PT  - JOURNAL ARTICLE
AU  - Proietti, Massimiliano
AU  - Pickston, Alexander
AU  - Graffitti, Francesco
AU  - Barrow, Peter
AU  - Kundys, Dmytro
AU  - Branciard, Cyril
AU  - Ringbauer, Martin
AU  - Fedrizzi, Alessandro
TI  - Experimental test of local observer independence
AID  - 10.1126/sciadv.aaw9832
DP  - 2019 Sep 01
TA  - Science Advances
PG  - eaaw9832
VI  - 5
IP  - 9
4099  - http://advances.sciencemag.org/content/5/9/eaaw9832.short
4100  - http://advances.sciencemag.org/content/5/9/eaaw9832.full
SO  - Sci Adv2019 Sep 01; 5
AB  - The scientific method relies on facts, established through repeated measurements and agreed upon universally, independently of who observed them. In quantum mechanics the objectivity of observations is not so clear, most markedly exposed in Wigner’s eponymous thought experiment where two observers can experience seemingly different realities. The question whether the observers’ narratives can be reconciled has only recently been made accessible to empirical investigation, through recent no-go theorems that construct an extended Wigner’s friend scenario with four observers. In a state-of-the-art six-photon experiment, we realize this extended Wigner’s friend scenario, experimentally violating the associated Bell-type inequality by five standard deviations. If one holds fast to the assumptions of locality and free choice, this result implies that quantum theory should be interpreted in an observer-dependent way.