#### DarMM

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Agreed, if it is possible in principal you have a form of outcome subjectivity. Crudely speaking in a Copenhagenish view QM is a probability calculus for impressions left in a Classical/Boolean background by Quantum/Non-Boolean systems. If we have a Masanes type superobserver in principal then it has to be acknowledged that this classical background is not in principle unique and there can be other classical backgrounds whose events cannot be logically combined with our own. I sketched a PR-box version of Masanes due to Bub here:For clarity we should separate two issues. 1) Is Wigner's operation possible in practice or in principle? 2) If Wigner's operation is possible in principle, and if we at least pretend it is therefore possible in practice with sufficient tech, is it conceivable Friend is alive and apparently sentient afterwards? I was only saying yes to the latter. I think, at a minimum, this is straighforwardly true in the Masanes type "full unitary reversal" versions of the protocol.

### A Realization of a Basic Wigner's Friend Type Experiment

Superobservers shouldn't be allowed to be outside the rules of QT I don't think anyone claims they are. But making the measurement I described would require that the superobserver can maintain quantum coherence over an entire human brain. That doesn't seem practically possible, and depending...

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In the Deutsch version of Wigner's friend where the backgrounds later combine this leads to observers with incompatible memories.

Regarding (1) I do think there are strong arguments it's not possible in principle. It seems ##\mathcal{X} \notin \mathcal{A}\left(\mathcal{O}\right)## where ##\mathcal{O}## is the observable horizon.