If you drive across the Rust Belt in the Lower 48, you’ll encounter them here and there: half-empty towns with schools and storefronts boarded up, waiting for an economic upswing that may never come. The feeling of a place with its best days in the rearview mirror is one of desperation: Without a plan to adapt to a changing world, the withering towns’ young people leave for places where jobs are more plentiful and opportunities are brighter. The older generation and those too poor or stubborn to relocate find themselves in a downward spiral of fewer services, declining value for their homes and the inescapable reality that in a generation or two, the place where they grew up may no longer exist.