Decoherence in Quantum Gravity: Issues and Critiques

TL;DR

This paper critically examines the concept of decoherence in quantum gravity, exploring its implications for spacetime structure, non-unitarity, and CPT violation, through analysis of two representative theories.

Contribution

It provides a detailed critique of existing theories on decoherence in quantum gravity, highlighting conceptual issues and clarifying the meaning of decoherence at the Planck scale.

Findings

Decoherence in quantum gravity involves complex issues like non-unitarity and nonlocality.

Theories claiming CPT violation due to decoherence face conceptual challenges.

Spacetime foam may behave like a thermal bath, as modeled by Brownian motion.

Abstract

An increasing number of papers have appeared in recent years on decoherence in quantum gravity at the Planck energy. We discuss the meaning of decoherence in quantum gravity starting from the common notion that quantum gravity is a theory for the microscopic structures of spacetime, and invoking some generic features of quantum decoherence from the open systems viewpoint. We dwell on a range of issues bearing on this process including the relation between statistical and quantum, noise from effective field theory, the meaning of stochasticity, the origin of non-unitarity and the nature of nonlocality in this and related contexts. To expound these issues we critique on two representative theories: One claims that decoherence in quantum gravity scale leads to the violation of CPT symmetry at sub-Planckian energy which is used to explain today's particle phenomenology. The other uses this process in place with the Brownian motion model to prove that spacetime foam behaves like a thermal bath.