Fundamentality and Levels in Everettian Quantum Mechanics

Raoni Wohnrath Arroyo, Jonas R. Becker Arenhart

Nadia Blackshaw, Alexander Franklin

Alastair Wilson

Abstract This chapter offers a theory of objective chance in the Everettian context, often seen as the main challenge facing EQM. By supplementing diverging EQM with quantum modal realist bridge principles connecting the physics of quantum mechanics with the metaphysics of modality, we obtain a package deal: Indexicalism. Indexicalist objective chance is an essentially self-locating phenomenon: chances are chances of self-location within the multiverse. I provide three arguments for Indexicalism: it establishes the right qualitative connections between chance and possibility, it establishes the right quantitative connection between chance and prediction, and it establishes the right epistemological story about how quantum mechanics is confirmed by empirical evidence. The resulting theory of chance is naturalistic and reductive; fundamental reality is deterministic, but chance arises at the non-fundamental level of Everett-worldbound perspectives. The theory provides unique resources for motivating an Everettian version of Lewis’s Principal Principle, helping to clarify at last the persistently mysterious connection between chance and rational credence.

Valia Allori

Alastair Wilson

Abstract In Everettian quantum mechanics, the universal quantum state is fundamental, non-contingent, and wholly determinate. By contrast, the parallel worlds of diverging EQM, and the contingency constituted by self-location amongst those worlds, are emergent and partly indeterminate. In particular, it is indeterminate both how many worlds there are, and what microscopic qualitative features those worlds have. This chapter discusses various ways to understand indeterminacy in the Everettian multiverse, and argues that the indeterminacies of EQM present no obstacle to the analytic ambitions of quantum modal realism. Everettians can understand quantum indeterminacy using models of indeterminacy that are familiar from the philosophical literature on vagueness.

Richard Corry

Abstract Our experience of the world is temporally asymmetric: coffee spontaneously cools, glasses smash, people age and die, while the reverse processes never occur. However, our best theories of fundamental physics are temporally symmetric, making no distinction between past and future directions. This creates a puzzle: how can our asymmetric experiences emerge from a symmetric foundation? The usual solution is to posit a special initial condition for the universe. This solution, however, amounts to putting in the asymmetry by hand, and one may be left looking for a further explanation of this asymmetric boundary condition. In this paper I explore another possible solution, namely that the asymmetry of experience can be explained anthropically, via an observer selection effect. In particular, I use the formalism of decoherent histories to argue that such an explanation is available in the Everettian, or “many worlds”, interpretation of quantum mechanics. Along the way, we will discover that Everettian quantum mechanics implies the existence of many more worlds than are traditionally recognised.