{{pp-semi-indef}}
{{Redirect|Turing}}
{{short description|English mathematician and computer scientist}} 
{{Use British English|date=June 2020}}
{{Use dmy dates|date=March 2020}}
{{Infobox scientist
| name = Alan Turing
| honorific_suffix = {{postnominals|country=GBR|OBE|FRS|size=100%}}
| image = Alan Turing Aged 16.jpg
| caption = Turing {{circa}}&nbsp;1928 at age 16<!-- original source says simply: "AMT aged 16, head and shoulders" -->
| birth_name = Alan Mathison Turing
| birth_date = {{Birth date|df=y|1912|6|23}}
| birth_place = [[Maida Vale]], London, England
| death_date = {{Death date and age|df=y|1954|6|7|1912|6|23}}
| death_place = {{Nowrap|[[Wilmslow]], Cheshire, England}}
| resting_place = Ashes scattered in gardens of [[Woking Crematorium]]
| death_cause = Suicide (disputed) by [[cyanide poisoning]]

| field = {{Plainlist|
* [[Logic]]
* Mathematics
* [[Cryptanalysis]]
* [[Computer science]]
* [[Mathematical and theoretical biology]]<ref name=googlescholar>{{Google scholar id}}</ref>}}
| work_institutions = {{Plainlist|
* [[University of Manchester]]
* [[Government Code and Cypher School]]
* [[National Physical Laboratory, UK|National Physical Laboratory]]}}
| education = [[Sherborne School]]
| alma_mater = {{Plainlist|
* [[University of Cambridge]] <!--[[King's College, Cambridge]] doestn't award degrees--> ([[Bachelor of Arts|BA]], [[Master of Arts|MA]])
* [[Princeton University]] (PhD)}}
| doctoral_advisor = [[Alonzo Church]]<ref name="mathgene">{{MathGenealogy|id=8014}}</ref>
| doctoral_students = [[Robin Gandy]],<ref name="mathgene"/><ref name=gandyphd>{{cite thesis|degree=PhD|title=On axiomatic systems in mathematics and theories in physics|first=Robin Oliver|last=Gandy|year=1953|url=https://www.repository.cam.ac.uk/handle/1810/245090|id={{EThOS|uk.bl.ethos.590164}}|publisher=University of Cambridge|doi=10.17863/CAM.16125|accessdate=9 December 2017|archiveurl=https://web.archive.org/web/20171209152236/https://www.repository.cam.ac.uk/handle/1810/245090|archivedate=9 December 2017|url-status=live}} {{free access}}</ref> [[Beatrice Worsley]]<ref name="bowen19">{{cite chapter| first=Jonathan P. |last=Bowen | authorlink=Jonathan Bowen | chapter=The Impact of Alan Turing: Formal Methods and Beyond | editor-last1=Bowen | editor-first1=Jonathan P. | editor-last2=Liu | editor-first2=Zhiming | editorlink2=Zhiming Liu (computer scientist) | editor-last3=Zhang | editor-first3=Zili | title=Engineering Trustworthy Software Systems. SETSS 2018 | series=[[Lecture Notes in Computer Science]] | volume=11430 | pages=202–235 |year=2019 | publisher=[[Springer Nature|Springer]] | location=Cham | doi=10.1007/978-3-030-17601-3_5 |isbn=978-3-030-17600-6 }}</ref>
| influences = [[Max Newman]]<ref>[[Ivor Grattan-Guinness|Grattan-Guinness, Ivor]], Chapter 40, ''Turing's mentor, Max Newman''. In {{cite book| author-link1 = Jack Copeland|last1 = Copeland | first1=B. Jack | authorlink2=Jonathan Bowen | last2=Bowen | first2=Jonathan P. | authorlink3=Robin Wilson (mathematician)| last3=Wilson | first3=Robin | last4=Sprevak | first4=Mark | title=The Turing Guide | publisher=[[Oxford University Press]] | year=2017 | isbn=978-0-19-874782-6|title-link = The Turing Guide }}</ref>
| thesis_title = Systems of Logic Based on Ordinals
| thesis_url = https://webspace.princeton.edu/users/jedwards/Turing%20Centennial%202012/Mudd%20Archive%20files/12285_AC100_Turing_1938.pdf
| thesis_year = 1938
| signature = Alan Turing signature.svg
| known_for = {{Plainlist|
* [[Cryptanalysis of the Enigma]]
* [[Turing's proof]]
* [[Turing machine]]
* [[Turing test]]
* [[Unorganized machine|Unorganised machine]]
* [[Turing pattern]]
* [[Turing reduction]]
* [[The Chemical Basis of Morphogenesis]]
}}
| prizes = [[Smith's Prize]] (1936)
| partner = [[Joan Clarke]]<br />(engaged in 1941; did not marry)
| nationality = English
}}

'''Alan Mathison Turing''' {{postnominals|country=GBR|OBE|FRS}} ({{IPAc-en|ˈ|tj|ʊər|ɪ|ŋ}}; 23 June 1912&nbsp;– 7 June 1954) was an English mathematician, [[computer scientist]], [[logic]]ian, [[cryptanalysis|cryptanalyst]], philosopher, and [[mathematical and theoretical biology|theoretical biologist]].<ref>{{cite web |publisher=The British Library |title=Who was Alan Turing? |access-date=29 July 2019 |url=https://www.bl.uk/people/alan-turing |archive-url=https://web.archive.org/web/20190723191531/https://www.bl.uk/people/alan-turing |archive-date=23 July 2019 |url-status=live }}</ref><ref name=whoswho>{{Who's Who | author=Anon| surname = Turing | othernames = Alan Mathison | id = U243891 | year = 2017 | doi = 10.1093/ww/9780199540884.013.U243891 | edition = online [[Oxford University Press]]|location=Oxford}} {{subscription required}}</ref> Turing was highly influential in the development of [[theoretical computer science]], providing a formalisation of the concepts of [[algorithm]] and [[computation]] with the [[Turing machine]], which can be considered a model of a [[general-purpose computer]].<ref name="frs">{{Cite journal
| last1 = Newman | first1 = M.H.A.
| authorlink = Max Newman
| doi = 10.1098/rsbm.1955.0019
| title = Alan Mathison Turing. 1912–1954
| journal = [[Biographical Memoirs of Fellows of the Royal Society]]
| volume = 1
| pages = 253–263
| year = 1955
| jstor = 769256
| s2cid = 711366
| doi-access = free
}}</ref><ref name=AFP/><ref>{{Harvnb|Sipser|2006|p=137}}</ref> Turing is widely considered to be the father of theoretical computer science and [[artificial intelligence]].<ref>{{Harvnb|Beavers|2013|p=481}}</ref> Despite these accomplishments, he was never fully recognised in his home country during his lifetime due to the prevalence of [[homophobia]] [[Timeline_of_LGBT_history_in_the_United_Kingdom#20th_century|at the time]] and because much of his work was covered by the [[Official Secrets Act]].

During the [[Second World War]], Turing worked for the [[Government Communications Headquarters#Government Code and Cypher School (GC&CS)|Government Code and Cypher School]] (GC&CS) at [[Bletchley Park]], Britain's [[cryptanalysis|codebreaking]] centre that produced [[Ultra]] intelligence. For a time he led [[Hut 8]], the section that was responsible for German naval cryptanalysis. Here, he devised a number of techniques for speeding the breaking of German [[cipher]]s, including improvements to the pre-war Polish [[Bomba (cryptography)|bombe]] method, an [[electromechanics|electromechanical]] machine that could find settings for the [[Enigma machine]].

Turing played a crucial role in cracking intercepted coded messages that enabled the Allies to defeat the Nazis in many crucial engagements, including the [[Battle of the Atlantic]], and in so doing helped win the war.<ref name="bbc-copeland"/><ref>A number of sources state that Winston Churchill said that Turing made the single biggest contribution to Allied victory in the war against Nazi Germany. However, both [[The Churchill Centre]] and Turing's biographer [[Andrew Hodges]] have stated they know of no documentary evidence to support this claim, nor of the date or context in which Churchill supposedly said it, and the Churchill Centre lists it among their Churchill 'Myths', see {{cite web | url=http://www.winstonchurchill.org/resources/myths/churchill-said-turing-made-the-single-biggest-contribution-to-allied-victory | title=Churchill Said Turing Made the Single Biggest Contribution to Allied Victory | first=Jonathan | last=Schilling | date=8 January 2015 | publisher=The Churchill Centre: Myths | accessdate=9 January 2015 | archive-url=https://web.archive.org/web/20150217170510/http://www.winstonchurchill.org/resources/myths/churchill-said-turing-made-the-single-biggest-contribution-to-allied-victory | archive-date=17 February 2015 | url-status=live }} and {{cite web | url=http://www.turing.org.uk/book/update/part4.html | title=Part 4: The Relay Race | first=Andrew | last=Hodges | authorlink=Andrew Hodges | publisher=Update to [[Alan Turing: The Enigma]] | accessdate=9 January 2015 | archive-url=https://web.archive.org/web/20150120190931/http://www.turing.org.uk/book/update/part4.html | archive-date=20 January 2015 | url-status=live }}  A [[BBC News]] profile piece that repeated the Churchill claim has subsequently been amended to say there is no evidence for it. See {{cite news | url=http://news.bbc.co.uk/2/hi/uk_news/8250592.stm | title=Profile: Alan Turing | first=Clare | last=Spencer | publisher=BBC News | date=11 September 2009 | quote=Update 13 February 2015 | access-date=17 February 2015 | archive-url=https://web.archive.org/web/20171213095303/http://www.bbc.com/news/technology-18419691 | archive-date=13 December 2017 | url-status=live }}</ref> Due to the problems of [[counterfactual history]], it is hard to estimate the precise effect Ultra intelligence had on the war,<ref>See for example {{cite book | title=A Century of Spies: Intelligence in the Twentieth Century | first=Jeffery T. | last=Richelson | authorlink=Jeffrey T. Richelson | publisher=Oxford University Press | location=New York | date=1997 | page=296}} and {{cite book | first=Guy | last=Hartcup | authorlink=Guy Hartcup | title=The Effect of Science on the Second World War | publisher=Macmillan Press | location=Basingstoke, Hampshire | date=2000 | pages=96–99}}</ref> but at the upper end it has been estimated that this work shortened the war in Europe by more than two years and saved over 14&nbsp;million lives.<ref name="bbc-copeland">{{cite news | last=Copeland | first=Jack | authorlink=Jack Copeland | title=Alan Turing: The codebreaker who saved 'millions of lives' | date=18 June 2012 | url=https://www.bbc.com/news/technology-18419691 | publisher=BBC News Technology | accessdate=26 October 2014 | archive-url=https://web.archive.org/web/20141011045451/http://www.bbc.com/news/technology-18419691 | archive-date=11 October 2014 | url-status=live }}</ref>

After the war Turing worked at the [[National Physical Laboratory, UK|National Physical Laboratory]], where he designed the [[Automatic Computing Engine]]. The Automatic Computing Engine was one of the first designs for a stored-program computer. In 1948, Turing joined [[Max Newman]]'s [[Computing Machine Laboratory]], at the [[Victoria University of Manchester]], where he helped develop the [[Manchester computers]]<ref>{{Harvnb|Leavitt|2007|pp=231–233}}</ref> and became interested in [[mathematical biology]]. He wrote a paper on the chemical basis of [[morphogenesis]]<ref name=googlescholar/> and predicted [[Chemical clock|oscillating]] [[chemical reaction]]s such as the [[Belousov–Zhabotinsky reaction]], first observed in the 1960s.

Turing was prosecuted in 1952 for homosexual acts; the [[Labouchere Amendment]] of 1885 had mandated that "gross indecency" was a criminal offence in the UK. He accepted [[chemical castration]] treatment, with [[Diethylstilbestrol|DES]], as an alternative to prison. Turing died in 1954, 16 days before his 42nd birthday, from [[cyanide poisoning]]. An inquest determined his death as a suicide, but it has been noted that the known evidence is also consistent with accidental poisoning.

In 2009, following an [[Internet campaign]], British Prime Minister [[Gordon Brown]] made an [[#Government apology and pardon support|official public apology]] on behalf of the British government for "the appalling way he was treated". [[Queen Elizabeth II]] granted Turing a posthumous pardon in 2013. The "[[Alan Turing law]]" is now an informal term for a 2017 law in the United Kingdom that retroactively pardoned men cautioned or convicted under historical legislation that outlawed homosexual acts.<ref name="BBC-pardon">{{cite news |url=https://www.bbc.com/news/uk-37711518 |title='Alan Turing law': Thousands of gay men to be pardoned |date=20 October 2016 |accessdate=20 October 2016 |publisher=BBC News |archive-url=https://web.archive.org/web/20161020125029/http://www.bbc.com/news/uk-37711518 |archive-date=20 October 2016 |url-status=live }}</ref>
{{TOC limit|3}}

==Early life and education==

===Family===
Turing was born in [[Maida Vale]], London,<ref name=whoswho/> while his father, Julius Mathison Turing (1873–1947), was on leave from his position with the [[Indian Civil Service]] (ICS) at [[Chatrapur]], then in the [[Madras Presidency]] and presently in [[Odisha]] state, in India.<ref name = "Hodges1983P5">{{Harvnb|Hodges|1983|p=5}}</ref><ref>{{cite web |url=http://www.turing.org.uk/turing/scrapbook/early.html |title=The Alan Turing Internet Scrapbook |publisher=[[Alan Turing: The Enigma]] |accessdate=2 January 2012 |archive-url=https://www.webcitation.org/6BOrKl1DB?url=http://www.turing.org.uk/turing/scrapbook/early.html |archive-date=14 October 2012 |url-status=live }}</ref> Turing's father was the son of a clergyman, the Rev.&nbsp;John Robert Turing, from a Scottish family of merchants that had been based in the Netherlands and included a [[baronet]]. Turing's mother, Julius's wife, was Ethel Sara Turing ({{nee|Stoney}} 1881–1976),<ref name=whoswho/> daughter of Edward Waller Stoney, chief engineer of the [[Madras and Southern Mahratta Railway|Madras Railways]]. The Stoneys were a [[Protestantism in Ireland|Protestant]] [[Anglo-Irish]] [[gentry]] family from both [[County Tipperary]] and [[County Longford]], while Ethel herself had spent much of her childhood in [[County Clare]].<ref>Phil Maguire, "An Irishman's Diary", p. 5. ''[[The Irish Times]]'', 23 June 2012.</ref>

Julius's work with the ICS brought the family to British India, where his grandfather had been a general in the [[Bengal Army]]. However, both Julius and Ethel wanted their children to be brought up in Britain, so they moved to [[Maida Vale]],<ref name="englishheritaget">{{cite web|url=http://www.english-heritage.org.uk/server/show/nav.001002006005/chooseLetter/T |archiveurl=https://web.archive.org/web/20090903150218/http://www.english-heritage.org.uk/server/show/nav.001002006005/chooseLetter/T |archivedate=3 September 2009 |title=London Blue Plaques |accessdate=10 February 2007 |work=English Heritage |url-status=live  }}</ref> London, where Alan Turing was born on 23 June 1912, as recorded by a [[blue plaque]] on the outside of the house of his birth,<ref>[http://blogs.nature.com/london/2011/03/16/the-scientific-tourist-in-london-17-alan-turings-birth-place The Scientific Tourist In London: #17 Alan Turing's Birth Place] {{Webarchive|url=https://web.archive.org/web/20130921054045/http://blogs.nature.com/london/2011/03/16/the-scientific-tourist-in-london-17-alan-turings-birth-place |date=21 September 2013 }}, ''Nature''. London Blog</ref><ref>{{openplaque|381}}</ref> later the [[Colonnade Hotel (London)|Colonnade Hotel]].<ref name="Hodges1983P5"/><ref name="turingorguk">{{cite web | url=http://www.turing.org.uk/turing/scrapbook/memorial.html | title=The Alan Turing Internet Scrapbook | accessdate=26 September 2006 | archive-url=https://wayback.archive-it.org/all/20110720214124/http://www.turing.org.uk/turing/scrapbook/memorial.html | archive-date=20 July 2011 | url-status=live }}</ref> Turing had an elder brother, John (the father of [[Dermot Turing|Sir John Dermot Turing]], 12th Baronet of the [[Turing baronets]]).<ref>[https://bletchleypark.org.uk/about-us/bletchley-park-trustees/sir-john-dermot-turing Sir John Dermot Turing] {{Webarchive|url=https://web.archive.org/web/20171018191443/https://bletchleypark.org.uk/about-us/bletchley-park-trustees/sir-john-dermot-turing |date=18 October 2017 }} on the Bletchley Park website.</ref>

