The Multiverse Interpretation of Quantum Mechanics

TL;DR

This paper explores the multiverse as an extension of the many-worlds interpretation of quantum mechanics, proposing that the multiverse provides the operational framework for exact quantum predictions and discussing the role of holography and causal diamonds.

Contribution

It introduces a novel interpretation linking the multiverse with many-worlds, and proposes conditions under which exact quantum predictions are possible within this framework.

Findings

The multiverse corresponds to many-worlds histories in a single geometry.

Exact observables require infinite experimental repetitions, which are not possible in finite holographic regions.

Hats in the multiverse may allow for exact quantum predictions and a form of complementarity.

Abstract

We argue that the many-worlds of quantum mechanics and the many worlds of the multiverse are the same thing, and that the multiverse is necessary to give exact operational meaning to probabilistic predictions from quantum mechanics. Decoherence - the modern version of wave-function collapse - is subjective in that it depends on the choice of a set of unmonitored degrees of freedom, the "environment". In fact decoherence is absent in the complete description of any region larger than the future light-cone of a measurement event. However, if one restricts to the causal diamond - the largest region that can be causally probed - then the boundary of the diamond acts as a one-way membrane and thus provides a preferred choice of environment. We argue that the global multiverse is a representation of the many-worlds (all possible decoherent causal diamond histories) in a single geometry. We propose that it must be possible in principle to verify quantum-mechanical predictions exactly. This requires not only the existence of exact observables but two additional postulates: a single observer within the universe can access infinitely many identical experiments; and the outcome of each experiment must be completely definite. In causal diamonds with finite surface area, holographic entropy bounds imply that no exact observables exist, and both postulates fail: experiments cannot be repeated infinitely many times; and decoherence is not completely irreversible, so outcomes are not definite. We argue that our postulates can be satisfied in "hats" (supersymmetric multiverse regions with vanishing cosmological constant). We propose a complementarity principle that relates the approximate observables associated with finite causal diamonds to exact observables in the hat.