# Haag's theorem

> English word · Proper noun

## Definitions
1. A theorem stating that the interaction picture does not exist in an interacting, relativistic quantum field theory.

## Etymology
Named after Rudolf Haag.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/haag-s-theorem