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Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist,
logic
logic
ian, cryptanalyst, philosopher, and theoretical biologist. Turing was highly influential in the development of theoretical computer science, providing a formalisation of the concepts of
algorithm
algorithm
and
computation
computation
with the
Turing machine
Turing machine
, which can be considered a model of a general-purpose computer. He is widely considered to be the father of theoretical computer science and artificial intelligence. Born in Maida Vale, London, Turing was raised in . He graduated at , with a degree in mathematics. Whilst he was a fellow at Cambridge, he published a proof demonstrating that some purely mathematical yes–no questions can never be answered by computation and defined a , and went on to prove that the halting problem for Turing machines is undecidable. In 1938, he obtained his PhD from the Department of Mathematics at . During the Second World War, Turing worked for the Government Code and Cypher School (GC&CS) at Bletchley Park, Britain's 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 ciphers, including improvements to the pre-war Polish bomba method, an 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 Axis powers in many crucial engagements, including the Battle of the Atlantic. After the war, Turing worked at the National Physical Laboratory, where he designed the Automatic Computing Engine (ACE), 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 and became interested in mathematical biology. He wrote a paper on the chemical basis of morphogenesis and predicted oscillating
chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

chemical reaction
s such as the Belousov–Zhabotinsky reaction, first observed in the 1960s. Despite these accomplishments, Turing was never fully recognised in Britain during his lifetime because much of his work was covered by the Official Secrets Act. Turing was prosecuted in 1952 for homosexual acts. He accepted hormone treatment with DES, a procedure commonly referred to as chemical castration, as an alternative to prison. Turing died on 7 June 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. Following a public campaign in 2009, the British Prime Minister made an official public apology on behalf of the British government for "the appalling way uringwas treated". granted a posthumous pardon in 2013. The term " Alan Turing law" is now used informally to refer to a 2017 law in the United Kingdom that retroactively pardoned men cautioned or convicted under historical legislation that outlawed homosexual acts. Turing has an extensive legacy with statues of him and many things named after him, including an annual award for computer science innovations. He appears on the current Bank of England £50 note, which was released on 23 June 2021, to coincide with his birthday. A 2019 BBC series, as voted by the audience, named him the greatest person of the 20th century.


Early life and education


Family

Turing was born in Maida Vale, London, while his father, Julius Mathison Turing (1873–1947), was on leave from his position with the Indian Civil Service (ICS) of the at Chatrapur, then in the Madras Presidency and presently in state, in India. Turing's father was the son of a clergyman, the Rev. 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 (; 1881–1976), daughter of Edward Waller Stoney, chief engineer of the Madras Railways. The Stoneys were a
Protestant Protestantism is a branch of Christianity Christianity is an Abrahamic religions, Abrahamic Monotheism, monotheistic religion based on the Life of Jesus in the New Testament, life and Teachings of Jesus, teachings of Jesus, Jesus of Na ...
Anglo-Irish Anglo-Irish people () denotes an ethnic, social and religious grouping who are mostly the descendants and successors of the English Protestant Ascendancy in Ireland. They mostly belong to the Anglican Church of Ireland, which was the establish ...
gentry Gentry (from Old French ''genterie'', from ''gentil'', "high-born, noble") are "well-born, genteel and well-bred people" of high social class, especially in the past. Word similar to gentle imple and decentfamilies ''Gentry'', in its widest ...
family from both
County Tipperary County Tipperary ( ga, Contae Thiobraid Árann) is a Counties of Ireland, county in Republic of Ireland, Ireland. It is in the Provinces of Ireland, province of Munster and the Southern Region, Ireland, Southern Region. The county is named afte ...
and
County Longford County Longford ( gle, Contae an Longfoirt) is a Counties of Ireland, county in Republic of Ireland, Ireland. It is in the Provinces of Ireland, province of Leinster. It is named after the town of Longford. Longford County Council is the Local g ...
, while Ethel herself had spent much of her childhood in
County Clare County Clare ( ga, Contae an Chláir) is a Counties of Ireland, county in Ireland, in the Southern Region, Ireland, Southern Region and the Provinces of Ireland, province of Munster, bordered on the west by the Atlantic Ocean. Clare County Coun ...
. Julius and Ethel married on 1 October 1907 at Batholomew's church on Clyde Road, in Dublin. Julius's work with the ICS brought the family to British India, where his grandfather had been a general in the
Bengal Army The Bengal Army was the army of the Bengal Presidency, one of the three presidencies of Presidencies and provinces of British India, British India within the British Empire. The presidency armies, like the presidencies themselves, belonged to ...
. However, both Julius and Ethel wanted their children to be brought up in Britain, so they moved to Maida Vale, London, where Alan Turing was born on 23 June 1912, as recorded by a
blue plaque A blue plaque is a permanent sign installed in a public place in the United Kingdom and elsewhere to commemorate a link between that location and a famous person, event, or former building on the site, serving as a historical marker. The term i ...
on the outside of the house of his birth, later the Colonnade Hotel. Turing had an elder brother, John (the father of Sir John Dermot Turing, 12th Baronet of the Turing baronets). Turing's father's civil service commission was still active and during Turing's childhood years, his parents travelled between
Hastings Hastings () is a large seaside town and Borough status in the United Kingdom, borough in East Sussex on the south coast of England, east to the county town of Lewes and south east of London. The town gives its name to the Battle of Hastings, ...
in the United Kingdom and India, leaving their two sons to stay with a retired
Army An army (from Old French ''armee'', itself derived from the Latin verb ''armāre'', meaning "to arm", and related to the Latin noun ''arma'', meaning "arms" or "weapons"), ground force or land force is a fighting force that fights primarily on ...
couple. At Hastings, Turing stayed at Baston Lodge, Upper Maze Hill, St Leonards-on-Sea, now marked with a blue plaque. The plaque was unveiled on 23 June 2012, the centenary of Turing's birth. Very early in life, Turing showed signs of the genius that he was later to display prominently. His parents purchased a house in
Guildford Guildford () is a town in west Surrey, around southwest of central London. As of the 2011 census, the town has a population of about 77,000 and is the seat of the wider Guildford (borough), Borough of Guildford, which had around inhabitants i ...
in 1927, and Turing lived there during school holidays. The location is also marked with a blue plaque.


