Necessity may be the mother of invention, but sometimes it can work the other way around. Invention — i.e., new technologies and techniques — creates obligations and opportunities that never existed before. Fifty years ago, nobody needed to charge their cell phones — because they didn’t have cell phones. Before the smallpox vaccine was invented, it would never have occurred to someone in government to require that all children be inoculated for smallpox. I’m not against mandatory inoculations; my point is to illustrate that invention often creates new necessities.

The arrival of “big data” — the ability to crunch massive amounts of information to find patterns and, ultimately, to manipulate human behavior — creates opportunities for government (and corporations) that were literally unimaginable not long ago. Behavioral economists, neuroscientists, and liberal policy wonks have already fallen in love with the idea of using these new technologies and insights to “nudge” Americans into making “better” decisions. No doubt some of these decisions really are better, but the scare quotes are necessary because the final arbiters of what constitutes the right choice are the would-be social engineers.

Until recently there was great anonymity in crowds. But the near-magic of math has changed that equation. Given a big enough data set, data-crunchers can figure out a great deal about every face in the crowd.