Our world is getting old. And it’s getting old fast. In the next two decades the number of people above the age of 65 is expected to nearly double, from 600 million to 1.1 billion. That trend has economists worried about what a greyer world means.

First, the obvious: older people cost government budgets more money through programs like Social Security and Medicare. These rising costs will mean either higher taxes for everyone, or fewer benefits and less economic security for a growing percentage of the population. Neither is a comforting thought.