School

Turing's parents enrolled him at St Michael's, a primary school at 20 Charles Road, St Leonards-on-Sea, from the age of six to nine. The headmistress recognised his talent, noting that she has "...had clever boys and hardworking boys, but Alan is a genius". 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 East Sussex is a ceremonial county, ceremonial and non-metropolitan county, non-metropolitan counties of England, county in South East England on the English Channel coast. It is bordered by Kent to the north and east, West Sussex to the west, ...
). In 1926, at the age of 13, he went on to
Sherborne School Sherborne School is a Public school (United Kingdom), public school (English Independent school (United Kingdom), independent boarding school for boys) located beside Sherborne Abbey, in the parish of Sherborne, Dorset. The school has been in c ...
, a boarding independent school in the market town of
Sherborne Sherborne is a market town and civil parishes in England, civil parish in north west Dorset, in South West England. It is sited on the River Yeo (South Somerset), River Yeo, on the edge of the Blackmore Vale, east of Yeovil. The parish includ ...
in Dorset, where he boarded at Westcott House. The first day of term coincided with the 1926 General Strike, in Britain, but Turing was so determined to attend that he rode his bicycle unaccompanied from
Southampton Southampton () is a port City status in the United Kingdom, city in the ceremonial county of Hampshire in southern England. It is located approximately south-west of London and west of Portsmouth. The city forms part of the South Hampshire, S ...
to Sherborne, stopping overnight at an inn. 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 Classics or classical studies is the study of classical antiquity. In the Western world, classics traditionally refers to the study of Classical Greek and Roman literature and their related original languages, Ancient Greek Ancient ...
. 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". Despite this, Turing continued to show remarkable ability in the studies he loved, solving advanced problems in 1927 without having studied even elementary
calculus Calculus, originally called infinitesimal calculus or "the calculus of infinitesimals", is the mathematics, mathematical study of continuous change, in the same way that geometry is the study of shape, and algebra is the study of generalizati ...
. In 1928, aged 16, Turing encountered
Albert Einstein Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born Theoretical physics, theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for d ...
'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 Newton's laws of motion are three basic Scientific law, laws of classical mechanics that describe the relationship between the motion of an object and the forces acting on it. These laws can be paraphrased as follows: # A body remains at re ...
from a text in which this was never made explicit.


Christopher Morcom

At Sherborne, Turing formed a significant friendship with fellow pupil Christopher Collan Morcom (13 July 1911 – 13 February 1930), 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 Bovines (subfamily Bovinae) comprise a diverse group of 10 genera of medium to large-sized ungulates, including cattle, bison, African buffalo, Bubalus, water buffalos, and the four-horned and spiral-horned antelopes. The evolutionary relationshi ...
, contracted after drinking infected cow's milk some years previously. 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: 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 birthday. A day before the third anniversary of Morcom's death (13 February 1933), he wrote to Mrs. Morcom: Some have speculated that Morcom's death was the cause of Turing's
atheism Atheism, in the broadest sense, is an absence of belief in the existence of Deity, deities. Less broadly, atheism is a rejection of the belief that any deities exist. In an even narrower sense, atheism is specifically the position that ther ...
and
materialism Materialism is a form of philosophical monism which holds matter to be the fundamental substance in nature, and all things, including mental states A mental state, or a mental property, is a state of mind of a person. Mental states compris ...
. 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:


University and work on computability

After Sherborne, Turing studied as an undergraduate from 1931 to 1934 at , where he was awarded first-class honours in mathematics. In 1935, at the age of 22, he was elected a
Fellow A fellow is a concept whose exact meaning depends on context. In learned or professional A professional is a member of a profession or any person who works in a specified professional activity. The term also describes the standards of educ ...
of King's College on the strength of a dissertation in which he proved a version of the
central limit theorem In probability theory Probability theory is the branch of mathematics concerned with probability. Although there are several different probability interpretations, probability theory treats the concept in a rigorous mathematical manner by expre ...
. Unknown to Turing, this version of the theorem had already been proven, in 1922, by Jarl Waldemar Lindeberg. Despite this, the committee found Turing's methods original and so regarded the work worthy of consideration for the fellowship. Abram Besicovitch's report for the committee went so far as to say that if Turing's work had been published before Lindeberg's, it would have been "an important event in the mathematical literature of that year". In 1936, Turing published his paper " On Computable Numbers, with an Application to the Entscheidungsproblem". 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. 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 s. The ''
Entscheidungsproblem In mathematics and computer science, the ' (, ) is a challenge posed by David Hilbert and Wilhelm Ackermann in 1928. The problem asks for an algorithm that considers, as input, a statement and answers "Yes" or "No" according to whether the statem ...
'' (decision problem) was originally posed by German mathematician
David Hilbert David Hilbert (; ; 23 January 1862 – 14 February 1943) was a German mathematician, one of the most influential mathematicians of the 19th and early 20th centuries. Hilbert discovered and developed a broad range of fundamental ideas in many a ...
in 1928. Turing proved that his "universal computing machine" would be capable of performing any conceivable mathematical computation if it were representable as an . 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 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". Although
Turing's proof Turing's proof is a proof by Alan Turing Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalyst, philosopher, and theoretical biologist. Turing was highly infl ...
was published shortly after
Alonzo Church Alonzo Church (June 14, 1903 – August 11, 1995) was an American mathematician, computer scientist, list of logicians, logician, philosopher, professor and editor who made major contributions to mathematical logic and the foundations of theoreti ...
's equivalent proof using his
lambda calculus Lambda calculus (also written as ''λ''-calculus) is a formal system in mathematical logic for expressing computability, computation based on function Abstraction (computer science), abstraction and function application, application using variable ...
, Turing's approach is considerably more accessible and intuitive than Church's. It also included a notion of a 'Universal Machine' (now known as a
universal Turing machine In computer science, a universal Turing machine (UTM) is a Turing machine that can simulate an arbitrary Turing machine on arbitrary input. The universal machine essentially achieves this by reading both the description of the machine to be simu ...
), 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 In computability theory, the Church–Turing thesis (also known as computability thesis, the Turing–Church thesis, the Church–Turing conjecture, Church's thesis, Church's conjecture, and Turing's thesis) is a thesis A thesis (plura ...
, Turing machines and the lambda calculus are capable of computing anything that is computable.
John von Neumann John von Neumann (; hu, Neumann János Lajos, ; December 28, 1903 – February 8, 1957) was a Hungarian-American mathematician, physicist, computer scientist, engineer and polymath. He was regarded as having perhaps the widest cover ...
acknowledged that the central concept of the modern computer was due to Turing's paper. To this day, Turing machines are a central object of study in
theory of computation In theoretical computer science and mathematics, the theory of computation is the branch that deals with what problems can be solved on a model of computation, using an algorithm, how algorithmic efficiency, efficiently they can be solved or t ...
. From September 1936 to July 1938, Turing spent most of his time studying under Church at , in the second year as a 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. In June 1938, he obtained his PhD from the Department of Mathematics at Princeton; his dissertation, '' Systems of Logic Based on Ordinals'', introduced the concept of ordinal logic and the notion of relative computing, in which Turing machines are augmented with so-called
oracles An oracle is a person or wikt:agency, agency considered to provide wise and insightful counsel or prophecy, prophetic predictions, most notably including precognition of the future, inspired by Deity, deities. As such, it is a form of divination ...
, allowing the study of problems that cannot be solved by Turing machines. John von Neumann wanted to hire him as his postdoctoral assistant, but he went back to the United Kingdom.


