New AI may pass the famed Turing Test. This is the man who created it.

Can machines think? The question has been on the minds of many with the emergence of powerful artificial intelligence and ChatGPT, a deep learning machine that can converse with—and sometimes fool—human users. Users of the Bing search engine’s chatbot, which draws on ChatGPT technology, even report unnerving conversations in which the AI professes its love for them.

In 1950, Alan Turing had an answer to that question—a computer was capable of “thought” if its output was so convincing that a person interacting with it couldn’t distinguish its answers from those of a real human. The concept, known as the Turing test, has regained new prominence today as some argue that this new generation of AI does in fact pass the Turing test.

(This ‘Countess of Computing’ wrote the first computer program.)

But who was Turing, and why are his ideas about computing and AI still so important today? Here’s what you should know about the legendary English mathematician, codebreaker, and computer scientist.

Alan Turing’s early life 

Born in London in 1912, Turing was the son of a high-ranking British colonial administrator based in India. His parents, however, did not want their children brought up there, so they left them to be raised by family friends. According to biographer Andrew Hodges, he was a lonely child raised in “various English homes where nothing encouraged expression, originality, or discovery.” But young Turing had a unique and brilliant mind.

At boarding school, a teenage Turing formed a close bond with his classmate, Christopher Morcom, over their love of science. When Morcom died unexpectedly in 1930, Turing was devastated. In letters to Morcom’s mother, he wondered whether Morcom’s mind could possibly live on without his body.

(Listen to Overheard at National Geographic’s podcast episode on the battle for the soul of artificial intelligence.)

The loss changed Turing, plunging him into a philosophical, mathematical, and scientific investigation of the human mind that would last a lifetime. He pursued advanced scientific and mathematical studies, receiving a degree in mathematics from Cambridge University in 1934 and a doctorate in mathematics from Princeton University in 1938.

As a postgraduate student, Turing wrote an influential proof challenging a theory of venerated mathematician David Hilbert, who surmised that there was no such thing as an unsolvable mathematical problem. As part of the proof, Turing laid out a thought experiment that described a device now known as the Turing “machine.” The hypothetical device could read input from an infinitely long tape and solve problems according to a set of rules. A true Turing machine was impossible to build, but the concept—a replicable machine that could be programmed, store information, and perform calculations—set the stage for modern computers.

Enigma and WWII codebreaking

During World War II, Turing worked on another form of complex computation: codebreaking. He was tasked with tackling how to decipher German messages scrambled by Enigma, a machine that turned words into gibberish. The code that resulted could only be deciphered by someone with their own Enigma machine and a separate key that told them to configure it—and changed daily.

Enigma could generate billions of possible combinations, and had stumped Allied codebreakers. But within weeks of arriving at Bletchley Park—a code and cypher school that was home to Allied codebreaking efforts—Turing cracked the code. He did so by designing Victory, a machine that mechanized codebreaking by using multiple Enigmas to narrow down the probable messages. With Turing’s help, Allied forces knew when and where German U-boats planned to attack.

(Learn about the women codebreakers of WWII with your kids.)

When the Germans switched to the Lorenz, an even more complex device, Turing developed a technique that helped crack its encoded messages, too, giving the Allies an inside look at detailed messages Hitler and his army exchanged with their most senior military officials.

The codebreaking effort at Bletchley Park is thought to have shortened the war by up to four years. Turing “saved Britain from a Nazi dark age,” wrote fellow codebreaker Jerry Roberts—and the British government agreed, awarding Turing the Order of the British Empire, the nation’s highest honor, for his wartime achievements. But the operation, and Turing’s role in it, remained secret until the 1970s, when Bletchley Park’s role in World War II was declassified.

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The Imitation Game

But the secrecy of Turing’s work at Bletchley Park hampered him professionally. In 1945 he proposed an advanced calculating device he called the Automatic Computing Engine (ACE)—a computer that would have been the most advanced of its era.

“ACE was the first complete electronic computer design,” writes computer engineer and historian Brian Edward Carpenter. However, Turing had trouble convincing his colleagues, who were in the dark about his earlier successes, that the idea was feasible. He had to fight to have it built, and when British government workers produced the first ACE, it was a simpler model.

Turing went on to work at the Victoria University of Manchester, where he continued exploring his idea of a universal computing machine. There, he also tackled the concept of artificial intelligence and grappled with questions about whether machines could think.

In 1950, Turing responded to a growing debate about these issues with a groundbreaking paper describing a thought experiment he called the “imitation game.” In the experiment, a person in an isolated room poses questions to a man and woman in another room, receives their answers in writing, then attempts to determine the sex of both. If one of the humans answering questions was replaced by a machine that fooled the questioner with human-like answers, Turing proposed, the machine was “intelligent.”

(Here’s how another of Turing’s theories is helping us unlock the secrets of flowers.)

In the paper, Turing also compared the human mind to a machine, and proposed that one day machines might be able to teach one another. Though unthinkable with the technology of his time, the concept is at the heart of modern machine learning and artificial intelligence. Modern technologies like ChatGPT are trained on huge datasets that they draw upon to solve problems and converse with humans.

Turing’s test remains hotly debated to this day, and has prompted decades of spinoffs, arguments, and experiments—all of which engage with the modern devices he envisioned while limited by his era’s insufficient technology.

Turing’s last days 

Turing had a brilliant mind. But his sexuality put him at risk at a time when homosexuality was against the law.

In 1952, Turing’s home was burgled and, during the course of the investigation, he told police that the burglar was his former boyfriend. Turing was charged with gross indecency and pleaded guilty. Rather than serve a jail sentence, which would have cost him his job, he opted for probation and “chemical castration”—injection with estrogen—designed to reduce his sexual libido.

As a convicted criminal, Turing lost his security clearance, and his year of estrogen injections rendered him impotent. On June 7, 1954, his housekeeper found him in his bed, dead at 41. A half-eaten apple, suspected by some to have been laced with cyanide, was found near his body.

Though his death was ruled a suicide due to cyanide poisoning, it remains unclear whether he intended to kill himself. Today, historians see Turing as a brilliant victim of his era’s biases. And over time, his contribution to both the war effort and modern computer science is becoming clearer.

So is his prescience. As he said in a 1951 interview, “If a machine can think, it might think more intelligently than we can. And then where would we be?”