I'm not sure objective reality needs preserving, it's the interpretation of that reality by conscious observers that's important to conscious observers - we like our shared objective reality to be consistent - and to establish that means comparing experiences.What always bugs me about these experiment explanations is that there is always not just two observers .. there's always another one observing the likes of both Wigner and his friend and its that one who is always preserving the objective reality. Its assumed that the third person (Ie: the passive narrator of the experiment .. Carroll .. an Everettian) is already part of the objective reality under test .. which completely undermines the whole purpose of the experiment.
Also, as was pointed out, a quantum measurement or observation occurs when a quantum system in superposition interacts with the environment and the superposition decoheres, leaving a record in the environment. Photons that interact in isolation just become entangled (with each other), but are not making a measurement - unless and until they interact with the environment.
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