Alan Mathison Turing (23 June 1912 – 7 June 1954) was one of the greatest mathematicians, logicians, cryptographers and theoretical computer scientists in history. Born in London and educated at some of the United Kingdom's most prestigious institutions, Turing made fundamental contributions that laid the groundwork for modern computing, artificial intelligence and cryptography.
His work during the Second World War at Bletchley Park, where he led the team that broke the Nazi Enigma code, is regarded by many historians as one of the decisive factors that shortened the conflict, helping to save millions of lives. Despite this, his life was marked by a tragic injustice: convicted of homosexuality at a time when it was still a criminal offence in the United Kingdom, Turing was subjected to a humiliating treatment that preceded his death at the age of just 41.
Today Turing is celebrated as a British national hero and a symbol for LGBTQ+ rights. His story stands both as a warning about discrimination and as an extraordinary testament to the power of scientific genius.
«Sometimes it is the people no one imagines anything of who do the things that no one can imagine.» — Alan Turing
The formative years (1912–1936)
Childhood and family
Alan Turing was born on 23 June 1912 in Paddington, London, to Julius Mathison Turing, an officer of the Indian Civil Service, and Ethel Sara Stoney. Since his father worked in India, Turing spent much of his childhood with his mother and elder brother John in England.
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1913–1921
the family moved to St Leonards-on-Sea, where Turing showed an early talent for mathematics and science, despite being a shy and solitary child.
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1922–1926
he attended Hazelhurst Preparatory School, in Sussex, developing a passion for chemistry and astronomy.
College and Cambridge
Between 1926 and 1931 Turing attended Sherborne School, in Dorset: despite a rigid curriculum poorly suited to his brilliant mind, he excelled in mathematics, catching the attention of a science teacher who encouraged him to pursue advanced study.
In 1931 he won a scholarship to King's College, University of Cambridge, where he studied mathematics. He graduated with distinction in 1934 and was elected a Fellow of King's College the following year.
The doctorate at Princeton and the Turing machine
Between 1936 and 1938 Turing moved to Princeton University, in the United States, to complete a doctorate in mathematics. Under the supervision of Alonzo Church, he developed the concept of the Turing machine, a theoretical model of computation that would go on to revolutionise computer science.
Cryptography and the Second World War
Recruitment to Bletchley Park
When the Second World War broke out in 1939, Turing was recruited by the Government Code and Cypher School (GC&CS), the British cryptography agency, and assigned to Bletchley Park, an estate in Buckinghamshire that became the nerve centre of the Allied effort to break enemy codes.
The Enigma challenge
The Enigma machine was an electromechanical cipher device used by the Nazis for military communications and considered unbreakable because of its complexity: multiple rotors (three or four) that changed electrical connections with every keystroke, an astronomical number of possible settings, and daily changes to those settings that made traditional cryptanalysis useless.
Turing's «bombe» and the breaking of Enigma
Turing arrived at Bletchley Park in September 1939 and joined Hut 8, the group tasked with breaking the German Navy's messages. Together with Gordon Welchman, he refined an earlier Polish electromechanical device, the «bombe», capable of simulating Enigma's settings and identifying the correct one.
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1940
the team succeeds in breaking Enigma traffic, giving the Allies vital intelligence on German U-boat routes in the Atlantic and allowing the Royal Navy to protect supply convoys.
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1941
the Germans introduce a more complex naval version of Enigma (M4); the team develops new methods to break it by the end of the year.
Impact on the war
According to several historical estimates, the work carried out at Bletchley Park helped shorten the conflict by a number of years and saved a very large number of lives, while also helping to avert a possible British defeat in the Battle of the Atlantic.
«Turing's contribution to the Allied victory in the Second World War was immeasurable. Without him, the course of history could have been entirely different.» — commonly attributed to Winston Churchill
Secrecy and the vow of silence
Because of Britain's Official Secrets Act, Turing was never able to speak openly about his work at Bletchley Park: the United Kingdom's role in breaking Enigma was only made public in the 1970s.
The Turing machine and the foundations of theoretical computing
The 1936 paper: «On Computable Numbers»
In 1936, while still at Cambridge, Turing published the paper «On Computable Numbers, with an Application to the Entscheidungsproblem». In it he defined the concept of the Turing machine — an abstract mathematical model capable of carrying out any algorithm —, addressed the decidability problem posed by David Hilbert, and laid the foundations of computability theory, introducing notions such as the algorithm and computability itself.
What is a Turing machine?
A Turing machine is a theoretical model made up of an infinite tape divided into cells, each of which can hold a symbol, a read/write head that can move along the tape, and a table of states that determines the machine's actions based on its current state and the symbol read.
Despite its simplicity, a Turing machine can simulate any modern computer, given sufficient time and memory — the principle underlying the so-called Church-Turing thesis, according to which every computable function can be computed by a Turing machine.
Influence on modern computing
Turing's work deeply influenced the architecture of the first digital computers, such as the Colossus at Bletchley Park and the ENIAC, and laid the conceptual groundwork for notions now central to programming languages, such as loops, conditionals and variables.
The Turing test and artificial intelligence
The 1950 paper: «Computing Machinery and Intelligence»
In 1950 Turing published another landmark paper, «Computing Machinery and Intelligence», in which he asked whether machines could think and proposed a method for assessing machine intelligence, now known as the Turing test.
