Can we control the past?

"I think that you can “control” events you have no causal interaction with, including events in the past, and that this is a wild and disorienting fact, with uncertain but possibly significant implications. This post attempts to impart such disorientation.

My main example is a prisoner’s dilemma between perfect deterministic software twins, exposed to the exact same inputs. This example that shows, I think, that you can write on whiteboards light-years away, with no delays; you can move the arm of another person, in another room, just by moving your own. This, I claim, is extremely weird.

My topic, more broadly, is the implications of this weirdness for the theory of instrumental rationality (“decision theory”). Many philosophers, and many parts of common sense, favor causal decision theory (CDT), on which, roughly, you should pick the action that causes the best outcomes in expectation. I think that deterministic twins, along with other examples, show that CDT is wrong. And I don’t think that uncertainty about “who are you,” or “where your algorithm is,” can save it.

Granted that CDT is wrong, though, I’m not sure what’s right. The most famous alternative is evidential decision theory (EDT), on which, roughly, you should choose the action you would be happiest to learn you had chosen. I think that EDT is more attractive (and more confusing) than many philosophers give it credit for, and that some putative counterexamples don’t withstand scrutiny. But EDT has problems, too.

In particular, I suspect that attractive versions of EDT (and perhaps, attractive attempts to recapture the spirit of CDT) require something in the vicinity of “following the policy that you would’ve wanted yourself to commit to, from some epistemic position that ‘forgets’ information you now know.” I don’t think that the most immediate objection to this – namely, that it implies choosing lower pay-offs even when you know them with certainty – is decisive (though some debates in this vicinity seem to me verbal). But it also seems extremely unclear what epistemic position you should evaluate policies from, and what policy such a position actually implies.

Overall, rejecting the common-sense comforts of CDT, and accepting the possibility of some kind of “acausal control,” leaves us in strange and uncertain territory. I think we should do it anyway. But we should also tread carefully."

https://www.lesswrong.com/posts/PcfHSSAMNFMgdqFyB