  The traditional, standard approach to quantum theory is to assume that the
theory ``really'' contains only unitary physical dynamics--i.e., that the only
physically quantifiable evolution is that given by the time-dependent
Schrodinger equation. This leads to two distinct classes of interpretations for
the standard theory in its orthodox form: (i) an Everettian-type approach
assuming that all mutually exclusive outcomes occur in different ``branches''
of the universe; or (ii) single-outcome approaches that assume a ``projection
postulate'' (PP) with no accompanying physical account within quantum theory. A
contrasting, unorthodox approach is to suggest forms of quantum theory that
involve physical non-unitarity; these are called ``objective collapse models.''
Among these are Penrose's theory of gravitation-induced collapse and the
Transactional Interpretation. The primary focus of this paper is an example
demonstrating that standard quantum theory (with or without the projection
postulate) can in-principle yield empirically consequential inconsistencies.
Thus, it appears that for quantum theory to be viable in a realist sense (as
opposed to being an instrumentalist protocol in which inconsistencies are
evaded by changing the protocol), it must possess genuine, physical
non-unitarity yielding well-defined single outcomes. This leads to the
conclusion that objective collapse models should be more seriously considered.
