Unknowns comments on AI cooperation in practice - Less Wrong

26 Post author: cousin_it 30 July 2010 04:21PM

You are viewing a comment permalink. View the original post to see all comments and the full post content.

Comments (157)

You are viewing a single comment's thread. Show more comments above.

Comment author: Unknowns 30 July 2010 08:09:09PM 0 points [-]

Does your proof of that take more than 3^^^^3 steps? If not, then doesn't your algorithm see that it defects against Defection Rock, and therefore it cooperates, which is inconsistent? If it does, when did you do that proof?

In other words, it seems to me that played against Defection Rock, your algorithm freezes-- it doesn't output either 1 or 0.

Comment author: cousin_it 30 July 2010 08:17:11PM *  5 points [-]

Here's my proof that A defects against Defection Rock: by assumption, A's proof checker is correct. If A cooperates against the Defection Rock, A must have arrived at a proof that A's choice is equal to B's choice. But A's choice is not equal to Rock's choice. Therefore A's proof checker is incorrect, contradiction, QED.

This proof doesn't take more than 3^^^^3 steps, but it doesn't matter. A can't use it anyway because it can't assume (or prove) that its proof checker is correct. Goedel's second theorem: if a formal system asserts or proves its own consistency, it is inconsistent. That's why all proof systems that people actually use cannot prove their own consistency.

Comment author: DanielVarga 31 July 2010 10:35:19AM *  4 points [-]

This comment, and another one ("No, A doesn't know that because it doesn't know B's proof checker is correct.") are buried deep down in the comment thread, but I think they deserve their own mentions in the main post, because they are extremely helpful for the inexperienced reader to understand what the real issues are here.

Comment author: orthonormal 31 July 2010 06:27:39PM 1 point [-]

Nice separation of levels in this comment. It's essential to point out the difference between what can be done by the automated proof-checker and what can be shown 'from the outside' about the operation of the proof-checker.

I second DanielVarga: you should incorporate this discussion into the post itself, since it's exactly the part that people get stuck on.

Comment author: Unknowns 30 July 2010 08:23:17PM 0 points [-]

That proves that A can't cooperate, but it doesn't prove that it defects, since there remains the possibility that the program doesn't output anything.

Comment author: cousin_it 30 July 2010 08:24:14PM *  2 points [-]

The program is guaranteed to finish because there's a finite number of proofs to check, and checking every proof takes finite time (a proof checker cannot loop forever on a given proof).

Comment author: Unknowns 30 July 2010 08:30:59PM 0 points [-]

So with an argument like the one that A defects, I can prove that your mind is inconsistent:

"Cousin_it will never prove this statement to be true."

I know that this is true, and presumably you know it too... which is a contradiction.

Comment author: cousin_it 30 July 2010 08:32:46PM *  0 points [-]

I don't know that it's true.

And I don't see how this makes the proof wrong.

Comment author: Unknowns 30 July 2010 08:35:41PM 0 points [-]

It doesn't make the proof wrong.

Comment author: cousin_it 30 July 2010 08:36:38PM *  1 point [-]

Oh, sorry then :-)

"Lucas cannot consistently assert this sentence" is an old philosophers' joke, actually.

Comment author: LucasSloan 30 July 2010 08:39:10PM 1 point [-]

Yes, I can.