The emergent multiverse. Quantum theory according to the Everett interpretation. (Q2892707)

This book undertakes the task to explain the foundations of Everett Quantum Mechanics (EQM) and its consequences. Committed to this picture of quantum mechanics, the author defends the thesis that there is no quantum measurement problem. The ``measurement problem'' introduced in order to explain why quantum mechanics doesn't provide unique outcomes to experiments is rejected based on the argument that quantum theory describes reality and it is not necessary to modify or supplement its framework so that the paradoxes of quantum mechanics are removed.NEWLINENEWLINEThe book is structured in three parts. The first two parts explain the Everett interpretation of quantum mechanics whereas the third part explore its consequences.NEWLINENEWLINEThe first part opens with a discussion on the ``measurement problem'' in quantum mechanics. Here the author remarks itself as a defender of the Everett claim that the mathematical formalism of quantum mechanics is in any need at all of modification and consequently the standard, umodified theory can be taken as representing the structure of the world. Chapter 2 is written with the aim of making clear the view that if the Everett interpretation is adopted, then the physical reality is represented by a vast number of distinct ``worlds'' (or ``universes'' or ``branches'') which are independent of one another from dynamical point of view. In Chapter 3 the author analyses how quantum dynamics give rise to the multiplicity of worlds. For that purpose the emergent quasi-classicality in quantum physics is illustrated for a single, isolated system with large characteristic action and showed that superpositions representing multiple quasi-classical worlds occur also when generalizing to a system with \(N\) degrees of freedom. The concept of branching in the many-worlds theory is introduced in relation to the spreading of initially localized quantum states. For the rest of the chapter, the problems related with directly reading off quasi-classical structure from the dynamics of isolated macroscopic systems is approached by appealing to the concept of decoherence.NEWLINENEWLINEPart II of the book continues the explanation of the Everett interpretation and advocates for the point of view that relative branch weights can be regarded as probabilities. In Chapter 4, after a short digression on the use of probability in science, the author considers various strategies for understanding probability and concludes by sketching a derivation of the Born probability rule within what he calls, rationalist approach. The concept of Born probability is further discussed in Chapter 5. In support of the argument that a rational agent, accepting that EQM correctly gives the structure and dynamics of the world, knows that measurement on a given quantum state will generally split his part of the multiverse into multiple branches with different measurement outcomes, and different versions of the agent, on different branches, the decision-theoretic approach is introduced. In the next chapter, it is shown that EQM allows a fully satisfactory account of how interference works. A brief review of recent results from the literature on the decision theoretic approach is provided at the end of the chapter.NEWLINENEWLINEThe third part of the book discusses various consequences of the realization that the world is a branching structure of superposed histories. Chapter 7 initiates the discussion on the consequences of the Everet interpretation for some of the most everyday notions such as uncertainty, possibility and identity. It is concluded here that the branching structure of EQM has negligible consequences for our everyday life. The purpose of Chapter 8 is to determine whether EQM is nonlocal in a relevant sense. To that end the author distinguishes two sets of nonlocality which are usually called ``action at distance'' and ``nonseparability''. The aim of Chapter 9 is to clarify some points related to the direction of time. To explain why in EQM branching occurs in the future and not also in the past, the author constructs a formal approach in which an irreversible dynamics emerges from a reversible deterministic microdynamics. The last chapter of the book is, as the author bluntly admits, a mixed bag where his intention is to develop a number of consequences of EQM. He first reconsiders quantum chaos, examines how predictable is the future according to the Everett interpretation and finally he explores Everettian probabilities in special contexts: cosmological probabilities and quantum Russian roulette. In this chapter also other captivating topics are shortly discussed: observability of parallel universes through interferometry and through quantum computation, and the quantum mechanics of time travel.NEWLINENEWLINEThe book is supplemented with appendices treating the branching-decoherence theorem, classical decision theory, proofs of decision-theoretic results and utility equivalence lemma.