Alan Turing

Alan Mathison Turing (23 June 1912 – 7 June 1954) was an English logician and mathematician, widely regarded as the father of theoretical computer science. He formalised the concepts of algorithm and computation with the Turing machine, a model of a general-purpose computer. His work in cryptanalysis helped the Allies of World War II decipher messages encrypted by the German Enigma machine. He also contributed the Turing test to the philosophy of artificial intelligence and the Turing pattern concept to mathematical and theoretical biology.

Turing was born in London and raised in southern England. He graduated from King's College, Cambridge and earned a doctorate from Princeton University in 1938. During World War II, he worked at the Government Code and Cypher School at Bletchley Park, Britain's codebreaking centre. As head of Hut 8, he focused on decrypting German naval messages. His techniques improved on the pre-war Polish bomba method and hastened cryptanalysis of the Enigma ciphering system. The resulting intelligence, known as Ultra, proved helpful in the Battle of the Atlantic. After the war, he joined the National Physical Laboratory, where he designed the Automatic Computing Engine, an early stored-program computer.

In 1948, Turing joined Max Newman's Computing Machine Laboratory at the University of Manchester, contributing to the development of early Manchester computers. He also turned to mathematical biology, working on the chemical basis of morphogenesis and theorizing chemical oscillators independently of their experimental observation. In 1952, after acknowledging a relationship with another man, Turing was prosecuted. He received probation with conditions and lost his security clearance. He died on 7 June 1954, aged 41.

Turing left a lasting legacy in mathematics, computing, and codebreaking. His wartime work, covered by the Official Secrets Act, went unrecognised during his lifetime. He later received numerous honours and memorials. Following a 2009 campaign, British prime minister Gordon Brown officially apologised for the "appalling way [Turing] was treated", and Queen Elizabeth II granted Turing a pardon in 2013.

The Alan Turing law refers to part of a 2017 UK law that retroactively pardoned men who had been cautioned or convicted under laws that criminalised homosexual acts.

Early life and education

Main article: Christopher Morcom

Alan Turing was born in Maida Vale, London, in 1912, while his father was on leave from the Indian Civil Service in India. His parents wanted their children to grow up in Britain, so they settled in England. Turing's parents often travelled between Hastings and India, and the two brothers stayed with a retired Army couple. As a boy, Turing went to a school in St Leonards-on-Sea, and his headmistress saw that he was very clever. At 13, he went to Sherborne School. Some teachers there wanted him to focus on subjects like the classics, but Turing loved mathematics and science. In 1928, he began to study the work of Albert Einstein.

At Sherborne, Turing became close friends with Christopher Morcom, who shared his interest in science and astronomy. Morcom died suddenly in 1930, which caused Turing great sadness. Turing then studied at King's College, Cambridge, where he earned top marks in mathematics. In 1936, he wrote a paper, "On Computable Numbers, with an Application to the Entscheidungsproblem", that described simple imaginary machines now called Turing machines. He showed that some problems could never be solved by any computer. The paper became one of the most important ideas in computer science. Turing then studied at Princeton University and earned his PhD there in 1938.

Career and research

When Turing returned to Cambridge, he attended lectures given in 1939 by Ludwig Wittgenstein about the foundations of mathematics. Turing defended formalism, while Wittgenstein argued that mathematics does not discover absolute truths but rather invents them. During the Second World War, Turing was a leading participant in breaking German ciphers at Bletchley Park. The historian Asa Briggs 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, concentrating on the cryptanalysis of the Enigma cipher machine used by Nazi Germany. He produced the functional specification of the bombe, an improved version of the Polish Bomba.

Turing's wartime work included several major advances. These included the bombe, a statistical method called Banburismus, and a technique called Turingery for the Lorenz SZ 40/42 cipher machine. Late in the war, he also helped develop a portable secure voice scrambler at Hanslope Park, codenamed Delilah. Turing was appointed an Officer of the Order of the British Empire in 1946 for his wartime services, but his work remained secret for many years. After the war, he worked on the design of the ACE computer at the National Physical Laboratory (NPL). In 1948, he was appointed reader at the University of Manchester, where he worked on the Manchester Mark 1. In "Computing Machinery and Intelligence", he proposed an experiment that became known as the Turing test, a way to decide whether a machine could be called "intelligent." In 1952, he published "The Chemical Basis of Morphogenesis", which studied how patterns and shapes form in living things. He suggested that a reaction–diffusion system could account for "the main phenomena of morphogenesis."

Personal life

In the 1940s, Turing worried that he might lose his savings if Germany invaded. He buried two silver bars in a wood near Bletchley Park, but later he could not work out the clues he had written to find them, and the area had changed, so he never got the silver back. Turing also invented a game called round-the-house chess, which combined chess with running around the house. In 1934, he received a Chad Valley teddy bear, which he named Porgy. He often used the bear in playful ways, and in 1945 he made it an outfit for a Christmas surprise for his niece.

In 1941, Turing proposed marriage to fellow codebreaker Joan Clarke, but the engagement ended after he told her that he was gay. In 1952, Turing was convicted of a crime because of his relationship with a man, which was illegal in the United Kingdom at that time. He accepted a treatment instead of going to prison, and his security clearance was removed. This ended his cryptography work for GCHQ, the British signals intelligence agency, although he kept his academic post.

Death

Turing kept a generally cheerful manner. In February 1954 he prepared his will, removing his brother as executor and naming P. N. Furbank, a close friend. On 8 June his housekeeper found him dead at his home at 43 Adlington Road, Wilmslow. A post-mortem found that he had died on 7 June, aged 41, from cyanide poisoning. A half-eaten apple lay beside his bed. An inquest was held on 9 June. Turing's brother, John, identified the body. Turing was cremated at Woking Crematorium on 12 June, attended by his mother, brother, and Lyn Newman. His ashes were scattered in the crematorium gardens.

The circumstances of Turing's death have been interpreted in different ways. The apple was never tested, but some biographers speculated that it had been laced with cyanide. Andrew Hodges and David Leavitt suggested that Turing may have been re-enacting a scene from the 1937 Disney film Snow White and the Seven Dwarfs, in which the Wicked Queen poisons an apple. Turing's mother never accepted the findings. She believed the poisoning came from careless storage of laboratory chemicals. John W. Dawson Jr. called this explanation "barely plausible." Jack Copeland argued that the evidence was more consistent with accidental cyanide inhalation, perhaps during an electroplating experiment. Hodges proposed that Turing may have made his death appear accidental to spare his mother.

Legacy and reception

Main article: Legacy of Alan Turing

Turing left a large legacy in mathematics and computing. He is honoured with statues and many things named after him, including an annual award for computing innovation. His portrait appears on the Bank of England £50 note, first released on 23 June 2021, his birthday. In a 2019 BBC series, the audience voted Turing the greatest scientist of the 20th century.

In 2009, British programmer John Graham-Cumming started a petition asking the British government to apologise for how Turing was treated for being gay. The prime minister, Gordon Brown, apologised later that year, calling the treatment "appalling." In 2011, John Leech and William Jones created an e-petition asking for a pardon for Turing's conviction. In December 2013, Queen Elizabeth II signed a royal warrant pardoning Turing. Later, the Policing and Crime Act 2017 became known as the Alan Turing law and pardoned 75,000 other men and women who had been convicted under similar old laws.