From the point of view of Schr\”odingerism, a wavefunction-only philosophy,
    thermodynamics must be recast in terms of an ensemble of wavefunctions, rather
    than classical particle configurations or Copenhagenist “found” values.
    Recapitulating the historical sequence, we consider here several models of
    magnets that classically can exhibit a phase transition to a low-temperature
    magnetized state. We formulate wavefunction analogues including a
    “Schr\”odingerist QUantum Ising Model” (SQUIM), a “Schr\”odingerist Curie-Weiss
    Model” (SCWM), and others. We show that the SQUIM with free boundary conditions
    and distinguishable “spins” has no finite-temperature phase transition, which
    we attribute to entropy swamping energy. The SCWM likewise, even assuming
    exchange symmetry in the wavefunction. But a variant model with “wavefunction
    energy” (introduced in prior communications about Schr\”odingerism and the
    Measurement Problem) does have a phase transition to a magnetised state. Our
    principle technique involves transforming the problem to one in probability
    theory, then applying results from Large Deviations, particularly the
    G\”artner-Ellis Theorem. Finally, we discuss Gibbs vs. Boltzmann/Einstein
    entropy in the choice of the quantum thermodynamic ensemble, as well as open

    PhySH: quantum theory, quantum statistical mechanics, large deviation & rare
    event statistics.

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