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 rs, the degrees of freedom inside rs 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.
- Black holes
- Quantum dissipative systems