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Alexander Prähauser's avatar

To be honest, I think Russell's paradox is, well, over-hyped. It's not that hard to avoid, just don't allow the forming of arbitrary subsets of classes.

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Alexander Prähauser's avatar

This isn't enough for a whole new post, but the main error you're committing is in the step of your reasoning where you argue that the entire universe could not be represented because representation requires differentiation. There are several components to this error:

- Representation does not require differentiation, only representiation of parts of a non-trivial system does. If we assume the surrounding context of the one-element set, every inhabitant of it can be represented with only one symbol and without being differentiated from one another. It's just not very interesting to do so.

- You're conflating the physical universe with a more general mathematical universe (which you have to assume exists to disprove my point from its premises, or simply to have a coherent physical theory). The physical universe is represented by one symbol all the time by physicists, usually in the form of a sentence like "Let X be spacetime…".

- Russell's paradox is only valid in regards to sets. In Von Neumann–Bernays–Gödel set theory, for instance, the "set of all sets" is not a set but a class, for which not all subsets can be taken. In such a context, it is not problematic whatsoever to assign to this universe a symbol, say U, and treat it just like a set, with only a slight number of additional restrictions of what can be done with it (namely not taking arbitrary subsets). The fact that ZFC is still used as the standard set theory, and not NBG or something better, is mostly due to institutional inertia. However, even in set theory using ZFC, the universe of sets is regularly signified by set theorists, though, depending on their metaphysics, if you were to press them they would say that they are using it as a shorthand. Lastly on that point, if we assume the existence of a class of all sets U, this class can still be differentiated from any other set or class X simply by the fact that X is contained within U but U is not contained within X. So simply because something contains everything that does not mean that it cannot be distinguished. It is also not clear how valid Russell's paradox remains if a paraconsistent logic is used, but I wouldn't hang my argument on that, it is perfectly plausible that no paraconsistent logic can be devised in which Russell's paradox could occur and which would still be rich enough to allow for the existence of the physical universe.

- It is not necessary to assume one final mathematical universe to treat the physical universe as a mathematical object, it can just be one node in an infinitely increasing network of connected nodes. Among category theorists, usually a framework of "Grothendieck Universes" U_i is assumed, where U_i contains all sets one size smaller and is in turn contained in U_{i + 1}. So U_0 contains all small sets, U_1 contains U_0 along with all small sets and all sets one size larger, which would appear as classes from the perspective of U_0, and so on. In fact, I do assume the existence of an "∞-category of ∞-categories", but only as shorthand for a pattern in such a hierarchy: there is an ∞-category of small ∞-categories, an ∞-category of next-larger ∞-categories and so on. In praxis however, one finds that very little changes as this size increases, the only thing to look out for is to not allow for constructions that would allow for something like Russell's paradox to occur.

I will also say that I don't find any of the variants of the Quine-Putnam indispensability argument addressed satisfactorily. Now, you are quite right in saying that I'm drawing from "string theory" (more precisely M-theory), which is not experimentally verified, which matters very little to me but does to you. What is experimentally verified (though not true) is the standard model however, as well as Einstein's relativity theory (whether special or general), which are gauge theories (to be completely precise, the standard model is actually a model of a gauge theory, namely Yang-Mills theory). What these gauge theories have in common is that they are invariant under the action of a symmetry group. In fact, the entire notion of a gauge theory, which is of fundamental importance in modern physics, whether M-theory or not, requires the notion of a symmetry group, one for every gauge theory (there might be some slight simplification here), so, again, symmetry groups have to be assumed to exist for gauge theory to make any sense.

On a more philosophical level, you are already assigning yourself to at least dualism when you write that "it seems possible we could one day have the rule which governs all reality. Is that not enough? Well, the universe is not just that rule, it’s that rule in motion, applying itself, or perhaps already applied infinitely, depending on your perspective, that’s what separates the rule written down from the universe itself." You now have two "substances": one, whatever the physical universe consists of, and one, the rule which governs how the first substance interacts, let's call it R. Now, there has to be some distinction between the "matter" of the universe and the rule governing its interactions, but to not be dualist those two would have to be brought together in some way, which can be done perfectly well if we assume the physical universe is a mathematical structure, because the axioms of one mathematical structure are themselves mathematical structures on a slightly higher level, and, while one one level distinct from the structure they regulate, they are fundamentally of the same substance. If meanwhile we do not make that assumption, we would need to introduce further logico-mathematical rules governing the consequences of the application of R in terms of logic/mathematics, otherwise the rule would be void and everything would be allowed since nothing could be deduced from it. Thus, you would have in fact a whole hierarchy of distinct substances: "matter"(/energy/whatever), the rule that governs the interactions of matter and rules governing the consequences of that rule as well as an open number of further rules giving coherence to those rules. It would be a nightmare!

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