27Oct

Sigma Club Seminar by Professor Kasia Rejzner (University of York)

Hosted by the Department of Philosophy, Logic and Scientific Method and CPNSS.

In person at LAK 2.06, Lakatos Building, London, WC2A 2AE United Kingdom. Online (Via Zoom)

Monday 27 October 2025 4pm - 5.30pm

Title: Quantum reference frames and semi-local observables in quantum field theory

Abstract: I will start with discussing various notions of locality in quantum field theory and how they are broken. In the Haag-Kastler approach to axiomatic QFT, the theory is specified by a net of local algebras of observables. In the recent paper by Fewster, Janssen, Loveridge, Waldron and myself we have argued that in the presence of symmetries, in order to operationally introduce measurement into this framework, one naturally arrives at the notion of quantum reference frames (QRF). Concretely, one constructs relational/relativised observables by taking the symmetry invariant observables of the joint algebra of the system and the QRF. Such observables can by seen as semi-local.

This event will take place in person on LSE’s campus. However, those unable to attend in person will have the option of taking part online.

To join online just follow these instructions:

Please note that these events are routinely recorded, with the edited footage being made publicly available on our website and YouTube channel. We will only record the audio, the slides and the speaker and will not include the Q&A section. However, any question asked during the talk itself will feature in the final edit.

LSE holds a wide range of events, covering many of the most controversial issues of the day, and speakers at our events may express views that cause offence. The views expressed by speakers at LSE events do not reflect the position or views of the London School of Economics and Political Science.