Epistemic Status: Exploratory

Consider Parfit's Hitchhiker from the perspective of a completely selfish agent:

"Suppose you're out in the desert, running out of water, and soon to die - when someone in a motor vehicle drives up next to you. Furthermore, the driver of the motor vehicle is a perfectly selfish ideal game-theoretic agent, and even further, so are you; and what's more, the driver is Paul Ekman, who's really, really good at reading facial microexpressions. The driver says, "Well, I'll convey you to town if it's in my interest to do so - so will you give me $100 from an ATM when we reach town?"

When you're in the desert, the deal is to your benefit, but once you're in town, you're incentivised to defect. So you should expect the driver to not believe you and leave you to die in the desert.

An agent using Updateless Decision Theory will avoid an untimely death, but I believe that someone should be able to survive without advanced decision theories (ie. just using Causal Decision Theory). And indeed, if you can successfully pre-commit to paying the driver the money, then you will survive, but this leads to the question of whether you can.

But first, I note that pre-commit has two meanings: in a broad sense, irrevocably deciding to follow a particular course of action; and in a narrow sense, as just described, but in a publicly verifiable manner. Since we are assuming that the driver has a high ability to guess your decision, these two definitions end up collapsing within this scenario.

Now, we can imagine a host of situation in which you could pre-commit: you could be trusted to pay if a court would fine you $150 if you didn't uphold your bargain, or if you were deontologist who thought that being moral was more important than a good outcome could be trusted or if God would let you into heaven if you are good. What about if we exclude outside rewards/punishments and we assume that you are completely self-interested and rational? Is pre-commitment possible is such circumstances?

The definition of "completely rational" is important here. If it means that they must make every decision rationally (according to CDT) and are forbidden to self-modify in a way that makes them lose this property, then it necessarily follows that they will defect. On the other hand, if it means that they alway...

Alexander Byaly

Alexander Byaly