's papers on the feasibility of extending PA in a way that leads to quickly discovering more of the halting sequence.