When Alan Turing died in 1954, at the age of 41, he was in a period of crisis. Two years earlier, he had been charged with "gross indecency" after his homosexual affair came to light, and he avoided prison time by agreeing to undergo chemical castration. He also lost his security clearance to work on secret code-breaking operations during the Cold War—a difficult blow for the pioneering mathematician and computer scientist, who had made vital contributions to Britain’s efforts to crack German codes during World War II.
In recent years, advocates have worked to clear Turing’s reputation, which had been tarnished by the homosexuality scandal. In 2009, then-British Prime Minister Gordon Brown issued a posthumous apology to Turing, calling his treatment “horrifying” and “utterly unfair.” In 2013, the Queen granted Turing a royal pardon. And now, as Amie Tsang of the New York Times reports, Turing will be honored on a new £50 note, due to enter circulation by the end of 2021.
The note currently features James Watt, an inventor who developed the steam engine, and Matthew Boulton, the manufacturer who financed Watt’s engine. Last year, the Bank of England announced that it would be redesigning the currency, and asked the public to nominate a deserving figure from the scientific field. According to the Bank, 227,299 nominations were submitted, consisting of 989 eligible individuals. Officials narrowed down that daunting list to a shortlist of 12 people, among them Ada Lovelace, James Clerk Maxwell and Stephen Hawking.
But it was Turing who was ultimately selected by Mark Carney, Governor of the Bank of England, who hailed Turing as the “father of computer science and artificial intelligence, as well as [a] war hero.”
“Alan Turing’s contributions were far ranging and path breaking,” Carney added. “Turing is a giant on whose shoulders so many now stand.”
A towering genius, Turing is best known for his work at Bletchley Park, the large estate near Milton Keynes in Buckinghamshire where codebreakers conducted top-secret operations during World War II. The Germans had been communicating vital military operation through the Enigma, an encription machine. Enigma “offered approximately 158,000,000,000,000,000,000 possible solutions,” according to the CIA. It was thought to be practically unbreakable.
But Turing, along with the code-breaker Gordon Welchman, developed a hulking device known as the Bombe, which was “capable of breaking any Enigma message where a small portion of plaintext could be guessed correctly,” writes Turing biographer Andrew Hodges. The invention allowed the Bletchley team to read German Air Force signals. Cracking the more complex Enigma system used to communicate German naval messages presented another problem—one that was vitally important to solve, since German submarines had been targeting Allied ships carrying cargo for the war effort, as Alan Cowell of the New York Times reported last month.
“Happy to work alone on a problem that defeated others, Turing cracked the system at the end of 1939,” Hodges writes. “Turing's section ‘Hut 8,’ which deciphered Naval and in particular U-boat messages, then became a key unit at Bletchley Park.”
It has been said that Turing’s contributions helped hasten the end of the conflict, and he was named an Officer of the Most Excellent Order of the British Empire for his wartime efforts—the details of which remained largely classified until decades after his death, according to Tsang.
But Turing’s contributions to the scientific field were not limited to secret code-breaking. He played a vital role in the development of early computers, conceptualizing what is known as the Universal Turing Machine, “a single machine capable of handling any programmed task,” Hodges explains. Turing, Hodges notes, “in effect invented the digital computer.” He also developed a method initially called the “Imitation Game,” but now known as the “Turing Test,” which seeks to gauge whether a computer is “intelligent.”
According to Kevin Peachey of the BBC, the new £50 note design will include, among other features, a 1951 photograph of Turing, a table and mathematical formulae from a landmark computer science paper that Turing published in 1936, and technical drawings for the Bombe. Along the bottom of the note will be printed a quotation from a 1949 interview, in which Turing spoke about one of the computers he had developed: “This is only a foretaste of what is to come, and only the shadow of what is going to be.”