Ruth Aylett

the inspiration behind Ruth Aylett’s poem, ‘Turing’

Turing: logic and death

Turing’s seminal paper on artificial intelligence has been part of my mental furniture for more than thirty years, from the time I first started research in this field myself. I cut my intellectual teeth in the 1980s on the argument that raged then about whether it was feasible in principle to build an artificially intelligent machine. Turing thought it was, and a mathematician and logician that was also interested in engineering, in building things, was always an attractive figure to me.

However his life, and the sheer range of his thought, was something I only encountered when Andrew Hodges’ now famous biography came out. I hadn’t known Turing was gay, had heard nothing of his time in Manchester, where I was actually living when I read the biography. In particular I knew nothing of his last years and death. Whether you believe the story of the poisoned apple or not – some don’t – it has an unforgettably dramatic impact on the imagination.

Many of us in computer science were aware of the coming centenary of Turing’s birth well ahead of its arrival. Ideas for commemorating it have been under discussion for some time ; here at Heriot-Watt we are running a short story competition called ‘Turing’s World’ for schools. I wanted to find a personal way of commemorating the centenary, and since I write poetry in my private life, this was an obvious route.

Poetry is often seen as dealing primarily with the subjective experience of the poet, especially their emotions. But if the poet is also a scientist and technologist, why should the form not stretch to cope with these themes too?  I have been trying to perform this stretch for a while, with pieces about cosmology and differential calculus for example. Writing about Turing, what struck me most was the tension between the logic on which he worked so brilliantly, and the life he lived while he was doing it.

In computer science, Turing’s fundamental contribution was to to prove that there was no definitive way in logic of proving whether a given piece of program code would halt, rather than running for ever. This proof of the ‘halting problem’ sets an inescapable limit on how far software engineering can produce correct code. Turing imagined a program whose sole function was to decide whether another program would or would not halt, and then thought about what would happen if it was applied to itself. He showed this would produce a logical paradox. Thus no such program can exist and there is no certain way of telling whether a program will halt. Ah – but for humans things are different. We all halt…

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