Alan Turing and his contemporaries pdf

Alan Turing and his contemporaries

Alan Turing  This photograph shows Alan Turing in 1946, the year 

in which he was appointed OBE (Order of the British Empire) for his 

wartime code-breaking efforts at Bletchley Park. By 1946 he was working 

at the National Physical Laboratory (NPL) on the design of the ACE 

computer. Turing’s involvement with computers is explained in more 

detail in Chapter 2 and Appendix B. Here is a summary of his brief but 

extraordinary life.

1912 Born at Paddington, London, on 23 June

1926–31 Sherborne School, Dorset

1931–4 Mathematics undergraduate at King’s College, Cambridge 

University

1934–5 Research student studying quantum mechanics, probability and 

logic

1935 Elected Fellow of King’s College, Cambridge

1936–7 Publishes seminal paper ‘On Computable Numbers’, with the 

idea of the Universal Turing Machine

1936–8 Princeton University – PhD in logic, algebra and number theory, 

supervised by Alonzo Church

1938–9 Returns to Cambridge; then joins Bletchley Park in September 

1939

1939–40 Specifies the Bombe, a machine for Enigma decryption

1939–42 Makes key contributions to the breaking of U-boat Enigma 

messages

1943–5 A principal cryptanalysis consultant; electronic work at Hanslope 

Park on speech encryption

1945 Joins National Physical Laboratory, London; works on the ACE 

computer design

1946 Appointed OBE for war services

1948 Joins Manchester University in October; works on early 

programming systems

1950 Suggests the Turing Test for machine intelligence

1951 Elected Fellow of the Royal Society; works on the non-linear theory 

of biological growth (morphogenesis)

1953–4 Unfinished work in biology and physics

1954 Death (suicide) by cyanide poisoning on 7 June

Why was the young Alan Turing, just back from completing a doctorate 

in America, one of the first mathematicians to be recruited to help with 

code-cracking at Bletchley Park in 1939? The answer probably lies in 

a theoretical paper that he had written back in 1935–6, whilst a post-

graduate at King’s College, Cambridge.

Turing’s paper was called ‘On Computable Numbers, with an appli-

cation to the Entscheidungsproblem’. In plain English, it was Turing’s 

attempt to tackle one of the important philosophical and logical prob-

lems of the time: Is mathematics decidable? This question had been 

posed by scholars who were interested in finding out what could, and 

what could not, be proved by a given mathematical theory. In order to 

reason about this so-called Entscheidungsproblem, Turing had the idea 

of using a conceptual automatic calculating device. The ‘device’ was a 

step-by-step process – more a thought-experiment, really – that manip-

ulated symbols according to a small list of very basic instructions.  

6

---

The ideas men

The working storage and the input–output medium for the process was 

imagined to be an infinitely long paper tape that could be moved back-

wards and forwards past a sensing device.

It is now tempting to see Turing’s mechanical process as a simple 

description of a modern computer. Whilst that is partly true, Turing’s 

Universal Machine was much more than this: it was a logical tool for 

proving the decidability, or undecidability, of mathematical problems. 

As such, Turing’s Universal Machine continues to be used as a concep-

tual reference by theoretical computer scientists to this day. Certainly 

it embodies the idea of a stored program, making it clear that instruc-

tions are just a type of data and can be stored and manipulated in the 

same way. (If all this seems confusing, don’t worry! It is not crucial to 

an understanding of the rest of this book.)

In the light of his theoretical work and his interest in ciphers, Alan 

Turing was sent to Bletchley Park on 4 September 1939. He was imme-

diately put to work cracking the German Naval Enigma codes. He 

succeeded. It has been said that as Bletchley Park grew in size and 

importance Turing’s great contribution was to encourage the other 

code-breakers in the teams to think in terms of probabilities and the 

quantification of weight of evidence. Because of this and other insights, 

Turing quickly became the person to whom all the other Bletchley Park 

mathematicians turned when they encountered a particularly tricky 

decryption problem.

On the strength of his earlier theoretical work Alan Turing was 

recruited by the National Physical Laboratory (NPL) at Teddington in 

October 1945, as described in Chapter 2. Senior staff at NPL had heard 

about ENIAC and EDVAC and wished to build a general-purpose digi-

tal computer of their own. Turing, they felt, was the man for the job. 

It is very likely that at NPL Turing saw an opportunity to devise a 

physical embodiment of the theoretical principles first described in his 

‘On Computable Numbers’ paper. Although he was well aware of the 

developments at the Moore School and knew John von Neumann per-

sonally, Turing was not usually inclined to follow anyone else’s plans. 

Within three months he had sketched out the complete design for his 

own general-purpose stored-program computer – which, however, did 

adopt the notation and terminology used in the EDVAC Report. For rea-

sons described in Chapter 2, Turing’s paper design for what was called 

ACE, the Automatic Computing Engine, remained a paper design for 

some years.

7

---