Christian Rudder, one of the founders of the online dating site OkCupid, got himself into a tangle a few weeks ago when he announced in a blog post, “We Experiment on Human Beings!” OkCupid had wanted to find out if its assertion of compatibility influenced how compatible couples could be. “To test this, we took pairs of bad matches . . . and told them they were exceptionally good for each other,” Rudder wrote. (He neglected to say that people have been doing this to friends and relatives for centuries.) As it turned out, being set up by OkCupid was enough to inspire bad matches to exchange nearly as many messages as good matches typically do. Rudder wrote, “When we tell people they are a good match, they act as if they are. Even when they should be wrong for each other.” Call it the If You Say So romance, and chalk it up to the trust people put in the site’s matching algorithms, or to the possibility that the algorithms aren’t trustworthy at all. Or maybe it’s just that wrongness takes a while to reveal itself. (One date? Seven years? A lifetime?)

Rudder fessed up to all this because it seemed germane, in light of the controversy surrounding Facebook’s recent admission that it had tweaked news feeds to test how negative or positive news affects people—what they repost and how it travels. He promptly took a beating. One journalist called him a sociopath. Another likened OkCupid to a restaurant that had intentionally poisoned its patrons. Many people thought that it was cruel to toy with human relationships, and that it was typically arrogant of a tech executive not to recognize this.

Ten days later, Rudder sat munching on raw cauliflower at a midtown bar. He had been thinking about the word “experiment,” which seems, despite its implicit virtues, to leave a sinister aftertaste, a residue of Mengele, Milgram, and frog dissections in middle school. “There’s no question that Web sites experiment on people,” he said. “People justifiably find that weird. But these experiments are so minor. They’re more like a chef changing a spice. So you use dill instead of cumin. It might be gross, but it might be delicious.” He’d assumed that on some level his revelation wouldn’t be taken as a revelation—that the world knew by now that Internet companies collate and analyze data about their users, and often manipulate behavior, in an attempt to refine their services or to achieve world domination. For better or worse, it’s part of the compact (and the terms of use): free service in exchange for personal information.

Rudder has written a book on the subject, called “Dataclysm: Who We Are (When We Think No One’s Looking).” In it, he doesn’t wring or clap his hands over the big-data phenomenon (see N.S.A., Google ads, that sneaky Fitbit) so much as plunge them into big data and attempt to pull strange creatures from the murky depths. Here’s one: in U.S. Google searches, the most common word to follow the phrase “Is my husband . . .” is “gay.” It is ten times more common than “depressed.” It won’t be long before Google will be able to provide the answer. Right now, just from your pattern of likes on Facebook (and without relying on status updates or comments), an algorithm can determine with eighty-eight-per-cent accuracy whether you are straight or gay. Sixty per cent of the time, it can tell whether your parents were divorced before you turned twenty-one. Rudder calls this trove of data “an irresistible sociological opportunity.” He writes, “You know the science is headed to undiscovered country when someone can hear your parents fighting in the click-click-click of a mouse.”

Rudder, who is thirty-eight, grew up in Little Rock, Arkansas, and, like his fellow OkCupid founders, majored in math at Harvard. He’s a “Magic: The Gathering” nut and a bit of a Luddite; he’s never been on an online date (he’s been married for eight years). He’s still a member of the indie rock band Bishop Allen, although he’s not going on its forthcoming tour. “This is the difference between being in a band and being the author of a nonfiction book,” he told his bandmate Justin Rice the other day. “When you’re in a band, there’s a guy with a microphone who’s asking you questions. When you write a book, there’s a guy with a microphone who’s trying to argue with you.”

But back to that argument: If the Internet is one giant experiment, are we all just lab rats? “I prefer the analogy of a glass-bottomed boat,” Rudder said. He derived the word “dataclysm” from the Greek word kataklysmos, for the Great Flood. He’d like for this current inundation, like Noah’s, to be thought of not just as an agent of destruction, “an unprecedented deluge,” but as a means of renewal, one that will wash away our old limited understanding of how people actually think and behave. The power of suggestion is strong. Dinner and a movie?