The most efficient and practical interpretation of quantum mechanics is... no interpretation at all. - F. J. Duarte

The Dirac notation, though originally applied to the propagation of single particles, also applies to describing the propagation of ensembles of coherent, or indistinguishable, photons.

Feynman uses Dirac's notation to describe the quantum mechanics of stimulated emission... he applies that physics to... dye molecules... In this regard, Feynman could have predicted the existence of the tunable laser.

As noted previously Bell's theorem is completely disconnected from the physics leading to <math>|\psi\rangle_+</math>, <math>|\psi\rangle_-</math>, <math>|\psi\rangle^+</math>, and <math>|\psi\rangle^-</math> .