Turing's father's civil service commission was still active and during Turing's childhood years Turing's parents travelled between [[Hastings]] in the United Kingdom<ref>{{Harvnb|Hodges|1983|p=6}}</ref> and India, leaving their two sons to stay with a retired [[British Army|Army]] couple. At Hastings, Turing stayed at [[Baston Lodge]], Upper Maze Hill, [[St Leonards-on-Sea]], now marked with a blue plaque.<ref name="Hastings & St. Leonards Observer - 29 June 2012 - Plaque unveiled at Turing's home in St Leonards">{{cite news|url=http://www.hastingsobserver.co.uk/news/plaque-unveiled-at-turing-s-home-in-st-leonards-1-4003535|title=Plaque unveiled at Turing's home in St Leonards|date=29 June 2012|work=[[Hastings & St. Leonards Observer]]|accessdate=3 July 2017|archive-url=https://web.archive.org/web/20170912121655/http://www.hastingsobserver.co.uk/news/plaque-unveiled-at-turing-s-home-in-st-leonards-1-4003535|archive-date=12 September 2017|url-status=dead}}</ref> The plaque was unveiled on 23 June 2012, the centenary of Turing's birth.<ref name="BBC News - 25 June 2012 - St Leonards plaque marks Alan Turing's early years">{{cite news|url=https://www.bbc.com/news/uk-england-sussex-18580826|title=St Leonards plaque marks Alan Turing's early years|date=25 June 2012|publisher=[[BBC News]]|accessdate=3 July 2017|archive-url=https://web.archive.org/web/20171203074933/http://www.bbc.com/news/uk-england-sussex-18580826|archive-date=3 December 2017|url-status=live}}</ref>

Very early in life, Turing showed signs of the genius that he was later to display prominently.<ref name=toolbox>{{cite web |title=Alan Turing&nbsp;– Towards a Digital Mind: Part 1 |first=G. James |last=Jones |date=11 December 2001 |url=http://www.systemtoolbox.com/article.php?history_id=3 |accessdate=27 July 2007 |work=System Toolbox |archiveurl=https://web.archive.org/web/20070803163318/http://www.systemtoolbox.com/article.php?history_id=3 |archivedate=3 August 2007 |url-status=dead  }}</ref> His parents purchased a house in [[Guildford]] in 1927, and Turing lived there during school holidays. The location is also marked with a blue plaque.<ref>{{cite web |url=http://www.guildford-dragon.com/2012/11/29/founder-of-computer-science-alan-turings-guildford-stargazing/ |title=Guildford Dragon NEWS |publisher=The Guildford Dragon |date=29 November 2012 |accessdate=31 October 2013 |archive-url=https://web.archive.org/web/20131019062927/http://www.guildford-dragon.com/2012/11/29/founder-of-computer-science-alan-turings-guildford-stargazing/ |archive-date=19 October 2013 |url-status=live }}</ref>

===School===
Turing's parents enrolled him at St Michael's, a day school at 20 Charles Road, [[St Leonards-on-Sea]], at the age of six. The headmistress recognised his talent early on, as did many of his subsequent teachers.

Between January 1922 and 1926, Turing was educated at Hazelhurst Preparatory School, an independent school in the village of [[Frant]] in Sussex (now [[East Sussex]]).<ref>{{cite web|url=http://oldshirburnian.org.uk/wp-content/uploads/2016/04/TURING-Alan-Mathison.pdf|title=Alan Turing Archive – Sherborne School (ARCHON CODE: GB1949)|author=Alan Mathison|work=Sherborne School, Dorset|date=April 2016|accessdate=5 February 2017|archive-url=https://web.archive.org/web/20161226093015/http://oldshirburnian.org.uk/wp-content/uploads/2016/04/TURING-Alan-Mathison.pdf|archive-date=26 December 2016|url-status=live}}</ref> In 1926, at the age of 13, he went on to [[Sherborne School]], a boarding independent school in the market town of [[Sherborne]] in Dorset. The first day of term coincided with the [[1926 United Kingdom general strike|1926 General Strike]], in Britain, but Turing was so determined to attend, that he rode his bicycle unaccompanied {{convert|60|mi|km}} from [[Southampton]] to Sherborne, stopping overnight at an inn.<ref name=metamagical>{{Cite book|title=Metamagical Themas: Questing for the Essence of Mind and Pattern |page=[https://books.google.com/books?id=o8jzWF7rD6oC&pg=PA484 484]|first=Douglas R. |last=Hofstadter |year=1985 |publisher=Basic Books |isbn=978-0-465-04566-2 |oclc=230812136}}</ref>

Turing's natural inclination towards mathematics and science did not earn him respect from some of the teachers at Sherborne, whose definition of education placed more emphasis on the [[classics]]. His headmaster wrote to his parents: "I hope he will not fall between two stools. If he is to stay at public school, he must aim at becoming ''educated''. If he is to be solely a ''Scientific Specialist'', he is wasting his time at a public school".<ref>{{Harvnb|Hodges|March 1983|p=26}}</ref> Despite this, Turing continued to show remarkable ability in the studies he loved, solving advanced problems in 1927 without having studied even elementary [[calculus]]. In 1928, aged 16, Turing encountered [[Albert Einstein]]'s work; not only did he grasp it, but it is possible that he managed to deduce Einstein's questioning of [[Newton's laws of motion]] from a text in which this was never made explicit.<ref>{{Harvnb|Hodges|1983|p=34}}</ref>

===Christopher Morcom===
At Sherborne, Turing formed a significant friendship with fellow pupil Christopher Collan Morcom (13 July 1911 – 13 February 1930),<ref>https://oldshirburnian.org.uk/wp-content/uploads/2015/01/Obituary-for-Christopher-Morcom-The-Shirburnian-March-1930.pdf</ref> who has been described as Turing's "first love". Their relationship provided inspiration in Turing's future endeavours, but it was cut short by Morcom's death, in February 1930, from complications of [[bovine tuberculosis]], contracted after drinking infected cow's milk some years previously.<ref name=NYReviewBooks>{{cite web|author=Caryl, Christian|title=Poor Imitation of Alan Turing|url=http://www.nybooks.com/blogs/nyrblog/2014/dec/19/poor-imitation-alan-turing/|newspaper=[[New York Review of Books]]|date=19 December 2014|access-date=9 January 2015|archive-url=https://web.archive.org/web/20150107010418/http://www.nybooks.com/blogs/nyrblog/2014/dec/19/poor-imitation-alan-turing/|archive-date=7 January 2015|url-status=live}}</ref><ref>Rachel Hassall, [http://oldshirburnian.org.uk/wp-content/uploads/2014/03/The-Sherborne-Formula-Vivat-2012-2013-optimised.pdf 'The Sherborne Formula: The Making of Alan Turing'] {{Webarchive|url=https://web.archive.org/web/20140415082353/http://oldshirburnian.org.uk/wp-content/uploads/2014/03/The-Sherborne-Formula-Vivat-2012-2013-optimised.pdf |date=15 April 2014 }} 'Vivat!' 2012/13</ref><ref name=teuscher>{{Cite book|editor-last=Teuscher |editor-first=Christof|editorlink=Christof Teuscher |title=Alan Turing: Life and Legacy of a Great Thinker |year=2004 |publisher=[[Springer Science+Business Media|Springer-Verlag]] |isbn=978-3-540-20020-8 |oclc=53434737 }}</ref>

The event caused Turing great sorrow. He coped with his grief by working that much harder on the topics of science and mathematics that he had shared with Morcom. In a letter to Morcom's mother, Frances Isobel Morcom (née Swan), Turing wrote:{{quote|I am sure I could not have found anywhere another companion so brilliant and yet so charming and unconceited. I regarded my interest in my work, and in such things as astronomy (to which he introduced me) as something to be shared with him and I think he felt a little the same about me&nbsp;... I know I must put as much energy if not as much interest into my work as if he were alive, because that is what he would like me to do.<ref>{{Harvnb|Hodges|1983|p=61}}</ref>}}

Turing's relationship with Morcom's mother continued long after Morcom's death, with her sending gifts to Turing, and him sending letters, typically on Morcom's birthdays.<ref>{{cite book |title=Alan Turing: The Enigma |publisher=Princeton University Press |authorlink=Andrew Hodges |last=Hodges |first=Andrew |page=[https://archive.org/details/alanturingenigma0000hodg/page/87 87] |year=2012 |isbn=978-0-691-15564-7 |url=https://archive.org/details/alanturingenigma0000hodg|url-access=registration }}</ref> A day before the third anniversary of Morcom's death (13 February 1933), he wrote to Mrs. Morcom: {{quote|I expect you will be thinking of Chris when this reaches you. I shall too, and this letter is just to tell you that I shall be thinking of Chris and of you tomorrow. I am sure that he is as happy now as he was when he was here. Your affectionate Alan.<ref>{{cite book |title=Alan Turing: The Enigma |publisher=Princeton University Press |authorlink=Andrew Hodges |last=Hodges |first=Andrew |page=[https://archive.org/details/alanturingenigma0000hodg/page/90 90] |year=2012 |isbn=978-0-691-15564-7 |url=https://archive.org/details/alanturingenigma0000hodg|url-access=registration }}</ref>}}

Some have speculated that Morcom's death was the cause of Turing's [[atheism]] and [[materialism]].<ref>Paul Gray, [http://www.time.com/time/magazine/article/0,9171,990624,00.html Alan Turing] {{Webarchive|url=https://web.archive.org/web/20110119181237/http://www.time.com/time/magazine/article/0,9171,990624,00.html |date=19 January 2011 }} Time Magazine's Most Important People of the Century, p. 2</ref> Apparently, at this point in his life he still believed in such concepts as a spirit, independent of the body and surviving death. In a later letter, also written to Morcom's mother, Turing wrote: {{quote|Personally, I believe that spirit is really eternally connected with matter but certainly not by the same kind of body&nbsp;... as regards the actual connection between spirit and body I consider that the body can hold on to a 'spirit', whilst the body is alive and awake the two are firmly connected. When the body is asleep I cannot guess what happens but when the body dies, the 'mechanism' of the body, holding the spirit is gone and the spirit finds a new body sooner or later, perhaps immediately.<ref>{{Harvnb|Hodges|1983|pp=82–83}}</ref>}}

===University and work on computability===
After Sherborne, Turing studied as an undergraduate from 1931 to 1934 at [[King's College, Cambridge]],<ref name=whoswho/> where he was awarded first-class honours in mathematics. In 1935, at the age of 22, he was elected a [[Fellow]] of King's College on the strength of a dissertation in which he proved the [[central limit theorem]].<ref>See Section 3 of John Aldrich, "England and Continental Probability in the Inter-War Years", Journal Electronique d'Histoire des Probabilités et de la Statistique, vol. 5/2 [http://www.jehps.net/decembre2009.html Decembre 2009] {{Webarchive|url=https://web.archive.org/web/20180421105727/http://www.jehps.net/decembre2009.html |date=21 April 2018 }} Journal Electronique d'Histoire des Probabilités et de la Statistique</ref> Unknown to the committee, the theorem had already been proven, in 1922, by [[Jarl Waldemar Lindeberg]].<ref>{{Harvnb|Hodges|1983|pp=88, 94}}</ref> A blue plaque at the college was unveiled on the centenary of his birth on 23 June 2012 and is now installed at the college's Keynes Building on King's Parade.<ref>{{cite web|url=http://www.kings.cam.ac.uk/news/2012/turing-plaque.html|title=Blue plaque to commemorate Alan Turing|publisher=King's College, Cambridge|accessdate=8 December 2018|archive-url=https://web.archive.org/web/20181207025216/http://www.kings.cam.ac.uk/news/2012/turing-plaque.html|archive-date=7 December 2018|url-status=live}}</ref><ref>{{cite web|url=http://www.kings.cam.ac.uk/news/2012/turing-plaque-fixed-place.html|title=Turing plaque fixed in place|publisher=[[King's College, Cambridge]]|accessdate=8 December 2018|archive-url=https://web.archive.org/web/20181209124354/http://www.kings.cam.ac.uk/news/2012/turing-plaque-fixed-place.html|archive-date=9 December 2018|url-status=live}}</ref>

In 1936, Turing published his paper "[[On Computable Numbers, with an Application to the Entscheidungsproblem]]".<ref>{{Harvnb|Turing|1937}}</ref> It was published in the ''Proceedings of the London Mathematical Society'' journal in two parts, the first on 30 November and the second on 23 December.<ref>{{cite book |url=https://books.google.com/books?id=MlsJuSj2OkEC&pg=PA211 |p=211 |title=Computability: Turing, Gödel, Church, and Beyond |author1=B. Jack Copeland |author2=Carl J. Posy |author3=Oron Shagrir |publisher=MIT Press |year=2013|isbn=9780262018999 }}</ref> In this paper, Turing reformulated [[Kurt Gödel]]'s 1931 results on the limits of proof and computation, replacing Gödel's universal arithmetic-based formal language with the formal and simple hypothetical devices that became known as [[Turing machine]]s. The ''[[Entscheidungsproblem]]'' (decision problem) was originally posed by German mathematician [[David Hilbert]] in 1928. Turing proved that his "universal computing machine" would be capable of performing any conceivable mathematical computation if it were representable as an [[algorithm]]. He went on to prove that there was no solution to the ''decision problem'' by first showing that the [[halting problem]] for Turing machines is [[Decision problem|undecidable]]: it is not possible to decide algorithmically whether a Turing machine will ever halt.  This paper has been called "easily the most influential math paper in history".<ref>{{cite book |p=15 |title=Mathematics and Computation |author=Avi Wigderson |publisher=Princeton University Press |year=2019|isbn=9780691189130 }}</ref>

[[File:20130808 Kings College Front Court Fountain Crop 03.jpg|thumb|right|[[King's College, Cambridge]], where Turing was a student in 1931 and became a Fellow in 1935. The computer room is named after him.]]
Although [[Turing's proof]] was published shortly after [[Alonzo Church]]'s equivalent proof using his [[lambda calculus]],<ref>{{Harvnb|Church|1936}}</ref> Turing's approach is considerably more accessible and intuitive than Church's.<ref>{{cite web|last1=Grime|first1=James|title=What Did Turing Do for Us?|url=https://nrich.maths.org/8050|website=[[NRICH]]|publisher=[[University of Cambridge]]|accessdate=28 February 2016|date=February 2012|archive-url=https://web.archive.org/web/20160304175703/http://nrich.maths.org/8050|archive-date=4 March 2016|url-status=live}}</ref> It also included a notion of a 'Universal Machine' (now known as a [[universal Turing machine]]), with the idea that such a machine could perform the tasks of any other computation machine (as indeed could Church's lambda calculus). According to the [[Church–Turing thesis]], Turing machines and the lambda calculus are capable of computing anything that is computable. [[John von Neumann]] acknowledged that the central concept of the modern computer was due to Turing's paper.<ref>"von Neumann&nbsp;... firmly emphasised to me, and to others I am sure, that the fundamental conception is owing to Turing—insofar as not anticipated by Babbage, Lovelace and others." Letter by [[Stanley Frankel]] to [[Brian Randell]], 1972, quoted in [[Jack Copeland]] (2004) ''The Essential Turing'', p.&nbsp;22.</ref> To this day, Turing machines are a central object of study in [[theory of computation]].

