Society of Catholic Scientists
Stephen M. Barr (Univ. of Delaware): “The Role of the Observer in Quantum Mechanics”
Delivered at the second conference of Society of Catholic Scientists at the Catholic University of America, June 8–10, 2018. Re-recorded August 17, 2018.
More information about the Society of Catholic Scientists is available at www.catholicscientists.org.
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Interpreting the wavefunction as somebody's state of knowledge (see e.g. 29:57) turns it into a subjective device and it turns quantum probabilities into epistemic probabilities: if things were that way, QM would surely not have been empirically confirmed once and again because the wavefunction would just express the cognitive bias of the experimenter and I don't see why nature would have to adapt to that bias. So, Barr is not arguing from QM but from a rather unlikely interpretation of it. I think there is a more parsimonious way to argue from QM to the indispensability of the observer: the most austere interpretation of QM suggests that quantum systems do not have all of its physical properties determinate until a measurement has been accomplished by an observer (consider Wheeler's delayed choice experiment https://www.youtube.com/watch?v=H6HLjpj4Nt4&t=260s). This suggests that quantum physical properties are just phenomenal properties and the phenomenal immediately requires an observer.
Its a crime that this does not have more views, one of the best lectures on quantum mechanics ive come across!