Chapter 4. The Limits of Classical Realism

Bernard d’Espagnat

Patrick A. Heelan

Alyssa Ney

Abstract This chapter considers and responds to criticism that wave function realism is only plausible as an approach to the interpretation of nonrelativistic quantum mechanics and not relativistic quantum theories and quantum field theories. This critique gains traction as wave function realism has until now been formulated and defended solely within the context of idealized, nonrelativistic quantum mechanics. The chapter considers five such arguments and responds to each. An important lesson is that wave function realists should only adopt the wave-function-in-configuration-space picture as part of an interpretation of an idealized nonrelativistic quantum mechanics. More generally, the space the wave function inhabits will vary as the quantum theory the wave function realist is developing an interpretation of varies. The chapter develops a sketch of what wave function realism looks like in one relativistic context. It then discusses the issue of the interpretation of quantum theories in the limit of physical theorizing.

Moamer Hasanovic

This chapter investigates quantum entanglement and teleportation, challenging local realism by demonstrating quantum mechanics' inconsistency with locality and realism. It begins with Einstein's skepticism towards entanglement and introduces Bell's theorem as a framework to test local realism, showing how quantum systems violate Bell's inequality. The chapter details experiments with entangled photon pairs, highlighting their non-local correlations and probabilistic nature, and contrasts these with classical correlations. It explains quantum teleportation, its process, and applications in quantum networks, concluding with the operational principles of an entanglement generator and its role in secure quantum communication.

A. J. Leggett