Renato Renner - Why Wigner’s friend matters for quantum gravity

An emerging insight in quantum gravity is that observable quantities gain meaning only when defined relative to explicitly modelled observers. These observers must themselves be physical and, hence, are subject to the laws of quantum theory. On a different front, it has long been understood in quantum foundations that treating observers as quantum systems leads to conceptual challenges, exemplified by Wigner’s friend thought experiments. In my talk, I will show how recent insights from these thought experiments can help clarify questions that arise when incorporating observers into quantum-gravitational scenarios. Related paper: arXiv:2504.03835 --------------------------------------------------------------------------------------------------------- For announcements of upcoming seminars you can visit https://withoutspacetime.org/#upcomin..., or join our mailing list from the website's footer. ---------------------------------------------------------------------------------------------------------