Tomorrow our new postdoc Vilasini will tell us about "Causality and its compatibility with space-time structure". See below for the abstract. We start at 2pm on zoom: https://ethz.zoom.us/j/362994444.

Best,

Joe


Abstract:

We often do not distinguish between the directions of causation and (space-)time, even though causality can be defined operationally and independent of a space-time structure. Separating the concepts of causality and space-time and characterising how they fit together would give crucial insights into the different notions of causality such as operational causality, relativistic causality and logical consistency. Motivated by this, we develop a causal modelling framework for operationally characterising causation in the presence of cyclic, fine-tuned and non-classical causal influences. In the process, we distinguish between two kinds of causal loops that can arise in our framework, depending on operational detectability. We then define how this general class of causal models can be embedded “compatibly” in a space-time structure i.e., without leading to signalling outside the future. We derive necessary and sufficient conditions for a causal model to be compatible with an embedding in a space-time structure, and to rule out certain kinds of causal loops in the model. In particular, this provides an operational framework for analysing causality in the post-quantum “jamming” theories proposed in [1,2], and generalises their results from Bell-type scenarios to arbitrary causal structures. Furthermore, we show that post-quantum jamming can lead to superluminal signalling, contrary to the claims of [1,2], we identify missing assumptions in these claims as well as new features of post-quantum theories that admit jamming non-local correlations. 

Joint work with Roger Colbeck.

[1] Grunhaus, J., Popescu, S., Rohrlich, D. Phys. Rev. A53, 3781–3784 (1996).
[2] Horodecki, P. , Ramanathan, R. Nat. Comms. 10, 1701 (2019).