Other signals are more subtle. A sudden spike in the prevalence of a word in a message stream--earthquake, say--may indicate an important event. If a message on a commonly discussed topic includes unusual phrasing, that may signal new information or a fresh insight. Google, says Singhal, continuously scans for shifts in language and other deviations from predicted behavior.

The company is also working to connect message content to the geolocation data that's transmitted by smart phones and other mobile computers, or broadcast through services like Foursquare. The location of someone sending a message can matter a great deal. If you know that a person tweeting about an earthquake is close to the epicenter, chances are those tweets will be more valuable than those of someone hundreds of miles away.

Singhal's view of real-time search is very much in line with Google's strategy: distilling from a welter of data the few pieces of content that are most relevant to an individual searcher at a particular point in time. Other search providers, including Google's arch rival, Microsoft, are taking a more radical view.

Sean Suchter, who runs Microsoft's Search Technology Center in Mountain View, CA, doesn't like the term real-time search, which he considers too limiting. He thinks Microsoft's Bing search engine should not just filter data flowing from social networks but become an extension of them.

Ultimately, says Suchter, one-on-one conversations will take place within Bing, triggered by the keywords people enter. Real-time search, he predicts, will be so different from what came before that it will erase Google's long-standing advantages. "History doesn't matter here," he says. After a pause, he adds, "We're going to wipe the floor with them."

Amit Singhal has heard such threats before, and so far they haven't amounted to much. But even he admits that real-time search comes as close to marking "a radical break" in the history of search as anything he's seen. Keeping Google on top in the age of chatter may prove to be Singhal's toughest test.