How the Turing test works
In its classic formulation, a human judge holds a written conversation with two interlocutors, a machine and a person: if the judge cannot reliably tell the machine apart from the human, the machine can, in this operational sense, be considered intelligent.
«If a machine can fool a human being into believing it is human, then it can be said, in an operational sense, to be intelligent.» — central idea of Turing's 1950 paper
Objections to the test and its legacy
In his essay, Turing anticipated and discussed several objections to his own test, including the idea that only a being with a soul can think, that a machine could never err the way a human does, or that it could never possess genuine consciousness. The debate he opened continues to this day.
In the following decades, various programs attempted to pass more or less rigorous versions of the test — from the well-known ELIZA, created by Joseph Weizenbaum in the 1960s, to the annual Loebner Prize competition, established in 1990. Today's large language models are capable of holding complex conversations, but the debate over what counts as genuine intelligence remains open.
Persecution and the final years (1952–1954)
Arrest for homosexuality
In January 1952 Turing reported a burglary at his home in Wilmslow, Cheshire. During the investigation, police discovered that he had been in a relationship with a young man. At the time, male homosexuality was illegal in the United Kingdom under a nineteenth-century public decency law.
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March 1952
Turing was charged with «gross indecency» and put on trial.
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31 March 1952
he pleaded guilty and was sentenced to twelve months of mandatory hormonal treatment — a form of chemical castration — as an alternative to prison.
Consequences of the conviction
As a result of the conviction, Turing lost his security clearance and could no longer work with the government agency that succeeded the GC&CS. The hormonal treatment he underwent weakened him physically and worsened his psychological state, while the social stigma attached to his conviction led some colleagues and acquaintances to distance themselves from him.
Death
On 7 June 1954 Turing was found dead at his home. The official cause of death was cyanide poisoning. Most historians believe it was suicide, linked to depression and the persecution he had suffered, although alternative theories have been put forward over the years, none supported by concrete evidence.
«Alan Turing died because the State he had helped save betrayed him.» — a recurring theme in the campaigns for his posthumous recognition
Death and the posthumous pardon
The funeral
Turing was cremated on 12 June 1954 and his ashes were scattered in the crematorium garden. No official honours were paid at the time of his death, partly because of the secret nature of his wartime work.
The royal pardon
It was only in 2013, following a long campaign led by activists and scientists, that Queen Elizabeth II granted Turing a posthumous royal pardon for his 1952 conviction. In 2017 a law informally known as the «Turing Law» came into force in the United Kingdom, extending posthumous pardons to thousands of men convicted of similar offences under the same statutes.
Memorials and honours
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1999
Time Magazine named him one of the hundred most influential people of the twentieth century.
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2002
he was voted among the greatest Britons of all time in a BBC poll.
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2011
a bronze statue of Turing, seated on a bench holding an apple, was unveiled at Bletchley Park.
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2021
his face entered circulation on the British £50 note, making him the first openly recognised LGBTQ+ scientist to appear on a UK banknote.
Turing's legacy: impact and honours
Scientific contributions at a glance
| Field | Contribution | Impact |
|---|---|---|
| Cryptography | Breaking Enigma at Bletchley Park | Helped shorten the Second World War |
| Theoretical computing | The Turing machine | Laid the conceptual foundations of modern computers |
| Artificial intelligence | The Turing test | Defined a still-debated criterion for assessing machines |
| Mathematical biology | Models of morphogenesis (1952) | Helped explain the formation of certain patterns in nature |
Academic honours
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1936
elected a Fellow of King's College, Cambridge.
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1945
awarded an OBE for his secret wartime work.
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1951
elected a Fellow of the Royal Society.
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1966
the Turing Award, often called the «Nobel Prize of computing», is established in his honour.
Institutions named after Turing
His name is now attached to numerous institutions: the Alan Turing Institute in London, the UK's national centre for data science and artificial intelligence, founded in 2015; the Turing Award, presented annually by the Association for Computing Machinery; and the computer science department at the University of Manchester, where Turing worked from 1948 to 1954.
Turing in popular culture
Films and documentaries
- «The Imitation Game» (2014), starring Benedict Cumberbatch as Turing, winner of the Academy Award for Best Adapted Screenplay.
- «Breaking the Code» (1996), a television mini-series starring Derek Jacobi.
- «Enigma» (2001), a film set against the backdrop of Bletchley Park.
Books
- «Alan Turing: The Enigma» (1983) by Andrew Hodges, the definitive biography that inspired «The Imitation Game».
- «The Annotated Turing» (2008) by Charles Petzold, a guided analysis of the 1936 paper.
Monuments and places of memory
- The Bletchley Park statue (2002), showing Turing seated on a bench with an apple in hand.
- The statue in Sackville Park, Manchester (2001).
- Alan Turing Way, a road in Manchester named in his honour.
Conclusion
Alan Turing was a scientific genius whose work had a profound impact on the modern world. Despite the injustices he suffered, his contribution to mathematics, cryptography and the birth of computer science remains fundamental.
His story remains a warning about the dangers of discrimination, but also a testament to the human mind's capacity to change, through sheer insight, the course of history.
«Sometimes it is the people no one imagines anything of who do the things that no one can imagine.» — commonly attributed to Alan Turing
Photo credits
- Cover: photo by Antoine Taveneaux, CC BY-SA 3.0, via Wikimedia Commons
- Image 1: photo, unknown author, public domain, via Wikimedia Commons
- Image 2: photo by Lmno, CC BY-SA 3.0, via Wikimedia Commons
