quantum mechanics Quantum mechanics is the fundamental physical Scientific theory, theory that describes the behavior of matter and of light; its unusual characteristics typically occur at and below the scale of atoms. Reprinted, Addison-Wesley, 1989, It is ...

, the totalitarian principle states: "Everything not forbidden is compulsory."

Physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate cau ...

s including

Murray Gell-Mann Murray Gell-Mann (; September 15, 1929 – May 24, 2019) was an American theoretical physicist who played a preeminent role in the development of the theory of elementary particles. Gell-Mann introduced the concept of quarks as the funda ...

borrowed this expression, and its satirical reference to totalitarianism, from the popular culture of the early twentieth century. The statement refers to a surprising feature of

particle In the physical sciences, a particle (or corpuscle in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass. They vary greatly in size or quantity, from s ...

interactions: that any interaction that is not forbidden by a small number of simple

conservation law In physics, a conservation law states that a particular measurable property of an isolated physical system does not change as the system evolves over time. Exact conservation laws include conservation of mass-energy, conservation of linear momen ...

s is not only allowed, but ''must'' be included in the sum over all " paths" that contribute to the outcome of the interaction. Hence if it is not forbidden, there is some probability amplitude for it to happen. In the

many-worlds interpretation The many-worlds interpretation (MWI) is an interpretation of quantum mechanics that asserts that the universal wavefunction is Philosophical realism, objectively real, and that there is no wave function collapse. This implies that all Possible ...

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 In quantum physics, a wave function (or wavefunction) is a mathematical description of the quantum state of an isolated quantum system. The most common symbols for a wave function are the Greek letters and (lower-case and capital psi (letter) ...

Origin of the phrase

Neither the phrase nor its application to quantum physics originated with Gell-Mann, but a 1956 paper by him contains the first published use of the phrase as a description of quantum physics.See footnote on p. 859 in Gell-Mann used it to describe the state of

particle physics Particle physics or high-energy physics is the study of Elementary particle, fundamental particles and fundamental interaction, forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the s ...

around the time he was formulating the Eightfold Way, a precursor to the

quark A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nucleus, atomic nuclei ...

-model of

hadron In particle physics, a hadron is a composite subatomic particle made of two or more quarks held together by the strong nuclear force. Pronounced , the name is derived . They are analogous to molecules, which are held together by the electri ...

s. According to the second edition of ''Strange Beauty: Murray Gell-Mann & the Revolution in Physics'' Gell-Mann incorrectly attributed the quote to George Orwell in a letter to the astrophysicist Jeremiah Ostriker. Formulations close to Gell-Mann's are used in T. H. White's 1958 (not 1938–39) version of '' The Once and Future King'', Jack Parsons's 1948 essay "Freedom is a Two-Edged Sword", and Robert Heinlein's 1940 short story "Coventry".Anthologized in Robert A. Heinlein, ''The Past Through Tomorrow'', Berkley Medallion mass-market paperback edition, 1967, p. 600. "The state was thought of as a single organism with a single head, a single brain, and a single purpose. Anything not compulsory was forbidden." They differ in details such as the order of the words "forbidden" and "compulsory", and Gell-Mann's footnote uses the words in both orders, although only one of these orders captures his precise logical meaning. 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 "Everything which is not forbidden is allowed" is a legal maxim. It is the concept that any action can be taken unless there is a law against it. It is also known in some situations as the "general power of competence" whereby the body or person ...

. Since White did not use the phrase in any published work until two years after Gell-Mann's paper, White cannot have been Gell-Mann's source. It is likely that writers such as White, Heinlein, and Gell-Mann were all simply making use of a phrase that was a part of popular culture at the time.

References

{{Reflist Quantum measurement Murray Gell-Mann

Origin of the phrase

See also

References