toto comments on Newcomb's Problem and Regret of Rationality - Less Wrong

64 Post author: Eliezer_Yudkowsky 31 January 2008 07:36PM

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Comment author: cousin_it 22 July 2010 06:58:56AM *  6 points [-]

Sometime ago I figured out a refutation of this kind of reasoning in Counterfactual Mugging, and it seems to apply in Newcomb's Problem too. It goes as follows:

Imagine another god, Upsilon, that offers you a similar two-box setup - except to get the $2M in the box B, you must be a one-boxer with regard to Upsilon and a two-boxer with regard to Omega. (Upsilon predicts your counterfactual behavior if you'd met Omega instead.) Now you must choose your dispositions wisely because you can't win money from both gods. The right disposition depends on your priors for encountering Omega or Upsilon, which is a "bead jar guess" because both gods are very improbable. In other words, to win in such problems, you can't just look at each problem individually as it arises - you need to have the correct prior/predisposition over all possible predictors of your actions, before you actually meet any of them. Obtaining such a prior is difficult, so I don't really know what I'm predisposed to do in Newcomb's Problem if I'm faced with it someday.

Comment author: toto 22 July 2010 09:16:49AM 0 points [-]

OK. I assume the usual (Omega and Upsilon are both reliable and sincere, I can reliably distinguish one from the other, etc.)

Then I can't see how the game doesn't reduce to standard Newcomb, modulo a simple probability calculation, mostly based on "when I encounter one of them, what's my probability of meeting the other during my lifetime?" (plus various "actuarial" calculations).

If I have no information about the probability of encountering either, then my decision may be incorrect - but there's nothing paradoxical or surprising about this, it's just a normal, "boring" example of an incomplete information problem.

you need to have the correct prior/predisposition over all possible predictors of your actions, before you actually meet any of them.

I can't see why that is - again, assuming that the full problem is explained to you on encountering either Upsilon or Omega, both are truhful, etc. Why can I not perform the appropriate calculations and make an expectation-maximising decision even after Upsilon-Omega has left? Surely Omega-Upsilon can predict that I'm going to do just that and act accordingly, right?

Comment author: cousin_it 22 July 2010 09:22:20AM *  0 points [-]

Yes, this is a standard incomplete information problem. Yes, you can do the calculations at any convenient time, not necessarily before meeting Omega. (These calculations can't use the information that Omega exists, though.) No, it isn't quite as simple as you state: when you meet Omega, you have to calculate the counterfactual probability of you having met Upsilon instead, and so on.