I didnt read all the links but as I understand Lubos take on the nature of symmetries, I associate this to basically mean that the choice of observer (in as I envision Lubos thinking here) is thought of a "gauge choice"; and to have a specific information state you need to fix the gauge (observer). The objectivity rather lies in the equivalence class of observers. And psi is not an equivalence class, its gauge dependent.I have read Lubos Motl blogposts (https://motls.blogspot.com/2012/11/why-subjective-quantum-mechanics-allows.html and https://motls.blogspot.com/2019/03/occams-razor-and-unreality-of-wave.html) stating that the wavefunction is subjective. This means that it is perfectly valid that two different observers use two different wavefunctions to describe the same system. I do not understand how it makes any sense.
I feel like I'm missing something in order to understand Lubos Motl and I feel like he's right
So I am entirely confused about ##|\psi \rangle##. Can someone shed some light?
One can make other comments on this view, ie. objection to reducing the observer to a gauge choice, but this has been discussed elsewhere in the BTSM section so i will not pull that up here. But if you ignore these objections the logic above is i think clear enough and makes perfect sense. Cases where it does not make sense are i think also edges of things where we are forced to BTSM discussions.