Quantum spatial superpositions and the possibility of superluminal signaling

TL;DR

This paper examines whether quantum superpositions involving gravitational or electromagnetic interactions could enable faster-than-light communication, and clarifies the quantum features preventing superluminal signaling, supporting the argument for quantized gravity.

Contribution

It provides a detailed analysis of entanglement spreading and offers a more general proof that superluminal signaling is impossible in these quantum protocols.

Findings

Superluminal signaling is fundamentally prevented by quantum entanglement properties.

A more general proof confirms the impossibility of superluminal communication in these scenarios.

Insights support the necessity of quantizing gravity to avoid paradoxes.

Abstract

A recently proposed gedankenexperiment involving the (gravitational or electromagnetic) interaction between two objects--one placed in a state of quantum superposition of two locations--seems to allow for faster-than-light communication. However, it has been argued that, if the mediating fields are endowed with quantum properties, then the possibility for superluminal signaling is fully avoided. Moreover, in the gravitational case, this conclusion has been used to argue for the view that the gravitational field must be quantized. In this work, we clarify and complement some aspects of the discussion. In particular, by focusing on the way in which entanglement spreads across the components of the system, we offer some insights into the fundamental quantum features behind the impossibility of superluminal signaling and we provide a more general proof of such an impossibility in this and related protocols.