In America more than half of all adults are single and roughly one out of seven lives alone. Worldwide, the number of solo dwellers has climbed from 153m in 1996 to 202m in 2006—a 33% jump in a decade, according to Euromonitor International, a market analyst. Yet little is known about the wider social effects of this unprecedented boom, writes Eric Klinenberg, a sociologist at New York University. His new book “Going Solo” offers a comprehensive look at the lures and perils of living alone.