PRINCETON, N.J. -- First came the tech-stock bubble. Then there were bubbles in housing and credit. Chinese stocks took off like a rocket. Now, as prices soar on every material from oil to corn, some suggest there's a bubble in commodities.
But how and why do bubbles form? Economists traditionally haven't offered much insight. From World War II till the mid-1990s, there weren't many U.S. investing manias for them to look at. The study of bubbles was left to economic historians sifting through musty records of 17th-century Dutch tulip-bulb prices and the like.
The dot-com boom began to change that. "You were seeing live, in action, the unfolding of lots of examples of valuations disconnecting from fundamentals," says Princeton economist Harrison Hong. Now, the study of financial bubbles is hot.
Its hub is Princeton, 40 miles south of Wall Street, home to a band of young scholars hired by former professor Ben Bernanke, now the nation's chief bubble watcher as Federal Reserve chairman. The group includes Mr. Hong, a Vietnam native raised in Silicon Valley; a Chinese wunderkind who started as a physicist; and a German who'd been groomed to take over the family carpentry business. Among their conclusions:
Bubbles emerge at times when investors profoundly disagree about the significance of a big economic development, such as the birth of the Internet. Because it's so much harder to bet on prices going down than up, the bullish investors dominate.
Once they get going, financial bubbles are marked by huge increases in trading, making them easier to identify.
Manias can persist even though many smart people suspect a bubble, because no one of them has the firepower to successfully attack it. Only when skeptical investors act simultaneously -- a moment impossible to predict -- does the bubble pop.
• Lots to Study: Research on financial bubbles is hot in academia these days.
• Jersey Boys: The hub is Princeton, where three young economists use mathematical methods to study them.
• One Finding: Investment manias can persist even though many investors see that a bubble is forming.As a result of all that and more, the Princeton squad argues that the Fed can and should try to restrain bubbles, rather than following former Chairman Alan Greenspan's approach: watchful waiting while prices rise and then cleaning up the mess after a bubble bursts.
If the tech-stock collapse didn't make that clear, the damage done by the housing and credit bubbles should, argues José Scheinkman, 60 years old, a theorist Mr. Bernanke recruited in 1999 from the University of Chicago. "Advanced economies are very dependent on the health of the financial system. What this bubble did was destroy the capacity of the financial system to finance the U.S. economy," Mr. Scheinkman says.
The Fed is giving the activist approach some thought. In a speech scheduled for delivery Thursday night, Fed Governor Frederic Mishkin suggested that while it was inappropriate to use the blunt instrument of interest-rate increases to prick bubbles, if too-easy credit appeared to be fueling a mania, policy makers might craft a regulatory response that could "help reduce the magnitude of the bubble."
Yet the very concept of bubbles is at odds with the view of some that market prices reflect the collective knowledge of multitudes. There are economists who dispute the existence of bubbles -- arguing, for instance, that what happened to prices in the dot-com boom was a rational response to the possibility that nascent Internet firms might turn into Microsofts. But these economists' numbers are thinning.
Bubbles don't spring from nowhere. They're usually tied to a development with far-reaching effects: electricity and autos in the 1920s, the Internet in the 1990s, the growth of China and India. At the outset, a surge in the values of related businesses and goods is often justified. But then it detaches from reality.
Mr. Hong, growing up in Sunnyvale, Calif., and teaching at Stanford, had a front-row seat to the technology boom. Recognizing a mania, he resisted investing in tech stocks himself -- until they were about to crest.
He recalls his thought process: "My sister's getting rich. My friends are getting rich....I think this is all crazy, but I feel so horrible about missing out, about being left out of the party." In 2000, "I finally caved in," he says. "I put in some money just as a hedge against other people getting richer than me and feeling better than me." But 2000, of course, was the year the bubble burst.
Mr. Hong, who came to Princeton two years later, and now is 37, argues that big innovations lead to big differences of opinion between bullish and bearish investors. But the deck is stacked in favor of the optimists.
One who believes a stock is too high can short it, borrowing shares and selling them in hopes of replacing them when they're cheaper. But this can be costly, both in the fees and in the risk of huge losses if the stock keeps rising. Many big investors rarely short stocks. When differences between bullish investors and bearish ones are extreme, many of the bears simply move to the sidelines. Then, with only optimists playing, prices go higher and higher.
In housing and the credit markets, the innovation was slicing and dicing loans in novel ways. As investors bought the resulting mortgage securities, they provided abundant capital for home buyers; buoyed by this and falling interest rates, house prices surged.
Betting against house prices is hard; only a few sophisticated investors found roundabout ways to do it, in derivatives markets. Most skeptics about the housing boom just sat it out; the optimists were unchecked.
At some point in a bubble, optimists' enthusiasm runs its course. Prices turn down. There's an expectation that at this point, investors who were skeptical may see prices as more reasonable and start buying. If they don't, that's a signal that prices had gotten way too high -- and then they tumble.