Physics, Philosophy, Observers and Multiverses

TL;DR

This paper discusses the limitations of certain quantum gravity models, highlighting that some may be untestable experimentally and thus indistinguishable from simpler models, based on principles of quantum measurement and classical gravity.

Contribution

It provides a conceptual analysis of the testability and distinguishability of mathematical models in quantum gravity, emphasizing the role of measurement theory and classical gravity.

Findings

Some quantum gravity models may be untestable experimentally.

Mathematically well-defined models can be indistinguishable from simpler ones.

General properties of measurement theory influence model distinguishability.

Abstract

We comment on the fact that certain mathematical models that have been proposed in the quantum gravity literature, may not be subject to experimental checks, even if they turn out to be mathematically well defined. This means that they would be indistinguishable from other models, with a smaller number of quantum states. These considerations follow from very general properties of quantum measurement theory and classical gravity.