I chose the green door ninety-three days ago. At the time, it seemed obviously correct. Not even a close call. The red door offered two billion dollars immediately—a sum so large it would solve every material problem I'd ever face, fund any project I could imagine, and still leave enough to give away amounts that would meaningfully change thousands of lives. But two billion is a number. It has a fixed relationship to the economy, to the things money can buy, to the world. The green door offered one dollar that doubles every day. I remember standing there, doing the mental math. Day 30: about a billion dollars. Day 40: over a trillion. Day 50: a quadrillion. The red door would be surpassed before the first month ended, and after that, the gap would grow incomprehensibly fast. Choosing the red door would be like choosing a ham sandwich over a genie's lamp because you were hungry right now. So I walked through the green door. The first few weeks were unremarkable. I had a dollar, then two, then four. By day ten I had $512, which felt like finding money in an old jacket. By day twenty I had over a million, and I started getting calls from financial advisors I'd never contacted. By day thirty-one I had crossed the two-billion threshold—officially richer than I would have been behind the red door. I didn't understand what was happening until around day sixty. The money, you see, had to exist somewhere. Not philosophically—I mean physically. Digitally. When I checked my bank balance, a computer somewhere had to store that number. And storing the number 2^n requires n bits. One bit per day. That's it. That's the rate at which my fortune's representation grows. A linear function. Almost comically modest. But here's what I'd failed to understand about exponential growth: the value doesn't care about the representation. The bits grow linearly. The dollars they encode grow exponentially. And dollars make claims on the physical world. Day sixty. My balance: 2^60 dollars. About 1.15 quintillion. Roughly 1,000 times the entire global GDP. The number itself required only 60 bits to store—less than a tweet, less than this sentence, trivially small from an information-theoretic perspective. But money is not information. Money is a claim. The calls started coming from the Treasury Department. Polite, confused, increasingly frantic. They explained that the M2 money supply of the United States was approximately 21 trillion dollars. I now held about 15,000 times that amount. When I tried to spend any of it—even a tiny fraction—the transaction represented a claim on more goods and services than the entire human economy had ever produced in its history. "The number in your account," a Treasury official said, "is not meaningful." "It's in your computer," I replied. ...