Cambridge University Press eBooks

Decoherence, Einselection, and Its Consequences

Wojciech Hubert Zurek

Published Mar 6, 2025• 0 citations

Abstract

Chapter 5 explores the consequences of decoherence. We live in a Universe that is fundamentally quantum. Yet, our everyday world appears to be resolutely classical. The aim of Chapter 5 is to discuss how preferred classical states, and, more generally, classical physics, arise, as an excellent approximation, on a macroscopic level of a quantum Universe. We show why quantum theory results in the familiar “classical reality” in open quantum systems, that is, systems interacting with their environments. We shall see how and why, and to what extent, quantum theory accounts for our classical perceptions. We shall not complete this task here—a more detailed analysis of how the information is acquired by observers is needed for that, and this task will be taken up in Part III of the book. Moreover, Chapter 5 shows that not just Newtonian physics but also equilibrium thermodynamics follows from the same symmetries of entanglement that led to Born’s rule (in Chapter 3).

DOI: 10.1017/9781009552868.006

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The measurement problem has been a central puzzle of quantum theory since its inception, and understanding how the classical world emerges from our fundamentally quantum universe is key to its resolution. While the 'Copenhagen' and 'Many Worlds' interpretations have dominated discussion of this philosophically charged question, Zurek builds on the physics of decoherence and introduces the theory of 'Quantum Darwinism' to provide a novel account of the emergence of classical reality. Opening with a modern view of quantum theory, the book reconsiders the customary textbook account of quantum foundations, showing how the controversial axioms (including Born's rule) follow from the consistent core postulates. Part II discusses decoherence and explores its role in the quantum-to-classical transition. Part III introduces Quantum Darwinism, explaining how an information-theoretic perspective complements, elucidates, and reconciles the 'Copenhagen' and 'Many Worlds' interpretations. This insightful book is essential reading for any student or researcher interested in quantum physics.

Cambridge University Press eBooksMar 6, 202512 citations

Introduction

Wojciech Hubert Zurek

Chapter 1 begins by re-examining the textbook quantum postulates. It concludes with the realization that some of them are inconsistent with quantum mathematics, but also that they may not have to be postulated. Indeed, in the following two chapters it is shown that their consequences follow from the other, consistent postulates. This simplification of the quantum foundations provides a consistent, convenient, and solid starting point. The emergence of the classical from the quantum substrate is based on this foundation of “core quantum postulates”—the “quantum credo”. Discussion of the postulates is accompanied by a brief summary of their implications for the interpretation of quantum theory. This discussion touches on questions of interpretation that are implicit throughout the book, but will be addressed more fully in Chapter 9. Chapter 1 ends with a “decoherence primer” that provides a quick introduction to decoherence (discussed in detail in Part II). Its aim is to provide the reader with an overview of the process that will play an important role throughout the book, and to motivate Chapters 2 and 3 that lay the foundations for the physics of decoherence (Part II) as well as for quantum Darwinism, the subject of Chapters 7 and 8.

Cambridge University Press eBooksMar 6, 20250 citations