anyone mathy here able to explain why people say it's wrong to think of df(x)/dx as a literal ratio of infinitesimal quantities?
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@CoronaCoreanici @starkatt epsilon is more properly 1/ω, right?
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@CoronaCoreanici @starkatt @Felthry Honestly, squaring to get -1 is a lot /easier/ for us, with the 2D thing and multiplying-by-i-as-rotation. :3
@CoronaCoreanici @starkatt @Felthry "You can't square something to get -1!" *plops a second axis on the number line*
@CoronaCoreanici @starkatt @Felthry Wait, it does?
@IceWolf @CoronaCoreanici @starkatt aaaa i can't keep up with this right now
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@CoronaCoreanici @IceWolf @starkatt also I feel like 0.9999... would still be equal to 1 even if infinitesimals exist? Because you can't write an infinitesimal out like that, 1-ε is not the same as 0.9999..., right?
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@Felthry @CoronaCoreanici @starkatt Well, wouldn't 0.999999... be an infinitely small amount smaller than 1, in that case? It's like a limit.
...whoo boy, this would totally break calculus wouldn't it...
@CoronaCoreanici @IceWolf @starkatt honestly limits always have felt really kludgey to us, like they're not a very elegant way of going about this kind of stuff
which is probably part of why we prefer to think of derivatives as literal ratios of infinitesimals
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@CoronaCoreanici @IceWolf @starkatt I guess all of this is an engineer's intuition more than a mathematician's rigor but I feel like our intuition could be made rigorous in a way that allows one to think of dx and dt and stuff as real infinitesimals that you can do math to
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@CoronaCoreanici @starkatt So now that I have the time to come back to this--what makes the archimedean property fundamental? It doesn't sound like some underpinning of mathematics, it sounds more like an interesting property.
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@CoronaCoreanici @starkatt we have a vague idea of what a dedekind cut is; it's considering a number as an ordered pair of ({the set of all numbers less than it}, {the set of all numbers greater than it}), right?
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@CoronaCoreanici @starkatt it feels kind of Weird that you can do that and get ℵ₁ reals, when you only have ℵ₀ rationals. It feels like there could only be ℵ₀ ways to divide them up in a consistent manner
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@CoronaCoreanici @starkatt I thought the cardinality of the reals was ℵ₁? huh
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@CoronaCoreanici @starkatt and with your saying that it's not fundamental, I have to wonder if there's a consistent formulation of mathematics that lets all our intuitive understanding be completely valid
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@CoronaCoreanici @starkatt Our intuitive understanding of stuff has so far worked pretty well for engineering work
I feel like we wouldn't be suited for pure mathematics, though
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@CoronaCoreanici @starkatt @Felthry So reading Wikipedia, to put it another way, if you keep adding copies of s it'll eventually get past r, for any s you can pick?
we don't know, we're speculating based on skimming wikipedia re: literal ratio of infinitesimal quantities
@Felthry according to https://en.wikipedia.org/wiki/Infinitesimal the infinitesimal was the original interpretation, but it wasn't rigorous so a lot of mathematicians said, "look, infinitesimals don't exist on the real number line and we can get the same theorems using limits, let's use limits"
and then around the 1960s some mathematicians started formalizing a way of doing it with infinitesimals after all
so apparently you can do it? it's called "nonstandard analysis" and we found out it existed five minutes ago so we don't know anything about it https://en.wikipedia.org/wiki/Nonstandard_analysis
and people probably say it's wrong because it was unrigorous until relatively recently
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@Felthry cc @CoronaCoreanici ?