PIRSA:22110098

Causality and Ideal Measurements of Smeared Fields in Quantum Field Theory

Jubb, I. (2022). Causality and Ideal Measurements of Smeared Fields in Quantum Field Theory. Perimeter Institute. https://pirsa.org/22110098

Jubb, Ian. Causality and Ideal Measurements of Smeared Fields in Quantum Field Theory. Perimeter Institute, Nov. 17, 2022, https://pirsa.org/22110098 

          @misc{ pirsa_PIRSA:22110098,
            doi = {10.48660/22110098},
            url = {https://pirsa.org/22110098},
            author = {Jubb, Ian},
            keywords = {Quantum Foundations},
            language = {en},
            title = {Causality and Ideal Measurements of Smeared Fields in Quantum Field Theory},
            publisher = {Perimeter Institute},
            year = {2022},
            month = {nov},
            note = {PIRSA:22110098 see, \url{https://pirsa.org}}
          }

Ian Jubb

Dublin Institute For Advanced Studies

Talk number
PIRSA:22110098
Collection
Talk Type
Subject
Abstract

The usual quantum mechanical description of measurements, unitary kicks, and other local operations has the potential to produce pathological causality violations in the relativistic setting of quantum field theory (QFT). While there are some operations that do not violate causality, those that do cannot be physically realisable. For local observables in QFT it is an open question whether the projection postulate, or more specifically the associated ideal measurement operation, is consistent with causality, and hence whether it is physically realisable in principle.

In this talk I will recap a criteria that distinguishes causal and acausal operations in real scalar QFT. I will then focus on operations constructed from smeared field operators - the basic local observables of the theory. For this simple class of operations we can write down a more practical causality criteria. With this we find that, under certain assumptions - such as there being a continuum spacetime - ideal measurements of smeared fields are acausal, despite prior heuristic arguments to the contrary. For a discrete spacetime (e.g. a causal set), however, one can evade this result in a ‘natural’ way, and thus uphold causality while retaining the projection postulate.

Zoom link:  https://pitp.zoom.us/j/94464896161?pwd=UkhPQnJONmlxYy9pQXJINThpY3l4QT09