From September 1936 to July 1938, Turing spent most of his time studying under Church at [[Princeton University]],<ref name="bowen19" /> in the second year as a [[Jane Eliza Procter Fellowship|Jane Eliza Procter Visiting Fellow]]. In addition to his purely mathematical work, he studied cryptology and also built three of four stages of an electro-mechanical [[binary multiplier]].<ref>{{Harvnb|Hodges|1983|p=138}}</ref> In June 1938, he obtained his PhD from the [[Princeton University Department of Mathematics|Department of Mathematics]] at Princeton;<ref>{{Cite journal
| last1 = Turing | first1 = A.M.
| authorlink = Alan Turing
| title = Systems of Logic Based on Ordinals
| doi = 10.1112/plms/s2-45.1.161
| journal = Proceedings of the London Mathematical Society
| pages = 161–228
| year = 1939
| volume=s2-45
| hdl = 21.11116/0000-0001-91CE-3
| hdl-access = free
}}</ref> his dissertation, ''[[Systems of Logic Based on Ordinals]]'',<ref name="turingphd">{{cite thesis |degree=PhD |first=Alan|last=Turing |title=Systems of Logic Based on Ordinals|publisher=Princeton University |year=1938 |doi=10.1112/plms/s2-45.1.161|authorlink=Alan Turing|id={{ProQuest|301792588}}|hdl=21.11116/0000-0001-91CE-3|hdl-access=free}}</ref><ref>{{cite web | last = Turing | first = A.M. | author-link = Alan Turing | title = Systems of Logic Based on Ordinals | year = 1938 | url = https://webspace.princeton.edu/users/jedwards/Turing%20Centennial%202012/Mudd%20Archive%20files/12285_AC100_Turing_1938.pdf | ref = harv | access-date = 4 February 2012 | archive-url = https://web.archive.org/web/20121023103503/https://webspace.princeton.edu/users/jedwards/Turing%20Centennial%202012/Mudd%20Archive%20files/12285_AC100_Turing_1938.pdf | archive-date = 23 October 2012 | url-status = dead }}</ref> introduced the concept of [[ordinal logic]] and the notion of [[Turing reduction|relative computing]], in which Turing machines are augmented with so-called [[oracle machine|oracles]], allowing the study of problems that cannot be solved by Turing machines. John von Neumann wanted to hire him as his [[Postdoctoral researcher|postdoctoral assistant]], but he went back to the United Kingdom.<ref>''John Von Neumann: The Scientific Genius Who Pioneered the Modern Computer, Game Theory, Nuclear Deterrence, and Much More'', Norman MacRae, 1999, American Mathematical Society, Chapter 8</ref>

==Career and research==
When Turing returned to Cambridge, he attended lectures given in 1939 by [[Ludwig Wittgenstein]] about the [[foundations of mathematics]].<ref>{{Harvnb|Hodges|1983|p=152}}</ref> The lectures have been reconstructed verbatim, including interjections from Turing and other students, from students' notes.<ref>[[Cora Diamond]] (ed.), ''Wittgenstein's Lectures on the Foundations of Mathematics'', University of Chicago Press, 1976</ref> Turing and Wittgenstein argued and disagreed, with Turing defending [[Philosophy of mathematics#Formalism|formalism]] and Wittgenstein propounding his view that mathematics does not discover any absolute truths, but rather invents them.<ref>{{Harvnb|Hodges|1983|pp=153–154}}</ref>

===Cryptanalysis===
During the Second World War, Turing was a leading participant in the breaking of German ciphers at [[Bletchley Park]]. The historian and wartime codebreaker [[Asa Briggs]] has said, "You needed exceptional talent, you needed genius at Bletchley and Turing's was that genius."<ref>{{Cite AV media | last = Briggs | first = Asa | author-link = Asa Briggs | title = Britain's Greatest Codebreaker | type = TV broadcast | publisher = [[Channel 4|UK Channel 4]] | date = 21 November 2011}}</ref>

From September 1938, Turing worked part-time with the [[Government Code and Cypher School]] (GC&CS), the British codebreaking organisation. He concentrated on [[cryptanalysis of the Enigma|cryptanalysis of the Enigma cipher machine]] used by [[Nazi Germany]], together with [[Dilly Knox]], a senior GC&CS codebreaker.<ref>{{Cite book | author-link = Jack Copeland | last = Copeland | first = Jack | chapter = Colossus and the Dawning of the Computer Age | page = 352 | title = Action This Day | publisher = Bantam | date = 2001 | isbn = 9780593049105  | editor-first1 = Michael | editor-last1 = Smith  | editor-first2 = Ralph | editor-last2 = Erskine }}</ref> Soon after the July 1939 meeting near [[Warsaw]] at which the [[Polish Cipher Bureau]] gave the British and French details of the wiring of [[Enigma rotor details|Enigma machine's rotors]] and their method of decrypting [[Enigma machine]]'s messages, Turing and Knox developed a broader solution.<ref>{{Harvnb|Copeland|2004a|p=217}}</ref> The Polish method relied on an insecure [[Cryptanalysis#Indicator|indicator]] procedure that the Germans were likely to change, which they in fact did in May 1940. Turing's approach was more general, using [[Cryptanalysis of the Enigma#Crib-based decryption|crib-based decryption]] for which he produced the functional specification of the [[bombe]] (an improvement on the Polish [[Bomba (cryptography)|Bomba]]).<ref>{{cite news |last=Clark |first=Liat |url=https://www.wired.co.uk/news/archive/2012-06/18/turing-contributions?page=all |title=Turing's achievements: codebreaking, AI and the birth of computer science (Wired UK) |work=Wired |date=18 June 2012 |access-date=31 October 2013 |archive-url=https://web.archive.org/web/20131102122933/http://www.wired.co.uk/news/archive/2012-06/18/turing-contributions?page=all |archive-date=2 November 2013 |url-status=live }}</ref>
[[File:Turing flat.jpg|thumb|right|Two cottages in the stable yard at [[Bletchley Park]]. Turing worked here in 1939 and 1940, before moving to [[Hut 8]].]]
On 4 September 1939, the day after the UK declared war on Germany, Turing reported to Bletchley Park, the wartime station of GC&CS.<ref name=Copeland2006p378>Copeland, 2006 p.&nbsp;378.</ref>
Specifying the bombe was the first of five major cryptanalytical advances that Turing made during the war. The others were: deducing the indicator procedure used by the German navy; developing a statistical procedure dubbed ''[[Banburismus]]'' for making much more efficient use of the bombes; developing a procedure dubbed ''[[Turingery]]'' for working out the cam settings of the wheels of the [[Lorenz SZ 40/42]] (''Tunny'') cipher machine and, towards the end of the war, the development of a portable [[secure voice]] scrambler at [[Her Majesty's Government Communications Centre|Hanslope Park]] that was codenamed ''Delilah''.

By using statistical techniques to optimise the trial of different possibilities in the code breaking process, Turing made an innovative contribution to the subject. He wrote two papers discussing mathematical approaches, titled ''The Applications of Probability to Cryptography''<ref>{{cite web | last = Turing | first = Alan | year = c. 1941 | title = The Applications of Probability to Cryptography | id = The National Archives (United Kingdom): HW 25/37 | url = http://discovery.nationalarchives.gov.uk/details/r/C11510465 | ref = harv | access-date = 25 March 2015 | archive-url = https://web.archive.org/web/20150407234050/http://discovery.nationalarchives.gov.uk/details/r/C11510465 | archive-date = 7 April 2015 | url-status = live }}</ref> and ''Paper on Statistics of Repetitions'',<ref>{{cite web | last = Turing | first = Alan | year = c. 1941 | title = Paper on Statistics of Repetitions | id = The National Archives (United Kingdom): HW 25/38 | url = http://discovery.nationalarchives.gov.uk/details/r/C11510466 | ref = harv | access-date = 25 March 2015 | archive-url = https://web.archive.org/web/20150408013845/http://discovery.nationalarchives.gov.uk/details/r/C11510466 | archive-date = 8 April 2015 | url-status = live }}</ref> which were of such value to GC&CS and its successor [[Government Communications Headquarters|GCHQ]] that they were not released to the [[The National Archives (United Kingdom)|UK National Archives]] until April 2012, shortly before the centenary of his birth. A GCHQ mathematician, "who identified himself only as Richard," said at the time that the fact that the contents had been restricted for some 70 years demonstrated their importance, and their relevance to post-war cryptanalysis:<ref name=bbcrichard>{{cite news |last=Vallance |first=Chris |title=Alan Turing papers on code breaking released by GCHQ |url=https://www.bbc.co.uk/news/technology-17771962 |accessdate=20 April 2012 |publisher=BBC News |date=19 April 2012 |archive-url=https://web.archive.org/web/20121004192554/http://www.bbc.co.uk/news/technology-17771962 |archive-date=4 October 2012 |url-status=live }}</ref> {{quote|text=[He] said the fact that the contents had been restricted "shows what a tremendous importance it has in the foundations of our subject". ... The papers detailed using "mathematical analysis to try and determine which are the more likely settings so that they can be tried as quickly as possible." ... Richard said that GCHQ had now "squeezed the juice" out of the two papers and was "happy for them to be released into the public domain".}}

Turing had a reputation for eccentricity at Bletchley Park. He was known to his colleagues as "Prof" and his treatise on Enigma was known as the "Prof's Book".<ref>{{Harvnb|Hodges|1983|p=208}}</ref> According to historian [[Ronald Lewin]], [[I.J. Good|Jack Good]], a cryptanalyst who worked with Turing, said of his colleague:

{{quote|In the first week of June each year he would get a bad attack of hay fever, and he would cycle to the office wearing a service gas mask to keep the pollen off. His bicycle had a fault: the chain would come off at regular intervals. Instead of having it mended he would count the number of times the pedals went round and would get off the bicycle in time to adjust the chain by hand. Another of his eccentricities is that he chained his mug to the radiator pipes to prevent it being stolen.<ref>{{Harvnb|Lewin|1978|p=57}}</ref>}}

[[Peter Hilton]] recounted his experience working with Turing in [[Hut 8]] in his "Reminiscences of Bletchley Park" from ''A Century of Mathematics in America:''<ref>{{Cite web|url=http://www.ams.org/publicoutreach/math-history/hmath1-hilton22.pdf|title=A Century of Mathematics in America, Part 1, Reminiscences of Bletchley Park|last=Hilton|first=Peter|website=|archive-url=https://web.archive.org/web/20190829112241/http://www.ams.org/publicoutreach/math-history/hmath1-hilton22.pdf|archive-date=29 August 2019|url-status=live}}</ref>

{{quote| It is a rare experience to meet an authentic genius. Those of us privileged to inhabit the world of scholarship are familiar with the intellectual stimulation furnished by talented colleagues. We can admire the ideas they share with us and are usually able to understand their source; we may even often believe that we ourselves could have created such concepts and originated such thoughts. However, the experience of sharing the intellectual life of a genius is entirely different; one realizes that one is in the presence of an intelligence, a sensibility of such profundity and originality that one is filled with wonder and excitement. 
Alan Turing was such a genius, and those, like myself, who had the astonishing and unexpected opportunity, created by the strange exigencies of the Second World War, to be able to count Turing as colleague and friend will never forget that experience, nor can we ever lose its immense benefit to us.|sign=|source=}}

Hilton echoed similar thoughts in the Nova [[PBS]] documentary ''Decoding Nazi Secrets''.<ref>{{Cite web|url=https://www.pbs.org/wgbh/nova/transcripts/2615decoding.html|title=NOVA {{!}} Transcripts {{!}} Decoding Nazi Secrets {{!}} PBS|last=Hilton|first=Peter|website=|archive-url=https://web.archive.org/web/20190829112240/https://www.pbs.org/wgbh/nova/transcripts/2615decoding.html|archive-date=29 August 2019|url-status=live}}</ref>

While working at Bletchley, Turing, who was a talented [[Long-distance running|long-distance runner]], occasionally ran the {{convert|40|mi}} to London when he was needed for meetings,<ref>{{Cite book | last = Brown | first = Anthony Cave | author-link = Anthony Cave Brown | title = Bodyguard of Lies: The Extraordinary True Story Behind D-Day | publisher=The Lyons Press | year = 1975 | isbn = 978-1-59921-383-5 | ref = harv }}</ref> and he was capable of world-class marathon standards.<ref>{{cite news|url=https://www.theguardian.com/commentisfree/2010/mar/10/alan-turing-2012-olympics|title=An Olympic honour for Alan Turing|author=Graham-Cumming, John|newspaper=The Guardian|date=10 March 2010|location=London|access-date=10 December 2016|archive-url=https://web.archive.org/web/20161201171628/https://www.theguardian.com/commentisfree/2010/mar/10/alan-turing-2012-olympics|archive-date=1 December 2016|url-status=live}}</ref><ref>{{cite web | first=Pat | last=Butcher | url=http://www.globerunner.org/index.php/09/in-praise-of-great-men/ | title=In Praise of Great Men | publisher=Globe Runner | date=14 September 2009 | access-date=23 June 2012 | archive-url=https://web.archive.org/web/20130818145759/http://www.globerunner.org/index.php/09/in-praise-of-great-men/ | archive-date=18 August 2013 | url-status=live }}</ref> Turing tried out for the 1948 British Olympic team but he was hampered by an injury. His tryout time for the marathon was only 11 minutes slower than British silver medallist Thomas Richards' Olympic race time of 2 hours 35 minutes. He was Walton Athletic Club's best runner, a fact discovered when he passed the group while running alone.<ref>{{cite web | last1 = Hodges | first1 = Andrew | authorlink = Andrew Hodges | title = Alan Turing: a short biography | url = http://www.turing.org.uk/bio/part6.html | publisher = Alan Turing: The Enigma | accessdate = 12 June 2014 | archive-url = https://web.archive.org/web/20130914091359/http://www.turing.org.uk/bio/part6.html | archive-date = 14 September 2013 | url-status = live }}</ref><ref>{{cite news | last1 = Graham-Cumming | first1 = John | authorlink = John Graham-Cumming | title = Alan Turing: a short biography | url = https://www.theguardian.com/commentisfree/2010/mar/10/alan-turing-2012-olympics | newspaper = The Guardian | date = 10 March 2010 | accessdate = 12 June 2014 | archive-url = https://web.archive.org/web/20141108165218/http://www.theguardian.com/commentisfree/2010/mar/10/alan-turing-2012-olympics | archive-date = 8 November 2014 | url-status = live }}</ref><ref>{{cite web | last1 = Butcher | first1 = Pat | title = Turing as a runner | url = http://www-groups.dcs.st-and.ac.uk/~history/Extras/Turing_running.html | publisher = The MacTutor History of Mathematics archive | date = December 1999 | accessdate = 12 June 2014 | archive-url = https://web.archive.org/web/20141113020916/http://www-groups.dcs.st-and.ac.uk/~history/Extras/Turing_running.html | archive-date = 13 November 2014 | url-status = live }}</ref>

In 1946, Turing was appointed an [[Order of the British Empire|Officer of the Order of the British Empire]] (OBE) by King [[George VI]] for his wartime services, but his work remained secret for many years.<ref>{{cite news | title = Alan Turing: Colleagues share their memories | url = https://www.bbc.co.uk/news/technology-18541715 | date = 23 June 2012 | publisher = BBC News | access-date = 21 June 2018 | archive-url = https://web.archive.org/web/20180707105436/https://www.bbc.co.uk/news/technology-18541715 | archive-date = 7 July 2018 | url-status = live }}</ref><ref name="thegazette.co.uk">{{cite web|url=https://www.thegazette.co.uk/all-notices/content/114|title=This month in history: Alan Turing and the Enigma code|website=thegazette.co.uk|accessdate=6 February 2019|archive-url=https://web.archive.org/web/20190626211800/https://www.thegazette.co.uk/all-notices/content/114|archive-date=26 June 2019|url-status=live}}</ref>

===Bombe===
{{Main|Bombe}}

Within weeks of arriving at Bletchley Park,<ref name="Copeland2006p378" /> Turing had specified an electromechanical machine called the [[bombe]], which could break Enigma more effectively than the Polish ''[[bomba (cryptography)|bomba kryptologiczna]]'', from which its name was derived. The bombe, with an enhancement suggested by mathematician [[Gordon Welchman]], became one of the primary tools, and the major automated one, used to attack Enigma-enciphered messages.<ref>{{Citation |last= Welchman |first= Gordon |author-link= Gordon Welchman |origyear= 1982 |year= 1997 |title= The Hut Six story: Breaking the Enigma codes |page= 81 |location= Cleobury Mortimer, England |publisher= M&M Baldwin |isbn= 978-0-947712-34-1 }}</ref>

[[File:Bombe-rebuild.jpg|thumbnail|right|A complete and working replica of a [[bombe]] now at [[The National Museum of Computing]] on Bletchley Park]]The bombe searched for possible correct settings used for an Enigma message (i.e., rotor order, rotor settings and plugboard settings) using a suitable ''[[crib (cryptanalysis)|crib]]'': a fragment of probable [[plaintext]]. For each possible setting of the rotors (which had on the order of 10<sup>19</sup> states, or 10<sup>22</sup> states for the four-rotor U-boat variant),<ref>Professor Jack Good in "The Men Who Cracked Enigma", 2003: with his caveat: "if my memory is correct".</ref> the bombe performed a chain of logical deductions based on the crib, implemented [[Electromechanics|electromechanically]].{{Citation needed|date=July 2018}}

The bombe detected when a contradiction had occurred and ruled out that setting, moving on to the next. Most of the possible settings would cause contradictions and be discarded, leaving only a few to be investigated in detail. A contradiction would occur when an enciphered letter would be turned back into the same plaintext letter, which was impossible with the Enigma. The first bombe was installed on 18 March 1940.<ref>{{Harvnb|Oakley|2006|p=40/03B}}</ref>

By late 1941, Turing and his fellow cryptanalysts Gordon Welchman, [[Conel Hugh O'Donel Alexander|Hugh Alexander]] and [[Stuart Milner-Barry]] were frustrated. Building on the [[Biuro Szyfrów#Gift to allies|work of the Poles]], they had set up a good working system for decrypting Enigma signals, but their limited staff and bombes meant they could not translate all the signals. In the summer, they had considerable success, and shipping losses had fallen to under 100,000 tons a month; however, they badly needed more resources to keep abreast of German adjustments. They had tried to get more people and fund more bombes through the proper channels, but had failed.<ref name=":0" />

