# Wei_Dai comments on Ingredients of Timeless Decision Theory - Less Wrong

44 19 August 2009 01:10AM

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Comment author: 19 August 2009 12:42:04PM *  7 points [-]

This is another open problem - "who acts first" in timeless negotiations.

You're right, I failed to realize that with timeless agents, we can't do backwards induction using the physical order of decisions. We need some notion of the logical order of decisions.

Here's an idea. The logical order of decisions is related to simulation ability. Suppose A can simulate B, meaning it has trustworthy information about B's source code and has sufficient computing power to fully simulate B or sufficient intelligence to analyze B using reliable shortcuts, but B can't simulate A. Then the logical order of decisions is B followed by A, because when B makes his decision, he can treat A's decision as conditional on his. But when A makes her decision, she has to take B's decision as a given.

Does that make sense?

Comment author: 19 August 2009 03:05:15PM *  7 points [-]

Moving second is a disadvantage (at least it seems to always work out that way, counterexamples requested if you can find them) and A can always use less computing power. Rational agents should not regret having more computing power (because they can always use less) or more knowledge (because they can always implement the same strategy they would use with less knowledge) - this sort of thing is a sure sign of reflective inconsistency.

To see why moving logically second is a disadvantage, consider that it lets an opponent playing Chicken always toss their steering wheel out the window and get away with it.

That both players desire to move "logically first" argues strongly that neither one will; that the resolution here does not involve any particular fixed global logical order of decisions.

(I should comment in the future about the possibility that bio-values-derived civs, by virtue of having evolved to be crazy, can succeed in moving logically first using crazy reasoning, but that would be a whole 'nother story, and of course also falls into the "Way the fuck too dangerous to try in real life" category relative to my present knowledge.)

With timeless agents, we can't do backwards induction using the physical order of decisions. We need some notion of the logical order of decisions.

BTW, thanks for this compact way of putting it.

Comment author: 19 August 2009 07:33:55PM 1 point [-]

Being logically second only keeps being a disadvantage because examples keep being chosen to be of the kind that make it so.

One category of counterexample comes from warfare, where if you know what the enemy will do and he doesn't know what you will do, you have the upper hand. (The logical versus temporal distinction is clear here: being temporally the first to reach an objective can be a big advantage.)

Another counterexample is in negotiation where a buyer and seller are both uncertain about fair market price; each may prefer the other to be first to suggest a price. (In practice this is often resolved by the party with more knowledge, or more at stake, or both - usually the seller - being first to suggest a price.)

Comment author: 20 August 2009 12:18:02AM 0 points [-]

Being logically second only keeps being a disadvantage because examples keep being chosen to be of the kind that make it so.

You're right. Rock-paper-scissors is another counter-example. In these cases, the relationship between between the logical order of moves and simulation ability seems pretty obvious and intuitive.

Comment author: 20 August 2009 12:19:37AM 1 point [-]

Except that the analogy to rock-paper-scissors would be that I get to move logically first by deciding my conditional strategy "rock if you play scissors" etc., and simulating you simulating me without running into an apparently non-halting computation (that would otherwise have to be stopped by my performing counterfactual surgery on the part of you that simulates my own decision), then playing rock if I simulate you playing scissors.

At least I think that's how the analogy would work.

Comment author: 20 August 2009 12:36:21AM *  2 points [-]

I suspect that this kind of problems will run into computational complexity issues, not clever decision theory issues. Like with a certain variation on St. Petersburg paradox (see the last two paragraphs), where you need to count to the greatest finite number to which you can count, and then stop.

Comment author: 20 August 2009 12:29:38AM 1 point [-]

Suppose I know that's your strategy, and decide to play the move equal to (the first googleplex digits of pi mod 3), and I can actually compute that but you can't. What are you going to do?

If you can predict what I do, then your conditional strategy works, which just shows that move order is related to simulation ability.

Comment author: 20 August 2009 03:32:21AM *  4 points [-]

In this zero-sum game, yes, it's possible that whoever has the most computing power wins, if neither can access unpredictable random or private variables. But what if both sides have exactly equal computing power? We could define a Timeless Paper-Scissors-Rock Tournament this way - standard language, no random function, each program gets access to the other's source code and exactly 100 million ticks, if you halt without outputting a move then you lose 2 points.

Comment author: 20 August 2009 09:13:40AM 1 point [-]

This game is pretty easy to solve, I think. A simple equilibrium is for each side to do something like iterate x = SHA-512(x), with a random starting value, using an optimal implementation of SHA-512, until time is just about to run out, then output x mod 3. SHA-512 is easy to optimize (in the sense of writing the absolutely fastest implementation), and It seems very unlikely that there could be shortcuts to computing (SHA-512)^n until n gets so big (around 2^256 unless SHA-512 is badly designed) that the function starts to cycle.

