A soap bubble looks like a bubble at the time, but you can only be sure of a financial bubble once it has popped. Allister Heath (The Business) thinks US housing is in a bubble, and suggests that China and hedge funds might also be. If that isn't enough, we have nanotechnology coming along.

Housing first. In Manias, Panics, and Crashes: A History of Financial Crises, Charles Kindleberger describes a bubble as "a series of price increases that are so large as to make an asset loose all relationship to fundamentals before ultimately suffering a price implosion."

Allister Heath points out that US housing has risen 50 percent in five years, with a quarter of that in the last year alone. Moreover, he tells us, housing supply in the US, unlike Britain, is outpacing demand. It is not the only potential bubble in town.

In an important report out this weekend, Bear Stearns is warning that China, hedge funds and nanotechnology are three other areas which are already or may soon succumb to bubbleonomics and where a meltdown is likely to occur.

There have been bubbles before, like the South Sea Company and Dutch tulips, and the world recovered. Yes, but it took time and only after much chaos and ruin. This time, says Heath, it could be worse.

There have been plenty of bubbles over the past five centuries, but with the exception of the equity boom of the 1920s, none that could wreak as much devastation as the current three - if they pop. Bubblenomics has always been a mad science; but the huge sums involved today are truly frightening.

Of course, people make money when a bubble is inflating. It's just that a lot more of them lose a lot more when it pops. If you're the nervous type, get out of US housing investment, Chinese stock and hedge funds. And look the other way when nanotech becomes flavour of the month.