On 28 October they wrote directly to [[Winston Churchill]] explaining their difficulties, with Turing as the first named. They emphasised how small their need was compared with the vast expenditure of men and money by the forces and compared with the level of assistance they could offer to the forces.<ref name=":0">{{Harvnb|Hodges|1983|p=218}}</ref> As [[Andrew Hodges]], biographer of Turing, later wrote, "This letter had an electric effect."<ref name="Hodges 1983 221">{{Harvnb|Hodges|1983|p=221}}</ref> Churchill wrote a memo to [[Hastings Ismay, 1st Baron Ismay|General Ismay]], which read: "ACTION THIS DAY. Make sure they have all they want on extreme priority and report to me that this has been done." On 18 November, the chief of the secret service reported that every possible measure was being taken.<ref name="Hodges 1983 221"/> The cryptographers at Bletchley Park did not know of the Prime Minister's response, but as Milner-Barry recalled, "All that we did notice was that almost from that day the rough ways began miraculously to be made smooth."<ref>Copeland, ''The Essential Turing'', [http://www.maths.ed.ac.uk/~aar/turingletter.pdf pp. 336–337] {{Webarchive|url=https://web.archive.org/web/20150218142127/http://www.maths.ed.ac.uk/~aar/turingletter.pdf |date=18 February 2015 }}.</ref> More than two hundred bombes were in operation by the end of the war.<ref name=codebreaker>{{cite web | last1 = Copeland | first1 = Jack | last2 = Proudfoot | first2 = Diane | authorlink = Jack Copeland | title = Alan Turing, Codebreaker and Computer Pioneer | url = http://www.alanturing.net/turing_archive/pages/Reference%20Articles/codebreaker.html | publisher = alanturing.net | date = May 2004 | accessdate = 27 July 2007 | archive-url = https://web.archive.org/web/20070709065520/http://www.alanturing.net/turing_archive/pages/Reference%20Articles/codebreaker.html | archive-date = 9 July 2007 | url-status = live }}</ref>

[[File:Turing-statue-Bletchley 14.jpg|thumb|right|upright|Statue of Turing by [[Stephen Kettle]] at Bletchley Park, commissioned by [[Sidney Frank]], built from half a million pieces of Welsh slate.<ref>{{cite web |title=Bletchley Park Unveils Statue Commemorating Alan Turing |url=http://www.bletchleypark.org.uk/news/docview.rhtm/454075 |accessdate=30 June 2007 |archive-url=https://web.archive.org/web/20070630083823/http://www.bletchleypark.org.uk/news/docview.rhtm/454075 |archive-date=30 June 2007 |url-status=live }}</ref>]]

===Hut 8 and the naval Enigma===
Turing decided to tackle the particularly difficult problem of [[Cryptanalysis of the Enigma#German naval Enigma|German naval Enigma]] "because no one else was doing anything about it and I could have it to myself".<ref name=MahonP14>{{Harvnb|Mahon|1945|p=14}}</ref> In December 1939, Turing solved the essential part of the naval [[Enigma machine#Indicator|indicator]] system, which was more complex than the indicator systems used by the other services.<ref name=MahonP14 /><ref>{{Harvnb|Leavitt|2007|pp=184–186}}</ref>

That same night, he also conceived of the idea of ''[[Banburismus]]'', a sequential statistical technique (what [[Abraham Wald]] later called [[sequential analysis]]) to assist in breaking the naval Enigma, "though I was not sure that it would work in practice, and was not, in fact, sure until some days had actually broken."<ref name=MahonP14 /> For this, he invented a measure of weight of evidence that he called the ''[[Ban (unit)|ban]]''. ''Banburismus'' could rule out certain sequences of the Enigma rotors, substantially reducing the time needed to test settings on the bombes.<ref>{{Cite journal|last=Gladwin|first=Lee|date=Fall 1997|title=Alan Turing, Enigma, and the Breaking of German Machine Ciphers in World War II|url=https://www.archives.gov/files/publications/prologue/1997/fall/turing.pdf|journal=Prologue Magazine|volume=Fall 1997|pages=202–217|via=National Archives|access-date=13 April 2019|archive-url=https://web.archive.org/web/20190626211657/https://www.archives.gov/files/publications/prologue/1997/fall/turing.pdf|archive-date=26 June 2019|url-status=live}}</ref> Later this sequential process of accumulating sufficient weight of evidence using decibans (one tenth of a ban) was used in [[Cryptanalysis of the Lorenz cipher]]<ref>{{Citation | last1 = Good | first1 = Jack | author-link = I. J. Good | last2 = Michie | first2 = Donald | author2-link = Donald Michie | last3 = Timms | first3 = Geoffrey | title = General Report on Tunny: With Emphasis on Statistical Methods | year = 1945 | id = UK Public Record Office HW 25/4 and HW 25/5 | url = http://www.alanturing.net/turing_archive/archive/t/t15/TR15-018.html | at = Part 3 Organisation: 38 Wheel-breaking from Key, Page 293 | access-date = 13 April 2019 | archive-url = https://web.archive.org/web/20190421091539/http://www.alanturing.net/turing_archive/archive/t/t15/TR15-018.html | archive-date = 21 April 2019 | url-status = live }}</ref>

Turing travelled to the United States in November 1942<ref>{{Harvnb|Hodges|1983|pp=242–245}}</ref> and worked with US Navy cryptanalysts on the naval Enigma and bombe construction in Washington; he also visited their [[United States Naval Computing Machine Laboratory|Computing Machine Laboratory]] in [[Dayton, Ohio]].

Turing's reaction to the American bombe design was far from enthusiastic:
{{quote|text=The American Bombe programme was to produce 336 Bombes, one for each wheel order. I used to smile inwardly at the conception of Bombe hut routine implied by this programme, but thought that no particular purpose would be served by pointing out that we would not really use them in that way.

Their test (of commutators) can hardly be considered conclusive as they were not testing for the bounce with electronic stop finding devices. Nobody seems to be told about rods or offiziers or banburismus unless they are really going to do something about it.<ref>{{Cite journal |last=Turing |first=Alan M. |year=2001 |journal=Cryptologia |volume=25 |issue=1 |pages=1–10 |doi=10.1080/0161-110191889734 |title=Visit to National Cash Register Corporation of Dayton, Ohio |s2cid=14207094 }}</ref>|source=}}

During this trip, he also assisted at [[Bell Labs]] with the development of [[secure speech]] devices.<ref>{{Harvnb|Hodges|1983|pp=245–253}}</ref> He returned to Bletchley Park in March 1943. During his absence, [[Colonel Hugh O'Donel Alexander|Hugh Alexander]] had officially assumed the position of head of Hut 8, although Alexander had been ''de facto'' head for some time (Turing having little interest in the day-to-day running of the section). Turing became a general consultant for cryptanalysis at Bletchley Park.<ref>{{Cite web|url=https://www.marshallfoundation.org/newsroom/marshall-legacy-series/codebreaking/|title=Marshall Legacy Series: Codebreaking – Events|website=marshallfoundation.org|access-date=7 April 2019|archive-url=https://web.archive.org/web/20190407030638/https://www.marshallfoundation.org/newsroom/marshall-legacy-series/codebreaking/|archive-date=7 April 2019|url-status=live}}</ref>

Alexander wrote of Turing's contribution:
{{quote|There should be no question in anyone's mind that Turing's work was the biggest factor in Hut 8's success. In the early days, he was the only cryptographer who thought the problem worth tackling and not only was he primarily responsible for the main theoretical work within the Hut, but he also shared with Welchman and Keen the chief credit for the invention of the bombe. It is always difficult to say that anyone is 'absolutely indispensable', but if anyone was indispensable to Hut 8, it was Turing. The pioneer's work always tends to be forgotten when experience and routine later make everything seem easy and many of us in Hut 8 felt that the magnitude of Turing's contribution was never fully realised by the outside world.<ref>{{Harvnb|Alexander|circa 1945|p=42}}</ref>}}

===Turingery===
In July 1942, Turing devised a technique termed ''[[Turingery]]'' (or jokingly ''Turingismus'')<ref>{{Harvnb|Copeland|2006|p=380}}</ref> for use against the [[Lorenz cipher]] messages produced by the Germans' new ''Geheimschreiber'' (secret writer) machine. This was a [[teleprinter]] [[Rotor machine|rotor cipher attachment]] codenamed ''Tunny'' at Bletchley Park. Turingery was a method of ''wheel-breaking'', i.e., a procedure for working out the cam settings of Tunny's wheels.<ref>{{Harvnb|Copeland|2006|p=381}}</ref> He also introduced the Tunny team to [[Tommy Flowers]] who, under the guidance of [[Max Newman]], went on to build the [[Colossus computer]], the world's first programmable digital electronic computer, which replaced a simpler prior machine (the [[Heath Robinson (codebreaking machine)|Heath Robinson]]), and whose superior speed allowed the statistical decryption techniques to be applied usefully to the messages.<ref>{{Harvnb|Copeland|2006|p=72}}</ref> Some have mistakenly said that Turing was a key figure in the design of the Colossus computer. Turingery and the statistical approach of Banburismus undoubtedly fed into the thinking about [[cryptanalysis of the Lorenz cipher]],<ref>{{Harvnb|Gannon|2007|p=230}}</ref><ref>{{Harvnb|Hilton|2006|pp=197–199}}</ref> but he was not directly involved in the Colossus development.<ref>{{Harvnb|Copeland|2006|pp=382, 383}}</ref>

===Delilah===
Following his work at [[Bell Labs]] in the US,<ref>{{Harvnb|Hodges|1983|pp=245–250}}</ref> Turing pursued the idea of electronic enciphering of speech in the telephone system. In the latter part of the war, he moved to work for the Secret Service's Radio Security Service (later [[Her Majesty's Government Communications Centre|HMGCC]]) at [[Hanslope Park]]. At the park, he further developed his knowledge of electronics with the assistance of engineer Donald Bayley. Together they undertook the design and construction of a portable [[secure voice]] communications machine codenamed ''Delilah''.<ref>{{Harvnb|Hodges|1983|p=273}}</ref> The machine was intended for different applications, but it lacked the capability for use with long-distance radio transmissions. In any case, Delilah was completed too late to be used during the war. Though the system worked fully, with Turing demonstrating it to officials by encrypting and decrypting a recording of a [[Winston Churchill]] speech, Delilah was not adopted for use.<ref>{{Harvnb|Hodges|1983|p=346}}</ref> Turing also consulted with Bell Labs on the development of [[SIGSALY]], a secure voice system that was used in the later years of the war.

===Early computers and the Turing test===
[[File:Alan Turing 78 High Street Hampton blue plaque.jpg|thumb|Plaque, 78 High Street, [[Hampton, London|Hampton]]]]
Between 1945 and 1947, Turing lived in [[Hampton, London|Hampton]], London,<ref>{{openplaque|1619}}</ref> while he worked on the design of the [[ACE (computer)|ACE]] (Automatic Computing Engine) at the [[National Physical Laboratory, UK|National Physical Laboratory (NPL)]]. He presented a paper on 19 February 1946, which was the first detailed design of a [[stored-program computer]].<ref>{{Harvnb|Copeland|2006|p=108}}</ref> [[John von Neumann|Von Neumann]]'s incomplete ''[[First Draft of a Report on the EDVAC]]'' had predated Turing's paper, but it was much less detailed and, according to [[John R. Womersley]], Superintendent of the NPL Mathematics Division, it "contains a number of ideas which are Dr. Turing's own".<ref>{{cite web | last = Randell | first = Brian | author-link = Brian Randell | title = A History of Computing in the Twentieth Century: Colossus | year = 1980 | url = http://www.cs.ncl.ac.uk/research/pubs/books/papers/133.pdf | accessdate = 27 January 2012 | ref = harv | archive-url = https://web.archive.org/web/20120127144927/http://www.cs.ncl.ac.uk/research/pubs/books/papers/133.pdf | archive-date = 27 January 2012 | url-status = live }} citing {{Cite journal | last = Womersley | first = J.R. | author-link = John R. Womersley | title = 'ACE' Machine Project | journal=Executive Committee, National Physical Laboratory, Teddington, Middlesex | date = 13 February 1946 | ref = harv }}</ref> Although ACE was a feasible design, the secrecy surrounding the wartime work at Bletchley Park led to delays in starting the project and he became disillusioned. In late 1947 he returned to Cambridge for a sabbatical year during which he produced a seminal work on ''Intelligent Machinery'' that was not published in his lifetime.<ref>See {{harvnb|Copeland|2004b|pp=410–432}}</ref> While he was at Cambridge, the [[Pilot ACE]] was being built in his absence. It executed its first program on 10 May 1950, and a number of later computers around the world owe much to it, including the [[English Electric DEUCE]] and the American [[Bendix G-15]]. The full version of Turing's ACE was not built until after his death.<ref>{{cite web|url=http://www.npl.co.uk/about/history/notable-individuals/turing/|title=Turing at NPL|access-date=3 July 2015|archive-url=https://web.archive.org/web/20150705082340/http://www.npl.co.uk/about/history/notable-individuals/turing/|archive-date=5 July 2015|url-status=live}}</ref>

According to the memoirs of the German computer pioneer [[Heinz Billing]] from the [[Max Planck Institute for Physics]], published by Genscher, Düsseldorf, there was a meeting between Turing and [[Konrad Zuse]].<ref>{{cite web|url=http://www.mathcomp.leeds.ac.uk/turing2012/Images/Turing_Zuse.pdf|title=Did Alan Turing interrogate Konrad Zuse in Göttingen in 1947?|author=Bruderer, Herbert|accessdate=7 February 2013|archive-url=https://web.archive.org/web/20130521211106/http://www.mathcomp.leeds.ac.uk/turing2012/Images/Turing_Zuse.pdf|archive-date=21 May 2013|url-status=live}}</ref> It took place in [[Göttingen]] in 1947. The interrogation had the form of a colloquium. Participants were Womersley, Turing, Porter from England and a few German researchers like Zuse, Walther, and Billing (for more details see Herbert Bruderer, ''Konrad Zuse und die Schweiz'').

In 1948, Turing was appointed [[Reader (academic rank)|reader]] in the [[School of Mathematics, University of Manchester|Mathematics Department]] at the [[Victoria University of Manchester]]. A year later, he became Deputy Director of the Computing Machine Laboratory, where he worked on software for one of the earliest [[Von Neumann architecture|stored-program]] computers—the [[Manchester Mark 1]]. Turing wrote the first version of the Programmer's Manual for this machine, and was recruited by Ferranti as a consultant in the development of their commercialised machine, the Ferranti Mark 1. He continued to be paid consultancy fees by Ferranti until his death.<ref>{{Cite book|url=https://www.manturing.net/|title=Alan Turing's Manchester|last=Swinton|first=Jonathan|publisher=Infang Publishing|year=2019|isbn=978-0-9931789-2-4|location=Manchester|pages=|access-date=18 March 2019|archive-url=https://web.archive.org/web/20190217172318/https://www.manturing.net/|archive-date=17 February 2019|url-status=live}}</ref> During this time, he continued to do more abstract work in mathematics,<ref name="doi10.1093/qjmam/1.1.287">{{Cite journal|last1 = Turing |first1 = A.M.|doi = 10.1093/qjmam/1.1.287 |title = Rounding-Off Errors in Matrix Processes |journal = The Quarterly Journal of Mechanics and Applied Mathematics |volume = 1| pages = 287–308 |year = 1948|hdl = 10338.dmlcz/103139}}</ref> and in "[[Computing Machinery and Intelligence]]" (''[[Mind (journal)|Mind]]'', October 1950), Turing addressed the problem of [[artificial intelligence]], and proposed an experiment that became known as the [[Turing test]], an attempt to define a standard for a machine to be called "intelligent". The idea was that a computer could be said to "think" if a human interrogator could not tell it apart, through conversation, from a human being.<ref>[[Stevan Harnad|Harnad, Stevan]] (2008) [http://eprints.soton.ac.uk/262954/ The Annotation Game: On Turing (1950) on Computing, Machinery and Intelligence] {{Webarchive|url=https://web.archive.org/web/20171018070225/https://eprints.soton.ac.uk/262954/ |date=18 October 2017 }}. In: Epstein, Robert & Peters, Grace (Eds.) ''Parsing the Turing Test: Philosophical and Methodological Issues in the Quest for the Thinking Computer''. Springer</ref> In the paper, Turing suggested that rather than building a program to simulate the adult mind, it would be better to produce a simpler one to simulate a child's mind and then to subject it to a course of education. A [[Turing test#Reverse Turing test and CAPTCHA|reversed]] form of the Turing test is widely used on the Internet; the [[CAPTCHA]] test is intended to determine whether the user is a human or a computer.

