For Alan Turing’s many admirers, the centenary of his birth on Saturday is an occasion for both celebration and mourning. Here, after all, is the architect of the modern computer, the code-breaker whose ingenuity ensured an Allied victory in World War II and the father of artificial intelligence. Yet Turing was also a victim of a pernicious and paranoid strain of sexual hypocrisy in 20th-century England. Nor, in the 21st, has the victimization wholly ceased.

 

Turing’s remarkable career was marked by happenstance. In 1936, when he was a student at Cambridge, he attended a lecture in which M.H.A. “Max” Newman characterized an old and thorny logic problem as a matter of finding a “mechanical process” for testing the validity of a mathematical assertion. Turing took the phrase “mechanical process” at face value and wrote a paper in which he laid out the architecture of a hypothetical machine to do the testing — what became known as the “Turing machine.” The paper, intended for specialists, amounted to a blueprint for the modern computer, a “universal machine” that could do the work of an infinity of single-use machines.

 

The fortuitous breakthroughs continued. During World War II, Turing was among a group of thinkers summoned by the British government to Bletchley Park to help crack the seemingly airtight German Enigma code. Because the code was generated by a machine, Turing decided, only a machine could break it. He went on to design and help build that machine — the “Bombe,” without which the Allies might have lost the war — thereby instigating a huge leap forward in the field of cryptanalysis.

 

After the war Turing moved to Manchester, where he oversaw the construction of several of the first functioning computers and posited a test that could determine whether a machine could be said to think — the “Turing test.” In so doing, he created what we now call the field of artificial intelligence.

 

Any one of these achievements, in a single lifetime, would have been extraordinary. Yet Turing managed all three...