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.