  The transactional interpretation of quantum mechanics, following the
time-symmetric formulation of electrodynamics, uses retarded and advanced
solutions of the Schrodinger equation and its complex conjugate to understand
quantum phenomena by means of transactions. A transaction occurs between an
emitter and a specific absorber when the emitter has received advanced waves
from all possible absorbers. Advanced causation always raises the specter of
paradoxes, and it must be addressed carefully. In particular, different devices
involving contingent absorbers or various types of interaction-free
measurements have been proposed as threatening the original version of the
transactional interpretation. These proposals will be analyzed by examining in
each case the configuration of absorbers and, in the special case of the
so-called quantum liar experiment, by carefully following the development of
retarded and advanced waves through the Mach-Zehnder interferometer. We will
show that there is no need to resort to the hierarchy of transactions that some
have proposed, and will argue that the transactional interpretation is
consistent with the block-universe picture of time.
