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What happens if our mathematical system is proven to be inconsistent? (lemmy.ml)
submitted 9 months ago by to c/asklemmy@lemmy.ml
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From my "watched a YouTube video" understanding of Gödel's Incompleteness Theorem, a consistent mathematical system cannot prove its own consistency, and any seemingly consistent system could always have a fatal contradiction that invalidates the whole system, and the only way to know would be to find the contradiction.

So if at some point our current system of math gets proven inconsistent, what happens next? Can we tweak just the inconsistent part and have everything else still be valid or would we be forced to rebuild all of math from basic logic?

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[–] 4 points 9 months ago* (4 children)

A banach space is just a vector space with a norm, there are many many weirder examples of spaces in topology. You're thinking of the banach-tarski paradox I think

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  • [–] 3 points 9 months ago* (last edited 9 months ago) (3 children)

    It wasn't a mistake. Usually you're talking about an infinite-dimensional TVS when you say Banach space - as in it's just Banach, that's the most you can say about it. I don't mean R^3^.

    Stuff like the axiom of choice has a way of coming up in functional analysis. Sure, there's weirder spaces, like from general topology or TVS theory in general, but Banach spaces are an example that are pretty widely used and studied. It seems like going with some pathological object I have to search around for would make the point less clear.

    The Banach-Tarski paradox wouldn't work either without the AoC, but it's just a specific counterexample, and Banach and Tarski's careers will be fine since they both died decades ago.

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  • [–] 1 point 9 months ago (2 children)

    ah I gotcha, thats fair then.

    On another note, you'd propose a von Neumann hierarchy without AoC? How would that class be defined?

    Admittedly I'm not that big into class theory so I am likely missing something obvious, but to me it seems like the definition of the class requires such a selecting function

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  • [–] 2 points 9 months ago (1 child)

    I mean, me neither. But if all sets are finite AoC just trivially holds, right? You can do it "manually".

    If you back off to just ZF, parts of functional analysis will break. L^infinity^ space isn't separable, and so isn't necessarily Baire anymore, for example.

    If we go all the way to finitism or ultrafinitism it doesn't really exist as a concept in the first place. But, whatever numerical engineering calculation will still work, and you can probably do something that looks like functional analysis to determine a mode of vibration, even if you're actually just using a series of high-dimensional but finite spaces. Probably, anyway. Don't ask me to prove it.

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