In 1948 Turing, working with his former undergraduate colleague, [[D.G. Champernowne]], began writing a [[chess]] program for a computer that did not yet exist. By 1950, the program was completed and dubbed the [[Turochamp]].<ref>{{cite web|last=Clark|first=Liat|title=Turing's achievements: codebreaking, AI and the birth of computer science|url=https://www.wired.co.uk/news/archive/2012-06/18/turing-contributions?page=all|work=Wired|accessdate=11 November 2013|archive-url=https://web.archive.org/web/20131102122933/http://www.wired.co.uk/news/archive/2012-06/18/turing-contributions?page=all|archive-date=2 November 2013|url-status=live}}</ref> In 1952, he tried to implement it on a [[Ferranti Mark 1]], but lacking enough power, the computer was unable to execute the program. Instead, Turing "ran" the program by flipping through the pages of the algorithm and carrying out its instructions on a chessboard, taking about half an hour per move. The game was recorded.<ref>[http://www.chessgames.com/perl/chessgame?gid=1356927 Alan Turing vs Alick Glennie (1952) "Turing Test"] {{Webarchive|url=https://web.archive.org/web/20060219033248/http://www.chessgames.com/perl/chessgame?gid=1356927 |date=19 February 2006 }} Chessgames.com</ref> According to [[Garry Kasparov]], Turing's program "played a recognizable game of chess."<ref>Kasparov, Garry, Smart machines will free us all, ''The Wall Street Journal'', 15–16 April 2017, p. c3</ref> The program lost to Turing's colleague [[Alick Glennie]], although it is said that it won a game against Champernowne's wife,
Isabel.<ref>{{cite web|last1=O'Connor|first1=J.J.|last2=Robertson|first2=E.F.|title=David Gawen Champernowne|url=http://www-history.mcs.st-and.ac.uk/Biographies/Champernowne.html|work=MacTutor History of Mathematics archive, School of Mathematics and Statistics, University of St Andrews, Scotland|accessdate=22 May 2018|archive-url=https://web.archive.org/web/20171019123016/http://www-history.mcs.st-and.ac.uk/Biographies/Champernowne.html|archive-date=19 October 2017|url-status=live}}</ref>

His Turing test was a significant, characteristically provocative, and lasting contribution to the debate regarding artificial intelligence, which continues after more than half a century.<ref>{{Cite journal | last1 = Pinar Saygin | first1 = A. | last2 = Cicekli | first2 = I. | last3 = Akman | first3 = V. | journal = Minds and Machines | volume = 10 | issue = 4 | pages = 463–518 | year = 2000 |title=Turing Test: 50 Years Later| doi = 10.1023/A:1011288000451 | hdl = 11693/24987 | s2cid = 990084 | hdl-access = free }}</ref>

===Pattern formation and mathematical biology===

When Turing was 39 years old in 1951, he turned to [[Mathematical and theoretical biology|mathematical biology]], finally publishing his masterpiece "[[The Chemical Basis of Morphogenesis]]" in January 1952. He was interested in [[morphogenesis]], the development of patterns and shapes in biological organisms. He suggested that a system of chemicals reacting with each other and diffusing across space, termed a [[reaction-diffusion system]], could account for "the main phenomena of morphogenesis".<ref>{{cite news| first=Alan M. | last=Turing | authorlink=Alan Turing | title=The Chemical Basis of Morphogenesis | journal=Philosophical Transactions of the Royal Society of London B | date=14 August 1952 | doi=10.1098/rstb.1952.0012 | volume=237 | number=641 | pages=37–72 | bibcode=1952RSPTB.237...37T }}</ref> He used systems of [[partial differential equations]] to model catalytic chemical reactions. For example, if a catalyst A is required for a certain chemical reaction to take place, and if the reaction produced more of the catalyst A, then we say that the reaction is [[autocatalytic]], and there is positive feedback that can be modelled by nonlinear differential equations. Turing discovered that patterns could be created if the chemical reaction not only produced catalyst A, but also produced an inhibitor B that slowed down the production of A. If A and B then diffused through the container at different rates, then you could have some regions where A dominated and some where B did. To calculate the extent of this, Turing would have needed a powerful computer, but these were not so freely available in 1951, so he had to use linear approximations to solve the equations by hand. These calculations gave the right qualitative results, and produced, for example, a uniform mixture that oddly enough had regularly spaced fixed red spots. The Russian biochemist [[Boris Pavlovich Belousov|Boris Belousov]] had performed experiments with similar results, but could not get his papers published because of the contemporary prejudice that any such thing violated the [[second law of thermodynamics]]. Belousov was not aware of Turing's paper in the ''[[Philosophical Transactions of the Royal Society]]''.<ref>John Gribbin, ''Deep Simplicity'', p. 126, Random House, 2004</ref>

Although published before the structure and role of [[DNA]] was understood, Turing's work on morphogenesis remains relevant today and is considered a seminal piece of work in mathematical biology.<ref>{{cite web|url=http://www.swintons.net/deodands/archives/000087.html |title=Turing's Last, Lost work |accessdate=28 November 2011 |url-status=dead |archiveurl=https://web.archive.org/web/20030823032620/http://www.swintons.net/deodands/archives/000087.html |archivedate=23 August 2003  }}</ref> One of the early applications of Turing's paper was the work by James Murray explaining spots and stripes on the fur of cats, large and small.<ref>James Murray, ''How the leopard gets its spots'', Scientific American, vol 258, number 3, p.&nbsp;80, March 1988</ref><ref>James Murray, ''Mathematical Biology I'', 2007, Chapter 6, Springer Verlag</ref><ref>John Gibbin, Deep Simplicity, p.&nbsp;134, Random House, 2004</ref> Further research in the area suggests that Turing's work can partially explain the growth of "feathers, hair follicles, the branching pattern of lungs, and even the left-right asymmetry that puts the heart on the left side of the chest."<ref>{{cite journal|doi=10.1126/science.338.6113.1406|pmid=23239707|title=Turing Pattern Fingered for Digit Formation|journal=Science|volume=338|issue=6113|pages=1406|year=2012|last1=Vogel|first1=G.|bibcode=2012Sci...338.1406V}}</ref> In 2012, Sheth, et al. found that in mice, removal of [[Hox genes]] causes an increase in the number of digits without an increase in the overall size of the limb, suggesting that Hox genes control digit formation by tuning the wavelength of a Turing-type mechanism.<ref>{{Cite journal |last1 = Sheth |first1 = R. |last2 = Marcon |first2 = L. |last3 = Bastida |first3 = M.F. |last4 = Junco |first4 = M. |last5 = Quintana |first5 = L. |last6 = Dahn |first6 = R. |last7 = Kmita |first7 = M. |last8 = Sharpe |first8 = J. |last9 = Ros |first9 = M.A. |doi = 10.1126/science.1226804 |title = Hox Genes Regulate Digit Patterning by Controlling the Wavelength of a Turing-Type Mechanism |journal = Science |volume = 338 |issue = 6113 |pages = 1476–1480 |year = 2012 |pmid =  23239739 |pmc = 4486416 |bibcode = 2012Sci...338.1476S }}</ref> Later papers were not available until ''Collected Works of A.&nbsp;M.&nbsp;Turing'' was published in 1992.<ref>{{cite web|title=The Alan Turing Bibliography|url=http://www.turing.org.uk/sources/biblio3.html|page=morphogenesis|publisher=turing.org.uk|accessdate=27 July 2015|author=Andrew Hodges|archive-url=https://web.archive.org/web/20150905180420/http://www.turing.org.uk/sources/biblio3.html|archive-date=5 September 2015|url-status=live}}</ref>

==Personal life==
{{LGBT UK sidebar|timeline}}
===Engagement===
In 1941, Turing proposed marriage to Hut 8 colleague [[Joan Clarke]], a fellow mathematician and cryptanalyst, but their engagement was short-lived. After admitting his homosexuality to his fiancée, who was reportedly "unfazed" by the revelation, Turing decided that he could not go through with the marriage.<ref>{{Harvnb|Leavitt|2007|pp=176–178}}</ref>

===Conviction for indecency===
In January 1952, Turing was 39 when he started a relationship with Arnold Murray, a 19-year-old unemployed man. Just before Christmas, Turing was walking along Manchester's [[Wilmslow Road|Oxford Road]] when he met Murray just outside the [[Dancehouse|Regal Cinema]] and invited him to lunch. On 23 January, Turing's house was burgled. Murray told Turing that he and the burglar were acquainted, and Turing reported the crime to the police. During the investigation, he acknowledged a sexual relationship with Murray. Homosexual acts were criminal offences in the United Kingdom at that time,<ref>{{Harvnb|Hodges|1983|p=458}}</ref> and both men were charged with "[[gross indecency]]" under [[Criminal Law Amendment Act 1885#Section 11|Section 11]] of the [[Criminal Law Amendment Act 1885]].<ref name=LeavittP268>{{Harvnb|Leavitt|2007|p=268}}</ref> Initial [[committal procedure|committal proceedings]] for the trial were held on 27 February during which Turing's solicitor "reserved his defence", i.e., did not argue or provide evidence against the allegations.

Turing was later convinced by the advice of his brother and his own solicitor, and he entered a plea of guilty.<ref>{{cite book |title=Alan Turing: The Enigma |publisher=Princeton University Press |authorlink=Andrew Hodges |last=Hodges |first=Andrew |page=[https://archive.org/details/alanturingenigma0000hodg/page/463 463] |year=2012 |isbn=978-0-691-15564-7 |url=https://archive.org/details/alanturingenigma0000hodg|url-access=registration }}</ref> The case, ''[[Elizabeth II|Regina]] v. Turing and Murray,'' was brought to trial on 31 March 1952.<ref>{{cite book |title=Alan Turing: The Enigma |publisher=Princeton University Press |authorlink=Andrew Hodges |last=Hodges |first=Andrew |page=[https://archive.org/details/alanturingenigma0000hodg/page/471 471] |year=2012 |isbn=978-0-691-15564-7 |url=https://archive.org/details/alanturingenigma0000hodg|url-access=registration }}</ref> Turing was convicted and given a choice between imprisonment and probation. His probation would be conditional on his agreement to undergo [[hormone|hormonal]] physical changes designed to reduce [[libido]]. He accepted the option of injections of what was then called stilboestrol (now known as [[diethylstilbestrol]] or DES), a synthetic [[oestrogen]]; this feminization of his body was continued for the course of one year. The treatment rendered Turing [[impotence|impotent]] and caused [[gynaecomastia|breast tissue to form]],<ref>{{cite book | title=Alan Turing: The Enigma The Centenary Edition | publisher=Princeton University | author= Hodges, Andrew | year=2012}}</ref> fulfilling in the literal sense Turing's prediction that "no doubt I shall emerge from it all a different man, but quite who I've not found out".<ref>{{cite web |title=Letters of Note: Yours in distress, Alan |last=Turing |first=Alan |year=1952 |url=http://www.lettersofnote.com/2012/06/yours-in-distress-alan.html |archivedate=20 January 2013 |archiveurl=https://web.archive.org/web/20130120024901/http://www.lettersofnote.com/2012/06/yours-in-distress-alan.html |url-status=dead  |access-date=16 December 2012 }}</ref><ref>{{cite book |title=Alan Turing: The Enigma |publisher=Princeton University Press |authorlink=Andrew Hodges |last=Hodges |first=Andrew  |page=xxviii |year= 2012 |isbn=978-0-691-15564-7 |url=https://archive.org/details/alanturingenigma0000hodg|url-access=registration }}</ref> Murray was given a conditional discharge.<ref>{{Harvnb|Hodges|1983|p=473}}</ref>

Turing's conviction led to the removal of his security clearance and barred him from continuing with his cryptographic consultancy for the [[Government Communications Headquarters]] (GCHQ), the British [[signals intelligence]] agency that had evolved from GC&CS in 1946, though he kept his academic job. He was denied entry into the United States after his conviction in 1952, but was free to visit other European countries. Turing was never accused of espionage but, in common with all who had worked at Bletchley Park, he was prevented by the [[Official Secrets Act]] from discussing his war work.<ref>{{Harvnb|Copeland|2006|p=143}}</ref>

===Death===
On 8 June 1954, Turing's housekeeper found him dead at the age of 41; he had died the previous day. [[Cyanide poisoning]] was established as the cause of death.<ref>{{Cite encyclopedia |url=https://www.britannica.com/biography/Alan-Turing#toc330986 |title=Alan Turing. Biography, Facts, & Education |encyclopedia=Encyclopædia Britannica |access-date=11 October 2017 |archive-url=https://web.archive.org/web/20171011184445/https://www.britannica.com/biography/Alan-Turing#toc330986 |archive-date=11 October 2017 |url-status=live }}</ref> When his body was discovered, an apple lay half-eaten beside his bed, and although the apple was not tested for cyanide,<ref>{{Harvnb|Hodges|1983|p=488}}</ref> it was speculated that this was the means by which Turing had consumed a fatal dose. An [[Inquests in England and Wales|inquest]] determined that he had committed suicide. Andrew Hodges and another biographer, [[David Leavitt]], have both speculated that Turing was re-enacting a scene from the [[Walt Disney]] film ''[[Snow White and the Seven Dwarfs (1937 film)|Snow White and the Seven Dwarfs]]'' (1937), his favourite fairy tale. Both men noted that (in Leavitt's words) he took "an especially keen pleasure in the scene where the Wicked Queen immerses her apple in the poisonous brew".<ref>{{Harvnb|Leavitt|2007|p=140}} and {{Harvnb|Hodges|1983|pp=149, 489}}</ref> Turing's remains were cremated at [[Woking Crematorium]] on 12 June 1954,<ref>{{Harvnb|Hodges|1983|p=529}}</ref> and his ashes were scattered in the gardens of the crematorium, just as his father's had been.<ref name="hodges2012">{{cite book |url=https://books.google.com/books?id=EpAl0piM38cC |title=Alan Turing: The Enigma |last=Hodges |first=Andrew |date=2012 |publisher=Random House |isbn=978-1-4481-3781-7 |access-date=16 January 2019 |archive-url=https://web.archive.org/web/20190117070027/https://books.google.co.uk/books?id=EpAl0piM38cC |archive-date=17 January 2019 |url-status=live }}</ref>

Philosophy professor [[Jack Copeland]] has questioned various aspects of the coroner's historical verdict. He suggested an alternative explanation for the cause of Turing's death: the accidental inhalation of cyanide fumes from an apparatus used to [[electroplating|electroplate]] gold onto spoons. The [[potassium cyanide]] was used to [[Gold#Commercial chemistry|dissolve the gold]]. Turing had such an apparatus set up in his tiny spare room. Copeland noted that the autopsy findings were more consistent with inhalation than with ingestion of the poison. Turing also habitually ate an apple before going to bed, and it was not unusual for the apple to be discarded half-eaten.<ref name = "Copeland">{{cite news | first = Roland | last = Pease | title = Alan Turing: Inquest's suicide verdict 'not supportable' | url = https://www.bbc.co.uk/news/science-environment-18561092 | publisher = [[BBC News]] | date = 23 June 2012 | accessdate = 23 June 2012 | quote = We have&nbsp;... been recreating the narrative of Turing's life, and we have recreated him as an unhappy young man who committed suicide. But the evidence is not there. | archive-url = https://web.archive.org/web/20120623101625/http://www.bbc.co.uk/news/science-environment-18561092 | archive-date = 23 June 2012 | url-status = live }}</ref> In addition, Turing had reportedly borne his legal setbacks and hormone treatment (which had been discontinued a year previously) "with good humour" and had shown no sign of despondency prior to his death. He even set down a list of tasks that he intended to complete upon returning to his office after the holiday weekend.<ref name = "Copeland"/> Turing's mother believed that the ingestion was accidental, resulting from her son's careless storage of laboratory chemicals.<ref>{{cite web |url=https://www.christies.com/lotfinder/lot_details.aspx?intObjectID=5685694 |title=TURING, Ethel Sara (1881–1976, mother of Alan Turing). Series of 11 autograph letters to Robin Gandy, Guilford, 28 July 1954 – 11 June 1971 (most before 1959), altogether 29 pages, 8vo (2 letters dated 17 May and 26 May 1955 incomplete, lacking continuation leaves, occasional light soiling) |website=christies.com |accessdate=6 February 2019 |archive-url=https://web.archive.org/web/20190207015923/https://www.christies.com/lotfinder/lot_details.aspx?intObjectID=5685694 |archive-date=7 February 2019 |url-status=live }}</ref> Biographer Andrew Hodges theorised that Turing arranged the delivery of the equipment to deliberately allow his mother [[plausible deniability]] with regard to any suicide claims.<ref>{{Harvnb|Hodges|1983|pp=488, 489}}</ref>
[[File:Alan Turing OBE.jpg|thumb|Turing's OBE currently held in [[Sherborne School]] archives]]

[[Conspiracy theory|Conspiracy theorists]] pointed out that Turing was the cause of intense anxiety to the British authorities at the time of his death. The secret services feared that [[communist]]s would entrap prominent homosexuals and use them to gather intelligence. Turing was still engaged in highly classified work when he was also a practising homosexual who holidayed in European countries near the [[Iron Curtain]]. According to the conspiracy theory, it is possible that the secret services considered him too great a security risk and assassinated one of the most brilliant minds in their employ.<ref>{{cite book |first=Joel |last=Levy |title=Mathematics: A curious history – From Early Number Concepts To The Chaos Theory |publisher=[[Carlton Publishing Group|Andre Deutsch]] |location=London |year=2018 |isbn=9780233005447 |page=177}}</ref>

