  Permanent spatial decomposition (PSD) is the (hypothesized) property of the
wave function of a macroscopic system of decomposing into localized permanently
non-overlapping parts when it spreads over a macroscopic region. The typical
example of this phenomenon is the measurement process, in which the wave
function of the laboratory (quantum system + apparatus + environment)
decomposes into n parts, corresponding to the n outcomes of the measurement:
the parts are non-overlapping, because they represent a macroscopic pointer in
different positions, and they are permanently non-overlapping due to the
irreversible interaction with the environment. PSD is often mentioned in the
literature, but until now no formal definition or systematic study of this
phenomenon has been undertaken. The aim of this paper is to partially fill this
gap by giving a formal definition of PSD and studying its possible connection
with scattering theory. The predictive and explanatory powers of this
phenomenon are also discussed and compared with those of Bohmian mechanics.
