Now that I think about it, I think probabilistic Newcomb still has the problem that perfect predictor Newcomb has: you are not told how the predictor achieves its predictions, only that it always has a certain success rate. This leaves you to conclude that it has that success rate even when you do strange things like run a copy of it and do the opposite of what the copy says.
All of the trippy aspects of the thought experiment have to do with this assumption. The predictor is a black box that somehow anticipates everything you could possibly think about it. (Even in the probabilistic version, it achieves the same success rate no matter what you think, which is sort of the same thing.)
Once you specify what the predictor is actually doing, the problem dissolves. If it is using some sort of detailed simulation that actually takes into account all of your thoughts about it, then that means something like backwards causation really is happening (and also means that the predictor cannot be accurate in the infinite regress case – you cannot ask it to faithfully simulate a copy of itself*). That situation is weird, but also very unlike the situations we tend to face in the real world. On the other hand, if the predictor is just using demographics or the like, it does not have the detailed information that you have about your decision procedure, and you don’t have to worry about your decision now “causing” suboptimal box fillings in the past.
(You do have to worry about ideas like “most people end up two-boxing because they think it can’t influence the result, which leads the predictor to think you’ll two-box, which you don’t want.” This is a real problem, but it’s more of a coordination problem than a trippy retro-causality problem. It’s analogous to a coordination problem with any kind of actuarial prediction, e.g. “insurance for my demographic will cost less if people in my demographic take fewer risks, but since the demographic trait is unchangeable, everyone figures they can’t affect the insurance price themselves, and end up taking a lot of risks that drive the price up for everyone.” Standard free rider problem.)
*(although if the <100% probabilistic accuracy were achieved by some sort of simplification, it’s possible that an infinite regress of simplified predictors could converge)
I think this is basically right. Relevant facts:
1. Yudkowsky is working in the hypothetical where the predictor is always, 100% of the time, right.
2. From this he concludes it can’t be doing anything boring and demographic, and must instead be completely simulating your thought process (because otherwise it wouldn’t be right 100% of the time regardless of what you do).
2a. As a subpoint, he’s assuming that the predictor has computational capacity that from your perspective might as well be infinite; the predictor can simulate anything you can do, but not necessarily anything the predictor can do.
3. Yudkowsky is worrying about strong general artificial intelligence, and believes that such entities are actually plausible.
