# The arrow of causality and quantum gravity

## TL;DR

This paper explores how causality in quantum field theory and quantum gravity depends on conventions and states, revealing potential violations of microcausality in certain quantum gravity models.

## Contribution

It uncovers the connection between quantization conventions and the arrow of causality, especially in quantum gravity theories like quadratic gravity and asymptotic safety.

## Key findings

- Mixed quantization conventions can violate microcausality.
- The arrow of causality is influenced by stable states in certain theories.
- Implications for quantum gravity models are discussed.

## Abstract

Causality in quantum field theory is defined by the vanishing of field commutators for space-like separations. However, this does not imply a direction for causal effects. Hidden in our conventions for quantization is a connection to the definition of an arrow of causality, i.e. what is the past and what is the future. If we mix quantization conventions within the same theory, we get a violation of microcausality. In such a theory with mixed conventions the dominant definition of the arrow of causality is determined by the stable states. In some quantum gravity theories, such as quadratic gravity and possibly asymptotic safety, such a mixed causality condition occurs. We discuss some of the implications.