this post was submitted on 06 Jan 2024
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I considered deleting the post, but this seems more cowardly than just admitting I was wrong. But TIL something!

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[–] nodsocket@lemmy.world 8 points 10 months ago (18 children)

Similar problem: which set is bigger, the set of all real numbers, or the set of all real numbers between 0 and 1?

[–] fishos@lemmy.world 2 points 10 months ago* (last edited 10 months ago) (17 children)

Not quite because it's easily shown that the set of all real numbers contains the set of all real numbers between 0-1, but the set of all real numbers from 0-1 does not contain the set of all real numbers. It's like taking a piece of an infinite pie: the slice may be infinite as well, but it's a "smaller" infinite than the whole pie.

This is more like two infinite hoses, but one has a higher pressure. Ones flowing faster than the other, but they're both flowing infinitely.

[–] WilloftheWest 1 points 10 months ago* (last edited 10 months ago)

Actually, the commenter is exactly right. The real line does contain the open interval (0,1). The open interval (0,1) has the exact same cardinality as the real numbers.

An easy map that uniquely maps a real number to a number of the interval (0,1) is the function mapping x to arctan(x)/π + 1/2. The existence of a bijection proves that the sets have the same size, despite one wholly containing the other.

The comment, like the meme, plays on the difference between common intuition and mathematical intuition.

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