Alan Turing
Lived: 1912-1954 Domain: Mathematics, computer science, cryptanalysis What they built: The concept of the universal computing machine (Turing machine). The breaking of the Enigma code. The foundations of artificial intelligence. The cost: Prosecuted for homosexuality. Subjected to chemical castration. Died of cyanide poisoning at 41, likely suicide.
The Story
Alan Turing was a mathematician at Cambridge and then at Bletchley Park. In 1936, before any electronic computer existed, he published “On Computable Numbers,” which defined the theoretical concept of a universal machine — a device that could compute anything computable, given the right instructions. This paper is the foundation of computer science. During World War II, he led the effort to break the German Enigma cipher at Bletchley Park. His work is estimated to have shortened the war by years and saved millions of lives. After the war, he worked on early computers and wrote “Computing Machinery and Intelligence” (1950), which proposed the Turing test for machine intelligence. In 1952, he was prosecuted for “gross indecency” — homosexuality was a criminal offense in Britain. He was convicted and given a choice: prison or chemical castration. He chose the chemicals. On June 7, 1954, he was found dead in his home. A half-eaten apple lay beside him, laced with cyanide. He was 41. The British government issued a formal apology in 2009. A royal pardon followed in 2013.
The World They Lived In
Britain during and after the Second World War. Turing broke the Enigma code at Bletchley Park — work so secret it remained classified for decades, arguably shortening the war by two years and saving millions of lives. After the war, he helped build early computers at Manchester and wrote the founding paper on artificial intelligence. But Britain in the 1950s still criminalized homosexuality under Victorian-era law. In 1952, Turing was prosecuted for “gross indecency.” Given the choice between prison and chemical castration, he chose the chemicals. Two years later, he was found dead of cyanide poisoning at 41. A royal pardon came in 2013 — fifty-nine years after the country he saved destroyed him.
What They Named
That computation has a structure that exists independent of any particular machine. The Turing machine is not a physical device — it is a mathematical definition of what it means to compute. He also named the limit: the halting problem proves that no algorithm can determine, for every possible input, whether a given program will halt or run forever. He defined the boundary of what machines can do — and that boundary is structural, not technological. No future machine will solve the halting problem. The limit is permanent.
Connections
- Turing Completeness — his definition of universal computation, the Ecclesia entry in CONSTRUCTION
- Halting Problem — his proof that computation has inherent limits, the Ecclesia entry in FORMAL-LANGUAGE
- Encryption and Hashing — Enigma was encryption; Turing broke it by finding structural weaknesses
- Godel’s Incompleteness Theorems — Godel proved limits of formal systems in 1931; Turing proved limits of computation in 1936 — the same boundary from a different angle
Their Words
“We can only see a short distance ahead, but we can see plenty there that needs to be done.”
“Sometimes it is the people no one imagines anything of who do the things that no one can imagine.”
Every stone was placed by a person. The names matter.