Is Superluminal Signaling Possible in Collapse Theories of Quantum Mechanics?

G. C. Ghirardi, Renata Grassi, Philip Pearle

Euan J. Squires

Adrian Kent

Theories involving localized collapse allow the possibility that classical information could be obtained about quantum states by mechanisms other than the standard quantum dynamical maps defined by positive operator valued measurements, but nonetheless without allowing superluminal signaling. We can model this by extending quantum theory to include hypothetical devices that read out information about the local quantum state at a given point, which is defined by considering unitary evolution modified only by the effects of collapses in its past light cone. Like Popescu-Rohrlich boxes, these hypothetical devices would have practical and scientific implications if realizable. These include signaling through opaque media, probing the physics of distant or opaque systems without needing a reflected signal and giving detailed information about collapse dynamics without requiring direct observation of the collapsing system. These potential applications add to the motivation for systematic searches for possible signatures of these nonstandard extensions of quantum theory, and in particular for relevant gravitational effects, such as the validity of semiclassical gravity on small scales.

R. Muciño, E. Okon, D. Sudarsky +1 more

Non-relativistic objective collapse theories have been remarkably successful in addressing the conceptual problems of standard quantum mechanics. Despite substantial efforts, the project of extending them to the relativistic domain remains burdened by significant conceptual objections and technical challenges, often taken to cast doubt on the viability of the program as a whole. On the conceptual side, relativistic collapse theories have been claimed to face challenges involving tension between instantaneous collapse and relativity, frame-dependence of property values and probabilities, the possibility of superluminal signaling and the failure of narratability. On the technical side, persistent infinities, difficulties in constructing fully covariant frameworks and the apparent need for non-standard fields have hindered the development of workable models. In this paper, we offer a systematic rebuttal of the conceptual objections and provide a structured account of the remaining technical challenges. We conclude that relativistic collapse theories do provide a promising route toward a fully relativistic quantum framework that overcomes the conceptual limitations of standard quantum theory.

Daniel J. Gauthier

George Svetlichny