Alan Turing

Alan Turing is one of the founders of information theory, but he was also a tragic figure. He is famous for the Turing test, and for contributions to artificial intelligence. Alan Turing’s ideas are also a contribution to philosophy, because he makes a simple distinction between solvable and unsolvable problems: If a problem can be broken down into simple steps, and after solving these smaller questions, we have a general answer, then a machine can eventually solve it. If this is not doable, then the problem is philosophical and requires a different approach.


(from the BBC Website)

“Alan Turing was born on 23 June, 1912, in London. His father was in the Indian Civil Service and Turing’s parents lived in India until his father’s retirement in 1926. Turing and his brother stayed with friends and relatives in England. Turing studied mathematics at Cambridge University, and subsequently taught there, working in the burgeoning world of quantum mechanics. It was at Cambridge that he developed the proof which states that automatic computation cannot solve all mathematical problems. This concept, also known as the Turing machine, is considered the basis for the modern theory of computation.

In 1936, Turing went to Princeton University in America, returning to England in 1938. He began to work secretly part-time for the British cryptanalytic department, the Government Code and Cypher School. On the outbreak of war he took up full-time work at its headquarters, Bletchley Park.

Here he played a vital role in deciphering the messages encrypted by the German Enigma machine, which provided vital intelligence for the Allies. He took the lead in a team that designed a machine known as a bombe that successfully decoded German messages. He became a well-known and rather eccentric figure at Bletchley.

After the war, Turing turned his thoughts to the development of a machine that would logically process information. He worked first for the National Physical Laboratory (1945-1948). His plans were dismissed by his colleagues and the lab lost out on being the first to design a digital computer. It is thought that Turing’s blueprint would have secured them the honour, as his machine was capable of computation speeds higher than the others. In 1949, he went to Manchester University where he directed the computing laboratory and developed a body of work that helped to form the basis for the field of artificial intelligence. In 1951 he was elected a fellow of the Royal Society.

In 1952, Turing was arrested and tried for homosexuality, then a criminal offense. To avoid prison, he accepted injections of oestrogen for a year, which were intended to neutralize his libido. In that era, homosexuals were considered a security risk as they were open to blackmail. Turing’s security clearance was withdrawn, meaning he could no longer work for GCHQ, the post-war successor to Bletchley Park.

He committed suicide on 7 June, 1954.”

The Turing test

The Turing test was introduced in a famous paper from 1950. Turing argues that the question is not “can computers think?”, because they can’t, but can computers become so good that their performance can’t be distinguished from human performers by an outside observer. “Are there imaginable digital computers which would do well in the imitation game?” They don’t act intelligent, they just simulate intelligent behavior. If a computer can perform so well, we consider it functionally equivalent to humans.

The test is simple: a human judge has to distinguish between a human and a computer based on their replies to questions that the interrogator poses. After a series of interactions, the judge attempts to determine which response comes from a human and which originates from artificial intelligence. The computer’s success at thinking can be quantified by its probability of being misidentified as the human subject.

External Links:

Stanford Encyclopedia: Turing Test

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