Career and research

When Turing returned to Cambridge, he attended lectures given in 1939 by
Ludwig Wittgenstein Ludwig Josef Johann Wittgenstein ( ; ; 26 April 1889 – 29 April 1951) was an Austrians, Austrian-British people, British philosopher who worked primarily in logic, the philosophy of mathematics, the philosophy of mind, and the philosophy o ...
about the
foundations of mathematics Foundations of mathematics is the study of the philosophy, philosophical and logical and/or algorithmic basis of mathematics, or, in a broader sense, the mathematical investigation of what underlies the philosophical theories concerning the natu ...
. The lectures have been reconstructed verbatim, including interjections from Turing and other students, from students' notes. Turing and Wittgenstein argued and disagreed, with Turing defending
formalism Formalism may refer to: * Form (disambiguation) * Formal (disambiguation) * Legal formalism, legal positivist view that the substantive justice of a law is a question for the legislature rather than the judiciary * Formalism (linguistics) * Scient ...
and Wittgenstein propounding his view that mathematics does not discover any absolute truths, but rather invents them.


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." 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 cipher machine used by
Nazi Germany Nazi Germany (lit. "National Socialist State"), ' (lit. "Nazi State") for short; also ' (lit. "National Socialist Germany") (officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945) was ...
, together with Dilly Knox, a senior GC&CS codebreaker. Soon after the July 1939 meeting near
Warsaw Warsaw ( pl, Warszawa, ), officially the Capital City of Warsaw,, abbreviation: ''m.st. Warszawa'' is the capital and List of cities and towns in Poland, largest city of Poland. The metropolis stands on the Vistula, River Vistula in east-cen ...
at which the Polish Cipher Bureau gave the British and French details of the wiring of Enigma machine's rotors and their method of decrypting Enigma machine's messages, Turing and Knox developed a broader solution. The Polish method relied on an insecure indicator procedure that the Germans were likely to change, which they in fact did in May 1940. Turing's approach was more general, using crib-based decryption for which he produced the functional specification of the
bombe The bombe () was an electro-mechanical In engineering, electromechanics combines processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focuses on the interaction of electrical and mechani ...
(an improvement on the Polish Bomba). On 4 September 1939, the day after the UK declared war on Germany, Turing reported to Bletchley Park, the wartime station of GC&CS.Copeland, 2006 p. 378. Like all others who came to Bletchley, he was required to sign the Official Secrets Act, in which he agreed not to disclose anything about his work at Bletchley, with severe legal penalties for violating the Act. 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 Secure voice (alternatively secure speech or ciphony) is a term in cryptography Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logy, -logia'', "study", respectively) ...
scrambler at 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'' and ''Paper on Statistics of Repetitions'', which were of such value to GC&CS and its successor
GCHQ Government Communications Headquarters, commonly known as GCHQ, is an intelligence Intelligence has been defined in many ways: the capacity for abstraction, logic, understanding, self-awareness, learning Learning is the process ...
that they were not released to the
UK National Archives , type = Non-ministerial department , seal = , nativename = , logo = Logo_of_The_National_Archives_of_the_United_Kingdom.svg , logo_width = 150px , logo_caption = , formed = , preceding1 = , dissolved = , superseding = , juri ...
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 under the Official Secrets Act for some 70 years demonstrated their importance, and their relevance to post-war cryptanalysis: 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". According to historian Ronald Lewin, Jack Good, a cryptanalyst who worked with Turing, said of his colleague: Peter Hilton recounted his experience working with Turing in Hut 8 in his "Reminiscences of Bletchley Park" from ''A Century of Mathematics in America:'' Hilton echoed similar thoughts in the Nova PBS documentary ''Decoding Nazi Secrets''. While working at Bletchley, Turing, who was a talented
long-distance runner Long-distance running, or endurance running, is a form of continuous running over distances of at least . Physiologically, it is largely Aerobic exercise, aerobic in nature and requires endurance, stamina as well as mental strength. Within e ...
, occasionally ran the to London when he was needed for meetings, and he was capable of world-class marathon standards. 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. When asked why he ran so hard in training he replied: Due to the problems of
counterfactual history Counterfactual history (also virtual history) is a form of historiography that attempts to answer the ''wikt:what if, What if?'' questions that arise from counterfactuals, counterfactual conditions. As a method of intellectual enquiry, counterfa ...
, it is hard to estimate the precise effect Ultra intelligence had on the war. However, official war historian
Harry Hinsley Sir Francis Harry Hinsley, (26 November 1918 – 16 February 1998) was an English historian and cryptanalyst. He worked at Bletchley Park during the Second World War and wrote widely on the history of international relations and British Inte ...
estimated that this work shortened the war in Europe by more than two years and saved over 14 million lives. Transcript of a lecture given on Tuesday 19 October 1993 at Cambridge University At the end of the war, a memo was sent to all those who had worked at Bletchley Park, reminding them that the code of silence dictated by the Official Secrets Act did not end with the war but would continue indefinitely. Thus, even though Turing was appointed an
Officer of the Order of the British Empire The Most Excellent Order of the British Empire is a British order of chivalry, rewarding contributions to the arts and sciences, work with charitable and welfare organisations, and public service outside the civil service. It was established o ...
(OBE) in 1946 by King
George VI George VI (Albert Frederick Arthur George; 14 December 1895 – 6 February 1952) was King of the United Kingdom and the Dominions of the British Commonwealth The Commonwealth of Nations, simply referred to as the Commonwealth, is a poli ...
for his wartime services, his work remained secret for many years.


