Britain makes Alan Turing, the father of AI, the face of its 50-pound note

The country only recently pardoned him for criminal charges of homosexuality, for which he was chemically castrated.

When Isaac Newton died, his pallbearers included two dukes and three earls. Upon Charles Darwin’s death, the dean of Westminster Abbey “did not hestitate” to admit him for burial in the prestigious London church, despite the evolutionary theorist’s troubling agnosticism. At Stephen Hawking’s 2018 funeral, actor Eddie Redmayne, who won an Academy Award for playing Hawking in The Theory of Everything, read from Ecclesiastes.

Alan Turing, the pioneering computer scientist, World War II codebreaker, and father of artificial intelligence, met a rather different end. When he died by suicide in 1954, his ashes were quietly scattered near the Woking Crematorium. He had spent his final years as a criminal: In 1952, police arrested Turing for homosexual acts. As punishment for his sexual orientation, which was then illegal to act upon, the British government chemically castrated him.

Activists have spent years agitating for the rehabilitation of Turing’s legacy. In 2009, a programmer named John Graham-Cumming started a petition asking the British government to apologize for its mistreatment of Turing. In response, then-Prime Minister Gordon Brown released a statement about the “appalling way [Turing] was treated” that concluded, “we’re sorry, you deserved so much better.” After years of subsequent debate in parliament, Queen Elizabeth issued Turing a posthumous royal pardon in 2013. Now, the Bank of England announced that Turing will be the next face of the £50 note. The bills will enter into circulation in 2021.

Born in 1912 in west London, Turing showed a single-minded aptitude for science starting in early childhood. He attended Cambridge University, where he studied math and dabbled in cryptography. In 1936, he published the first of several ground-breaking papers, “On Computable Numbers.” Turing argued “it is possible to invent a single machine which can be used to compute any computable sequence.” In contrast with the highly-specialized machines of the day, he envisioned his “universal computing machine” as a single scanner that could process any set of data or instructions.

Turing’s work was interrupted when Britain declared war on Germany in 1939. He went to work at Bletchley Park, a Victorian mansion co-opted by the Government Code and Cypher School. There, he and other experts set about cracking the German’s secret communications apparatus, specifically its Enigma machine.

At first glance, the Enigma looks kind of like a typewriter, which in some sense it was, only weaponized. To send an encrypted message, you’d simply type it into the machine, which would then translate the letters into a “cipher-text” agents could pass along in secret. If you received an encrypted correspondence, you would simply type the strange “cipher-text” into the Enigma, and one by one, the decoded letters would light up on the screen until the real message appeared. While the most basic codes might swap all “A”s for “Bs,” the Enigma had 17,000 different combinations, as “A”s could be “B”s, “M”s, “Z”s, or any letter, all in the same message, depending on the combination of letters that preceded it. And it did it all automatically.

Working off earlier investigations into the Enigma by Polish mathematicians, Turing’s solution was to assume that within any given message, there would be a piece of decrypted text that would match identically to the encrypted text. If one could identify these “cribs,” they could work backward to determine the pattern of the Enigma’s motors, thereby deciphering the rest of the transmission. Turing named the resulting class of machines “the bombe.” It successfully translated all matter of messages, including those between Nazi secret servicemembers and those pinpointing the position of German U-boats. Experts think Turing’s contributions shaved several years off the war and saved millions of lives.

But it was all in secret. After the armistice, the research teams at Bletchley Park split up, the enigma machines were destroyed, and Turing continued working for the government in other high-security clearance capacities. He worked on the Manchester computers, the first stored-program computer. He also dabbled in mathematical biology, specifically the morphogenesis of zebra stripes. Most notably, in 1950, Turing published “Computing Machinery and Intelligence,” which opens with the provocative line, “I propose to consider the question, ‘Can machines think?'” While he ultimately dismisses the framing of that question, he expresses his optimism about the field that would become artificial intelligence. (The paper has another claim to fame: Its opening section, titled “The Imitation Game,” lent its name to the 2014 movie about Turing’s life and career.)

In 1952, Turing pled “guilty” to charges of “gross indecency”, the legal name for homosexual acts, which were criminal at that time. The court gave him two choices: imprisonment or chemical castration with the estrogen medication diethylstilbestrol. He chose the “organo-therapy.” The chemicals were intended to reduce his libido; they also rendered Turing impotent, and caused him to develop increased breast tissue.

Two years later, his housekeeper found him, dead of apparent cyanide poisoning. He was 41.

Appearing on a banknote raises Turing to the scientific pantheon alongside Newton, Darwin, and Hawking. But it doesn’t erase the government’s mistakes. If anything, the bright spot only enhances the darkness of what Turing, and countless other LGBTQ people like him, experienced and continue to experience. As Turing wrote in his 1950 paper on machine intelligence, “We can only see a short distance ahead, but we can see plenty there that needs to be done.”