A mathematical thought experiment once claimed that if China's population walked past you in single file, the line would never end due to reproduction rates—but China's population is now declining for the first time since 1961.
The Chinese Population Paradox That's No Longer True
There's a famous mathematical claim that has circulated for decades: if the entire population of China walked past you in single file, the line would never end because people would be born faster than they could pass by. It's a mind-bending thought experiment that captures the imagination—but here's the twist: it's no longer mathematically possible.
When the Math Actually Worked
This thought experiment made sense during China's population boom in the mid-20th century. Picture this: 1.4 billion people walking past you, one person per second. That's roughly 44 years of continuous walking. Now add births during that time, and theoretically, you'd never reach the end of the line.
The math was elegant: if births occurred faster than the line moved, you'd have an infinite queue. It was a clever way to illustrate exponential population growth and became popular in mathematics education.
The Demographic U-Turn
Fast forward to 2025, and the situation has completely reversed. China's population is declining for the first time since 1961. The current growth rate sits at -0.23%, meaning more people die each day (approximately 32,100) than are born (around 23,800).
The fertility rate has plummeted to approximately 1.09—one of the lowest in the world. Even after ending the one-child policy in 2016 and actively encouraging larger families, births continue to fall. The endless line? It now has a very definite end.
What Changed?
Several factors contributed to this dramatic shift:
- Economic development: As China urbanized and incomes rose, family sizes naturally decreased
- Education: Higher education rates, especially among women, correlate with lower birth rates
- Cost of living: Raising children in modern Chinese cities is expensive, discouraging large families
- Aging population: The one-child policy created a demographic time bomb that's now detonating
From Thought Experiment to Time Capsule
The "endless line" paradox hasn't disappeared—it's just become historical. It's now a snapshot of a specific moment in demographic history, a reminder that populations don't grow infinitely. What once seemed like an inexhaustible human tide has become a story about the surprising dynamics of human populations.
The real lesson? Mathematical thought experiments based on current trends can become obsolete faster than you'd think. China's endless line, once a symbol of unstoppable population growth, is now a cautionary tale about assuming the present will extend forever into the future.