You write for Wired. You did prescient reporting about social networks and the Egyptian revolution. Why this book? It started—like these things do—small. I was interested in people who want to abolish the penny. I thought they’d just be fun to spend time with. But it turned out they had a totally legitimate argument. That evolved into a Wired essay that said, basically, “let’s kill cash entirely.” This small essay got a huge response—the ACLU and the gun nuts were breathing fire. Interesting. I also discovered that there’s a whole world of business people and scholars who consider cash a menace. And it’s most crippling to the people who have the least of it.

What do you mean? A Gates Foundation guy I talked to calls cash “the enemy of the poor.” The informal, cash economy, by definition, keeps you out of the formal economy. “The formal economy” doesn’t sound fun, until you remember what it means: access to student loans, savings, retirement. Your drunk uncle can’t take the money you saved to send your daughter to school. Cash makes poor people completely vulnerable.

I just paid for a coffee and a biscuit with six paper dollars. Dinosaur!

Maybe. But why should I want an electronic record of that small transaction? Sure, your wife doesn’t need to know about the biscuit. I get it. The larger issue, though, is that cash is the currency of crime. In Spain, they call the 500-euro note a “Bin Laden,” because everyone knows what one looks like, but no one has ever seen one. In Mexico, they found a room with $200 million in cash, right next to guns and drugs. About 70 percent of US $100 bills go overseas. What are they really used for?

How will I pay for this biscuit in 10 years? It’s still early. Most people don’t know how to use PayPal Mobile, let alone alternative forms of currency. But let’s say I could buy you coffee today with Bike Gallery points, because I know you ride a bike. Maybe the next day it’s rainy, so we trade in airline miles. Our smartphones would do the conversions in real time.

But what will hip-hop artists use as props in videos? If our faith in pieces of paper and little metal rounds is kind of insane, our faith that jewelry and gold have value is even more insane. They can just hold a bunch of emeralds in the air.