Causality violations in quantum field theory? A ping-pong ball test

Abstract: It has been pointed out that there are local operations in quantum field theory which can lead to superluminal effects. A prominent example is the "impossible measurements scenario" put forward by Sorkin. In this presentation, it will be explained that such apparent difficulties are not a specific defect or pathology of quantum field theory, but that they also occur in classical relativistic field theory. On the other hand, if the operations are required to be mediated by local interactions, then there are no superluminal effects. If time allows, it will also be explained that the time-travel analogue scenario in quantum circuits proposed by Deutsch (D-CTC) is, on one hand, not related to closed timelike curves in the sense of general relativity, and on the other hand, can be realized also in classical statistical theories and is therefore not based on quantum mechanics.

HEP - theorymathematical physicsquantum 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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