 At the heart of the transactional interpretation is the “transaction”: real physical events are identified with so-called “handshakes” between forward-evolving quantum states \(\psi\) and backward-evolving complex-conjugates \(\psi^*\). When a quantum emitter (such as a vibrating electron or atom in an excited state) is to emit a single quantum (a photon, in these cases), the source produces a radiative field—the “offer” wave. Analogously to the Wheeler-Feynman description, this field propagates outwards both forward and backward in time (as well as across space). When this field encounters an absorber, a new field is generated—the “confirmation” wave—that likewise propagates both forward and backward in time, and so is present as an advanced incident wave at the emitter at the instant of emission. Both the retarded field produced by the absorber and the advanced field produced by the emitter exactly cancel with the retarded field produced by the emitter and advanced field produced by the absorber for all times before the emission and after the absorption of the photon; only between the emitter and the absorber is there a radiative field. Thus the transaction is completed with this “handshake”: a cycle of offer and confirmation waves 