For its help with the design of the new £50 bank note featuring Alan Turing, the London Mathematical Society (LMS) has been presented with a low serial number (AA01 001936) version by the Bank of England. The presentation took place on 23 June, the anniversary of Turing’s birth, and the day that the new £50 bank note went into circulation.
The Society contributed to the design of the bank note in 2019 by giving approval and permission for the use on the bank note of two mathematical excerpts from the Turing article On computable numbers, with an application to the Entscheidungsproblem (submitted 28 May 1936, published in Proceedings of the London Mathematical Society;(2) 42 (1937) 230–265)1.
LMS Executive Secretary, Caroline Wallace, accepted the note on behalf of the Society at its headquarters in De Morgan House. She said “I am delighted and humbled to receive this bank note on behalf of the London Mathematical Society. The Society is pleased to have been able to contribute to the successful development of this new design. This bank note continues the process of recognising and celebrating the enormous contribution made by Turing to mathematics, to computer science and to the country”.
Alan Mathison Turing OBE FRS (1912–1954) was a mathematician, computer scientist, logician, cryptanalyst, philosopher and theoretical biologist who was instrumental in formalising the concepts of algorithm and computation. Turing worked as a code-breaker during the second world war and is widely accredited with having helped bring an earlier end to the war. The story of his life has had wide implications for changes in political, legal and social attitudes towards human diversity and homosexuality.
The first excerpt is a table from page 240 which provides a schema for succinctly representing Turing machines. The table gives a complete description of how to specify such machines and therefore can be thought of as one of the first examples of a programming language.
The second excerpt, from page 241, is a sequence of Turing machine transitions that helps explain how to encode a Turing machine as a number. The more modern analogue of what Turing describes is how to take an abstract representation of a computer program and convert it into a binary sequence of 0s and 1s so that it can be stored on a disc or in the memory of a computer. The idea that a program can be stored as a number and used as data (by an operating system) in order to execute the program, is hugely important.
Turing went on further in his article to describe large classes of real numbers whose binary expansions are computable by his machines; to describe a ‘universal machine’ that could serve the purpose of an operating system; and to describe the theoretical limits of his machines. Ultimately, Turing showed that there can be no algorithmic method for determining whether or not a given mathematical statement can be proved in a certain axiomatic system. This proved that David Hilbert's famous Entscheidungsproblem has no solution (which was also proved independently by Alonzo Church).
Alan Turing is the second mathematician to appear on a Bank of England banknote. A £1 banknote in circulation between 1978 and 1988 depicted Sir Isaac Newton. Famous Britons have featured on the reverse of Bank of England banknotes since 1970.
1The Turing article is © London Mathematical Society. All rights reserved. The London Mathematical Society is a not-for-profit Charity registered with the UK Charity Commission. All surplus income from its publishing programme is used to support the mathematics community in the form of research grants, conference grants, prizes, initiatives for early career researchers and the promotion of mathematics.
A collection of Turing's articles in the Proceedings is now available on Wiley Online Library.