Everett's Multiverse and the World as Wavefunction

TL;DR

This paper explores Everett's multiverse interpretation of quantum mechanics, addressing issues of wavefunction collapse, pointer basis, probability, and wavefunction monism, and discusses evolving models of branching and their relation to uncertainty.

Contribution

It analyzes the development of Everettian models, critiques their handling of probability and basis selection, and proposes a potential resolution to wavefunction monism.

Findings

Decoherence is key to pointer basis selection.

Two models of branching have emerged from the evolution of ideas.

A suggested resolution to wavefunction monism is proposed.

Abstract

Everett suggested that there is no such thing as wavefunction collapse. He hypothesized that for an idealized spin measurement the apparatus evolves into a superposition on the pointer basis of two apparatuses, each displaying one of the two outcomes which are standardly thought of as alternatives. And as a result the observer splits into two observers, each perceiving a different outcome.There have been problems. Why the pointer basis? Decoherence is generally accepted by Everettian theorists to be the key to the right answer there. And in what sense is probability involved when all possible outcomes occur? Everett's response to that problem was inadequate. A first attempt to find a different route to probability was introduce by Neil Graham in 1973 and the path from there has led to two distinct models of branching. I describe how the ideas have evolved and their relation to the concepts of uncertainty and objective probability. Then I describe the further problem of wavefunction monism, emphasized by Maudlin, and make a suggestion as to how it might be resolved.