quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, ...

, 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 caus ...

s including

Murray Gell-Mann Murray Gell-Mann (; September 15, 1929 – May 24, 2019) was an American physicist who received the 1969 Nobel Prize in Physics for his work on the theory of elementary particles. He was the Robert Andrews Millikan Professor of Theoretical ...

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

particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object which can be described by several physical property, physical or chemical property, chemical ...

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 energy, conservation of linear momentum, c ...

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 objectively real, and that there is no wave function collapse. This implies that all possible outcomes of quantum me ...

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 A wave function in quantum physics is a mathematical description of the quantum state of an isolated quantum system. The wave function is a complex-valued probability amplitude, and the probabilities for the possible results of measurements mad ...

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 fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) an ...

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 nuclei. All commonly o ...

-model of

hadron In particle physics, a hadron (; grc, ἁδρός, hadrós; "stout, thick") is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules that are held together by the ele ...

s. Formulations close to Gell-Mann's are used in T. H. White's 1958 (not 1938–39) version of ''

The Once and Future King ''The Once and Future King'' is a collection of fantasy novels by T. H. White about the legend of King Arthur. It is loosely based upon the 1485 work '' Le Morte d'Arthur'' by Sir Thomas Malory. It was first published in 1958 as a collection ...

'' and in

Robert Heinlein Robert Anson Heinlein (; July 7, 1907 – May 8, 1988) was an American science fiction author, aeronautical engineer, and naval officer. Sometimes called the "dean of science fiction writers", he was among the first to emphasize scientific accu ...

'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

Quantum measurement {{quantum-stub

Origin of the phrase

See also

References