Bombe

Within weeks of arriving at Bletchley Park, Turing had specified an electromechanical machine called the
bombe The bombe () was an electro-mechanical In engineering, electromechanics combines processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focuses on the interaction of electrical and mechani ...
, which could break Enigma more effectively than the Polish '' 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. 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'': a fragment of probable
plaintext In cryptography, plaintext usually means unencrypted information pending input into Cryptographic algorithm, cryptographic algorithms, usually encryption algorithms. This usually refers to data that is transmitted or stored unencrypted. Overvie ...
. For each possible setting of the rotors (which had on the order of 1019 states, or 1022 states for the four-rotor U-boat variant), the bombe performed a chain of logical deductions based on the crib, implemented electromechanically. 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.


Action This Day

By late 1941, Turing and his fellow cryptanalysts Gordon Welchman, Hugh Alexander and Stuart Milner-Barry were frustrated. Building on the 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. On 28 October they wrote directly to
Winston Churchill Sir Winston Leonard Spencer Churchill (30 November 187424 January 1965) was a British statesman, soldier, and writer who served as Prime Minister of the United Kingdom twice, from 1940 to 1945 Winston Churchill in the Second World War, dur ...
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. As Andrew Hodges, biographer of Turing, later wrote, "This letter had an electric effect." Churchill wrote a memo to 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. 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." More than two hundred bombes were in operation by the end of the war.


Hut 8 and the naval Enigma

Turing decided to tackle the particularly difficult problem of German naval Enigma "because no one else was doing anything about it and I could have it to myself". In December 1939, Turing solved the essential part of the naval indicator system, which was more complex than the indicator systems used by the other services. That same night, he also conceived of the idea of '' Banburismus'', a sequential statistical technique (what
Abraham Wald Abraham Wald (; hu, Wald Ábrahám, yi, אברהם וואַלד;  – ) was a Jewish Hungarians, Hungarian mathematician who contributed to decision theory, geometry, and econometrics and founded the field of statistical sequential analysi ...
later called
sequential analysis In statistics Statistics (from German language, German: ''wikt:Statistik#German, Statistik'', "description of a State (polity), state, a country") is the discipline that concerns the collection, organization, analysis, interpretation, and ...
) 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". For this, he invented a measure of weight of evidence that he called the '' ban''. ''Banburismus'' could rule out certain sequences of the Enigma rotors, substantially reducing the time needed to test settings on the bombes. 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 Cryptanalysis of the Lorenz cipher was the process that enabled the British to read high-level German army messages during World War II. The British Government Communications Headquarters#Government Code and Cypher School (GC&CS), Government Cod ...
. Turing travelled to the United States in November 1942 and worked with US Navy cryptanalysts on the naval Enigma and bombe construction in Washington; he also visited their Computing Machine Laboratory in
Dayton, Ohio Dayton () is the List of cities in Ohio, sixth-largest city in the U.S. state of Ohio and the county seat of Montgomery County, Ohio, Montgomery County. A small part of the city extends into Greene County, Ohio, Greene County. The 2020 United S ...
. Turing's reaction to the American bombe design was far from enthusiastic: During this trip, he also assisted at
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company A com ...
with the development of secure speech devices. He returned to Bletchley Park in March 1943. During his absence, 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. Alexander wrote of Turing's contribution:


Turingery

In July 1942, Turing devised a technique termed '' Turingery'' (or jokingly ''Turingismus'') for use against the
Lorenz cipher The Lorenz SZ40, SZ42a and SZ42b were German rotor Rotor may refer to: Science and technology Engineering *Rotor (electric), the non-stationary part of an alternator or electric motor, operating with a stationary element so called the stator ...
messages produced by the Germans' new ''Geheimschreiber'' (secret writer) machine. This was a
teleprinter A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point (telecommunications), point-to-point and point- ...
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. He also introduced the Tunny team to
Tommy Flowers Thomas Harold Flowers MBE (22 December 1905 – 28 October 1998) was an English engineer with the British General Post Office. During World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a wor ...
who, under the guidance of Max Newman, went on to build the
Colossus computer Colossus was a set of computers developed by British cryptanalysis, codebreakers in the years 1943–1945 to help in the cryptanalysis of the Lorenz cipher. Colossus used vacuum tube, thermionic valves (vacuum tubes) to perform Boolean algebra ...
, the world's first programmable digital electronic computer, which replaced a simpler prior machine (the Heath Robinson), and whose superior speed allowed the statistical decryption techniques to be applied usefully to the messages. 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 Cryptanalysis of the Lorenz cipher was the process that enabled the British to read high-level German army messages during World War II. The British Government Communications Headquarters#Government Code and Cypher School (GC&CS), Government Cod ...
, but he was not directly involved in the Colossus development.


