Wigner's convoluted friends

Abstract

Considering a complicated extension of a Wigner's friend scenario, Frauchiger and Renner (FR) allegedly showed that “quantum theory cannot consistently describe the use of itself.” However, such a result has been under severe criticism, as it has been convincingly argued to crucially depend on an implicit, non-trivial assumption regarding details of the collapse mechanism. In consequence, the result is not as robust or general as intended. On top of all this, in this work we show that a much simpler arrangement—basically an EPR setting—is sufficient to derive a result fully analogous to that of FR. Moreover, we claim that all lessons learned from FR's result are essentially contained within the original EPR paper. We conclude that FR's result does not offer any novel insights into the conceptual problems of quantum theory.