Separability and fundamentality

Alyssa Ney

Abstract This chapter presents the argument for wave function realism that it is the only realist interpretation of quantum theories that can maintain a fundamentally separable and local metaphysics. It is commonly seen as a consequence of entanglement and Bell’s Theorem that quantum mechanics entails quantum nonseparability and nonlocality. Yet although all rival realist ontological interpretations of quantum mechanics involve either a nonseparable or a nonlocal fundamental metaphysics, the metaphysics of wave function realism is fundamentally both separable and local, although the view also makes room for nonfundamental nonseparability and nonlocality. The chapter considers several arguments that could explain why one should prefer interpretations of quantum theories that are separable and local, and concludes with a defense of intuitions in quantum interpretation.

Shengjun Wu, J. Anandan

Andrew N. Jordan, John C. Howell

We establish fundamental bounds on subwavelength resolution for the radar ranging problem, ``superradar.'' Information-theoretical metrics are applied to probe the resolution limits for the case of both direct electric field measurement and photon-counting measurements. To establish fundamental limits, we begin with the simplest case of range resolution of two point targets from a metrology perspective. These information-based metrics establish fundamental bounds on both the minimal discrimination distance of two targets and the precision on the separation of two subwavelength resolved targets. For the minimal separation distance, both the direct field method and photon counting method show that the discriminability vanishes quadratically as the target separation goes to zero, and is proportional to the variance of the second derivative of the electromagnetic field profile. Nevertheless, robust subwavelength estimation is possible. Several different band-limited function classes are introduced to optimize discrimination. We discuss the application of maximum likelihood estimation to improve the range precision with optimal performance. The general theory of multiparameter estimation is analyzed, and a simple example of estimating both the separation and relative strength of the two point reflectors is presented.

Oliver Rudolph

Ehsan Azari

Persistent attempts to interpret quantum theory in terms of classical separability have obscured the structural origins of non-separable phenomena in modern physics. This paper argues that non-separability is not an exclusively quantum feature, but the culmination of a structural transition already implicit in the breakdown of integrability in classical mechanics. Building on insights from Poincaré, Planck, Einstein, and Bohr, the analysis traces how global separations fail under generic dynamics and how fundamental constants encode obstructions to arbitrary decomposition. Complementarity and contextuality are then reinterpreted as emergent structural constraints arising from mutually defining dynamical and observational frameworks, rather than as fundamental postulates. This perspective situates quantum theory within a broader structural continuum and aligns naturally with contemporary relational and structural realist approaches to physical theory.