In The Numerati, Stephen Baker envisions a world in which our email and blog postings, our credit-card and grocery purchases, our pulse rates and facial expressions, and even our physical movements (handily tracked by our cell phones) will be fed to a new Brahmin class of math geeks devoted to sending us customized shopping choices, targeted political ads, real-time medical alerts, and the names of potential dating partners, not to mention (lest we be shirking on the job or hiding an illness) alerts to our bosses and insurance companies. If you’re a crook or a would-be terrorist, an army of data-interpreting sleuths (the Numerati of Baker’s title) will model your behavior and ferret you out. If you’re a potential Tide buyer or an undecided voter in a swing state, they’ll do pretty much the same. If you’re a candidate for Parkinson’s or Alzheimer’s—maybe the vocabulary in your email becomes less expansive—they’ll know it before your doctor does. Baker, a longtime BusinessWeek writer, foresees our having a technological “dashboard” that will serve as a “control panel for our lives.” Sensors attached to our bodies will provide streams of data on our health and wellness. Though the technology is still in its infancy, it will one day “empower” us.

Human beings have always produced oceans of information. (Some might call it garbage.) Every phone call, every trip to the watercooler, every purchase of gum or cigarettes, adds to the kaleidoscope of who we are. But until now, most of that data has been lost. Our written words “moldered on pages,” as Baker notes, and our movements went untracked. Now that those troves of information can be digitized, it remains only for them to be modeled and the disparate and random streams of data to be sifted and interpreted for their hidden coherence. Do more nocturnal trips to the bathroom (recorded by a swatch of “magic carpet” in the hallway) signal the onset of a medical problem? If you listen to the same music as other likely Barack Obama voters, are you worth an extra marketing expense to his campaign?

Baker is convinced that his Numerati, a half-dozen of whom he profiles, will eventually bring this world about. He is pretty much their cheerleader. In a typical passage, he describes Nathan Eagle, who is attempting to use cell-phone data to map “the DNA of our behavior.” Will he link us to new friends and lovers? Will he discover in our text messages valuable commercial information? Eagle’s scheme, Baker writes approvingly, “is about using our data to make ourselves happier, richer, and surrounded by more friends—or perhaps just to know ourselves better.”

The era when technology was not so unreservedly trusted is now only dimly recalled. The computers of my youth were fortresses of metal, forbidding accomplices to the Department of Defense and the Rand Corp. Members of the present generation, though tethered to their Apples, associate technology with openness and freedom.

In the former Soviet Union, the computer busted what had been a monopoly on information flow. It became a tool of liberation. But surely, in a free society, prying electronic eyes should also have their limits. And we should question whether we want a dashboard to control our lives.