Preferred basis, decoherence and a quantum state of the Universe

TL;DR

This paper reviews foundational issues in quantum theory and cosmology, focusing on the preferred basis problem, decoherence, and the quantum state of the Universe, highlighting the legacy of H. D. Zeh.

Contribution

It synthesizes key concepts in quantum cosmology, connecting decoherence, many-worlds interpretation, and the notion of a fundamentally mixed quantum state of the Universe.

Findings

Analysis of the preferred basis problem in many-worlds interpretation

Discussion of decoherence's role in quantum cosmology

Proposal of a fundamentally mixed quantum state of the Universe

Abstract

We review a number of issues in foundations of quantum theory and quantum cosmology including, in particular, the problem of the preferred basis in the many-worlds interpretation of quantum mechanics, the relation between this interpretation and the decoherence phenomenon, application of decoherence approach to quantum cosmology, the relation between the many-worlds interpretation and Anthropic Principle along with the notion of quantum-classical duality. We also discuss the concept of fundamentally mixed quantum state of the Universe represented by a special microcanonical density matrix and its dynamical realization in the form of the semiclassically treated path integral over spacetime geometries and quantum matter fields. These issues can be considered as a part of the scientific legacy of H. D. Zeh generously left to us in his two seminal papers published at the beginning of seventies in Foundations of Physics.