In quantum mechanics, Gell-Mann's Totalitarian Principle states: "Everything not forbidden is compulsory." Physicist Murray Gell-Mann borrowed this expression from T.H. White's The Once and Future King to describe the state of particle physics around the time he was formulating the Eightfold Way, a precursor to the quark-model of hadrons.
The statement is in reference to a surprising feature of particle interactions: that any interaction which is not forbidden by a small number of simple conservation laws is not only allowed, but must be included in the sum over all "paths" which contribute to the outcome of the interaction. Hence if it isn't forbidden, there is some probability amplitude for it to happen.
In any of the Everett-based interpretations of quantum mechanics, such as Bryce DeWitt's many-worlds or Gell-Mann's many-histories interpretations, the principle has a more literal meaning: that every possibility at every interaction which is not forbidden by such a conservation law will actually happen (in some branch of the wavefunction).
- T.H. White, The Once and Future King, Ace, 1996, p. 121. The passage describes an ant-hill from the point of view of an ant: "The fortress was entered by tunnels in the rock, and, over the entrance to each tunnel, there was a notice which said: EVERYTHING NOT FORBIDDEN IS COMPULSORY."
- George Johnson, "Strange Beauty: Murray Gell-Mann and the Revolution in Twentieth-Century Physics," p. 224. Johnson describes Gell-Mann's application of the quote to physics, but incorrectly attributes the original to Orwell.