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Alan Turing
Alan Mathison Turing (June
23, 1912 - June 7, 1954) was a British mathematician and cryptographer, and is
considered to be one of the fathers of modern computer science.
He
provided an influential formalisation of the concept of algorithm and
computation: the Turing machine.
He
formulated the now widely accepted 'Turing' version of the Church-Turing
thesis, namely that any practical computing model has either the equivalent or
a subset of the capabilities of a Turing machine.
During
World War II he was the director of the Naval Engima Hut at Bletchley Park for
some time and remained throughout the War the chief cryptanalyst for the Naval
Enigma effort.
After
the war, he designed one of the earliest electronic programmable digital
computers at the National Physical Laboratory and, shortly thereafter, actually
built another early machine at the Universtiy of Manchester.
He
also, amongst many other things, made significant and characteristically
provocative contributions to the discussion "Can machines think?"
Childhood and
youth
He was born in Paddington to Civil Service
officer Julius Mathison Turing and his wife Ethel (née Stoney).
father's Indian Civil Service commission
was still active, and during Turing's childhood years his father travelled
between England and India, leaving his family to stay with friends in England
due to concerns over the dangers of the British colony.
Very early in life, Turing early showed
signs of the genius he was to display more prominently later. He is said to
have taught himself to read in three weeks, and to have shown an early affinity
for numbers and puzzles.
His
parents enrolled him at St. Michael's, a day school, at six years of age. The
headmistress recognised his genius early on, as did many of his subsequent
educators at Marlborough College (a public school).
At
Marlborough, he first reported having problems with bullies.
He
went on to the Sherborne boarding school at 13, where his first day was
actually covered in the local press. There was a general strike in England, and
Turing rode his bike sixty miles to school, stopping overnight at an inn.
Turing's natural inclination toward the
sciences did not earn him respect with the teachers and administrators at
Sherborne, whose definition of education emphasised the classics rather than
science.
But
despite this, Turing continued to show remarkable ability in the studies he
loved, solving advanced (for his age) problems in 1927 without having even
studied elementary calculus.
In 1928, Turing encountered Albert
Einstein's work, and grasped it at a mere sixteen years of age, even
extrapolating Einstein's Law of Motion from a text in which it was never made
explicit.
College and his work on computability
Due to his unwillingness to work as hard on
his classical studies as on science and mathematics, Turing failed his final
examinations several times, and went on to the college of his second choice,
King's College, Cambridge, rather than his first choice, Trinity.
He studied under G. H. Hardy, a well
respected mathematician who held the Sadleirian Chair at Cambridge, then a
centre for mathematical research and study, from 1931-1934. In 1935 he was
elected a Fellow at King's College.
In
his monumental paper "On Computable Numbers, with an Application to the
Entscheidungsproblem" (1936), he reformulated Kurt Gödel's 1931 results on
the limits of proof and computation, substituting Gödel's universal
arithmetics-based formal language by what are now called Turing machines,
formal and simple devices.
He
proved that such a machine would be capable of performing any conceivable
mathematical problem if it were representable as an algorithm, even if no
actual Turing machine would be likely to have practical applications, being
much slower than alternatives.
Turing
machines are to this day the central object of study in computational theory.
He went on to prove that there was no solution to the Entscheidungsproblem by
first showing that the halting problem for Turing machines is unsolvable: it is
not possible to algorithmically decide whether a given Turing machine will ever
halt.
While
his proof was published subsequent to Alonzo Church's equivalent proof in
respect to his lambda calculus, Turing's work is considerably more accessible
and intuitive.
It
was also novel in its notion of a "Universal (Turing) Machine", the
idea that such a machine could perform the tasks of any other machine. The
paper also introduces the notion of definable numbers.
Most of 1937 and 1938 he spent at
Princeton University, studying under Alonzo Church.
In
1938 he obtained his Ph.D. from Princeton; his dissertation introduced the
notion of hypercomputation where Turing machines are augmented with so-called
oracles, allowing a study of problems that cannot be solved algorithmically.
Back in Cambridge in 1939, he attended
lectures by Ludwig Wittgenstein about the foundations of mathematics.
