Turing was conceived in 1911 in Chatrapur,
India. His father, Julius Mathison Turing, was a member
of the Indian civil service. Julius and wife Ethel (née Stoney)
wanted Alan to be brought up in Britain, so they returned to Paddington,
London. His father's civil service commission was still active, and during
Turing's childhood years his parents travelled between Guildford, England
and India, leaving their two sons to stay with friends in England, rather
than risk their health in the British colony. Very early in life, Turing
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
recognized his genius early on, as did many of his subsequent educators.
In 1926, at the age of 14, he went on to the Sherborne boarding school
in Dorset. His first day of term coincided with a general strike in England,
and so determined was he to attend his first day that he rode his bike
unaccompanied over sixty miles from Southampton to school, stopping overnight
at an inn — a feat reported in the local press.
Turing's natural inclination
toward mathematics and science did not earn him respect with the teachers
at Sherborne, a famous and expensive public school (a
British private school with charitable status), whose definition of education
placed more emphasis on the classics. His headmaster wrote to his parents:
"I hope he will not fall between two schools. If he is to stay at
Public School, he must aim at becoming educated. If he is to be solely
a Scientific Specialist, he is wasting his time at a Public School,"
But despite this, Turing
continued to show remarkable ability in the studies he loved, solving
advanced problems in 1927 without having even studied elementary calculus.
In 1928, aged sixteen, Turing encountered Albert Einstein's
work; not only did he grasp it, but he extrapolated Einstein's questioning
of Newton's laws of motion from a text in which this
was never made explicit.
Turing's hopes and ambitions
at school were raised by his strong feelings for his friend Christopher
Morcom, with whom he fell in love, though the feeling was not
reciprocated. Morcom died only a few weeks into their last term at Sherborne,
from complications of bovine tuberculosis, contracted after drinking infected
cow's milk as a boy. Turing was heart-broken.
to his unwillingness to work as hard on his classical studies
as on science and mathematics, Turing failed to win a scholarship
to Trinity College, Cambridge, and went on to the college of his
second choice, King's College, Cambridge. He studied under G.
H. Hardy, a respected mathematician, who held the Sadleirian Chair
at Cambridge, then a center for mathematical research and study,
from 1931 to 1934. In 1935 he was elected a Fellow at King's College.
Hardy was a member of the infamous Cambridge Apostles, which gained
notoriety during this period from the Cambridge Spy Ring scandal.
Oddly, but perhaps the better for him, Turing was either not invited
to join the circle, or declined the invitation.
In his momentous paper
"On Computable Numbers, with an Application to the Entscheidungsproblem"
(submitted on May 28, 1936), Turing 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 theory
of computation. He went on to prove that there was no solution to the
Entscheidungsproblem by first showing that the halting problem for Turing
machines is uncomputable: 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.
aller Gewissheit - Die Begegnung zwischen Alan Turing und Ludwig Wittgenstein,
World War II he was a major participant in the efforts at Bletchley
Park to break German ciphers. Turing's codebreaking work was kept
secret until the 1970s; not even his close friends knew about
it. He contributed several mathematical insights into breaking
both the Enigma machine and the Lorenz SZ 40/42
(a teletype cipher attachment codenamed "Tunny" by the
Two cottages in the
stable yard at Bletchley Park. Turing worked here from
1939–1940 until he moved to Hut 8.Turing realised that it was not
necessary to test all the possible combinations to crack the Enigma machine.
He proved that it was possible to test for the correct settings of the
rotors (approximately one million combinations) without having to consider
the settings of the plugboard (approximately 157 million combinations).
Whilst still a formidable task, one million combinations was achievable
using an electromechanical machine — the bombe, named after the
Polish-designed bomba — which could be used to eliminate large numbers
of candidate Enigma settings. For each possible setting, a chain of logical
deductions was implemented electrically, and it was possible to detect
when a contradiction had occurred and rule out that setting.
bombe, with an enhancement suggested by mathematician
Gordon Welchman, was the primary tool used by British and American
codebreakers to read Enigma traffic, with over 200 bombes in operation
by the end of the war. The design and production of the machine
itself was undertaken by Harold Keen of the British Tabulating
Machine company. For a time, Turing was head of Hut 8, the section
responsible for cryptanalysing German Naval signals. Turing also
invented the technique of Banburismus to assist in breaking Enigma.
Turing devised some
methods for attacking Tunny, termed Turingismus or Turingery, although
other methods were also used. To assist in the codebreaking, the first
digital programmable electronic computer was developed, Colossus. Turing,
however, was not directly involved — Colossus was designed and built
at the Post Office Research Station at Dollis Hill by a team led by Thomas
Flowers in 1943.
In the later part of
the war, Turing undertook (with engineer Donald Bayley)
the design of a portable machine codenamed Delilah to allow secure voice
communications, teaching himself electronic theory at the same time. Intended
for different applications, Delilah lacked the ability to be used over
long-distance radio transmissions. Delilah was completed too late to be
used in the war. While Turing demonstrated it to officials by encoding/decoding
a recording of a Winston Churchill speech, it was not adopted for use.
From 1945 to 1947 he
was at the National Physical Laboratory, where he worked on the design
of ACE (Automatic Computing Engine). He presented a paper
on February 19, 1946, which was the first complete design of a stored-program
computer. Although he succeeded in designing the ACE, there were delays
in starting the project and he became disillusioned. In late 1947 he returned
to Cambridge for a 'sabbatical' year. While he was at Cambridge work on
building the ACE stopped before it was ever begun. 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 —
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 1948, Turing, working
with his former undergraduate colleague, D.G. Champernowne, began writing
a chess program for a computer that did not yet exist. In 1952, lacking
a computer powerful enough to execute the program, Turing played a game
in which he simulated the computer, taking about half an hour per move.
The game was recorded; the program lost to a colleague of Turing, however,
it is said that the programme won a game against Champernowne's wife.
Turing worked from 1952
until his death in 1954 on mathematical biology, specifically morphogenesis.
He published one paper on the subject called "The Chemical
Basis of Morphogenesis" in 1952. His central interest in
the field was understanding Fibonacci phyllotaxis, the existence of Fibonacci
numbers in plant structures. He used reaction-diffusion equations which
are now central to the field of pattern formation. Later papers went unpublished
until 1992 when Collected Works of A.M. Turing was published.
Prosecution 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,
Turing was said to have had a sexual relationship with a 19-year-old man,
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 oestrogen hormone injections,
which lasted for a year, with side effects including the development of
In 1954, he died of
cyanide poisoning, apparently from a cyanide-laced apple he left half-eaten.
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. Friends
of his have said that Turing may have killed himself in this ambiguous
way quite deliberately, to give his mother some plausible deniability.
A statue of Turing was
unveiled in Manchester on June 23, 2001. It is in Sackville Park, between
the University of Manchester building on Whitworth Street and the Canal
Street gay village. To mark the 50th anniversary of his death, a memorial
plaque was unveiled at his former residence, Hollymeade, in Wilmslow on
June 7, 2004.
Award is given by the Association for Computing Machinery
to a person for technical contributions to the computing community. It
is widely considered to be the equivalent of the Nobel Prize in the computing
The Alan Turing Institute
was initiated by UMIST and University of Manchester in Summer 2004.
celebration of Turing's life and achievements was held at the
University of Manchester on 5 June 2004; it was arranged by the
British Logic Colloquium and the British Society for the History
In the book,
Zeroes and Ones, author Sadie Plant speculates that the rainbow
Apple logo with a bite taken out of it was a
homage to Turing. This seems to be an urban legend as the Apple
logo was designed in 1976, two years before Gilbert Baker's rainbow