Since undertaking this research project, Raj and his collaborators have been trying to figure out why the map looks like this. Why do kids in places like Silver Spring, Maryland, have a much better shot of rising out of poverty than kids in Little Rock, Arkansas?

The places where the American Dream is something close to pure fiction have a lot of bad things going on. They have high rates of poverty, significant inequality, a large fraction of single-parent households, bad schools, and other factors that might explain why they see a lower rate of upward mobility than other places.

"The big question is: why is the American Dream more alive in some places than others?" Raj says. "And, along the way, lots of folks talked about the idea that social capital — or who you're friends with, who you're interacting with — might be an important factor."

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