Colossal Genius: Alan Turing

A black and white portrait of Alan Turing - the man behind the Enigma decryption.60 Years Hence

Today’s the 60th Anniversary of the Death of Alan Turing – a genial mathematician, a cryptographer and one of the pioneers of computer science at Bletchley Park.  He is considered one of the greatest minds of the 20th Century.  Alan Turing‘s life was one of complexity and secret triumphs, overshadowed by a very public tragedy. 

Alan Turing (1912-1954) was born in Maida Vale, London, U.K., while his father was on leave from his position with the Indian Civil Service (ICS).  His mother, Ethel was the daughter of Edward Waller Stoney, chief engineer of the Madras Railways in India.


Early Feats of a Remarkable Mind

Early on, Alan Turing was labelled a “genius”.  At a very early age, Alan Turing’s legend has it that he taught himself to read in only three weeks.

As a child, Alan had a bike that had a problem with its chain, which would dislodge itself from the gears after a regular, repeatable, number of revolutions.  First, Alan counted the revolutions of the gears throughout his ride until it was time to re-adjust the chain after it derailed.  His elegant solution was to rig a mechanical device that would keep count and readjust the faulty chain by itself.  Assumingly, the chain’s issues presented young Alan Turing with a unique problem set for his mind to solve.  It was both a challenging and fun opportunity for him to think in a different way.  Perhaps more so than if he’d simply bought a new chain…

A black and white photograph showing a young Alan Turing reading in his garden.Turing was probably one of a handful of sixteen year olds who actually ever grasped Einstein’s theories.  He could fully understand Einstein’s doubts concerning the veracity of Galilei-Newtonian laws.  He was even able to deduce Einstein’s Law of Motion (“the separation between any two events in the history of a particle shall be a maximum or minimum when measured along its world line”) from his readings alone though it wasn’t specifically stated in the text.

By 1929, Alan had begun studying Quantum Physics.  It was a heady time as Schrödinger and others turned what was considered a “dead” science on its head. At the time, Schrödinger’s Quantum Theory of Matter was only three years old.


During the War…

During World War 2, Alan Turing was a leading participant in the breaking of German ciphers at Bletchley Park.  From 1938, he had been working part-time with the GC&CS (Government Code & Cypher School), the British WW2 code breaking station.  Turing concentrated on cryptanalysis of the Enigma machine, with Dilly Knox, a senior GC&CS code-breaker.

After the July 1939 Warsaw meeting at which the Polish Cipher Bureau had provided the British and French with the details of the wiring of Enigma rotors and their method of decrypting Enigma messages, Turing and Knox started work on a less fragile approach to the problem.

On 4 September 1939, a day after the UK declared war on Germany, Alan Turing reported to Bletchley Park.  The Polish decryption method relied on an insecure indicator procedure that the Germans were likely to change, which they did in May 1940.  Turing’s approach was more general, using crib-based decryption for which he produced the functional specification of the bombe.


The Turing-Welchman Bombe

A photograph showing an original German Enigma machine.
A WWII German Enigma Cipher Machine

The bombe was an electromechanical device used by the British to help decipher the German Enigma-machine-encrypted secret messages. 

The initial design of the bombe was produced in 1939 by Alan Turing, with an important refinement devised in 1940 by Gordon Welchman.  The engineering design and construction was the work of Harold Keen of the British Tabulating Machine Company.  It was a substantial development from the device that had been previously designed by Marian Rejewski at the Polish Cipher Bureau, and known as the “cryptologic bomb“.

The bombe was designed to discover some of the daily settings of the Enigma machines on the various German military networks, specifically, the set of rotors in use and the rotor positions in the machine, the rotor core start positions for the message (i.e. the message key), and one of the wirings of the plugboard.



Specifying the bombe was the first of five major cryptanalytical advances that Turing made possible during the war.  The others included: deducing the indicator procedure used by the German navy, developing a statistical procedure for making much more efficient use of the bombes dubbed Banburismus, developing a procedure for working out the cam settings of the wheels of the Lorenz SZ 40/42 (Tunny) dubbed ‘Turingery’.

A black and white WW2 photograph showing German soldiers operating an Enigma machine.
German soldiers enciphering a message on an Enigma Machine

In July 1942, Turing devised a technique for use against the Lorenz cipher messages produced by the Germans’ new Geheim schreiber (secret writer) machine.  This was a teleprinter rotor cipher attachment codenamed Tunny at Bletchley Park.

‘Turingery’ was a method of wheel-breaking – a procedure for working out the cam settings of Tunny’s wheels. 

