this post was submitted on 10 May 2024
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hexbear
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sure, you can extend the real line but you're basically defining a new value that behaves a lot like NaN in software. you have to be very careful about the operations because of the strange properties of the new terms introduced. what you get out loses a lot of the basic properties you're used to with arithmetic - ie afaik it's neither a field nor a ring. it's also a really misleading statement to say it's dividing by zero - you're changing what division by zero even means. and the infinity you get back isn't infinity in the usual sense - the supremum of the natural numbers. rather it's a symbolic infinity.
basically, it's as much division by zero as -1/12 is the sum of the natural numbers. they're both true in a very particular sense but only after you change the meaning of all the words in the statement.
said another way, you can make anything you like true by introducing new axioms but those axioms have deep impacts on what's true in the new system those axioms generate and it's misleading to say that the ability to introduce those axioms makes an undefined operation sensible in a system that lacks those axioms.
Ok I suppose that's fair, most people probably are taking division as meaning in the sense it applies in what is it even called, default maths? real analysis or whatever, and while people call the operation division in other systems it's sort of a homophone for a rather different thing that shares characteristics.
People should still learn about the Riemann sphere though and it's a sensible operation under that. We do it all the time in quantum shit mwahahahaha.
it's a version of field theory where the rules aren't all properly explained? I wish we just taught groups, rings, and fields as soon as modular arithmetic gets introduced. it's not really that complicated and it makes sense if you have matrices, integer rings, Z, R, and Q available as examples. we just leave things poorly explained by not teaching the axioms.
Riemann spheres are awesome, I just want to be careful with my language in a space where people don't even know what a field is, generally. but god I love math. I really want to go back to grad school and finish a phd - I've been settling for teaching myself with books and free online lectures.
Literally lol, that's the funniest thing I've heard in a few days. I do remember studying physics and getting a bit like "ok but wtf are numbers cause this is a mess?" and studying sets in my own time, then a bit of field theory and going "Oh yes, this actually makes sense now" although I was only ever at the level of amateur dabbler.
I burned out of a physics PhD (funniest thing I've heard that referred to is "I have a post mortem in X") but even by the time I started it I just wished I could go back and choose pure maths, it's not like there are jobs for physics anyway :P (unless you want to make bankers richer, or build weapons which both indelibly mar the soul). Algebraic topology is something I will understand one day. I just need more time, and to move closer to a uni. Even if I'm like 70 and wasting state money I'm gonna study it some day.
Yeah it's reasonable, I guess I don't want people just thoughtstopping at "you can't divide by zero" and never thinking there's anything deeper to it instead of maybe going "well, what is division by zero why can you do it sometimes and not other times? why do we sometimes pretend we can do it in systems where we can't?". At the end of the day I think we're on the same side of "maths is cool and people should learn more of it's nuances" but worry about people taking different things from the same trivial remark haha.
Good luck on getting back to it! I hope you do better than me at your studies. It's such a fun little world of order and puzzles.