# Workshop: Relativistic Locality (4 May 2019)

## Idea & Motivation

The problem of whether quantum theory is compatible with the causal structure of the spacetime as this is understood by the theory of relativity is an old and central problem in contemporary physics and philosophy of physics. The talks of this mini-workshop address this issue from different perspectives, paying special attention to the diversity of the locality concepts that have been suggested to test whether quantum theory is relativistically local.

## Speakers

- Neil Dewar (MCMP)
- John Dougherty (MCMP)
- Gábor Hofer-Szabó (Budapest)
- Miklós Rédei (LSE/MCMP)
- Federico Zalamea (Paris)

## Attendance

**April 23**if you intend to attend.

## Program

Time | Event |
---|---|

09:30 - 10:30 | Neil Dewar: Locality and Causal Graphs |

10:30 - 11:00 | Coffee Break |

11:00 - 12:00 | Federico Zalamea (collaboration with P. Martin-Dussaud and C. Rovelli): Bell’s Local Causality and Relational Quantum Mechanics |

12:00 - 14:00 | Lunch Break |

14:00 - 15:00 | Gábor Hofer-Szabó: Bell's Local Causality in Local Physical Theories |

15:00 - 16:00 | Miklós Rédei: How to Express Locality in Categorial Quantum Field Theory? |

16:00 - 16:15 | Coffee Break |

16:15 - 17:15 | John Dougherty: Subsystem Independence in Gauge Theories |

## Abstracts

### Neil Dewar: Locality and Causal Graphs

There has recently been a great deal of interest in relating the locality conditions discussed in foundations of physics (Bell locality, Einstein locality, etc.) to conditions on causal graphs (such as the Causal Markov Condition), by treating spacetime theories as causal graphs. In this talk, I attempt to give a synoptic overview of these efforts, and consider what the implications might be for our understanding of these issues.top

### John Dougherty: Subsystem Independence in Gauge Theories

A quantum field theory associates algebras of observables to regions of spacetime. The categorial quantum field theory program aims to understand quantum field theories by characterizing the properties that such an assignment should satisfy. Of particular interest are locality properties; as Rédei (2014) shows, the intuitive notion of locality ramifies into various technical notions, of which some are spatiotemporal in nature and some causal. Gyenis and Rédei (2018) define a notion of subsystem independence that is well-defined in any category and propose a novel locality axiom on the basis of this independence notion. However, this axiom---or, more accurately, one of its presuppositions---is typically violated by gauge theories, such as the quantum theories of electromagnetism and the weak and strong forces. In this talk I explain the reason for the violation of this axiom and consider whether and how Gyenis and Rédei's proposal can modified so that it holds in gauge theories.

top

### Gábor Hofer-Szabó: Bell's Local Causality in Local Physical Theories

First, I implement Bell's notion of local causality in the framework of local physical theories, a framework which is rich enough to integrate probabilistic and spatiotemporal concepts and intuitions. Next, I relate Bell's notion of local causality to other locality and causality concepts such as the common cause principle, local primitive causality, no-signaling, stochastic Einstein locality, causal Markov condition, the EPR scenario and Bell's inequalities.top

### Miklós Rédei: How to Express Locality in Categorial Quantum Field Theory?

The talk reviews the basic ideas of the categorial approach to quantum field. The key concept in this approach is a covariant functor between the category of spactimes and the category of C* algebras representing observables localized in a given spacetime. The causal independence of spacelike separated quantum systems is implemented in this framework by imposing locality conditions on the covariant functor. The talk presents a purely categorial notion of subobject independence in a general category. It is argued that specifying the suggested categorial subobject independence concept in terms of the category of operator algebras with operations as morphisms one obtains an independence condition that should be postulated for the covariant functor to hold in order to express physical locality in categorial local quantum field theory.top

### Federico Zalamea (collaboration with P. Martin-Dussaud and C. Rovelli): Bell’s Local Causality and Relational Quantum Mechanics

It is sometimes claimed that relational quantum mechanics is local. The goal of this talk will be to clarify in which sense this claim can be compatible with Bell’s theorems. To do so, we will comeback to Bell’s formulation of the concept of “local causality” and stress the role played by the notion of “beables”. On the one hand, they provide the basic framework outside of which local causality is meaningless. On the other, “beable” is also a flexible concept that each interpretation of quantum mechanics has to mold. After having discussed what “beables” are in the relational interpretation, we will question whether Bell’s non-local causality manages to capture the idea of space-like influence it was designed for.top

## Venue

Professor-Huber-Platz 2

80539 München**Room W 401**

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