Delilah

Following his work at
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company A com ...
in the US, 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 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 Secure voice (alternatively secure speech or ciphony) is a term in cryptography Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logy, -logia'', "study", respectively) ...
communications machine codenamed ''
Delilah Delilah ( ; , meaning "delicate";Gesenius's ''Hebrew-Chaldee Lexicon'' ar, دليلة, Dalīlah; grc, label=Ancient Greek, Greek, Δαλιδά, Dalidá) is a woman mentioned in the sixteenth chapter of the Book of Judges in the Hebrew Bible. ...
''. 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 Sir Winston Leonard Spencer Churchill (30 November 187424 January 1965) was a British statesman, soldier, and writer who served as Prime Minister of the United Kingdom twice, from 1940 to 1945 Winston Churchill in the Second World War, dur ...
speech, Delilah was not adopted for use. 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

Between 1945 and 1947, Turing lived in Hampton, London, while he worked on the design of the ACE (Automatic Computing Engine) at the National Physical Laboratory (NPL). He presented a paper on 19 February 1946, which was the first detailed design of a
stored-program computer A stored-program computer is a computer that stores Instruction (computer science), program instructions in electronically or optically accessible memory. This contrasts with systems that stored the program instructions with plugboards or simila ...
.
Von Neumann Von Neumann may refer to: * John von Neumann John von Neumann (; hu, Neumann János Lajos, ; December 28, 1903 – February 8, 1957) was a Hungarian-American mathematician, physicist, computer scientist, engineer and polymath. He w ...
'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". Although ACE was a feasible design, the effect of the Official Secrets Act surrounding the wartime work at Bletchley Park made it impossible for Turing to explain the basis of his analysis of how a computer installation involving human operators would work. This 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. While he was at Cambridge, the
Pilot ACE The Pilot ACE (Automatic Computing Engine) was one of the first computers built in the United Kingdom. Built at the National Physical Laboratory (United Kingdom), National Physical Laboratory (NPL) in the early 1950s, it was also one of the earl ...
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 The DEUCE (''Digital Electronic Universal Computing Engine'') was one of the earliest United Kingdom, British commercially available computers, built by English Electric from 1955. It was the production version of the Pilot ACE, itself a cut-do ...
and the American
Bendix G-15 The Bendix G-15 is a computer introduced in 1956 by the Bendix Corporation, Computer Division, Los Angeles, California. It is about and weighs about . The G-15 has a drum memory of 2,160 29-bit words, along with 20 words used for special purpos ...
. The full version of Turing's ACE was not built until after his death. According to the memoirs of the German computer pioneer Heinz Billing from the
Max Planck Institute for Physics The Max Planck Institute for Physics (MPP) is a physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its motion and behavior through Spacetime, space and time, and the related e ...
, published by Genscher, Düsseldorf, there was a meeting between Turing and
Konrad Zuse Konrad Ernst Otto Zuse (; 22 June 1910 – 18 December 1995) was a German civil engineer, List of pioneers in computer science, pioneering computer scientist, inventor and businessman. His greatest achievement was the world's first programmab ...
. 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 in the 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 stored-program computers—the
Manchester Mark 1 The Manchester Mark 1 was one of the earliest stored-program computers, developed at the Victoria University of Manchester, England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It shares la ...
. 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. During this time, he continued to do more abstract work in mathematics, and in "
Computing Machinery and Intelligence "Computing Machinery and Intelligence" is a seminal paper written by Alan Turing on the topic of artificial intelligence. The paper, published in 1950 in ''Mind (journal), Mind'', was the first to introduce his concept of what is now known as the ...
" (''
Mind The mind is the set of faculties responsible for all mental Phenomenon, phenomena. Often the term is also identified with the phenomena themselves. These faculties include thought, imagination, memory, Will (philosophy), will, and Sensation (psy ...
'', October 1950), Turing addressed the problem of artificial intelligence, and proposed an experiment that became known as the
Turing test The Turing test, originally called the imitation game by Alan Turing in 1950, is a test of a machine's ability to artificial intelligence, exhibit intelligent behaviour equivalent to, or indistinguishable from, that of a human. Turing propos ...
, 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. 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 reversed form of the Turing test is widely used on the Internet; the
CAPTCHA A CAPTCHA ( , a contrived acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart") is a type of challenge–response authentication, challenge–response test used in computing to determine whether the user is h ...
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 Chess is a board game between two Player (game), players. It is sometimes called international chess or Western chess to distinguish it from chess variant, related games, such as xiangqi (Chinese chess) and shogi (Japanese chess). The current ...
program for a computer that did not yet exist. By 1950, the program was completed and dubbed the Turochamp. In 1952, he tried to implement it on a
Ferranti Mark 1 The Ferranti Mark 1, also known as the Manchester Electronic Computer in its sales literature, and thus sometimes called the Manchester Ferranti, was produced by British electrical engineering firm Ferranti, Ferranti Ltd. It was the world's fir ...
, 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. According to
Garry Kasparov Garry Kimovich Kasparov (born 13 April 1963) is a Russian chess Grandmaster (chess), grandmaster, former World Chess Champion, writer, political activist and commentator. His peak Elo rating system, rating of 2851, achieved in 1999, was the hi ...
, Turing's program "played a recognizable game of chess". The program lost to Turing's colleague
Alick Glennie Alick Edwards Glennie (1925–2003) was a British computer scientist A computer scientist is a person who is trained in the academic study of computer science. Computer scientists typically work on the theoretical side of computation, as o ...
, although it is said that it won a game against Champernowne's wife, Isabel. 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.


Pattern formation and mathematical biology

When Turing was 39 years old in 1951, he turned to
mathematical biology Mathematical and theoretical biology, or biomathematics, is a branch of biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent ...
, finally publishing his masterpiece "
The Chemical Basis of Morphogenesis "The Chemical Basis of Morphogenesis" is an article that the English mathematician Alan Turing wrote in 1952. It describes how patterns in nature, such as stripes and spirals, can arise naturally from a homogeneous, uniform state. The theory, w ...
" 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". He used systems of
partial differential equations In mathematics, a partial differential equation (PDE) is an equation which imposes relations between the various partial derivatives of a Multivariable calculus, multivariable function. The function is often thought of as an "unknown" to be sol ...
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 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 The second law of thermodynamics is a physical law based on universal experience concerning heat and Energy transformation, energy interconversions. One simple statement of the law is that heat always moves from hotter objects to colder objects ( ...
. Belousov was not aware of Turing's paper in the ''
Philosophical Transactions of the Royal Society ''Philosophical Transactions of the Royal Society'' is a scientific journal published by the Royal Society. In its earliest days, it was a private venture of the Royal Society's secretary. It was established in 1665, making it the first journa ...
''. 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. 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. 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". 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. Later papers were not available until ''Collected Works of A. M. Turing'' was published in 1992.


Personal life


Engagement

In 1941, Turing proposed marriage to Hut 8 colleague
Joan Clarke Joan Elisabeth Lowther Murray, Member of the Order of the British Empire, MBE (''née'' Clarke; 24 June 1917 – 4 September 1996) was an English cryptanalyst and numismatist best known for her work as a Cryptanalysis, code-breaker at Bletchle ...
, 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.