It has been suggested that Turing's belief in [[fortune-telling]] may have caused his depressed mood.<ref name="hodges2012" /> As a youth, Turing had been told by a fortune-teller that he would be a genius. Shortly before his death, during a day-trip to [[Lytham St Annes|St Annes-on-Sea]] with the Greenbaum family,{{when|date=January 2019}} Turing again decided to consult a fortune-teller.<ref name="hodges2012"/> According to the Greenbaums' daughter, Barbara:<ref name="dowd">{{cite web |url=https://www.bbc.co.uk/news/magazine-27701207 |title=What was Alan Turing really like? |author=Vincent Dowd |publisher=BBC |date=6 June 2014 |access-date=16 January 2019 |archive-url=https://web.archive.org/web/20190117020715/https://www.bbc.co.uk/news/magazine-27701207 |archive-date=17 January 2019 |url-status=live }}</ref>
<blockquote>
But it was a lovely sunny day and Alan was in a cheerful mood and off we went... Then he thought it would be a good idea to go to the [[Blackpool Pleasure Beach|Pleasure Beach at Blackpool]]. We found a fortune-teller's tent[,] and Alan said he'd like to go in[,] so we waited around for him to come back... And this sunny, cheerful visage had shrunk into a pale, shaking, horror-stricken face. Something had happened. We don't know what the fortune-teller said[,] but he obviously was deeply unhappy. I think that was probably the last time we saw him before we heard of his suicide.
</blockquote>

===Government apology and pardon===
{{anchor|Government apology and pardon support}}
In August 2009, British programmer [[John Graham-Cumming]] started a petition urging the British government to apologise for Turing's prosecution as a homosexual.<ref>{{Cite book |title=Thousands call for Turing apology |url=http://news.bbc.co.uk/2/hi/technology/8226509.stm |publisher=BBC News |date=31 August 2009 |accessdate=31 August 2009 |archive-url=https://web.archive.org/web/20090831100747/http://news.bbc.co.uk/2/hi/technology/8226509.stm |archive-date=31 August 2009 |url-status=live }}</ref><ref>{{Cite book|title=Petition seeks apology for Enigma code-breaker Turing |url=http://www.cnn.com/2009/WORLD/europe/09/01/alan.turing.petition/index.html |publisher=CNN |date=1 September 2009 |accessdate=1 September 2009 |archiveurl=https://web.archive.org/web/20091005081407/http://www.cnn.com/2009/WORLD/europe/09/01/alan.turing.petition/index.html |archivedate=5 October 2009 |url-status=live |df= }}</ref> The petition received more than 30,000 signatures.<ref name="PMapology"/><ref>The petition was only open to UK citizens.</ref> The Prime Minister, [[Gordon Brown]], acknowledged the petition, releasing a statement on 10 September 2009 apologising and describing the treatment of Turing as "appalling":<ref name="PMapology">{{cite news | title = PM's apology to codebreaker Alan Turing: we were inhumane | url = https://www.theguardian.com/world/2009/sep/11/pm-apology-to-alan-turing | work = The Guardian | location = UK | date = 11 September 2009 | first = Caroline | last = Davies | access-date = 10 December 2016 | archive-url = https://web.archive.org/web/20170204085908/https://www.theguardian.com/world/2009/sep/11/pm-apology-to-alan-turing | archive-date = 4 February 2017 | url-status = live }}</ref><ref name="PM-apology">{{cite news | url = http://news.bbc.co.uk/2/hi/technology/8249792.stm | title = PM apology after Turing petition | date = 11 September 2009 | publisher = BBC News | access-date = 11 September 2009 | archive-url = https://www.webcitation.org/67yu9WGUa?url=http://news.bbc.co.uk/2/hi/technology/8249792.stm | archive-date = 27 May 2012 | url-status = live }}</ref>
{{quote|Thousands of people have come together to demand justice for Alan Turing and recognition of the appalling way he was treated. While Turing was dealt with under the law of the time and we can't put the clock back, his treatment was of course utterly unfair and I am pleased to have the chance to say how deeply sorry I and we all are for what happened to him&nbsp;... So on behalf of the British government, and all those who live freely thanks to Alan's work I am very proud to say: we're sorry, you deserved so much better.<ref name="PMapology"/><ref>[http://www.cs.auckland.ac.nz/~ian/TuringApology.html Full text of the Prime Minister's apology] {{Webarchive|url=https://web.archive.org/web/20121109124247/http://www.cs.auckland.ac.nz/~ian/TuringApology.html |date=9 November 2012 }}.</ref>}}

In December 2011, William Jones and his Member of Parliament, [[John Leech (politician)|John Leech]], created an [[e-petition]]<ref name="PardonPetition">{{cite web | title = Grant a pardon to Alan Turing | url = https://submissions.epetitions.direct.gov.uk/petitions/23526 | date = 6 December 2011 | url-status=dead | archiveurl = https://web.archive.org/web/20120110183548/http://submissions.epetitions.direct.gov.uk/petitions/23526 | archivedate = 10 January 2012 | df = dmy-all }}</ref> requesting that the British government [[pardon]] Turing for his conviction of "gross indecency":<ref name="BBBCPardon">{{cite news | title = Petition to pardon computer pioneer Alan Turing started | url = https://www.bbc.co.uk/news/uk-england-manchester-16061279 | date = 6 December 2011 | publisher = BBC News | access-date = 21 June 2018 | archive-url = https://web.archive.org/web/20180619135127/https://www.bbc.co.uk/news/uk-england-manchester-16061279 | archive-date = 19 June 2018 | url-status = live }}</ref>
{{quote|We ask the HM Government to grant a pardon to Alan Turing for the conviction of "gross indecency". In 1952, he was convicted of "gross indecency" with another man and was forced to undergo so-called "organo-therapy"—chemical castration. Two years later, he killed himself with cyanide, aged just 41. Alan Turing was driven to a terrible despair and early death by the nation he'd done so much to save. This remains a shame on the British government and British history. A pardon can go some way to healing this damage. It may act as an apology to many of the other gay men, not as well-known as Alan Turing, who were subjected to these laws.<ref name="PardonPetition" />}}

The petition gathered over 37,000 signatures,<ref name=PardonPetition /><ref name=turingindependent24dec2013>{{cite news |url=https://www.independent.co.uk/news/uk/home-news/alan-turing-gets-his-royal-pardon-for-gross-indecency--61-years-after-he-poisoned-himself-9023116.html |title=Alan Turing gets his royal pardon for 'gross indecency'&nbsp;– 61 years after he poisoned himself |work=The Independent |date=23 December 2013 |author=Wright, Oliver |location=London |access-date=21 August 2017 |archive-url=https://web.archive.org/web/20131224035745/http://www.independent.co.uk/news/uk/home-news/alan-turing-gets-his-royal-pardon-for-gross-indecency--61-years-after-he-poisoned-himself-9023116.html |archive-date=24 December 2013 |url-status=live }}</ref> and was submitted to Parliament by the Manchester MP [[John Leech (politician)|John Leech]] but the request was discouraged by Justice Minister [[Tom McNally, Baron McNally#Political career|Lord McNally]], who said:<ref name="PardonPetitionDiscouraged">{{cite web |title=Government rejects a pardon for computer genius Alan Turing |url=https://www.theguardian.com/uk/the-northerner/2012/feb/07/alan-turing-pardon-lord-mcnally-lord-sharkey-computers |date=7 February 2012 |last=Wainwright |first=Martin |work=The Guardian |access-date=10 December 2016 |archive-url=https://web.archive.org/web/20170204091026/https://www.theguardian.com/uk/the-northerner/2012/feb/07/alan-turing-pardon-lord-mcnally-lord-sharkey-computers |archive-date=4 February 2017 |url-status=live }}</ref>
{{quote|A posthumous pardon was not considered appropriate as Alan Turing was properly convicted of what at the time was a criminal offence. He would have known that his offence was against the law and that he would be prosecuted. It is tragic that Alan Turing was convicted of an offence that now seems both cruel and absurd—particularly poignant given his outstanding contribution to the war effort. However, the law at the time required a prosecution and, as such, long-standing policy has been to accept that such convictions took place and, rather than trying to alter the historical context and to put right what cannot be put right, ensure instead that we never again return to those times.<ref>{{cite web |url=https://publications.parliament.uk/pa/ld201212/ldhansrd/text/120202w0001.htm |title=hansard |publisher=Parliament of the United Kingdom |date=2 February 2012 |access-date=29 August 2017 |archive-url=https://web.archive.org/web/20170706132556/https://www.publications.parliament.uk/pa/ld201212/ldhansrd/text/120202w0001.htm |archive-date=6 July 2017 |url-status=live }}</ref>}}

[[John Leech (politician)|John Leech]], the MP for [[Manchester Withington (UK Parliament constituency)|Manchester Withington]] (2005–15), submitted several bills to Parliament<ref>{{cite web|url=http://www.politics.co.uk/news/2013/12/24/better-late-than-never-alan-turing-is-finally-pardoned|title=Better late than never, Alan Turing is finally pardoned|first=Alex|last=Stevenson|publisher=politics.co.uk|accessdate=25 September 2016|archive-url=https://web.archive.org/web/20160816015157/http://www.politics.co.uk/news/2013/12/24/better-late-than-never-alan-turing-is-finally-pardoned|archive-date=16 August 2016|url-status=live}}</ref> and led a high-profile campaign to secure the pardon. Leech made the case in the House of Commons that Turing's contribution to the war made him a national hero and that it was "ultimately just embarrassing" that the conviction still stood.<ref name="Fitzgerald">{{cite web|url=http://www.manchestereveningnews.co.uk/news/greater-manchester-news/alan-turings-court-convictions-go-11931942|title=Alan Turing's court convictions go on display for the first time|first=Todd|last=Fitzgerald|date=24 September 2016|publisher=manchestereveningnews.co.uk|accessdate=25 September 2016|archive-url=https://web.archive.org/web/20160925151625/http://www.manchestereveningnews.co.uk/news/greater-manchester-news/alan-turings-court-convictions-go-11931942|archive-date=25 September 2016|url-status=live}}</ref> Leech continued to take the bill through Parliament and campaigned for several years until it was passed.<ref>{{cite news|url=https://www.bbc.co.uk/news/uk-england-manchester-16833621|title=MP calls for pardon for computer pioneer Alan Turing|date=1 February 2012|publisher=BBC News|accessdate=25 September 2016|archive-url=https://web.archive.org/web/20160702135251/http://www.bbc.co.uk/news/uk-england-manchester-16833621|archive-date=2 July 2016|url-status=live}}</ref> Leech is now regularly described as the "architect" of Turing's pardon and subsequently the Alan Turing Law which went on to secure pardons for 75,000 other men and women convicted of similar crimes.<ref>{{Cite web |url=https://www.manchestereveningnews.co.uk/news/greater-manchester-news/manchester-computer-pioneer-alan-turing-16585966 |title=Archived copy |access-date=19 July 2019 |archive-url=https://web.archive.org/web/20190719082039/https://www.manchestereveningnews.co.uk/news/greater-manchester-news/manchester-computer-pioneer-alan-turing-16585966 |archive-date=19 July 2019 |url-status=live }}</ref><ref>{{Cite web |url=https://metro.co.uk/2019/07/15/alan-turing-announced-face-new-50-banknote-10319103/ |title=Archived copy |access-date=19 July 2019 |archive-url=https://web.archive.org/web/20190716161545/https://metro.co.uk/2019/07/15/alan-turing-announced-face-new-50-banknote-10319103/ |archive-date=16 July 2019 |url-status=live }}</ref> At the UK premiere of a film based on Turing's life, ''[[The Imitation Game]]'', the producers thanked Leech for bringing the topic to public attention and securing Turing's pardon.<ref>{{Cite news|url=https://www.libdemvoice.org/my-proudest-day-as-a-liberal-democrat-43430.html|title=My proudest day as a Liberal Democrat|work=Liberal Democrat Voice|access-date=24 June 2018|archive-url=https://web.archive.org/web/20180624204354/https://www.libdemvoice.org/my-proudest-day-as-a-liberal-democrat-43430.html|archive-date=24 June 2018|url-status=live}}</ref> His campaign turned to acquiring pardons for the 75,000 other men convicted of the same crime. Leech's campaign gained public support from leading scientists, including [[Stephen Hawking]].<ref>{{Cite news|url=https://www.manchestereveningnews.co.uk/news/greater-manchester-news/manchester-codebreaker-alan-turing-pardoned-6442836|title=Alan Turing pardoned by The Queen for his 'unjust and discriminatory' conviction for homosexuality|last=Britton|first=Paul|work=Manchester Evening News|date=24 December 2013|access-date=24 June 2018|archive-url=https://web.archive.org/web/20180624204418/https://www.manchestereveningnews.co.uk/news/greater-manchester-news/manchester-codebreaker-alan-turing-pardoned-6442836|archive-date=24 June 2018|url-status=live}}</ref> He is often described as the "architect" of 'Turing's Law', which used Turing's pardon as a precedent to eventually successfully grant a posthumous pardon to more than 49,000 other men historically criminally convicted of 'Gross Indecencey'. <ref>{{Cite web|url=http://outnewsglobal.com/john-leech-secures-historic-deal-with-government-on-alan-turing-law/|title=John Leech secures historic deal with Government on 'Alan Turing Law'|date=20 October 2016|website=outnewsglobal.com}}</ref> <ref>{{Cite web|url=https://aboutmanchester.co.uk/turing-on-50-note-will-be-painful-reminder-of-what-we-lost/|title=Turing on £50 note will be painful reminder of what we lost"|first=Nigel|last=Barlow|date=3 November 2018}}</ref> <ref>{{Cite web|url=https://metro.co.uk/2019/07/15/alan-turing-announced-face-new-50-banknote-10319103/|title=Alan Turing announced as face of new £50 banknote|date=15 July 2019}}</ref> <ref>{{Cite web|url=https://www.theguardian.com/business/2019/jul/15/alan-turing-to-feature-on-new-50-note|title=Alan Turing to feature on new £50 banknote|first1=Larry Elliott Economics|last1=editor|first2=Josh|last2=Halliday|date=15 July 2019|via=www.theguardian.com}}</ref> <ref>{{Cite web|url=https://www.thegayuk.com/this-is-who-is-on-the-new-50-note/|title=This is who is on the new £50 note|date=15 July 2019|website=www.thegayuk.com}}</ref> <ref>{{Cite web|url=http://www.mirror.co.uk/news/uk-news/tory-minister-refuses-apologise-killing-9108424|title=Tory refuses to apologise for 'killing bad law' pardoning thousands of gay men|first=Dan|last=Bloom|date=23 October 2016|website=mirror}}</ref> <ref>{{Cite web|url=https://www.dunfermlinepress.com/news/national-news/17771381.alan-turings-fearless-approach-problems-intellectual-curiosity-praised/|title=Alan Turing's 'fearless approach to problems and intellectual curiosity' praised|website=Dunfermline Press}}</ref> <ref>{{Cite web|url=https://thetab.com/uk/manchester/2017/01/31/alan-turing-law-finally-pardons-thousands-unfairly-convicted-25615|title=The Alan Turing Law finally pardons thousands of unfairly convicted gay and bisexual men|date=31 January 2017|website=University of Manchester}}</ref> <ref>{{Cite web|url=https://qnews.com.au/bank-of-england-honours-alan-turing-on-50-note/|title=Bank of England honours Alan Turing on £50 note|date=15 July 2019|website=QNews}}</ref> 

On 26 July 2012, a bill was introduced in the [[British House of Lords|House of Lords]] to grant a statutory pardon to Turing for offences under section 11 of the Criminal Law Amendment Act 1885, of which he was convicted on 31 March 1952.<ref>{{cite web |url=http://services.parliament.uk/bills/2012-13/alanturingstatutorypardon.html |title=Bill |publisher=Parliament of the United Kingdom |date=26 July 2012 |accessdate=31 October 2013 |archive-url=https://web.archive.org/web/20131102040318/http://services.parliament.uk/bills/2012-13/alanturingstatutorypardon.html |archive-date=2 November 2013 |url-status=live }}</ref> Late in the year in a letter to ''[[The Daily Telegraph]]'', the physicist Stephen Hawking and 10 other signatories including the [[Astronomer Royal]] [[Martin Rees, Baron Rees of Ludlow|Lord Rees]], [[List of presidents of the Royal Society|President of the Royal Society]] Sir [[Paul Nurse]], [[Jean Barker, Baroness Trumpington|Lady Trumpington]] (who worked for Turing during the war) and [[John Sharkey, Baron Sharkey|Lord Sharkey]] (the bill's sponsor) called on Prime Minister [[David Cameron]] to act on the pardon request.<ref>Pearse, Damian, [https://www.theguardian.com/science/2012/dec/14/alan-turing-pardon-stephen-hawking "Alan Turing should be pardoned, argue Stephen Hawking and top scientists"] {{Webarchive|url=https://web.archive.org/web/20170204090812/https://www.theguardian.com/science/2012/dec/14/alan-turing-pardon-stephen-hawking |date=4 February 2017 }}, ''The Guardian'', 13 December 2012. Retrieved 15 December 2012.</ref> The government indicated it would support the bill,<ref name=turingguardian19july2013>{{cite news|url=https://www.theguardian.com/uk-news/2013/jul/19/enigma-codebreaker-alan-turing-posthumous-pardon|title=Enigma codebreaker Alan Turing to be given posthumous pardon|work=The Guardian|date=19 July 2013|author=Watt, Nicholas|location=London|access-date=10 December 2016|archive-url=https://web.archive.org/web/20170104124001/https://www.theguardian.com/uk-news/2013/jul/19/enigma-codebreaker-alan-turing-posthumous-pardon|archive-date=4 January 2017|url-status=live}}</ref><ref>{{cite news|url=http://www.v3.co.uk/v3-uk/news/2302744/alan-turing-pardon-moves-a-step-closer|title=Alan Turing pardon sails through House of Lords|last=Worth|first=Dan|date=30 October 2013|publisher=V3|accessdate=24 December 2013|archive-url=https://web.archive.org/web/20131224114746/http://www.v3.co.uk/v3-uk/news/2302744/alan-turing-pardon-moves-a-step-closer|archive-date=24 December 2013|url-status=live}}</ref><ref>{{cite web | title =Alan Turing (Statutory Pardon) Bill | url =http://services.parliament.uk/bills/2013-14/alanturingstatutorypardon.html | accessdate =20 July 2013 | ref =harv | archive-url =https://web.archive.org/web/20130705084023/http://services.parliament.uk/bills/2013-14/alanturingstatutorypardon.html | archive-date =5 July 2013 | url-status =live }}</ref> and it passed its third reading in the Lords in October.<ref name=turingpinknewsdec2013>{{cite news|url=http://www.pinknews.co.uk/2013/12/02/lib-dem-mp-john-leech-disappointed-at-delay-to-alan-turing-pardon-bill|title=Lib Dem MP John Leech disappointed at delay to Alan Turing pardon bill|newspaper=Pink News|date=2 December 2013|author=Roberts, Scott|access-date=24 December 2013|archive-url=https://web.archive.org/web/20131225050250/http://www.pinknews.co.uk/2013/12/02/lib-dem-mp-john-leech-disappointed-at-delay-to-alan-turing-pardon-bill|archive-date=25 December 2013|url-status=live}}</ref>

