Relativity of Causal Structure in Quantum Theory

TL;DR

This paper demonstrates that in quantum theory, the causal structure of events is not absolute but can vary between observers, challenging the traditional fixed view of causality in physics.

Contribution

It introduces the concept of relativity of causal structure in quantum theory, showing that different observers can assign different causal orders to the same events based on operational considerations.

Findings

Observers can assign different causal structures to the same quantum experiment.

The causal structure in quantum theory is not fixed and can depend on the observer's perspective.

Challenges the assumption of absolute causal order in traditional physics.

Abstract

Quantum theory is a mathematical formalism to compute probabilities for outcomes happenning in physical experiments. These outcomes constitute events happening in space-time. One of these events represents the fact that a system located in the region of space where is situated a physical device has a certain value of a physical observable at the time when the device fires the outcome corresponding to that value of the observable. The causal structure of these events is customarily assumed fixed in an absolute way. In this paper we show that this assumption cannot be substantiated on operational grounds proving that two observers looking at the same quantum experiment can calculate the probabilities of the experiment assuming a different causal structure for the space-time events constituted by the outcomes. We will thus say that in quantum theory we have relativity of causal structure.