Big deals on Wall Street that change an industry are frequently described as "catalytic." But that term seems too mild to characterize what happened yesterday.

"Chain reaction," a more aggressive process, is better.

In the hour after the markets opened, any stock anywhere in the Western world potentially affected in any way by the merger of America Online and Time Warner took off.

I counted 30 in the opening minutes alone, including Disney, Viacom, CBS, Comcast, Yahoo, Excite At Home, AT&T, Lycos, RealNetworks, EarthLink, Broadvision, Cablevision, Liberty Media, Seagram and CMGI.

Media properties, cable properties, Internet portal properties and anything connected with them, all rose, as the realization sank in that the process of "convergence" that techno-visionaries had been predicting was suddenly accelerating, faster than any of them had predicted.

So fast is this accelerating that the term convergence no longer seems adequate, either. This is a technology vortex, sucking in, and transforming, anything that comes close to it.

There were good reasons for the market to react as it did, about which more later.

But amid the excitement, keep in mind a simple fact: Apart from the announcement of the AOL-Time Warner merger, nothing much happened. Personally, I wouldn't buy or sell anything too fast until the dust settles. Everything expensive got more expensive yesterday, indiscriminately.

While the particular stocks involved in the potential merger had every reason to move, all the other stock market action was based on conjecture.

This conjecture, though, is powerful stuff for the market to digest. In less than a year, the wave of technology has washed away walls between old companies and new. Cable television, for example, was perceived as threatened by the Internet just a while ago.

Now they are interdependent.

Where Netheads used to speak derisively of bricks and mortar, of companies that "got it" and those that didn't, now they speak of clicks and bricks.

Where they were once at war, now they are all in it together.

There was news that all but got buried yesterday about Ford Motor Co.'s deal with Internet giant Yahoo and General Motors Corp.'s deal with AOL. Those aren't just about selling cars over the Internet. These companies are planning Internet access in their vehicles: the ability to send instant messages from behind the wheel or order some tickets via Moviefone. The service would use wireless technology provided by Nokia or Qualcomm, bearing microprocessors from Texas Instruments and carrying chips from RF Micro Devices.

It used to be that investors were confronted with industries. Choose one. Choose another. Learn it. Buy it.

Now they are confronted by "synergy," long, loopy value chains, and competitive juices that surge with the speed of light--all of which fueled yesterday's phenomenal market performance.

A great merger of market cap Goliaths is big news any time, for sure. But in this decade, in today's technology vortex, it's much bigger, because investors assume it forms an imperative, which all others must now follow, fast.

What is that imperative? Content needs platform. Platform needs content. Both need broadband (high-speed delivery) and both need customers, as many as they can corner. There isn't a company in the business that has it all. They have differing configurations of each. They can either develop what they need themselves or join forces to make it happen sooner.

In the case of this merger, Time Warner brings to the table both content--news and entertainment--and platform, through its cable operations. Since its cable operations reach only 12 percent of American households, however, it needs AOL's reach, currently more than 22 million customers.

AOL, in turn, needs cable, desperately. While it has agreements with companies that offer high-speed DSL service and fixed wireless, it had no cable, a deficit that could cripple it competitively, even with its 22 million customers.

Repeat this with seven, eight or nine huge companies, each of which may be strong in one area but deficient in another, and you can appreciate why all those shares changed hands yesterday.

Suddenly, Disney's efforts with Go.com look kind of feeble. Will it try to buy Yahoo? Or will Yahoo buy it?

Seagram, which I used to drink, is now also a music provider that needs streaming media software that can go out over broadband via an Internet portal, to be downloaded onto a digital device, wireless or wired.

As of yesterday morning, every company in this field or anywhere near it had become either a potential buyer or a potential seller, a targeter or a target. It happened not just here but in Britain, where shares of Internet provider Freeserve shot up on the theory that someone would now buy it.

Among the forces caught in this whirlpool yesterday were notions of "overvaluation" of stocks, perceived to be a big concern just a week ago, and hand-wringing about rising interest rates, yet another worry last week.

Those warning flags remain in place, despite yesterday's excitement. Keep in mind how quickly the climate changes now. In the course of one week, the Nasdaq composite index closed at a new high, tanked and resurfaced to set yet another record.

To me, the biggest warning flag yesterday was that all remotely affected tech companies, with a few exceptions, seemed somehow to be winners.

That's eerie. And it can't last.

Fred Barbash (barbashf@washpost.com) is The Post's business editor.