Physicists including Murray Gell-Mann borrowed this expression, and its satirical reference to totalitarianism, from the popular culture of the early twentieth century.
In the many-worlds interpretation of quantum mechanics, the principle has a more literal meaning: that every possibility at every interaction that is not forbidden by such a conservation law will actually happen (in some branch of the wave function).
[2] Gell-Mann used it to describe the state of particle physics around the time he was formulating the Eightfold Way, a precursor to the quark-model of hadrons.
Formulations close to Gell-Mann's are used in T. H. White's 1958 (not 1938–39) version of The Once and Future King,[4] Jack Parsons's 1948 essay "Freedom is a Two-Edged Sword",[5] and Robert Heinlein's 1940 short story "Coventry".
The phrase, and variations on it, appear to have been common in this period, and probably trace back to an older legal principle, that everything which is not forbidden is allowed.