From observer-dependent facts to frame-dependent measurement records in Wigner friend scenarios

Abstract: The description of Wigner-friend scenarios -- in which external agents describe a closed laboratory containing a friend making a measurement -- remains problematic due to the ambiguous nature of quantum measurements. One option is to endorse assumptions leading to observer-dependent facts, given that the friend's measurement outcome is not defined from the point of view of the external observers. We introduce in this work a model in a relativistic context showing that these assumptions can also lead to measurement records that depend on the inertial reference frame in which the agents make their observations. Our model is based on an entangled pair shared by the friend and a distant agent performing space-like separated measurements. An external observer at rest relative to the closed laboratory and observers in a moving frame do not agree on the observed records, which are not Lorentz transforms of one another.