The Incomputable Alan Turing

The last century saw dramatic challenges to the Laplacian predictability which had underpinned scientific research for around 300 years. Basic to this was Alan Turing’s 1936 discovery (along with Alonzo Church) of the existence of unsolvable problems. This paper focuses on incomputability as a powerful theme in Turing’s work and personal life, and examines its role in his evolving concept of machine intelligence. It also traces some of the ways in which important new developments are anticipated by Turing’s ideas in logic. This paper is based on the talk given on 5th June 2004 at the conference at Manchester University marking the 50th anniversary of Alan Turing’s death. It is published by the British Computer Society on http://www.bcs.org/ewics . It was submitted on 10th January, 2005; some minor amendments were made, and references added for publication, in March 2005.