Wigner’s friend and relational objectivity

The ‘Wigner’s friend’ thought experiment illustrates the puzzling nature of quantum measurement. Časlav Brukner discusses how recent results suggest that in quantum theory the objectivity of measurement outcomes is relative to observation and observer.

Credit: Image courtesy of Michele Sclafani.

The Wigner-friend paradox continues to fascinate physicists and philosophers alike 60 years after its discovery. This thought experiment conceived in 1961 by Eugene Wigner describes a physical situation in which two observers experience different facts. Since then, various attempts have been made to reconcile the observers’ different views, but a series of recent studies shows that they are fundamentally incompatible. The results can be interpreted to imply that in quantum physics the objectivity of facts is not absolute, but only relative to the observation and the observer.


Publication in Nature Reviews Physics:

Časlav Brukner "Wigner’s friend and relational objectivity", 2022

DOI: 10.1038/s42254-022-00505-8