An economist examines three modern forces that have redefined what "money" means, who controls it, and what the future of finance might look like.   Money is increasingly cheap, digital, and mobile. In Money in the Twenty-First Century, economist Richard Holden examines the virtues and risks of low interest rates, mobile money, and cryptocurrencies, and explains how these three elemental forces will continue to play out—in our wallets, on the blockchain, and throughout major economies—in the decades to come.   Holden weaves in the stories of three people who have exerted massive...