Homosexuality and indecency conviction

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 Oxford Road when he met Murray just outside the 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, and both men were charged with "
gross indecency Gross indecency is a crime in some parts of the English-speaking world, originally used to criminalize Men who have sex with men, sexual activity between men that fell short of sodomy, which required Sexual penetration, penetration. The term was fir ...
" under Section 11 of the
Criminal Law Amendment Act 1885 The Criminal Law Amendment Act 1885 (48 & 49 Vict. c.69), or "An Act to make further provision for the Protection of Women and Girls, the suppression of brothels, and other purposes," was an Act of the Parliament of the United Kingdom, the late ...
. Initial 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. The case, '' Regina v. Turing and Murray,'' was brought to trial on 31 March 1952. Turing was convicted and given a choice between imprisonment and probation. His probation would be conditional on his agreement to undergo
hormonal A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology Physiology (; ) is the scient ...
physical changes designed to reduce
libido Libido (; colloquial: sex drive) is a person's overall sexual drive or desire for Human sexual activity, sexual activity. Libido is influenced by biological, psychological, and social factors. Biologically, the sex hormones and associated neurotr ...
, known as "chemical castration". He accepted the option of injections of what was then called stilboestrol (now known as
diethylstilbestrol Diethylstilbestrol (DES), also known as stilbestrol or stilboestrol, is a nonsteroidal estrogen medication, which is presently rarely used. In the past, it was widely used for a variety of indications, including pregnancy support for those with a ...
or DES), a synthetic
oestrogen Estrogen or oestrogen is a category of sex hormone Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the an ...
; this feminization of his body was continued for the course of one year. The treatment rendered Turing
impotent Erectile dysfunction (ED), also called impotence, is the type of sexual dysfunction in which the Human penis, penis fails to become or stay Erection, erect during Human sexual activity, sexual activity. It is the most common sexual problem in ...
and caused breast tissue to form, 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". Murray was given a conditional discharge. 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 Government Communications Headquarters, commonly known as GCHQ, is an intelligence agency, intelligence and security agency, security organisation responsible for providing signals intelligence (SIGINT) and information assurance (IA) to the G ...
(GCHQ), the British
signals intelligence Signals intelligence (SIGINT) is list of intelligence gathering disciplines, intelligence-gathering by interception of ''Signal, signals'', whether communications between people (communications intelligence—abbreviated to COMINT) or from ele ...
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.


Treasure

In the 1940s, Turing became worried about losing his savings in the event of a German invasion. In order to protect it, he bought two silver bars weighing and worth £250 (in 2022, £8,000 adjusted for inflation, £48,000 at spot price) and buried them in a wood near Bletchley Park. Upon returning to dig them up, Turing found that he was unable to break his own code describing where exactly he had hidden them. This, along with the fact that the area had been renovated, meant that he never regained the silver.


Death

On 8 June 1954, at his house at 43 Adlington Road,
Wilmslow Wilmslow ( ) is a market town and civil parish in the unitary authority of Cheshire East in Cheshire, England, south of Manchester city centre. The population was 24,497 at the 2011 Census. History Toponymy Wilmslow derives its name from Old ...
, Turing's housekeeper found him dead. He had died the previous day at the age of 41.
Cyanide poisoning Cyanide poisoning is poisoning that results from exposure to any of a number of forms of cyanide. Early symptoms include headache, dizziness, tachycardia, fast heart rate, Dyspnea, shortness of breath, and vomiting. This phase may then be follow ...
was established as the cause of death. When his body was discovered, an apple lay half-eaten beside his bed, and although the apple was not tested for cyanide, it was speculated that this was the means by which Turing had consumed a fatal dose. An
inquest An inquest is a judicial inquiry in common law jurisdictions, particularly one held to determine the cause of death, cause of a person's death. Conducted by a judge, jury, or government official, an inquest may or may not require an autopsy carrie ...
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 Walter Elias Disney (; December 5, 1901December 15, 1966) was an American animator, film producer and entrepreneur. A pioneer of the Modern animation in the United States, American animation industry, he introduced several developments in th ...
film ''
Snow White and the Seven Dwarfs "Snow White and the Seven Dwarfs" is a 19th-century German fairy tale that is today known widely across the Western world. The Brothers Grimm published it in 1812 in the first edition of their collection ''Grimms' Fairy Tales'' and numbered as Ta ...
'' (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". Turing's remains were cremated at Woking Crematorium on 12 June 1954, and his ashes were scattered in the gardens of the crematorium, just as his father's had been. Philosopher 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
electroplate Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal A metal (from ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly p ...
gold onto spoons. The
potassium cyanide Potassium cyanide is a compound with the chemical formula, formula KCN. This colorless crystalline salt, similar in appearance to sugar, is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller a ...
was used to 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. Furthermore, 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 before his death. He even set down a list of tasks that he intended to complete upon returning to his office after the holiday weekend. Turing's mother believed that the ingestion was accidental, resulting from her son's careless storage of laboratory chemicals. Biographer Andrew Hodges theorised that Turing arranged the delivery of the equipment to deliberately allow his mother
plausible deniability Plausible deniability is the ability of people, typically senior officials in a formal or informal chain of command, to denial, deny knowledge of or responsibility for any damnable actions committed by members of their organizational hierarchy. Th ...
with regard to any suicide claims. It has been suggested that Turing's belief in
fortune-telling Fortune telling is the practice of prediction, predicting information about a person's life.J. Gordon Melton, Melton, J. Gordon. (2008). ''The Encyclopedia of Religious Phenomena''. Visible Ink Press. pp. 115-116. The scope of fortune telling ...
may have caused his depressed mood. As a youth, Turing had been told by a fortune-teller that he would be a genius. In mid-May 1954, shortly before his death, Turing again decided to consult a fortune-teller during a day-trip to St Annes-on-Sea with the Greenbaum family. According to the Greenbaums' daughter, Barbara:


