Canute said:
It is my opinion that they are G-sentences, undecidable within any formally consistent system of reasoning, but it would take a few thousand words to attempt a proof, and I don't know whether I could make it stick.
Heh, I'm in the same boat, in a sense that what I stated is also my opinion and that it'd take a few thousand words to attempt a proof, even though I believe I know how to proceed with it. I'm not saying you're wrong, and I believe your sources have a lot of merit. I'm just stating there's some inconsistency with my understanding of Godel and I wanted to contribute to this discussion to keep it more informative and detailed.
I hope we're going to avoid coding natural language into binary strings here but, as I said in my early post, I don't believe the metaphysical statements presented here are undecidable. Let me take another shot, but this time in a little more detail.
How did Godel prove incompleteness? He mapped natural language to an axiomatic arithmetic system. He then translated, I believe, a version of Liar’s paradox – “this statement is not provable” or “the statement on the other side of the page is not true….” into this arithmetic system. He thus produced a mathematical version of the Liar paradox. Note, it’s the same kind of contradictory paradox you’re referring to when discussing materialism. The translation is a statement G that says “G is not provable”. So, you have If G is provable, it is not provable, a contradiction. However, if G says it is not provable and it really is not provable, then G is true, but not provable. The first choice makes the system inconsistent, that’s not what we want, so logicians settled for the second choice. The proof is quite interesting and not that complicated but requires focus, in case you haven't indulged yourself yet. Anyhow, the bottom line is the Liar paradox is translatable into a finite formal language, and thus into a finite binary string that can be accepted or rejected by a Turing machine! Let me give you an analogy. Nobody proved Golbach’s conjecture (every even number above 2 is a sum of two primes). However, I can say, let’s define number P as 67 if Golbach’s conjecture is true, and P is 97 if the conjecture is false. We know the number exists, we just don’t know which one it is! Similarly, I can feed the conjecture into 2 Turing machines, one that accepts all input, the other one that rejects. One if them might have the solution, but we don’t know which one. That’s Godel’s G statement. Note that the conjecture, just like the paradox can be coded into a finite binary string. This class of statements is considered to be decidable!
Now, consider the famous Halting problem – is there a general algorithm that can determine if a Turing machine will halt on a given input. Think about it, the general algorithm is a Universal Turing Machine (UTM) that accepts as its input a pair of strings – one is the Turing machine to be tested, the other - that machine’s input binary string. But there is an infinity of the input binary strings and Turing machines. So, the input to the UTM is an infinite set of strings, meaning there’s no effective way to determine if the UTM will halt or not. If you changed the problem to a specific pair of strings, not general, the problem would be decidable. Well, it depends on the nature of the input string to the machine under test. If it’s infinite, like in your infinite regress with causality example, the situation gets convoluted, at least for me, because you start dealing with countable infinity, Cantor set and the whole continuity problem. And speaking of which, here’s another good example of undecidable statement – the continuity hypothesis (uncountable infinity of real numbers “between” a pair of rational numbers, which in their turn form a countable infinity line). Godel proved that the assertion of the hypothesis is consistent with an axiomatic set theory. In fact, I think he made it an axiom, but then Cohen came along and proved that the negation of the hypothesis is also consistent with the set theory. So, now you have truth and negation of the same statement consistent within the same axiomatic system! This is not the same assertion and negation of idealism because it’s unfalsifiable. If translated into formal language, I’m certain the negation will be inconsistent with its assertion, but please don’t make me do it, it’ll be quite a home work.
Canute said:
Funnily enough I believe this can be done. But only by creating a formal system which has a (formally) undecidable axiom its heart (one that is formally acknowledged to be undecidable), and which embodies (apparent) contradictions. This is the epistemilogical structure of Buddhism, Taoism, and so on.
But are you sure such system will be consistent? I'm not familiar with Buddhist and Tao epistemological structure, they have a consistent system?
Canute said:
However, roughly speaking, it's very similar to the epistemilogical system used in QM, in which the question of whether a wavicle is a particle or a wave is undecidable, and two complementary/contradictory formal systems arise as a result, one in which they are waves, one in which they are particles.
Somehow I considered QM simply to show that waves and particles are not mutually exclusive but there's really no undecidability about it. The only other thing I thought was that QM showed to intuitionists that a number can exist even if there is no way to construct it, until you prove it, just like the position of an electron is unknown, until you look. If anything, there's an existence of possible
physical worlds, but without corresponding formal systems accompanying each one of them. That's how I view it, but to be quite honest, I'm not that sure about it, as I haven't given it too much thought

What's the general consensus among the logicians?
Pavel.