A historically important but little known debate regarding the necessity and meaning of macroscopic superpositions, in particular those containing different gravitational fields, is discussed from a modern perspective.
I review arguments demonstrating how the concept of particle numbers arises in the form of equidistant energy eigenvalues of coupled harmonic oscillators representing free fields. Their quantum numbers (numbers of nodes of the wave functions) can be
interpreted as occupation numbers for objects with a formal mass (defined by the field equation) and spatial wave number (momentum) characterizing classical field modes. A superposition of different oscillator eigenstates, all consisting of n modes having one node, while all others have none, defines a nondegenerate n-particle wave function. Other discrete properties and phenomena (such as particle positions and events) can be understood by means of the fast but smooth process of decoherence: the irreversible dislocalization of superpositions. Any wave-particle dualism thus becomes obsolete. The observation of individual outcomes of this decoherence process in measurements requires either a subsequent collapse of the wave function or a branching observer in accordance with the Schrodinger equation - both possibilities applying clearly after the decoherence process. Any probability interpretation of the wave function in terms of local elements of reality, such as particles or other classical concepts, would open a Pandoras box of paradoxes, as is illustrated by various misnomers that have become popular in quantum theory.
The concept of time as used in various applications and interpretations of quantum theory is briefly reviewed.
