Live data from Hacker News

Turing's topological proof that every written alphabet is finite (2010)

divisbyzero.com

21–30 of 120 posts

Re: Turing's topological proof that every written alphabet is finite (2010)

#21
post #7

Turing's argument says "conditionally compact" but the article talks only about "compact". They are not the same; "conditionally compact" means every sequence has a Cauchy subsequence, while (sequentially) compact means every sequence has a convergent subsequence. If the metric space Turing mentions is complete, then I guess they're the same. Is that obvious?

Convergent sequences are always Cauchy; for metric spaces, compactness and sequential compactness are the same.

Re: Turing's topological proof that every written alphabet is finite (2010)

#22

Interesting argument. This assumes that cognition must also be happening on a compact manifold which seems like a reasonable assumption but the conclusion is somewhat counterintuitive because it means there are only finitely many personality types and ways of thinking.

Who said this had anything to do with cognition at all? I think Turing's argument goes through with humans replaced by automata and eyes by cameras. It's just that perception has finite resolution.

Re: Turing's topological proof that every written alphabet is finite (2010)

#23

Earlier quoted context omitted.

I guess that means reincarnation is real.

Assuming you're not trolling: nope, that would be an empirical question of how many brain states ever actually arise in the world during the time humans exist, and how much space and time it takes to maintain a given brain state. The universe is currently expected to stop being able to support human life at some point in the future, so the pigeonhole principle argument requires some physical parameters to be known be…

We do have https://en.m.wikipedia.org/wiki/Boltzmann_brain

That may appear every (10^10)^50 years according to

https://en.m.wikipedia.org/wiki/Timeline_of_the_far_future

Re: Turing's topological proof that every written alphabet is finite (2010)

#24
post #16
post #6

Earlier quoted context omitted.

Is that counterintuitive? There's a finite number of electrons in a human brain (which fits in a space of size 1m^3), and information takes time to propagate across any distance, and humans die before 150 years; this all gestures at there being not only finitely many personality types and ways of thinking, but finitely many human mind states .

But there may yet be more brain states than number of possible thoughts by the finite humans.

Oh, 100%, it seems extremely unlikely that multiple brain states in this sense don't code for the same thought! If nothing else, you could only avoid that with an absurdly precise definition of "brain"; any practical definition of "brain" is very likely to include matter that is physically irrelevant to at least some thoughts. I hedged with "1m^3" because the argument goes through even if you take the entire body to be the brain.

Re: Turing's topological proof that every written alphabet is finite (2010)

#25

Interesting argument. This assumes that cognition must also be happening on a compact manifold which seems like a reasonable assumption but the conclusion is somewhat counterintuitive because it means there are only finitely many personality types and ways of thinking.

Well, this is true only if you think cognition and thought as a pure biological process totally dependent on state of brain.

Re: Turing's topological proof that every written alphabet is finite (2010)

#26

Interesting argument. This assumes that cognition must also be happening on a compact manifold which seems like a reasonable assumption but the conclusion is somewhat counterintuitive because it means there are only finitely many personality types and ways of thinking.

Well, this is true only if you think cognition and thought as a pure biological process totally dependent on state of brain.

I don't think that. I'm just explaining what follows logically if the cognitive manifold is compact.

Re: Turing's topological proof that every written alphabet is finite (2010)

#27
I don't agree. What if the next symbol's meaning conditionally depends on the previous ones?

For example, in 1937 the third glyph is number three, but in ВАЗ, the third glyph is Cyrillic letter Z. They're not different in writing.

It would not be hard to devise a symbolic system where new symbols are context dependent, and there are infinitely many of these depending on the context. The context will be governed by a finite number of rules. The glyphs will not change meaning in a specific text.

Human language is an example of such system. If you treat words as a whole as symbols, you can have infinitely many different words as they become defined via the specific text, but obviously you can't have infinitely many different words in a single text because they will stop being mutually intelligible at some point.

Re: Turing's topological proof that every written alphabet is finite (2010)

#28

Interesting argument. This assumes that cognition must also be happening on a compact manifold which seems like a reasonable assumption but the conclusion is somewhat counterintuitive because it means there are only finitely many personality types and ways of thinking.

Who said this had anything to do with cognition at all? I think Turing's argument goes through with humans replaced by automata and eyes by cameras. It's just that perception has finite resolution.

I made the obvious connection. It's an original thought from me and no one else.

Re: Turing's topological proof that every written alphabet is finite (2010)

#29
post #7

Turing's argument says "conditionally compact" but the article talks only about "compact". They are not the same; "conditionally compact" means every sequence has a Cauchy subsequence, while (sequentially) compact means every sequence has a convergent subsequence. If the metric space Turing mentions is complete, then I guess they're the same. Is that obvious?

Convergent sequences are always Cauchy; for metric spaces, compactness and sequential compactness are the same.

I think the question is more like:

> Turing says that a certain space, the space of all compact subsets of [0,1]^2 endowed with the metric "integral of minimal distance required to transform {1 ink at each point of P1} u {infinite amount of ink at (2, 0)} into {1 ink at each point of P2} u {infinite amount of ink at (2,0)}", is conditionally-compact. How is that related to the article's argument?

This is not obvious, I think. The article has moved away from Turing's "integral of the distance we have to transfer ink", instead using "maximum distance we have to transfer any ink", and I don't have a great intuition for whether this is a legit transformation of the argument. (I'm sure both proofs are correct, but it's not obvious to me that they are the same proof.)

Re: Turing's topological proof that every written alphabet is finite (2010)

#30

I don't agree. What if the next symbol's meaning conditionally depends on the previous ones? For example, in 1937 the third glyph is number three, but in ВАЗ, the third glyph is Cyrillic letter Z. They're not different in writing. It would not be hard to devise a symbolic system where new symbols are context dependent, and there are infinitely many of these depending on the context. The context will be governed by a…

Of course you can have infinitely many different semantics, but this is a question about available syntaxes. (Trivial proof: for each n, take the semantics S_n which assigns to the symbol "X" the meaning "integer n", just as English usually assigns to the symbol "3" the meaning "integer 3".)
Post reply on HN