An operational approach to spacetime symmetries: Lorentz transformations from quantum communication

TL;DR

This paper derives Lorentz transformations from an operational, quantum information perspective without assuming spacetime structure, revealing their fundamental role in describing quantum systems and observers' synchronization efforts.

Contribution

It introduces an operational approach that derives Lorentz transformations from quantum information principles, challenging traditional assumptions in fundamental physics.

Findings

Lorentz transformations emerge from information-theoretic synchronization.

Relativistic behavior of Stern-Gerlach devices is accurately modeled.

Quantum systems exhibit Lorentz group representations of different spins.

Abstract

In most approaches to fundamental physics, spacetime symmetries are postulated a priori and then explicitly implemented in the theory. This includes Lorentz covariance in quantum field theory and diffeomorphism invariance in quantum gravity, which are seen as fundamental principles to which the final theory has to be adjusted. In this paper, we suggest, within a much simpler setting, that this kind of reasoning can actually be reversed, by taking an operational approach inspired by quantum information theory. We consider observers in distinct laboratories, with local physics described by the laws of abstract quantum theory, and without presupposing a particular spacetime structure. We ask what information-theoretic effort the observers have to spend to synchronize their descriptions of local physics. If there are "enough" observables that can be measured universally on several different quantum systems, we show that the observers' descriptions are related by an element of the orthochronous Lorentz group O^+(3,1), together with a global scaling factor. Not only does this operational approach predict the Lorentz transformations, but it also accurately describes the behavior of relativistic Stern-Gerlach devices in the WKB approximation, and it correctly predicts that quantum systems carry Lorentz group representations of different spin. This result thus hints at a novel information-theoretic perspective on spacetime.