The security argument for cashlessness has been helped along by support both popular and pop. ABBA the Museum—an interactive athenaeum for the art and artistry of Sweden’s superfamous quartet—does not take cash, mostly owing to the deeply held beliefs of Björn Ulvaeus, the smaller and less bearded of the “B”s. “What happens to street crime when an advanced economy goes completely cashless?” Ulvaeus, who first registered the risks of cash after his son had a home robbery, wrote to me in an e-mail not long ago. “Why don’t politicians ask questions like that?” However costly cash-handling is for businesses, it’s more so for the banks. Cash requires elaborate security for transportation and disbursement. It is a pain to track bill by bill. Financial institutions can make money from card transactions and account maintenance, but cash, for all its ubiquity, has questionable returns and a growing air of obsolescence. Sweden’s central bank, the Riksbank, has recently joined many of its peers in looking at blockchain technology. Björn Segendorf, a Riksbank economist, said it was an “open question” whether the central bank would be issuing digital currency in the future.