Abstract

This is a detective story. The starting-point is a philosophical discussion in 1949, where Alan Turing mentioned a machine whose program, he said, would in practice be “impossible to find.” Turing used his unbreakable machine example to defeat an argument against the possibility of artificial intelligence. Yet he gave few clues as to how the program worked. What was its structure such that it could defy analysis for (he said) “a thousand years”? Our suggestion is that the program simulated a type of cipher device, and was perhaps connected to Turing’s postwar work for GCHQ (the UK equivalent of the NSA). We also investigate the machine’s implications for current brain simulation projects.