Entanglement and Nonunitary Evolution

TL;DR

This paper investigates how tracing over internal degrees of freedom in a collapsing shell leads to nonunitary evolution observable externally, highlighting implications for entanglement and black hole physics.

Contribution

It demonstrates that nonunitary evolution arises naturally in entangled systems when internal degrees are traced out, with potential relevance to black hole information loss.

Findings

External observer perceives nonunitary evolution after tracing over interior degrees

Nonunitarity is a generic feature of entangled systems undergoing partial tracing

Discussion of implications for black hole information paradox

Abstract

We consider a collapsing relativistic spherical shell for a free quantum field. Once the center of the wavefunction of the shell passes a certain radius R, the degrees of freedom inside R are traced over. We show that an observer outside this region will determine that the evolution of the system is nonunitary. We argue that this phenomenon is generic to entangled systems, and discuss a possible relation to black hole physics.