Equivalence of interpretations in more elaborate setups

[greypilgrim]

Hi.

One of the first things I was told about quantum interpretations was that they are all equivalent, i.e. make the same experimentally testable predictions. This seems reasonable for simple experiments whose mathematical description is straightforward, like preparation – unitary evolution – measurement. But is this necessarily true for more elaborate setups like Wigner's friend type experiments, where different interpretations don't even agree when and how many measurements are taking place?

Usually it's said that all interpretations must lead to the same experimentally testable predictions because they all use the same math/postulates. However, some of them differ in when to apply which postulate, especially concerning the postulate about unitary evolution and the measurement postulate. So if different interpretations don't agree when to use which mathematical description, why is it still general consensus that they necessarily must all lead to the same experimental results in the end?

Some more recent papers like Frauchiger–Renner seem to address this, though they are highly controversial.

 

[PeterDonis]

is this necessarily true for more elaborate setups like Wigner's friend type experiments, where different interpretations don't even agree when and how many measurements are taking place?

If you have a disagreement about when a measurement takes place in a given scenario, it's not about the interpretation of QM; it's a disagreement about how to apply basic QM to that scenario. Part of the process by which basic QM makes predictions requires specifying when a measurement takes place in any particular scenario. So two "interpretations" of a Wigner's friend experiment that disagree on when a measurement takes place are not really disagreeing about the interpretation of QM: they are disagreeing about how to apply basic QM to the scenario.

Unfortunately, the possibility of such disagreements is inherent in QM as it currently stands, since as it currently stands basic QM does not tell you exactly when a measurement takes place. It just says to assume one takes place wherever you need to to make correct predictions.