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.

Baker grapples with at least the first of these issues. He acknowledges that the Numerati’s vision troubles those who want to preserve an iota of privacy. But he does not seem bothered by it. Writing about technologies that exploit the dynamics of social networks like Facebook, Baker hypothesizes that when employees misbehave, their bosses will be able to figure out which of their office friends to monitor as likely accomplices. If this sounds like prying, Baker urges us to “look at the bright side.” Meaning: “Once the Numerati master these techniques on us, maybe they can use them to catch terrorists.” This is a tad too facile. Security has always been the excuse of snoops. When Baker concludes, “We’re going to have to reevaluate our ideas about privacy,” I was reminded of those nightmare scenes of an ultraconformist future out of The Twilight Zone.

This darker threat is probably less political than sociological—that the ­Numerati will redefine people as the mere sum of their data. To the man with a hammer, as the saying goes, everything looks like a nail. To the Numerati, our every breath becomes a nail for digital marketing.

It’s true that many of the applications that have so enchanted Baker are undeniably appealing. In the medical world, data flows too slowly; would that it were wired. And Baker is a charming writer. In a chapter on digital matchmaking, he wonders why the computer can’t match him to the wife to whom he is happily married.

Yet I keep thinking that he embraces the commercial bent of the Numerati too unconditionally. Baker speculates that technology will enable political candidates to target their pitches, and on that happy day, “it will be as though they finally understand us.” Not quite. It’s more likely that pols will have finally mastered the art of selling their campaigns like soap. Baker himself likens voters to “buckets of broccoli eaters or Mars Bars buyers in the supermarkets.”

This leads to a troubling question: Can one’s character really be deconstructed into predictive “buckets”? In other words, are we fully reducible to math?

A final question is whether the technology will work. For instance, will scouring the random jottings of bloggers for references to deodorant or beer actually predict their behavior and tastes? There is a serious risk of “garbage in, garbage out.”

To his credit, Baker makes no claim of perfection on the part of the Numerati. (He tells of how one electronic sensor relayed news of an apparent sudden weight gain by a patient; it turned out that her cat had joined her in bed.) And he admits that the technology has a long way to go before it is viable. In the meantime, this is an eye-opening and chilling book.