In this chapter, the fully relativistic form of the transactional interpretation is presented in terms of the Davies quantum direct-action theory (QDAT). Aspects of the QDAT are clarified and reinterpreted. Specifically, the coupling constant (charge) is identified as the basic amplitude for the generation of offers and confirmations, which herald the onset of non-unitarity constituting the measurement interaction. Thus, the QDAT has both unitary and non-unitary processes, the former being force-type interactions mediated by virtual photons and the latter being radiative processes in which energy is transferred via real photons. The nature of the so-called light-tight box condition for the quantum level is clarified, and it is noted that no particular cosmological structure is required for this to be fulfilled. It is argued that RTI has advantages over another relativistic collapse-type theory, rGRWf.

In this chapter, the relativistic transactional interpretation (RTI) is shown to completely nullify the Maudlin objection (a type of contingent absorber experiment) to the original, nonrelativistic TI. RTI is applied to some prominent quantum “paradoxes” such as the quantum eraser and the Frauchiger–Renner paradox and shown to resolve these. In addition, RTI derives standard decoherence results while also providing an account of concrete measurement outcomes that is missing in standard (unitary-only) decoherence theory.

This chapter discusses the necessity of interpreting offer and confirmation waves as possibilities whose structure is described by Hilbert space. The transactional process leads to a set of incipient transactions, with spontaneous symmetry breaking resulting in the actualization of one, which constitutes the process of “measurement” and the emergence of spacetime events from the quantum substratum.

This chapter serves as an elementary introduction to the basic quantum puzzles such as the measurement problem, indeterminacy, nonlocality, entanglement, and ambiguity surrounding the projection postulate. It briefly reviews the standard extant interpretations such as the Copenhagen interpretation, many-worlds interpretation, and hidden variables interpretation, and introduces the idea that quantum theory is about a new metaphysical category: physical possibility or res potentia.

In this epilogue, key points of the book are summarized, highlighting the transactional account of the measurement transition and thus TI’s resolution of the measurement problem. Reasons for historical neglect of the Wheeler–Feynman theory and the transactional formulation are discussed. It is noted that certain metaphysical and even cultural preconceptions such as the yang-heavy emphasis of Western thought may have inhibited open consideration of the direct-action theory of fields, which involves the yin element of response/reception/dissolution, just as the same preconceptions inhibited scientific understanding of the active role of the female ovum in reproductive biology.

In this chapter, spacetime is identified as the empirical realm, to be understood in a relational sense. The spacetime construct emerges from the quantum substratum by way of actualized transactions, which establish spacetime events and their structural connections. This process is discussed in terms of causal set theory. The quantum substratum constitutes the reference for “absolute motion,” and rest-mass systems in the substratum define inertial frames. The transactional process breaks time symmetry, thus establishing an arrow of time and shedding light on the Second Law of Thermodynamics. Implications for free will are also discussed.

In this chapter, the metaphysics of quantum possibilities, as a form of res potentia, is discussed. The transactional picture, together with quantum possibility, can be understood in terms of Kant’s contrast between phenomena and noumena, with quantum possibility constituting an element of the noumenal realm. This formulation sheds light on the connection between the two realms. It also provides a “middle way” between realism and antirealism and resolves puzzles surrounding the notion of causation. Concerns about structural realism are also addressed.

This chapter reviews the original transactional interpretation as based on the Wheeler–Feynman absorber theory of radiation and demonstrates how the Born Rule for the probabilities of outcomes is a direct physical consequence of the transactional formulation. The chapter also accounts for the nature of “null measurements” and applies the transactional picture to the famous two-slit experiment to gain a better understanding of what it means for the experiment to be “finished” and how transactions illuminate the appearance and disappearance of interference based on the type of measurement being performed.

This chapter provides a brief overview of the history of the development of quantum theory, with a critical focus on the antirealist tradition inaugurated by Niels Bohr. The distinction between “principle theories” and “constructive theories” is discussed, and it is noted that quantum mechanics is a “principle theory.” It is argued that quantum theory is amenable to a fully realist interpretation provided we let go of the demand that reality be classically picturable.