Some Lessons from Haag's Theorem

Abstract: Haag’s theorem is a classic no-go theorem: it rigorously demonstrates that there is a conflict between the interaction picture and other basic, intuitive-seeming assumptions in QFT. The precise significance of the theorem continues to be debated, however. I will focus on two big-picture questions in this talk. First, why are there multiple, distinct responses to Haag's theorem? Here I will compare and contrast these and, in so doing, articulate the methodological choices motivating them. Second, if our goal is building usable models of phenomena, why should we care about esoteric results like Haag's theorem? Here I will draw on an analogous result in the social sciences to make the case that results like Haag's theorem help us organize models' varied applications and prioritize investigations in model development.

HEP - theoryhistory and philosophy of physics

Audience: advanced learners

( paper | video )

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Tricontinental Quantum Fundamentals Seminar

Series comments: The Tricontinental Quantum Fundamentals Seminar (3C-QFS) is an online seminar series connecting researchers from Australia, Europe, and America. Our goal is to facilitate discussion between the three continents and bring together those working on foundational topics in relativistic quantum physics, covering but not limited to:

• Measurement, localisation, and causality in relativistic quantum theory
• Energy conditions and quantum inequalities
• Non-locality and observer-dependence of entanglement
• Quantum reference frames and symmetries in quantum theory
• Holography, AdS/CFT, and analogue gravity

For 3C-QFS, we wish to foster an inclusive community and promote open discussion by encouraging a casual atmosphere during the seminars.

The seminars are held online via Zoom, consisting of 40-60 minute talks followed by additional time for questions. We meet every three weeks on Tuesday, alternating between two times in order to connect research communities across two of the three continents.

For those unable to join the seminars live, talks are recorded and hosted on the 3C-QFS YouTube channel.

The seminar series is primarily for students and academics active in the foundations of physics. To sign up for the mailing list and join the seminars live, please complete the registration form on the 3C-QFS website.

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