Spin-Spacetime Censorship

TL;DR

This paper proposes a thought experiment showing that quantum entanglement and relativity imply a censorship mechanism that prevents detecting spin-induced spacetime deviations, ensuring causality and informing quantum gravity theories.

Contribution

It introduces a theory-independent gedanken experiment demonstrating a censorship mechanism that preserves spherical symmetry around particles with spin, linking quantum information and gravity.

Findings

Spin-related spacetime deviations would violate causality.

Causality-preserving symmetry requires a censorship mechanism.

The experiment can test quantum gravity theories.

Abstract

Quantum entanglement and relativistic causality are key concepts in theoretical works seeking to unify quantum mechanics and gravity. In this article, we show that the interplay between relativity theory and quantum entanglement has intriguing consequences for the spacetime surrounding elementary particles with spin. Classical and quantum gravity theories predict that a spin-generated magnetic dipole field causes a (slight) bending to the spacetime around particles, breaking its spherical symmetry. Motivated by the apparent break of spherical symmetry, we propose a very general gedanken experiment that does not rely on any specific theory of classical or quantum gravity, and analyze this gedanken experiment in the context of quantum information. We show that any spin-related deviation from spherical symmetry would violate relativistic causality. To avoid the violation of causality, the measurable spacetime around the particle's rest frame must remain spherically symmetric, potentially as a back-action by the act of measurement. This way, our gedanken experiment proves that there must be a censorship mechanism preventing the possibility of spacetime-based spin detection, which sheds new light on the interface between quantum mechanics and gravity. We emphasize that our proposed gedanken experiment is independent of any theory and by allowing spacetime to be quantized its purpose is to be used for testing present and future candidate theories of quantum gravity.