The
two argued and disagreed vehemently, with Turing defending formalism and
Wittgenstein arguing that mathematics is overvalued and does not discover any
absolute truths.
Cryptanalysis
(code breaking)
During the World War II he was a major
participant in the efforts at Bletchley Park on cracking Nazi Enigma ciphers.
He contributed several mathematical
insights, both to breaking the Enigma code and the Fish teletype cyphers
(teletype cypher machines made by both Lorenz and Siemens).
The Fish insights were useful in the
development of the special-purpose digital computer Colossus, which was
designed by Max Newman and team, and built at the Post Office Research Station
at Dollis Hill by a team led by Thomas Flowers in 1943.
It was used to crack Fish cyphers, in
particular the Siemens machine traffic).
Turing also helped design the "Bombe's,"
advanced versions of Polish Rejewski's "Bomba" machine used to assist
in finding keys for Enigma messages.
These were electromechanical devices
coupling several "Enigma machine clones" which were able to eliminate
at high speed large numbers of possible key settings for Enigma messages.
Turing's
work on breaking the Enigma cypher was kept secret until the 1970s; not even his
close friends knew about it.
Work on early computers; the Turing Test
From 1945 to 1948 he was at the National
Physical Laboratory, where he worked on the design of ACE (Automatic Computing
Engine).
In 1949 he became Deputy Director of the
computing laboratory at the University of Manchester, and worked on software
for one of the earliest true computers &mdash the Manchester Mark I.
During this time he continued to do more
abstract work, and in "Computing machinery and intelligence" (Mind,
October 1950), Turing tackled the problem of artificial intelligence, and
proposed an experiment now known as the Turing test, an attempt to define a
standard for a machine to be called "sentient".
In
1952 Turing wrote a chess program. Lacking a computer powerful enough to
execute it, he himself simulated the computer, taking about half an hour per
move. One game was recorded; the program lost to a colleague of Turing.
Persecution for homosexuality, and Turing's death
Persecution of Turing for his homosexuality
crippled his career. In 1952, his male lover helped an accomplice to break into
Turing's house and commit larceny.
Turing went to the police to report the
crime. As a result of the police investigation, a 19-year-old man was said to
have sexual relationship with him and Turing was charged with "gross indecency
and sexual perversion."
He unapologetically offered no defence, and
was convicted. Following the well-publicised trial, he was given a choice
between incarceration and libido-reducing hormonal treatment.
He chose the hormone injections, which
lasted for a year, with side effects including the development of breasts
during that period.
In 1954, he died of poisoning after eating
a cyanide-laced apple. Most believe that his death was intentional, and the
death was ruled a suicide.
His mother, however, strenuously argued
that the ingestion was accidental due to his careless storage of laboratory
chemicals.
Quotes
"We can only see a short distance ahead, but we can see
plenty there that needs to be done." -- From his paper on the Turing test
(1943,
New York: the Bell Labs Cafeteria) His high pitched voice already stood out
above the general murmur of well-behaved junior executives grooming themselves
for promotion within the Bell corporation.
Then he was suddenly heard to say: "No, I'm not interested in developing a powerful brain. All I'm
after is just a mediocre brain, something like the President of the American
Telephone and Telegraph Company." --Quoted in A Hodges - Alan Turing: the Enigma of Intelligence, (London 1983) 251.
"Science
is a differential equation. Religion is a boundary condition." --Quoted in J D Barrow - Theories
of everything
"...I
believe that at the end of the century the use of words and general educated
opinion will have altered so much that one will be able to speak of machines
thinking without expecting to be contradicted."
"Mathematical
reasoning may be regarded rather schematically as the exercise of a combination
of two facilities, which we may call intuition and ingenuity."
"In
the time of Galileo it was argued that the texts, 'And the sun stood still ...
and hasted not to go down about a whole day' (Joshua x. 13) and 'He laid the
foundations of the earth, that it should not move at any time' (Psalm cv. 5) were an adequate refutation of the
Copernican theory." --Computing
Machinery and Intelligence, Mind 59 (1950), 443.
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