Government apology and pardon

In August 2009, British programmer
John Graham-Cumming John Graham-Cumming is a British software engineer and writer best known for starting a successful petition to the Government of the United Kingdom asking for an apology for its persecution of Alan Turing. , he serves as Chief Technology Officer ...
started a petition urging the British government to apologise for Turing's prosecution as a homosexual. The petition received more than 30,000 signatures. The Prime Minister, , acknowledged the petition, releasing a statement on 10 September 2009 apologising and describing the treatment of Turing as "appalling": In December 2011, William Jones and his Member of Parliament, John Leech, created an e-petition requesting that the British government
pardon A pardon is a government decision to allow a person to be relieved of some or all of the legal consequences resulting from a criminal conviction. A pardon may be granted before or after conviction for the crime, depending on the laws of the ju ...
Turing for his conviction of "gross indecency": The petition gathered over 37,000 signatures, and was submitted to Parliament by the Manchester MP John Leech but the request was discouraged by Justice Minister Lord McNally, who said: John Leech, the MP for Manchester Withington (2005–15), submitted several bills to Parliament 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. Leech continued to take the bill through Parliament and campaigned for several years, gaining the public support of numerous leading scientists, including Stephen Hawking. At the British premiere of a film based on Turing's life, ''
The Imitation Game ''The Imitation Game'' is a 2014 American historical drama A historical drama (also period drama, costume drama, and period piece) is a work set in a past time period, usually used in the context of film and television. Historical drama in ...
'', the producers thanked Leech for bringing the topic to public attention and securing Turing's pardon. 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. On 26 July 2012, a bill was introduced in the
House of Lords The House of Lords, also known as the House of Peers, is the Bicameralism, upper house of the Parliament of the United Kingdom. Membership is by Life peer, appointment, Hereditary peer, heredity or Lords Spiritual, official function. Like the ...
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. Late in the year in a letter to ''
The Daily Telegraph ''The Daily Telegraph'', known online and elsewhere as ''The Telegraph'', is a national British daily broadsheet newspaper published in London by Telegraph Media Group and distributed across the United Kingdom and internationally. It was fou ...
'', the physicist Stephen Hawking and 10 other signatories including the Astronomer Royal Lord Rees,
President of the Royal Society The president of the Royal Society (PRS) is the elected Head of the Royal Society of London who presides over meetings of the society's council. After informal meetings at Gresham College, the Royal Society was officially founded on 28 November ...
Sir
Paul Nurse Sir Paul Maxime Nurse (born 25 January 1949) is an English geneticist, former President of the Royal Society and Chief Executive and Director of the Francis Crick Institute. He was awarded the 2001 Nobel Prize in Physiology or Medicine along w ...
, Lady Trumpington (who worked for Turing during the war) and Lord Sharkey (the bill's sponsor) called on Prime Minister
David Cameron David William Donald Cameron (born 9 October 1966) is a British former politician who served as Prime Minister of the United Kingdom from 2010 to 2016 and Leader of the Conservative Party (UK), Leader of the Conservative Party from 2005 to ...
to act on the pardon request. The government indicated it would support the bill, and it passed its third reading in the House of Lords in October. At the bill's second reading in the
House of Commons The House of Commons is the name for the elected lower house of the bicameral parliaments of the United Kingdom and Canada. In both of these countries, the Commons holds much more legislative power than the nominally upper house of parliament. T ...
on 29 November 2013, Conservative MP
Christopher Chope Sir Christopher Robert Chope (born 19 May 1947) is a British barrister A barrister is a type of lawyer in common law jurisdiction (area), jurisdictions. Barristers mostly specialise in courtroom advocacy and litigation. Their tasks include ...
objected to the bill, delaying its passage. The bill was due to return to the House of Commons on 28 February 2014, but before the bill could be debated in the House of Commons, the government elected to proceed under the
royal prerogative of mercy In the Kingdom of England, English and United Kingdom, British tradition, the royal prerogative of mercy is one of the historic royal prerogatives of the British monarch, by which they can grant pardons (informally known as a royal pardon) to c ...
. On 24 December 2013, signed a pardon for Turing's conviction for "gross indecency", with immediate effect. Announcing the pardon, Lord Chancellor
Chris Grayling Christopher Stephen Grayling (born 1 April 1962) is a British Conservative Party (UK), Conservative Party politician and author who served as Secretary of State for Transport from 2016 to 2019. He has served as Member of Parliament (United King ...
said Turing deserved to be "remembered and recognised for his fantastic contribution to the war effort" and not for his later criminal conviction. The Queen officially pronounced Turing pardoned in August 2014. The Queen's action is only the fourth royal pardon granted since the conclusion of the Second World War. 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. 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". 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.


Legacy


Awards, honours, and tributes

Turing was appointed an officer of the
Order of the British Empire The Most Excellent Order of the British Empire is a British order of chivalry, rewarding contributions to the arts and sciences, work with charitable and welfare organisations, and public service outside the civil service. It was established o ...
in 1946. He was also elected a Fellow of the Royal Society (FRS) in 1951. Turing has been honoured in various ways in
Manchester Manchester () is a city in Greater Manchester, England. It had a population of 552,000 in 2021. It is bordered by the Cheshire Plain to the south, the Pennines to the north and east, and the neighbouring city of City of Salford, Salford to ...
, the city where he worked towards the end of his life. In 1994, a stretch of the A6010 road (the
Manchester Manchester () is a city in Greater Manchester, England. It had a population of 552,000 in 2021. It is bordered by the Cheshire Plain to the south, the Pennines to the north and east, and the neighbouring city of City of Salford, Salford to ...
city intermediate ring road) was named "Alan Turing Way". A bridge carrying this road was widened, and carries the name Alan Turing Bridge. A 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. 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. 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 Bertrand Arthur William Russell, 3rd Earl Russell, (18 May 1872 – 2 February 1970) was a British mathematician, philosopher, logician, and public intellectual. He had a considerable influence on mathematics, logic, set theory, linguistics, ar ...
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 Amstrad was a British electronics company, founded in 1968 by Alan Sugar at the age of 21. The name is a contraction of Alan Michael Sugar Trading. It was first listed on the London Stock Exchange in April 1980. During the late 1980s, Amstrad ...
computer under the
plinth A pedestal (from French ''piédestal'', Italian ''piedistallo'' 'foot of a stall') or Wikt:plinth, plinth is a support at the bottom of a statue, vase, column, or certain altars. Smaller pedestals, especially if round in shape, may be called S ...
as a tribute to "the godfather of all modern computers". In 1999, ''
Time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past, through the present, into the future. It is a component quantity of various me ...
'' magazine named Turing as one of the 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." A blue plaque was unveiled at King's College, Cambridge on the centenary of his birth on 23 June 2012 and is now installed at the college's Keynes Building on King's Parade. A high steel sculpture, designed in Turing's honour by Sir
Antony Gormley Sir Antony Mark David Gormley (born 30 August 1950) is a British sculptor. His works include the ''Angel of the North The ''Angel of the North'' is a contemporary sculpture by Antony Gormley, located in Gateshead, Tyne and Wear, Engla ...
, is planned to be installed at King's College, but
Historic England Historic England (officially the Historic Buildings and Monuments Commission for England) is an executive non-departmental public body of the British Government sponsored by the Department for Digital, Culture, Media and Sport. It is tasked ...
deemed the sculpture too abstract for the setting, saying that it "would result in harm, of a less than substantial nature, to the significance of the
listed building In the United Kingdom, a listed building or listed structure is one that has been placed on one of the four statutory lists maintained by Historic England in England, Historic Environment Scotland in Scotland, in Wales, and the Northern Irel ...
s and landscape, and by extension the conservation area". On 25 March 2021, the
Bank of England The Bank of England is the central bank of the United Kingdom and the model on which most modern central banks have been based. Established in 1694 to act as the Kingdom of England, English Government's banker, and still one of the bankers fo ...
publicly unveiled the design for a new £50 note, featuring Turing's portrait, before its official issue on 23 June, Turing's birthday. Turing was selected as the new face of the note in 2019 following a public nomination process.


