Entanglement is an inevitable feature of any non-classical theory

TL;DR

This paper argues that entanglement is an unavoidable feature of any non-classical theory with reversible interactions, based on fundamental principles like no-cloning and local transitivity.

Contribution

It introduces two postulates that imply entanglement must exist in all non-classical theories with reversible interactions, explaining its fundamental nature.

Findings

Entanglement is necessary for reversible interactions in non-classical theories.

No-cloning and local transitivity imply the existence of entangled states.

Entanglement is an inevitable feature of any non-classical universe.

Abstract

One of the most striking features of quantum theory is the existence of entangled states, responsible for Einstein's so called "spooky action at a distance". These states emerge from the mathematical formalism of quantum theory, but to date we do not have a clear idea of which physical principles give rise to entanglement. Why does quantum theory have entangled states? Would any theory superseding classical theory have entangled states, or is quantum theory special? We demonstrate that without entanglement, non-classical degrees of freedom cannot reversibly interact. We present two postulates, no-cloning / no-broadcasting and local transitivity, either of which are sufficient to imply the existence of entangled states in any non-classical theory with reversible interactions. Therefore we argue that entanglement is an inevitable feature of a non-classical universe.