The Independence of) The Continuum Hypothesis
In the late 19th century, a German mathematician named Georg Cantor blew ev= >eryone=E2=80=99s minds by figuring out that infinities come in different si= >zes, called cardinalities. He proved the foundational theorems about cardin= >ality, which modern day math majors tend to learn in their Discrete Math cl= >asses.
Cantor proved that the set of real numbers is larger than the set of natura= >l numbers, which we write as |=E2=84=9D|>|=E2=84=95|. It was easy to establ= >ish that the size of the natural numbers, |=E2=84=95|, is the first infinit= >e size; no infinite set is smaller than =E2=84=95.
Now, the real numbers are larger, but are they the second infinite size? Th= >is turned out to be a much harder question, known as The Continuum Hypothes= >is (CH).
If CH is true, then |=E2=84=9D| is the second infinite size, and no infinit= >e sets are smaller than =E2=84=9D, yet larger than =E2=84=95. And if CH is = >false, then there is at least one size in between.
So what=E2=80=99s the answer? This is where things take a turn.
CH has been proven independent, relative to the baseline axioms of math. It=
can be true, and no logical contradictions follow, but it can also be fals=
e, and no logical contradictions will follow.
It=E2=80=99s a weird state of affairs, but not completely uncommon in moder= >n math. You may have heard of the Axiom of Choice, another independent stat= >ement. The proof of this outcome spanned decades and, naturally, split into=
two major parts: the proof that CH is consistent, and the proof that the n=
egation of CH is consistent.
The first half is thanks to Kurt G=C3=B6del, the legendary Austro-Hungarian=
logician. His 1938 mathematical construction, known as G=C3=B6del=E2=80=99=
s Constructible Universe, proved CH compatible with the baseline axioms, an= >d is still a cornerstone of Set Theory classes. The second half was pursued=
for two more decades until Paul Cohen, a mathematician at Stanford, solved= it by inventing an entire method of proof in Model Theory known as =E2=80=
=9Cforcing.=E2=80=9D
G=C3=B6del=E2=80=99s and Cohen=E2=80=99s halves of the proof each take a gr= >aduate level of Set Theory to approach, so it=E2=80=99s no wonder this uniq= >ue story has been esoteric outside mathematical circles.
(Wikimedia Commons)
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