You should be able to justify any particular course of action without a metaphysical commitment to the reality of unobservable components of the universe's wave function.
A (counterfactual) agent is accelerated (very) rapidly away from you, taking with him someone you care about and leaving someone he cares about. He passes out of your future light cone. Both the agent and your loved one are now an unobservable components of the universe's wave function. You and the agent have enough information about each other that you can make predictions about each other's behavior. Each of you can choose to be kind to the loved one of the other (at a slight net cost in utility to yourself and a significant gain to the other) or to exploit them for a slight gain to yourself. You know that the agent behaves according to UDT. Do you exploit the agent's loved one or cooperate, being kind?
If you corrupt your model of reality such that you believe parts of the universe's wave function don't exist when you can not observe them then you will defect. You will be making a mistake. Your policy would make you Lose!
Your hypothetical has nothing to do with quantum mechanics or many worlds, and everything to do with special relativity. "Unobservable components of the wavefunction", in the many world sense, are areas where a different decisions was made or a different outcome observed.
In fact, extending it to many worlds actually hurts the point you want to make. The "(counterfactual) agent" makes both decisions (exploit, be kind), and you make both decisions. Further, you can't win in every world. Consider Newcomb's problem- even if omega (the...
Today's post, Living in Many Worlds was originally published on 05 June 2008. A summary (taken from the LW wiki):
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