Hegerfeldt's theorem

Hegerfeldt's theorem is a result in quantum mechanics that addresses the phenomenon of faster-than-light (FTL) signaling in the context of quantum information and relativistic quantum field theory. The theorem was first presented by Hegerfeldt in a 1998 paper. It demonstrates that certain quantum states evolve in such a way that they can lead to superluminal communication, which contradicts the principles of relativity that prohibit faster-than-light signaling.