Editing Totalitarian principle

{{Short description|Quantum mechanics principle stating: "Everything not forbidden is compulsory"}}
{{about|a principle of quantum mechanics|the political system|Totalitarianism}}
In [[quantum mechanics]], the '''totalitarian principle''' states: "Everything not forbidden is compulsory." [[Physicist]]s including [[Murray Gell-Mann]] 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 [[Elementary particle|particle]] interactions:  that any interaction that is not forbidden by a small number of simple [[conservation law]]s is not only allowed, but ''must'' be included in the sum over all "[[Path integral formulation|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]] 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]]).

==Origin of the phrase==
Neither the phrase nor its application to quantum physics originated with Gell-Mann,<ref>{{cite arXiv |last1=Kragh |first1=Helge |title=Physics and the Totalitarian Principle |year=2019 |arxiv=1907.04623 |class=physics.hist-ph}}</ref> but a 1956 paper by him contains the first published use of the phrase as a description of quantum physics.<ref name="Gell-Mann1956">See footnote on p.&nbsp;859 in {{Cite journal | doi = 10.1007/BF02748000| title = The interpretation of the new particles as displaced charge multiplets| journal = Il Nuovo Cimento| volume = 4| pages = 848–866| year = 1956| last1 = Gell-Mann | first1 = M. | issue = S2|url=http://tuvalu.santafe.edu/~mgm/Site/Publications_files/MGM%2014.pdf |quote="Among baryons, antibaryons, and mesons, any process which is not forbidden by a conservation law actually does take place with appreciable probability. We have made liberal and tacit use of this assumption, which is related to the state of affairs that is said to prevail in a perfect totalitarian state. Anything that is not compulsory is forbidden. Use of this principle is somewhat dangerous, since it may be that while the laws proposed in this communication are correct, there are others, yet to be discussed, which forbid some of the processes that we suppose to be allowed."| bibcode = 1956NCim....4S.848G| s2cid = 121017243}}</ref> Gell-Mann used it to describe the state of [[particle physics]] around the time he was formulating the [[Eightfold way (physics)|Eightfold Way]], a precursor to the [[quark]]-model of [[hadron]]s. According to the second edition of ''Strange Beauty: Murray Gell-Mann & the Revolution in Physics'' <ref>{{cite book |last=Johnson |first=G. |year=2023 |title=Strange Beauty: Murray Gell-Mann & the Revolution in Physics, |page=341 |publisher=SFI Press |isbn=978-1947864498}}</ref> 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]]'',<ref>{{cite book |last=White |first=T. H. |year=1996 |title=The Once and Future King |publisher=[[Ace Trade]] |edition=Reprint |page=[https://archive.org/details/oncefutureking00whit_0/page/121 121] |isbn=978-0441003839 |url=https://archive.org/details/oncefutureking00whit_0/page/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." This passage does not appear in the 1938 and 1939 editions of The Sword and the Stone, but only in the 1958 revision incorporated into The Once and Future King.</ref> [[Jack Parsons]]'s 1948 essay "Freedom is a Two-Edged Sword",<ref>{{cite book | first=John Whiteside | last=Parsons | author-link=Jack Parsons | title=Freedom is a Two-Edged Sword | chapter=II. The Sword and the State | publisher=Falcon Press | year=1989 | url=https://archive.org/details/marvel-whiteside-parsons/FREEDOM%20is%20a%20TWO%20EDGED%20SWORD/page/13/mode/2up }} "I do not mean his potential activities. It is a sophistry, fascist in essence, that a man should be restrained because he might be dangerous. Following this argument, a man should be restrained for any reason, on anybody's judgment. This is simply placing unlimited power in the hands of the state. All that is not forbidden is compulsory. This is the ultimate conclusion of such a dogma."</ref> and [[Robert Heinlein]]'s 1940 short story "Coventry".<ref>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."</ref> 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]]. 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.

==See also==
* {{annotated link|Everything which is not forbidden is allowed}}
* {{annotated link|Modal realism}}

==References==
{{Reflist}}

[[Category:Quantum measurement]]
[[Category:Murray Gell-Mann]]