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The notorious quantum measurement problem brings out the difficulty toreconcile two quantum postulates: the unitary evolution of closed quantumsystems and the wave-function collapse after a measurement. This problematicsis particularly highlighted in the Wigner's friend thought experiment, wherethe mismatch between unitary evolution and measurement collapse leads toconflicting quantum descriptions for different observers. A recent no-gotheorem has established that the (quantum) statistics arising from an extendedWigner's friend scenario is incompatible when one try to hold together threeinnocuous assumptions, namely no-superdeterminism, parameter independence andabsoluteness of observed events. Building on this extended scenario, weintroduce two novel measures of non-absoluteness of events. The first is basedon the EPR2 decomposition, and the second involves the relaxation of theabsoluteness hypothesis assumed in the aforementioned no-go theorem. To provethat quantum correlations can be maximally non-absolute according to bothquantifiers, we show that chained Bell inequalities (and relaxations thereof)are also valid constraints for Wigner's experiment.

Events in quantum mechanics are maximally non-absolute