BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Anne-Catherine de la Hamette (University of Vienna) DTSTART:20240611T070000Z DTEND:20240611T080000Z DTSTAMP:20260417T072446Z UID:3cqfs/19 DESCRIPTION:Title: I dentification is pointless: Localisation of systems and events in superpos itions of spacetimes\nby Anne-Catherine de la Hamette (University of V ienna) as part of Tricontinental Quantum Fundamentals Seminar\n\n\nAbstrac t\nA first step towards scenarios at the interface of quantum theory and g ravity is to consider a quantum superposition of semiclassical spacetimes\ , such as the one\, arguably\, sourced by a gravitating object in superpos ition. But what does it mean that a gravitational source is in a superposi tion of “different” locations? How can one compare points across the d ifferent manifolds? Due to the diffeomorphism invariance of general relati vity\, there is a priori no notion of the “same” or “different” po ints across the branches. In fact\, there are multiple ways of relating po ints or events on the different spacetimes. Here\, we make this concrete b y using coincidences of four scalar fields to construct a comparison map b etween all spacetimes in superposition\, which allows us to determine whet her a system or an event is located at the “same” or “different” p oints across the branches. Different choices of scalar fields can be under stood as different instantiations of quantum reference frames (QRFs)\, con necting the construction to recent research in the field of quantum founda tions. As an explicit application of this formalism\, we explore how the l ocalisation of events is relative to the choice of QRF and formulate a qua ntum generalisation of Einstein’s famous hole argument. The latter calls into question the metaphysical meaning of not just spacetime points but a lso the identification between spacetime points across manifolds in superp osition. Finally\, we discuss the implications of QRF changes for indefini te causal order\, the locality of interaction\, and potential empirical co nsequences in interference experiments.\n LOCATION:https://researchseminars.org/talk/3cqfs/19/ END:VEVENT END:VCALENDAR