ewbrownv comments on Problematic Problems for TDT - Less Wrong
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You can construct a "counterexample" to any decision theory by writing a scenario in which it (or the decision theory you want to have win) is named explicitly. For example, consider Alphabetic Decision Theory, which writes a description of each of the options, then chooses whichever is first alphabetically. ADT is bad, but not so bad that you can't make it win: you could postulate an Omega which checks to see whether you're ADT, gives you $1000 if you are, and tortures you for a year if you aren't.
That's what's happening in Problem 1, except that it's a little bit hidden. There, you have an Omega which says: if you are TDT, I will make the content of these boxes depend on your choice in such a way that you can't have both; if you aren't TDT, I filled both boxes.
You can see that something funny has hapened by postulating TDT-prime, which is identical to TDT except that Omega doesn't recognize it as a duplicate (eg, it differs in some way that should be irrelevant). TDT-prime would two-box, and win.
Indeed. These are all scenarios of the form "Omega looks at the source code for your decision theory, and intentionally creates a scenario that breaks it." Omega could do this with any possible decision theory (or at last, anything that could be implemented with finite resources), so what exactly are we supposed to learn by contemplating specific examples?
It seems to me that the valuable Omega thought experiments are the ones where Omega's omnipotence is simply used to force the player to stick to the rules of the given scenario. When you start postulating that an impossible, acausal superintelligence is actively working agaisnt you it's time to hang up your hat and go home, because no strategy you could possibly come up with is going to do you any good.
The trouble is when another agent wins in this situation and in the situations you usually encounter. For example, an anti-traditional-rationalist, that always makes the opposite choice to a traditional rationalist, will one-box; it just fails spectacularly when asked to choose between different amounts of cake.