(Note: A version of this episode originally ran in 2024 .) $40,000,000,000,000. Four commas. Thirteen zeroes. It’s an eye-popping, almost infinite-sounding pile of money. And every time the debt passes a big round number, almost everyone asks the same question: How much debt is too much? It’s maybe the most important question in macroeconomics. It’s also surprisingly hard to answer. When two…