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Mathematicians Bridge Finite-Infinite Divide

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Re: Mathematicians Bridge Finite-Infinite Divide

#61

Earlier quoted context omitted.

I'll try to summarize my finitist position, which I seem stuck with despite years of trying to accept the mainstream / Cantorian view. One criticism is that the mainstream treatment of infinity is more invented, and less grounded in nature, relative to other areas of math. Another is that it is rife with equivocation, especially between the notion of infinity, and the notions of number and quantity. It's commonly deb…

> Infinity is neither a number nor a quantity. It's not a number, because you can't get there by counting. That's an oddly narrow implied definition of "number" which, as well as infinity, would exclude everything other than the natural numbers. Maybe it extends to the integers, if you use an unusually generous definition of "counting". But it certainly excludes non-integral rationals, and, a fortiori , all irrationa…

Maybe "count" is too restrictive depending on how you think of counting. Substitute "reached" or "located" if you like. As another comment here says (paraphrasing) if a real can't be named, is it even a thing? I'd say any real that can be named can be "counted to" from another real that's arbitrarily close to it. If that's still too restrictive, then for any real that can be named, I can point to a segment of the number line and say "It's roughly, round about... there." Can't do that for infinity, again, because it's not a number.

Re: Mathematicians Bridge Finite-Infinite Divide

#62
post #19

Earlier quoted context omitted.

In high-school calculus (if you've taken that), you apply things like "d/dx" which LOOKS like it is just a fraction, dividing "d" by "d times x". The notation was first dreamed up by mathematicians who were thinking "but if we keep making the d-slices really REALLY small we would move from the discrete approximation to the formula for the correct continuous answer". Unfortunately, while SOME such formulas worked (the…

Question: Isn't there an axiom that says "for any real number, there's always a bigger number"? What stopped Patey and Yokoyama from proving Ramsey's Theorem For Pairs/Triples by saying "for any pair which satisfies some relation X, there exists another pair which also satisfies relation X"?

> What stopped Patey and Yokoyama from proving Ramsey's Theorem For Pairs/Triples by saying "for any pair which satisfies some relation X, there exists another pair which also satisfies relation X"?

Because it's not an axiom? I feel like I'm not understanding your question completely

Re: Mathematicians Bridge Finite-Infinite Divide

#63

Earlier quoted context omitted.

I tried to give my reasons by using only appeals to objects of our common understanding. You have countered my claim by appealing to "the well-definedness of the TREE function". Do you expect me (and everyone else) to know what that is? In order for us to be able to follow your argument you would need to spell that out in a bit more detail. If I'm not thinking about this properly, which of the assertions I made was i…

Your understanding of the point of the theorem is very different to mine, and I'm moderately sure my understanding is pretty close to correct. It is a fact of mathematics that there are some statements which are solely about finite objects, but to prove them requires reasoning about an infinite object. For a more accessible example than TREE, I think the Ackermann function falls into this category. The Ackermann func…

I really appreciate your reasonable and measured tone but I'll need some time to digest your comment. It's a brain-full :)
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