Turing also introduced the Tunny team to Tommy Flowers who, under the guidance of Max Newman, went on to build the Colossus computer, the world’s first programmable digital electronic computer, whose superior speed allowed the statistical decryption techniques to be applied usefully to the messages.

Towards the end of the war, Alan Turing also carried out the development of a portable secure voice scrambler, codenamed Delilah, at Hanslope Park.

In 1945, Turing was awarded the OBE by King George VI for his wartime services, but his work remained secret for many years.


The Turing Test – Imitation of Life

In 1948, Turing was appointed Reader in the Mathematics Department at the University of Manchester.  In 1949, he became Deputy Director of the Computing Laboratory there, working on software for one of the earliest stored-program computers – the Manchester Mark 1.  During this time he continued to do more abstract work in mathematics.

Turing addressed the problem of artificial intelligence in “Computing machinery and intelligence” (Mind, 1950), and proposed an experiment which became known as the Turing test – an attempt to define a standard for a machine to be called “intelligent”.

Alan Turing put forward the idea of an ‘imitation game’, in which a human being and a computer would be interrogated under conditions where the interrogator would not know which was which, the communication being entirely by textual messages.  Turing argued that if the interrogator could not distinguish them by questioning, then it would be unreasonable not to call the computer intelligent, because we judge other people’s intelligence from external observation in just this way.

The Test allows Turing to avoid any discussion of what consciousness is.  It seems to provide a scientific, objective, criterion of what is being discussed – but with the rather odd necessity of ‘imitation’ and deceit coming into it, for the machine is obliged to assert a falsity, whilst the human being is not.

Turing’simitation game‘ is now usually called the ‘Turing test’ for intelligence:

I PROPOSE to consider the question, ‘Can machines think?’  This should begin with definitions of the meaning of the terms ‘machine ‘and ‘think’.  The definitions might be framed so as to reflect so far as possible the normal use of the words, but this attitude is dangerous.  If the meaning of the words ‘machine’ and ‘think ‘are to be found by examining how they are commonly used it is difficult to escape the conclusion that the meaning and the answer to the question, ‘Can machines think?’ is to be sought in a statistical survey such as a Gallup poll.  But this is absurd.  Instead of attempting such a definition I shall replace the question by another, which is closely related to it and is expressed in relatively unambiguous words.

The problem can be described’ in terms of a game, called the ‘imitation game’, played with three people, a man (A), a woman (B), and an interrogator (C) who may be of either sex.

The Imitation Game

The interrogator stays in a room apart from the other two.  The object of the game for the interrogator is to determine which of the other two is the man and which is the woman.  He knows them by labels X and Y, and at the end of the game he says either ‘X is A and Y is B’ or ‘X is B and Y is A’.  The interrogator is allowed to put questions to A and B thus:

C: Will X please tell me the length of his or her hair?

Now suppose X is actually A, then A must answer.  It is A’s object in the game to try and cause C to make the wrong identification.  His answer might therefore be

‘My hair is shingled, and the longest strands, are about nine inches long.’

A black and white photograph showing Alan Turing and his work colleagues using the Mark I computer.
Alan Turing at the console of the Manchester Mark I computer

We now ask the question, ‘What will happen when a machine takes the part of A in this game?’  Will the interrogator decide wrongly as often when the game is played like this as he does when the game is played between a man and a woman?

These questions replace our original, ‘Can machines think?’

The idea was that a computer could be said to “think” if a human interrogator could not tell it apart, through conversation, from a human being.  In his paper, Turing suggested that rather than building a program to simulate the adult mind, it would be better rather to produce a simpler one to simulate a child’s mind and then to subject it to a course of education.

Today, a reversed form of the Turing test is widely used on the Internet: the CAPTCHA test, which is intended to authenticate whether the user is a human or a computer.


Alan Turing’s Public Tragedy

Alan Turing was prosecuted for gross indecency in 1952, at a time when homosexuality was still criminalised in the UK.  He accepted treatment with oestrogen injections (chemical castration) as an alternative to prison detention.

Turing’s criminal conviction led to the removal of his security clearance, which barred him from continuing with his cryptographic consultancy for the Government Communications Headquarters (GCHQ), – the British signals intelligence agency that had evolved from GC&CS in 1946 – although he did retain his academic job.

Alan Turing died in 1954.  Just 16 days short of his 42nd birthday.

The cause of death was cyanide poisoning.  When his body was discovered, an apple lay half-eaten beside his bed, and it was speculated that this was the means by which a fatal dose was delivered.

An inquest determined that his death was a suicide, but his mother amongst others believed that it was accidental.

Fade to black…..


On his death, Turing left a number of unfinished work in Biology and Physics…


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