A new insight from the Frauchiger and Renner paper affecting MWI

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I don't want to get too off-topic, but just to respond to this: I think Vaidman's view is sufficient. You assume that Hilbert space represents a density of worlds and the only sensible (non-contextual) choice for a measure on Hilbert space is the amplitude squared . Then with some reasonable model of an observer, it's possible to show the observer will experience outcomes according to the Born rule.

Maybe you call that circular because it requires some assumption, but I don't see why that's a MW issue; it seems like most derivations of the Born rule apply to most interpretations. For example, The measurement postulates of quantum mechanics are operationally redundant (2019).
You're correct it is not just a MW problem - making the Born rule an assumption, as in Copenhagen, hardly seems to solve the issue.
Vaidman's solution seems very similar, or even identical, to Everett's?
 
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DarMM
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Basically yes, some equivalent assumption is made. But unlike with Copenhagen where the Born rule and unitary evolution are in conflict, this form of a Born-like assumption is compatible with unitary evolution.
That can be done in Copenhagen as well by showing the unitary evolution is compatible with the existence of a Boolean lattice or similar for macroscopic quantities.

The difference is in Copenhagen views this is considered to show compatibility as collapse is viewed as a kinematic relation. Where as in MWI collapse is shown to be an effective description of a dynamic process. Ironically work by Bub and Pitowsky is probably one of the better ones for showing the Born rule in MWI, it just doesn't have a solely MWI reading.
 
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You're correct it is not just a MW problem - making the Born rule an assumption, as in Copenhagen, hardly seems to solve the issue.
Vaidman's solution seems very similar, or even identical, to Everett's?
Vaidman's preferred approach is to just postulate it. It's called the the Born-Vaidman rule (see Tappenden 2011): an observer should set his subjective probability of the outcome of a quantum experiment in proportion to the total measure of existence of all worlds with that outcome. See also Vaidman's summary of his view.
 
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