  The statement that all physical action is in effect computable goes beyond Turing's explicit words, but is a fair characterisation of the implicit assumptions behind the 1950 paper. Turing's consideration of ‘The Argument from Continuity in the Nervous System,’ in particular, simply asserts that the physical system of the brain can be approximated as closely as is desired by a computer program (Turing 1950b, p. 451). Certainly there is nothing in Turing's work in the 1945–50 period to contradict Penrose's interpretation. The more technical precursor papers (Turing 1947, 1948) include wide-ranging comments on physical processes, but make no reference to the possibility of physical effects being uncomputable.