Right now, the economy is running hot. Inflation is high, and central banks are pushing up interest rates to fight it. But before the pandemic, economies around the world were stuck in a different rut: low inflation, low interest rates, low growth. In 2013, Larry Summers unearthed an old term from the Great Depression to explain why the economy was in this rut: secular stagnation. The theory resonated with Olivier Blanchard, another leading scholar, because he had made similar observations himself. Larry and Olivier would go on to build a case for why secular stagnation was a defining theory of the economy and why government policies needed to respond to it. They helped reshape many people's understanding of the economy, and suggested that this period of slow growth and low interest rates was here to stay for a long time.But today, Larry and Olivier are no longer the duo they used to be. As inflation has spiked worldwide, interest rates have followed suit. Earlier this year, Larry announced that he was no longer on the secular stagnation train. Olivier, meanwhile, believes we're just going through a minor blip and will return to a period of low interest rates within the near future. He doesn't see the deep forces that led to a long-run decline in interest rates as just vanishing. Who's right? The future of the global economy could depend on the answer.Help support Planet Money by subscribing to Planet Money+ in Apple Podcasts or at plus.npr.org/planetmoney.