*Last updated: Nov 27, 2021.*]

This post is (a seed of) a bibliography covering the primordial research area that goes by some of the following names:

- The “preferred-factorization problem”, aka “quantum mereology”, in the context of decoherence.
- The “set-selection problem” in the context of consistent histories.
^{a } - The “problem of defining wavefunction branches,” especially in the context of a many-body lattice.
- The “quantum reality problem”.

Although the way this problem tends to be formalized varies with context, I don’t think we have confidence in any of the formalizations. The different versions are very tightly related, so that a solution in one context is likely give, or at least strongly point toward, solutions for the others.

As a time-saving device, I will mostly just quote a few paragraphs from existing papers that review the literature, along with the relevant part of their list of references. Currently I am drawing on five papers: Carroll & Singh [arXiv:2005.12938]; Riedel, Zurek, & Zwolak [arXiv:1312.0331]; Weingarten [arXiv:2105.04545]; Kent [arXiv:1311.0249]; and Zampeli, Pavlou, & Wallden [arXiv:2205.15893].

I hope to update this from time to time, and perhaps turn it into a proper review article of its own one day. If you have a recommendation for this bibliography (either a single citation, or a paper I should quote), please do let me know.

### Carroll & Singh

From “Quantum Mereology: Factorizing Hilbert Space into Subsystems with Quasi-Classical Dynamics” [arXiv:2005.12938]:

… [continue reading]While this question has not frequently been addressed in the literature on quantum foundations and emergence of classicality, a few works have highlighted its importance and made attempts to understand it better.