Would the Existence of CTCs Allow for Nonlocal Signaling?

TL;DR

This paper examines whether closed timelike curves (CTCs) could enable nonlocal signaling in quantum mechanics, challenging the assumption that relativity forbids such signaling and analyzing the foundational conflicts in existing models.

Contribution

It critically analyzes the implications of CTCs for nonlocal signaling and highlights conflicts between quantum information principles and Deutsch's D-CTC model.

Findings

CTCs could theoretically allow nonlocal signaling.

The No Signaling principle conflicts with Deutsch's D-CTC model.

Foundational assumptions of quantum mechanics and relativity are in tension.

Abstract

A recent paper from Brun et al. has argued that access to a closed timelike curve (CTC) would allow for the possibility of perfectly distinguishing nonorthogonal quantum states. This result can be used to develop a protocol for instantaneous nonlocal signaling. Several commenters have argued that nonlocal signaling must fail in this and in similar cases, often citing consistency with relativity as the justification. I argue that this objection fails to rule out nonlocal signaling in the presence of a CTC. I argue that the reason these authors are motivated to exclude the prediction of nonlocal signaling is because the No Signaling principle is considered to a fundamental part of the formulation of the quantum information approach. I draw out the relationship between nonlocal signaling, quantum information, and relativity, and argue that the principle theory formulation of quantum mechanics, which is at the foundation of the quantum information approach, is in tension with foundational assumptions of Deutsch's D-CTC model, on which this protocol is based.