In the U.K., 50-pound notes are not commonly used in many daily transactions, and some retailers refuse to accept them. They've also been called the "currency of corrupt elites," as the BBC notes.
In recent years, other updates to the Bank of England's currency have featured Jane Austen on the 10-pound note and Winston Churchill on the 5-pound. A new 20-pound note is expected next year, bearing a self-portrait by the artist J.M.W. Turner.
The Turing commemoration is the U.K. government's latest public reevaluation of the genius who was convicted of homosexuality under "gross indecency" laws in 1952. By the time he died, Turing had been stripped of his security clearance and was forced to undergo a "chemical castration" regime of estrogen shots to avoid serving a two-year prison term.
According to biographer David Leavitt, who wrote a book about Turing titled The Man Who Knew Too Much, some of the persecution that Turing faced was due to the government's fears that he could become a security risk. It was a sharp fall for Turing, who had toiled in secret at Britain's military intelligence headquarters at Bletchley Park to help defeat an existential threat to his country.
As for how Turing saw his own sexuality, Leavitt told NPR in 2012: "His attitude was that it was perfectly normal and not a big deal. And so he behaved as if everyone else felt the same way, which was obviously a big mistake at that time."
In astrophysicist Adam Frank's view, Turing's groundbreaking and important work was more than enough to earn a Nobel Prize—an honor Turing never received. Elaborating on Turing's achievements, Frank wrote for NPR:
"In 1935, at the ripe age of 22, Turing devised the abstract mathematical background to define a computing machine. Now called a 'Turing machine,' it would sequentially respond to input and generate output in a step-by-step (i.e., algorithmic) fashion. Turing machines are the essence of every device with a chip in it that you have ever encountered. That's why Turing stands, essentially, at the head of the line when it comes to the creation of the digital age. He is the father of all computers."
The anti-homosexuality laws that snared Turing remained in effect until 1967.
Queen Elizabeth II issued a royal pardon for Turing in late 2013. Three years later, the U.K. justice minister issued a mass pardon for thousands of gay men.
"It was a momentous day for all our family when we heard that Alan Turing was going to be pardoned back in 2013," Turing's great-niece, Rachel Barnes, told NPR in 2016. "One of the best days ever, and we celebrated like mad. But the same pardon is deserved by everybody else."
Those breakthroughs came after repeated attempts to secure a posthumous pardon for Turing in Parliament. When one such bid failed in the House of Lords, opponents of the measure said it wasn't appropriate, reasoning that Turing must have known he was breaking the law.
In 2009, then-Prime Minister Gordon Brown issued a full apology to Turing, thanking him for his "contribution to humankind" and for fighting fascism and war.
"You deserved so much better," Brown said.
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