14:00:53 yuuki ゆうき(金野裕希) @yuukikonno@mastodon.social
13:55:56 yuuki ゆうき(金野裕希) @yuukikonno@mastodon.social
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the nature of
• the size of a "large" number
is
• how many smaller numbers can it prove to be consistent if they exist.

the largest number proves the consistency of all numbers, including itself.
by Gödel's theorem, it is a "contradiction".

13:55:29 yuuki ゆうき(金野裕希) @yuukikonno@mastodon.social
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let us write Fin + Inf as ZFC.

similarly, if we add "a large cardinal exists", then we can prove the consistency of ZFC.
• ZFC + LC ⊢ Con(ZFC)

13:52:22 yuuki ゆうき(金野裕希) @yuukikonno@mastodon.social
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this means that Fin + Inf is a stronger theory than Fin.

this corresponds to
• 1 < 2 < 3 < … < ℵ₀.

ℵ₀ is not just large; it is beyond "…".
it's much larger than any number before it.

ℵ₁ is not "large" in this sense;
it's just after ℵ₀.

02:52:06 yuuki ゆうき(金野裕希) @yuukikonno@mastodon.social
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the axioms "finite numbers exist" can't prove their own consistency.¹
• Fin ⊬ Con(Fin)

however, if we add "an infinite number exists", then we can prove the consistency of finite numbers.
• Fin + Inf ⊢ Con(Fin)

¹ Gödel's second incompleteness theorem

02:49:18 yuuki ゆうき(金野裕希) @yuukikonno@mastodon.social
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¹ this indicates "direct implications or relative consistency implications", tho.
(e.g., huge < supercompact)

in order of size and strength:
• inaccessible < measurable < huge < rank-into-rank < 0=1

02:49:03 yuuki ゆうき(金野裕希) @yuukikonno@mastodon.social
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so the Q is, what tf is the largest infinite number.
n it's a "contradiction" (aka 0=1).
as drawn in this pic.¹

let me explain from scratch.

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02:37:26 yuuki ゆうき(金野裕希) @yuukikonno@mastodon.social
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actually, large cardinals refer to large ♾ with specific properties.

(the successor of an inaccessible cardinal is not inaccessible by definition.)