Original URL: http://www.theregister.co.uk/2008/11/18/alan_turing_anniversary/

## Happy Birthday, Turing's universal machine

Solving the unsolvable

Posted in Science, 18th November 2008 00:21 GMT

It's just 71 years ago this month that a seminal paper from Alan Turing was published, which helped pave the way to today's multi-billion dollar IT industry and confer on Turing the title of father of modern computer science.

As is often the case in scientific endeavour, Turing was actually working on an entirely different task when he stumbled on a way to create a general-purpose computer.

The paper that encapsulated this machine? *On Computable Numbers with an Application to the Entscheidungsproblem*.

The Entscheidungsproblem - which translated from German literally means "decision problem" - referred to a mathematical challenge laid down by German mathematician David Hilbert.

The Entscheidungsproblem goes to the very heart of Hilbert's thoughts on the nature of mathematics. At the start of the twentieth century deep questions were being asked about science and the tools used to think about scientific problems. In the same way that Einstein's work had challenged orthodox views of physics, so Hilbert and others questioned mathematics.

Hilbert posed three fundamental questions: is mathematics "complete", is it "consistent," and - the Entscheidungsproblem - is it "decidable". The first two were answered - negatively - in 1931 by the Austrian mathematician Kurt Godel.

Turing scuppered Hilbert's final question with his 1937 paper although the American mathematician Alonzo Church - later Turing's professor at Princeton - came up with a similar negative analysis a year earlier. The two approaches are generally combined as the Church-Turing Theorem.

Turing's real insight was, of course, the concept of a "Universal (or Turing) machine." He conceived the Universal Machine as a way to demonstrate that it was impossible to solve the Entscheidungsproblem.

But he had also stumbled on what was effectively the blue print for a general-purpose computer and this almost certainly justifies his status as the founder of modern computing.

Copies of Turing's original paper are available online both in facsimile and in text form. ®