Comment author: 23 May 2012 11:51:39AM 1 point [-]

Schneier et al here prove that being able to calculate H^n(x) quickly leads to a faster way of finding collisions in H. http://www.schneier.com/paper-low-entropy.html

Comment author: 20 August 2009 10:11:17PM 1 point [-]

Well, it's probably not all that interesting from a purely theoretical perspective, but if the prize money was divided up among only the top fifth of players, you'd actually have to try to win, and that would be an interesting challenge for computer programmers.

Comment author: 19 August 2009 07:31:16PM *  1 point [-]

Moving second is a disadvantage (at least it seems to always work out that way, counterexamples requested if you can find them) and A can always use less computing power.

But if you are TDT, you can't always use less computing power, because that might be correlated with your opponents also deciding to use less computing power, or will be distrusted by your opponent because it can't simulate you.

But if you simply don't have that much computing power (and opponent knows this) then you seem to have the advantage of logically moving first.

(I should comment in the future about the possibility that bio-values-derived civs, by virtue of having evolved to be crazy, can succeed in moving logically first using crazy reasoning, but that would be a whole 'nother story, and of course also falls into the "Way the fuck too dangerous to try in real life" category relative to my present knowledge.)

Lack of computing power could be considered a form of "crazy reasoning"...

Why does TDT lead to the phenomenon of "stupid winners"? If there's a way to explain this as a reasonable outcome, I'd feel a lot better. But is that like a two-boxer asking for an explanation of why, when the stupid (from their perspective) one-boxers keep winning, that's a reasonable outcome?

Comment author: 19 August 2009 07:55:42PM *  0 points [-]

But if you are TDT, you can't always use less computing power, because that correlates with your opponents also deciding to use less computing power.

Substitute "move logically first" for "use less computing power"? Using less computing power seems like a red herring to me. TDT on simple problems (with the causal / logical structure already given) uses skeletally small amounts of computing power. "Who moves first" is a "battle"(?) over the causal / logical structure, not over who can manage to run out of computing power first. If you're visualizing this using lots of computing power for the core logic, rather than computing the 20th decimal place of some threshold or verifying large proofs, then we've got different visualizations.

The idea of "if you do this, the opponent does the same" might apply to trying to move logically first, but in my world this has nothing to do with computing power, so at this point I think it'd be pretty odd if the agents were competing to be stupider.

Besides, you don't want to respond to most logical threats, because that gives your opponent an incentive to make logical threats; you only want to respond to logical offers that you want your opponent to have an incentive to make. This gets into the scary issues I was hinting at before, like determining in advance that if you see your opponent predetermine to destroy the universe in a mutual suicide unless you pay a ransom, you'll call their bet and die with them, even if they've predetermined to ignore your decision, etcetera; but if they offer to trade you silver for gold at a Ricardian-advantageous rate, you'll predetermine to cooperate, etc. The point, though, is that "If I do X, they'll do Y" is not a blank check to decide that minds do X, because you could choose a different form of responsiveness.

But anyway, I don't see in the first place that agents should be having these sorts of contests over how little computing power to use. That doesn't seem to me like a compelling advantage to reach for.

But if you simply don't have that much computing power then you seem to have the advantage of logically moving first.

If you've got that little computing power then perhaps you can't simulate your opponent's skeletally small TDT decision, i.e., you can't use TDT at all. If you can't close the loop of "I simulate you simulating me" - which isn't infinite, and actually terminates rather quickly in the simple cases I know how to analyze at all, because we perform counterfactual surgery inside the loop - then you can't use TDT at all.

Lack of computing power could be considered a form of "crazy reasoning"...

No, I mean much crazier than that. Like "This doesn't follow, but I'm going to believe it anyway!" That's what it takes to get "unusual reasons" - the sort of madness that only strictly naturally selected biological minds would find compelling in advance of a timeless decision to be crazy. Like "I'M GOING TO THROW THE STEERING WINDOW OUT THE WHEEL AND I DON'T CARE WHAT THE OPPONENT PREDETERMINES" crazy.

Why does TDT lead to the phenomenon of "stupid winners"?

It has not been established to my satisfaction that it does. It is a central philosophical intuition driving my decision theory that increased computing power, knowledge, or self-control, should not harm a rational agent.

Comment author: 20 August 2009 12:11:18AM 0 points [-]

That both players desire to move "logically first" argues strongly that neither one will; that the resolution here does not involve any particular fixed global logical order of decisions.

...possibly employing mixed strategies, by analogy to the equilibrium of games where neither agent gets to go first and both must choose simultaneously? But I haven't done anything with this idea, yet.

Comment author: [deleted] 13 June 2014 06:52:49AM -1 points [-]

This reminds me of logical Fatalism and the Argument from Bivalence