With enough effort, you can find anyone. Wired Magazine readers took about three weeks to track down the journalist Evan Ratliff. Osama bin Laden evaded the C.I.A. for 10 years but no more. Somewhere on the University of Oklahoma campus sit bone fragments thought to be remnants of Amelia Earhart. Disappearing in this age, like any other, turns largely on the tenacity of one’s pursuers.

Of course, technology has its role to play. You are more likely to search for a needle in a haystack if you have a metal detector. The ability of a government to sift through a database at a keystroke or monitor thousands of airport cameras for one face will no doubt influence the calculus of its surveillance.