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The man who counted

Alan Turing, born 100 years ago, created the theoretical basis for computer science

NPL ARCHIVE, SCIENCE MUSEUMThe word computer was only used in one sense at the beginning of the 20th century. The meaning indicated a person who made calculations, a professional involved in the use of algorithms. Computing required long hours of great concentration with only an abacus or an adding machine as instruments. In 1936, Alan Mathison Turing, an Englishman born 100 years ago, wrote an academic paper on logic suggesting an abstract mathematical structure that he referred to as “a universal machine” capable of doing any kind of calculation. The article On Computable Numbers, with an Application to the Entscheidungsproblem, published at the beginning of 1937, is considered the foundation of computer science.

When he wrote On Computable Numbers, he did not have in mind a machine that might eventually be constructed, but rather which aimed to solve a logic problem. “His universal machine, also known as ‘Turing’s machine,’ was in fact a metaphor of ideas later used to build a computer,” says mathematician Ubiratan D’Ambrosio, professor emeritus of the State University of Campinas (Unicamp).

In the same article, Turing proposed a solution to a mathematical question – Entscheidungsproblem (decision problem): certain problems cannot be solved by theoretical machines or computers. The Englishman was not the only one to think about this. In 1936 as well, the American logician Alonzo Church, at the time already a PhD, independently wrote and published an article with the same conclusion. The 25 year old Turing did his PhD under Church’s guidance at the University of Princeton in the United States. He returned to England in 1939 and worked for the government. It all began when the British military learned of his fondness for creating and deciphering codes and called him to work with a group of scientists on a secret project. The aim was to decipher German orders coded by a machine called Enigma and sent to the submarines patrolling the Atlantic. The question was crucial for the English, as German submarines prevented the movement of British ships, almost isolating England. Turing was able to crack the code by perfecting an enormous decoder called Bomba, the first version of which was built by Polish scientists. As a result, the English fleet was no longer surprised by Third Reich attacks.


ACE prototype from 1952, Turing’s project that was later abandonedNATIONAL PHYSICAL LABORATORY © CROWN COPYRIGHT / SCIENCE PHOTO LIBRARY/ SPL DC / LATINSTOCK

“Besides being a brilliant theoretician, Turing had a strong practical side,” says Newton da Costa, a retired mathematician from the University of São Paulo and philosophy professor at the Federal University of Santa Catarina. For example, among other projects, he created the prototype ACE to “attack complex problems.” The abbreviation ACE stands for Automatic Computing Engine and was a sort of ancestor to the computer.

In 1950, the mathematician published his seminal article Computing Machinery and Intelligence. “I suggest that we consider this question: ‘can machines think?’,” he wrote in the opening phrase. “Turing introduces a discussion about whether it is justifiable to call a computer an electronic brain and sets the foundations of what was later to become artificial intelligence,” says D’Ambrosio. “With publications such as this one, he influenced all of contemporary culture and not only logic and mathematics,” says Costa.

Turing’s personal life was far more complicated than his academic career. Being homosexual, he was imprisoned in 1952 for severe indecency with another man – based on the same 1885 law that took Oscar Wilde to prison in 1895. The mathematician agreed to swap the penalty for chemical castration and to take estrogen “to cure” his homosexuality. In 1954, Turning passed away after biting a cyanide poisoned apple at the age of 41. According to English police, it was suicide. His family and friends never accepted this version.