Across the rich world, populations are greying. Long-simmering concerns over the viability of welfare states are becoming louder as the baby-boomer generation has started to withdraw from the workforce, depending on for the most part generous retirement packages to keep them comfortable in the twilight of their lives. The core challenge is that people are living longer. While the dramatic expansion of life expectancies is one of humanity’s accomplishments, what was once only a decade subsisting on savings and pension plans, has often become two or more decades. At the same time, the number of young workers replacing them has atrophied, as birth rates have fallen across most of the developed world in the years since the generational bulge of people born in the aftermath of the second world war.