Are quantum subsystems invariant?

Abstract: What is a physical subsystem? How classical physical subsystems localized in spacetime (causally independent) are identified from quantum ones? Traditionally, classical systems have been uniquely identified with quantum systems, typically represented as factors in Hilbert space for finite-dimensional systems or associated with a local (microcausality) algebra of operators in QFT. Both representations aim to instantiate a specific prescription of subsystems' independence, that they must be statistically independent for state preparations and measurements. Despite this prescription, it is easy to show that canonical linearized quantum gravity prevents us from obtaining a gauge-invariant local algebra, thus undermining one of the conditions needed for statistical independence of subsystems in QFT. Arguably, this precludes most of the modeling associated with early universe cosmology as well as current attempts to model gravity-induced-entanglement table-top experiments. Nonetheless, primarily it presents a major roadblock towards a theory of quantum gravity. In this talk, after reviewing the aforementioned points, I will propose that a way forward is that the unique identification between quantum and classical systems should be dropped, and instead this mapping should be dynamical, which opens the possibility for a single-world unitary quantum mechanics.

general relativity and quantum cosmologyHEP - theoryquantum 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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