Are we heading for a cashless future? Eswar Prasad, a senior fellow at Brookings and author of the forthcoming book, “The Future of Money: How the Digital Revolution Is Transforming Currencies and Finance,” thinks so. Credit card and cell phone payments have disrupted the physical cash market already, but Prasad says the real driving force will be central banks—as new cryptocurrencies continue to emerge and their popularity expands, central banks will react by developing their own more stable forms.