Wavefunction reality, indeterminate properties and degrees of presence

Author-Highlights•Intermediate predictions for individual quantum systems are discussed.•Spatial ‘delocalization’ is extended to the spectra of all observables.•Important views from the literature are quoted and compared with the advocated view.•Everett's relative-state interpretation of quantum mechanics is discussed.

The degree-of-presence (of the quantum system) concept, accompanying that of the wavefunction-reality postulate, is introduced and studied in two ways. To begin with, an incomplete exposition of the present author's views is given. Subsequently, a short historical and philosophical review of answers to the question about the meaning of indeterminate individual-system probabilities is presented from the literature. It is done in the form of a carefully selected collage of quotations mostly with polemic comments by the present author and with further elaboration of his point of view. The advocated notion of ‘degree of presence’ generalizes the intuitively most easily acceptable idea of ‘delocalization’ in (roughly called) wavelike behavior of a quantum system.