A chorus of whistling—completely unplanned—rose from one corner of the mob and spread across the room. Tens of lips forced out the strains to “Happy Birthday.”

When the song concluded, applause resounded. And then they left.

At 7:21 p.m., as their instructions dictated, the mob makers filed out of the Coop as briskly as possible, heading into countless different directions. Within minutes, the greeting card section was as it had been before.

Howard Rheingold, who has made a career of writing about the implications of technology, last year published Smart Mobs: The Next Social Revolution—a book positing that technological innovation was redefining age-old patterns of collective action.

The recent flash mob craze, he said, reflects trends that govern his theory.

“The combination of Internet and mobile communication has lowered the threshold for collective action of all kinds,” he said.

Rheingold says that the same patterns of communication that have given rise to flash mobs are responsible for a variety of recent worldwide phenomena—a list that includes Estrada demonstrations in the Philippines, globally coordinated protests against war in Iraq and the shocking last-minute victory in a recent Korean election.

The use of new communication technology to effect social movement—whether it be a spontaneous mob or a change in the outcome of an election—is consistent with the role technological innovation has always held in society, he said.

“In a lot of ways, new generations embrace new technology as the emblem of their zeitgeist, just as the television was for the baby-boom generation,” he said.

Use of communication technology as a powerful organizational tool, he said has so far been resigned mainly to the younger generations.

“The young people who use the mobile phones, who access the Internet over their phones, are used to using this technology for their empowerment,” he said. “I think is going to have a very significant impact as they enter the workforce and become citizens and voters.”

But for most of yesterday’s mob makers, the event was nothing more than a simple diversion—or, for Undergraduate Council President Rohit Chopra ’04, an errand.

“I was just there to get a card,” he said.

—Staff writer Nathan J. Heller can be reached at heller@fas.harvard.edu.