I believe this hypothesis assumes some sort of metaphysical property to consciousness. Also, Permutation City did it first (consider this a book recommendation).

Disclaimer: I'm not a physicist. I'm just some random internet dude who likes learning things. My understanding is that a single photon wouldn't count as an observer. It doesn't even experience time (from the point of view of the photon, admission and absorption are simultaneous). Now if that photon is entangled with another photon, that can then be considered an observer. Someone please correct me if this is not accurate.

As in "an observer which/who requires causality and cannot exist in superposition". Whatever that is. Is causality a product of at least a minimal level of awareness? (We won't be able to tell, as exploring the concept of causality already presupposes awareness.)