Observational Consequences of Many-Worlds Quantum Theory

TL;DR

This paper discusses how observational differences between single-history and many-worlds quantum theories can arise when the number of observers varies, affecting predictions about the universe's expansion and cosmological constant.

Contribution

It demonstrates that many-worlds theories can be distinguished observationally from single-history theories when observer counts are considered, challenging common claims of their equivalence.

Findings

Observational distinctions depend on observer counts in different histories.

Many-worlds theories predict different observational weights than single-history theories.

The differences have implications for cosmological measurements.

Abstract

Contrary to an oft-made claim, there can be observational distinctions (say for the expansion of the universe or the cosmological constant) between "single-history" quantum theories and "many-worlds" quantum theories. The distinctions occur when the number of observers is not uniquely predicted by the theory. In single-history theories, each history is weighted simply by its quantum-mechanical probability, but in many-worlds theories in which random observations are considered, there should also be the weighting by the numbers or amounts of observations occurring in each history.