Editing Paul Cohen (section)

==Career==
Cohen is noted for developing a mathematical technique called [[forcing (mathematics)|forcing]], which he used to prove that neither the [[continuum hypothesis]] (CH) nor the [[axiom of choice]] can be proved from the standard [[Zermelo–Fraenkel axioms]] (ZF) of [[set theory]]. In conjunction with the earlier work of [[Kurt Gödel|Gödel]], this showed that both of these statements are [[logical independence|logically independent]] of the ZF axioms: these statements can be neither proved nor disproved from these axioms. In this sense, the continuum hypothesis is undecidable, and it is the most widely known example of a natural statement that is independent from the standard ZF axioms of set theory.

For his result on the continuum hypothesis, Cohen won the [[Fields Medal]] in mathematics in 1966, and also the [[National Medal of Science]] in 1967.<ref>{{cite web|url=https://www.nsf.gov/od/nms/recip_details.cfm?recip_id=80|title=The President's National Medal of Science: Recipient Details - NSF - National Science Foundation|website=www.nsf.gov|access-date=21 March 2018}}</ref> The Fields Medal that Cohen won continues to be the only Fields Medal to be awarded for a work in mathematical logic, as of 2022.

Apart from his work in set theory, Cohen also made many valuable contributions to analysis. He was awarded the [[Bôcher Memorial Prize]] in [[mathematical analysis]] in 1964 for his paper "On a conjecture by [[John Edensor Littlewood|Littlewood]] and [[idempotent measure]]s",{{sfn|Cohen|1960}} and lends his name to the [[Cohen–Hewitt factorization theorem]].

Cohen was a full professor of mathematics at [[Stanford University]]. He was an Invited Speaker at the [[International Congress of Mathematicians|ICM]] in 1962 in Stockholm and in 1966 in Moscow.

[[Angus MacIntyre]] of the [[Queen Mary University of London]] stated about Cohen: "He was dauntingly clever, and one would have had to be naive or exceptionally altruistic to put one's 'hardest problem' to the Paul I knew in the '60s." He went on to compare Cohen to [[Kurt Gödel]], saying: "Nothing more dramatic than their work has happened in the history of the subject."<ref name="chronicle">{{cite news |newspaper=[[San Francisco Chronicle]] |url=http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/03/30/BAG8DOUKEG1.DTL |title=Paul Cohen -- Stanford professor, acclaimed mathematician |first=Keay |last=Davidson |date=2007-03-30 |access-date=2007-10-31}}</ref> Gödel himself wrote a letter to Cohen in 1963, a draft of which stated, "Let me repeat that it is really a delight to read your proof of the ind[ependence] of the cont[inuum] hyp[othesis]. I think that in all essential respects you have given the best possible proof & this does not happen frequently. Reading your proof had a similarly pleasant effect on me as seeing a really good play."<ref>[[Solomon Feferman]], The Gödel Editorial Project: A synopsis [http://math.stanford.edu/~feferman/papers/Goedel-Project-Synopsis.pdf] p. 11.</ref>

===Continuum hypothesis===
While studying the continuum hypothesis, Cohen is quoted as saying in 1985 that he had "had the feeling that people thought the problem was hopeless, since there was no new way of constructing models of set theory. Indeed, they thought you had to be slightly crazy even to think about the problem."<ref name="nytimes">{{cite news |work=[[The New York Times]] |title=Paul J. Cohen, Mathematics Trailblazer, Dies at 72 |first=Jeremy |last=Pearce |date=2007-04-02 |url=https://www.nytimes.com/2007/04/02/us/02cohen.html?_r=1&oref=slogin |access-date=2007-10-31}}</ref>

{{blockquote|1=A point of view which the author [Cohen] feels may eventually come to be accepted is that CH is obviously false. The main reason one accepts the [[axiom of infinity]] is probably that we feel it absurd to think that the process of adding only one set at a time can exhaust the entire universe. Similarly with the higher axioms of infinity. Now <math>\aleph_1</math> is the cardinality of the set of countable ordinals, and this is merely a special and the simplest way of generating a higher cardinal. The set <math>C</math> [the continuum] is, in contrast, generated by a totally new and more powerful principle, namely the [[axiom of power set|power set axiom]]. It is unreasonable to expect that any description of a larger cardinal which attempts to build up that cardinal from ideas deriving from the [[axiom schema of replacement|replacement axiom]] can ever reach <math>C</math>.<p>Thus <math>C</math> is greater than <math>\aleph_n, \aleph_\omega, \aleph_a</math>, where <math>a = \aleph_\omega</math>, etc. This point of view regards <math>C</math> as an incredibly rich set given to us by one bold new axiom, which can never be approached by any piecemeal process of construction. Perhaps later generations will see the problem more clearly and express themselves more eloquently.</p>|2={{harvtxt|Cohen|2008}}}}

An "enduring and powerful product" of Cohen's work on the continuum hypothesis, and one that has been used by "countless mathematicians"<ref name="nytimes"/> is known as [[forcing (mathematics)|"forcing"]], and it is used to construct mathematical models to test a given hypothesis for truth or falsehood.

Shortly before his death, Cohen gave a lecture describing his solution to the problem of the continuum hypothesis at the 2006 Gödel centennial conference in [[Vienna]].<ref>{{YouTube|VBFLWk7k1Zo|Paul Cohen lecture video, six parts, Gödel Centennial, Vienna 2006}}</ref>