Some Tenets of QBism | Chris Fuchs

[Achrononmaster]

@1:00 To make sense of Frauchiger and Renner's "no go" theorem one has to first make sense of "I am certain that..." which is not a statement in physics. So single-world theory is safe. Frauchiger and Renner were doing philosophy, not quantum physics. Also their 3rd "Assumption S" was single-world. So it is only two other conditions one must accept for single-world to make no sense. BUT one must, thirdly, accept all of orthodox quantum mechanics as a complete theory of reality, without this third claim of faith there is no manifest "no go" theorem.
The Frauchiger and Renner result thus only bothers someone who believes QM is a complete theory of physics, so it would not bother Einstein. It also does not bother Bohmians, and yes, also it is no bother to QBism. So Frauchiger and Renner have really not said anything much of substance about certainty or inevitability or possibility of Many Worlds theories, they certainly have not at all ruled out single-world physics. You cannot argue in favour of Many Worlds by arguing, "Hey, a lot of other philosophies are inconsistent." Bohmian or QBist says, "So what?"
Heck, even Copenhagen Interpretations escape the Frauchiger and Renner "no go" so it is not really much of a "no go." In fact their "Table 4" shows that there is no popular existing interpretation of QM that their result rules out.

[paulaustinmurphy]

Christopher Fuchs states that QBists wrote the Wikipedia page on QBism. So that's how Wiki works!?

[Achrononmaster]

No one in the Lab has ever been able to produce anything that is subjective in basic quantum physics. All real laboratory QM is measurement-dependent, but that is not subjectivity. So, while I like the epistemological elements of QBism, it is barking up the wrong tree most probably (pun intended). Epistemology is key, QM is all about what we can know and measure and what we cannot. Explain _that_ and you can explain QM without needing to mention subjectivity.
Subjectivity is (I would guess) epiphenomenal, it emerges in complex systems at higher levels, and is how we observers gain knowledge and understanding and the whole capacity to _do_ quantum physics and conduct measurements, but the elementary quantum processes do not depend upon any subjective observer. How we see the world does depend upon what we do, but that is true regardless of the basic physics, it is true in classical mechanics.