asr comments on My summary of Eliezer's position on free will - Less Wrong

16 Post author: Solvent 28 February 2012 05:53AM

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Comment author: asr 29 February 2012 06:38:39AM 0 points [-]

In general, no. To predict the output of an arbitrary algorithm, you have to have equivalent states to the algorithm. If I give you a Turing machine and ask you what its output is, you can't do any better than running it.

You can do various trivial transforms to it and say "no, I'm running a new machine", but it's as expensive as running the original and will have to be effectively isomorphic to it, I suspect.

Comment author: Jonathan_Graehl 29 February 2012 11:36:43PM 1 point [-]

I agree.

But if you're saying that it's proven that "you have to ...", I wasn't aware of that.

Comment author: asr 01 March 2012 07:47:39PM *  2 points [-]

I don't have a proof of that claim, either, just a strong intuition. I should have specified that more clearly. If some other LWer has a proof in mind, I'd love to see it.

Here are some related things I do have proofs for.

There's no general procedure for figuring out whether two programs do the same thing -- this follows from Rice's theorem. (In fact, this is undecidable for arbitrary context-free languages, let alone more general programs.)

For any given problem, there is some set of asymptotically optimal algorithms, in terms of space or time complexity. And a simulator can't improve on that bound by more than a constant factor. So if you have an optimal algorithm for something, no AI can improve on that.

Now suppose I give you an arbitrary program and promise that there's a more efficient program that produces the same output. There can't be a general way to find the optimal program that produces the answer.*

  • Proof by reduction from the halting problem: Suppose we had a an oracle for minimizing programs. For an arbitrary Turing machine T and input I, create a program P that ignores its input and simulates T on I. If we could minimize this program, we'd have a halting oracle.)
Comment author: Jonathan_Graehl 01 March 2012 10:31:37PM 1 point [-]

When you say "optimal" you mean space or time used.

When you say "minimize" you mean "shortest equivalent program"?

I love this list of undecidable problems.

Comment author: asr 02 March 2012 02:12:17PM 0 points [-]

I meant to minimize in terms of asympototic time or space complexity, not length-of-program.

Comment author: [deleted] 29 February 2012 11:00:12PM 0 points [-]

Oh. That makes sense (since you can't even tell if the machine will halt or not). I'm still not convinced it applies to free will, but I will not argue the point further since I agree with the conclusion anyway.