Fundamental Physics and Molecular Chirality: Parity Violation and Spin–Orbit Coupling as Independent, Not Unified, Origins

Abstract

Two independent lines of physics have each been proposed to connect fundamental particle interactions to the chirality-dependent behavior of molecules relevant to life: electroweak parity violation (PV), a minute Z⁰-exchange-mediated energy splitting between enantiomers hypothesized since the 1980s as a possible driver of biological homochirality; and spin–orbit coupling (SOC) in chiral molecular structures, invoked to explain chirality-induced spin selectivity (CISS) in electron transport. We examine whether these are two manifestations of one deeper, subatomic-scale chiral field, or physically independent phenomena. Combining dimensional analysis, symmetry arguments, and published experimental bounds on new spin-dependent forces, we show that a common quark- or QCD-vacuum-sourced origin is excluded: quark confinement forbids a residual quark field outside hadrons; the chiral magnetic effect — the one established mechanism by which quark-level chirality manifests macroscopically — requires conditions (quark–gluon plasma or engineered Weyl semimetals) entirely absent from molecular chemistry; and a hypothetical new pseudoscalar mediator with the coupling needed to produce CISS-scale polarizations is excluded by torsion-balance and comagnetometer experiments by roughly 18–29 orders of magnitude. We further show, through an explicit coherent-transport tight-binding calculation verified for two independent microscopic SOC constructions, that elastic two-terminal spin–orbit-only transport cannot produce net transmission polarization at a non-magnetic collector — consistent with Onsager–Büttiker reciprocity — which is why the CISS literature requires dephasing or inelastic mechanisms to reproduce experiment. We conclude that parity violation and CISS are independent, genuine, and individually unresolved problems in their own right, and discuss their experimental status and their common technological descendant, CISS-based molecular spintronics.