Where did I imply 1)? We never finish producing the numbers, so unless our production order was fixed from the beginning, we never know the full value of the diagonalized number. But the partial diagonalized number (which we refine at each step by looking at the produced number) will gradually converge to a limit, which is a real number different from any number we will ever produce. At no point in the process do we know the limit exactly, but it is there nonetheless.
> Of course the order will change from iteration to iteration. But in this way the generated real numbers will always have a corresponding natural number.
The real numbers that you generate will always have a corresponding natural number. But the diagonalized number will never have a corresponding natural number, no matter how much you shuffle your generated values.
You are saying that when you stop counting, the diagonal number will be different.
That means that you stop. Which implies you are not going to infinity.
If you are going to infinity, there is no side that “wins” (real or naturals). You can always keep generating an additional one for either side.
The same way, we could continue this discussion forever if we just want to keep going back and forth (although HN does impose a limit of replies). And you could only make an assertion about the length of each side of the conversations, after the conversation ends. But if the conversation keeps going forever, you could never say to talked more than the other. Unless you specify a finite range for which you want to measure.
Naturals and Reals are both infinite. Saying that the cardinality of one is different than the cardinality of the other, is just comparing the ideas of cardinality about them that we have come with, but their actual cardinality can never be known.
> You are saying that when you stop counting, the diagonal number will be different.
Where, in all my comments, do I say that we must stop counting? You're putting words in my mouth here.
Since we don't stop counting, we never know the diagonal number's full value (unless our order is predefined). All we know is that the diagonal number exists, and it is different from all the real numbers we will ever count.
> If you are going to infinity, there is no side that “wins” (real or naturals). You can always keep generating an additional one for either side.
Of course. I am not disputing this. If we count through two different sets in the same way, then the subsets of values we count through will have the same cardinality (equal to the cardinality of the set of natural numbers).
But there's an important distinction. If we count through the natural numbers one-by-one without stopping, it's possible to exhaust the whole set of natural numbers, such that every single number will eventually get counted to.
Meanwhile, if we count through the real numbers one-by-one, it is impossible to reach all of them. There will always be a bunch of real numbers that we will never ever count to. That's why we say that there are more real numbers than can be counted: there are uncountably many.
We assign the label ℵ₀ to an infinite set when we want to express the property that any given element can eventually be reached in a finite time if we keep counting for long enough. That's what it means, no more and no less. I don't see what it has to do with "assigning a label to infinity" or "assuming you can finish counting them". We don't use cardinalities to magically make the infinite finite (well, I don't, but I'm sure some pop-math explanations do), we use them to compare and contrast the properties of infinite sets, and refusing to acknowledge these properties doesn't make them go away.
> We assign the label ℵ₀ to an infinite set when we want to express the property that any given element can eventually be reached in a finite time if we keep counting for long enough.
Look at your definition: “if we keep counting long enough”
You are reducing infinity to “long enough” and using that as a label for infinity.
You can’t know ahead of time that you will be able to finish without finishing.
You are saying you can know the unknown. But you won’t until you go and try to count the numbers.
You will never be able to count all the natural numbers. Regardless of what you think the formulas/symbols mean.
Math doesn’t happen by itself, it needs an interpreter to “execute the operations”. Without an operator, math is just a bunch of symbols.
The operator will never finish counting natural numbers. Or any other sequence/set/group of numbers that is infinite.
Perhaps I have not been as clear as I should be. The sequence of counted numbers is infinite, and we would never be able to finish counting all of it. But all we care about for defining ℵ₀ is whether or not the sequence contains some particular value. If it does contain the value, then we can confirm that in finite time, even though the sequence is infinite.
Let me try reframing it a bit. First, you think of some natural number N (e.g., 978) and keep it to yourself. Then, I start counting, "0, 1, 2, 3, 4, 5, ..." and never stop. You listen to me count until you hear N. Then, you can stop listening, even though I'll never stop counting. At that point, you already know that my sequence contains N, and you don't have to keep listening.
I hope you agree that no matter which N you choose, you'll hear me say it sooner or later, as long as I keep counting up by 1. If N is a smaller number, you'll hear me say it sooner; if N is a bigger number, you'll hear me say it later. But there's no N you can choose that forces you to listen to me forever. (And again, just because you stop listening doesn't keep me from talking forever.)
The same thing cannot be done with the real numbers. If you think of some real number R that I don't know, then there's no way for me to count through the real numbers to guarantee that you will eventually hear R and stop listening. Even if I do try to pick a certain sequence, there's a very good chance that you'll never hear R and you'll have to keep listening forever.
> Of course the order will change from iteration to iteration. But in this way the generated real numbers will always have a corresponding natural number.
The real numbers that you generate will always have a corresponding natural number. But the diagonalized number will never have a corresponding natural number, no matter how much you shuffle your generated values.