for henry david thoreau, an ideal. for howard hughes, an obsession.ut for more and more americans today, it's just reality. >> i would argue that the rise of living alone represents the greatest social change of the last 60 years, that we have failed to name or identify. >> reporter: nyu sociologist eric kleinenberg has spent years tracking the seismic spike in solo dwelling. >> today in the united states there are about 32.7 million americans living alone. >> reporter: that's an incredible number. >> an incredible number. >> reporter: it's a massive increase over, you know, where we were in 1950 when it was just four million americans. >> reporter: clearly if you live alone, you're not alone. >> this is like finding an island. it's like finding an island with a society that no one had ever studied before. ♪ one is the loneliest number that you'll ever do ♪ >> reporter: in cities like seattle, san francisco, denver, and cleveland, roughly four out of ten households are single-person homes. one is no longer the loneliest number. and then there's manhat