04:08
@Deusovi Soooooooo we just ended our discussion on the concept of infinity yesterday and my brain hurts
And that, in fact, all RATIONAL NUMBERS are the same as the integers, because you can make like a 2-d list of something
And then he showed how the size of all real numbers is the same as the size of all possible numbers between 0 and 1
6 hours later…
10:51
Basically two infinities are the same if you can biject between them (one-to-one correspondence between two sets means they must be the same size).
When you're looking at the set of all numbers between 0 and 1, don't think of its "size" as like the distance from 0 to 1! That would be measure theory, and you're not measuring the set, just counting its elements. Think of it as a set of dots where every dot is a number between 0 and 1. You can see that the set is infinitely big, there's infinitely many numbers between 0 and 1.
It makes sense that that set has the same size as the set of all real numbers, because there's a bijection between one set and the other. Think of the tan and arctan functions: you've got a bijective increasing function which maps one-to-one between a finite interval (-pi/2 to pi/2, but that can easily be changed to (0,1) by a linear transformation) and the whole real line.
Whereas the set of integers, or the set of rational numbers, is not the same size. You can count those sets, even if your counting goes on forever, but you can't count the set of real numbers, because you'll always miss some. Counting is basically an informal way of describing "bijects with the natural numbers": one, two, three, four, ...
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