Nonstationary quantum mechanics

It is shown that the formalism of quantum theory needs modification in the case of potential fields swiftly varying with time. The necessity of a time-irreversible 'master equation' for such cases is discussed. The underlying idea is that any (sub)system will undergo a spontaneous transition to a state of definite energy in the process of separating spatially from the rest of the 'universe', assuming the 'universe' is isolated and has a definite energy. This requires what might be termed a 'pragmatic' interpretation of the wave function. If a composite, separated system is represented by a linear superposition of product states, it may be said that the actual state of the composite system is represented by some particular component of the superposition for the purposes of statistical inferences relevant to each subsystem alone, but the entire superposition - and not the corresponding mixture of the product components - must be used to compute the statistics of correlations. The considerations are illustrated with thought experiments which are real enough to make the application of the usual quantum mechanical formalism possible. Cases of disagreement between conventional theory and experiment in the field of interest are indicated. (author)