The line to check in snaked through the terminal like a single great beast, a centipede with a million legs, a thousand heads, and at least five hundred backpacks. Children tugged on their parents’ hands and whined about boredom. Young lovers kissed frantically, ignoring the glances—whether indulgent or disapproving—of the people around them. Air travel was expensive and invasive enough that no one wanted to say anything. That couple might go a year or more without seeing each other again.