James Fraser – "The Long S-matrix Program"
In 1943, Heisenberg proposed a radical reformulation of relativistic quantum theory in which the basic dynamical object is not a local Schrödinger-type time-evolution equation but a set of global conditions imposed directly on the asymptotic S-matrix. Contrary to the standard historical narrative, this idea was not rendered obsolete by the success of renormalised quantum electrodynamics. Instead, it shaped a wide range of post-war research programmes. The causal perturbation approach, early axiomatic quantum field theory, dispersion-relation techniques, and Chew’s S-matrix bootstrap can all be read as continuations of Heisenberg’s project, each adding various “causality conditions” to Heisenberg’s original stock of condition. Although the original ambition of eliminating local time-evolution equations was never fully realised, these developments had a lasting impact on our understanding of quantum field theory.
Laurie Letertre – "Temporal nonlocality from indefinite causal orders"
A temporal counterpart to Bell nonlocality would intuitively refer to the presence of non-classical correlations between timelike-separated events. The hypothesis of temporal nonlocality has received recent support in the literature, and its existence would likely influence the future development of physical theories. This paper shows how Adlam's principle of temporal locality can be violated within a protocol involving indefinite causal orders. While the derivations of Leggett-Garg inequalities or the temporal CHSH inequality are said to involve problematic assumptions preventing a targeted probing of a well-defined notion of temporal nonlocality, the present test is free from such worries. However, it is shown that the test, in its current formulation, fails to be fully model-independent. We provide several considerations regarding the physicality of ICOs that could help alleviate this drawback. In the present work, a specific physical interpretation of ICOs in terms of retrocausal influences would explain the presence of temporally nonlocal correlations. It is argued that, as the physical underpinnings of temporal nonlocality might also account for standard Bell nonlocality, focusing on the former as a consequence of ICOs might support under-explored strategies to make sense of the latter.
Mike Miller – "Narratability in Quantum Field Theory"
A number of arguments have been advanced which suggest that relativistic quantum theories will exhibit a phenomenon called narratability failure (Aharonov and Albert 1984; Myrvold 2002; Albert 2016), though significant limitations on the failure of narratability have been established by Myrvold (Myrvold 2016). Extant arguments in the debate are inconclusive because they address quantum mechanics in a quasi-relativistic setting, rather than treating the problem directly in quantum field theory. In this talk I employ the separating property of states in quantum field theory to extend Myrvold’s limitative results, and I show that the possible worlds of quantum field theory are almost always narratable.
Maria Papageorgiou – "Recent developments on local measurement theory for QFT: no superluminal causal influences and signalling"
Recent developments in measurement theory for relativistic QFT offer new perspectives on the long-standing Measurement Problem. The strict dichotomy between measurement and dynamics is absent in relativistic theories. This is because the representation of dynamics in such theories imposes crucial constraints on relativistic quantum measurements. Sorkin's "impossible measurements" scenario, and related work, demonstrates that microcausality alone is insufficient to prevent superluminal signalling in relativistic quantum theories employing Lüders' rule for non-selective measurements. This raises fundamental questions about local operations and their interpretation in QFT. In this talk, we will examine how recently developed measurement theories, particularly detector based approaches and the Fewster-Verch framework in algebraic QFT, address these challenges. Further, we will argue that when represented using the FV framework, an intervention on a quantum field system by performance of a local selective measurement does not bring about a physical change in the local properties of the system in any spacelike separated region.
Yanis Pianko – "Quantization and Relativistic Dynamics"
Porter Williams – "Causality and Causation in Quantum Field Theory"
Adamantia Zampeli – "Spacetime quantum theories and operational causality"