As sure as we know the economy is going up, we know that the economy shall also, sooner or later, come back down. Whence shall the next poisonous economic tumor begin? Today we turn our alert gaze to the predictions of a dude who should know.

Jeremy Grantham: investor, manager of a massive amount of money, and a frequent predictor of bubbles, such as the last housing bubble. (Which, to be fair, was not so hard to predict!) Grantham has been warning of, among other things, the rise of a new bubble in the stock market for at least several years now. Like a roulette player betting steadily on black, he is sure to be right sooner or later. Perhaps sooner? Here's a bit of what he said an interview with the Wall Street Journal today:

[The stock market] can go a lot higher than this with the Fed pushing it. And we can have another real bubble. Based on the Fed's history, that seems to be what they like. You know we had one in 2000 with Greenspan, and then we had a housing bubble and a financial bubble with Bernanke and Greenspan. And it looks like Bernanke is perfectly happy to keep the rates down and watch as stock prices rise. They do that because as the rising stock prices give you a little consumer kick, you feel richer—and then, when you least need it, the whole thing bites you, and the prices go back to fair price or lower, like they did in '09, and the consumer reacts, and you have a recession and a bad stock market. But they've had two of these, and they seem bound and determined to do it a third time.

So: the stock market will go down, some time. He's absolutely right about this, in a manner so vague as to be useless, for gambling purposes. Place your bets on when the music will stop, or not! With any luck, the value of your home will collapse long before your stock portfolio does.

Other bubble contenders today: Shanghai equities, tech IPOs, and the edge of our solar system.

[Photo: Getty]