Who Was Alan Turing?

Alan Turing was a complex man: founder of computer science, philosopher, world class marathoner, mathematician, code breaker, visionary and a homosexual before his time.

Turing had a vision that one day computers could be programmed to achieve abilities indistinguishable from human intelligence. His thesis can be summed up as: "the operations of the brain must be computable".

Turing developed a famous game/ exercise now known as the 'Turing test' for intelligence. He believed that if a computer program could pass this test, it could justifiably be labeled "intelligent".

Turing's 'imitation game' involved a human interrogator who would type text questions and comments via a computer terminal to two subjects. One subject would be human and the other would be a computer program. Turing argued that if the interrogator could not tell which of the two subjects was the human one, based on the textual message replies to his questions, then the computer had passed the test of intelligence.

Early years / Education
Alan Mathison Turing was born on 23 June 1912, the second and last child of Julius Mathison and Ethel Sara Turing. His parents returned to England from India before his birth, in a nursing home in Paddington, London. His life was not one of family values or tradition but of a troubled isolation.

Alan Turing and his elder brother John were fostered in various English homes until his father's retirement in 1926. In these places originality, curiosity and expression were not encouraged. But Turing showed early interest in things philosophical and scientific, even as they became his hobbies.

Turing graduated from King's College, Cambridge in 1934 with a distinguished degree and enjoyed more successes with a Fellowship of King's College in 1935 and a Smith's Prize in 1936 for work on probability theory. He would complete his Ph.D. at Princeton in 1938. At this time his homosexuality became a defining part of Turing's identity.

The concept of the Turing Machine

Turing analysed what could be done by a human performing a methodical process. He seized the idea of something being done  'mechanically', and described his analysis in terms of a theoretical machine. This machine would be able to perform precisely defined elementary operations on symbols on a continuous paper tape. He extended his analysis to include the comparison of 'machine states' to the 'states of mind' of a human being.

The integration of logical instructions, the action of the mind, and a theoretical machine which could in plausibly be engineered into a physical device, was Turing's ultimate contribution.

Without overstating its importance, the concept of the Turing machine has become the foundation of the modern theory of computation and computability.

The Universal Turing Machine

The concept of 'the Turing machine' corresponds to that of 'the formula'. Turing imagined that any particular algorithm or 'definite method' could be described in a standardized set of instructions. The task of interpreting and executing the instructions is itself a mechanical process, and so can be the function of a particular version of a Turing machine: the Universal Turing machine.

The Universal Turing machine would be capable of doing what any other general Turing machine could do, by supplying it with the standard algorithm describing that individual Turing machine. This single general purpose machine would then be suitable for handling any and all algorithms and tasks.

Today, it is impossible not to think of a Turing machine as a computer program,  and the Universal Turing Machine as our ubiquitous digital computer: A single machine which can perform any well defined task when provided with the appropriate program.

But in Turing's time, in 1936, computers did not exist in the physical world, only in the mind of  Dr. Alan Turing.

Turing in the Second World War

In 1938 Turing  returned to Cambridge where he worked in secret for the British cryptanalytic department, the Government Code and Cypher School.

When the British entered the war in September, Turing went to work full time at Bletchley Park code breaking. From late 1940 onwards, a machine known as the "Bombe", developed by Turing and greatly contributed to by Cambridge mathematician, W. G. Welchman Bombe made reading of German Luftwaffe coded signals routine.

The German Navy used a more advanced system, called Enigma, which was regarded as unbreakable. Turing happily went to work alone on a problem that had stopped others and made a breakthrough in 1939. With the capture of intelligence materials from the German Navy and developments in statistical methods, regular decryption of Enigma began in 1941.

During his time at Bletchley, electronic technology made its first appearance at the British code breaking center. Turing, exploiting electronic computing, contributed greatly to the breaking of the so called 'Fish' material, the system used for Hitler's strategic communications. Turing was affectionately known as the "Prof" at Betchley, the center's resident genius, shabby, and often awkward in speech and manner.

The Basis for the Stored Program Electronic Computer

At the end of World War II, Turing envisaged his design for the Universal Turing Machine in electronic form. His key integrated ideas were his 1936 concept of the universal machine, the speed and reliability of electronic technology and the inefficiency in building separate machines for different logical processes.

These ideas combined to form the motivation for the modern digital computer: a general purpose machine for any programmable task. This was, if effect, the theoretical invention of the digital computer.

Alan Turing's Crisis and End

Alan Turing was arrested then tried in March, 1952 for homosexual relations with young man. He did not refute or defend against the charges. He felt and proclaimed that he had done nothing wrong. As an alternative to a prison term sentence
he accepted injections of estrogen intended to neutralize his libido, for one year.

Turing's end came at his own hand, on 7 June, 1954 by cyanide poisoning. But his contributions to computer science will live forever.