Quantum-to-classical transition of primordial cosmological perturbations in de Broglie--Bohm quantum theory

TL;DR

This paper demonstrates how the de Broglie-Bohm quantum theory provides a clear framework for understanding the quantum-to-classical transition of primordial cosmological perturbations, avoiding conceptual issues present in standard quantum theory.

Contribution

It applies the de Broglie-Bohm theory to cosmology, offering an objective and unambiguous explanation of the quantum-to-classical transition of early universe fluctuations.

Findings

Overcomes conceptual issues in quantum cosmology

Provides a clear criterion for classicality in the early universe

Supports the quantum origin of cosmic structures

Abstract

There is a widespread belief that the classical small inhomogeneities which gave rise to all structures in the Universe through gravitational instability originated from primordial quantum cosmological fluctuations. However, this transition from quantum to classical fluctuations is plagued with important conceptual issues, most of them related to the application of standard quantum theory to the Universe as a whole. In this paper, we show how these issues can easily be overcome in the framework of the de Broglie-Bohm quantum theory. This theory is an alternative to standard quantum theory that provides an objective description of physical reality, where rather ambiguous notions of measurement or observer play no fundamental role, and which can hence be applied to the Universe as a whole. In addition, it allows for a simple and unambiguous characterization of the classical limit.