Multilevel Quantum-Classical Physics and Schr?dinger’s Cat

The simplest way to understand Schr?dinger’s cat is how Schr?dinger intended it: The cat is a self-contained, self-existing system and is always either dead or alive (Fig. 1). For a system as thermodynamically complex as a cat, the only variable that remains sufficiently quantum to permit superposition is the cat’s travel path through XYZ space.

That means that if you isolate a cat sufficiently from the outside universe, you can make it interfere when passing through two doors so that you can never tell which door it went through. However, if you send enough cats through enough doors, you find that where they land on the other side produces an interference pattern indicating that the cat went through the doors like a wave.

The cat is dead or alive as it goes through the doors, but its isolation means the outside world cannot know this until data exchanges restart. In contrast, the paths through the barrier can stay quantum and superposed as long the cat cannot see which door it uses. While this degree of data isolation is not feasible for cats, interference experiments with large molecules show there is no clearly defined upper limit to how large of an object can experience path (versus internal) quantum superpositions.

(A PDF version of this article is available at https://sarxiv.org/apa.2023-10-10.1230.pdf)