  This paper explains the delayed choice quantum eraser of Kim et al. in terms
of the transactional interpretation of quantum mechanics by John Cramer. It is
kept deliberately mathematically simple to help explain the transactional
technique. The emphasis is on a clear understanding of how the instantaneous
"collapse" of the wave function due to a measurement at a specific time and
place may be reinterpreted as a gradual collapse over the entire path of the
photon and over the entire transit time from slit to detector. This is made
possible by the use of a retarded offer wave, which is thought to travel from
the slits (or rather the small region within the parametric crystal where
down-conversion takes place) to the detector and an advanced counter wave
traveling backward in time from the detector to the slits. The point here is to
make clear how simple the Cramer transactional picture is and how much more
intuitive the collapse of the wave function becomes if viewed in this way. Also
any confusion about possible retro-causal signaling is put to rest. A delayed
choice quantum eraser does not require any sort of backward in time
communication. This paper makes the point that it is preferable to use the
Transactional Interpretation (TI) over the usual Copenhagen Interpretation (CI)
for a more intuitive understanding of the quantum eraser delayed choice
experiment. Both methods give exactly the same end results and can be used
interchangeably.

Quantum Physics