The Oracle

What did Turing mean by an oracle?

In his Princeton doctoral thesis, published in 1939 as Systems of Logic Based on Ordinals, Alan Turing imagined an ordinary computing machine with a black box bolted on, a box that answers questions no machine can work out for itself. He called it an oracle, and he declined to say how it worked. It worked by “unspecified means”, he wrote, and he saw no need to go into its nature. Product brochures have been using the same technique ever since, with a lot less excuse.

That was the point, and it was the honest kind of vagueness, which is rarer than it should be. The oracle let mathematicians ask what a machine could do if it had help that no machine can have, and Emil Post later built his theory of degrees of unsolvability on the idea. Turing put the part no machine can do in a sealed box and said so, in print. Plenty of products since have managed the sealed box.

Turing never pretended his oracle was real. The one on this shirt is real, beige and enthroned on a milk crate with its plug hanging loose, and it already has a budget line, a launch date and its own steering committee. Nobody on the committee has asked what’s inside. Somebody did ask once, and was told it works by “unspecified means”.

Evidence: Turing’s O-Machines, Jack Copeland, AlanTuring.net, Oracle machine, Wikipedia