A strong no-go theorem on the Wigner’s friend paradox

https://www.nature.com/articles/s41567-020-0990-x

lDoes quantum theory apply at all scales, including that of observers? New light on this fundamental question has recently been shed through a resurgence of interest in the long-standing Wigner’s friend paradox. This is a thought experiment addressing the quantum measurement problem—the difficulty of reconciling the (unitary, deterministic) evolution of isolated systems and the (non-unitary, probabilistic) state update after a measurement

originally posted at https://stacker.news/items/631721