Wigner’s Friend Extended Thought Experiment. A Philosophers’ look

Frauchiger and Renner (2018) presented a no-go theorem inspired by the well-known Wigner’s friend paradox. Their work is a remarkable contribution to the foundations of quantum mechanics, insofar as it allows evaluation of the interpretations of the theory based on the assumptions that must be dropped to circumvent the contradiction. This paper aims to review the philosophically salient aspects of the paradox. To do so, we firstly introduce the original Wigner’s paradox and its consequences. Then we make explicit the logical structure of the extended paradox through the aid of multi-agent epistemic logic. Such work is useful not only for presenting a more accessible formulation of the paradox but also for evaluating its bearings on the main interpretations of quantum mechanics. We conclude that despite the fact that prima facie the paradox encourages an antirealist view, some possibilities are left open for realist interpretations of quantum mechanics