metachirality

[Epistemic status: I may have gotten some things wrong so please point out any errors. I also papered over a lot of technical details in favor of presenting my intuitions. A lot of this is me thinking out loud. If you already know a lot about decision theory or want the gory details, I've listed a bunch of resources on decision theory at the bottom of this post.] Rationality is sometimes considered to be "maximizing expected utility". This seems pretty unambiguous but it turns out that what this means is pretty tricky to define, and different decision theories have different definitions of it. In this post, I will summarize causal decision theory, evidential decision theory, and updateless/functional/logical decision theory. For a while, there were two dominant decision theories, causal decision theory (CDT), and evidential decision theory (EDT): * Causal decision theory: Take actions that physically cause you to get higher expected utility. * Evidential decision theory: Take actions that would be evidence of you getting higher expected utility. To illustrate their differences and point out their problems, I'll introduce two scenarios: Newcomb's problem Omega is an entity who can predict your actions with 99% certainty. Importantly, Omega simulates you to predict your actions. They put $1,000 in a transparent box and $1,000,000 in an opaque box if and only if they predict that you would open only the opaque box to acquire the $1,000,000. Since picking only the transparent box doesn't maximize expected utility in either scenario, we are left with two options: picking only the opaque box (one-boxing) or picking both the transparent and opaque boxes (two-boxing). Do you one-box or two-box? A CDT agent two-boxes because Omega already put in or didn't put in the money in the opaque box, and they can't physically cause the past. An EDT agent one-boxes, because that would be evidence of them having received $1,000,000 instead of $1,000. EDT wins in Newcomb's pro