If you come to a fork in the road, and go left, you shouldn't update your priors to assume that the right-hand fork didn't really exist. Equally, if you end up in WorldA, you shouldn't update your priors to assume that WorldB doesn't exist.
Of course, we don't have any evidence for WorldB existing, unlike the right-hand fork, since there's no experimental difference between MWI and Copenhagen right now. Given that, I'd assume the proper belief is "Either MWI or Copenhagen, with even odds between the two"?
If there is no experimental difference between MWI and Copenhagen, the "proper" belief is the one that serves your purposes other than seeking universal truths.
This is the public group instrumental rationality diary for the week of August 6th. It's a place to record and chat about it if you have done, or are actively doing, things like:
Or anything else interesting which you want to share, so that other people can think about it, and perhaps be inspired to take action themselves. Try to include enough details so that everyone can use each other's experiences to learn about what tends to work out, and what doesn't tend to work out.
Thanks to everyone who contributes!
Last week's diary; archive of prior diaries.
(Sorry for being late this week -- I'm on vacation and got distracted :-)