At the bill's second reading in the [[House of Commons of the United Kingdom|House of Commons]] on 29 November 2013, Conservative MP [[Christopher Chope]] objected to the bill, delaying its passage. The bill was due to return to the House of Commons on 28 February 2014,<ref>{{Cite news|url=https://www.pinknews.co.uk/2013/12/02/lib-dem-mp-john-leech-disappointed-at-delay-to-alan-turing-pardon-bill/|title=Lib Dem MP John Leech disappointed at delay to Alan Turing pardon bill|last=Roberts|first=Scott|date=2 December 2013|work=PinkNews|access-date=20 June 2018|archive-url=https://web.archive.org/web/20180612210914/https://www.pinknews.co.uk/2013/12/02/lib-dem-mp-john-leech-disappointed-at-delay-to-alan-turing-pardon-bill/|archive-date=12 June 2018|url-status=live}}</ref> but before the bill could be debated in the House of Commons,<ref>{{cite web | title =Alan Turing (Statutory Pardon) Bill | url =http://services.parliament.uk/bills/2013-14/alanturingstatutorypardon.html | accessdate =24 December 2013 | ref =harv | archive-url =https://web.archive.org/web/20131102040315/http://services.parliament.uk/bills/2013-14/alanturingstatutorypardon.html | archive-date =2 November 2013 | url-status =live }}</ref> the government elected to proceed under the [[royal prerogative of mercy]]. On 24 December 2013, [[Queen Elizabeth II]] signed a pardon for Turing's conviction for "gross indecency", with immediate effect.<ref name=turingpardon24dec2013>{{cite web |url=https://www.telegraph.co.uk/history/world-war-two/10536246/Alan-Turing-granted-Royal-pardon-by-the-Queen.html |title=Alan Turing granted Royal pardon by the Queen |last=Swinford |first=Steven |date=23 December 2013 |work=The Daily Telegraph |access-date=5 April 2018 |archive-url=https://web.archive.org/web/20180502103553/https://www.telegraph.co.uk/history/world-war-two/10536246/Alan-Turing-granted-Royal-pardon-by-the-Queen.html |archive-date=2 May 2018 |url-status=live }}</ref> Announcing the pardon, Lord Chancellor [[Chris Grayling]] said Turing deserved to be "remembered and recognised for his fantastic contribution to the war effort" and not for his later criminal conviction.<ref name=turingindependent24dec2013 /><ref name="BBC-pardon24Dec">{{cite news|title=Royal pardon for codebreaker Alan Turing|url=https://www.bbc.co.uk/news/technology-25495315|accessdate=24 December 2013|publisher=BBC News|date=24 December 2013|archive-url=https://web.archive.org/web/20131224002121/http://www.bbc.co.uk/news/technology-25495315|archive-date=24 December 2013|url-status=live}}</ref> The Queen officially pronounced Turing pardoned in August 2014.<ref>{{cite web|url=http://www.advocate.com/world/2014/08/22/queens-decree-alan-turing-now-officially-pardoned|title=With Queen's Decree, Alan Turing Is Now Officially Pardoned|publisher=Advocate.com|accessdate=1 November 2014|archive-url=https://web.archive.org/web/20141101212528/http://www.advocate.com/world/2014/08/22/queens-decree-alan-turing-now-officially-pardoned|archive-date=1 November 2014|url-status=live}}</ref> The Queen's action is only the fourth royal pardon granted since the conclusion of the Second World War.<ref>Pardoned: Alan Turing, Computing patriarch. ''Time'' Magazine, vol. 183, no. 1, 13 January 2014, p.&nbsp;14. Retrieved 6 January 2014.</ref> Pardons are normally granted only when the person is technically innocent, and a request has been made by the family or other interested party; neither condition was met in regard to Turing's conviction.<ref name = grauniad>{{Cite news | last =Davies | first =Caroline | title = Codebreaker Turing is given posthumous royal pardon | newspaper =The Guardian | location =London | pages =1, 6 | date =24 December 2013 }}</ref>

In a letter to the Prime Minister, [[David Cameron]], human rights advocate [[Peter Tatchell]] criticised the decision to single out Turing due to his fame and achievements when thousands of others convicted under the same law have not received pardons.<ref name = "UKHP">{{cite news | first = Peter | last = Tatchell | title = Alan Turing: Was He Murdered By the Security Services? | url = http://www.huffingtonpost.co.uk/peter-g-tatchell/alan-turing-pardon_b_4498564.html | work = The Huffington Post UK | date = 24 December 2013 | accessdate = 29 December 2013 | archive-url = https://web.archive.org/web/20131229002716/http://www.huffingtonpost.co.uk/peter-g-tatchell/alan-turing-pardon_b_4498564.html | archive-date = 29 December 2013 | url-status = live }}</ref> Tatchell also called for a new investigation into Turing's death:

{{quote|A new inquiry is long overdue, even if only to dispel any doubts about the true cause of his death—including speculation that he was murdered by the security services (or others). I think murder by state agents is unlikely. There is no known evidence pointing to any such act. However, it is a major failing that this possibility has never been considered or investigated.<ref>{{cite web|last=Tatchell|first=Peter|title=The Big Questions: Do we need an inquiry into the death of Alan Turing? Should Britain boycott Sochi?|url=https://www.independent.co.uk/voices/comment/the-big-questions-do-we-need-an-inquiry-into-the-death-of-alan-turing-should-britain-boycott-sochi-9027526.html|website=The Independent|accessdate=14 February 2017|date=27 December 2013|archive-url=https://web.archive.org/web/20170215124545/http://www.independent.co.uk/voices/comment/the-big-questions-do-we-need-an-inquiry-into-the-death-of-alan-turing-should-britain-boycott-sochi-9027526.html|archive-date=15 February 2017|url-status=live}}</ref>}}

In September 2016, the government announced its intention to expand this retroactive exoneration to other men convicted of similar historical indecency offences, in what was described as an "[[Alan Turing law]]".<ref>{{cite news|url=https://www.bbc.co.uk/news/uk-37436417|title=Government 'committed' to Alan Turing gay pardon law|date=22 September 2016|publisher=BBC News|access-date=22 September 2016|archive-url=https://web.archive.org/web/20160922041224/http://www.bbc.co.uk/news/uk-37436417|archive-date=22 September 2016|url-status=live}}</ref><ref>{{Cite web|url=https://www.independent.co.uk/news/uk/politics/theresa-may-committed-to-introducing-alan-turing-law-and-pardon-gay-men-convicted-of-outdated-crimes-a7320851.html|title=Theresa May committed to introducing the 'Alan Turing Law'|last=Cowburn|first=Ashley|date=21 September 2016|website=The Independent|access-date=22 September 2016|archive-url=https://web.archive.org/web/20160922133219/http://www.independent.co.uk/news/uk/politics/theresa-may-committed-to-introducing-alan-turing-law-and-pardon-gay-men-convicted-of-outdated-crimes-a7320851.html|archive-date=22 September 2016|url-status=live}}</ref> The [[Alan Turing law]] is now an informal term for the law in the United Kingdom, contained in the [[Policing and Crime Act 2017]], which serves as an [[amnesty law]] to retroactively pardon men who were cautioned or convicted under historical legislation that outlawed homosexual acts. The law applies in England and Wales.<ref>{{cite web|url=http://www.legislation.gov.uk/ukpga/2017/3/section/182/data.htm|title=Policing and Crime Act 2017|first=Expert|last=Participation|publisher=Government of the United Kingdom|accessdate=6 February 2019|archive-url=https://web.archive.org/web/20190305145933/http://www.legislation.gov.uk/ukpga/2017/3/section/182/data.htm|archive-date=5 March 2019|url-status=live}}</ref>

==Legacy==
{{main|Legacy of Alan Turing}}
{{see also|List of things named after Alan Turing}}

===Awards, honours, and tributes===
[[File:Alan Turing Building 1.jpg|thumb|The [[Alan Turing Building]] at the University of Manchester in 2008]]
Turing was appointed an officer of the [[Order of the British Empire]] in 1946.<ref name="thegazette.co.uk"/> He was also elected a [[List of Fellows of the Royal Society elected in 1951|Fellow of the Royal Society (FRS)]] in 1951.<ref name="frs"/>

Turing has been honoured in various ways in [[Manchester]], the city where he worked towards the end of his life. In 1994, a stretch of the [[A6010 road]] (the [[Manchester]] city intermediate ring road) was named "Alan Turing Way". A bridge carrying this road was widened, and carries the name Alan Turing Bridge. A [[Alan Turing Memorial|statue of Turing]] was unveiled in Manchester on 23 June 2001 in [[Sackville Park]], between the University of Manchester building on Whitworth Street and [[Canal Street, Manchester|Canal Street]]. The memorial statue depicts the "father of computer science" sitting on a bench at a central position in the park. Turing is shown holding an apple. The cast bronze bench carries in relief the text 'Alan Mathison Turing 1912–1954', and the motto 'Founder of Computer Science' as it could appear if encoded by an [[Enigma machine]]: 'IEKYF ROMSI ADXUO KVKZC GUBJ'. However, the meaning of the coded message is disputed, as the 'u' in 'computer' matches up with the 'u' in 'ADXUO'. As a letter encoded by an enigma machine cannot appear as itself, the actual message behind the code is uncertain.<ref>{{Cite news|url=https://benosteen.wordpress.com/2010/09/23/what-does-the-code-on-the-alan-turing-memorial-actually-say/|title=What does the code on the Alan Turing Memorial actually say?|date=23 September 2010|work=Random Hacks|access-date=28 June 2018|archive-url=https://web.archive.org/web/20180628125202/https://benosteen.wordpress.com/2010/09/23/what-does-the-code-on-the-alan-turing-memorial-actually-say/|archive-date=28 June 2018|url-status=live}}</ref>
[[File:Sackville Park Turing plaque.jpg|thumb|right|Turing memorial statue plaque in [[Sackville Park]], Manchester]]
A plaque at the statue's feet reads 'Father of computer science, mathematician, logician, wartime codebreaker, victim of prejudice'. There is also a [[Bertrand Russell]] quotation: "Mathematics, rightly viewed, possesses not only truth, but supreme beauty—a beauty cold and austere, like that of sculpture." The sculptor buried his own old [[Amstrad]] computer under the [[plinth]] as a tribute to "the godfather of all modern computers".<ref name="computerburied">{{cite news | url=http://www.manchestereveningnews.co.uk/news/greater-manchester-news/computer-buried-in-tribute-to-genius-1186583 | title=Computer buried in tribute to genius | work=Manchester Evening News | date=17 February 2007 | accessdate=7 December 2014 | archive-url=https://web.archive.org/web/20131104022559/http://www.manchestereveningnews.co.uk/news/greater-manchester-news/computer-buried-in-tribute-to-genius-1186583 | archive-date=4 November 2013 | url-status=live }}</ref>

In 1999, ''[[Time (magazine)|Time]]'' magazine named Turing as one of the [[Time 100: The Most Important People of the Century|100 Most Important People of the 20th century]] and stated, "The fact remains that everyone who taps at a keyboard, opening a spreadsheet or a word-processing program, is working on an incarnation of a Turing machine."<ref name=AFP>{{cite news |title=Alan Turing&nbsp;– Time 100 People of the Century |url=http://www.time.com/time/magazine/article/0,9171,990624,00.html |work=Time |quote=Providing a blueprint for the electronic digital computer. The fact remains that everyone who taps at a keyboard, opening a spreadsheet or a word-processing program, is working on an incarnation of a Turing machine. |first=Paul |last=Gray |date=29 March 1999 |access-date=10 January 2011 |archive-url=https://web.archive.org/web/20110119181237/http://www.time.com/time/magazine/article/0,9171,990624,00.html |archive-date=19 January 2011 |url-status=live }}</ref>

===Centenary celebrations===
{{main|Alan Turing Year}}

To mark the 100th anniversary of Turing's birth, the Turing Centenary Advisory Committee (TCAC) co-ordinated the [[Alan Turing Year]], a year-long programme of events around the world honouring Turing's life and achievements. The TCAC, chaired by [[S. Barry Cooper]] with Turing's nephew Sir John Dermot Turing acting as Honorary President, worked with the University of Manchester faculty members and a broad spectrum of people from Cambridge University and [[Bletchley Park]].
{{-}}

=== Historic England controversy ===
In May 2020 it was reported by ''[[Gay Star News]]'' that a {{convert|12|foot|adj=on}} high steel sculpture, to honour Turing, designed by Sir [[Antony Gormley]], was planned to be installed in [[King's College, Cambridge]]. [[Historic England]], however, was quoted as saying that the abstract work of 19 steel slabs "... would be at odds with the existing character of the College. This would result in harm, of a less than substantial nature, to the significance of the listed buildings and landscape, and by extension the conservation area."<ref>{{Cite web |url=https://www.gaystarnews.com/article/heritage-watchdog-objects-to-statue-of-gay-hero-alan-turing-at-kings-college-cambridge/ |title=Heritage watchdog objects to statue of gay hero Alan Turing at Kings College Cambridge |first=Tris |last=Reid-Smith |date=1 May 2020 |website=Gay Star News |accessdate=8 May 2020}}</ref>

