The Totalitarian Principle states: "Everything which is not forbidden, is compulsory." Physicist Murray Gell-Mann used this expression to describe the state of particle physics around the time he was creating 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).