**It's Alan Mathison Turing's birthday, the one generally considered as the "father of computers"! Born on June 23, 1912, this scientist is the subject of a synthetic biography by the CIGREFwhich UP is proposing to introduce you here. **

Alan Mathison Turing spent his childhood in England, but in a foster family and then in a boarding school, his father being a civil servant posted in India, where he already expressed this atypical character. He entered King's College of Cambridge University in 1931 to study mathematics before specializing in probability calculus.

Alan Turing's intellectual atypicality emulates a wealth of thought that pushes him, starting from mathematics, on scientific paths as eclectic as calculability, cryptography, morphogenesis of biological forms, then the calculability of intelligence...

The first step in this unusual path was in 1936, some 10 years before the beginnings of computer science, when he wrote an article entitled "Calculable Number Theory, followed by an application to the problem of decision". In this text, Turing gives his own definition of calculability: "Calculable numbers can be summarily defined as real numbers whose decimal expression is calculable with finite means. ...] According to my definition, a number is calculable if its decimal representation can be described by a machine". In this article, he also describes what will become, a decade later, the computer. He assumes that a machine can calculate various tasks as long as they are sufficiently well formulated. In concrete terms, this article describes the first mathematical model of an algorithm, and identifies its potentials and limitations. This is how the "Turing Machine" was born!

**2012, a lego machine from Turing...**

Before going into the history of this "Turing Machine", it is interesting to give a visual representation of it. To mark the centenary of the birth of Alan Turing, students of the Master's degree in fundamental computer science at the Ecole Normale Supérieure de Lyon have chose to pay tribute to him by making a "Lego Turing Machine" to embody this view of the mind of the visionary scientist.

To view the film produced by CNRS Images : http://videotheque.cnrs.fr/video.phpurlaction=visualisation&method=QT&action=visu&id=3001&type=grandPublic

The "Turing Machine" is a completely original approach to the notion of calculability, as it expresses for the first time the idea that a machine can calculate without human intervention.

Turing describes a machine with a ribbon on which a reading head can alternately read and write symbols. When the read head reads a symbol, it acts according to the internal state of the machine, modifying it by moving to the left or right. The internal state is what tells the reading head what to do with a symbol, in which direction it will move, and according to this writing what the next internal state of the machine will be... Without technically describing his machine, Turing explains its operation as that of a human who would have just enough memory to write symbols on the tape, and unroll it over the necessary length as the calculation progresses. He assumes that the tape will always have the desired length, i.e. almost infinite.

**"MU", a universal Turing machine**

Based on the same principle of calculability, Turing goes one step further by offering "MU", a "universal machine" that can simulate the task execution of all Turing machines. The principle consists in examining the infinity of machines allowing all types of calculations, from the simplest such as basic operations to the most complex such as the calculation of the positions of the stars... To do this, as for a "simple" Turing machine, it is sufficient to give it a precise description of the task to be executed, in other words a "program"!

With hindsight today, we can clearly see the model of the computer whose principle is that of this universal machine with a program, albeit a little faster than the writing on the initial ribbon of the machine designed by Turing. But the computer does indeed have the DNA of this universal Turing machine capable of executing the prescribed calculations for an infinite number of "calculable tasks" to be performed.

Besides, Alan Turing himself will work on the first computers. After having been asked by the British government during the Second World War to decipher the messages of the German army addressed to the submarines circling England (Enigma system), he left for a few months for the United States, at Princeton University, to discover the emerging electronic technologies by working with a specialist in what would become the theory of programming languages.

On his return to England, he worked on a computer with the British technical teams. He notes that when the reading head has to move from one square to another on the tape, time is wasted and finds that it should be able to go directly to a desired square. To do this, the box must have an address. The finite length of the ribbon on her machine is also an obstacle, which will be overcome by the computer's memory principle .

**The "Turing Test", or Calculable Thinking...**

It was in 1950 that Turing sought to use the progress made by the computer to put it to the test of an intelligence test, confronting it with human intelligence. Can the machine show intelligence? He then developed a "test" that was played out between human beings and then with the computer. The first phase thus pits a human player against a human player who must determine, from their written answers, the sex of two individuals: a man and a woman. The principle of the test is that the man tries to deceive the player, the woman tries to help him. The machine is then substituted for the man to see if the human answers are able to deceive "the intelligence of the computer". Turing imagined that the computer would eventually succeed in winning over the human, but that hasn't happened yet. The "Turing Test", on the other hand, has inspired many conversational agent-type computer implementations, giving the illusion of intelligent thinking that can create a "man-machine" dialogue. Since 1990, the Loebner Prize annually rewards the best achievements inspired by the Turing test and meeting his criteria.

Is it possible to see a computer machine exchanging written answers with a human without the human being being being able to distinguish whether he is conversing with a computer or one of his fellow human beings? In such contests, computers can be programmed to "trick" judges by refusing to answer (or delaying their answers to figure out a human-specific response time) calculation questions that they can solve in a fraction of a second. To unmask the computer, it may be enough for the judge to wield the humour to which the machine is not yet very receptive...

**From life sciences to artificial intelligence**

Blocked by the limits of formal language, Alan Turing has been interested throughout his career in the biological notion of life "whose internal organization is not governed by a formal code". He seeks to identify the principle of the creation of forms of living beings. Thus, morphogenesis, in other words "the set of laws that determine the shape and structure of tissues, organs and organisms", captivates him. From the very beginning of his work, Turing was concerned with everything that escaped calculation. That's why he is interested in biological forms that organize themselves outside of any deterministic program, and more generally in the unpredictability of the evolution of living things. Calculus then becomes for him a measuring tool enabling him to explore nature and living things.

As early as 1952, he put forward theories that would be confirmed by biologists years later, notably on the formation of shells or the formation of spots on the fur of animals such as tigers and zebras.

The human brain is one of the biological forms affected by the unpredictability that affects all living forms. In his approach confronting the calculable thought of the machine and human intelligence, materialized by his "Turing Test", he believes that in the long run it will no longer be possible to distinguish between machine and human intelligence, thus laying the foundations for what is called "artificial intelligence". For Turing, if the computer contains the notion of calculation, starting from this very notion, one must manage to determine, by a negative reasoning already demonstrated in his 1936 article, another nature of problems that escape calculation.

Turing took his own life in June 1954, when he was only 42 years old; he had been particularly affected by the conviction for homosexuality, forced to choose between chemical castration or imprisonment. He had to choose the former in order to continue his work... In 2009, the English Government issued a formal apology for the "inhuman" treatment Alan Turing received as a result of his homosexuality.

**Turing's centenary**

Numerous events pay tribute to Alan Mathison Turing on the centenary of his birth:

– CNRS celebrates Alan Turing 1912-2012

– Alan Turing or the foundations of computer science (Cycle of 3 lectures)

– How the universal machine has turned our society upside down (ENS de Lyon from 2 to 4 July 2012)

– 2012, the Alan Turing year (world events)

{Jacuzzi on}