Centenary celebrations

To mark the 100th anniversary of Turing's birth, the Turing Centenary Advisory Committee (TCAC) co-ordinated the Alan Turing Year in 2012, 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.


Notes and references


Notes


References


Sources

* * * * * * * * * * * * * * * * * ** in * * * * * * * * * * * * * * * * * and * 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 St John's College is a Colleges of the University of Cambridge, constituent college of the University of Cambridge founded by the House of Tudor, Tudor matriarch Lady Margaret Beaufort. In constitutional terms, the college is a charitable corpo ...
). 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, as well as a never-before-published memoir by Turing's older brother John F. Turing. * This 1986 Hugh Whitemore play tells the story of Turing's life and death. In the original West End and Broadway runs,
Derek Jacobi Sir Derek George Jacobi (; born 22 October 1938) is an English actor. He has appeared in various stage productions of William Shakespeare such as ''Hamlet'', ''Much Ado About Nothing'', ''Macbeth'', ''Twelfth Night'', ''The Tempest'', ''King ...
played Turing and he recreated the role in a 1997 television film based on the play made jointly by the BBC and WGBH, Boston. The play is published by Amber Lane Press,
Oxford Oxford () is a city in England. It is the county town and only city of Oxfordshire. In 2020, its population was estimated at 151,584. It is north-west of London, south-east of Birmingham and north-east of Bristol. The city is home to the Un ...
, ASIN: B000B7TM0Q * *


Further reading


Articles

* * * * * *


Books

* * * * * (originally published in 1983); basis of the film ''
The Imitation Game ''The Imitation Game'' is a 2014 American historical drama A historical drama (also period drama, costume drama, and period piece) is a work set in a past time period, usually used in the context of film and television. Historical drama in ...
'' * (originally published in 1959 by W. Heffer & Sons, Ltd)


External links


Oral history interview with Nicholas C. Metropolis
Charles Babbage Institute The IT History Society (ITHS) is an organization that supports the history and scholarship of information technology by encouraging, fostering, and facilitating archival and historical research. Formerly known as the Charles Babbage Foundation, ...
, University of Minnesota. Metropolis was the first director of computing services at
Los Alamos National Laboratory Los Alamos National Laboratory (often shortened as Los Alamos and LANL) is one of the sixteen research and development Laboratory, laboratories of the United States Department of Energy National Laboratories, United States Department of Energy ...
; topics include the relationship between Turing and
John von Neumann John von Neumann (; hu, Neumann János Lajos, ; December 28, 1903 – February 8, 1957) was a Hungarian-American mathematician, physicist, computer scientist, engineer and polymath. He was regarded as having perhaps the widest cover ...

How Alan Turing Cracked The Enigma Code
Imperial War Museums
Alan Turing Year

CiE 2012: Turing Centenary Conference

Science in the Making
Alan Turing's papers in the Royal Society's archives
Alan Turing
site maintained by Andrew Hodges including
short biography

AlanTuring.net – Turing Archive for the History of Computing
by Jack Copeland
The Turing Archive
nbsp;– contains scans of some unpublished documents and material from the King's College, Cambridge archive
Alan Turing Papers
University of Manchester Library, Manchester *
Sherborne School Archives
– holds papers relating to Turing's time at Sherborne School
Alan Turing plaques
recorded on openplaques.org
Alan Turing
archive on New Scientist {{DEFAULTSORT:Turing, Alan Mathison 1912 births 1954 suicides 20th-century English mathematicians 20th-century atheists 20th-century English philosophers Academics of the University of Manchester Academics of the University of Manchester Institute of Science and Technology Alumni of King's College, Cambridge Artificial intelligence researchers Bayesian statisticians Bletchley Park people British anti-fascists British cryptographers British people of World War II Computability theorists Computer designers English atheists English computer scientists English inventors English logicians English male long-distance runners English people of Irish descent English people of Scottish descent Fellows of King's College, Cambridge Fellows of the Royal Society Former Protestants Foreign Office personnel of World War II Gay academics Gay scientists Gay sportsmen GCHQ people History of artificial intelligence History of computing in the United Kingdom LGBT-related suicides LGBT mathematicians LGBT philosophers LGBT scientists from the United Kingdom LGBT sportspeople from England LGBT track and field athletes Officers of the Order of the British Empire People educated at Sherborne School People from Maida Vale People from Wilmslow People convicted for homosexuality in the United Kingdom People who have received posthumous pardons Princeton University alumni Recipients of British royal pardons Theoretical biologists Theoretical computer scientists Deaths by cyanide poisoning Suicides by cyanide poisoning Suicides in England