==References==
{{Reflist|30em}}

===Sources===
{{Refbegin|30em}}
* {{Cite book | last = Agar | first = Jon | title = Turing and the Universal Machine | location = Duxford | publisher=Icon | year=2001 | isbn = 978-1-84046-250-0 | ref = harv}}
* {{Cite book | last = Agar | first = Jon | title = The government machine: a revolutionary history of the computer | publisher=MIT Press | year = 2003 | location = Cambridge, Massachusetts | isbn = 978-0-262-01202-7 }}
* {{Cite journal | last = Alexander | first = C. Hugh O'D. | author-link = Conel Hugh O'Donel Alexander (circa 1945) | title = Cryptographic History of Work on the German Naval Enigma | url = http://www.ellsbury.com/gne/gne-000.htm | publisher=The National Archives, Kew, Reference HW 25/1 | ref = {{harvid|Alexander|circa 1945}}}}
* {{cite book |last=Beavers |first=Anthony |editor1-first=S. Barry |editor1-last=Cooper|editor2-first=Jan |editor2-last=van Leeuwen |title=Alan Turing: His Work and Impact |publisher=Elsevier |location=Waltham |year=2013 |pages=481–485 |chapter=Alan Turing: Mathematical Mechanist |isbn=978-0-12-386980-7 |chapter-url=https://books.google.com/books?id=C9WQbm4ovFoC&pg=PA481 |ref=harv}}
* {{Cite book | last = Beniger | first = James | authorlink = James R. Beniger | title = The control revolution: technological and economic origins of the information society | publisher=Harvard University Press | year = 1986 | location = Cambridge, Massachusetts | isbn = 978-0-674-16986-9 | title-link = The control revolution: technological and economic origins of the information society }}
* {{Cite book | last = Babbage | first = Charles | author-link = Charles Babbage | year = 1864
 | publication-date = 2008 | editor-last = Campbell-Kelly | editor-first = Martin | editor-link = Martin Campbell-Kelly | title = Passages from the life of a philosopher | publisher=Rough Draft Printing | isbn = 978-1-60386-092-5 | ref = harv}}
* {{Cite book | last = Bodanis | first = David | author-link = David Bodanis | title = Electric Universe: How Electricity Switched on the Modern World | year = 2005 |publisher=Three Rivers Press | location = New York | isbn = 978-0-307-33598-2 | oclc = 61684223}}
* Bruderer, Herbert: [http://www.oldenbourg-verlag.de/wissenschaftsverlag/konrad-zuse-und-schweiz/9783486713664 ''Konrad Zuse und die Schweiz. Wer hat den Computer erfunden? Charles Babbage, Alan Turing und John von Neumann''] Oldenbourg Verlag, München 2012, XXVI, 224 Seiten, {{isbn|978-3-486-71366-4}}
* {{Cite book | last1 = Campbell-Kelly | first1 = Martin | authorlink = Martin Campbell-Kelly | last2 = Aspray | first2 = William | title = Computer: A History of the Information Machine | publisher = Basic Books | year = 1996 | location = New York | isbn = 978-0-465-02989-1 | url = https://archive.org/details/computerhistoryo00camp }}
* {{Cite book | last = Ceruzzi | first = Paul E. | authorlink = Paul E. Ceruzzi | title = A History of Modern Computing | publisher=MIT Press | year = 1998 | location = Cambridge, Massachusetts, and London | isbn = 978-0-262-53169-6}}
* {{Cite book | last = Chandler | first = Alfred | authorlink = Alfred D. Chandler Jr. | title = The Visible Hand: The Managerial Revolution in American Business | publisher = Belknap Press | year = 1977 | location = Cambridge, Massachusetts | isbn = 978-0-674-94052-9 | url = https://archive.org/details/visiblehandmanag00chan }}
* {{cite journal|last1=Church|first1=Alonzo|authorlink=Alonzo Church|title=An Unsolvable Problem of Elementary Number Theory|journal=[[American Journal of Mathematics]]|volume=58|issue=2|year=1936|pages=345–363|issn=0002-9327|doi=10.2307/2371045|ref=harv|jstor=2371045}}
* {{cite book | last1 = Cooper | first1 = S. Barry | last2 = van Leeuwen | first2 = Jan | title = Alan Turing: His Work and Impact | year = 2013 | location = New York | publisher = Elsevier | isbn = 978-0-12-386980-7 | ref = harv }}
* {{Cite journal | last = Copeland | first = B. Jack  | authorlink = Jack Copeland | title = Colossus: Its Origins and Originators | journal=[[IEEE Annals of the History of Computing]] | volume = 26 | issue = 4 | pages = 38–45 | year = 2004a |doi = 10.1109/MAHC.2004.26 | s2cid = 20209254 | ref = harv }}
* {{Cite book |editor-last = Copeland |editor-first = B. Jack| authorlink = | title = The Essential Turing | year = 2004b | publisher=Oxford University Press | location = Oxford | isbn = 978-0-19-825079-1 | oclc = 156728127  | ref = harv }}
* {{Cite book | editor-last = Copeland | editor-first = B. Jack | authorlink =  | title = Alan Turing's Automatic Computing Engine | year = 2005 | publisher = Oxford University Press | location = Oxford | isbn = 978-0-19-856593-2 | oclc = 224640979 | url-access = registration | url = https://archive.org/details/alanturingsautom0000unse }}
* {{Cite book | last = Copeland | first = B. Jack | authorlink = | title = Colossus: The secrets of Bletchley Park's code-breaking computers | year = 2006 | publisher=Oxford University Press | isbn = 978-0-19-284055-4 | ref = harv }}
** {{Cite book | last = Hilton | first = Peter | author-link = Peter Hilton | year = 2006 | chapter = Living with Fish: Breaking Tunny in the Newmanry and Testery | ref = harv |title=Colussus}} in {{Harvnb|Copeland|2006|pp=189–203}}
* {{Cite book | last = Edwards | first = Paul N | title = The closed world: computers and the politics of discourse in Cold War America | publisher=MIT Press | year = 1996 | location = Cambridge, Massachusetts | isbn = 978-0-262-55028-4 }}
* {{Cite book | last = Gannon | first = Paul | title = Colossus: Bletchley Park's Greatest Secret | place = London | publisher=Atlantic Books | origyear = 2006 | year = 2007 | isbn = 978-1-84354-331-2 | ref = harv }}
* {{cite book | last = Hodges | first = Andrew| authorlink = Andrew Hodges | title = Alan Turing : the enigma|location = London | publisher=Burnett Books | isbn = 978-0-09-152130-1 | year = 1983 | ref = harv}}
* {{Cite book | last = Hochhuth | first = Rolf | authorlink = Rolf Hochhuth | title = Alan Turing: en berättelse | publisher=Symposion | year = 1988 | isbn = 978-91-7868-109-9 }}
* {{Cite book | last = Leavitt | first = David | authorlink = David Leavitt | year = 2007 | title = The man who knew too much: Alan Turing and the invention of the computer | publisher=Phoenix | isbn = 978-0-7538-2200-5 | ref = harv }}
* {{Cite book | last = Levin | first = Janna | authorlink = Janna Levin | title = A Madman Dreams of Turing Machines | publisher=Knopf | year = 2006 | location = New York | isbn = 978-1-4000-3240-2 }}
* {{Cite book | last = Lewin | first = Ronald | authorlink = Ronald Lewin | title = Ultra Goes to War: The Secret Story | edition = Classic Penguin | series = Classic Military History | year = 1978 | publication-date = 2001 | publisher=Hutchinson & Co | location = London | isbn = 978-1-56649-231-7 | ref = harv }}
* {{Cite book | last = Lubar | first = Steven | year = 1993 | title = Infoculture | location = Boston, Massachusetts and New York | publisher = Houghton Mifflin | isbn = 978-0-395-57042-5 | url = https://archive.org/details/infoculturesmith00luba }}
* {{Cite journal | last = Mahon | first = A.P. | title = The History of Hut Eight 1939–1945 | publisher=UK National Archives Reference HW 25/2 | year = 1945 | url = http://www.ellsbury.com/hut8/hut8-000.htm | accessdate =10 December 2009 | ref = harv }}
* {{Cite book | editor-last = Oakley | editor-first = Brian | editor-link = Brian Oakley | title = The Bletchley Park War Diaries: July 1939&nbsp;– August 1945 | publisher=Wynne Press | year = 2006 | edition = 2.6 | ref = harv }}
* {{Cite journal | last1 = O'Connell | first1 = H | last2 = Fitzgerald | first2 = M | title = Did Alan Turing have Asperger's syndrome? | journal=Irish Journal of Psychological Medicine | volume = 20 | issue = 1 | pages = 28–31 | publisher=Irish Institute of Psychological Medicine | year = 2003 | issn = 0790-9667 | ref = harv | doi=10.1017/s0790966700007503| pmid = 30440230 }}
* {{MacTutor Biography|id=Turing|title=Alan Mathison Turing}}
* Petzold, Charles (2008). "[[The Annotated Turing]]: A Guided Tour through Alan Turing's Historic Paper on Computability and the Turing Machine". [[Indianapolis]]: Wiley Publishing. {{isbn|978-0-470-22905-7}}
* Smith, Roger (1997). ''Fontana History of the Human Sciences''. London: Fontana.
* {{Cite book | last = Sipser | first = Michael | title = Introduction to the Theory of Computation | publisher=PWS Publishing | isbn = 978-0-534-95097-2 | year = 2006 | ref = harv }}
* Weizenbaum, Joseph (1976). ''Computer Power and Human Reason''. London: W.H. Freeman. {{isbn|0-7167-0463-3}}
* {{Cite news | last= Turing | first= A.M. |year = 1937 | title = On Computable Numbers, with an Application to the Entscheidungsproblem | origyear = Delivered to the Society November 1936 | periodical = Proceedings of the London Mathematical Society | series = 2 | volume = 42 | pages = 230–65 | doi= 10.1112/plms/s2-42.1.230 | url = http://www.comlab.ox.ac.uk/activities/ieg/e-library/sources/tp2-ie.pdf | ref= harv }} and {{Cite news| last = Turing | first = A.M. | publication-date = 1937 | title = On Computable Numbers, with an Application to the Entscheidungsproblem: A correction | periodical = Proceedings of the London Mathematical Society | series = 2 | volume = 43 | pages = 544–46 | doi = 10.1112/plms/s2-43.6.544 | year = 1938 }}
* {{Cite book | last = Turing | first = Sara Stoney | title = Alan M Turing | publisher=W Heffer | year = 1959}} Turing's mother, who survived him by many years, wrote this 157-page biography of her son, glorifying his life. It was published in 1959, and so could not cover his war work. Scarcely 300 copies were sold (Sara Turing to Lyn Newman, 1967, Library of [[St John's College, Cambridge]]). The six-page foreword by [[Lyn Irvine]] includes reminiscences and is more frequently quoted. It was re-published by Cambridge University Press in 2012, to honour the centenary of his birth, and included a new foreword by [[Martin Davis (mathematician)|Martin Davis]], as well as a never-before-published memoir by Turing's older brother John F. Turing.
* {{Cite book | last1 = Whitemore | first1 = Hugh | authorlink = Hugh Whitemore | last2 = Hodges | first2 = Andrew | authorlink2 = Andrew Hodges | title = Breaking the code | publisher=S. French | year = 1988}} This 1986 Hugh Whitemore play tells the story of Turing's life and death. In the original West End and Broadway runs, [[Derek Jacobi]] played Turing and he recreated the role in a 1997 television film based on the play made jointly by the BBC and [[WGBH-TV|WGBH, Boston]]. The play is published by Amber Lane Press, [[Oxford]], ASIN: B000B7TM0Q
* Williams, Michael R. (1985) ''A History of Computing Technology'', [[Englewood Cliffs]], [[New Jersey]]: [[Prentice-Hall]], {{isbn|0-8186-7739-2}}
* {{Cite book|last=Yates |first=David M. |title=Turing's Legacy: A history of computing at the National Physical Laboratory 1945–1995 |year=1997 |publisher=[[Science Museum, London|London Science Museum]] |location=London |isbn=978-0-901805-94-2 |oclc=123794619  }}
{{Refend}}

==Further reading==
===Articles===
* {{cite journal| year=1950|last=Turing|first=Alan|title=Computing Machinery and Intelligence|journal=[[Mind (journal)|Mind]] |volume=49|issue=236|pages= 433–460 |url=https://www.csee.umbc.edu/courses/471/papers/turing.pdf | ref=harv|doi=10.1093/mind/LIX.236.433}}
* {{cite journal| title=The Mind and the Computing Machine: Alan Turing and others|journal=[[The Rutherford Journal]] |url=http://www.rutherfordjournal.org/article010111.html |editor-first=B. Jack | editor-last=Copeland | ref=harv}}
* {{cite journal| title=Alan Turing: Father of the Modern Computer|journal=[[The Rutherford Journal]] |url=http://www.rutherfordjournal.org/article040101.html |editor-first=B. Jack | editor-last=Copeland | ref=harv}}
* {{cite encyclopaedia |last=Hodges |first=Andrew |editor=Edward N. Zalta|encyclopedia=[[Stanford Encyclopedia of Philosophy]] |title=Alan Turing |url=http://plato.stanford.edu/entries/turing/ |accessdate=10 January 2011 |edition=Winter 2009 |date=27 August 2007 |publisher=[[Stanford University]] |ref=harv}}
* {{cite ODNB|id=36578|title=Turing, Alan Mathison|year=2004|last=Hodges|first=Andrew}}
* {{cite journal|last=Gray|first=Paul|date=29 March 1999|title=Computer Scientist: Alan Turing|journal=Time|url=http://www.time.com/time/magazine/article/0,9171,990624,00.html|ref=harv}}

===Books===
* {{Citation |last= Bernhardt |first= Chris |title= Turing's Vision: The Birth of Computer Science |publisher= MIT Press |year= 2017 |isbn= 978-0-262-53351-5 }}
* {{cite book| authorlink1=Jack Copeland | last1=Copeland |first1=B. Jack | authorlink2=Jonathan Bowen | last2=Bowen | first2=Jonathan P. | authorlink3=Robin Wilson (mathematician) | last3=Wilson | first3=Robin | last4=Sprevak | first4=Mark | title=The Turing Guide | publisher=[[Oxford University Press]] | date=2017 | isbn=978-0-19-874783-3 | title-link=The Turing Guide }}
* {{cite book| title=Turing's Cathedral: The Origins of the Digital Universe | authorlink=George Dyson (science historian) | first=George | last=Dyson | isbn=978-1-4000-7599-7 | year=2012 | publisher=Vintage }}
* {{cite book| authorlink=James Gleick | last=Gleick | first=James | title=The Information: A History, a Theory, a Flood | location=New York | publisher=Pantheon | date=2011 | isbn=978-0-375-42372-7 | title-link=The Information: A History, a Theory, a Flood }}
* {{cite book| title=Alan Turing: The Enigma| year=2014 | first=Andrew | last=Hodges | authorlink=Andrew Hodges | publisher=[[Princeton University Press]] | isbn=978-0-691-16472-4 }} (originally published in 1983); basis of the film ''[[The Imitation Game]]''

==External links==
{{Commons category|Alan Turing}}
{{Wikiquote}}
* [http://purl.umn.edu/107493 Oral history interview with Nicholas C. Metropolis], [[Charles Babbage Institute]], University of Minnesota. Metropolis was the first director of computing services at [[Los Alamos National Laboratory]]; topics include the relationship between Turing and [[John von Neumann]]
* [http://www.iwm.org.uk/history/how-alan-turing-cracked-the-enigma-code How Alan Turing Cracked The Enigma Code] Imperial War Museums
* [https://web.archive.org/web/20080828060019/http://www.rkbexplorer.com/explorer/#display=person%2D{http://dblp.rkbexplorer.com/id/people-a27f18ebafc0d76ddb05173ce7b9873d-e0b388b7c1e0985b1371d73ee1fae8b5} Alan Turing] RKBExplorer
* [http://www.turingcentenary.eu/ Alan Turing Year]
* [http://cie2012.eu/ CiE 2012: Turing Centenary Conference]
* [https://makingscience.royalsociety.org/s/rs/people/fst00117605 Science in the Making] Alan Turing's papers in the Royal Society's archives
* [http://www.turing.org.uk/ Alan Turing] site maintained by [[Andrew Hodges]] including a [https://web.archive.org/web/20180721235734/http://www.turing.org.uk/bio/part1.html short biography]
* [https://web.archive.org/web/20181012014022/http://www.alanturing.net/ AlanTuring.net&nbsp;– Turing Archive for the History of Computing] by [[Jack Copeland]]
* [http://www.turingarchive.org/ The Turing Archive]&nbsp;– contains scans of some unpublished documents and material from the King's College, Cambridge archive
* [https://archiveshub.jisc.ac.uk/manchesteruniversity/data/gb133-tur/add Alan Turing Papers, [[University of Manchester Library]], Manchester]
* {{cite journal|last=Jones|first=G. James|date=11 December 2001|title=Alan Turing&nbsp;– Towards a Digital Mind: Part 1|journal=System Toolbox|publisher=The Binary Freedom Project|url=http://www.systemtoolbox.com/article.php?history_id=3|ref=harv|url-status=dead|archiveurl=https://web.archive.org/web/20070803163318/http://www.systemtoolbox.com/article.php?history_id=3|archivedate=3 August 2007}}
* [http://blog.stephenwolfram.com/2012/06/happy-100th-birthday-alan-turing/ Happy 100th Birthday, Alan Turing] by [[Stephen Wolfram]] June 2012.
* [https://web.archive.org/web/20160104203150/http://oldshirburnian.org.uk/wp-content/uploads/2015/09/TURING-Alan-Mathison.pdf Sherborne School Archives] – holds papers relating to Turing's time at Sherborne School
* [https://openplaques.org/people/368 Alan Turing plaques] recorded on openplaques.org
* [https://www.newscientist.com/people/alan-turing/ Alan Turing] archive on New Scientist
* {{findagrave|12651680}}

{{FRS 1951}}
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[[Category:Former Protestants]]
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[[Category:Gay academics]]
[[Category:GCHQ people]]
[[Category:History of artificial intelligence]]
[[Category:Inventors who committed suicide]]
[[Category:LGBT-related suicides]]
[[Category:LGBT scientists]]
[[Category:LGBT scientists from the United Kingdom]]
[[Category:Male suicides]]
[[Category:Mathematicians who committed suicide]]
[[Category:Officers of the Order of the British Empire]]
[[Category:People educated at Sherborne School]]
[[Category:People from Maida Vale]]
[[Category:People from Wilmslow]]
[[Category:People prosecuted under anti-homosexuality laws]]
[[Category:People who have received posthumous pardons]]
[[Category:Princeton University alumni]]
[[Category:Computer programmers who committed suicide]]
[[Category:Recipients of British royal pardons]]
[[Category:Suicides by cyanide poisoning]]
[[Category:Suicides in England]]
[[Category:Theoretical computer scientists]]
[[Category:Gay sportsmen]]
[[Category:LGBT sportspeople from England]]
[[Category:LGBT track and field athletes]]
[[Category:History of computing in the United Kingdom]]
[[Category:20th-century British scientists]]
[[Category:Deaths by poisoning]]

